CT and MR Imaging of the Whole Body

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Author: John R. Haaga | Charles F. Lanzieri | Robert C. Gilkeson

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4h.

RoshanKetab Medical Publishers

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Tel: +98 (21) 66950639 TelFax: +98 (21) 66963783_6

Mosby

11830 Westline Industrial Drive St. Louis, Missouri 63146

COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING OF THE WHOLE BODY Copyright 2003, Mosby, Inc All rights resewed.

ISBN 0-323-01133-0

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior permission of the publisher (Mosby Inc., 11830 Westline Industrial Drive, St. Louis).

Pharmacology is an ever-changing field. Standard safety precautions must be followed, but as new research and clinical experience broaden our knowledge, changes in treatment and drug therapy become necessary or appropriate. Readers are advised to check the product information currently provided by the manufacturer of each drug to be administered to verify the recommended dose, the method and duration of administration, and the contraindications. It is the responsibility of the treating physician, relying on experience and knowledge of the patient, to determine dosages and the best treatment for the patient. Neither the publisher nor the editor assumes any responsibility for any injury and/or damage to persons or property. The Publisher

Library of Congress Cataloging-in-PublicationData Computed tomography and magnetic resonance imaging of the whole body/[edited by] John R. Haaga, Charles F. Lanzieri4th ed. p. cm. Includes bibliographical references and index. ISBN 0-323-01 133-0 1. Tomography. 2. Magnetic resonance imaging. I. Haaga, John R. (John Robert). II. Lanzieri, Charles F.

Acquisitions Editor Janice Gaillard Developmental Editor: Rebecca Gmliow Project Manager: Norman Stellander Design Cooniinafoc Gene Harris

Printed in the United States of America. Last digit is the print number: 9 8 7 6 5 4 3 2

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This book is dedicated to Elizabeth E. Haaga, daughter of John and Ellen Haaga, who was born on August 19, 1972, and died December 9, 1985. Beth had a disseminated neuroblastoma, which was diagnosed in 1984. She was treated with a bone marrow transplant and died from graft versus host disease and infection. As her parents, we loved her dearly and cherish the memory of her early years when she was well. After the onset of her illness, we came to know that her gentle and loving nature was accompanied by a remarkably strong character. She endured her pain and suffering without bitterness and never sought to hurt those who loved her. Indeed, most incredulously, she tried to lessen our emotional pain even while enduring her physical discomforts. Many authors have marveled at the qualities of children, and although Beth's short life and premature death have left us saddened beyond comprehension, her remarkable courage and sweetness have given us a lasting pride and respect. We remember her lovingly.


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Contributors James J. Abrahams, MD

Lawrence M. Boxt, MD

Associate Professor (Diagnostic Radiology and Surgery) and Director of Medical Studies, (Diagnostic Radiology), Section of Neuroradiology, Yale University School of Medicine, New Haven; Attending Physician, Yale-New Haven Medical Center, New Haven; West Haven Veterans Administration Hospital, West Haven, Connecticut The Orbit

Professor of Clinical Radiology, Albert Einstein College of Medicine; Chief of Cardiovascular Imaging, Beth Israel Medical Center, New York, New York Magnetic Resonance Imaging of the Heart

Hans-Juergen Brambs, MD Full Professor, Medical School, University of Ulm; Chairman, University Hospitals of Ulm, Ulm, Germany Liver: Normal Anatomy, Imaging Techniques, and Diffuse Diseases

Jamshid Ahmadi, MD Professor of Radiology, Neurology and Neurological Surgery, University of Southern California Keck School of Medicine and Los Angeles County-University of Southern California Medical Center, Los Angeles, California Cerebral Infections and Injhmution

Lynn S. Broderick, M D Associate Professor, University of Wisconsin-Madison, Madison, Wisconsin Computed Tomography of the Heart and Pericardium

Kimberly E. Applegate, MD, MS Associate Professor of Radiology, Department of Radiology, Indiana University School of Medicine and Riley Hospital for Children, Indianapolis, Indiana Pediatric Spleen

Mark A. Augustyn, M D Neuroradiology Fellow, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania Temporal Bone

Errol M. Bellon, MD Professor of Radiology, Case Western Reserve University School of Medicine; Chairman, Department of Radiology, MetroHealth Medical Center, Cleveland, Ohio Magnetic Resonance Physics: An Introduction

Javier Beltran, MD Clinical Professor of Radiology, New York University School of Medicine, New York; Chairman, Department of Radiology, Maimonides Medical Center, Brooklyn, New York The Knee

Ellen C. Benya, MD Associate Adjunct Clinical Professor of Radiology, University of Florida College of Medicine; Attending Physician, Department of Radiology, Shands Hospital at the University of Florida, Gainesville, Florida Hepatobiliary System

Sheila C. Berlin, M D

Kenneth A. Buckwalter, MD ;

Associate Professor of Radiology, Indiana University School of Medicine, Indianapolis, Indiana Multislice Helical Computed Tomography: Clinical Applications

Donald W. Chakeres, MD Professor of Radiology, Head of Neuroradiology, and Director of MRI Research, The Ohio State University College of Medicine and Public Health, Columbus, Ohio Temporal Bone

Ja-Kwei Chang, MD Professor of Radiology, State University of New York Upstate Medical University; Director, Division of Neuroradiology, Department of Radiology, University Hospital, Syracuse, New York Intracranial Neoplasms

Wui K. Chong, MBBS, FRCR Assistant Professor of Radiology, Virginia Commonwealth University School of Medicine, Richmond, Virginia; Medical College of Pennsylvania, Philadelphia, Pennsylvania; Vanderbilt University School of Medicine, Nashville, Tennessee Thyroid and Parathyroid Glands

Richard H. Cohan, MD Professor, University of Michigan School of Medicine and University of Michigan Hospital, Ann Arbor, Michigan The Retroperitoneurn

Hugh D. Curtin, MD

Assistant Professor of Radiology, Case Western Reserve University School of Medicine; Staff, Division of Pediatric Radiology, University Hospital of Cleveland, Cleveland, Ohio Heart and Great Vessels

Professor and Chief of Radiology, Harvard Medical School and Massachusetts Eye and Ear Infirmary, Boston, Massachusetts The Larynx

Daniel T. Boll, M D

Professor of Radiology and Chief, Musculoskeletal Radiology, University of Pennsylvania School of Medicine and Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania The Shoulder

Resident, University Hospitals of Ulm, Ulm, Germany Liver: Normal Anatomy, Imaging Techniques, and DifSuse Diseases

Murray K. Dalinka, M D


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Contributors

Mony J. de Leon, MD

Thorsten R. Fleiter, MD

Professor of Psychiatry and Radiology, and Director of the Neuroimaging Research Laboratory, New York University School of Medicine, New York, New York , Neurodegenerative Disorders

Associate Professor of Radiology, University of Ulm Medical School; Staff Radiologist, University Hospitals of Ulm,Ulrn, Germany Liver: Nonnal Anatomy, Imaging Techniques, and D i m e Diseases; Multislice Helical Computed Tomography: Clinical Applications

Pedro J. Diaz, PhD Assistant Professor, Departments of Radiology and Biomedical Engineering, Case Western Reserve University School of Medicine and MetroHealth Medical Center, Cleveland, Ohio Magnetic Resonance Physics: An Introduction

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Huy M. Do, MD Assistant Professor of Radiology and Neurosurgery, Stanford University Medical Center, Stanford, California Image-Guided Spinal Interventions

Vikram Dogra, MD

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Melanie B. Fukui, MD

Formerly, Associate Professor of Radiology, University of Pittsburgh School of Medicine; Director of Neuroradiology, !&L Allegheny General Hospital, Pittsburgh, Pennsylvania Meningeal Processes J 7

Assistant Professor of Radiology, Case Western Reserve University School of Medicine; Section Head, Genitourinary Radiology, and Head, Director of Ultrasound, University Hospitals of Cleveland, Cleveland, Ohio The Kidney

Lane F. Donnelly, M d

Donald P. Frush, MD Associate Professor, Department of Radiology, Duke University School of Medicine and Medical Center, Durham, North Carolina Computed Tomography and Magnetic Resonance Imaging in the r Pediatric Patient: Special Considerations 4

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Professor of Radiology and Pediatrics, University of Cincinnati College of Medicine; Associate Director, Department of Radiology, Children's Hospital Medical Center, Cincinnati, Ohio Chest

8

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Amilcare Gentili, MD Assistant Professor, Musculoskeletal Section, University of California, Los Angeles, Department of Radiological Sciences, Los Angeles, California 7'* ' f i p - ~ ' w ;I* - I - . Musculoskeletal Tumor I

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Ajax E. George, MD

Professor of Radiology, New York University School of Medicine, New York, New York M .,:--d)euuc Neurodegenerative Disorders

- 4I2 1

Jeffrey L. Duerk, PhD Professor Departments of Radiology and Biomedical Engineering and Director, Physics Radiology, Department of Radiology, University Hospitals of Cleveland/Case Western Reserve University School of Medicine, Cleveland, Ohio Magnetic Resonance Physics: An Introduction

James D. Eastwood, MD Assistant Professor, Department of Radiology, Division of Neuroradiology, Duke University School of Medicine, Durham, North Carolina Stroke

John C. Egelhoff, DO hofessor of Radiology and Pediatrics, University of Cincinnati College of Medicine; Staff Neuroradiologist, Children's Hospital - . ., , Medical Center, Cincinnati, Ohio Pediatric Head and Neck Imaging

,

Associate Professor of Radiology, Diagnostic Radiology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas Primary Pulmonary Neoplasms; The Mediastinwn

Jon Mark Fergenson, MD Neuroradiology Fellow, Yale-New Haven Medical Center, New Haven; West Haven Veterans Administration Hospital, West Haven, Connecticut The Orbit

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Section Head, Chest Radiology, and Assistant Professor of Radiology, University Hospitals of Cleveland and Case Westerq Reserve University, Cleveland, Ohio Computed Tomography and Magnetic Resonance Imaging of the Thoracic Aorta 1,.

John L. Go, MD Assistant Professor of Radiology and Otolaryngology, University of Southern California Keck School of Medicine, Los Angeles, , I-. California Cerebral Infections and Infimmation I 1 I -

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Ashok K. Gupta, MD

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Clinical Associate, Duke University, Durham, North carolin:' The Retroperitoneum 8 1

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Hyun Kwon Ha, MD Jeremy J. Erasmus, MD

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Robert C. Gilkeson, MD

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Associate Professor, University of Ulsan College of Medicine; Staff Radiologist, Abdominal Radiology, Department of Radiology, Asan Medical Center, Seoul, Korea The Gastrointestinal Tract 4

8

.

E. Mark Haacke, PhD Director, The MRI Institute for Biomedical Research, Detroit, Michigan; Professor and Director of MRI Center of Radiology, Wayne State University; Adjunct Professor of Physics, Case 4 Western Reserve University, Cleveland, Ohio Magnetic Resonance Angiography: Fundamentals and Techniques


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Contributors

John R. Haaga, MD

J. Bruce Kneeland, MD

Chairman and Medical Director, Department of Radiology, University Hospitals of Cleveland, Cleveland, Ohio The Gallbladder and Biliary Tract; The Pancreas; Peritoneum and Mesentery; Image-Guided Micro Procedures: CT and MRI Interventional Procedures

Professor, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania The Shoulder

Tamara Miner Haygood, PhD, MD Radiologist, Fayette Memorial Hospital, LaGrange, Texas The Shoulder

Thomas E. Herbener, MD Assistant Professor, Department of Radiology, University of Ohio, Cleveland, Ohio The Gallbladder and Biliary Tract

Leo Hochhauser, MD

Scott Kolodny, MD Assistant Professor of Radiology, Case Western Reserve University, Cleveland, Ohio The Spinal Cord; Computed Tomography and Magnetic Resonance Imaging of the Thoracic Aorta

Kenyon K. Kopecky, MD

Associate Professor of Radiology, State University of New York, Upstate Medical University, Syracuse, New York Central Nervous System Trauma

Professor of Radiology, Indiana University School of Medicine, Indianapolis, Indiana Multislice Helical Computed Tomography: Clinical Applications

Roy A. Holliday, MD

Janet E. Kuhlman, MD, MS

Department of Radiology, New York University School of Medicine, New York, New York Cervical Adempathy and Neck Masses

Professor of Radiology, University of Wisconsin Medical School, Hospital and Clinics, Madison, Wisconsin L Non-neoplastic Parenchymal Lung Disease

Andrei I. Holodny, MD Associate Professor of Radiology, Memorial Sloane-Kettering Cancer Center, New York, New York Neurodegenerative Disorders '

Barbara L. Knisely, MD Assistant Professor of Diagnostic Radiology, University of Wisconsin Medical School, Hospital, and Clinics, Madison, Wisconsin Pleura and Chest Wall

David S. Jacobs, MD Director of Neuroradiology and MRI, Hillcrest Hospital, Cleveland Clinic Health System, Mayfield Heights, Ohio Degenerative Diseases of the Spine

Sassan Karimi, MD Assistant Professor of Radiology, Memorial Sloane-Kettering Cancer Center, New York, New York Neurodegenerative Disorders

Stephen A. Kieffer, MD Professor of Radiology, University of Minnesota Medical School; Attending Neuroradiologist, Fairview-University Medical Center, Minneapolis, Minnesota Intracranial Neoplasms

Jeong Kon Kim, MD Fellow, University of Ulsan College of Medicine, Abdominal Radiology, Department of Radiology, Asan Medical Center, Seoul, Korea The Gastrointestinal Tract

Paul Kim, MD Assistant Professor of Clinical Radiology, University of Southern California Keck School of Medicine, Los Angeles, California Cerebral Infections and I n . t i o n

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r

Lester Kwock, PhD Professor of Radiology, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina Brain Magnetic Resonance Spectroscopy

Barton Lane, MD, FACR Professor of Neuroradiology and Neurosurgery, Stanford University Medical School and Medical Center, Stanford; Chief of Radiology, Palo Alto Veterans Administration Medical Center, Palo Alto, California Leukoencephalopathies and Demyelinating Disease; ImageGuided Spinal Interventions

Charles F. Lanzieri, MD, FACR Professor of Radiology and Neurosurgury, Department of Radiology, University Hospitals of ClevelandICase Western Reserve University School of Medicine, Cleveland, Ohio The Sirtonasal Caviv; Magnetic Resonance Imaging of Infections of the Spine

Theodore C. Larson Ill, MD Associate Professor of Radiology and Radiological Sciences and Associate Professor of Otolaryngology, Vanderbilt University School of Medicine; Director of Head and Neck Radiology and Director of Interventional Neuroradiology, Vanderbit University Medical Center, Nashville, Tennessee Cerebral Aneurysms and Vascular Malformations; Thyroid and Parathyroid Glands

Errol Levine, MW, PhD, FACR, FRCR Professor and Head, Sections of Computed Body Tomography, Magnetic Resonance Imaging, and Uroradiology, Department of Diagnostic Radiology, University of Kansas Medical Center, Kansas City, Kansas The Kidney


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Contributors

Jonathan 5. Lewin, MD

M. Hossain Naheedy, MD

Professor of Radiology, Oncology, and ~euro~ogical Surgery, Case Western Reserve University School of Medicine; Vice Chairman, Research and Academic Affairs, and Director of Magnetic Resonance Imaging, University Hospitals of Cleveland, Cleveland, Ohio Nasopharynx and Oropharynr

Associate Professor of Radiology, Case Western Reserve University School of Medicine; Director, Radiology, at Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, Ohio Normal Computed Tomography and Magnetic Resonance Imaging Anatomy of the Brain and the Spine

Weili Lin, PhD Associate Professor, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina Magnetic Resonance Angiography: Fundamentals and Techniques

Neal Mandell, MD Visiting Professor, Yale University School of Medicine, New Haven; Chairman, Department of Radiology, Charlotte Hungerford Hospital, Tomngton, Connecticut The Orbit

William H. Martin, MD Assistant Professor of Radiology and Medicine, Vanderbilt University School of Medicine and Veterans Administration Medical Center, Nashville, Tennessee Thyroid and Parathyroid Glands

H. Page McAdams, MD Associate Professor, Department of Radiology, Duke University Medical Center; Staff Radiologist, Duke University Hospital, Durham, North Carolina Primary Pulmonary Neoplasms; The Mediastinurn

Jeffrey D. McTavish, MD Instructor in Radiology, Harvard Medical School; Director of Body MRI, Brigham & Women's Hospital, Boston, Massachusetts Hepatic Mass Lesions

Dean A. Nakamoto, MD Assistant Professor, Department of Radiology, Case Western Reserve University School of Medicine and University Hospitals of Cleveland, Cleveland, Ohio The Spleen

Sherif Gamal Nour, MD MR. Research Associate, School of Medicine, Case Western Reserve University; Research Fellow of Interventional MRI, Department of Radiology, University Hospitals of Cleveland1 Case Western Reserve University, Cleveland, Ohio; Assistant Lecturer of Diagnostic Radiology, Department of Diagnostic Radiology, Cairo University Hospitals, Cairo, Egypt Nasopharynx and Oropharynx

Raymond F? Onders, MD Assistant Professor, Department of Surgery, University Hospitals at Cleveland and Case Western Reserve University School of Medicine, Cleveland, Ohio The Spleen

Eric K. Outwater, MD Professor of Radiology, University of Arizona School of Medicine; Attending Physician, University Medical Center, Veterans Hospital, and Kino Community Hospital, Tucson, Arizona Magnetic Resonance Imaging of the Pelvis

Carolyn Cidis Meltzer, MD

Kathleen Gallagher Oxner, MD

Associate Professor of Radiology and Psychiatry, University of Pittsburgh School of Medicine; Medical Director, Positron Emission Tomography Facility, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania Meningeal Processes

Radiologist, Greenville Radiology, Greenville, South Carolina The Shoulder

Elmar M. Merkle, MD Associate Professor of Radiology, Medical School, Case Western Reserve University; Director of Body MR Imaging, Department of Radiology, University Hospitals of Cleveland, Cleveland, Ohio Liver: Nonnal Anatomy, Imaging Techniques, and Diffuse Diseases

Floro Miraldi, MD, PhD President, Neo-pet, LLC, Cleveland Heights, Ohio Imaging Principles in Computed Tomography

Mark D. Murphey, MD Chief, Musculoskeletal Radiology, Department of Radiologic Pathology, Armed Forces Institute of Pathology, Washington, D.C.; Associate Professor, Uniformed Services University of the Health Sciences, Departments of Radiology and Nuclear Medicine, Bethesda; Clinical Professor, University of Maryland School of Medicine, Department of Radiology, Baltimore, Maryland The Hip

Cheryl A. Petersilge, MD Assistant Clinical Professor of Radiology and Orthopedic Surgery, Case Western Reserve University School of Medicine; Director, Musculoskeletal and Emergency Radiology, Hillcrest Hospital, Cleveland, Ohio The Hip

Jay J. Pillai, MD Associate Professor of Radiology, Medical College of Georgia School of Medicine; Staff Attending Neuroradiologist, Medical College of Georgia Hospital and Clinics, Angusta, Georgia Brain Magnetic Resonance Spectroscopy

Donna M. Plecha, MD Assistant Professor of Radiology, Case Western Reserve University School of Medicine and University Hospitals of Cleveland, Cleveland, Ohio Extramedullary Spinal Tumors

Deborah L. Reede, MD Long Island College of Medicine, Brooklyn, New York Cervical Adenopathy and Neck Masses


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Contributors

Pablo R. Ros, MD, MPH

Michelle M. Smith, MD

Professor of Radiology, Harvard Medical School; Executive Vice Chair, Department of Radiology, Brigham & Women's Hospital, Boston, Massachusetts Hepatic Mass Lesions

Department of Radiology, Froedtert Hospital, Milwaukee, Wisconsin Thyroid and Parathyroid Glands

Santiago E. Rossi, MD Jefe de Trabajos Practices, Universidad de Buenos Aires and Universidad de Ciencias Biomedicas Rene Tavaloro; Hospital Universitario de Clinicas Jose de San Martin; Director, Centro de Diagnostic0 Dr. Enrique Rossi, Buenos Aires, Argentina Primary Pulmonary Neoplasms

Anna Rozenshtein, MD Assistant Professor of Clinical Radiology, College of Physicians and Surgeons of Columbia University; Director of Thoracic Radiology, St. Luke's-Roosevelt Hospital Center, New York, New York Magnetic Resonance Imaging of the Heart

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John A. Spencer, MA, MD, MRCP, FRCR Consultant Radiologist, St. James's University Hospital, Leeds, United Kingdom, and Rijntgen Professor of the Royal College of Radiologists Computed Tomography of the Pelvis

Charles E. Spritzer, MD Professor, Department of Radiology, Duke University, School of Medicine and Medical Center; Staff Radiologist, Duke University Hospital, Durham, North Carolina The Mediastinum

Peter J. Strouse, MD

Associate Professor of Radiology, Indiana University School of Medicine, Indianapolis, Indiana Multislice Helical Computed Tomography: Clinical Applications

Assistant Professor, Section of Pediatric Radiology, Department of Radiology, University of Michigan Medical School; Ann Arbor, Attending Physician*C. S. Matt Michigan Musculoskeletal 'ystem

Ken L. Schreibman, PhD MD

Jeffrey L. Sunshine, MD, PhD

Jonas Rydberg, MD

Associate Professor of Radiology, University of Wisconsin School of Medicine, Madison, Wisconsin The Foot and Ankle

Assistant Professor of Radiology, Case Western Reserve University, Cleveland, Ohio The Spinal Cord

Hervey D. Segall, MD

Sarah E. Swift, MR, MRCP, FRCR

Professor of Radiology, University of Southern California Keck School of Medicine and Los Angeles County-University of Southern California Medical Center, Los Angeles, California Cerebral Infections and Inflammation

Consultant Radiologist, St. James's University Hospital, Leeds, United Kingdom Computed Tomography of the Pelvis

Steven Shankman, MD

Professor, Department of Radiology, Indiana University School of Medicine, Indianapolis, Indiana The Mediastinum

Vice-Chairman, Department of Radiology and Resident Program Director, Maimonides Medical Center, Brooklyn, New York The Knee

Patrick F. Sheedy II, MD Professor, Department of Radiology, Mayo Medical School; Department of Radiology, Mayo Clinic and Mayo Foundation; Department of Radiology, Saint Marys Hospital and Rochester Methodist Hospital, Rochester, Minnesota The Adreml Glands

Robert D. Tarver, MD

John J. Wasenko, MD Associate Professor of Radiology and Director of Magnetic Resonance Imaging, State University of New York Upstate Medical University, Syracuse, New York Central Nervous System Trauma

Timothy J. Welch, MD Marilyn J. Siegel, MD Professor of Radiology, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri Pediatric and Adolescent Pelvis

Associate Professor, Mayo Medical School; Consultant, Mayo Clinic, Rochester, Minnesota The Adrenal Glands

Ernest 1. Wiesen, BSEE Michael S. Sims President and CEO, UltraGuide, Inc., Cleveland, Ohio Imaging Principles in Computed Tomography

Carlos J. Sivit, MD Professor of Radiology and Pediatrics, Case Western Reserve University; Director of Pediatric Radiology, Rainbow Babies and Childrens Hospital, Cleveland, Ohio Pancreas; Gastrointestinal Tract, Peritoneal Cavity, and Mesentery

Formerly, Assistant Professor, Department of Radiology, Case Western Reserve University School of Medicine; Radiologic Physicist, Department of Radiology, MetroHealth Medical Center, Cleveland, Ohio Imaging Principles in Computed Tomography

Wade H. Wong, MD Professor of Radiology, University of California, San Diego, California Image-Guided Spinal Interventions


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Contributors

Chi-Shing Zee, MD

J. Michael Zerin, MD

Professor of Radiology and Neurosurgery and Director of Neuroradiology, University of Southern California Keck School of Medicine, Los Angeles, California Cerebral Infections and InpMunation

Professor of Radiology, Wayne State University School of Medicine; Director of Ultrasound Imaging, Department of Pediatric Imaging, Children's Hospital of Michigan, Detroit, Michigan Kidneys and Adrenal Glands


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Preface The progress in computed imaging over the past 25 years has been remarkable, to say the very least. These new modalities have revolutionized the delivery of health care around the world and improved the lives of innumerable citizens of the planet. The astonishing development of technology has truly spread worldwide so that even people in the remotest country or island have the benefit of imaging (albeit the highest technology still is present in the developed countries). A graphic demonstration of this spread of technology and medical knowledge can be appreciated by noting the new trend to have international interpretation of night-time studies around the world. Medicine now chases the sun in its use of computerized imaging and beams the images between countries so that nighthawk reading services help rationalize radiology care by making the best use of manpower around the world. The impact of computed tomography (CT) and magnetic resonance imaging (MRI) on medicine can be further appreciated by noting a recent survey of physicians' views on the importance of 30 medical innovations. Fuchs and Sox published an article, titled "Physicians' Views of the Relative Importance of Thirty Medical Innovations in Health Affairs," in SeptemberIOctober 2001. In their survey of 225 leading internists in the United States, the replies showed that 75% of respondees believed CT and MRI were the most significant innovation, followed by ACE inhibitors, angioplasties, statins, and mammography. The acceptance and wide application have come at a philosophical and pragmatic price and risk to the profession of radiology. While government planners and HMOs have tried to stem the tide of imaging progress, the science and technology have moved ahead with unstoppable momentum. The result of the attempts of these organizations to prevent the application of these new modalities was an illconceived movement to limit the training of radiologists during the era of primary-care physician promotion. By attempting to prevent the use of imaging in health care, they interfered with the natural market forces of manpower supply and demand. The result is the current manpower shortage at a time when the need for imaging grows on a daily basis. The shortage has impaired training programs because faculty required to train radiologists have been enticed into more lucrative positions in the marketplace. It is quite evident that the role of imaging will continue to grow and provide a positive impact on the health of all citizens. Its future is ensured by the new emphasis by the National Institutes of Health (NIH) on molecular imaging and also the image-guided microsurgery procedures performed with CT and MFU. We are quite proud to note that a radiologist, Elias Zerhouni, MD, has been appointed as current director of the NM. Furthermore, we are proud that Dr. Zerhouni was a section editor in the third edition of this text.

Figure 1

It is exciting to reflect back on other high technology developments that have occurred, such as aviation (Fig. 1). If one looks at the progress made in aviation since the first flight of the Wright flyer and contrast it with the Space Shuttle, there was an increase in speed of approximately 600 times (42 mph compared to 25,000 mph) in a 100year period. With CT scanning (Fig. 2), there has been an increase in scan time of almost 1200 times in a 25-year period (7 minutes per single scan compared to 300 msec on current multislice devices).

Figure 2


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Preface

We are pleased to note the wide application of the new

We are especially grateful to all of our colleagues who

image-guided microsurgical procedures (the term interven-

have contributed to this edition because of the many diffi-

tional radiology is not specific enough or a unique descriptor). Progress in this area will continue and further improve the delivery of health care. Indeed, at the time of publication of this edition, we are even working on methodology using CT procedures to treat mediastinal collections of anthrax-laden lymph nodes in patients with inhalational anthrax. Data are very preliminary, but it seems that the heat from radiofrequency can be used to kill the vegetative forms of anthrax, and other strategies can be used to stimulate spores to germinate and become susceptible to local instillation of polymer-containing antibiotics.

culties they have overcome. Historically, it has always been difficult for authors to find time to contribute high-quality work. During this current period of faculty shortage at university centers, the commitment and dedication to our project required even more effort by our contributors. We are delighted with the content of this fourth edition and believe it provides the most up-to-date information on MRI and CT. Information about the new, fast-sequence MRI and multislice scanners is provided. We are confident that the readers of this book will be intellectually rewarded.


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Preface t o First Edition Since the introduction of computed tomography (CT) in 1974, there has been a remarkable revolution in the medical treatment of patients. The clinical use of CT has had a broad positive impact on patient management. Literally thousands of patients have been saved or their quality of life improved as a result of the expeditious and accurate diagnosis provided by CT. This improvement in diagnosis and management has occurred in all medical subspecialties, including neurological, pulmonary, cardiac, gastrointestinal, genitourinary, and neuromuscular medicine. Aside from the imaging advantages provided, the role of CT in planning and performing interventional procedures is now recognized. It is the most accurate method for guiding procedures to obtain cytological, histological, or bacteriological specimens and for performing a variety of therapeutic procedures. The evolution and refinement of CT equipment have been as remarkable as the development of patient diagnosis. When we wrote our k t book on CT, the scanning unit used was a 2-minute translate-rotate system. At the time of our second book the 18-second translate-rotate scanning unit was in general use. Currently standard units in radiological practice are third and fourth generation scanners with scan times of less than 5 seconds. All modem systems are more reliable than the earlier generations of equipment. The contrast and spatial resolution of these systems are in the range of 0.5% and less than 1 mm, respectively. The sophistication of the computer programs that aid in the diagnosis is also remarkable. There are now programs for three-dimensional reconstructions, quantitation of blood flow, determination of organ volume, longitudinal scans (Scoutview, Deltaview, Synerview, and Topogram), and even triangulation programs for performing percutaneous biopsy procedures. CT units are now being installed in virtually every hospital of more than 200 beds throughout the United States. Most radiologists using these units are generalists who scan all portions of the anatomy. Because of the dissemination of this equipment and its use in general diagnosis, there exists a significant need for a general and complete textbook to cover all aspects of CT scanning. Our book is intended to partially supplement the knowledge of this group of physicians. We have attempted to completely and succinctly cover all portions of CT scanning to provide a complete general reference text. In planning the book, we chose to include the contributions of a large number of talented academicians with expertise different from and more complete than our own in their selected areas. By

including contributors from outside our own department, we have been able to produce an in-depth textbook that combines the academic strengths of numerous individuals and departments. The book is divided into chapters according to the organ systems, except for some special chapters on abscesses and interventional procedures. In each of the chapters the authors have organized the material into broad categories, such as congenital, benign, or neoplastic disease. Each author has tried to cover the major disease processes in each of the general categories in which CT diagnosis is applicable. Specific technical details, including the method of scanning, contrast material, collimation, and slice thickness, are covered in each chapter. The interventional chapter extensively covers the various biopsy and therapeutic procedures in all the organ systems. Finally, the last chapter presents an up-to-the-minute coverage of current and recent developments in the CT literature and also provides extensive information about nuclear magnetic resonance (NMR) imaging. At this time we have had moderate experience with the NMR superconducting magnetic device produced by the Technicare Corporation and have formulated some initial opinions as to its role relative to CT and other imaging modalities. A concise discussion of the physics of NMR and a current clinical status report of the new modality are provided. We would like to thank all those people who have worked so diligently and faithfully for the preparation of this book. First, we are very grateful to our many contributors. For photography work, we are deeply indebted to Mr. Joseph P. Molter. For secretarial and organizational skills, we are indebted especially to Mrs. Mary Ann Reid and Mrs. Rayna Lipscomb. The editorial skills of Ms. B. Hami were invaluable in preparing the manuscript. Our extremely competent technical staff included Mr. Joseph Agee, Ms. Ginger Haddad, Mrs. E. Martinelle, Mr. Mark Clampett, Mrs. Mary Kralik, and numerous others. Finally, we are, of course, very appreciative of the support, patience, and encouragement of our wonderful families. In the Haaga family this includes Ellen, Elizabeth, Matthew, and Timothy, who provided the positive motivation and support for this book. Warm gratitude for unswerving support is also due to Rose, Sue, Lisa, Chris, Katie, Mary, and John Alfidi. John R. Haaga Ralph J. Alfidi


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Contents 13 Leukoencephalopathies and Demyelinating Disease Barton Lane

VOLUME ONE

Part I Principles of Computed Tomography and Magnetic Resonance Imaging

431

Part III Imaging of the Head and Neck

Edited by Jeffrey L. Duerk

Edited by Charles F. Lanzieri 1 Imaging Principles in Computed Tomography Floro Miraldi, Michael S. Sims, Ernest J. Wiesen

2

2 Magnetic Resonance Physics: An Introduction Enrol M. Bellon, Pedro J. Diaz, Jeffrey L. Duerk

37

3 Magnetic Resonance Angiography: Fundamentals and Techniques

51

14 The Orbit Jon Mark Fergenson, Neal Mandell, James J. Abrahams

474

15 Temporal Bone Donald W. Chakeres, Mark A. Augustyn

495 553

Charles F. Lanzieri

E. Mark Haacke, Weill Lin

17 Cervical Adenopathy and Neck Masses Roy A. Holliday, Deborah L. Reede

Part II Brain and Meninges

575 601

Edited by Charles Lanzieri

Hugh D. Curtin 619

4 Normal Computed Tomography and Magnetic Resonance Imaging Anatomy of the Brain and the Spine M. Hossain Naheedy

Sherif Gamal Nour, Jonathan S. Lewin 88

20 Thyroid and Parathyroid Glands Theodore C. Larson III, Michelle M. Smith, Wui K. Chong, William H. Martin

663

124 691

Stephen A. Kieffer, Ja-Kwei Chang John C. Egelhoff 6 Cerebral Infections and Inflammation Chi-Shing Zee, John L. Go, Paul Kim, Hervey D. Segall, Jamshid Ahmadi

207

Part IV Imaging of the Spine 246

James D. Eastwood 8 Cerebral Aneurysms and Vascular 285 Theodore C. Larson III 317 John J. Wasenko, Leo Hochhauser 10 Neurodegenerative Disorders Andrei I. Holodny, Ajax E. George, Mony J. de Leon, Sassan Karimi

351

11 Brain Magnetic Resonance Spectroscopy Jay J, Pillai, Lester Kwock

371

22 Degenerative Diseases of the Spine

724

David S. Jacobs

765 Donna M. Plecha 783 Jeffrey L. Sunshine, Scott Kolodny 25 Magnetic Resonance Imaging of 805 Charles F. Lanzieri

401 Melanie B. Fukui, Carolyn Cidis Meltzer

Edited by Jeffrey L Sunshine

26 Image-Guided Spinal Interventions Wade H. Wong, Huy M. Do, Barton Lane

814


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Contents

Part V

41 The Kidney

Imaging of the Chest

42 Peritoneum and Mesentery

Edited by John R. Haaga

1611

John R. Haaga

43 The Retroperitoneum 27 Non-neoplastic Parenchymal Lung Disease

1537

Vikram Dogra, Enrol Levine

838

Janet E. Kuhlman

1657

Ashok K. Gupta, Richard H. Cohan

44 Computed Tomography of the Pelvis

1715

John A. Spencer, Sarah E. Swift

28 Primary Pulmonary Neoplasms

904

Jeremy J. Erasmus, H. Page McAdams, Santiago E. Rossi

29 Mediastinum

937

Part VII Imaging of the Musculoskeletal System

997

Edited by Mark Robbin

Barbara L. Knisely

46 Musculoskeletal Tumors

31 Computed Tomography and Magnetic Resonance Imaging of the Thoracic Aorta 1017 Robert C. Gilkeson, Scott Kolodny

32 Computed Tomography of the Heart and Pericardium 1063 Lynn S. Broderick

1806

Amilcare Gentili

47 Computed Tomography and Magnetic Resonance Imaging of the Foot and Ankle

1825

Ken L. Schreibman

48 The Knee

1869

Steven Shankman, Javier Beltran

49 The Hip

33 Magnetic Resonance Imaging of the Heart Anna Rozenshtein, Lawrence Nl Boxt

1751

Eric K. Outwater

H. Page McAdams, Jeremy J. Erasmus, Robert D. Tarver, Charles E. Spritzer

30 Pleura and Chest Wall

45 Magnetic Resonance Imaging of the Pelvis

1089

1909

Mark D. Murphey, Cheryl A. Petersilge

50 The Shoulder

1939

Tamara Miner Haygood, Kathleen Gallagher Oxner, J. Bruce Kneeland, Murray K. Dalinka

VOLUME TWO

Part VI Imaging of the Abdomen and Pelvis

Part VIII

Pediatric Radiology

Edited by Carlos J. Sivit 51 Computed Tomography and Magnetic Resonance Imaging in the Pediatric Patient: Special Considerations

Edited by John R. Haaga

1974

Donald P. Frush

34 The Gastrointestinal Tract

1154

52 Heart and Great Vessels Sheila C. Berlin

1985

1271

53 Chest Lane F. Donnelly

2000

54 Hepatobiliary System

2013

Hyun Kwon Ha, Jeong Kon Kim

35 Hepatic Mass Lesions Jeffrey D. McTavish, Pablo R. Ros

36 Liver: Normal Anatomy, Imaging Techniques, and Diffuse Diseases

Ellen C. Benya

1318

Elmar M. Merkle, Thorsten R. Fleiter, Daniel T. Boll, Hans-Juergen Brambs

37 The Gallbladder and Biliary Tract

55 Pediatric Spleen

2023

Kimberly E. Applegate

56 Pancreas 1341

John R. Haaga, Thomas E. Herbener

2032

Carlos J. Sivit

57 Kidneys and Adrenal Glands

2039

J, Michael Zerin

38 The Pancreas

1395

John R. Haaga

39 The Spleen

1487

Dean A. Nakamoto, Raymond R Onders

40 The Adrenal Glands Timothy J. Welch, Patrick R Sheedy II

58 Gastrointestinal Tract, Peritoneal Cavity, and Mesentery

2061

Carlos J. Sivit

59 Pediatric and Adolescent Pelvis

2075

Marilyn J. Siegel 1511

60 Musculoskeletal System Peter J. Strouse

2095


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Part IX

62 Multislice Helical Computed Tomography: Clinical Applications 2259

Special Considerations

61 Image-Guided Micro Procedures: CT and MRI Interventional Procedures John R. Haaga

XVU

Kenyon K. Kopecky, Jonas Rydberg, Thorsten R. Heiter, Kenneth A. Buckwalter 2123

Index


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Part

Principles of Computed Tomography and Magnetic Resonance Imaging Edited by

Jeffrey L. Duerk


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Imaging Principles in Computed Tomography Floro Miraldi, Michael S. Sims, Ernest J. Wiesen

A computed tomography (CT) image is a display of the anatomy of a thin slice of the body developed from multiple x-ray absorption measurements made around the body's periphery. Unlike conventional tomography, in which the image of a thin section is created by blurring out the information from unwanted regions, the CT image is constructed mathematically using data arising only from the section of interest. Generating such an image is confined to cross-sections of the anatomy that are oriented essentially perpendicular to the axial dimension of the body (Fig. 1-1). Reconstruction of the final image can be accomplished in any plane, but conventionally it is performed in the transaxial plane. In its most basic form, the fundamental principles of CT are the same as those for radiography and tomography. Each approach directs a source of ionizing radiation through an object to recreate an image of the original object based on the x-ray absorption of the object. The basic equation used is the same for each,

where

I, is the incident intensity of an x-ray beam on the surface of an object of thickness, x I is the transmitted intensity e is Euler's constant (2.718) )I, is the linear attenuation coefficient (Fig. l-2)'f

I9

Attenuation is dependent on (1) the atomic number and density of the material through which the x-rays pass and (2) the energy spectrum of the incident x-ray beam.lg With conventional radiography and tomography, the differential absorption of x-rays passing through an object is recorded on film, a qualitative measurement that cannot accurately reflect subtle differences in object contrast. On the other hand, differential absorption for CT is recorded by special detectors, which are quantitative and can measure subtle changes in x-ray attenuation. Radiography's most major shortfall is the superimposition of the structures on film, which has been only partially overcome by conventional tomography. The earliest CT was designed by Godfrey Hounsfield to overcome the visual representation challenges in radiography and tomography by collimating the x-ray beam and transmitting x-rays only through small cross-sections of an

object. The idea revolutionized the practice of radiology and helped win Hounsfield a share of the Nobel Prize. More recent CT developments since the mid- 1980s have advanced CT from a radiology tool l h t e d to anatomic representations to a tool capable of demonstrating physiologic and pathogenic information. This chapter presents the physics of CT image production in qualitative terms to familiarize the practicing radiologist with the basic principles of CT. Equipment and factors that affect CT image quality are discussed, and an introduction to emerging applications using CT is provided.

Basic Principles The fundamental concept of CT is that the internal structure of an object can be reconstructed from multiple projections of the object (Fig. 1-3). The object in Fig. 1-3A is composed of a number of equal blocks from which the central four have been removed to represent an internal structure. For the sake of simplicity, assume that an x-ray beam is passed through each row and column of blocks and the transmitted radiation is measured. Since each block is the same, the measured attenuation is proportional to the number of blocks encountered in each row or column. The numbers shown at the right and beneath the object represent the relative measured attenuation (i.e., the number of blocks in each row or column). These attenuation measurements are then added (Fig. 1-3B) to produce a numeric representation of the object (Fig. 1-3C). Although this array of numbers contains all the information of the process, it is difficult to interpret; thus, the array is converted into picture form by assigning a gray scale to the numbers. Large numbers are represented by light shades of gray, and small numbers are represented by dark shades of gray. The result is the image shown in Figure 1-30. The resultant image can then be manipulated to highlight certain areas. For example, if the gray scale is narrowed to include only black and white, a perfect reproduction of the object is obtained by assigning black to d l numbers equal to four or less and white to all numbers greater than four. In Figure 1-3E, an imperfect representation is obtained because the gray scale is chosen so that values of six and lower are black and values above six are white. In CT, the method of obtaining the array of numbers is more complex


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Chapter 1

and the number of projections obtained is much greater; however, the principle is the same. The example of Figure 1-3 also provides a basis for a number of definitions of CT terms. Each of the blocks in Figure 1-3A represents a small attenuating volume of material and is referred to as a voxel. The numbers at the side and bottom of Figure 1-3A represent single attenuation measurements and are called ray projections, or ray sums. The array of numbers in Figure 1-3C is a matrix, and the individual numbers are elements of that matrix. Each of the blocks of gray that are used for the construction of the images in Figure 1-3D-F is a picture element (pixel).The process of choosing the number of gray shades for a display is referred to as "selecting a window." The width of the window (Fig. 1-3E and F) is narrow because it only contains two shades of gray (black and white) compared with the wider window in Figure 1-30, which contains three shades of gray. The number at which the

L (em) Figure 1-2. Exponential behavior of x-ray beam attenuation.

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Imaging Principles in Computed Tomography

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window setting is centered is called the w i d o w level. In Figure 1-3E, the level is set at four; in Figure 1-3F, it is set at six. To present attenuation data (either I or p) at every point throughout the body would be ideal in an x-ray examination. The degree to which this is attained depends on the manner in which the measured intensities, I and b, are registered or manipulated. In conventional radiography, the transmitted intensity (I) is seen as the darkening of a film. Because x-ray exposure of the film blackens it, the image of a dense object is lighter on the film than the image of a less dense material. In a typical radiographic film of the chest, for example, the image is light where many x-rays are absorbed or scattered (large p), such as in bone, and dark where many x-rays are transmitted because of low absorption (small p), such as in the regions of the lung parenchyma. Two different areas of such a chest film may show the same darkening and therefore demonstrate equal total attenuation of the beam in the two positions. However, the attenuation profile through the body may be quite different. This is diagrammatically shown in Figure 1-4, with one beam passing through a region of relatively uniform density and the other beam passing through a region of nonuniform densities. In conventional radiography, therefore, the different shades of gray seen on the film represent the differences in the transmission of an x-ray beam as it passes through the body. CT, however, approaches the ideal by presenting the average attenuation of each small volume element that comprises the body slice. Thus, CT unscrambles the attenuation information of the x-ray beam and presents it quantitatively with accuracy far greater than that accomplished by conventional techniques. This is equivalent to providing the individual values p,, p,, and k, of Figure 1-4 rather than the total value described for conventional radiography. All CT systems use a similar three-step process to generate a CT image: (1) scan, or data acquisition, (2)


Part 1

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Principles of Computed Tomography and Magnetic Resonance Imaging X-rays

4+4

X-rays

Figure 1-3. Principle of image reconstruction. (From Christensen EE, Cuny TS 111, Dowdey JE: An Introduction to the Physics of Diametric Radiology, 2nd ed. Philadelphia, Lea & Febiger, 1978.)

reconstruction, and (3) display; each process is considered separately throughout this chapter. In the most basic form, the flow of all CT systems includes the conversion of an x-ray source consisting of a collection of rays (projection or view). A single ray is considered the portion of the xray beam that falls onto one detector.

we address the evolution of CT data acquisition and CT scanning geometry, it is valuable to review the basic components of every CT data acquisition system.

Data Acquisition

Scan Frame

The scanning process begins with data acquisition. CT scanning is the systematic collection of projection data. Data collection encompasses all of the geometric properties of the x-ray beam and the relationship of the x-ray tube to the detector, including all of the beam-shaping devices and conversion of transmitted x-rays to digital signals for use by the reconstruction system. Since Hounsfield's invention, CT scanning geometry has evolved considerably. Before

Early CT scanners (in the 1980s) deployed rotating frames and recoiling system cables. This design was limited to step-and-shoot scan methods and considerably limited scanner rotation times. Current systems employ slip rings, electromechanical devices that transmit electrical energy across a rotating surface. Slip rings permit the scan frame to rotate continuously, enabling spiral or helical CT scanning and eliminating the need to rewind system cables.

Components of a Data Acquisition System

Figure 1-4. Total attenuation of equal amount in two different cases. A, Nonuniform attenuation coefficients. B, Uniform medium.


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Chapter 1

X-ray G e n e r a t o r s Most CT scanners today use high-frequency generators to produce x-ray quanta required for today's demanding CT protocols. 'Qpical operating frequencies range from 5 to 50 kHz. Generator power can range from as low as 15 kilowatts (kW) to as high as 60 kW, and recent develop ments are likely to support ranges as high as 70 to 80 kW. In any case, most generators support a wide range of exposure techniques from 80 to 140 kilovolts (kV) and 30 to 500 milliamperes (rnA). The generators are located on rotating scan frames within the CT gantry to accommodate new spiral scanning requirements. X-ray T u b e s Early-generation CT technology used fixed-anode, oilcooled x-ray tubes with fairly limited capability. Today's x-ray tubes include rotating anodes with unique cooling methods designed to enhance a system's ability to cover large areas of anatomy at diagnostic levels of x-ray output. Tube ratings typical in CT scanners today vary from 2 million heat units (2 MHU)of storage capability, with 300 thousand heat units (IcHU)/minute cooling, up to 7 MHU of anode heat storage capability and cooling rates as fast as 1 million heat units (MHU)/minute. Future enhancements will not preclude tubes with greater than 10 MHU capacity and continuous output power capability of 60 kW. Both x-ray generator and x-ray tube developments are expected to open up the door for true volumetric CT applications with large area detectors designed to cover entire sections of patient anatomy within one revolution of the CT scanner's rotating frame. X-ray Beam Filtration System It is assumed that CT employs a monochromatic beam. The opposite is true; radiation from CT x-ray tubes is polychromatic. To compensate for this fact, the x-ray beam is shaped by compensation filters. The filters serve two purposes: 1. They remove the long-wavelength x-rays, which do not contribute to the CT image but do contribute to patient dose as these so-called soft rays are absorbed by the patient. 2. They serve to minimize the effects of beam hardening and provide a more uniform beam, as seen from the perspective of the detector. Different filters are used for half-field (head) scanning and full-field (body) scanning. Additional corrections for beam hardening are made during the CT reconstruction process with software. D a t a Acquisition Systems Data acquisitions systems are the heart of a CT scanner. They include (1) the detector system, (2) analog-to-digital conversion, and (3) some data preprocessing for use by the scanners reconstruction system. The major functions are as follows"4: To convert x-ray flux to electric current To convert electric current to voltage To convert analog voltage to digital form

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Imaging F'rinciples in Computed Tomography

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To subtract background offset signal To provide logarithmic conversion of data To transmit data to the preprocessing system Early data acquisition systems employed xenon (gas ionization detectors). These detectors directly convert xray energy to electrical energy but are inefficient. Most modem systems include the use of solid-state detectors. Two primary crystal materials are in use today, cadmium tungstate and gadolinium oxysulfide. The crystals convert the x-rays to light proportional to the quantity of photons striking the crystal. The light is converted to current and hence a voltage across a resistance and then to digital data for use by the reconstruction system. The conversion of analog signals to digital data (A to D conversion) by the data acquisition system creates a quantization error. Sampling speed of the A to D converter and the number of digital output combinations available determine quantization error. This quantization error, along with electronic noise in the amplifier, generally characterizes the performance of the data acquisition system. The system's ability to measure low-level signals accurately over a wide dynamic range largely contributes to CT's overall image quality capabilities per a given x-ray flux.

Evolution of Data Acquisition Systems and CT System Geometry First-Generation System Fist-generation CT data acquisition was based on parallel-beam geometry with a translate-rotate principle of the tubeldetector combination. The x-ray beam was collimated to dimensions of roughly 2 X 13 rnm. The 13-mm dimension corresponded to the slice thickness (voxel length). Small detectors monitored the intensity of the beam before entering the body to yield the value of the incident intensity (I,,). After passing through the body, the beam was detected by a scintillation crystal, collimated to receive, primarily, those photons that were not scattered or absorbed. The amount of transmitted intensity (I) was then recorded and stored in the computer memory. The x-ray tube and detector system were moved continuously across the patient, making 160 multiple measurements during the translation. At the end of each translation, the x-ray tube and detector system were rotated 1 degree and the translation repeated. The translate-rotate process was repeated for 180 translations, yielding 28,800 (160 X 180) measurements. The 160 measurements made during one complete translation are called a profile or view. From a clinical standpoint, the first-generation machine had the major disadvantage of long scanning times. Image quality severely suffered from the effects of patient motion, since 5 minutes was required to gather the 28,800 ray sums. This disadvantage limited use to body parts such as the head, which can be made immobile. S e c o n d - G e n e r a t i o n System Second-generation data acquisition and scanner geometry included fan-beam reconstruction with a linear detector array. The x-ray beam was converted to a fan shape with a

6

RoshanKetab Medical Publishers Part I I Principles of Computed Tomography and

Direction of motion

:. '

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Magnetic Resonance Imaging radially and do not view the scan area uniformly. Only the

X-ray source

A

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Detector

I I

I

A >a
TI). If this is not the case, steady-state effects must be taken into account because their effect on contrast can be significant. For these short TR cases, the RF pulse alters the residual transverse magnetization as well as the partially recovered longitudinal magnetization. A steady state of unrecovered magnetization is maintained by the fast repetition. This different (from fully recovered) initial magnetization can be manipulated to provide additional contrast possibilities. Depending on the manufacturer, these sequences go by the names FAST, GRASS, or FISP. The longitudinal component of the magnetization is dependent on the steady-state magnetization which is, in turn, dependent on the amount of T2 decay between pulses.


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Magnetic Resonance Physics: An Introduction

49

Table 2-1. Tissue Characteristics for Various Scan Seauences Sequence Spin echo Spin echo Spin echo Inversion recovery Inversion recovery Gradient echo Gradient echo

Parameter

Parameter

Long TR Short TR Long TR

Short TE Short TE Long TE Long TE Short T1 ShortTE Flip angle UO Short TE

Contrast Qpe (Weighting) Spin density TI

T2 T2 T1 T2 TI

CSF

Gray Matter

White Matter

Fat

Muscle

Disk

Gray Dark Bright Bright Dark Bright Dark

Isointense Gray Gray Gray Gray Gray Gray

Gray-black Bright ,gay Black Black Bright gray Dark Bright gray

Bright Bright Gray-black Gray-black Bright Gray-black Bright

Isointense Isointense Gray-black Gray-black Isointense Isointense Gray-black

Bright gray Isointense Bright Bright Isointense Isointense Bright

CSE cerebrospinal fluid; TE, echo time; TR, repetition time.

Three-Dimensional Gradient-Echo Acquisitions In most conventional acquisitions, the imaged volume results from signal from distinct planes excited by the selective RF pulses applied in the presence of a magnetic field gradient. At soon as the signal from one slice is collected, excitation of the next spatial location can occur. In this way, the acquisition of slice information is interleaved in time within the TR.The acquisition time largely appears independent of the number of slices acquired. In rapid gradient-echo acquisitions, TR is very short (i.e., on the order of tens of msec versus hundreds or thousands of msec or less), thereby leaving little time for slice interleaving when multiple slices are needed. A different mechanism is used to obtain information over the image volume. In three-dimensional (3D) gradient echo acquisitions, instead of information being acquired from distinct planes, signal is obtained from the entire imaging volume for each acquisition. Frequency encoding and phase encoding are performed along the image planes as in a typical acquisition, yet an additional phase encoding is also applied along the slice select direction. Excitation is performed over a slab instead of a slice, and the phase encoding along the slice select direction subdivides the signal in this direction just as it does in conventional MRI. Thus, in 3D acquisitions, image resolution along the slabselect direction is not dependent on the slice select RF pulse bandwidth and the gradient strength but, instead, on the slab thickness and the phase-encoding gradient process, just as the phase-encoding process determines the image resolution along the phase-encoding axis in a two-dimensional (2D) image.

Figure 2-14. A 2D gradient-echo sequence consists of a radiofrequency (RF)slice selection and phase encoding along a separate axis. The read gradient is used for encoding along the third image axis. The RF pulse excites a thin slice of tissue, and signal only comes from that slice. In a 3D sequence, a weaker gradient pulse is used to excite a slab of tissue. The slab is then subdivided by a phase encoding, also performed along the slice direction in a manner comparable to dividing the field of view with the phaseencoding gradients in a normal sequence. A 3D Fourier transform reconstruction is used.

slice

Phase

Read+

A 2D and a 3D pulse sequence is shown in Figure 2-14. Because phase encodings are performed along multiple axes, the total acquisition time becomes TR * Ny * NSA * Nz. Typical values for Ny in any acquisition are 128 to 512, whereas Nz for a 3D acquisition may vary from 4 to 256. Although the acquisition time in 3D acquisitions seems to be Nz times longer in a 3D gradient-echo than a spin-echo acquisition, the TRs in these sequences are typical only a few milliseconds in duration in comparison to the hundreds or thousands in spin-echo methods. The advantages of a 3D acquisition are the high spatial resolution along the slab select direction and the wide range of contrasts available from spoiled or unspoiled gradient-echo sequences.

Review and Integration Any MRI study directly shows received signal arnplitude as a function of position. For a given pixel, amplitude depends on the (1) TI, T2, and proton density of the substance being imaged; (2) motion, such as flow; (3) system noise, and (4) pulse sequence used. Most components of the body contain approximately similar quantities of hydrogen and, therefore, have similar equilibrium magnetization. Air spaces are an exception. The MRI signal elicited in solids disappears extremely rapidly (often within microseconds) and can take hours or days to reestablish equilibrium magnetization. Thus, solids have a long T1 and a short T2.The solid tissues encountered in clinical practice are cortical bone, tooth enamel, and dentin. Conversely, in liquids potential signal can be

nu

A

slice

Phase

r

F

RoshanKetab TEHRAN - IRAN Medical Publishers 50 Part I I Principles of Computed Tomography and Magnetic Resonance Imaging

regained almost as quickly as actual signal is lost; that is,

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Net z-axis Magnetization vs.

Time

T2 approaches T l and the value for both is on the order of milliseconds to seconds. The remaining body components are tissues that are neither entirely solid nor liquid. They have a higher viscosity than liquids and less crystalline structure than solids. Making a liquid more viscous would shorten its TI. The T2 cannot be longer than TI, and thus viscous liquids have short and roughly equal T1 and T2. If the viscosity increases further, the substance becomes more like a solid, and T1 is longer than its T2. In clinical imaging most tissues have a T1 between 200 msec (fat) and 3 or 4 seconds (CSF). The T2 values lie between 30 msec (muscle) to about 2 or 3 seconds (CSF). Cortical bone and teeth are exceptions in both cases and are not typically seen in images because of low proton density and relaxation times that hinder signal detection and generation. For a given field strength and a Constant temperame, the strength of a substance's equilibrium magnetization is directly proportional to its proton density (p). In imaging objects that are not chemically uniform, such as the brain, in which all tissues have essentiallv the same Droton density and therefore the same equilibrium magnetization, one can exploit the difference in T1 values. Plotting the curve of longitudinal magnetization versus time, all curves start at zero value following the 90-degree pulse and recover longitudinal magnetization along their own TI. After a long waiting period the magnetization will be near maximum for each; each pixel value will also be near its maximum, and the pixels will be uniformly bright over the whole image, provided that T2 differences are minimized via short TEs. If one shortens the waiting period to an intermediate point, the signal strength will be moderately reduced; however, the signal from areas with long T1 will be more diminished than from areas with short TI. Thus, the image will reflect differences in T1 values, so that the shorter the T1 of a substance, the brighter it will appear on the image. Finally, if the waiting period is very short, the pulses will be too close to each other to allow any significant recovery of longitudinal magnetization during the waiting period, so that signal strength is weak and the S M ratio will be low. Thus, for T1 weighting in SE sequences, the TR should be low-but not so low as to allow an insufficient time for magnetization T1 recovery between pulses. The difference in signal strength, as reflected by the separation between the curves of the various tissues in the previous example, constitutes the contrast in the image (see Figs. 2-7 and 2-8). Reference to the figures allows selection of an appropriate waiting time after the 90-degree pulse, at which one can obtain maximum separation between the curves and thus obtain maxim m contrast between tissues in the MR image. Because of differences in tissue composition (e.g., differences in proton density), in some circumstances the curves referred to previously do not follow the same contour but, instead, cross each other (Fig. 2-15). At such crossover points, there is no difference in perceived signal intensity, and thus the image will not show any contrast

7

Time 9 00

Figure 2-15. Recovery of z-axis magnetization for two substances with different proton density and TI.Note the crossover of signal difference, which results in contrast reversal.

between the two tissues. Gray matter and white matter in brain are examples of this crossover phenomenon, as a function of TR. Gray matter has a longer T1 and a higher proton density than whiter matter. Thus, white matter exhibits rapid recovery of longitudinal magnetization (because of its short TI) and appears brighter than gray matter. At a slightly longer pulse delay, the gray matter and the white matter become indistinguishable; at even longer r e covery times, the gray matter achieves higher equilibrium magnetization and appears brighter than white matter in the image (see Fig. 2-11A-C). For almost any two substances, an RF pulse sequence and TR can be selected to completely obscure any visible distinction between the two substances; however, imaging parameters that provide maximum contrast between tissues can also be found. However, maximum contrast is rarely obtained because other considerations (e.g., imaging time, slice coverage) cause compromises in one of the pulse sequence parameters so that "adequate versus optimal" contrast is obtained. In addition, the contrast observed on one side of the crossover point produces a different kind of contrast than on the other side. In similar fashion, a family of curves results as one plots transverse magnetization against time. The height of each curve is at peak amplitude initially and decays exponentially. In spin-echo sequences, the longer the delay between the 90-degree and the 180-degree pulses, the more T2 relaxation will have occurred and the less signal there will be to recover. The signal from substances with short T2 values falls off more than from those with long T2 values (see Fig. 2-7). Eventually, all signal disappears except for the signal from substances with long T2 values. Thus, in a T2-weighted image, only substances with long T2 values remain visible. Tissues with long T2 values produce more signal than signals with short T2 values.


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Magnetic Resonance Angiography: Fundamentals and Techniques E. Mark Haacke, Weili Lin

Magnetic resonance angiography (MRA) has become commonplace in the last few year^.'.^^^^^ The improvements in pulse sequence design, hardware design, and postprocessing methods make it possible to acquire data in a short period with excellent vascular visualization in a variety of clinical applications. This chapter introduces the concepts behind MRA, the techniques used to obtain MRA studies, and its clinical applications.

Fundamentals of Imaging Gradient Echoes The ability to collect an image with magnetic resonance is the result of the dependence of the frequency on the local field. This relationship is governed through the Larmor equation: 1)

Phase Relative to the echo time, for a constant gradient, the phase as a function of time is determined from

where w =

the bipolar gradient structure is able to give only one side of the frequency spectrum (either positive or negative frequency components), which, in theory (as in the FID case) is sufficient to reconstruct an image by taking advantage of the hennitim symmetry (see "Partial Fourier Imaging" later on) of the Fourier transform. In practice, it is not enough to reconstruct an image by using only one side of the frequency spectrum because of signal distortion caused by local field inhomogeneities. Therefore, the second lobe of this gradient structure is lengthened by a factor of two, so that both the positive and negative frequency spectra can be obtained. Using all the data gives a more robust image when the echo is not properly centered or when local gradients are present as a result of field inhomogeneities. Further, it also gives a ,h improvement in the signal-to-noise ratio (SNR).

the angular frequency known as the Larmor frequency

y = the gyromagnetic ratio (2- X 42.6 MHz/T)

B,

= the static magnetic field

For example, for a field strength of 1.5 Tesla (T), the Larmor frequency is equal to 64 MHz. This frequency dependence is used to spatially discriminate information by applying a gradient field (G) throughout the region of interest in one or more directions. Now the frequency response is spatially dependent (Fig. 3-1):

If the signal is measured during the application of the gradient and subsequently Fourier transformed, the spectral amplitudes (the signal as a function of frequency) are obtained. This sampled signal is referred to as the free induction decay (FID) (Fig. 3-2). The signal can also be obtained by using a bipolar gradient structure to create an echo (Fig. 3-3). However,

Position(x) Figure f 1. In the presence of a gradient, the magnetic field has a linear dependence on position. The horizontal axis represents the position, and the vertical axis represents the magnetic field.


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G Figure 3-2. When a radiofrequency (RF)pulse is applied followed by a single-lobed gradient (G), a free induction decay (FID)of spins is formed. The time constant of the FID depends on the 2 . 1 of the material.

FID

\

Figure %3. When a radiofrequency pulse is applied, followed by bipolar gradient structure, an echo is formed. At the echo the stationary tissue has accumulated a net phase of zero.

Signal

Figure 3 4 . Phase behavior for stationary spins. Phase is a function of time, gradient strength, and location of spins. As shown, at t = 0 an echo is formed a d the phase of stationary spins is zero. Here we assume x is nonzero.

0

Time (t)


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53

The velocity phase behavior is quadratic and overshoots the zero phase mark at the echo.

Bipolar Gradient

I Gl

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>

-L

T2 * Dephasing

A

t

-G I--

I--

t,

4

t

... ,,. ....

In the presence of a local field inhomogeneity, the effective decay of the signal is quickened, and T2* is modified as

where R2* = lm*and R2,, = 1/T2,, where T2, is the T2 value when no field inhomogeneities (AB)are present. This can be qualitatively understood, since the spins "see" different fields and become out of phase. If the time of the echo is calculated locally, it is discovered that it has shifted away from the center. The farther the echo shifts, the less signal remains in the sampling window (Fig. 3-6).

Chemical Shift

#

The presence of local field variations causes a shift in the frequency for different molecules. Lipids, for example, precess at a frequency (Af), 3.35 parts per million (ppm)

Stationary Spins

c o n s k t Velocity Spins Figure 3-5. A, Pictorial representation of the phase for stationary and constant velocity spins as a function of time when a bipolar gradient structure is used. B and C, Graphical and vector representations of the phase, respectively. The solid line is for stationary spins, and the dotted line is for constant velocity spins. indi-

+

cates the phase shift of constant moving spins at the echo.

As shown in Figure 3-4, the phase is a function of time and gradient strength. Since GI = G, Gz = -G and t, = k equation 3a can be rewritten as

Therefore, the accumulated phase at the echo is always zero for these bipolar gradient structures (Fig. 3-5). For stationary spins, the phase is generally determined from +(t) = yxSG(t)dt

(4)

Figure 3-5B shows a linear growth in phase during the dephase portion of the gradient and a linear decrease in phase after the gradient is reversed for stationary tissues. No change in phase occurs when there is no gradient on.

Figure 3-6. Local field inhomogeneities introduce a shift of the location of the echo. A, A two-lobed gradient structure is shown with an echo at the center of the second lobe (TE1);therefore, the signal is symmetrical. The gray indicates the area under the gradient from local field inhomogeneities. B, The location of the ,hO is shifted to the left (733) with A, and the signal becomes asymmetsical. If the shift is large enough, it will cause significant signal loss.


Fawater Cancellation for GFE

FaWater Cancellation for SE Fat = 80% and Water = 20% 1.0 \

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Fat = 80% and Water = 20% I

TE (msec)

B

TE (msec)

Figure 3-7. When a voxel contains water (20%) and lipid (80%) components, the signal intensity of the voxel is a function of echo time (TE). As shown in the plot, the signal intensity is modulated by a sinusoidal function with a period of 224 Hz (3.35 parts per million at 1.5 T). The spin-echo behavior is shown in A, and gradient field echo (GFE) behavior is shown in B. A T1 of 950 msec, T2 of 100 msec, and T2* of 50 msec (gray matter) are used as water relaxation parameters and Tlm/T2* = 250/80/10 msec (fat) are used as lipid relaxation parameters. The signal behavior for a fat and water voxel is further modulated by an exponential decay (T2*). The frequency of modulation appears to be doubled at the lower values of TE because fat overwhelms the water and creates a negative signal, which is then made positive by taking the magnitude of the image. SE, spin echo.

lower than that for water. They therefore have a different phase development as a function of time and at the echo will not necessarily be in phase with water. When a voxel contains fat and water components, the signal intensity of this voxel depends on the echo time (TE) used (Fig. 3-7). At 1.5 T, for a voxel containing 50% each of water and fat, the signal intensity of this voxel will be one unit when TE = 4.5 msec (since fat and water are in phase so that the total signal is the sum of both components) and zero when TE = 6.7 msec (since fat and water are out of phase, and signal intensity is the absolute difference between these two components). To see this, note that the phase difference between the two is yABTE, which is 2.sr at 4.5 msec and IT at 6.7 msec. Consequently, the opposed phase nature can be used to suppress fat signal.". 60

Resolution The data are sampled in the read direction over n points. If the field of view (FOV) is defined as L, the resolution in the image will be (at best) Lln, or

For example, if the carotid vessel is being imaged, its lumen is 10 mm before the bifurcation and the magnetic resonance imaging (MRI) resolution is 1 mm, the smallest percentage of stenosis that can be measured is 100110%. To detect a high percentage of stenosis, the resolution of images must be improved. Clearly, high-resolution imaging plays an important role in MRA.25,37-39, 56 First, it can be used to reduce flowrelated artifacts through the reduction of the intravoxel depha~ing.~~. 37' 56 Second, it is able to improve the visibility

of the vascular system3738 (Fig. 3-8). This is especially true for the peripheral vascular system and stenotic regions. Third, the partial volume artifacts can be reduced, and hence vascular contrast is improved (Fig. 3-9). However, there are two major disadvantages associated with highresolution imaging methods. The SNR will be reduced because of the smaller voxel size, and the minimum repetition time (TR) will be increased because the number of sampling points is increased. Therefore, when the SNR is poor, more acquisitions may be needed to compensate for the SNR lost.

Contrast The main strength underlying the success of MRI studies is the soft tissue contrast. Contrast is defined as the signal difference between two tissues. Relative contrast is the signal difference normalized to the signal of one of the two signals. The contrast is the result of the tissue properties p, TI, and T2. Blood flow adds another variable to the calculation of contrast. Consider a simple imaging experiment with a very short TE and a long TR relative to the T1 values of all tissues. In this case, contrast is determined solely by spin density (Fig. 3-10). As TR is shortened to on the order of the T1 of a tissue, the image becomes T1-weighted (Fig. 3-11). For gradient-echo sequences, the TR can be shortened much below T1 and the radiofrequency (RF) pulse reduced to an angle well under 90 degrees. For no transverse magnetization before any RF pulse and after equilibrium has been reached, the signal as a function of flip angle (0) can be expressed as s(0) =

psin0(l - El) 1 - El cos 0


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Figure 3-8. Comparison of vascular visibility when different matrix sizes are used. The field of view was kept constant for this comparison. The matrix sizes used were 128 X 256 (A), 256 X 256 (B), and 512 X 256 (C), respectively. When the in-plane resolution is improved, more peripheral vessels can be seen in the images. However, the signal-to-noise ratio is reduced accordingly. The 512 image has little stair-step artifact, although it does suffer a DC bright line artifact in the

where p is the effective spin density and E l = exp( -TR/T1). The response as a function of flip angle shows why an intermediate flip angle between 0 and 90 degrees gives the best signal. The peak signal occurs when cos 0 = El; this is referred to as the Enzst angle (Fig. 3-12).

Two-Dimensional and Three-Dimensional Imaging Two-dimensional (2D) and three-dimensional (3D) images can be obtained by adding a phase-encoding gradient table in each remaining direction to be imaged. The resolu-

tion in each phase-encoding direction is the FOV divided by the number of phase-encoding steps, as

for the in-plane phase encoding or

for the through-plane phase encoding (also referred to as partition encoding). In general, the 3D imaging method is preferable when a thinner slice is desired and flow velocity is high enough so that the flow saturation problem is nit significant. Moreover, 3D imaging methods have a better SNR and are less sensitive to field inhomogeneities than


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Figure 3-9. Comparison of vascular contrast when a different slice thickness was used to acquire images. A maximal intensity projection (MIP) was used to create axial projection images. The coverage of all three MIPS was kept the same, but with a slice thickness of 2 mm (A), 1.5 mm (B), and 1 mrn (C). Since the thinner slice was used, the vascular contrast was improved because of the reduction of partial volume effects.

2D imaging methods. This is easily understood from two perspectives. First, the smaller the voxel size, the less dephasing is across a pixel, since the phase error (e.g., that caused by field inhomogeneity = yABTE) is invariant spatially as the imaging parameters are changed. If there is a IT phase variation across a voxel, this would cause complete signal loss for a uniform distribution of spins (Fig. 3-13A). However, for twice the resolution, the phase variation is cut in half, being 0 to pi in the first, smaller voxel and IT to IT in the second voxel (Fig. 3-13B). The conventional sequence diagrams for both 2D and 3D acquisition methods are shown in Figure 3-14. The phase encoding in the slice select direction is often referred to as the partition encoding, a term we will use here. The fieldecho time (FE) refers to the time from the beginning of the gradient structure to the echo along the read direction.

The echo time refers to the time from the center of the RF pulse to the echo.

+

Fundamentals of Flow Effects Effects of Motion on the Phase The previous discussion of phase needs to be modified when a spin moves. As an example, consider just the simple case of constant velocity moving spins:

where xo,V,and t represent the initial position of the spins, constant velocity, and time, respectively.


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Figure 3-1U. Spm-density image of the head acquired with a 5degree flip angle (Figure 3-11 provides imaging parameters). Because blood vessels sit in gray matter (GM) and GM and blood have the same spin density, it is not possible to distinguish between the two. The sagittal sinus (arrow) is saturated and isointense with GM.

I Figure 3-11. TI-weighted image of the head for (A) 15 degrees and (B) 30 degrees. Since the T1 of blood is longer than that of gray matter, it appears darker if it is saturated but may appear isointense if some inflow effect remains. Imaging parameters: TR = 40 msec, TE = 8 msec; 64 partitions, 2-mm slice thickness; matrix size, 256 X 256.


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Principles of Computed Tomography and Magnetic Resonance Imaging

In-Flow Effects

Figure 3-12. Signal intensity as a function of flip angle (see Equation 7 in text). A TR of 35 msec is used with T1 of blood equal to 1200 msec and gray matter (GM) equal to 950 msec. The solid line indicates the ideal case that blood experiences only one (N = 1) radiofrequency (RF)pulse. In contrast, when blood experiences more RF pulses, as when N = 5 (line of circles), N = 10 (line of squares), or N = 20 (line of diamonds), the signal of blood is reduced. The signal behavior of GM is also plotted (long dashed line). As shown, the blood may become isointense with GM at 15 degrees when N is greater than 10 and less than 20.

! b

0.0

20.0

40.0

60.0

80.0

100.0

Flip Angle

Figure 3-13. A, Pictorial representation of intravoxel dephasing. When a larger pixel is used, the integration of spins from 0 to 2a will give a zero signal (0).In contrast, when the resolution is reduced by a factor of 2, the integration of spins will be from 0 to .rr for the first pixel and a to 2a for the second pixel (B) and Iittle signal loss occurs (see Table 3-1).

3D Gradient Echo Sequence

Figure 3-14. Sequence diagrams of both 2D (A) and 3D (B) sequences. The only difference between these two sequences is in the slice select direction. For the 3D sequence, an extra phase table (dashed line) is added to encode information along the slice select direction, L.


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59


The phase during samglin8 is found from the exg~essipn w, *)-.' - ',.' ,=* T 5,+(t) = yS~(t)x(t)dt ill) 8

8,

-

7

For a simple bipolar pulse as shown in Figure 3-5, the phase at the echo is

This simple dependence of the phase on velocity is the fundamental behavior from which many MRA concepts can be understood.

Dephasing For plug flow, all spins move in the same direcion at the same speed independent of the location of the spins with respect to the vessel wall. When all the spins within a voxel are added together, they add coherently and the final signal has the same phase. In contrast, for laminar flow, the velocity of spins is dependent on the location with respect to the vessel wall (Fig. 3-15). The spins at the center of the vessel have the highest speed, and those at the edge of the vessel have the lowest. Consequently, a velocity distribution inside a given voxel causes a different phase shift for each isochromat of spins inside the voxel. The total signal in one voxel is obtained from an integration of the local signal across the entire voxel. When the total phase shift across a voxel is uniformly distributed from 0 to IT, there will be complete signal dropout. This phenomenon is known as Jlow dephasing or flow void. It usually can be seen in stenotic regions or tortuous vessels when insufficient motion compensation is used. For example, in the regions of the carotid bulb and poststenosis, a secondary flow or vortex flow is normally seen. This flow pattern also introduces signal loss (Fig. 316). Table 3-1 shows the relationship between the degree of dephasing and the remaining signal.

-

Flow Direction

-

Figure 3-16. A, The same concept as in Figure 3-15 also holds for poststenosis regions, where secondary flow develops inside an aneurysm or beyond an aneurysm. B, In the region of the carotid bulb, a secondary flow pattern is normally seen because of the pressure gradient change. This causes flow dephasing as well as saturation and results in signal void in this part of the blood vessel.

Compensating Moving Spins To eliminate or reduce the problems associated with spin dephasing, a short echo time can be used.32. 54 Alternatively, a velocity compensation gradient structure can be used." It is possible to keep both stationary and moving spins in phase at the echo. This is accomplished by adding a third gradient lobe to the original gradlent structures so that the total area still adds to zero, and the stationary spins are therefore still rephased, while the first moment of the phase is also zero for any speed. Expressed mathematically, the following conditions are applied: 392

343

and

To compensate constant acceleration spins, four lobes are required to give three degrees of freedom so that stationary spins, constant velocity spins, and acceleration spins can all have a zero phase at the echo. The tradeoff by using a four-lobed gradient structure is that the echo time will be increased. This can cause some spin dephasing problems when higher-order motion effects are present, such as in secondary or disturbed flow, or for tortuous flow, such as in the carotid syphon.

Blood Vessel

+

B

-

Figure 3-15. Laminar flow pattern inside a blood vessel. Because flow velocity is location-dependent, the spins have a nonuniform distribution compared with that of plug flow. As shown,

the voxel close to the center of the vessel has more uniform spin distribution compared with that at the edge of the vessel. This nonuniform spread in velocity can lead to spin dephasing.

Table 3-1. Relationship Between Degree of Dephasing and Remaining Signal A+

SfS,

2 ' ~ 3~12

2h3n

0

'R

U'R

'R/2

2hl'R


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Figure 3-17. A, Image ot the necK acqulrea ~y a LJJ sequence with a flip angle of 90 degrees. Because of the pulsatility of blood flow, ghosting artifacts are seen along the phase-encoding direction (y-axis). B, When the flip angle was decreased to 20 degrees with the same sequence, the signal intensity of the "ghosts" was decreased.

Hiaher-Order Terms a Even with velocity compensation, higher-order motion effects can still be seen in tortuous or stenotic flow. For the same bipolar gradient structure, acceleration compensation varies as FE3 or as FE2 if constant velocity spins are compensated.

RF pulses and is essentially saturated (Fig. 3-18). This phenomenon is well known as flow enhicement or an inflow effect. The MRA imaging method based on this concept is called time-of-flight (TOF) MRA to differentiate it from the phase-contrast (PC) method (see later), which uses the phase shift introduced by moving spins.

Ghosting Artifacts

Saturation

-

Ghosting artifacts are commonly seen in MRI studies. Two reasons can account for this type of artifact. Fist, uncompensated (or pulsatility of) moving blood causes the duplication of the blood vessels along the phase-encoding direction. The locations of the ghosting depend on the cardiac cycle and TR. This phenomenon is usually seen in peripheral MRA studies (i.e., of the legs) because of the high degree of pulsatility. When a large flip angle is used, the signal intensity of the ghosting artifacts will be significant (Fig. 3-17). On the other hand, physiologic motion such as eye or cerebrospinal fluid (CSF) movement can also cause ghosting along the phase-encoding direction. To avoid having "ghosts" obscure other structures, the frequency and phase-encoding directions are usually swapped before any data acquisition so that the direction of ghosting becomes horizontal instead of vertical.

The inflow effect makes it possible to obtain good contrast between vessels and stationary tissue because the stationary tissue experiences more RF pulses and eventu-

I I I

I I

3

lnflow Given that all spins are now rephasing at TE, any velocity profile can be imaged. The main effect of obtaining a blood signal comes from the fact that inflowing blood has experienced fewer RF pulses and has more signal than tissue with similar T1 values, which experience many

2-

1-

1

t

Flow Direction

Figure 3-18. For through-plane flow with a laminar flow profile, blood will have higher signal at the entry region (slice I ) when compared with the region where blood flows deep into the slab. Numbers represent slice numbers.


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ally the magnetization becomes saturated. Consequently, when the velocity of blood in a vessel is slow, both background tissue and blood magnetization are saturated; hence blood vessels become isointense to the stationary tissue. This is usually the case in the head because gray matter (GM) and blood have similar spin densities and T1 values. In addition, this problem is seen more in 3D TOF imaging methods, since a larger imaging volume is normally acq ~ i r e d .41~ ~ .

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61

It is also possible to apply another RF pulse just before the usually low flip angle pulse to saturate the signal from stationary tissue and see fresh blood flow into this saturated band. Flow that takes place between the saturation pulse and the echo time can be seen as bright in the saturated band. This band can also be applied parallel to the usual 3D slice select direction, but offset from it, to saturate spins coming from one side of the slab to be imaged. An example is shown in Figure 3-19, in which a saturation pulse was used to saturate the venous blood magnetization and only the arteries were seen in the image (Fig. 3-19B).

Figure 3-20. This method has the advantage that when saturation is a problem (as it is for slow flow), the background is easily removed. The resulting phase images contain values only from - IT to IT as long as the peak velocity is such that I+(v)l < a.The velocity at which I+(v)l = IT is referred to as the velocity-encoding value (VENC). Unfortunately, several disadvantages are associated with PC methods, which require at least four separated scans to extract flow in all three directions yet given the very short TR values that can be used, rapid acquisition of data is still possible. Because subtraction is used to remove the background signal and extract flow information from four scans, patient motion must be avoided. Eddy currents also affect the phase behavior in the images. Moreover, this method requires a choice of the maximum velocity so that aliasing will not occur in the phase images. One way to overcome the problem of the correct choice for the VENC is to use a multiple VENC in one sequence so that a wide range of velocity information can be obtained. Finally, this method, like TOF methods, is apt to suffer from spin dephasing because of the rapid flow. A shorter TE is necessary for PC methods as well. The TOF and PC methods are likely to complement each other in the future.

Phase Contrast

Projection Images

One way to eliminate the problems associated with flow saturation is to obtain flow information by collecting two images, each of which is not perfectly compensated in one direction so that a phase shift exists at the echo along the uncompensated direction, which is different for the two sequence^.'^. This is the primary difference between PC methods and TOF MRA. Subtracting one image from the next eliminates the background. This can be done with the complex data or the phase images themselves. The sequence diagram of an interleaved PC method is shown in

The use of 2D TOF over thick slices is often referred to as projection imaging because of the projection of information over the slice thickness. In these methods, excellent background suppression is required. Interleaved 2D PC is the method of choice when rapid imaging is required.

Saturation Pulses

Sequence Parameters As mentioned earlier, 2D and 3D imaging methods have different advantages and disadvantages and are suitable for

Figure 3-19. Images acquired with a conventional 2D sequence in the region of the neck. A, When saturation was not used, both arteries and veins were seen in the image. B, In contrast, when a saturation pulse was placed above the image slice, the veins were

saturated and only arteries were seen in the image.

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I

I

Positive Velocity Encode

I I

I

I I

ADC

j ADC

terieaved phase contrast acquisition method. A flow-encoding gradient (bipolar gradient) shown in gray was placed along the slice select direction. As shown, the sign of this flow-encoding gradient was reversed for the second part of the data acquisition when compared with the first part. Because an interleaved data acquisition method was used, the effective TR was increased by a factor of 2. Slice select (SS), phase-encoding (PE), frequency-encoding (FE) directions; and analog-to-digital converter (ADC). RF, radiofrequency.

Negative Velocity Encode

different applications. Consequently, the imaging parameters for 2D and 3D imaging methods are different to optimize vascular contrast.

Two-Dimensional lmaging In general, 2D imaging is used to image slow flow because this method is less sensitive to flow saturation. Moreover, 2D imaging is also suitable for dynamic studies because of its short data acquisition time. Unfortunately, 2D imaging is highly sensitive to local field inhomogeneities. It is also more difficult to achieve high resolution along the slice select direction compared with 3D imaging.

Three-Dimensional lmaging In contrast to 2D imaging, 3D acquisition is used to cover a large region of interest and to achieve high resolution along the slice select direction. Moreover, the SNR is normally higher than in 2D imaging because more points are acquired along the slice select direction. However, 3D TOF suffers from flow saturation effects when a large volume is covered or when slow flow is present. As discussed previously, 3D PC is less affected. General advantages of 2D versus 3D imaging are shown in Table 3-2.

Rectangular Field o f View A simple trick is to reduce the number of phase-encoding steps while decreasing the FOV in the phase-encoding direction. For example, reducing the number of steps from 256 to 128 and reducing the FOV from 256 to 128 mm maintain the resolution, cut the imaging time in half, but reduce the SNR by a factor of ,h. For imaging a child's head, this is possible; for adults, however, the reduction is usually to 192 steps-still giving a considerable savings in time of 25%. When nonintegral ratios between the original FOV and the reduced FOV are used, a careful interpolation algorithm must be employed to retain the correct aspect ratio of images. Figure 3-21 shows a comparison with (Fig. 3-2LA) and without (Fig. 3-21B) the use of rectangular FOV.

Partial Fourier Imaging Use in the Phase-Encoding Diition. There is a special symmetry property of the Fourier transform for a real object that makes it possible to design a data collection

Table 3-2. Comparison of Two-Dimensional (2D)

and Three-Dimensional (3D)lmaaina

Technical Developments in MRA Sequences Saving Time

Advantages

Disadvantages

Advantages

Disadvantages

Once a good MRA scan has been collected, one can look at methods to speed up its acquisition. This will invariably mean a loss of SNR, given that resolution remains the same.

Faster

Better inflow

Thicker slice More T2* loss

Slower Blood saturation

High CNR

Low

T h i i r slices Less T2* loss High SNR

SNR

CNR, contrast-to-noise ratio; SNR,signal-to-noiseratio.

Low CNR


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63

Figure S21. A, Image acquired with a conventional 3D sequence in the region of the neck. The imaging parameters are TR, 35 msec; TE, 8 msec; flip angle, 15 degrees; and matrix size, 256 X 256. The total data acquisition time is about 10 minutes. B, The same imaging parameters are used, except that the matrix is reduced to 160 X 256 and the rectangular field of view (FOV) is used to acquire the image. Although the signal-to-noise ratio (SNR) is reduced accordingly, the total data acquisition time is reduced to 7 minutes. C, At this stage, data in the neck are often collected with a 256 X 512 acquisition. Although this image was not obtained using a reduced FOV, the SNR is sufficient that it would be possible to do so if the carotid bifurcation were the region of interest.

method that in theory saves a factor of 2 in data collection time. This property, known as hermitian symmetry, relates the negative data to the positive data so that only the positive data, for example, need be collected and the negative data will be recreated from it. The expression is simply s(-k)

=

s X (k)

(15)

where k represents the phase-encoding value s(k) is the signal

In practice, more than half the data is collected and special algorithms are used to reconstruct the data (Fig. 3-22). Once again, a factor of nearly ,h is lost in SNR.25 A comparison is shown in Figure 3-23 to demonstrate the partial Fourier reconstruction method.

Use in the Read Direction. This trick can also be used to reduce the echo time by putting the echo off center with respect to the data sampling windowzs (Fig. 3-24). This reduced echo time allows better suppression of the dephasing of moving spins from hlgher-order motion. For example, a 25% asymmetrical echo with 256 sampling points indicates 64 points before the echo and 192 points collected after the echo. Mathematically it represents a symmetrical echo multiplied by a rectangular pulse in the time domain, and it translates to a convolution of the ideal image with a complex filter function. This reduces the sharpness of the

reconstructed image. Therefore, the half-Fourier reconstruction is necessary to eliminate this artifact. Figure 3-25 shows sequence diagrams of the TE = 5.1 msec sequence (even shorter echo times are available today). To achieve high resolution, longer echo times may have to be used because of the limitation of the maximum gradient strength in the system. Consequently, the longer echo time would increase the flow-related artifact since the higher-order motion-dephasing effects increased. Alternatively, an off-center echo can be used such as 6.25%, 12.5%, or 25%, and the echo time decreases accordingly.

Overcoming Saturation Effects %O solutions can be used to reduce the saturation problems associated with 3D TOF imaging methods: (1) increase the blood signal, andlor (2) reduce the background tissue signal so that the contrast between blood vessels and background tissue can be improved. Alternatively, postprocessing methods can be used to remove unwanted tissue structures (see "Processing and Image Display").

Increasing Signal from Blood Central k-Space Reordering. In certain sequences, there is a wait time (TW) between application of the partition and phase-encoding loops. In this case, central reordering collects the largest signal at the lowest values


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Phase Encoding

I -m

0

Read Direction B

1 p

Figure S22. Pictorial representation of k-space coverage. Instead of collecting the entire k-space, only three fourths of the k-space was

acquired along the read direction. A partial Fourier reconstruction was used to recover the lost information without blumng the image. The shaded portion represents the data used for the partial Fourier reconstruction. and the entire figure remesents the data collected from the imager (A). B, After reconstruction, data space is symmetrically covered. The data are collected with m points before the echo and P points after the echo, with m P - i = 2n.

+

of the k-space or at the low spatial frequency values (Fig. 3-26). This enhances the signal not only from the fast blood but also from any blood that has this TW to regrow. In addition, when a T1 reduction contrast agent such as gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) is administered, the centric reordered k-space scheme can be used to further improve the vascular contrast, since the half-life of Gd-DTPA is short and Gd-DTPA is most effective immediately after the injection of contrast agents.

Variable Flip Angle as a Function of Radiofrequency Pulse Number. Signal can also be enhanced by not applying a constant RF pulse angle every time. A constant RF pulse usually leads to saturation of the signal (it always does for stationary tissue if the angle is greater than the Ernst angle). If the flip angle is varied to give constant transverse magnetization each time the RF pulse is applied, the signal can be enhanced (even specifically at low kspace if desired).

Contrast Agents. One of the main difficulties associated with 3D TOF MRA studies is the saturation of slow flow. To reduce the saturation problem, a thinner 3D slab can be used so that more fresh blood can flow into the imaging volume.6. 45 However, this method requires several overlapping thin slabs to cover the region of interest, and 3 '

cooperation of the patient is required. Alternatively, a contrast agent, Gd-DTPA, may be used to shorten the T1 over reasonably long periodss, 38 (its half-life in the blood is about 12 minutes). For example, when a high dose of GdDTPA is used, the T1 of blood may be reduced by a factor of 4 and the contrast between blood and stationary tissue will be substantially increased (Fig. 3-27). An example of preadministration and postadministration Gd-DTPA is shown in Figure 3-28. As expected, after injection (Fig. 3-28B), more small vessels are seen as compared with Figure 3-28A. It can also be used to see 'El* effects during the first minute of its application, after which its concentration is so low that T2* effects disappear. "9

Multiple Thin-Slab Acquisition. Multiple thin-slab acquisition methods can also be used to reduce spin saturation problems because spins experience fewer RF pulses compared with single thick-slab acquisition methods (Fig. 329). Consequently, the region of coverage is reduced accordingly. To cover a large region of interest, several thin slabs with 25% to 50% overlap can be used. Better-quality images in the regions of overlap and in the rest of the images can then be combined using maximum intensity projection (MIP) processing to generate the projection images (see later).


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Figure S23. A, Image collected with 64 points before the echo and 192 points after. It is zero filled in-plane to 512 and then reconstructed with a 2D fast Fourier transform to create a 512 X 512 image. B, The image was reconstructed using 64 points before and 192 points after the echo with the partial Fourier reconstruction method to create an equivalent 384 points along the read direction and zero filled to make 512 X 512 images. C, The image was collected with 64 points before the echo and 448 points after, with 5 12 phase-encoding steps to create 5 12 X 5 12 images. Note the improved resolution and loss of signal-to-noise ratio compared with B. Even the 512 X 512 acquisition with the conventional reconstruction does not lose the same vessel sharpness. (Courtesy of Ramesh Venkatesan, B. S., Case Western Reserve University, Cleveland, Ohio.)

Improving Background Tissue Suppression Too high a signal from background obscures the blood vessels. By reducing background signal, the vessels become more visible.

Spatially Variable Flip Angle or TONE Pulses. One method of keeping the signal uniform in response across the FOV in the slice select direction (for blood flow perpendicular to the imaging plane-that is, in the slice select direction) is to vary the flip angle spatially (Fig. 3-30). Using small flip angles and increasing to large flip angles keep inflowing blood fairly uniform as it passes through the volume.35The principle is the same as that previously described, but it is accomplished by appropriately redesigning the RF pulse to accomplish the desired shape of the RF response. This is most often useful in neck studies (Fig. 3-31). .

#

.

Magnetization Transfer Saturation. Bound macromolecules have very short T2 values (330 although metastases account for only about 1% of intrasellar and parasellar tumors.237 Often multiple and tiny, metastases are demonstrated only on postcontrast high resolution images.

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Inhacranial Neoplasms

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Nonneoplastic inflammatory entities that may involve the anterior lobe of the pituitary gland include lymphocytic hypophysitis and sarcoidosis. Lymphocytic hypophysitis is a rare disorder, likely autoimmune, that occurs mainly in young women during late pregnancy or postpartum. It is characterized by diffuse lymphocytic infiltration of the anterior pituitary. On imaging studies, the pituitary gland appears diffusely enlarged and demonstrates contrast enhancement.lg2 Sarcoidosis, another autoimmune disorder, affects the CNS in about 5% of cases, notably involving the meninges and parenchymal structures at the base of the brain. On imaging studies, multiple foci of ill-defined contrast enhancement are seen within and enveloping the surfaces of the hypothalamus, optic chiasm, and pituitary stalk (Fig. 5-54).72 Intrapituitary focal abnormalities are commonly identified on MRI of asymptomatic volunteers130and as incidental findings in large autopsy series.'" These include not only microadenomas but also Rathke's cleft cysts (see Fig. 5-59) (see later) and other benign cysts of uncertain origin. The incidence of such cysts on autopsy series varies from 5.8% to 8.3% of individuals older than 30 years.17' In one double-blinded series of asymptomatic adult volunteers, MRI demonstrated intrapituitary focal hypointensities on TI-weighted imaging that were consistent with microadenoma or benign pituitary cyst in 15% of subjects."O Another possible explanation proposed for these "incidentalomas" is magnetic susceptibility induction of signal distortion in the floor of the sella near the junction with

-&.&mv,lr,-

L'L Figure 5-54. Sarcoidosis involving the base of the brain. Axial postgadolinium TI-weighted MR image demonstrates patchy diffuse contrast enhancement of the leptomeninges enveloping the base of the brain. A large focus (arrow) involves the pituitary stalk.

RoshanKetab Medical Publishers 188 Part II I Brain and Meninges

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the sphenoid sinus.20' Most of these lesions, apparent or real, are very small (

.-.'

-17.

.T

-I6

j. i d . ,

where MlT is the mean transit time of a nondiffisible tracer in a volume of brain tissue.34 The pathophysiology of ischemia can be considereu in four stages, based on autoregulatory physiology:


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Figure 7-40. Dision-weighted imaging. Acute right hemiparesis. A, T2-weighted, echo-planar image without diffusion weighting (b = 0). Hyperintense signal is seen in the periventricular regions bilaterally (arrows). B, Diffusion-weighted image (b = 1000) obtained with the direction of sensitization running in the frequency-encoding (front to back) direction. A region of hyperintensity is now seen in the left internal capsule (arrow).Increased signal is also seen in the splenium of the coxpus callosurn as a result of anisotropy artifact (small arrows). C,Trace-weighted, diffusionweighted image (b = 1000) shows the lesion in the left internal c a p sule more clearly (arrow); the anisotropic artifacts seen in the previous image are absent. D, Exponential diffusionweighted image. The effect of T2 is removed from the image. The acute infarct is still depicted as hyperintense (large arrow), but the chronic ischemic lesions in the white matter are depicted as areas of diminished signal (small arrows). E, Apparent diffusion coefficient (ADC) map. The internal capsule lesion (arrow) is depicted as dark (diminished ADC). F, Quantitative analysis shows that ADC is diminished 37% in the acute infarct compared with a control region.


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Chapter 7

First stage, normal hemodynamics. Second stage, characterized by an initial decrease in perfusion pressure. Initially, autoregulatory vasodilation preserves CBF, at the same time increasing CBV. MIIT is also typically increased. Third stage, characterized by greater decrease in perfusion pressure and by an initial decrease in CBF value. CBV typically remains increased. Fourth stage, characterized by further decrease in perfusion pressure and decreases in both CBF and CBV. This stage is associated with tissue ischemia and hemodynarnic failure. .*+. a?r;;t1i..,

Perfusion Imaging in Stroke

-

.#

...r$

,- k - I -

An important goal of hemodynamic stro e imaging is the depiction of tissue at risk for infarction that might be saved though intervention. In the setting of acute stroke, if the location and extent of viable tissue at risk for infarction were known, such knowledge could help clinicians to weigh the risks associated with stroke therapies. Viable tissue that is at risk for infarction is commonly called the ischemic penumbra, or the tissue outside the (nonviable) core of infarction that is nonetheless underperfused. It is postulated that the ischemic penumbra differs from viable tissue that is not at risk by the (decreased) amount of blood flow that it receives. A number of methods of imaging cerebral perfusion are available. Imaging with radioisotopes is possible with single-photon emission computed tomography (SPECT) and

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positron emission tomography (PET). It is also possible to image CBF with CT using inhaled stable xenon.1° This method is capable of depicting extent of hemodynamic abnormality in stroke?' Although xenon CT remains an attractive tool for the assessment of CBF, this method has not yet achieved widespread clinical use. One possible reason may be the requirement for speciahed equipment to administer and ventilate the gas. It is now possible to obtain dynamic, contrast-enhanced perfusion scans using either CT or MR scanners3" (Figs. 7 4 1 and 7-42). Generally, a volume of contrast material is injected rapidly into an arm vein by an automatic (power) injector, and the bolus of contrast material is tracked by the scanner through a slice or slab of brain tissue that is repeatedly scanned over the course of about 45 to 60 seconds. For best results, temporal resolution of 2 seconds or faster is needed. It has been proposed that MR perfusion imaging may complement DW imaging in depicting the region of penumbra.26 The premise is that DW imaging is thought to depict the region of core infarction, whereas the region of perfusion abnormality represents both the core and the penumbra. The difference between the extent of the diffusion abnormality and the extent of perfusion abnormality is thus thought to represent penumbra. An alternate approach for determining the extent of penumbra is to use perfusion maps alone to distinguish the core of infarction from the penumbra, usually with the use of perfusion parameter value thresholds. The most commonly used perfusion parameter is the mean CBF value. Earlier work with xenon CT in stroke patients has

Figure 7-41. Acute stroke of the ngnr middle cerebral artery. A, bne~anceaaxla L I scan or me main snows no substantial abnormalities. B, Mean transit time (M'IT) map from dynamic CT perfusion scan depicts a well-defined region of MTT prolongation. The extent and degree of regional hemodynamic abnormalities can be determined by perfusion imaging techniques.


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Figure 7-42. Acute dissection of the right internal carotid artery. A, Trace-weighted, diffusion-weighted image (b

= 1000) shows cortically based region of hyperintense signal consistent with acute middle cerebral artery temtory infarction (arrow). B, Negative enhancement integral image (relative cerebral blood volume) from gadolinium-enhanced dynamic sequence. The extent of a region of (arrow) diminished perfusion is identical to the diffusion-weighted image abnormality (arrow).This represents a "matched" perfusion and diffusion defect.

described thresholds for infarct core (CBF values < 7 mL/ 100 g per minute) and penumbra (CBF values between 7 and 20 mu100 g per minute).'* The perfusion parameter CBV may provide additional information about tissue viability that CBF alone cannot provide. Studies using MRI with SPECT and xenon CT with dynamic CT have shown that for tissues associated with moderately low CBF values, CBV value can help to .~ studies suggest that moderpredict tissue ~ i a b i l i t yThese ately decreased CBF values and increased CBV values may carry a better prognosis than that for tissues in which both CBF and CBV values are diminished.

References 1. Asato R, Okumua R, Konishi J: "Fogging effect" in MR of cerebral infarct. J Comput Assist Tomogr 15:160-162, 1991. 2. Astrup J, Siesjo B, Symon L: Thresholds in cerebral ischemia--the ischemic penumbra. Stroke. 12:723-725, 1981. 3. Ayanzen RH,Bird CR, Keller PJ, et al: Cerebral MR venography: Normal anatomy and potential diagnostic pitfalls. AJNR Am J Neuroradiol 21:74-78, 2000 4. Barnford J, Sandercock P, Dennis M, et al: A prospective study of acute cerebrovascular disease in the community: The Oxfordshire Community Stroke Project, 1981-1986: Part 2. Incidence, case fatality rates, and overall outcome at one year of cerebral infarction, primary intracerebral and subarachnoid hemorrhage. J Neurol Neurosurg Psychiatry 53:1&22, 1990. 5. Bernaudin F, Verlhac S, Freard F, et al: Multicenter prospective study of children with sickle cell disease: Radiographic and psychometric correlation. J Child Neurol 15:333-343, 2000. 6. Bladin CF, Chambers BR: Frequency and pathogenesis of hemodynamic stroke. Stroke 25:2179-282, 1994. 7. Bonita R: Epidemiology of stroke. Lancet 339:343-344, 1992.

8. Boyko OB, Burger PC, Shelbourne JD, Ingram P: Non-heme mechanisms for T1 shortening: Pathologic, CT,and MR elucidation. AJNR Am J Neuroradiol 13:1439-1445, 1992. 9. Brandt T, Steinke W, Tbie A, et ak Posterior cerebral artery temtory infarcts: Clinical features, infarct topography, causes, and outcome. Cerebrovasc Dis 10:17&182,2000. 10. Caille JM, Constant P, Renou AM, Billerey J: Prognostic value of rCBF measurements and CT in focal cerebral ischemia. Neuroradiology 16:238-241, 1978. 11. Dulli DA, Luzzio CC, Williams EC, Schutta HS: Cerebral venous thrombosis and activated protein C resistance. Stroke 27:1731-1733, 1996. 12. Fisher M: Occlusion of the internal carotid artery. Arch Neurol Psychiatry 65:34&377, 1951. 13. Ford CC, Griffey RH, Matwiyoff NA, Rosenberg GA: Multivoxel 'H-MRS of stroke. Neurology 421408-1412, 1992. 14. Gerhard GT, Duell PB: Homocysteine and atherosclerosis. Curr Opin Lipidol 10:417428, 1999. 15. Grohn OH, Lukkarinen JA, Oja JM,et ak Noninvasive detection of cerebral hypoperfusion and reversible ischemia f?om reductions in the magnetic resonance imaging relaxation time, T2. J Cereb Blood Flow Metab 18:911-920, 1998. 16. Hacke W, Kaste M, Fieschi C, et al: Intravenous thronlbolysis with recombinant tissue plasminogen activator for acute hemispheric stroke: The European Cooperative Acute Stroke Study. JAMA 274: 1017-1025, 1995. 17. Hankey GJ, Sudlow CL, Dunbabin DW: Thienopyridines or aspirin to prevent stroke and other serious vascular events in patients at high risk of vascular disease? A systematic review of the evidence from randomized trials. Stroke 31:1779-1784, 2000. 18. Hatazawa J, Shimosegawa E, Toyoshima H, et al: Cerebral blood volume in acute brain infarction: A combined study with dynamic susceptibility contrast MRI and Tc-HMPAO-SPECT. Stroke 30: 800406, 1999. 19. Heinsius T, Bogousslavsky J, Van Melle G: Large infarcts in the middle cerebral artery temtory: Etiology and outcome patterns. Neurology 50:341-350, 1998" *- .

. ,,


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Chapter 7 20. Henriksen 0, Gideon P, Sperling B, et al: Cerebral lactate production and blocd flow in acute stroke. J Magn Reson Imaging 2:511-517, 1992. 21. Hossmann KA: Viability thresholds and the penumbra of foeal ischemia. Ann Neurol 36:557-565, 1994. 22. Ida M, Mizunuma K, Hata Y, Tada S: Subcortical low intensity in early cortical ischemia AJNR Am J Neuroradiol 15:1387-1393, 1994. 23. Johnson WD, Ganjoo AK, Stone CD, et al: The left atrial appendage: Our most lethal human attachment! Surgical implications. Eur J Cardiothorac Surg 17:718-722, 2000. 24. Jones SC, Perez-Trepichio AD, Xue M, et al: Magnetic resonance diffusion-weighted imaging: Sensitivity and apparent diffusion constant in gtroke. Acta Neurochir Suppl (Wien) 60:207-210, 1994. 25. Jungreis CA, Kanal E, Hirsch WL,et al: Normal perivascular spaces mimicking lacunar infarction: MR imaging. Radiology 169:lOl104, 1988. 26. Kaufmann AM, Firlik AD, Fukui MB, et al: Ischemic core and penumbra in human stroke. Stroke 30:93-99, 1999. 27. Kazui S, Levi CR, Jones EF, et al: Risk factors for lacunar stroke: A case-control transesophageal echocardiographic study. Neurology 54: 1385-1387, 2000. 28. Keiper MD,Ng SE, Atlas SW, Grossman RI: Subcortical hemorrhage: Marker for radiographically occult cerebral vein thrombosis on CT. J Comput Assist Tomogr 19527-531, 1995. 29. Kenet G, Sadetzki S, Murad H, et al: Factor V Leiden and antiphospholipid antibodies are significant risk factors for ischemic stroke in children. Stroke 31:1283-1288, 2000. 30. Kidwell CS, Saver JL, Mattiello J, et al: Thrombolytic reversal of acute human cerebral ischemic injury shown by diffusiodperfusion magnetic resonance imaging. Ann Neurol47:462-469,2000. 31. Kim YJ. Chang KH, Song IC, et al: Brain abscess and necrotic or cystic brain tumor: Discrimination with signal intensity on diffusionweighted MR imaging. AJR Am J Roentgenol 171:1487-1490, 1998. 32. Koenig M, Klotz E, Luka B, et al: Perfusion CT of the braio: Diagnostic approach for early detection of ischemic stroke. Radiology 209:85-93, 1998. 33. Koh MS. Goh KY, Tung MY, Chan C: Is decompressive craniectomy for acute cerebral infarction of any benefit? Surg Neurol 53:225230, 2000. 34. Kohlmeyer K, Graser C: Comparative studies of computed tomography and measurements of regional cerebral blood flow in stroke patients. Neuroradiology 16:233-237, 1978. 35. Lafitte F, Boukobza M, Guichard JP, et al: Deep cerebral venous thrombosis: Imaging in eight cases. Neuroradiology 41:410-418, 1999. 36. Lansberg MG, Albers GW, Beanlieu C, Marks MP: Comparison of diffusion-weighted MRI and CT in acute stroke. Neurology 54: 1557-1561,2000. 37. Lanska DJ, Kryscio RJ: Risk factors for peripartum and postpartum stroke and intracranial venous thrombosis. Stroke 3 1:1274-82, 2000. 38. Lassen NA, Astrup J: Ischemic penumbra. In Wood JH (ed): Cerebral Blood Flow: Physiologic and Clinical Aspects. New York, McGrawHill, 1987, 1994. 39. Launes J, Ketonen L: Dense middle cerebral artery sign: An indicator of poor outcome in middle cerebral artery area infarction. J Neurol Neurosurg Psychiatry 50:1550-1552, 1987. 40. Le Bihan D, Breton E, Lallemand D, et al: Separation of diffusion and perfusion in intravoxel incoherent motion MR imaging. Radiology 168:497-505, 1988. 41. Lepore FE, Gulli V, Miller DC: Neuro-ophthalmological findings with neuropathological correlation in bilateral thalamic-mesencephalic infarction. J Clin Neuroophthalmol 5:22&228, 1985. 42. Lev MH, Farkas J, Gemmete JJ, et al: Acute stroke: Improved nonenhanced CT detection-benefits of soft-copy interpretation by using variable window width and center level settings. Radiology 213:150-155, 1999. 42a. Liu AY, Maldjian JA, Bagley LJ, et al: Traumatic brain injury: Diffusion-weighted M R imaging findings. AJNR Am J Neuroradiol 20: 1636-1641, 1999. 43. MacWalter RS: Secondary prevention of stroke. Thromb Haemost 82(Suppl):95-103, 1999. 44. Marks,@I Holmgren EB, Fox AJ, et al: Evaluation of early computed tomographic findings in acute ischemic stroke. Stroke 30:389-392, 1999.

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45. Mathews VP, King JC, Elster AD, Hamilton CA: Cerebral infarction: Effects of dose and magnetization transfer saturation at gadoliniumenhanced MR imaging. Radiology 190:547-552, 1994. 46. Mattle J3P, Wentz KU, Edelman RR, et al: Cerebral venography with MR. Radiology 178:453458, 199I. 47. Meier P, Zierler KL: On the theory of the indicator-dilution method for measurement of blood flow and volume. J Appl Physiol 6: 73 1-744, 1954. 48. Merboldt KD,Bruhn H, Frahm J, et al: MRI of "diffusion" in the human brain: New results using a modified CE-FAST sequence. Magn Reson Med 9:423-429, 1989. 49. Mosely ME, Kucharczyk J, Mintorovitich J, et al: Diffusion-weighted MRI of acute stroke: Correlation with T2-weighted and magnetic susceptibity-enhanced MRI in cats. AJNM Am J Neuroradiol 11: 423429, 1990. 50. Muizelaar JP, Fatouros PP, Schroder ML: A new method for quantitative regional cerebral blood volume measurements using computed tomography. Stroke 28:1998-2005, 1997. 51. Mull M, Schwarz M, Thron A: Cerebral hemispheric low-flow infarcts in arterial occlusive disease: Lesion patterns and angiomorphological conditions. Stroke 28: 118-123, 1997. 52. Muller TB, Haraldseth 0, Jones RA, et al: Combined perfusion and diffusion-weighted magnetic resonance imaging in a rat model of reversible middle cerebral artery occlusion. Stroke 26:451457, 1995. 53. Murakami Y, Yamashita Y, Matsuishi T, et al: Cranial MRI of neurologically impaired children suffering from neonatal hypoglycaemia. Pediatr Radio1 29:23-72, 1999. 54. Murray CJ, Lopez AD: Mortality by cause for eight regions of the world: Global Burden of Disease Study. Lancet 349:1269-1276, 1997. 55. Noms DG, Niendorf T, Leibfritz D: Healthy and infarcted brain tissues studied at short diffusion times: The origins of apparent restriction and the reduction in apparent diffusion coefficient. NMR Biomed 7:304-310, 1994. 56. Pantano P, Lenzi GL, Guidetti B, et al: Crossed cerebellar diaschisis in patients with cerebral ischemia assessed by SPECT and lUIHIPDM. Eur Neurol 27:142-148, 1987. 57. Pessin MS, Duncan GW, Mohr JP, Poskanzer DC: Clinical and angiographic features of carotid transient ischemic attacks. N Engl J Med 296:358-362, 1977. 58. Petty GW, Brown RD, Whisnant JP, et al: Ischemic stroke subtypes: A population-based study of incidence and risk factors. Stroke 30: 2513-2516, 1999. 59. Pressman BD, Tourje El, Thompson JR: An early CT sign of ischemic infarction: Increased density in a cerebral artery. AJR Am J Roentgenol 149:583-586, 1987. 60. Provenzale JM, Engelter ST, Petrella JR,et al: Use of MR exponential diffusion-weighted images to eradicate T2 "shine-through" effect. AJR Am J Roentgenol 172537-539, 1999. 61. Provenzale JM,Loganbill HA: Dural sinus thrombosis and venous infarction associated with antiphospholipid antibodies: MR findings. J Comput Assist Tomogr 18:719-723, 1994. 62. Rademacher J, Sohngen D, Specker C, et al: Cerebral microembolism, a disease marker for ischemic cerebrovascular events in the antiphospholipid syndrome of systemic lupus erythematosus? Acta Neurol Scand 99:356-361, 1999. 63. Rauch RA,Bazan C 3d, Larsson EM, Jinkins JR: Hyperdense middle cerebral arteries identified on CT as a false sign of vascular occlusion. AJNR Am J Neuroradiol 14:669-673, 1993. 64. Rudolf J, Grond M, Stenzel C, et al: Incidence of space-occupying brain edema following systemic thrombolysis of acute supratentorial ischemia. Cerebrovasc Di 8:166-171, 1998. 65. Salgado ED, Weinstein M, Furlan AJ, et al: Proton magnetic resonance imaging in ischemic cerebrovascular disease. Ann Neurol 20: 502-507, 1986. 66. Schlaug G, Benfield A, Baird AE, et al: The ischemic penumbra: Operationally defined by d i i s i o n and perfusion MRI. Neurology 53: 1528-1537, 1999. 67. Schlaug G, Siewert B, Benfield A, et al: Time course of the apparent diffusion coefficient (ADC) abnormality in human stroke. Neurology 49~113-119, 1997. 68. Scuotto A, Cappabianca S, Melone MB,Puoti G: MRI "fogging" in cerebellar ischemia: Case report. Neuroradiology 39:785-787, 1997. 69. Shamoto H, Chugani HT: Glucose metabolism in the human cerebellum: An analysis of crossed cerebellar diaschisis in children with unilateral cerebral injury. J Child Neurol 12:407414, 1997.


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70. So EL, Toole IF,Dalal P, Moody DM: Cephalic fibromuscular dysplasia in 32 patients: Clinical findings and radiologic features. Arch Neurol38:619-622, 1981. 71. Sorensen AG, Copen WA, Ostergaard L, et al: Hyperacute stroke: Simultaneous measurement of relative cerebral blood volume, relative cerebral blood flow, and mean tissue transit time. Radiology 210: 519-527, 1999. 72. Tomura N, Uemura K, Inugami A, et al: Early CT finding in cerebral infarction: Obscuration of the lentifonn nucleus. Radiology 168: 463-467, 1988. 73. T ~ w iCL, t Barkovich AJ, Gean-Marton A, e4 al: Loss of the insular ribbon: Another early CT sign of acute middle cerebral artery infarction. Radiology 176:801-806, 1990. 74. Valanne L, Ketonen L, Majander A, et al: Neuroradiologic findings in children with mitochondrial disorders. AJNR Am J Neuroradiol 19:369-377, 1998. 75. van Gelderen P, de Vleeschouwer MH,DesPres D, et al: CT: Water diffusion and acute stroke. Magn Reson Med 31:154-163, 1994.

76. Wein TH, Bornstein NM: Stroke prevention: Cardiac and carotidrelated stroke. Neurol Clin 18:321-341, 2000. 77. Wetzel SG, Kirsch E, Stock KW, et al: Cerebral veins: Comparative study of CT venography with intmmrial digital subtraction angiography. AJNR Am J Neuroradiol20:249-255, 1999. 78. Wijman CA, Babiian VL, Winter MR, Pochay VE: Distribution of cerebral microembolism in the anterior and middle cerebral arteries. Acta Neurol Scand 101:122-127, 2000. 79. Willis BK, Greiner F, Onison WW, Benzel EC: The incidence of vertebral artery injury after midcervical spine fracture or subluxation. Neurosurgery 34:43541, 1994. 80. Wong EC, Cox RW, Song AW: Optimized isotropic diffusion weighting. Magn Reson Med 1995 34139-143, 1995. 81. Woodring JH, Lee C, Duncan V: Transverse process fractures of the cervical vertebrae: Are they insignificant? J Trauma 34:797-802, 1993. 82. Yamauchi H, Fukuyama H, Nagahama Y, et al: Decrease in regional cerebral blood volume and hematocrit in crossed cerebellar diaschisis. Stroke 30: 1429-1431, 1999.


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Cerebral Aneurysms and Vascular Malformations Theodore C. Larson I11

Cerebral Aneurysms

I4l. =la. U6a.297; thereafter, the bleeding rate is approximately 3% per year.13'. 139 Initial aneurysm size is not a prognostic factor influencing rebleeding in the acute period.I4' ApproxIncidence and Natural History imately 14% to 23% of survivors of rupture of a cerebral Cerebral aneurysms are found in approximately 0.5 to aneurysm are left with significant morbidityzs5.267;in 13% 5% of the population.lM".139, 193. 242.255. 261. 262 326.339a Women to 32% of cases, the morbidity is the direct result of have a variably greater incidence of cerebral aneurysms delayed vasospasm-caused ischernia.Ig323'a. 236". 267 Twentycompared with men, and aneurysm development increases one percent of patients who enter the hospital for treatment with advancing age.15. 139. 242. 297. 326 Some families demonof subarachnoid hemorrhage eventually die.267Surgical strate a genetic predisposition to develop cerebral aneuclipping of acutely ruptured aneurysms results in improved r y s m ~ .214. ~ ~M5 . The risk of new aneurysm development is functional outcome compared with delayed intervention.218 approximately 2% per year.139Subarachnoid hemorrhage, These data also argue for elective treatment of an unrupthe most common presenting symptom of a cerebral aneutured aneurysm. rysm, is the second most common cause of subarachnoid Unruptured cerebral aneurysms are most often asymphemorrhage, after trauma.261Eighty percent to 90% of tomatic but can cause local mass effect and headache. nontraumatic subarachnoid hemorrhages are due to a rupFocal mass effect can compress adjacent cranial nerves or tured cerebral aneurysm, a far more common cause than brain parenchyma, a typical example being third nerve an arteriovenous malformation, which accounts for 15% of palsy due to a posterior communicating aneurysm. Other subarachnoid hemorrhages.301Other, less common prediseases can cause neurologic deficits similar to those due senting signs and symptoms, which are due to mass effect to aneurysms, however. For example, third nerve palsy or neighboring inflammation, aneurysm thrombosis, or ancould be caused by diabetes or microvascular disease ineurysm-generated emboli, are cranial nerve palsy, headstead of a posterior communicating aneurysm. When magache, seizure, and transient or permanent neurologic dysnetic resonance imaging (MRI) and MR angiography fun~tion."~ These nonhemorrhagic symptoms can be seen (MRA) fail to diagnose the cause of the patient's third with aneurysms of any size but occur more commonly with nerve palsy, catheter cerebral angiography may be required posterior circulation or internal carotid aneurysm^.^^ to exclude a cerebral aneurysm, because the morbidity The annual incidence of rupture of an asymptomatic and mortality associated with cerebral aneurysms are so cerebral aneurysm has been estimated at approximately significant. When catheter cerebral angiography does not 0.5% to 2%, or roughly 10 cases per 100,000 pop~1ation.I~~.demonstrate an aneurysm in a patient with no history of 139, 255. 273.326 Symptomatic intact aneurysms have a higher subarachnoid hemorrhage, the patient can be assumed to rate of bleeding4% or more per year. Some studies have have small-vessel cerebrovascular disease. Sometimes the suggested that for aneurysms less than 1 cm in diameter, angiogram supports this diagnosis by showing other areas the incidence of annual rupture is less than 0.1%.315a326 of atherosclerotic disease. Other reports, however, have documented that the majority of ruptured aneurysms are less than 9 to 10 rnm in diarneter,I3Oa.14'.35 and that even small (2 to 3 mm) aneurysms Types of Aneurysms, Etiology, and The presmay cause subarachnoid hemorrhage.Ih. 273.288.340 Pathology ence of a daughter sac probably raises the likelihood of 3M Younger patients may have a greater propenAneurysms may be divided into different classifications sity for aneurysmal hemorrhage, especially if they have according to morphology, size, location, or etiology. Most multiple aneurysms.i39 cerebral aneurysms are acquired lesions and are saccular A ruptured cerebral aneurysm carries significant morbidor fusiform. Older medical reports proposed that saccular ity and mortality, the 30-day mortality traditionally being or beny cerebral aneurysms were due to an embryologic stated as 40% to 60%.139. I4l 255. 262 Untreated patients with abnormality of the walls of cerebral vessels.22LS t e h b e n ~ ~ ~ ~ ruptured cerebral aneurysms have a rebleeding rate of 10% and others have refuted this theory. Most cerebral aneuto 50% in the first 2 weeks to 6 months. The rebleeding 262. 293 which rysms develop from hernodynamic stresses,143a. . ~ " . typically occur at vessel bifurcations or terminations, or rate is highest in the first day, with a 50% m ~ r t a l i t y ~ 135.


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along the outer curvature of looping ve~sels.'~~3" 197. 244, 273. The aneurysm's location is a continuation of the primary flow direction in the parent vessel, especially if the parent vessel is tortuous.244Rupture and thrombosis of cerebral aneurysms are also believed to be due to hemodynamic forcesg?293 Supporting this theory of an underlying etiology is the higher incidence of cerebral aneurysms in patients with intracranial vascular anomalies, including fenestrations and congenital or iatrogenic vascular variants of the circle of Willis (e.g., persistent trigeminal artery, unilateral absence of the A1 segment of an anterior cerebral artery, azygous proximal anterior cerebral artery, and occlusion or absence of an internal carotid artery).205 264, 272 Primary causes of aneurysms are as follows: (1) atherosclerosis, (2) hypertension, (3) smoking, (4) abuse of cocaine, methamphetamine, ephedrine, heroin, and other drugs with resul139, 206, 2w (5) vascular maltant arteritis or hyperten~ion,'~~. formations (approximately 6% to 10% incidence of aneurysm, both proximal flow-related and nidalllz 44' 60*90. 148'86,204), (6) specific vascular diseases, such as fibromuscular dysplasia (20% to 50% incidence of aneurysm113.272),spontaneous cervical carotid or vertebral artery dissection (more commonly seen in women272),Takayasu's arteritis,lll polycystic kidney disease (10% incidence of aneurysm), and neurofibro~natosis,~~~ and (7) the connective tissue disorders, such as Marfan's syndrome and Ehlers-Danlos syndrome (in which aneurysms of the carotid siphon to supraclinoid segment are more common).z72The walls of saccular cerebral aneurysms contain intima and adventitia but the media and internal elastic membrane are thinned or absent.4950 A number of patients with cerebral aneurysms demonstrate collagen type 111 abnormalities.272Most cerebral aneurysms arise from the circle of Willis and middle cerebral artery bifurcations. Ninety percent involve the anterior circulation, and 10% the posterior circulation.ll The most common sites are the anterior communicating artery at its junction with the adjacent anterior cerebral artery (30% to 35%), the posterior communicating artery at its union with the internal carotid artery (30% to 35%), the middle cerebral artery bifurcation (20% to 25%), the basilar terminus (5%), the carotid terminus (5%), and the origin of the ophthalmic artery (5%).227Less commonly, aneurysms occur along the course of the anterior cerebral arteries, particularly at the origin of the callosomarginal artery, the middle cerebral arteries, posterior cerebral arteries, superior cerebellar arteries, anterior inferior cerebellar arteries, and posterior inferior cerebellar arteries.15 130a.*,259 In 15% to 30% of patients, multiple aneurysms are found, more often in women than in men by a 5:l 141, 297, 297a. 307a. 316 and most frequently involving the middle cerebral artery.340Of the patients with multiple cerebral aneurysms, 75% have two, 15% have three, and 10% have four or more.297When one of multiple aneurysms ruptures and causes subarachnoid hemorrhage, it is most often the largest340although this is not always the case. For instance, Nehls and colleagues209have reported the propensity for anterior communicating aneurysms to rupture when several are present simultaneously. Vasculopathies, such as fibromuscular dysplasia and connective tissue disorders, as well as syndromes such as polycystic kidney disease are associated with a higher incidence of multiple cerebral aneurysms. Bilateral symmetrical aneurysms are called mirror 293

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aneurysms, and they most often involve the internal carotid arteries or the middle cerebral artery bifurcations.297 Other causes of cerebral aneurysms, identified in less than 5% of patients, are (1) penetrating and nonpenetrating trauma, (2) dissection (post-traumatic or otherwise), (3) inflammation or mycosis due either to septic emboli causing destruction of the endothelium or to spread of infection to the vasa vasorum with subsequent vessel wall destruction and focal dilatation, and (4) neoplasm; rarely, cerebral aneurysms may be congenital?. I6l. 170 2 L 2 Except for congenital aneurysms, aneurysms with these uncommon causes often develop in unusual locations that are distal to the circle of Willis. Trauma typically results in a pseudoaneurysm rather than a true aneurysm, because no normal vascular components constitute the sac within a hematoma that comm66cates with the injured vessel. Post-traumatic pseudoaneurysms occur in locations not common for other cerebral aneurysms, including the proximal internal carotid artery, particularly at the skull basezm; the meningeal vessels, which often are associated with overlying skull fractures and epidural hematomas3"; the posterior cerebral or anterior cerebral arteries, caused by tentorial or falcine impaction, and in extracranial vessels within the scalp, such as the superficial temporal artery and the occipital artery.281Penetrating, high-velocity trauma, such as from gunshot wounds, is more likely to produce a traumatic aneurysm if the entrance site is in the temporal or peritemporal region, if fragments cross the midline, and if the pseudoaneurysm is surrounded by hematoma. The surrounding anterior and middle cerebral arteries are most often involved? Initially, traumatic pseudoaneurysms may not be visualized, but then they rapidly enlarge.2". 280 Fifty percent of untreated, post-traumatic aneurysms bleed, with an almost uniformly fatal out~ome.~. 205 Uncommon neoplastic aneurysms are also pseudoaneurysms, resulting from primary or metastatic tumor invasion of a vessel or metastatic emboli to the vessel lumen or its adenomas are associated with vasa ~ a s o r u m . ~ ~Pituitary , a higher incidence of cerebral aneurysms, acromegalyproducing adenomas theorized to sometimes produce diffuse cerebrovascular ectasia and unilateral or bilateral cavernous carotid aneurysms due to growth hormone secretion. H, 327 Dissection of the internal carotid artery or more commonly the vertebral artery can be spontaneous, post-traumatic, or secondary to disease of the vessel wall such as fibromuscular dysp1asia.- A pseudoaneurysm accompanies up to a third of internal carotid dissections and 7% of vertebral artery di~sections.~~Dissecting pseudoaneurysms may manifest as ischemic symptoms due to emboli or small arterial branch occlusion in addition to subarachnoid hem~rrhage.~ Dissecting pseudoaneurysms more commonly present as subarachnoid hermorrhage when occurring in the posterior cir~ulation.~~" Rebleed rates are particularly high with accompanying significant mortality.Fusiform aneurysms are vascular ectasias due to advanced focal atherosclerotic disease that has degraded the vessel's media.5. 293 The vertebrobasilar system is more commonly affected than the anterior circulation. The involved vessel is frequently elongated and tortuous, so that 1399


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in effect, the native vessel is replaced by aneurysmal dilatation with no neck. Although fusiform aneurysms may rupture, thrombosis due to blood stagnation may be the mode of presentation. Local mass effect, ischemia due to penetrating vessel occlusion, and cranial nerve palsies are other pathologic sequelae.'. 302 An infundibulum represents the residua of a developmental vessel that has undergone incomplete regression. It most commonly involves the junction of the internal carotid artery and posterior communicating artery, and less commonly the origin of the anterior choroidal artery from the internal carotid artery. Infundibula are usually 3 mm or less in diameter. They can be difficult to differentiate from cerebral aneurysms unless the characteristic origination of the emerging vessel from the dome of the infundibulum is identified.

Imaging Evaluation of Cerebral Aneurysms Imaging objectives for the identification of a cerebral aneurysm are (1) visualization of subarachnoid hemorrhage, (2) confirmation of the size, location, and morphology of the cerebral aneurysm, (3) evaluation of the adjacent cerebral vasculature, including evidence of spasm, atherosclerosis, displacement, and incorporation into the aneurysm's wall, and (4) demonstration of any accompanvinq adjacent brain pathology. The typical patient with a ruptured cerebral aneurysm IS a woman between 40 and 60 years old who presents with "the worst headache of my life," with or without a neurologic deficit. Clinical assessment of the patient classifies into Hunt and Hess grades I through V (Table 8-1).12@ CT scan of the head identifies subarachnoid hemorrhage, and the patient undergoes catheter angiography, which is timed to precede surgical treatment with either craniotomy or endovascular coiling. In patients in whom CT scan shows no hemorrhage, lumbar puncture should be performed. Patients with a positive lumbar puncture result then undergo catheter cerebral angiography, unless the lumbar tap was traumatic. In some situations, MRI and MRA may be performed to evaluate the subarachnoid hemorrhage and to identify a cerebral aneurysm, for example, when the suspicion for a cerebral aneurysm is low or the patient is a poor candidate for cerebral angiography or aneurysm intewention (i.e., is elderly or severely injured). MRI and MRA may also be employed as screening tests in populations known to have a higher incidence of cerebral aneurysms (see preceding discussion) or for monitoring known, untreated aneurysms. Although the permanent neurologic risk

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of catheter cerebral angiography is low-approximately 0.8% in the usual patient population with ruptured cerebral aneurysms-ne should always keep in mind the morbidity of stroke when deciding whether a particular patient should undergo the procedure.

Computed Tomography The most important role for CT in the patient with a cerebral aneurysm is in the identification of acute subarachnoid hemorrhage, which is demonstrated as increased density within a cisternal space (Fig. 8-1). The location of the subarachnoid hemorrhage may help determine the location of the underlying cerebral a n e u r y ~ m . ' . ~Zn. . ~297 ~ , For example, blood in the sylvian fissure most likely has arisen from a middle cerebral aneurysm, and blood in the fourth ventricle is a common sign of rupture of a posterior inferior cerebellar artery aneurysm.259Some subarachnoid hemorrhage patterns are not diagnostic of aneurysm location, and none is foolproof. The CT demonstration of subarachnoid hemorrhage progressively decreases until it disappears by approximately 3 week^,'^.^^ depending on the initial amount of subarachnoid hemorrhage. In 5% to 10% of CT scans, subarachnoid hemorrhage is not identifiable. For this reason, any patient in whom acute subarachnoid hemorrhage is suspected but CT scanning does not demonstrate intracranial blood should undergo lumbar puncture. A small amount of aneurysmal subarachnoid hemorrhage adjacent to the brain stem may be mistaken for perimesencephalic (prepontine and interpeduncular) hemorrhage, a finding believed to be due to the rupture of small perimesencephalic and usually resulting in a good outcome, unlike an aneurysm rupture.

TABLE 8-1. Hunt and Hess Grading Scale for Subarachnoid Hemorrhaqe Grade I Grade II Grade 111 Grade IV Grade V

Asymptomatic or minimal headache Moderate to severe headache, nuchal rigidity, oculomotor palsy, normal level of consciousness Confusion, drowsiness, mild focal neurologic deficit Stupor or hemiparesis Comatose or moribund with decerebrate posturing

Fig. 8-1. CT demonstrating subarachnoid hemorrhage (arrow) from aneurysm rupture.


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CT is also excellent for identifying intraventricular hemorrhage (seen in 13% to 28% of casesa9), parenchymal hematoma (20% to 30%), and the occasional subdural hematoma, findings that often help localize the underlying aneurysm. CT examination is secondarily important to identify cerebral aneurysms, typically 5 mm or larger in diameter. The rate of identification of cerebral aneurysms by thinsection, high-resolution, contrast-enhanced CT scanning has been reported to be at least 67% for aneurysms 3 to 5 mm in diameter and to approach 100% for larger aneurysm~."~.274 Focal, slightly dense areas of luminal blood in

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typical locations where aneurysms arise,= focal globular or elongated areas of contrast enhan~enient,~'~ variable calcification involving the aneurysm's walls, and clot within larger aneurysms characterize cerebral aneurysms.'08 Large aneurysms have a transverse dome diameter of 1.0 to 2.4 cm, and giant aneurysms are 2.5 cm or more in diameter. Large and giant cerebral aneurysms are typically more easily identifiable because of their conspicuous size but also often from the presence of internal clot and peripheral wall calcifications, especially in giant aneurysms (Fig. 8-2). Giant aneurysms are most commonly identified in middle-aged women, are typically located in the extradural


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carotid artery, the middle cerebral artery bifurcation, or the basilar summit, and usually manifest with a mass effect but can present as subarachnoid hemorrhage.& 69.14' AnY large aneurysm can have a mass effect on adjacent brain or cranial nerves. CT is excellent for identifying skull base erosion due to large or giant aneurysms, especially if thin sections (3 rnm or less) are obtained. Brain parenchymal hemorrhage, which may be associated with any of the cerebral aneurysms, is thought to occur from acute or chronic rupture of the cerebral aneurysm into adjacent brain substance after the blood passes through overlying pia. Both parenchymal and subarachnoid hemorrhages often obscure an underlying ruptured cerebral aneurysm.

MRI The identification of acute subarachnoid hemorrhage by *~" there routine MRI has been notoriously p o ~ r , ' ~ although ' ~ ~ following two reaare reports that claim o t h e r ~ i s e . The sons have been postulated for the lack of visualization of acute subarachnoid hemorrhage on MRIIo4 (1) normal Poz (partial pressure of oxygen) in CSF inhibits the development of deoxyhemoglobin and (2) lysis of red blood cells in subarachnoid CSF prevents heterogenous magnetic susceptibility. However, with the employment of pulse sequences including intermediate-weighted spin-echo with TE (echo time) values of 22 to 45 msec, T1 weighting, FLAIR (fluid-attenuated inversion recovery) imaging, and gradient-echo imaging, acute subarachnoid hemorrhage can frequently be identified. Other imaging problems can obscure precise identification of subarachnoid hemorrhage on MRI, including CSF and vascular pulsation artifact and magnetic susceptibility artifact along the skull base. Significant experience is therefore required to correctly identify acute subarachnoid hemorrhage on MRI. Subarachnoid hemorrhage older than 12 to 24 hours can routinely be identified on MR images, often helping pinpoint the underlying ruptured cerebral aneurysm by a collection of blood. Thin-section MRI examination can often identify cerebral aneurysms more than 3 mm in diameter.lWThe identification may be easier if the aneurysm is unruptured. It may be difficult, however, to differentiate normal vascular tortuous anatomy or bone such as the anterior clinoid process from a cerebral aneurysm. When large enough, cerebral aneurysms can be positively identified on MRI as flow artifacts or characteristic findings with the use of dfferent pulse sequences. Phase-encoding artifact due to flow-producing signal rnismapped in the phase-encoding direction is optimally seen on the short TE, long TR,spinecho pulse sequence, which may be the best sequence for positive identification of aneurysms (Fig. 8-3). Other flow effects, such as a swirling appearance inside the aneurysm due to spin dephasing, rephasing, and turbulence, evenecho or gradient rephasing, diastolic pseudogating, slow flow, variable intraluminal flow rates, entry slice enhancement, and signal void due to rapidly flowing blood on all pulse sequences except those using short TE, short TR, relatively large flip angle gradient echo scans that are typically employed for time-of-flight (TOF) MRA studies, are often also helpful to identify cerebral aneurysm^.^^ 399

2%. 321

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Contrast enhancement of the aneurysm highlights its central lumen and can exaggerate the aforementioned artifacts, particularly the phase mismapping effects. For instance, these clues can often reliably diagnose cavernous carotid segment aneurysms and differentiate them from pituitary masses. A partially thrombosed aneurysm contains peripheral layers of clot of different ages, usually with the oldest clot located most peripherally.l3. Io8* 3M MRI may identify intramural thrombus in dissecting aneurysms, aiding in their distinction from fusifonn aneury~ms.~ The signal intensities of intralurninal clot correspond to the expected age of hemorrhage on MRI according to the magnetic field strength employed.13.Io8 Fibrosis and cellular infiltration can accompany the clot. Completely thrombosed aneurysms or aneurysms with extremely slow flow can rarely mimic tumors, including sellar and parasellar masses. Catheter cerebral angiography should be undertaken in these problematic cases, to prevent "surprises" during craniotomy and potentially catastrophic hemorrhage during trans-sphenoidal or other operations. The brain parenchymal chhges adjacent to cerebral aneurysms may be absent unless the aneurysm is large enough to cause edema and localized mass effect. MRI is superior for evaluating the relationship of the aneurysm with adjacent brain structures because of the inherent soft tissue contrast limitations to and posterior fossa beamhardening artifact seen with CT. If the aneurysm has ruptured, an adjacent intraparenchymal or subarachnoid clot may be identified. This finding is especially useful for determining which aneurysm has ruptured in a patient with multiple aneurysms, especially when clinical localizing signs are not helpful.Io7.Zm The imaging location of the clot can subsequently guide treatment.'07 Chronic changes include gliosis and deposition of hemosiderin or fenitin; the latter two substances represent hemorrhagic breakdown products, which are best demonstrated on long TE, long TR,T2-weighted spin-echo or T2* gradient-echo MRI sequences. Superficial siderosis represents intracellular (most often macrophage) and extracellular hemosiderin or ferritin coating the leptomeninges, cranial nerves, and superficial central nervous system parench~ma.~~ The siderosis is secondary to any cause of subarachnoid hemorrhage, usually repetitive, but can also occur on the ventricular ependymal surfaces.95Focal or generalized neurologic deficits correspond to the location and extent of central nervous system invol~ement.~~ MRI is superior to CT for the localization of cerebral aneurysms, their relationship with adjacent structures, and associated changes in neighboring brain tissue.

MRA and CT Angiography MRA has made tremendous strides in the identification of cerebral aneurysms. Between 55% and 86% of cerebral aneurysms may be identified with routinely available MR4.l'. 12" 256. 275 Sensitivity of MRA for detection of aneurysms can be increased when MRA is combined with MRI,a6. n5 thereby overcoming the inherent difficulties of imaging slow flow, turbulent flow, or intraluminal clot with MRA. Because almost all aneurysms larger than 3 m m ~0240.


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Fig. 8-3. MRI and MRA examination demonstrating flow effects associated with a giant left cavernous carotid aneurysm. A, Axial short TE, long TR MR image demonstrating the aneurysm (long arrow) with internal and external phase encoding artifact (short arrows) due to mismapped flow. B, Sagittal T1-weighted image falsely gives the appearance of thrombus within the aneurysm (arrow) due to slow flow. C, Three-dimensional time-of-flight MRA poorly outlines the aneurysm (arrow) because of internal slow flow. D,AP view of left carotid angiogram confirms giant left cavernous carotid aneurysm (arrow). (Case courtesy of Daryl Harp, MD.)

can be visualized,149MRA can function as a screening exarninati~n.~~. 240 The most commonly employed sequence is TOF threedimensional (3D) MRA, which typically provides submillimeter in-plane resolution. A variant of this is MOTSA (multiple overlapping thin-slab acquisiti0n),3~,34* 232 which attempts to combine the advantages of 3D with two-dimensional (2D) MRA. MOTSA is especially helpful when the slow flow in an aneurysm located distally within the imaging slab is not imaged on a 3D TOF study because of flow saturation. The T1 shortening effect of subacute subarachnoid blood or intraluminal or perianeurysmal clot can obscure an aneurysm or mimic flowing blood on a TOF imaging sequence.Iz6

An alternative pulse sequence is phase-contrast (PC) MRA, which has excellent background, susceptibility artifact, and stagnant blood suppression and may help image in-plane flow and slow flow, two causes of flow saturation degradation of TOF MRA.733lZ7 It can be combined with cardiac gating using electrocardiogram leads or peripheral photoplethysmography to create cine PC MRA, a technique that has been used to document a greater pulsatility change in aneurysm size with ruptured than with unruptured aneur y s m ~PC . ~ MRA ~ has poorer spatial resolution, depends on a prescribed velocity encoding gradient with the potential for aliasing, can be altered by complex flow, and requires longer imaging and processing times than TOF MRA.12' Although PC MRA may identify fewer aneurysms


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than TOF MRA,137the slow flow within fusiform aneuevaluates only the intralurninal portion of the aneurysm that rysms is often better imaged with PC MRA. A patent contains flowing blood. The inability of catheter cerebral double lumen in a dissecting aneurysm would also be best angiography to demonstrate aneurysmal clot can lead to imaged with PC MRA. underestimation of the size of the aneurysm. This defiMRA combined with MRI can often demonstrate interciency of catheter cerebral angiography is significant in nal flow patterns within large and giant cerebral aneurysms; comparison with MRI, which can demonstrate not only faster flow is located more peripherally, and stagnant flow clot but also its age as well as the relationship of the 298 Vascular loops may be confused more centrally.", aneurysm with adjacent brain structures. Cerebral angiograwith cerebral aneurysms on MRA. Gadolinium-based intraphy has the benefit, however, of better demonstrating cerevenous contrast agents are not typically employed in the bral vasospasm, the aspects of the aneurysm's morphology, identification of cerebral aneurysms but can be helpful to such as dome irregularity or lobulation, which are possible highlight aneurysms that are small, are in atypical locapredictors of hemorrhage, and a focal tit or dimple indicating the site of recent aneurysmal hemorrhage.340Aneurysms tions, or have slow or stagnant flow or to document the residual patent lumen in an incompletely thrombosed aneuevaluated soon after ruDture often are smaller than when r y ~ m . ~ 'The ~ " use of contrast enhancement with MRI or intact, because of clot cimpression and spasm of either the MRA increases flow-dependent artifact and can obscure aneurysm or adjacent artery, but they subsequently enlarge cerebral aneurysms because of enhancement of dural siif surgery is delayed.141.U)9.273.326 unnuses, intracranial veins, and extracranial stru~tures,5~ less a PC MRA technique is utilized.Iz7In large or giant, Cerebral Aneurysm Evaluation after partially or completely thrombosed aneurysms, the aneurysSurgery mal wall may show enhancement. Special MRI techniques may help in the positive identiControversy has arisen regarding the use of MRI to fication of cerebral aneurysms; they include magnetization evaluate patients who have undergone cerebral aneurysm transfer pulses,7" progressive increases in radiofrequency clipping. Most cerebral aneurysm clips are currently MRI pulse flip angles, and multiple postprocessing algorithrn~.~~.compatibleBla but create local ferromagnetic artifact on '23. It is important that both the 3D reconstructed MRA MRI that obscures precise evaluation of the neck of the images and the source, 2D planar images are scrutinized, clipped aneurysm (Fig. 84).lo3 Issues have been raised so that small aneurysms and aneurysms with slow flow are regarding clip-to-clip variability, distortion of the aneurysm not missed. Standard maximum intensity projection (MIP) clip during surgical application, manufacturer liability, Targeted images have some artifact-derived li~nitations.~ warnings from the U.S. Food and Drug Administration MIPS select a region of interest and help exclude confoundregarding rotational and translational aneurysm clip motion ing extraneous vessels and other structures.lZ7Review of in a magnetic field, and the necessity of institutional assurthe source images also best demonstrates the neck of the ance that all aneurysm clips are MR compatible.139bBeaneurysm and its relationship to the parent vessel. Vessel cause of these issues, many facilities have denied MFU to loops and magnetic susceptibility artifact from air-filled patients with cerebral aneurysm clips, even though an MRI sinuses or bone at the skull base may obscure aneurysms. permits better evaluation of brain parenchyma than CT. CT angiography (CTA) is a relatively new development In fact, fatal cerebral hemorrhage attributed to the MR's that can well demonstrate the morphology and location magnetic field has been reported in a patient in whom a of cerebral aneurysms. Thin-section spiral CT slices are stainless steel, MFU-incompatible aneurysm clip had been acquired during rapid intravenous infusion of a contrast placed on a middle cerebral artery aneurysm.'* agent. The axial images and the reconstructed 3D images, Gugliemi detachable platinum coils, which are used to created with MIP and other processing methods, reproduce treat cerebral aneurysms endovascularly, are MRI compati~ .217 Both the proximal cerebral vasculature for a n a l y s i ~ .2'6, ble.67" However, localized artifact caused by the platithe source images and the reconstructed images should be num coils on either MRI or CT often do not pennit precise reviewed.345The exclusion of adjacent skull base bone and evaluation of the aneurysm.66".96". 313 Less metallic artifact the contrast enhancement of nonarterial structures can be is present in both the endovascularly treated and surgically problematic.274 clipped aneurysm patient than CT.'36Catheter angiography 3D CTA has a reported sensitivity of 67% to 90% for remains the only method to determine whether the aneuidentifying cerebral aneurysms.274.345 Aneurysms less than rysm has been completely clipped or coiled. 5 mm in diameter may be missed.345CTA has some benefits over MRA for evaluation of calcified atherosclerotic disease of adjacent vessels and, in some instances, for visualCerebral Vascular Malformations ization of the aneurysm neck or dome and their relationship Cerebral vascular malformations can be divided into to osseous skull base structures such as the anterior clinoid four primary types38.Ig4. z8: process. 3D rotational views of both CT angiograms and Arteriovenous malformation (AVM) MR angiograms help elucidate the precise anatomic relaCavernous angioma tionships of cerebral aneurysms with adjacent vessels. SoftCapillary telangiectasia ware reconstruction enhancements can provide endoscopic Venous angioma views of the dome and neck of an aneurysm.I8" Catheter cerebral angiography remains the standard for These types of vascular malformations can also be evaluation of cerebral aneurysms. Catheter-based angiogramixed-incorporating elements of two or more types.23 phy has better spacial resolution than MRA or CTA, but it 219, 246. 247, 3 0 ~The four classic types of cerebral vascular luz3

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Fig, 8 4 . Iimromgne&c met produced by m r e b l meurys.m clip on hlKI. SXmt TE,long TR ('A) and mroaal post-contrast T1weighted (23) images demanstrating m ophthalmic aneurysm clip (arrows). malformations arc? based on their congenital origin and do tri.cular location have b n reported as other characteristics not include acquired arteriovenous cerebral fistulas, which indicating a propensity for ATJn hemorrhage. Mpheral are dural in lwtion, or acquired or congenital direct artevenous drainage or mixed peripheral and ce~tralvenous ri.ovenous fistulas. The term occtllr cerebral vascuIar d- drainage, dong with angiomtow change, dilated arterial fonmtims has been used to describe cavernous angiomas, collaterals that pass though brain to supply the A W , capiUmy tehgitxtasias, and tbrombosed A W s k i t u s e have been eomiated with a decreased iscidence of A W they could not be visualized with ca&eter cerebral angioghem~rrhage.~a AVMs 3 em or less in diameter have raphy. Because all of these lesions, e m p t some capillary been reparted to bleed more frequently and to produce telangieetasim, ean be demonstrated on MU., they ate no lar$.er hematomas than larger m8 The rate of longer truly "occult," and the term therefore has little hemorrhage of a cerebral A W is estimated to be 2% to 3.5% per year and to increase with wkvancing age; this current relevance. The overall incidence of vascular mdformations of all figure is higher than the yearly rupture rate for cerebral t y p in the genmal population is estimated to be 2%. aneurysms.~4s$58*99. li% a23.294 Mortality of 10% to 30% is ass&iated with .each i n s W of hemmhage, for an o v d annual mortality rate of less than 1% ?Ihe risk of permaArteriovenous M t ! f o I ' m a t i ~ ~ ~ nent neurologic deficit is 20% to 30% with each A'oFM: Incidence and Pathology hemmhage920e. 94L resulting in an annual incidence of Appro&mtely 0.1% of the general population harbar a approximately 1%. The risk of rebleeding after a k t cerebral A m , the most common symptomatic cerebral hemorrhage is approxkmtely 6% in the first ye@ and vacular m a l f ~ r m a t i o nAVNIs ~ ~ ~ are most commonly idensubsqaenfly decreases to an annual rate of 3%33123s5 0 3 * ~ tified in women in the swond to fourth decades.332Roughly The second most common dinieal presentation of cere30% to 55% of patients present with intracranial hemortvral AVMs is seizure5, which are reported in 22% to 60% rhage?. 43* zc+,237 a heralding event that is also most of ~ases.~~. m5,23T. 322 Seizures manifest more commdy common in children with oerebral AVMs. Seventy percent in patients who are younger than 30 years md with A W s of patients with intracranial hemorrhage due to A W s that are large or diffuse. Large A W s afe also more compresent prior to age 40.%% 94 Inmanial hemorrhage is monly identiiied with progressive neurologic deficit. The most commonly ilatraparenchymal but may be intraventri~ overall risk of a seizure disorder in a patient with an A W ular or subarachnoid. Nontraumatic submhnoid and intrais 18%# and the risk of a neurologic deficit is 25% to ventricular hemorrhages are more commonly due to rupture 30%.+a?58 There is an approximately 1 in 4 risk that a of cerebral aneurysms. Spontaneous thrombosis of a drainpatient will b m e intell&ally disabled because of a ing vein & r u p ~ r of e a nidal aaeurysm are believed to be brain A W , without or with previous hemorrhage. the most common causes of AVM hemorrhage. Exclusive Brain AVMs cause nonhemorrhagk symptoms because of (1) blood flow steal from adjacent n o d territories and central venous drainage and a periventricular or intraven-


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(2) regional venous hypertension due to the engorged, highflow, draining veins of the AVM. Clinical sequelae are seizures, neurologic deficit, and headache. Acute neurologic deficits, however, are most commonly associated with intracranial hemorrhage due to an AVM. Occasionally, brain AVMs can result in mass effect or hydrocephalus due either to vascular compression of CSF pathways or communicating hydrocephalus secondary to previous hemorrhage. Headache is identified in more than 50% of paThirty percent of patients report tients with brain AVMS.~"~ a bruit, which is due to transmission of blood pulsations from the AVM.43Calvarial auscultation of a cranial bruit is unusual, however. Occasionally, an AVM may cause either hemifacial spasm or cranial nerve neuralgia or palsy if the AVM in whole or in part is located in the basilar cisterns341 or if subarachnoid hemorrhage has occurred previously. More than 80% of cerebral AVMs are located supratentorially, and the remainder within the posterior fossa. AVMs may be multiple in up to 2% of patients,263often as part of Rendu-Osler-Weber disease: an autosomal dominant inherited condition in which mucosal, skin, gastrointestinal, and cerebral hereditary hemorrhagic telangiectasias, brain cavernous angiomas, and pulmonary AVMs are also found (Fig. 8-5), and in the Wyburn-Mason syndrome (also termed mesencephalo-occulofacial angiomatosis), which is signified by the presence of cutaneous nevi and retinal angiomas together with brain A V M S . ~336 ~ ~AVMs . may also be located extracranially or intracranial AVMs may be associated with additional extracranial AVMs. Pathologically, the cerebral AVM represents a direct communication between arteries and veins without in, ~ ~ZZL~ the communicating vascular tervening c a p i l l a r i e ~ 1409 channels being larger than capillaries yet arbitrarily smaller

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than fistulas. Fistulas often reside within the AVM nidus, however. The nidus represents the central compact tangle of low-resistance vessels constituting the junction of the feeding arteries and draining veins. The nidus does not contain normal brain parenchyma, although the enlarged feeding arteries and draining veins can traverse n o d ti~sue.4~ Large, diffuse AVMs may contain normal neurons and white matter, however."" Brain AVMs may be located in the subarachnoid space, intraparenchymally, or intraventricularly or may transgress several spaces, including the cranial vault. The AVM nidus volume together with characteristics such as the presence of fistulas, the chronicity of the lesion (the age of the patient), and the rate of flow through the AVM determine the size and tortuosity of feeding arteries and draining veins. AVMs may be supplied by any of the cerebral vessels, including meningeal contributors in 15% to 50% of cases.198Approximately 10% of AVMs have an arterial feeder, nidus, or remote arterial aneurysm,1s6, 339 the flow-related aneurysms most often located on feeding vess e l ~ .148, ~ ~ . u2 Some of these flow-related aneurysms are pseudoaneurysms.u4The aneurysms contribute to the incidence of hemorrhage from A V M S . ~Varices ~ ~ can develop in draining veins and can become quite large. Areas of stenosis, thrombosis, or occlusion can occur in supplying arteries or exiting veins. The findings of vascular stenoses and aneurysm formation are attributed to local hemodynamic s t r e s s e ~ . ~ Histologic examination of cerebral AVMs demonstrate thickened walls of both variably enlarged feeding arteries and draining veins, the walls demonstrating smooth muscle hyperplasia, fibroblast infiltration, and increased connective tissue. Arteries are differentiated from veins on the basis 2329

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Y Fig. 8-5. A, Axial 12-welgntea MK image aemonstrates an AVM with venous drainage to an enlarged left thalamostriate vein (arrow). B, Axial Ceretec SPECT brain scan demonstrating diminished cerebral perfusion within the AVM (arrow).


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effect, surrounding edema, calcification (25% to 30% of cases), or adjacent brain atrophy may be identified.Is3IntraAssigned Points venous contrast enhancement is essential for identifying Nidus size the typical "bag of worms" appearance of a brain AVM as Small (6 cm) 3 for identifying and evaluating cerebral AVMs. MRI not Adjacent brain eloquence only outlines the nidus and permits evaluation of its size Noneloquent 0 but also identifies supplying arteries and draining veins. A Eloquent 1 cluster of vessels of variable signal intensities, depending Venous Drainage upon the imaging sequences used, characterize the AVM Superficial only 0 nidus. Flow-dependent phenomena such as dephasing, reDeep I phasing, slow flow, entry slice enhancement, and phase Total number of points = Grade I-V encoding mismapping may all be demonstrated (Fig. 8-6).39 Most often, the nidus vessels demonstrate signal void on spin-echo pulse sequences and bright signal intensity on gradient-echo sequences, findings that are also typical of the presence of elastic lamina and muscular layers within within enlarged feeding arteries and draining veins. Adjaarteries. Adjacent brain parenchyma may exhibit atrophy, cent brain parenchyma can be well evaluated for edema or gliosis, and demyelinizati~n~~, 220- 222 due to ischemic steal gliosis, which has bright signal intensity on TZweighted by the AVM,52 compressive mass effect, venous hypertenspin-echo studies (Fig. &7).50".287 MRI is crucial for losion, and prior hemorrhage. If previous hemorrhage has calizing the AVM in relationship to eloquent cortex or occurred, ferritin and hemosiderin staining of brain will deeper gray matter structures and significant white matter be demonstrated. Calcification may be identified within fiber tracts as well as demonstrating any mass effect. MRI component vessel walls as well as in adjacent brain parenwell demonstrates the expected evolutionary appearance of chyma because of chronic venous hypertension or hemoracute, subacute, and chronic hemorrhage. Chronic hemorrhage. Overlying leptomeninges may be thickened by verhage with resultant femtin- or hemosiderin-stained brain, nous engorgement or as a result of previous hemorrhage, including superficial or ependymal hemosider~sis,'~ 95.287 which is also denoted by hemosiderin or ferritin ~taining.~" is displayed as areas of parenchymal decreased signal inThe most commonly used AVM grading system was tensity on T2-weighted spin-echo and T2*-weighted gradiproposed by Spetzler and Martin.291This system assigns a ent-echo sequence^.^^ Gadolinium-based contrast agents are numerical grade to the AVM on the basis of the size of the of limited if any utility in the MRI evaluation of cerebral nidus, the location of the nidus in relationship to eloquent AVMs because of inconsistent enhancement and the profunctional brain, and the venous drainage (superficial or duction of excessive flow artifact. Functional MRI utilizes deep) (Table 8-2). The intent of such a grading system is cortical blood flow changes based on deoxyhemoglobin to predict therapeutic risk and outcome, and its application levels to create activation maps, which may be used to is fairly simple; the details of many AVMs are not comevaluate brain function adjacent to an AVM before therapletely explained by this classification system, however. peutic interventions are undertaken.'22. 178 In some inThe therapy of brain AVMs is based on one of the stances, the tested neurologic function is expressed in an following four options: conservative observation, surgical unexpected cerebral region secondary to neural plasticity, resection, radiosurgery, and endovascular embolization. a consequence of the congenital nature of the AVM and The various treatment options may be combined. Complete the development of alternative neural circuit^."^ surgical resection has been reported in approximately 80% MRA and CTA can help in the evaluation of cerebral of brain AVMs, with morbidity and mortality rates reaching AVMs, but these studies may be nonrevealing for AVMs approximately 10% regardless of AVM grade.'16 Radiosurthat are small or have slow flow. CTA and MRA of the gery is typically employed for brain AVMs that are 3 cm circle of Willis as well as the temtory containing the nidus or less in diameter, but it can be used for an AVMs whose must be performed so that all critical features of the AVM nidus is larger. Radiosurgery has obliterated AVMs at 3are imaged. Evaluation of the source planar images acyear follow-up in more than 80% of reported series. The quired during MRA may reveal a small AVM as bright procedure has a complication rate of less than 3%, adverse vessels differentiated from intravascular or extravascular events being most often due to radiation necrosis.79. clot, which may obscure an AVM on conventional MRI 294+295 Embolization is often performed to reduce the flow and the reconstructed 3D MRA. Both TOF and PC methods and size of brain AVMs prior to surgical resection or can be used in MRA examinations.18* MOTSA and radiosurgery, but in a few instances, complete cure can be PC MRA are better suited to diagnose AVMs with slow achieved with embolization al0ne.3~ la8 MRA is notorious for incomvletelv visualizing AVMs because of variable flow effects &d reiated artifact. CT and MRI Aneurysms are frequently unidentifiable. Both MRA and CTA have difficulty discriminating the AVM's supplying CT imaging of brain AVMs demonstrates a focal collecarteries from draining veins. The precise angioarchitecture tion of isointense to slightly hyperintense vessels on unenof cerebral AVMs is best demonstrated with traditional hanced scans but may be completely unremarkable without catheter angiography, which can identify flow-related and the administration of a contrast agent. Acute hemorrhage is well documented when present.= Occasionally, mass nidal aneurysms, the rate of AVM flow, characteristic early TABLE 8-2. Cerebral AVM Grade

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Fig. 8-6. A. Shorf ial MR i ereb~ LVM ending fi corb I ventricle. The AVM nidus is of decreased signal intensity due to rapid flow, which produces phase encoding artifact (arrow). B, Axial T2-weighted MR image demonstrates some of the AVM's draining veins (short arrows) and less uniform decreased signal intensity in smaller nidus vessels, some of which have increased signal intensity (long arrow). C, Coronal TI-weighted MR image illustrates the triangular shape of the AVM. D, Coronal TI-weighted contrast-enhanced image illustrates variable contrast enhancement of the AVM's nidus due to differential flow rates, faster flow producing less enhancement. Note the phase encoding artifact (arrow).

filling veins, all of the contributing arteries and draining veins, and arterial and, particularly, venous stenoses. The differential diagnosis of cerebral A W s is limited. Incompletely or totally thrombosed AVMs can appear similar to other masses, including vascular neoplasms such as hemangioblastoma. When a thrombosed AVM has an accompanying intraparenchymal hematoma, differentiating it from a hemorrhagic metastasis, a high-grade glioma, or a nonmalignant cause of hemorrhage, such as hypertension or amyloid angiopathy, can be difficult. Occasionally, moyamoya can mimic basilar cistern or basal ganglia AVMs. An unusual occurrence in North America, moyamoya is more commonly identified in Japan. It may manifest as intraparenchymal (60%), intraventricular (40%), or, rarely, subarachnoid hem0rrhage,3~~* 3" tran-

sient or permanent ischemic stroke, or seizures and is seen in both children and adults. The most typical age at presentation in adults is in the fourth decade. Moyamoya is characterized by progressive obliteration of large proximal anterior circulation vessels with the development of small "puff of smoke" arterial collaterals. Causes of findings similar to those of moyamoya include neurofibromatosis, sickle cell disease, prior radiation therapy, and Down syndrome. The MRI appearance of moyamoya is notable for the numerous small vessels seen within the inferior brain substance, which represent the collaterals for severely narrowed or occluded distal internal carotid or proximal anterior or middle cerebral arteries.86.'IZ Hemorrhage or infarction may also be demonstrated. MRI examination is also well suited to evaluate cerebral


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Fig. 8-7. Brain AVM with bordering reactive astrocytosis (gliosis). A, T2-weighted axial MR study demonstrating a high flow right frontoparietal AVM. Draining vein (arrow). B, More inferior T2-weighted axial section reveals enlarged right MCA and ACA branches (arrows) supplying the AVM. C, Coronal T2-weighted image illustrating the AVM's extent from cortex to ventricle. D,FLAIR image highlighting reactive astrocytosis (glinniqb hordering the AVM, seen as bright signal intensitv (arrow).


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AVMs after therapy, particularly radiosurgery or embolizat i ~ n , ' 287 ~ ~to, demonstrate decreased size and reduced Is2. 183 The use of a contrast agent is helpful for ikntdying any residual AVM nidus; however, contrast enhancement may also be secondary to postoperative gliosis, radiation necrosis, or infarction. Hemorrhage may sometimes occur as a component of radiation necrosis, which may develop as soon as 3 months after radiation therapy. Perinidal edema after radiosurgery, seen as increased signal intensity on T2-weighted spin-echo MR images, is expected and does not necessarily indicate impending radiation necrosis.

Cavernous Angioma Cavernous angiomas account for approximately 10% to 15% of all cerebral vascular malformation^,^^ and are found in approximately 0.4% of the general population.234 They are the second most common type of symptomatic vascular malformation. Cavernous angiomas typically present as focal parenchymal intracranial hemorrhages between the third and fifth decades of life. Those found in the brain occur equally in males and females. The most common location is in the cerebral hemispheres, with only 10% identified in deep gray matter or white matter tracts. Approximately 25% are found infratentonally, in equal numbers within the brain stem and cerebellum. The pons is the most common location in the brain stem. Unusual dura, epencases may arise from the leptorneninge~,"~~~~~ dyma, choroid plexus, or cranial nerves, or extradurally. In 30% to 50% of cases, cavernous angiomas are multiple. Spinal cord cavernous angiomas may be isolated or may be associated with cerebral cavernous angi~mas.~'A genetic predisposition manifests when cavernous angiomas are found in 10% to 15% of family members in addition to the index case.31. 245 When a familial tendency exists, the propensity for multiple cavernous angiomas rises to 80%.346 Multiple cavernous angiomas can be seen in Rendu-OslerWeber disease. The clinical presentation of cavernous aiAgiomas typically consists of seizure activity or of acute or progressive neurologic deficit due to cerebral h e m ~ r r h a g ebut , ~ ~in one study, only 61% of patients were symptomatic.". 55. ** 346 Seizures, the most common symptom, occur in approximately 50% of patients. Seizures are believed to be secondary to mass effect from the cavernous angioma and adjacent brain parenchymal hemosiderin or ferritin and gliosis. Symptomatic hemorrhage manifesting as headache, seizures, or acute neurologic deficit most often occurs in the second and third decades of life and has an incidence of approximately 0.5% to 1% per year.28. 2x1 Subclinical hemorrhage is not uncommon, and clinically significant hemorrhage occurs in only 10% to 13% of cases.49Hemorrhage from a cavernous angioma uncommonly extends into the ventricular system or the subarachnoid space. It is unclear whether cavernous angiomas, once having bled, have a propensity for subsequent hemorrhage. Cavernous angiomas may initially be tiny and grossly unrecognizable, then suddenly enlarge because of new hemorrhage and thrombosis. They often change over time in size, shape, and character because of intermittent and recurrent hemorrhage and thrombosis, recannulization, vascular ingrowth,

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and granulation tissue.37,2&2 When an angioma is large enough, mass effect can produce cranial nerve palsies and focal neurologic deficits. Cranial radiation therapy may cause thrombosis and hemorrhage to develop in preexistent, unrealized cavernous angiomas, making them appear as new findings on serial MRI studies. On pathologic examination, cavernous angiomas are well circumscribed and have a mulberry configuration. The lesions are not encapsulated but contain a compact or sometimes racemose network of multiple endotheliumlined, sinusoidal, nonuniform vascular channels containing thrombosed blood of varying ages.49.220 Compartment walls are irregularly thickened with collagen, hyalin, and scattered calcium deposition and contain no muscularis or elastic lamina layers. No interposed brain tissue is identified within the cavernous angioma. Adjacent brain may be calcified, laden with hemosiderin or femtin, atrophic, and gliotic. Cavernous angiomas are typically parenchymal lesions sometimes marginating a pial or ependymal surface. Capillary telangiectasias may coexist with or may be mixed with the cavernous a n g i ~ m a .210 ~ ~Venous . angiomas may also c0exist.9~~ 247, 305

CT and MRI CT scans of cavernous angiomas typically demonstrate an isodense to hyperdense focal area within the brain parenchyma that may or may not contain calcification (Fig. 8-8). They may or may not enhance after intravenous administration of an iodinated contrast agent.269Mass effect

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Fig. 8-8. CT examination without contrast of a pontine cavernous angioma demonstrating focal calcification (curved arrow) and

peripheral (short arrow) and central (long arrow) hemorrhagic degradation products.

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tion of a cavernous angioma variegated appearance convarying ages. A, T2-weighted nticular nucleuslthalaangioma. Note the pepheral hemosiderin/ferritin (long arrow) and edema located at the site of recent hemorrhage (short arrow). B, TI-weighted image without contrast. Note the subacute hemorrhage (arrow).C,TI-weighted image with contrast. Note the lack of appreciable contrast enhancement. (Case courtesy of David Watts, MD.)

and edema associated with the cavernous angioma may be present, depending on its size.'" MRI is superior to CT for the identification of cavernous a n g i ~ m a s It . ~typically ~~ demonstrates a mass characterized as popcorn in appearance owing to the varying ages of internal hemorrhages.% The margin of the cavernous angioma is of decreased signal intensity on T2*-weighted gradient-echo and T2-weighted spin-echo images if chronic hemorrhage is present.% This finding is due to the magnetic susceptibility-caused phase incoherence created by the he-

mosiderin and femtin residua from previous hemorrhage (Fig. 8-9)." The signal intensity of the rim of the cavernous angioma is also decreased because of fibrin and collagen deposition. T2*-weighted gradient-echo scans, which are best for the identification of hemosiderin and ferritin, should always be performed in the evaluation for intracranial hemorrhage. In some cases, the T2* gradient-echo study reveals multiple cavernous angiomas when the T2weighted spin-echo study illustrates only a solitary lesion. Hemosiderin and ferritin may cause a dark flaring appear-


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ance extending into the adjacent brain parenchyma because macrophages and astrocytes remove blood breakdown products, including hemosiderin and ferritin, along white matter fibers.49 Owing to MRI's exquisite sensitivity for blood degradation products, cavernous angiomas may be incidentally discovered as asymptomatic le~ions.2~~ Gadolinium-based contrast agents typically produce some enhancement of the cavernous angioma. Unusual extra-axial cavernous angiomas may have a typical or atypical MIU appearance. Extra-axial cavernous angiomas may resemble meningiomas with homogeneous, intense contrast enhancement but bright signal intensity on T2-weighted spin-echo images.14&IM. 17' Catheter cerebral angiography is indicated only to exclude a true arteriovenous malformation as the cause of intracranial hemorrhage when the diagnosis of cavernous angioma using MRI is uncertain. Catheter angiography displays cavernous angiomas as avascular masses, occasionally demonstrating very late capillary staining without When present, an associated vearteriovenous ~hunting.2~~ nous angioma may be demonstrated. Therapy for cavernous angiomas consists of medical treatment for seizure control, surgical excision when the lesion is accessible and clinically indicated, and radiosurgery. The differential diagnosis of cavernous angiomas includes previous hypertensive hemorrhage, treated toxoplasmosis, previous radiation therapy, amyloid angiopathy, and disseminated intravascular coagulopathy. The demonstration of a lesion containing hemorrhages of multiple ages, a complete peripheral hemosideridferritin ring with flaring into neighboring brain, and the lack of surrounding edema help differentiate cavernous angioma from hemorrhagic metastasis; in some instances, however, particularly with melanoma, only follow-up MRI examinations documenting typical hemorrhage evolution confirm the diagnosis of cavernous angioma.

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Capillary telangiectasias are small, usually clinically silent lesions that most commonly occur in the pons or cerebellum but can occur in other locations in the brain parenchyma. They are the second most common cerebral vascular malformation, after venous angiomas, and are usually m~ltiple."~ The histology of capillary telangiectasias is characterized by dilated, thin-walled capillaries. Unlike cavernous angiomas, normal brain parenchyma is identified within the capillary telangie~tasia."~. 220 Adjacent brain is most often normal but may contain gliosis or hemosideridferritin from previous h e m ~ r r h a g eCapillary .~~ telanpiectasias are believed to bleed rarely, however. Other types of cerebral vascular malformations can be found together with capillary telangiectasias, especially cavernous a n g i o m a ~ .Cerebral ~~ capillary telangiectasias can be found in Rendu-Osler-Weber disease, also known as hereditary hemorrhagic telangiectasias, along with telangiectasias in other visceral, mucosal, and cutaneous sites plus pulmonary and cerebral true A W s . Approximately 28% of patients with Rendu-Osler-Weber disease have cerebral AVMs, with cerebral capillary telangiectasias being less common.&167 Cerebellar capillary telangiectasias may also be a component of the ataxia-telangiectasia syndrome.

CT and MRI Capillary telangiectasias are most often not identified on unenhanced MRI studies using all available pulse sequences. Rare capillary telangiectasias that have hemorrhaged demonstrate expected MR findings of blood. Most often the hemorrhage is minor and remote, best demonstrated on T2*-weighted gradient-echo studies. Enhancement with gadolinium-based contrast agents demonstrates a lacy network of vessels constituting the capillary telangiectasia (Fig. 8-10). A coexisting cavernous angioma may

Fig. 8-10. Contrast-enhanced TI-weighted MRI examination (A) demonstrating a pontine capillary telangiectasia (arrow) that is not well visualized on the T2-weighted study (3).

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obscure identification of the capillary telangie~tasia.~ CT usually demonstrates no abnormality.

Venous Angiomas Venous angiomas are the most common cerebral vascular malformation, accounting for almost two thirds of the total and having an incidence in the general population of approximately 2%.lS69 266* 312 This vascular malformation represents a developmental variant of normal venous drainage,lS composed entirely of venous elements, and some writers prefer to call them "developmental venous anomalies," dropping the term "angioma."lM The association of venous angiomas with neuronal migration anomalies and the absence of normal venous drainage from regional brain containing the venous angioma emphasizes their embryologic origin (Fig. &ll).156.312 'Qpically solitary and located

Fig. 8-11. Venous angioma associated with a neuronal migration anomaly. A, T2-weighted MR image

demonstrates a right parietal schizencephalic cleft (short arrow) containing a venous angioma (long arrow). Bordering cortical dysplasia (curved a m w ) B, Coronal post-contrast TI-weighted MR image illustrating the venous angioma (arrow) within the schizencephaly. C,AP view of right carotid cerebral angiogram confirming the venous angioma (amw). (Case courtesy of David Watts, MD.)

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in any part of the brain parenchyma, although most often , ~ ~venous , angioin the frontal lobe, then the ~ e r e b e l l u m 318 mas range in size from small to large enough to drain an entire hemisphere.312Multiple venous angiomas are not rare, particularly when they occur bilaterally in the cerebellum?'* and their multiplicity has been described in the blue rubber bleb nevus syndrome. Venous angiomas are characterized by a medusa head of enlarged medullary veins draining to a collector vein, which continues to either the superficial or subependymal cerebral venous drainage system or a combination of these.98-312. 329 Venous angiomas are occasionally found intraventricularly. An unusual case of a venous angioma draining to the foramen of Monro and resulting in obstructive hydrocepha3'8 The brain parenchyma through lus has been rep~rted.~lz which the venous angioma passes is typically normal and shows no evidence of previous bleeding. 3189


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Some writers aeLleve mat venous angiomas mayr&eIjl cause venous infarction with or without hemorrhage, or hemorrhage alone, more often subarachnoid than parenchymall5*.l6O, 314 318, 337, 339 the hemorrhage is possibly due to acquired venous outflow restriction by stenosis or thrombosis6s. 156 secondary to hernodynamic stresses. A venous varix or ectatic component is rarely seen and is explained

Fig. 8-12. MRI examination demonstrating a venous angioma in association with a cavernous angioma. A, TZweighted image demonstrates a cavernous angioma in the anterior medial fight occipital lobe (long arrow) with a neighboring venous angioma (short arrow). B and C, TI-weighted image after contrast demonstrating the venous angioma's periphery (B, arrow) and its collector vein (C, arrow). (Case Courtesy of Robert . Weil, . MD.) - t

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by similar obstructive mechanisms or hemodynamic forces.Is6 The higher incidence of associated contiguous cavernous angiomas in as many as one third of case~,9~. 229 however, is often used to explain any clinically significant hemorrhage being derived from the cavernous angiomas (fig. 8-12).=. 170. 192,247. 312 Rarely, seizures, focal neurologic deficit, cerebellar signs, tinnitus, and headache have been


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Fig. 8-13. Contrast-enhanced CT examination demonstrating a frontal lobe venous angioma (A, arrow). Note the collector vein (arrow) illustrated in B.

ascribed to venous angi0mas,3~~ 1K"zz9*314, 318, 337, 339 depending on their location, but these clinical presentations are controversial. CT scanning of a venous angioma demonstrates a contrast-enhancing vascular structure with a thistle-shaped collection of veins coursing to a single dominant draining vein (Fig. &13).3'2. 318 Calcification of these lesions is unusual, and without calcification, they are typically not identified on unenhanced CT scans. A large venous angioma, however, may be demonstrated by CT as a slightly dense solitary vessel or collection of vessels.318 MRI best demonstrates venous angiomas and has revealed their true incidence in the general population. A venous angioma appears as a cluster of small vessels with signal void if flow within them is rapid or dephased; or the vessels may produce increased signal intensity due to slow Bow, entry slice phenomena, even-echo rephasing, or when gradient-moment nulling techniques are utilized. Spatial ®istration artifact occurs in venous angiomas when gradient-moment nulling techniques are used on T2weighted spin-echo images.lS4T2*-weighted gradient-echo (techniques or TOF or PC MRA can demonstrate venous mgiomas as a bright grouping of veins if the flow is fast enough or if MRA techniques crafted to take advantage of )slow flow, such as thin-slice, 2D TOF, oriented perpendicular to venous inflow are employed (Fig. &14).U9 MRA is typically not necessary to image venous angiomas, however. The rate of blood flow within the venous ~angiomausually depends on its overall size and determines ,its signal intensity on Iv~RP'~ together with its orientation to the plane of acquisition. Contrast-enhanced TI-weighted spin-echo or gradient-echo MRI sequences best demonstrate venous angiomas and their relationship to adjacent

brain parenchyma.229.337. 339 Contrast-enhanced CT or MRI may reveal a focal parenchymal stain around the venous angioma's caput medusa. Frequently, venous angiomas are imaged on MRI as incidental findings because most are clinically silent. They also can be overlooked on MRI scans if small and similar to normal venous drainage. Venous angiomas should be differentiated from aberrant venous drainage on the basis of the classic findings of a cluster of enlarged medullary veins continuing into a larger collector vein in venous angiomas, anomalous veins lacking more than one or two visualized upstream small veins. The MRI appearance of venous angiomas is so characteristic that catheter cerebral angiography should not be performed in their evaluation. It should be noted that small venous angiomas can be overlooked on catheter cerebral angiography, being thought another example of variant venous drainage, although characteristically they appear later and persist longer than normal veins.229

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Sinus Pericranii

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Sinus pericranii is a soft, compressible venous malformation that by definition lies adjacent to the skull and communicates with the intracranial dural sinuses, most 260 Its etiology is most often by enlarged emissary ~eins.3~. likely congenital, although it has been reported to occur spontaneously or after trauma.35.260 Sinus pericranii may be associated with other vascular malformations, such as cavernous angiomas and venous angiomas, or may be seen as a component of the blue rubber bleb nevus synd r ~ m e .260 ~~.


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Sinus pericranii most commonly occurs in the frontal scalp near the midline.35.260 An asymptomatic cosmetic scalp lump is found typically in a patient younger than 30 years. The lesion is twice as common in men as in women and is remarkable for its enlargement with Valsalva maneuver~.~~ On imaging, sinus pericranii has been described as a vascular soft tissue scalp mass that is slightly hyperdense on unnenhanced CT,demonstrates flow on MRI, and enhances strongly with use of a contrast agent on both CT and MRI.3S.260 CT best identifies associated osteolytic changes from the vascular mass and its associated diploic veins.35,2a'

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Fig. 8-14. MR venography examination demonstrating typical characteristics of a venous angioma. A, Slightly oblique lateral and B, is a posterior coronal view of a left frontal venous angioma (arrows) demonstrated on MR

venography. Lateral view of venous phase during carotid angiography confirms the venous angioma (arrow).

Arteriovenous Fistulas Terminology

Arteriovenous fistulas (AVFs) are us~ally'acquired~~ but may be congenital in some instances. Congenital fistulas most often represent an anomaly of cerebral vascular development and are part of a spectrum of cerebral vascular disorders. Single or multiple arterial venous connections or a true AVM nidus with one or more associated arterial venous fistulae illustrates the variety of pathologic presentations (Fig. 8-15). AVFs may be located intracranially or extracranially within the scalp or facial structures. The arterial venous shunting with increased venous pressure

304

RoshanKetab Medical Publishers Part II I Brain and Meninges

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Fig. 8-15, Congenital single arteriovenous fistula between a right middle cerebral artery branch and an adjacent cortical vein documented on MRI.A demonstrates an enlarged right middle cerebral artery (arrow) while B illustrates the enlarged angular artery (short arrows) and proximal draining vein (long arrow) on these T2-weighted images. C is the APlTownes view of the right carotid injection confirming the fistula.

and flow within any of the AVFs can result in variably sized varices that, when large enough, can produce mass effect such as brain parenchymal or cranial nerve compression or obstructive hydrocephalus.65. 120. 121.157. 179.319.320 Most dural arterial venous fistulae are spontaneous and are believed to be acquired after thrombosis of the draining dural sinus with the subsequent development of multiple fistulous shunts to the involved sinus.'21.133 Chronic venous hypertension without dural sinus thrombosis has also been postulated.307Other causes of dural AVFs are trauma, surgery, infection, systemic hypertension, and hypercoagulable

states, including pregnancy, contraception pills, and dehydration.". lZ0. I2l. 179 Another type of acquired AVF is best illustrated by the post-traumatic direct carotid cavernous fistula. Dural AVFs are characterized pathologically by abnormal, direct communications between normal sinus wall arteries and veins.211Hemodynamic stresses lead to pathologic disorganization and thickening (less commonly, thinning) of the walls of supplying arteries, draining cortical and medullary veins, and the dural sinus wall at the site of the fistula as well as thrombosis, stenosis, and occlusion of


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the involved vascular elements, most commonly the dural sinus itself and least commonly the feeding arteries.I2'. '79, 211 Angiogenesis factors are probably involved in the propagation of dural AVFs.lm Dural AVFs represent approximately 10% to 15% of intracranial vascular malformationsq5.lZ0*'90- 320 and are more common in women than men.320Most often, the dural AVF involves a single sinus, sometimes with involvement of contiguous sinuses. Multiple disparate dural AVFs are rare45 and are typically in close proximity,'79 even the bilateral dural carotid cavernous fistulas possibly related by the interconnecting circular sinus and clival veins. '79; however, Dural AVFs may spontaneously ~bliterate'~. closure of such a lesion may be associated with intracranial hemorrhage.'" Approximately 15% of patients present with intraparenchymal, subarachnoid, or subdural hemorrhage, lZ0. Is7 Significant listed in decreasing order of frequen~y.4~3 in the production of intracranial hemorrhage is reversal of flow within the involved dural sinus into variably dilated cortical veins, which results in venous rupture or venous Is7. u8The hypertension in the involved cerebral territ~ry.'~, risk of hemorrhage from a dural AVF is 1.8% per year, with a 20% mortality for each hemorrhage." Risk factors for producing hemorrhage include AVF location in the anterior cranial fossa (ethmoidal), superior petrosal sinus, or deep veins, leptomeningeal venous drainage, draining 3m vein stenosis, and a venous varix.". 'lo. Dural AVFs have been categorized on the basis of their venous drainage pattern (Table 8-3).55a Over time, dural AVFs may change and so be assigned to a different type.lm Symptomatology and risk of hemorrhage roughly correspond to more abnormal venous drainage.179 Dural AVFs may also cause seizures or neurologic deficits owing to venous hypertension-caused hemorrhage or ischernia/infarction or, less commonly, to arterial steal.". l 2 l , lS7. 304. 3m Pulsatile tinnitus and headache, the most 320 may be mild enough and of such common complaint~,4~. chronicity that the patient does not seek medical attention until other symptoms develop, such as cranial nerve palsies due to arterial steal or abnormal venous drainage and congestion.1s7Dural AVFs most often become symptomatic in patients between 40 and 60 years of age.u5 Communicating hydrocephalus may be the result of the dural AVF producing dural sinus hypertension, dural sinus thrombosis, or prior subarachnoid hemorrhage.lS7Increased intracranial pressure without communicating hydrocephalus 179s

3153

TABLE 8-3. Classification of Dural AVFs TspeI Antegrade drainage into sinus Type 11 II a Antegrade and retrograde drainage into sinus IIb Antegrade drainage into sinus and retrograde drainage into cortical veins II a & b Antegrade drainage into sinus and retrograde drainage into sinus and cortical veins Type Retrograde drainage into cortical veins

Type n '

Retrograde drainage into cortical veins with venous ectasia

Tppev

Drainage into s~inalveins

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may be due to cerebral venous congestion, increased cerebral blood volume, elevated intrasinus pressure, and impaired cerebral venous drainage.I2'. 320 Arterial supply to dural AVFs is from meningeal branches of the external carotid artery (e.g., the middle meningeal, ascending pharyngeal, and occipital arteries), the internal carotid artery (e.g., the tentorial artery of the meningohypophyseal trunk), and the vertebral artery (e.g., the posterior meningeal artery).". 226 Pial arteries derived from the carotid or vertebrobasilar system can also supply dural arteriovenous fistulae. In one third to two thirds of cases, dural AVFs involve The cavernous sinus the sigmoid and transverse sin~ses.4~." is the second most common location, accounting for 12% to 20% of AVFs and being most common in middle-aged w0men.4~365 The symptoms of cavernous sinus dural AVFs include palsies of cranial nerves 111, IV, and VI, which produce diplopia, proptosis, conjunctival engorgement, retro-orbital or cranial nerve V pain, increased intraocular pressure and secondary glaucoma; all of these are due to the abnormal venous hypertension within the cavernous sinus and retrograde venous drainage into the involved 147. 306 More ominous consequences are papilledema, choroidal or retinal detachment, central retinal vein thrombosis, and diminished visual acuity.'79 Other sites of dural AVF are the tentorium and its incisura, the superior and inferior petrosal sinuses, the occipital and marginal sinuses, the superior and inferior sagittal sinuses, the straight sinus, the vein of Galen, and the anterior and middle cranial fossae.d5- Adjacent cortical veins may also incorporate AVFs within their ~ a l 1 s . l ~ ~ Unenhanced CT scans of dural AVFs are normal unless intracranial hemorrhage, edema or infarction from venous hypertension, or thrombosis of a dural sinus or draining vein is identified. Contrast-enhanced scans may occasionally demonstrate enlarged cortical or medullary veins or stenotic or enlarged dural sinuses (Fig. 8-16). These findings are noted in up to half of patients with dural carotid cavernous fistulas, with expansion of the involved cavernous sinus and increased size of the draining superior ophthalmic vein. MRI demonstration of cerebral AVFs depends on the type of fistula encountered. With congenital direct AVF, MRI demonstrates an enlarged supplying artery that communicates directly within an enlarged draining vein (see Fig. 8-15). In a post-traumatic direct carotid cavernous fistula, MRI shows enlargement of the cavernous sinus containing diminished signal intensity due to excessive blood flow within the sinus, and dilated superior and inferior ophthalmic veins as well as other smaller orbital veins with accompanying orbital proptosis and extraocular muscle enlargement. Dural carotid cavernous fistulas oftea show similar but less dramatic findings.lq7Either type of carotid cavernous fistula may produce bilateral cavernous sinus and orbital findings on MRI because of intersinus midline venous communications. The MRI findings with dural AVFs are more subtle if the more easily appreciated findings of intracranial hemorrhage, edema, or infarction are not present. MRI and MRA are notorious for missing uncomplicated dural AVF unless the venous drainage into enlarged cortical or medullary veins is demon~trated.~~ In such instances,


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Fig. 8-16. Contrastenhanced

examination of a congenital superior sagittal sinus dural amrial venous fistula demonstrating (A) an enlarged superior sagittal sinus ( a m w ) and subcortical calcifications (small a r m s ) and (B) an enlarged torcula (long m w ) , right transverse sinus and tentorial veins (open m w ) , and deep perksencephalic veins (small arrows).Note also the subcortical and lenticular nuclei calcifications (small curved arrows). C, Lateral left external carotid angiogram illustrates Ieft middle meningeal branches (arrows) and left occipital branches (curved arrow) supplying the amgenital superior sagittal sinus dural arteriovenous fistula (long arrows). Note the fenestration of the superior sagittal sinus (open arrow).

venous varices may also be identified. Although MRI can be used to document an occluded or stenosed dural sinus or vein,268the evaluation can be problematic because of typically encountered variable venous signal intensity, caused by flowing blood within dural sinuses on various spin-echo pulse sequences, and the changing appearance of clot depending on its age. Other difficulties with MRI are the small caliber of the feeding arteries in dural arteriovenous malformations and the focal or diffuse rather that masslike site of the abnormal dural shunts, which are often

located next to flowing blood and near cortical bone making their distinction difficult. MR venography can be used to define patent, occluded, or stenotic dural sinuses. Catheter cerebral angiography is always necessary for full evaluation of the angioarchitecture of cerebral AVFs.

Vein of Galen Malformations The vein of Galen malformation is a congenital anomaly in which AVFs supply the embryologic precursor to the


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vein of Gale&. Some writers have divided vein of Galen malformations ht~ types, choroidal and mural. The choroidal type (Type I), which is more common, consists of one or more anterior and postedor choroidal, distal peiicallosal, tlxdmoperEorating, and s o r m h e s superior cerebellar arteries h t e d to the darsal vein of the prosencephalon, whicb continues into the median prosencephalic vein. With this type, the p o s e o r choroidal vessels are typically the domhant supply: The mural type (Qpe II) of malformation consists af mllicular and posterior chomidal arteries s u p p l tbe ~ wall of the median prosencephalic win, although a d d i f i d mteries, such as the thalam~perferators, may be contributors. These features distinguish the ve&. & Gale9 malformation fiom congenital parenchymal AWs, acquired dural AVFs, and vein of Galen or s ~ P . *noses, ~ s which feature a dilated vein of Galen. Tkii primitive. median prosencephalic vein, the precursor af the win of Men, is usually a b n o d y dated in vein of Gala malfomtions. Nonnal deep veins b i n not into the median prosencephalic vein but through

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alternate routes, because the true vein of Galen is absent. The persistent median prosencephalic vein drains to a falcine sinus rather than the straight sinus, and the straight sinus is often absent. Venbus outflow restriction is common in the vein of Galen malformation and contributes to further dilatation of the median prosencephalic vein, also commonly refmed to as a dilated vein of Galen. Other venous anomalies are often associated with the vein of Galen malformation, including absence of or hypoplastic sigmoid or jugular sinuses, duplicated sinuses, and persistent marginal or occipital sinuses.a9 Venous-to-arterial shunting through a patent formen ovde or persistent ductus arteriosus may coexisL5~ 191a The venous drainage of the enlwgd median prosencephalic vein or vein of Galen typically demonstrates a dilated venous varix continuing into an accessory or inferior falcine sinus. If the venous outjlow stenosis is severe enough, some Vein of Galen malformations have been documented to proceed to thrombosis which may lead to spontaneous cure but also can result in acute hydrocepha-

Fig. 8-17. CT examination of a vein of Galen malformation before (A) and after (B) contrast. B, C, D, Note the enlarged primitive median prosencephalic vein (short arrow) continuing to the falcine sinus (long arrow). Both structure are dense without contrast in an infant. C and D illustrate numerous enlarged arteries supplying this choroidal type of vein of Galen malformation.


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lus, intracranial hemorrhage, or central venous hypertension. The extent of high-flow shunting and the amount of venous outflow restriction in a vein of Galen malformation determine the age of the patient at presentation. Patients with high-flow multiple fistulas and no venous outflow stenosis (usually type I) are often identified at birth with high-output congestive heart failure, intracranial bruit, macrocephaly, and hydrocephalus. If the vein of Galen shunt is severe enough, the infants can demonstrate metabolic lactic acidosis due to multiorgan hypoperfusion and quickly progress to death. Patients who have decreased flow through the a vein of Galen malformation, typically those with high-grade venous outflow restriction (usually type II), may present later in childhood, even as adults. In such patients, cardiomegaly may be asymptomatic, and developmental delay and ocular symptoms are more common. Seizures, enlarging head circumference, intracranial hemorrhage that may be parenchymal, subarachnoid, or intraventricular, focal neurologic deficit, pulsatile tinnitus, and cranial bruit can be seen in any patient with a vein of Galen malformation, although hemorrhage is rare and is usually seen only with venous drainage thrombosis.

CT and MRI CT scans clearly demonstrate the enlarged primitive median prosencephalic vein, which appears as a mass in the tentorial incisura of slightly increased density on unenhanced scans and markedly enhances with use of an iodin-

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ated contrast agent (Fig. 8-17). Intravenous contrast administration also may demonstrate the feeding arteries as well as the disproportionate outflow restriction, which is often characterized by diffuse or focal narrowing of the falcine sinus or, less commonly, of the straight sinus. Unenhanced CT scanning is valuable for identifying brain parenchymal calcifications located in the hemispheric venous watershed zones owing to chronic deep venous hypertension. MRI provides a 3D display of the vein of Galen malformation, documenting the dilated primitive median prosencephalic vein, the falcine sinus, and the abnormal arterial supply (Fig. 8-18). Flow-related artifacts are related to the size of and rate of flow through the vein of Galen malformation. MRA can also display the malformation. MRI, CT, and ultrasonography can demonstrate brain parenchymal encephalomalacia, atrophy, hemorrhage, thrombosis, and ischemic changes. Each modality's efficacy depends on the patient's age at presentation and the corresponding degree of brain myelination or, in the case of ultrasonography, the size of the skull fontanels. Each imaging technique also accurately depicts hydrocephalus. The enlargement of the ventricular system is due to venous hypertension and impedance of CSF resorption (communicating hydrocephalus) or, less commonly, to obstruction of the aqueduct of Sylvius by the enlarged vein of Galen (obstructive hydrocephalus). In utero, hydrocephalus may produce cerebral developmental dysplasia. Transcranial ultrasound examination in the fetus or neonate is often used to provide the initial diagnosis of vein of Galen malformations. Catheter cerebral angiography is

Fig. 8-18. Short TE, long TR axial MRI of a vein of Galen malformation. Note the enlarged vein of Galen (primitive median prosencephalic vein) (long arrow) producing flow artifact (short arrows). B, Sagittal TI-weighted MRI illustrates the vein of Galen malformation including the enlarged vein of Galen (primitive median prosencephalic vein) (straight arrow) and a low falcine vein (curved arrow). (Case courtesy of Michelle Smith, MD.)



necessary to define the angioarchitecture of the malfomations and to correctly categorize it. Vein of Galen malformations are typically treated with endovascular or combined operative transtorcular and endovascular methods.

References

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1. Aalmaani WS, Richardson AE: Multiple intracranial aneurysms: Identifying the ruptured lesion. Surg Neurol 9:303-305, 1978. 2. Aesch R, Lioret E, de Toffol B, Jan M: Multiple cerebral angiomas and Rendu-Osler-Weber disease: Case report. Neurosurgery 29:599602, 1991. 3. Anderson CM, Saloner D, Tsuruda JS, et al: Artifacts in maximum intensity projection display of MR angiograms. AJR Am J Roentgenol 154:623429, 1990. 4. Anderson EB, Petersen J, Mortensen EL, Udesen H: Conservatively treated patients with cerebral arteriovenous malformation: Mental and physical outcome. J Neurol Neurosurg Psychiatry 5 1:12081212, 1988. 5. Andoh T, Shirakami S, Nakashima T, et al: Clinical analysis of a series of vertebral aneurysm cases. Neurosurgery 31:987-993, 1992. 6. Anson J, Cromwell RM: Craniocervical arterial dissection. Neurosurgery 29:89-96, 1991. 7. Anzalone N, Triulzi F, Scotti G: Acute subarachnoid hemorrhage: 3D time-of-flight MR angiography versus intra-arterial digital angiography. Neuroradiology 37:257-261, 1995. 8. Aoki S, Sasaki Y, Machida T, et ak Cerebral aneurysms: Detection and delineation using 3-D-CT angiography. AJNR Am J Neuroradiol 13:1115-1120, 1992. 9. Arabi B: Traumatic aneurysms of brain due to high velocity missile head wounds. Neurosurgery 22: 1056-1063, 1988. 10. Armstrong K: Presented at the 29th Annual Scientific Meeting of the American Society of Neuroradiology, Washington, DC, May 1991. 11. Atkinson JLD, Sundt TM Jr, Houser OW, et ak Angiographic frequency of anterior circulation intracranial aneurysms. J Neurosurg 70:551-555, 1989. 12. Atlas SW, Fram EK, Mark AS, Grossman RI: Vascular intracranial lesions. Applications of fast scanning. Radiology 169:455-461, 1988. 13. Atlas SW, Grossman RI, Goldberg HI, et al: Partially thrombosed giant intracranial aneurysms: Correlation of MR and pathologic findings Radiology 162:ll 1-114, 1987. 14. Atlas SW, Grossman RI, Gomod JM, et al: Hemorrhagic intracranial malignant neoplasms: Spin-echo MR imaging. Radiology 1647177, 1987. 15. Atlas SW, Listerud J, Chung W, Flamm E: Intracranial aneurysms: Depiction on MR angiograms with a multi-feature extraction postprocessing algorithm. Radiology 192:129-139, 1994. 16. Atlas SW: Inmacranial vascular malformations and aneurysms: Current imaging applications. Radio1 Clin North Am 262321437, 1988. 17. Atlas SW: MR angiography in neurological disease: State of the art. Radiology 193:l-16, 1994. 18. Atlas SW: Imaging vascular intracranial disease: Current status. Curr Opin Rddiol 2: 18-25, 1990. 19. Atlas SW: MR imaging is highly sensitive to acute subarachnoid hemorrhage. . . not! Radiology 186:319, 1993. 20. Atlas S (ed): Intracranial Vascular Malformations and Aneurysms: Magnetlc Resonance Imaging of the Brain and Spine, 2nd ed. Philadelphia, Lippincott-Raven, 1996. m a . Auger RG, Wiebers DO: Management of umptured intracranial arteriovenous malformations: A decision analysis. Neurosurgery 30: 561-569, 1992. 21. Augustyn G, Scott J, Olson E, et ak Cerebral venous angiomas: MR imaging. Radiology 156:391-395, 1985. 22. Awad I. Little J: Dural arteriovenous malformations. In Barrow D ( 4 ) : htracranial Vascular Malformations. Park Ridge, Ill, AANS, 1990, pp 219-226, 23. Awad I, Robinson J, Mohanty S, Estes M: Mixed vascular malformations of the brain: Clinical and pathogenetic considerations. Neurosurgery 33:17%188, 1993. 24. Axel L Blood flow effects in magnetic resonance imaging. AJR Am J Roentgenol 143: 1157-1 166, 1984.

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50. Burger PC, Schuthaver BW, Vogel FS: Surgical Pathology of the Nervous System and its Coverings, 3rd ed. New York, Churchill Livingstone, 1991, pp 439, 443.


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Brain and Meninges

254. Rosenorn J, Eskesen V, Madsen F, Schmidt K: Importance of cerebral pan-angiography for detection of multiple aneurysms in patients with aneurysmal subarachnoid haemorrhage. Acta Neurol Scand 87: 215-218, 1993. 255. Rosenorn J, Eskesen V, Schmidt K: Unruptured intracranial aneurysms: An assessment of the annual risk of rupture based on epidemiological and clinical data. Br J N e m u r g 2:369-378, 1988. 256. Ross JS, Masaryk TJ, Modic MT, et al: Intracranial aneurysms: Evaluation by MR angiography. AJNR Am J Neuroradiol 11:449456, 1990. 257. Ruggieri PM: Presented at the 78th Annual Scientific Assembly of the Radiological Society of North America, Chicago, Nov 29-Dee 4, 1992. 258. Russell DS, Rubinstein LJ: Pathology of Tumors of the Nervous System, 5th ed. Baltimore, Williams & Willcins, 1989. 259. Sadato N, Numaguchi T, Rigamonti D, et al: Bleeding patterns in ruptured posterior fossa aneurysms: a CT study. J Comp Asst Tomogr 15:612-617, 1991. 260. Sadler LR, Tam RW, Jungreis CA, Sekhar L: Sinus pericranii: CT and MR findings. J Comp Asst Tomogr 14:124-127, 1990. 261. Sahs AL, Perret GE, Locksley HB, et al: Intracranial Aneurysms and Subarachnoid Hemomhage: A Cooperative Study. Philadelphia, JB Lippincott, 1969. 262. Sakaki T, Tominaga M, Miyamoto K, et al: Clinical studies of de novo aneurysms. Neurosurgery 32512-517, 1993. 263. Salcman M, Scholtz H, Numaguchi Y: Multiple intracerebral arteriovenous malformations: Report of three cases and review of the literature. Surg Neurol 38:121-128, 1992. 264. Sanders WP, Sorek PA, Mehta BA: Fenestration of intracranial arteries with special attention to associated aneurysms and other anomalies. AJNR Am J Neuroradiol 14675680, 1993. 265. San-Galli F, Leman C, Kein P, et al: Cerebral arterial fenestrations associated with intracranial saccular aneurysms. Neurosurgery 30: 279-283, 1992. 266. Sarwar M, McCormick W Intracerebral venous angioma: Case report and review. Arch Neurol35:323-325, 1978. 267. Saveland H, Hillman J, Brandt L, et al: Overall outcome in aneurysmal subarachnoid hemorrhage. J Neurosurg 76:729-734, 1992. 268. Savino PJ, Grossman RI, Schatz NJ, et al: High-field magnetic resonance imaging in the diagnosis of cavernous sinus thrombosis. Arch Neurol43:1081-1082, 1986. 269. Savoiardo M, Strada L, Passerini A: Intracranial cavernous hemangio m : Neuroradiologic review of 36 operated cases. AJNR Am J Neuroradiol4945-950, 1983. 270. Scazzeri F, Prosetti D, Nenci R, et al: Angioma venoso. Riv di Neu~nadiol4201-208, 1991. 271. Schievink WI, Limburg M, Dreissen J Jr, et al: Screening for unruptured familiar aneurysms: Subarachnoid hemorrhage 2 years after angiography negative for aneurysms. Neurosurg 29:434438, 1991. 272. Schievink WI, Mokri B, Piepgras DG: Angiographic frequency of saccular intracranial aneurysms in patients with spontaneous cervical arterial dissection. J Neurosurg 76:6246, 1992. 273. Schievink WI, Piepgras DG, Wirth FP: Rupture of previously documented small asymptomatic saccular intracranial aneurysms. J Neurosurg 76: 1019-1024. 1992. 274. Schmid UD, Steiger HJ, Huber P: Accuracy of high resolution computed tomography in direct diagnosis of cerebral aneurysms. Neuroradiology 29: 152-159, 1987. 275. Schuierer G, Huk WJ, Laub G: Magnetic resonance angiography of intracranial aneurysms. Neuroradiology 35:5&54, 1992. 276. Scott RM,Barnes P, Kupsky W, Adelman LS:Cavernous angiomas of the central nervous system in children. J Neurosurg 76:38-46, 1992. 277. Scotti G, Ethier R, Melancon D, et ak Computed tomography in the evaluation of intracranial aneurysms and subarachnoid hemorrhage. Radiology 123:85-90, 1977. 278. S e i d e n w D, Berenstein A, Hyman A, Kowalsla H: Vein of Galen malformation: Correlation of clinical presentation, arteriography, and MR imaging. AJNR Am J Neuroradiol 12347-345, 1991. 279. Seidenwurm D, Berenstein A: Vein of Galen malformation: Clinical relevance of angiographic classification, and utility of MRI in treatment planning. Neuroradiology 33(Suppl): 153-155, 1991. 280. Senegor M: Traumatic pericallosal aneurysm in a patient with no major trauma. J Neurosurg 75:475-477, 1991.

281. Sharma A Tyagi G, Sahai A, Baijal SS: Traumatic aneurysm of superficial temporal artery: CT demonstration. Neuroradiol 33:510512, 1991. 282. Sheny RG, Walker ML, Olds MY Sinus pericranil and venous angioma in the blue-rubber bleb nevus syndrome. AJNR Am J Neuroradiol 5:832-834, 1984. 283. Shi YQ, Chen XC: A proposed scheme for grading intracranial arteriovenous malformations. J Neurosurg 65:484-489. 1986. 284. Sigal R, Krief 0, Houtteville JP, et al: Occult cerebrovascular malformations: Follow-up with MR imaging. Radiology 176:815819, 1990. 285. Simard JM,Garcia-Bengochea F, Ballinger WET, et al: Cavernous angioma: A review of 126 collected and 12 new clinical cases. Neurosurgery 18:162-172, 1986. 286. Sisti MD, Kader A, Stein BM: Microsurgery for 67 intracranial arteriovenous malformations less than 3 cm in diameter. J Neurosurg 79:653460, 1993. 287. Smith HJ, Strother CM, Kikuchi Y, et al: MR imaging in the management of supratentorial intracranial AVMs. AJNR Am J Neuroradiol 9:225-235, 1988. 288. Solomon RA, Fink ME, Pie-Spellman J: Surgical management of unruptured intracranial aneurysms. J Neurosurg 80:440446, 1994. 289. Sorek PA, Silbergleit R: Multiple asymptomatic cervical cephalic aneurysms. AJNR Am J Neuroradiol 1 4 31-33, 1993. 290. Spetzler RF, Hargraves RW, McCormick PW, et ak Relationship of perfusion pressure and size to risk of hemorrhage from arteriovenous malformation. J Neurosurg 76:918-923, 1992. 291. Spetzler RE Martin NA: A proposed scheme for grading intracranial arteriovenous malformations. J Neurosurg 65:476483, 1986. 292. Spetzler RF,Wilson CB, Weinstein P, et al: Normal perfusion pressure breakthrough theory. Clin Neurosurg 25:651472, 1978. 293. Stehbens WE: Etiology of intracranial berry aneurysms. J Neurosurg 70:823-831, 1989. 294. Steiner L, Lindquist C, Adler JR, et al: Clinical outcome of radiosurgery for cerebral arteriovenous malformations. J Neurosurg 77:1-8, 1992. 295. Steiner L: Radiosurgery in cerebral arteriovenous malformations. In Flamm E (ed): Cerebrovascular Surgery. New York, SpringerVerlag, 1986. 296. Steinmeier R, Schramm J, Muller H, Fahlbush R: Evaluation of prognostic factors in cerebral arteriovenous malformations. Neurosurgery 24: 193-200, 1989. 297. Stone JL, Crowell RM, Gandhi YN, Jafar JJ: Multiple intracranial aneurysms: Magnetic resonance imaging for determination of the site of rupture. Neurosurgery 23:97-100, 1988. 298. Strother CM, Graves VB, Rappe A: Aneurysm hemodynamics: An experimental study. AJNR Am J Neuroradiol 13: 1089-1095, 1992. 299. Sugita K, Kobayashi S, Takemae T, et al: Giant aneurysm of the vertebral artery. J Neurosurg 68:96&966, 1988. 300. Suzuki J, Kodama N: Moyamoya disease: A review. Stroke 14: 104-109, 1983. 301. Suzuki S, Kayama T, Sakurai Y,et al: Subarachnoid hemorrhage of unknown origin. Neurosurg 21:3 10-3 13, 1987. 302. Symon L: Surgical experiences with giant intracranial aneurysms. Acta Neurochir (Wien) 118:53-58, 1992. 303. Szabo M, Crosby G, Sundaram P, et al: Hypertension does not cause spontaneous hemorrhage of intracranial arteriovenous malformations. Anesthesiology 70:761-763, 1989. 304. Takahashi S, Tomura N, Watarai J, Mizoi K, Manabe H: Dural arteriovenous fistula of the cavernous sinus with venous congestion of the brain stem: report of two cases, AJNR Am J Neuroradiol 20: 886-888, 1999. 305. Takamiya Y, Takayama H, Kobayashi K, et al: Familial occurrence of multiple vascular malformations of the brain. Neurol Med Chir (Tokyo) 24271-277, 1984. 306. Taniguchi RM, Goree JA, Odom GL: Spontaneouscarottd cavemous shunts presenting diagnostic problems. J Neurosurg 35:384-391, 1971. -- 307. Terada T, Hgashida R, Halbach W, et al: Development of acquired arteriovenous fistulas in rats due to venous hypertension. J Neurosurg 80:884-889, 1994. 308. Tien RD, Wilkins RH: MRA delineation of the vertebrovascular system in patients with hemifacial spasm and trigemioal neuralgia, AJNR Am J Neuroradiol 1434-36, 1993. 309. Toffol GJ, Gruener G, Naheedy MH:Early-filling cerebral veins. J Am Osteopath Assoc 88: 1007-1009, 1988.


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310. Tomlinson FH, Howser OW, Scheithauer BW, et al: Cavernous angioma: Angiographically occult vascular malformations: A correlative MR imaging and histological study. J Neurosurg 78:328, 1993. 311. Toro VE, Fravel JF, Weidman TA: Posttraumatic pseudoaneurysm of the posterior meningeal artery associated with intraventricular hemorrhage. AJNR Am J Neuroradiol 14:264-266, 1993. 312. Truwit CL: Venous angioma of the brain: History, sigmficance and imaging findings. AJR Am J Roentgen01 159:1299-1307, 1992. 313. Tsuruda J, Saloner D, Norman D: Artifacts associated with MR neuroangiography. AJNR Am J Neuroradiol 13:1411-1422, 1992. 314. Uchino A, Imador H, Ohno M: Magnetic resonance imaging of intracranial venous angioma. Clin Imaging 14:309-314, 1990. 315. Uchino A, Kato A, Kuroda Set al: Pontine venous congestion caused by dural carotid-cavernous fistula: Report of two cases. Eur Radiol 7:405408, 1997. 315a. Unruptured intracranial aneurysms-Risk of rupture and risks of surgical intervention. N Engl J Med 3391725-1733, 1998. 316. Vajda J: Multiple intracranial aneurysms: A high-risk condition. Acta Neurochir (Wien) 118:59-75, 1992. 317. Valavanis A, Schubiger 0,Wichrnann W: Classification of brain arteriovenous malformation nidus by magnetic resonance imaging. Acta Radiol Suppl 369:86-89, 1986. 318. Valavanis A, Wellauer J, Yasargil MG: The radiological diagnosis of cerebral venous angioma: Cerebral angiography and computed tomography. Neuroradiology 24: 193-199, 1983. 319. Vmuela F, Drake CG, Fox AJ, Pelz DM: Giant intracranial varices secondary to high-flow arteriovenous fistulae. J Neurosurg 66:19&203, 1987. 320. Vinuela F, Fox AJ,Pelz DM, Drake CG: Unusual clinical manifestations of dural arteriovenous malformations. J Neurosurg 64554558, 1986. 321. von Schulthess GK, Higgins CB: Blood flow imaging with MR: Spin-phase phenomena. Radiology 157:687-695, 1985. 322. Waltimo 0: The relationship of size, density and localization of intraccanial arteriovenous malformations to the type of the initial symptom. J Neurol Sci 19:13-19, 1973. 323. Wascher TM, Golfinos J, Zabramski JM, Spetzler RF: Management of uruuptured intracranial aneurysms. BNI Q 8:2-7, 1992. 324. Wedeen VJ, Rosen BR, Chesler D, Brady TH.MR velocity imaging by phase display. J Comput Assist Tomogr 9:530-536, 1985. 325. Wehrli FW, Shimakawa A, Gullberg GT, MacFall JR: Time-offight MR flow imaging: Selective saturation recovery with gradient refocusing. Radiology 160:781-785, 1986. 326. Weibers DO, Whisnant JP, Sundt T, et al: The significance of unruptured intracranial aneurysms. J Neurosurg 66:23-29, 1987. 327. Weir B: Pituitary tumors and aneurysms: Case report and review of the literature. Neurosurgery 30:585-591, 1992. 328. Weir BKA: Intracranial aneurysms. Curr Opin Neurol Neurosurg 3: 55-62, 1990. 329. Wending LR, Moore JS Jr, Kieffer SA, et al: Intracerebral venous angioma. Radiology 119:141-147, 1976. 330. Westra SJ, Curran JG, Duckwiler GR, a ak Pediatric intracranial

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vascular malformations: Evaluation of treatment results with color doppler US. Radiology 186:775-783, 1993. 331. Wiebers DO, Torner JC, Meissner I: Impact of unruptured intracranial aneurysms on public health in the United States. Stroke 23: 1416-1419, 1992. 332. Wilkins RH,Rengachary SS: Vascular malformations. In N e m u r gery. New York, McGraw-Hill, 1985, pp 1448-1473. 333. W~llinskyR, TerBrugge K, Montanera W, et al: Microarteriovenous malformations of thi brain: Superselective angiography in diagnosis and treatment. AJNR Am J Neuroradiol 13:325-330, 1992. 334. Willinsky R, TerBrugge K, Montanera W, et ak Venous congestion: an MR finding in dural arteriovenous malformations with cortical venous drainage. AJNR Am J Neuroradiol 15:1501-1507, 1994. 335. Willinsky RA, Fitzgerald M, TerBrugge K, et ak Delayed angiography in the investigation of intracranial intracerebral hematomas caused by small arteriovenous malformations. Neuroradiology 35: 307-311, 1993. 336. Willinsky RA, Lasjaunias P, TerBrugge K, Burrows WP: Multiple cerebral arteriovenous malformations (AVMs): Review of our e x p s rience from 203 patients with cerebral vascular lesions. Neuroradiology 32207-210, 1990. 337. W i G, Demaerel P, Marchi G, et ak Gadolinium-enhanced MR imaging of cerebral venous angiomas with emphasis on their drainage. J Comput Assist Tomogc 15: 199-206, 1991. 338. Wilms G, Goffin J, VanDriessche J, Demaerel P: Posterior fossa venous anomaly and ipsilateral acoustic neuroma: ' h o cases. Neuroradiology 34:337-339, 1992. 339. Wilms G, Marchal G, Vas Hecke P, et al: Cerebral venous angioma: MR imaging at 1.5 tesla. Neuroradiology 328145, 1990. 340. Wood EH: Angiographic identification of the ruptured lesion in patients with multiple cerebral aneurysms. J Neurosurg 21:182198, 1964. 341. Woodard E, Barrow D: Clinical presentation of intracranial arteriovenous malformations. In Barrow D ( 4 ) : Intracranial Vascular Malformations. Park Ridge, Ill, AANS, 1990, pp 53-61. 342. Yamamoto Y, Asari S, Sunami N et ak Computed angiotomography of unruptured cerebral aneurysms. J Comp Assist Tomogr 10:2127, 1986. 343. Yapor WY,Gutierrez FA: Cocaine-induced intratumoral hemorrhage: Case report and review of the literature. Neurosurgery 30:288-291, 1992. 344. Yonakawa Y, Handa J, Okuno T: Moyarnoya disease: Diagnosis, treatment, and recent achievement. In Barnett HJ,Stein BM, Mohr JP,Yatsu FM (eds): Stroke: Pathophysiology, Diagnosis, and Management, 2nd ed. New York, Churchill Livingstone, 1985, pp 805831. 345. Young N, Dorsch NW, Kingston RJ: Pitfalls in the use of spiral CT for identification of intracranial aneurysms. Neuroradiology 41: 93-99, 1999. 346. Zambramski JM, Wascher TM, Spetzler RF, et al: The natural history of familial cavernous malformations: Results of an ongoing study. J Neurosurg 80:422-432, 1994.


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Central Nervous System Trauma John J. Wasenko Leo Hochhauser

The neuroradiology of trauma has undergone dramatic changes since the advent of computed tomography (CT) and more recently with the establishment of magnetic resonance imaging (MRI) as a diagnostic imaging tool. With the ubiquitous availability of CT in the 1970s, the diagnosis and management of head trauma have changed significantly. Elaborate neurologic testing to appropriately localize a space-occupying lesion such as an intracerebral hemorrhage is no longer of paramount importance, because CT precisely defines the nature and location of the lesion, thus facilitating rapid implementation of treatment. Since the early days of CT scanning, when the contents of the skull were imaged noninvasively for the first time, CT has been the primary modality for evaluating patients with acute head The ability of CT scans to rapidly demonstrate a surgically correctable lesion, fracture, and subarachnoid hemorrhage (SAH) makes it the modality of choice in the evaluation of acute head injury. CT scans delineate acute hemorrhage from brain edema and allow one to determine whether a hematoma is intracerebral or extracerebral. Modem high-resolution CT scanning, with the direct display of axial anatomy, has replaced angiography as the prevalent method of demonstrating the indirect sign of intracerebral, epidural, or subdural hematomas (SDHs). Although the extent and multiplicity of lesions can be well evaluated by CT scans, MRI, with its greater sensitivity, frequently shows additional areas of contusion and shear injury. MRI is playing an increasingly important role in the evaluation of head trauma. It has proved more sensitive than CT in the detection of diffuse axonal (shear) injury, nonhemorrhagic contusions, and SDHs and is equivalent to CT in the depiction of hemorrhagic cont~sions.~'-~~. L36 The development of MRI-compatible life-support equipment, such as nonferromagnetic ventilators, allows the severely injured, comatose patient to be evaluated with MRI. The use of adequate sedation minimizes patient discomfort and motion, which may severely degrade image quality. Disadvantages of MRI that preclude its use in the evaluation of acute head injury include long scan time and the inability to detect fractures, SAH, and hyperacute hemorrhage. MRI is the modality of choice in the subacute and chronic stages of head injury because it is more sensitive than CT in the detection of both hemorrhagic and nonhemorrhagic lesions.

Technique Computed Tomography Ten-millimeter scans without interslice gap are made at an angle of 15 to 20 degrees to the canthomeatal line and parallel to the skull base. To reduce beam-hardening artifacts and increase the conspicuity of small lesions, the posterior fossa may be studied with 5-mm slices from the C1 arch, through the level of the posterior clinoids, followed by 10-mm slices from the sella through the vertex. From the array of image-processing algorithms, the one specially designed for soft tissue densities or a combination of soft tissues and bone is best suited for making a diagnosis and establishing appropriate management in the acute trauma situation. Algorithms for high spatial resolution imaging are necessary for trauma to regions with great density differences such as the face (air-soft tissue and airbone interfaces), the skull base and the temporal bone, and occasionally, the cranial vault. We frequently use the intermediate algorithm ("Detail," GE; "High," Siemens; "Soft," Picker) because it provides good resolution for soft tissues, gives excellent resolution for edema and hemorrhage, and defines fractures well without blooming artifact from bone (which often occurs with the soft tissue algorithms). Therefore, this algorithm is particularly well suited to image associated facial injuries in which density differences range from air to bone densities. Specific algorithms for bone densities are well suited to examine fracture sites of the facial bones, skull base, and cranial vault. Hard copies are printed in the following three different window settings to allow for routine viewing of three different areas of interest: (1) the soft tissues of the brain for infarct or hemorrhage, (2) the extracerebral spaces to detect hematomas adjacent to the dense bone of the skull vault and skull base, and (3) the bones for the detection of fractures. Intravenous contrast agent usually not required. If, however, there is unexplainable mass effect or the study is normal but the patient is comatose or lethargic or presents with a focal neurologic deficit, the administration of intravenous contrast material may become necessary. Often, MRI, with its inherent greater sensitivity, may be required for these patients. Small SDHs are difficult to visualize with CT, whereas they pose no difficulty with MRI. Isodense SDHs can usually be visualized with current third- and fourth-generation CT imaging equipment. Intravenous contrast agents may facilitate their detection by


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closure of the disrupted dura to prevent cerebrospinal (CSF) leakage and infection. Some surgeons treat only the severely comminuted fracture or when there is overt CSF leakage or pneumocephalus, and "simple" comminuted fractures are treated conservatively.lZ Fractures of the cribriform plate are commonly associated with anosmia.

Pneumocephalus Air locules in the extracerebral spaces usually indicate traumatic air entry resulting from fracture of a paranasal sinus or mastoid air cells abutting the dura (Fig. 9-3). When associated with a dural tear, they may be complicated by CSF leakage, empyema, meningitis, or brain abscess. Most post-traumatic CSF leaks cease spontaneously, and the responsible fractures may never be visualized.'23

Growing Fracture

A ..b..

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Figure 9-2. Depressed fracture with fragment of the left frontal bone (arrow).

Enlarging skull fractures have been described in 0.75% of skull fractures in children. Most cases are associated with a history of significant trauma, such as experiencing a motor vehicle accident, beiig struck by a train, or falling out of a window, that causes a skull fracture and contusion of the underlying brain. Growing fractures commonly occur in the growing skull, although occasional reports of such lesions in adults are on record.71 The ongoing normal growth of the child's brain is considered an aggravating f a ~ t 0 r . Children I~~ with growing fractures present weeks to

the depression can usually be identified during CT on the preliminary computer generated scout image of the skull. Depressed fractures near the vertex or the skull base require direct coronal imaging or reconstructions in a plane parallel to the vector of impact. Delineation of a depressed fracture is important because it may be the cause for an underlying dural tear, extracerebral hematoma, or brain contusion. Although compound depressed fractures frequently require surgical treatment, the majority of such injuries are managed conservatively. The goals of treatment are the prevention of infection and post-traumatic epilepsy and the amelioration of neurologic deficits.125Depressed fractures adjacent to venous sinuses are usually left in place because of the danger of uncontrollable hemorrhage when fragments are removed.

Basilar Skull Fracture If a basilar skull fracture is clinically suspected, high spatial resolution CT scans with a thickness of 3 mm or less are required to delineate a fracture of the chondrocranium. Alternatively, CT scans may suggest a basilar skull fracture before it becomes clinically evident. An air-fluid level in the paranasal sinuses or the mastoid in cells should be viewed as secondary to a basilar skull fracture until proven otherwise.

Frontal Sinus Fracture It is important to visualize fractures of the posterior wall of the frontal sinus because they frequently require surgical

Figure 9-3. Pneumocephalus. Collections of air overlie the frontal lobes and extend along the anterior interhemispheric fissure (arrows).


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years after injury with a pulsatile mass or rarely with a depressed calvarial defe~t.7~ Kingsley and coworkers reported 10 cases in children seen over 10 years." The lesions seem to occur when a skull fracture in childhood is accompanied by a dural tear or rent, with focal protrusion of the arachnoid membrane into the fracture gap. The unabating CSF pulsations transmitted to the entrapped

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arachnoid prothsion resat in ihe remodeling of boneof the growing skull at the fracture site, causing enlargement of the fracture line (Fig. 9 4 ) . The frequently underlying porencephaly or encephalomalacia appears to be the result of an associated contusion from the initial trauma rather than the pathogenetic factor in the enlargement of the fracture. The term "leptomeningeal cyst" is ~ b s o l e t e . ~ ~ . ~ '

Figure P-4. A, Growing fracture. Unenhanced CT can shows a defect in the left parietal bone (arrow).B and C, Axial T1-weighted (500115) and T2-weighted (2500180)MR images reveal mass isointease with CSF larmws\. D. Coronal enhanced TI-weighted 15001 15) image shows no enhancement of lesion (arrow).


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Figure Y-3. A and S, Cephalhematoma. UI scans wth sort tlssue and, bone wlndows snow partially ossineu cepnamematoma overlying the right parietal bone. Note remodeling of the underlying parietal bcme. Soft tissue swelling is present, overlying and posterior to the cephalhematoma.

Cephalhematoma may occur as a result of a difficult labor and delivery. A shell of cortical bone forms around the periphery of a subperiosteal hematoma, which may result in deformity of the calvarium (Fig. 9-5). I

A A , .i 18€racerebraHematoma

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Intracerebral hematornas are differentiated from hemor rhagic contusions in that the former are homogeneous1 hyperdense, sharply marginated, and surrounded by a ri of decreased density (Fig. 9-6).& Considerable mass effect may be present, depending on the size of the lesion. The most common sites of involvement are the frontal and temporal 10bes.~.132 Other rare sites of involvement are the ~ ~Hematomas . may be basal ganglia and posterior f o ~ s a .[I9 bilateral or multiple and are frequently associated with other lesions, such as SAH and SDHS.~~, 66* 132 Not infrequently there is associated rupture of the hematoma into the ventricular system.132 Intracerebral hematomas occur most commonly at the time of injury; however, they may be delayed, with most appearing within 48 hours following head injury.'3 Rarely an intracerebral hematoma appears several weeks after the episode of trauma. Possible etiologies of a delayed intracerebral hematoma include focal loss of autoregulation in an area of brain contusion and surgical evacuation of a lesion such as an SDH with relief of a tamponade effect and subsequent hemorrhage into the area of traumatized brain.73 Intracerebral hematomas demonstrate a typical pattern of evolution as blood products are gradually broken down

Figure 9-6. Intracerebral hematoma. Large, well-marginated he-

matoma in the right parietal lobe with rupture into the ventricular system.


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and resorbed.82Initially the intracerebral hematoma is hyperdense from clotted blood with surrounding edema and mass effect. Enhancement may be evident within or around the hematoma with the administration of intravenous contrast material.120The hematoma gradually becomes isodense with brain parenchyma over several weeks to a month.23.82 Mass effect persists after the hematoma has become isodense because the decrease in mass effect does not occur simultaneously with decrease in the density of the h e m a t ~ m a .82~ . At this time, the hematoma exhibits ringlike enhancement from the surrounding capillary proliferation.'" Decreased density eventually appears over 1 to several months. Encephalomalaciais evident as low density with adjacent sulcal enlargement and ventricular dilatation. The MRI appearance of intracerebral hematoma has been described at low and high field strength^.^'. 44' 11°, 13' The following description of the evolution of intracerebral hematomas is at a field strength of 1.5 T.44,45 Acute hematomas are less than 1 week old, subacute hematomas are more than 1 week and less than 4 weeks old, and chronic hematomas are more than 1 month old. Acute hematomas are isointense or slightly hypointense on TI-weighted images and very hypointense on T2-weighted images. The extreme hypointensity is caused by preferential T2 proton relaxation enhancement (PRT2PRE) of intracellular deoxyhemoglobin, which is dependent on the square root of the magnetic field strength and the interecho interval. The PRT2F'RE phenomenon is caused by the dephasing of water protons in areas of local magnetic field inhomogeneity. As the echo time lengthens, signal loss increases as water protons experience the local field inhomogeneity for a 25s

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longer period. Acute hemorrhage is therefore slightly hypoIntense on a proton-density-weighted image and very hypointense on a T2-weighted image. Subacute hematomas have a variable appearance at high field strength." The hematoma in the subacute state is composed of methemoglobin, a paramagnetic material. Paramagnetic materials produce T1 and T2 shortening, which theoretically results in hyperintensity on T1weighted images and hypointensity on T2-weighted images. The concentration of methemoglobin, however, determines the signal intensity present on any image sequence. Concentrated (undiluted) intracellular methemoglobin acts as a true paramagnetic material and appears hyperintense on TI-weighted images and very hypointense on T2weighted images. Undiluted extracellular methemoglobin is hyperintense on TI-weighted images and slightly hypointense on TZweighted images. Dilute extracellular methemoglobin is hyperintense on both TI- and T2-weighted images (Fig. 9-7). The mechanism of relaxation for methemoglobin is proton-electron dipole-dipole relaxation enhancement (PEDDRE). The hyperintense signal is present initially at the periphery of the hematoma and gradually progresses toward the center of the hematoma. Chronic hematomas are isointense to slightly hypointense on T1weighted images and very hypointense on T2-weighted images because of the presence of hemosiderin. The signal intensity of the chronic hematoma is similar to that of acute hematoma because of a similar mechanism of relaxation-PRT2PRE. GRE acquisition imaging is highly sensitive to the detection of acute and chronic hemorrhage,3*28, Io3 122 because

Figure 9-7. A and B, Right frontal lobe subacute intracerebral hematoma is hyperintense on sagittal TI-weighted (500115) and axial

T2-weighted (2500180) MR images. The hyperintensity reflects the presence of dilute intracellular methemoglobin. Note the right convexity subacute subdural hematoma.


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of the sensitivity of GRE sequences to the magnetic susceptibility effects of acute and chronic hemorrhage.% Hemorrhagic lesions are more evident, and more are detected with GRE than with conventional SE sequence^.^' The conspicuity of hemorrhagic lesions on SE sequences is superior at 1.5 T than at 0.5 T. The addition of a GRE sequence at lower field strength provides depiction of a hemorrhagic lesion equal to that obtained at higher field strength.lo3 The development of FSE sequences results in decreased scan time and motion artifact. Lesion conspicuity with FSE sequences is similar to that obtained with SE sequen~es.5~ FSE sequences are, however, less sensitive in the detection of hemorrhage because they are not as sensitive to magnetic susceptibility effects as conventional SE sequence^.^^ Despite the relative lack of sensitivity of FSE sequences to the presence of hemorrhage, they are comparable to SE sequences in hemorrhage detection?' The addition of a GRE sequence allows the detection of small foci of hemorrhage that may not be visualized on FSE images.

Epidural Hematoma Epidural hematomas are characteristically biconvex or lentiform (Fig. 9-8).25 Uncommonly, epidural hematomas may be bilenticular, crescentic, or irregular.I9 The shape is determined by the dura, which is firmly adherent to the inner table of the skull. A blow to the calvarium results in damage to the underlying vessel, with subsequent displacement of the dura away from the inner table of the skull. The vessel may be damaged, even without fracture of the adjacent bone, as is commonly seen in children. Fracture of the adjacent bone is, however, c o m m ~ n . 'The ~ most

Figure 9-8. Typical biconvex epidural hematoma is present over the right parietal lobe.

Figure 9-9. Heterogeneous left temporal convexity epidural he-

matoma exhibits considerable mass effect. Heterogeneous areas represent unclotted blood.

common location for epidural hematomas is over the temporal lobe, followed by the parietal, frontal, and occipital lobes with the posterior fossa the least common location.19 Damage to the-middle meningeal artery is responsible for most epidural hematomas; however, they may occur as a result of laceration of diploic veins or dural sinuses.lZ Epidural hematomas-may be classified as acute, subacute, and chronic. An acute epidural hematoma is heterogeneous in attenuation, containing areas of hyperdense blood and isodense serum (Fig. 9-9). Subacute epidural hematoma is homogeneously hyperdense in attenuation, consisting of solid blood clot (Fig. 9-10). Heterogeneous or decreased attenuation, as well as an enhancing membrane, are characteristics of chronic epidural hematoma, as a result of degradation of blood product^.'^ Peripheral enhancement representing dura and membrane formation between the epidural hematoma and adjacent brain parenchyma may be seen in chronic epidural hematomas with the use of intravenous contrast.g0 Delayed epidural hematoma is most commonly from slow venous bleeding from rupture of a dural sinus (Fig. 9-11).54". "O Other causes of delayed epidural hematoma are pseudoaneurysm rupture of an e~iduralvessel and arteriovenous fistula.84 In some instances, when minimal neurologic signs and symptoms are present, epidural hematoma may undergo spontaneous resolution, which is visualized on serial CT scanning.124 Some hematomas expand 1 to 2 weeks after injury and then gradually resolve. This expansion correlates with an increase in or persistence of symptoms.92 The imaging


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Figure 9-10. Right temporal convexity epidural hematoma is largely homogeneous in density, indicating the presence of clotted blood. Note the effacement of the basal cisterns (arrowheads).

criteria in determining whether an epidural hernatoma may be treated conservatively are (1) a diameter of less than 1.5 cm and (2) a minimal midline shift of less than 2 mm. The patient must be neurologically intact without focal d e f i ~ i t . ~Parenchymal ~,'~ abnormalities are not present as frequently with epidural hematomas as with acute SDHs. Surgical evacuation of the hematoma results in marked clinical improvement. Little or no residual hematoma is evident on postoperative scans." Posterior fossa epidural hematomas-se rare; however, delay in detection may result in fatal brain stem injury."g Many posterior fossa epidural hematomas are not readily visualized on CT because of beam-hardening artifact. The use of contrast material facilitates the detection by demonstrating displacement of the dural sinuses, the torcular herophili, or both as well as displacement of the dura away from the cal~arium."~ MRI studies allow the distinction between epidural hematomas and SDHs, which may not be possible with CT scans when a hematoma is small or is not typically biconvex. In epidural hematomas, the dura is seen as a curvilinear band of decreased signal intensity between the hematoma and brain parenchyma (Figs. 9-12 and 9-13).39 Venous epidural hematomas may be differentiated from arterial hematomas on the basis of the former's proximity to a dural sinus and of the sinus away from the inner table of the s k ~ l l . The ~ . ~majority ~ of posterior fossa epidural hematomas are of venous origin and may not be well visualized with CT scans because of beam-hardening artifact from adjacent bone structure.'28 r .

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Figure 9-11. Delayed epidural hematoma. A, Acute subdural hematoma is present over the left parietal convexity (arrowheads). Note the small hemorrhagic contusion in the left parietal lobe. B, The patient has undergone craniectomy and drainage of the subdural *I , hematoma. Note the new posterior parieto-occipital epidural hematoma (arrowheads).


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Figure 9-12. A and B, Sagittal TI-weighted (500115) and axial T2-weighted (2500180) MR images show large subacute epidural hematoma overlying t&e left frontal lobe. Note the displacement of the hypointense dura away from the inner table of the calvarium (arrowhe&). '

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Figure 9-13. A and B, Subacute right temporal convexity epidural hematoma is hyperintense on both sagittal TI-weighted (500115) (arrow)and axial fast spin-echo T2-weighted (40001108) MR images (arrowheads). The band of hypointensity corresponds to the displaced dura (arrowheads). Retention cyst is present in the sphenoid sinus.


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The lack of artifact from bone on MRI studies readily enables the detection of a small epidural hematoma.

Subdural Hematoma SDHs are most commonly caused by shear forces that result in the tearing of the bridging veins present in the subdural space.35Laceration of cortical arteries and parenchymal contusions are other causes of SDHs.Io5 Rarely, an SDH may be caused by rupture of an aneurysm or arteriovenous malformation.% Unlike an epidural hematoma, which is focal, an SDH is diffuse and may overlie an entire cerebral hemisphere. The potential subdural space offers little or no resistance to the expansion of the hematoma within the subdural space. Underlying brain injury, such as hemorrhagic contusion and edema, are frequently seen with acute SDH.26J32 These injuries are seen more commonly with SDH than with . ~ ~ degree of mass effect seen with epidural h e m a t ~ m aThe SDH is often out of proportion to the size of the hematoma. This mass effect is from the presence of hemorrhagic contusions and edema rather than the SDH.w132 The typical appearance of an acute SDH is a hyperdense crescent-shaped collection with a convex lateral border and concave medial border overlying the cerebral convexity (Fig. 9-14).26.132Occasionally the hematoma may be biconcave, simulating the appearance of an epidural hematoma.l2 This biconcavity can be seen particularly when the hematoma is large.34The majority of acute SDHs are hyperdense because of the attenuating properties of the hemoglobin molecule. In one report, SDHs were found to be hyperdense in all patients with a history of acute injury.IM An

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acute SDH may be isodense with brain parenchyma in patients with anemia as a result of a reduced concentration of hern~globin."~The typical acute SDH gradually approaches the density of brain parenchyma and appears isodense with brain over an interval of 1 to 5 weeks.26This change occurs from the breakdown and absorption of blood products. The classic homogeneous, hyperdense appearance of acute SDH is not always present. The hematoma may appear mixed rather than homogeneous in attenuati~n.~~ It may have one of three patterns: marginal hypodensity, central irregular areas of hypodensity, or laminar areas of hypodensity (Figs. 9-15 and 9-16). The low density may be secondary to unclotted blood or possibly CSF resulting from arachnoid tears. The mixed SDH is usually larger and has more mass effect than the classic hyperdense SDH. SDHs located adjacent to the tentorium may simulate an intra-axial lesion. Several features serve to distinguish the subdural location of the lesion. Supratentorial SDHs located adjacent to the tentorium have a well-defined medial margin corresponding to the edge of the tentorium. A sheetlike area of increased density that slopes laterally is present, and the trigone of the lateral ventricle is rotated anteriorly and ~uperiorly.~~ When the hematoma is located below the tentorium, the lesion has a sharp lateral margin corresponding to the tentorium and increased density that slopes medially (Fig. 9-17). Interhemispheric SDHs occur in the posterosuperior aspect of the interhemispheric fissure (Fig. 9-18).135 Anterior extension of the lesion occurs less commonly. This lesion may be differentiated from a normal or calcified falx and SAH. SDH in the interhemispheric location has a character-

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Figure 9-14. A, Crescentic right convexity acute subdural hematoma 1s evident from the irregular contour on the brain window setting. B, The subdural hematoma is better demonstrated with an intermediate window setting.


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Figure P-16. Irregular areas of hypodensity indicate that unclotted blood or cerebrospinal fluid is present in this acute left convexity subdural hematoma.

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Figure 9-17. A, It is difficult to localize this ill-defined subdural hematoma (arrow). B, Coronal reconstruction localizes the hematoma to the infratentorial space by its smooth-appearing superior border (arrow).


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Figure 9-18. Interhemispheric subdural hematoma, The flat me-

dial border of this acute hematoma localizes it to the subdural space above the tentorium.

istic crescentic shape with a flat medial border that abuts the falx and a convex lateral border that abuts the brain. The hematoma is located posterior and superior to the splenium of the corpus callosum. When anterior extension is present, the hyperdensity extends inferiorly in the subdural space to the termination of the falx, which is superior to the genu of the corpus callosum. It can be differentiated from SAH that occurs in the anterior interhemispheric fissure, which has a zigzag configuration conforming to the cortical sulci. In children, increased density along the falx represents SAH because falx calcification rarely occurs in The SAH extends from the calvarium this age inferiorly to the rostrum of the corpus callosum, differentiating it from an SDH. Posterior fossa SDHs are rare les i o n ~ . "Distinction ~ between SDHs and epidural hematomas may be accomplished with the use of intravenous contrast agents that allow differentiation between the two lesions.LLg Postoperatively, residual SDH may be seen from failure to find the origin of bleeding and difficulty in removing blood clot adherent to the arachnoid (Fig. 9-19).31 Small SDHs are not surgically evacuated and are managed by observation. These lesions are gradually resorbed over time as fibrinolysis and absorption of blood clot o ~ c u r s . ~ The majority of SDHs differ in attenuation from adjacent brain, being either hyperdense or hypodense relative to brain, and are readily diagnosed with CT scanning. Isodense SDHs-with attenuation values near or equal to those of brain parenchyma-may be difficult to diagnose. As blood products become degraded, a hyperdense SDH

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gradually decreases in attenuation, becoming isodense with brain. Occasionally, rebleeding into a chronic SDH results in an isodense lesion.26Acute isodense SDH may rarely be seen, occuning in patients with anemia.l13 Other possible causes of isodense SDH are dilution with CSF secondary to arachnoidal tear and local or disseminated coag~lopathy.~~' Effacement of the cortical sulci over the cerebral convexity and mass effect on the ventricular system or midline shift indicate the presence of an isodense SDH (Fig. 9-20)? Mass effect on the ventricular system may be negligible or absent when bilateral collections are present.34 Delayed contrast-enhanced CT scans performed 4 to 6 hours after injection of the contrast agent reveal enhancement of the subdural collection?^ 82 Contrast-enhanced CT scans may also demonstrate enhancement of cortical veins that are displaced medially from the inner table of the calvarium; however, this enhancement is not seen in all cases.63 The use of rapid high-dose contrast enhancement allows the more accurate detection of an isodense SDH.49The majority of patients with an isodense SDH may have three or four of the following signs: posterior displacement of the ipsilateral anterior horn of the lateral ventricle, compression of the ipsilateral posterior and temporal horns, anterior displacement of the ipsilateral posterior and temporal horns, anterior displacement of the ipsilateral glomus calcification, and widening of the contralateral v e n t r i ~ l e In . ~ ~a patient with a history of head trauma, the presence of small compressed ventricles with the absence of cortical sulci should raise the possibility of bilateral isodense SDH.63 High-resolution CT scans allow the differentiation of gray matter from white matter. The presence of an extra-axial mass displaces the gray-white matter interface medially, producing buckling of the central white mattera40Buckling of the white matter is virtually diagnostic of an extra-axial mass (see Fig. 9-20). Chronic SDHs are most commonly caused by trauma; however, the traumatic episode is frequently so minor that it is forgotten or ignored.I6-59 The chronic SDH is caused by a torn bridging vein in the subdural space through which venous blood slowly flows." In one series, no acute SDH evolved into a chronic SDH." Chronic SDHs are most commonly hypodense on CT scans (Fig. 9-21).66 The are typically crescentic, however, they may be biconcave or lentiform as a result of fluid absorption into the h e m a t ~ m a Another .~~ possible cause is the formation of adhesions. A capsule composed of a capillary-rich membrane develops and surrounds the SDH.59 This capillary-rich membrane is responsible for repeated episodes of rebleeding and subsequent increase in size of the hematoma. As the hematoma enlarges, the patient becomes symptomatic, showing signs of increased intracranial pressure, hemiparesis, or intellectual and personality change.16 Repeated episodes of rebleeding may result in a mixeddensity collection containing areas of hypodense, isodense, and increased attenuation (Fig. 9-22). A chronic SDH may appear hyperdense from acute hemorrhage, simulating an acute process.26.'" Fluid-fluid levels may be seen as blood products settle in the dependent aspect of the subdural collection, which becomes hyperdense relative to the superior aspect. Enhancement of the SDH may be seen on delayed CT scans obtained 3 and 6


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Figure 9-19. A, Acute subdural hematoma is present over the right cerebral convexity with extension into the interhemispheric fissure posteriorly. B, Postoperative scan reveals small residual hematoma (arrow).

Figure 9-20. A, Left convexity isodense: subdural hematoma causes mass effect on and shift of the left lateral ventricle. B, White matter buckling (arrows) indicates the presence of the extra-axial subdural collection.

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Figure 9-21. Bilateral frontal convexity chronic subdural hematornas are present. Note the slight shift of the septum pellucidurn to the right.

hours after intravenous administratian . . of contrast material.59 A subdural hygroma is a h y p o d e n s e % c o b tion equal in density to CSF (Fig. 9-23). The lesions are crescentic and may be bilateral. It is not possible to distinguish a subdural hygroma from a chronic SDH with CT scanning, because the two lesions are identical in appearance. At surgery, clear fluid and lack of a membrane allow the diagnosis of a subdural h y g r ~ m a . ~ ' J ~ The MRI appearance of SDH has been well documented.33.86.111 In the acute phase (1 one week and 2 weeks and 1 month old) are isointense relative to gray matter on TI-weighted images and hyperintense on T2-weighted images (Fig. 9-25). Usually no hypointensity is evident in chronic SDHs on T2-weighted images, most likely because of the lack of a blood-brain barrier and resorption of hemosiderin from the collection. Occasionally hemosiderin may be seen in thickened membranes and areas of rehemorrhage. Nuid-fluid levels of different signal intensity suggest rebleeding. It is possible to distinguish a chronic subdural hygroma from a chronic SDH because the hygroma is of CSF signal intensity on all pulse sequences (Fig. 9-26).33

Figure 9-22. Large chronic subdural hernatoma overlies the left cerebral convexity. The hyperdense area represents recurrent hemorrhage (long arrow). Note the septations within the hematoma (small arrows).

Figure 9-23. Cerebrospinal fluid-density collection representing a cerebrospinal fluid hygroma is present over the right frontal convexity (arrows). The initial CT scan 3 days earlier showed no subdural collection.


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Figure 9-24. A and 3,Sagittal TI-weighted (500115) and axial T2-weighted (2500180) MR images demonstrate hyperintense left frontal convexity subacute subdural hemorrhage. Right frontal convexity subacute hematoma is seen on the axial T2-weighted image (small arrows).

Figure 9-25. A and B, Right frontal convexity chronic subdural hematoma is slightly hyperintense on sagittal TI-weighted (500115) and isointense on axial T2-weighted (2500180) MR images relative to cerebrospinal fluid (arrows). Note displacement of the subdural veins away from inner table of the calvarium (arrowheads).A small left frontal convexity subdural hemorrhage is present.

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Figure 9-26. A and B, Same case as shown in Figure 6-23. Sagittal TI-weighted (50011.5) and axial fast spin-echotT2-weighted (3.5001 108) M R images show cerebrospinal fluid hygroma over right frontotemporoparietalconvexity (arrows). The small left frontal convexity hygroma not evident on the CT scan is well visualized on the MRI study (small arrows). Note the right temporal lobe contusion and herniation of the temporal lobe through the temporal bone fracture (black arrow).

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It is not always possible to distinguish a subdural hygroma from atrophy because the findings of mass effect and sulcal effacement associated with subdural hygroma may be subtle. Visualization of cortical veins adjacent to displaced cortex is indicative of subdural hygroma. A diagnosis of atrophy is made when cortical veins are seen traversing a widened subarachnoid space.79

Subarachnoid Hematoma SAH is frequently present in the acutely injured patient. It is often associated with other lesions, such as intracerebral hematoma. SAH is caused by damage to blood vessels on the pia-arachnoid. Intraparenchymal hematoma with rupture into the ventricular system may gain access to the subarachnoid space via the foramina of Mangendie and Cuschka. On CT scans, hyperdensity representing acute hemorrhage is visualized in the sulci overlying the cerebral convexities, w i t h the sylvian fissures, basal cisterns, and interhemispheric fissure (Fig. 9-27). Hemorrhage is rapidly cleared from the subarachnoid space. The majority of CT scans performed within 1 week appear normal.@ CT is the modality of choice in the evaluation of SAH because of the hyperdensity of clotted blo~d.It is difficult to visualize with MRI studies because the high oxygen concentration in CSF prevents the degradation of oxyhemoglobin to deoxyhern~globin.~~~ 21* 39 This process has been described in detail in both clinical and experimental situation~.'~. l7 SAH may be seen on MRI studies only when large volumes of clot are present.39Acute SAH is isointense

Figure 9-27. Subarachnoid hematoma is present along the interhemispheric fissure. Blood in the sulci is responsible for the zigzag appearance of the interhemispheric hemorrhage. Hemorrhagic contusion is present adjacent to the fak in the left frontal lobe (arrowhead).


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Figure 9-28. A, Acute subarachnoid hemorrhage in pontine cistern is isointense on axial T1-weighted (500115) MR image (arrows). B, Hypointense hemorrhage is poorly seen on axial fast spin-echo T2-weighted (39001108) image (arrows) because it is masked by hyperintense cerebrospinal fluid.

on TI-weighted images and hypointense on T2-weighted images with respect to brain (Fig. 9-28). Toward the end of the first week, the SAH exhibits T1 shortening and appears hyperintense on T1-weighted images.1° Subacute SAH does not evolve like intraparenchymal hematoma, which as stated previously becomes isointense or slightly hypointense on TI-weighted images and very hypointense on T2-weighted images in the chronic stage. This may be from the high oxygen concentration of CSF, which may prevent the further degradation of methemoglobin to hemosiderin, or from CSF pulsation, which may aid in clot dissolution and resorption. The residual of SAH may be evident as hypointensity in the leptomeninges because of hemosiderin deposition present in macrophages." This reflects the preferential T2 shortening that occurs as water protons precess through a local heterogeneous magnetic field and lose signal intensity. The effect is more evident at high field strength.44A T2" GRE sequence with a short flip angle and relatively long TE has been utilized in the lu improved detection of intraparenchymal hem~rrhage.~~. The improved ability of these sequences to detect hemorrhage stems from their sensitivity to inhomogeneities in the magnetic field that are produced by paramagnetic blood products. The use of GRE sequences may allow improved detection of acute SAH. Fast fluid-attenuated inversion recovery (FLAIR)sequences have proved to be sensitive in the detection of SAH. It is, however, nonspecific as leptomeningeal carcinomatosis and meningitis can have a similar appearance.lm

Contusion Contusions are the most commonly encountered lesions due to head trauma.2K" "" The lesions are characterized

pathologically as areas of hemorrhage, necrosis, and edema. The mechanism of contusion production is complex and depends on many factors, with lesions occurring at the site of impact as well as at sites remote from impact; they are referred to as coup and contrecoup lesions, respectively. A coup lesion is produced by transient inbending of the calvarium with resultant compression of the underlying brain. Fracture of the calvarium is not always present. The contrecoup Lesion is produced when the calvarium decelerates but the brain continues in motion and strikes the irregular inner surface of the c a l ~ a r i u m . ~ ~ Contusions appear as areas of heterogeneous increased density mixed with or surrounded by areas of decreased or normal density (Figs. 9-29 to 9-3 66, lU). 132 Mass effect may or may not be present, depending on the size of the lesion. The frontal lobe convexity and the lateral temporal areas are the most common sites for coup injury.130 Contrecoup injuries typically involve the inferior surface of the frontal and temporal lobes.lU) Hemorrhagic contusions have a typical pattern of evolution that occurs over several months.130The initial area of heterogeneous increased density progresses to an area of decreased density within 1 week. At 2 weeks, the contusion is not visualized because it is isodense with brain parenchyma. Enhancement occurs during the acute and subacute stages.120. Focal encephalomalacia becomes evident by 1 month after injury. Contusions may be isodense if they consist of equal amounts of hemorrhage and edema. The use of intravenous contrast material allows the detection of these isodense lesions as contrast material accumulates in areas of blood-brain barrier breakdown.ll'. IZ0 In the posterior fossa, contusions may be difficult to detect because of beam-hardening artifact from adjacent


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Figure 9-29. A, Hemorrhagic contusions with surrounding edema are evident in the inferior left frontal and anterior right temporal lobe (arrowheads).B, CT scan at higher level reveals additional cortical hemorrhagic contusions in the frontal lobe (arruwheadr).

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Figure 9-30. Axial CT scan demonstrates multiple hemonhagic contusions in the temporal lobes. Note the smdl left occipital lobe convexity subdural hematoma (arrow).

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I Figure 9-31. Deep gray matter contusion. Hemorrhagic contusion involves the right lentiform nucleus (arrow).


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bony structure (Fig. 9-32). In some instances, no lesion can be identified, and the presence of indirect signs such as effacement of the pontine, cerebellopontine angle, and perimesencephalic cisterns must be used to suggest the presence of brain stem injury.lL8Isodense contusions not visualized on unenhanced CT scans will become evident with the use of intravenous contrast material.u8Brain stem injuries may be primary, occurring at the time of injury, or secondary, occurring at a later time from downward transtentorial herniation or direct compression by other lesion^."^ Hemorrhagic lesions in the rostral midbrain may also occur at the time of injury (Fig. 9-33).83 Injury to the brain stem carries a grave prognosis and is associated with a high m~rtality."~ MRI studies are equivalent to CT scans in the detection of hemorrhagic cortical contusions but are more sensitive in the detection of nonhemorrhagic contusion^.^^.'^^ In some cases, acute hemorrhagic contusions visible on CT scans may not be visualized with MRI.= AS the hemorrhagic contusion evolves, it becomes isodense and finally hypodense on CT scans and is poorly seen. It is in the subacute and chronic stages that MRI studies are more sensitive than CT in the detection of contusion^.^^ MRI studies also Contuallow the contusions to be better ~haracterized.~~ sions tend to be multiple and to involve the cortex with sparing of the underlying white matter. A hemorrhagic component is evident in many lesions?' Acute hemorrhagic contusions are isointense or slightly hypointense in signal on TI-weighted images and very hypointense on TZweighted images (Fig. 9-34). This feature reflects the preferential T2 shortening of intracellular deoxyhemoglobin. Subacute lesions are hyperintense on

L F'igure 9-32. Pontine contusion. Hemorrhag~ccontusion is seen in the left posterolateral pons (arrowhead).

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Figure 9-33. Acute hemorrhagic contusion is demonstrated in the rostral midbrain (arrow). Note the effacement of the quadrigeminal cistern (arrowheads) and the left temporal lobe contusion (small arrow).

T1- and TZweighted images because of the effect of extracellular methemoglobin (Fig. 9-35).'14 Hypointensity from hemosiderin and encephalomalacia are evident in chronic lesions. The discrepancy between CT and MRI in the detection of nonhemorrhagic contusions is due to the superior spatial resolution of MRI and its sensitivity in the detection of changes in water content in damaged tissue. The use of supplemental T2* GRE sequences should allow the detection of small hemorrhagic contusions that are visualized on CT scans but not with conventional SE MRI studies (Fig. 9-36). In the posterior fossa, contusions typically occur along the posterolateral aspect of the midbrain and lateral aspect of the cerebral pedun~le.3~ They are primary injuries occurring at the time of injury. Secondary injuries occur later in the ventral, ventrolateral, and paramedian aspects of the brain stem.38MRI studies are more sensitive than CT scans in the detection of contusions in the posterior fossa because of the lack of artifact from the adjacent bone. Indirect signs of brain stem injury, which may be the only abnormalities present on the CT scan, are well demonstrated in addition Secondary foci of hemorrhage, loto intrinsic lesi0ns.~~5~ cated in the midline of the rostral midbrain, occur from tearing of penetrating arteries that supply the brain stem.38 Although a high percentage of patients with brain stem contusions and normal CT findings have a good clinical Outcome, 20% with normal CT scans do poorly because of undetected lesions or secondary cornpli~ations.~~ MRI stud-


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Figure 9-34. A, Acute left temporal lobe hemorrhagic contusion is isointense with gray matter on sagital TI-weighted (500115) MR image (arrow). B, Hemorrhagic contusion is hypointense on axial T2-weighted (2500180) image (arrow). Note additional hemorrhagic contusions in the right frontal and temporal lobes (arrowheads).

:ontusion in left fronw loDe is nyperintense on coronal TI-weighted (500115) ana largely hyperintense on coronal T2-weighted . 00180) MR images, indicating the presence of methemoglobin (arrows). In addition, there is a small left frontal, convexity subacute subdural hematoma (curved arrows).

Figure 9-35. A and B, Subacute hemorrhal


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Figure 9-36. A, Axial T2-weighted (2600180) MR image shows no abnormality in a comatose patient. B, Axial T2* gradient-recalled echo (600117), 20-degree flip-angle image reveals a small acute hemorrhagic contusion in the pons (arrow).

CT findings in diffuse axonal injury include diffuse cerebral swelling, corpus callosal hemorrhage, and SAH. Hemorrhage may also be present in the area of the third ventricle and hemispheric white matter.132Although CT scans do not reveal the actual axonal lesion demonstrated with histology, they do show the associated edema and Diffuse Axonal (Shear) Injury hemorrhage (Fig. 9-37). lZ8 Diffuse axonal (shear) injury is frequently encountered MRI studies are more sensitive than CT scans in the in patients with head trauma.39 Shearing injuries to the detection of diffuse axonal injury. Lesions are readily demwhite matter were first described in the CT literature in onstrated by MRI in patients in whom the CT scan shows 1978Iz9and have been described extensively in the neurono a b n ~ r m a l i t y . ~ ~The - ~ ~injuries . ' ~ ~ are demonstrated with pathological literature in the past. A study by Strich and CT only when greater than 1.5 cm or when present in the Oxon115in 1961 described these injuries as axonal tears capsule.39 corona radiata or internal with or without microscopically visible hematoma. They Diffuse axonal injury lesions are usually multiple, range reported on five patients who sustained head injury, died from 0.5 to 1.5 cm, and are typically oval or elliptical. The of brain swelling, and were found at autopsy to have white lesions are most commonly located in the subcortical white matter degeneration. Midbrain damage in patients with matter of the frontal and temporal lobes, splenium of the closed head injury has been frequently described at aucorpus callosum, corona radiata, and internal capsule (Figs. topsy. In another study, 80% of patients dying of injuries 9-38 and 9-39). The parieto-occipital lobes and cerebellum resulting from head trauma had midbrain lesions at autopsy are less commonly involved.37 In the brain stem, the lesions that were not visualized by CT scans.98 Although blunt are located in the dorsolateral aspect of the midbrain and head trauma has been associated with a significant number of hemorrhagic foci in the corpus callosum at a~topsy,'~ upper pons (Fig. 9 4 0 ) . More than 80% of the lesions are nonhemorrhagic, being most evident as foci of hyperintenthe outcome of corpus callosum hematoma is not invariably sity on T2-weighted images.38 dismal, because many patients with such lesions diagnosed bv CT scans have been shown to survive. Coma, decerebrate posturing, vegetative state, and no increase in intracranial pressure are present in many paBrain Swelling and Edema tients with diffuse axonal i n i u r ~ . This ' ~ ~ iniuw is caused by rotational forces that shear strain, resulting in Brain swelling and edema occur commonly in patients tissue damage. Shear strain is maximum at the junction with head trauma. Brain swelling is observed more comof tissues with different densities such as the gray-white monly in children than in adults.I3l Minor episodes of j~nction.~'The presence of diffuse axonal injury is of trauma may result in brain swelling. Patients may experigreat prognostic significance because the lesions are often ence a lucid interval after the episode of trauma, followed associated with a poor out~orne.l~~ by the sudden onset of headache, nausea, vomiting, and

ies are more accurate in the assessment of subacute and chronic injuries and may provide a more reliable correlation with clinical findings to better predict clinical outcome.

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Figure 9-37. Diffuse axonal injury. CT scan demonstrates small hemorrhagic diffuse axonal injuries in the deep white matter and corpus callosum.

~-3a. Diffuse axonsu injury. Axial T2-weighted (25001 80) MR image demonstrates typical locations of diffuse axonal injury: subcortical white matter, corpus callosum, and corona radiata.

Figure 9-39. A and B, Diffuse axonal injury in two different patients. Hyperintense lesions are present in the splenium of the corpus callosum on axial T2-weighted (2500180) MR images (arrows).


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Figure 9-40. Axial T2-weighted (2500180) MR image shows areas of diffuse axonal injury in the pons, middle cerebellar peduncles, and left-cerebellar hemisphere. The pontine lesion contains a focus of acute hemorrhage (small arrow). Hemorrhagic c pPs i o n is present in the left temporal lobe.

Figure 9-41. Brain swelling. Effacement of the perimesencephalic cistern indicates brain swelling (arrowheads). Note the bilatera1 temporal lobe contusions.

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loss of consciousness.~31SAH and contusions are often seen in association with this type of abn~rmality.'~. 55 Brain swelling is evident in the majority of patients with head trauma, occurring at the time of injury or several hours a f t e r ~ a r d sCT . ~ ~findings consist of compression of the lateral and third ventricles and perimesencephalic cistern (Figs. 9 4 1 and 942). There is an associated increase in density of the white matter from transient hyperemia.I3' It is thought that loss of autoregulation results in an increase in cerebral blood flow and blood volume. This increase in blood flow forces CSF out of the ventricles and subarachnoid space, resulting in the compressed appearance. Serial CT scans show the gradual resolution of brain swelling over a period of 3 to 5 days.55 The initial white matter hyperdensity gradually returns to normal as the swelling subsides. In more than one third of cases in children, extracerebral collections and sulcal and ventricular enlargement are seen to develop on follow-up CT scans.I3' Cerebral edema may be cytotoxic, interstitial, or vasogenic in origin. In the immediate post-traumatic interval, cerebral edema is vasogenic, reflecting breakdown of the blood-brain barrier with leakage of intravascular contents into and around areas of damaged tissue. Edema is evident as decreased density within and surrounding areas of contusion and intraparenchymal hemat~ma.~~. 6 82 Edema may occur as an isolated finding, appearing as an area of decreased density.66 Cerebral edema typically appears 24 hours after injury, then increases and becomes maximum at 3 to 5 days and then gradually resolves. Brain swelling and edema are evident with MRI stud-

Figare 9-42. Axial CT scan shows effacement of bawl cisterns, and third ventricle representing brain swelling. Note pneumocephalus overlying the right frontotemporal convexity (arrowheads).


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i e ~ . ~ ~ 136 , The exquisite sensitivity of MRI to the presence of extracellular free water enables the detection and visualization of small regions of edema, particularly on T2weighted images.

Penetrating Injury Gunshot wounds are a common cause of penetrating head injury. CT scans allow one to rapidly locate the position of a missile and determine the extent of intracranial injury!. log The missile, its track and fragments, as well as skull fracture and displaced intraparenchymal bone fragments are readily identified (Fig. 9-43). Hematoma along the missile track, intraventricular hemorrhage and SAH, diffuse edema, and pneumocephalus, both extracerebral and intracerebral, are frequently seen on CT scans.'0g Laceration of a major blood vessel may result in massive intraparenchymal hemorrhage, which is an indication for early surgical intervention.Iw Injuries beyond the missile track may sometimes be seen if the missile is of a largecaliber or high-velocity type.4 Prognosis is best when damage is limited to a single lobe, worse with unilateral multilobe injury, and poorest with bilateral hemispheric Damage to v i d structures such as the diencephalon and mesencephalon is also associated with a poor prognosis.lw Complications of penetration injuries include CSF leak, osteomyelitis, abscess, and seizures.88Repeat CT scans may reveal the development of encephalomalacia along the missile track and intraparenchymal cystic areas

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of CSF density." The presence of metal projectiles is a relative contraindication to an MRI study because projectiles containing steel are deflected when placed in a magnetic field. Nonferromagnetic missiles are a contraindication to MRI when they contain ferromagnetic c~ntaminants."~ Any metal distorts the local magnetic field, the magnitude of which depends on the degree of ferromagnetism of the metal alloy. In addition to undergoing deflection, stainless steel or alloys with ferromagnetic contaminants distort the local magnetic field to a greater degree than titanium compounds and, if in the region of interest, severely degrade image quality.

Vascular Injury Injury to the carotid or vertebral arteries may be produced by blunt force, penetrating injury, strangulation, and hypere~tension.4~ Dissection, laceration, thrombosis, and pseudoaneurysm or arteriovenous fistula formation may occur.20 The site of injury depends on the nature of the forces on the vessels and the occurrence of nearby skull fractures.87Arterial injury may be diagnosed with CT scanning; however, angiography remains the modality that best defines the site of arterial injury. An intimal tear in the arterial wall may result in dissection and thrombus formation.87Although one third of patients are symptomatic at the time of injury, the majority experience a lucent interval varying from hours to days before the onset of ~yrnptoms.~'Symptoms are variable and

Figure 9-43. A, Axial CT scans with bone window setting demonstrates missile adjacent to the left temporal bone, temporal bone fracture, and missile-fragments in brain parenchyma. B, Brain window setting reveals multiple hemorrhagic-foci in the frontal and temporal lobes, effacement of the basal cisterns, and pneumocephalus.


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include headache, Homer's syndrome, transient ischemic attacks, and completed stroke. The diagnosis of arterial dissection may also be accomplished with MRI studies." Abnormal signal intensity r e p resenting hemorrhage is seen in a thickened arterial wall on all pulse sequences. The signal intensity depends on the age of the hematoma. The hematoma is usually contained by a thin rim of hypointensity that represents the adventitia.

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In addition, the arterial lumen appears narrow. Arteries normally appear hypointense or demonstrate flow void phenomena on MRL9 In arterial dissection, the slow flow distal to the area of dissection produces hyperintense signal within the vessel lumen. However, the hyperintense signal is not specific for dissection and may be the result of slow flow from stenosis caused by atherosclerotic disease. The hyperintensity of slow arterial flow must be differentiated

Figure m.A, Arterial dissection. Sagittal TI-weighted (500115) MR image shows cortical ribbon of hyperintensity representing subacute hemorrhage in the right temporal lobe (arrowheads).B, Hyperintense signal is evident on axial T2-weighted (2500180) image. Findings are consistent with acute infarction. C,Two-dimensional time-of-flight MR angiography study demonstrates irregular narrowing of the right vertebral artery consistent with dissection (arrows).D, Intraarterial digital subtraction angiogram of the right vertebral artery confirms the dissection (arrows).


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Mgure M. A, P o s t - ia ~W ~ carotid artery aneurysm. Coronal TI-weighted (5W-5)MR image shows aneurysm ariing from left internal carotid artery (arrow). Note the soatdl b m d the internal carotid artery (arr~wheadj. B, Tttree-dimensional jbse-contrast MR mgipesaphy W y wormed with a vel.ocity enmdbg of 10 om;fsemd demonstrates flow w:thin the aneurysm (arrow). C,kft common carotid arteriogram shows the a n e m arising from the p r m b l cavemars istmdcafbxid artery.

from arterial thrombosis, which appears as isointense signal within the vessel lumen. Arterial thrombus is composed of fibrin and platelets, rather than hemoglobin containing red blood cells, and as a result is isointense in signal intensity. This is in contradistinction to the signal intensity of intraparenchymal hematoma or venous thrombus in various stages of e v ~ l u t i o n Magnetic .~~ resonance angiography (MRA) can demonstrate the concentric luminal narrowing and irregularity of carotid dissection and may eliminate the need for conventional angiography (Fig. 9 4 ) . Disruption of the three layers of the arterial wall-intima, media, and adventitia-may result in pseudoaneurysm formation.87 Symptoms are variable, include headache, tinnitus, and vertigo, and may appear years after injury." Although CT and MRI studies are capable of demonstrating a pseudoaneuysm, angiography is required to accurately depict the lesion. The MRI appearance of a pseudoaneurysm is variable, depending on the size and presence of thrombus. Areas of signal void, representing

residual lumen, and areas of mixed signal intensity, representing thrombus of variable age, may be seen. An advantage of MRI is that it demonstrates the true size of the aneurysm, including the patent lumen as well as intraluminal thrombus, whereas conventional angiography demonstrates only the patent lumen (Fig. 9-45). MRA has the capability to demonstrate both small and large aneurysms. Aneurysms as small as 3 mm may be visualized with current imaging techniques.'" The threedimensional time-of-flight technique is sensitive to the detection of small aneurysms, whereas the phase-contrast technique is better able to depict large a n e u r y ~ r n s . ~ ~ . ~ ~ Laceration of the intracavernous carotid artely with rupture into the cavernous sinus results in traumatic carotid cavernous fistula.89 Symptoms and signs include orbital bruit, proptosis, conjunctival redness and swelling, blurred vision, pain, and pulsatile exophthalmos. CT and MRI studies demonstrate proptosis, enlargement of the rectus muscles, superior ophthalmic vein, and cavernous sinus


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Figure 9-46. A, Carotid cavernous fistula. Axial T2weighted image (TR = 2500 m m , TE = 80 msec). Increased flow void is present in the region of the cavernous right internal carotid artery (arrowheads). B, C a d s m T1-

mic vein ( e ,

(Fig. 9-46). MRI shows flow void within the enlarged superior ophthalmic vein and cavernous sinus. Angiography is, however, necessary to visualize the site of the fistula. Phase-contrast MRA studies show promise in the detection of the fistulous comm~nication.'~~

Child Abuse Child abuse is a major cause of morbidity and mortality. Most victims of child abuse are younger than 2 years, with the majority younger than 1 year; however, older children up to adolescence may also be victim^.'^.^" The abused child may present with a variety of symptoms, including

breathing difficulty, irritability, lethargy, poor feeding, and seizures." The clinical outcome depends on the severity of the injuries sustained. Minor disabilities may be present, such as visual disturbance, extremity weakness, and seizures.18 Children with severe impairment, such as mental retardation, or those existing in a vegetative state require institutional placement. It is important to recognize the CT findings encountered in child abuse; these findings may be the only signs of abuse because commonly there is no external evidence of injury.I3 Clinical features may not allow the differentiation of the abused child from the child injured in an accident. The mechanism of injury in child abuse was previously thought to be caused by shaking-the so-called shaken


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baby syndrome. Shaking alone, however, does not generate the force required to produce head injury.26 Rather, most victims of child abuse have evidence of blunt trauma to the head, and it is the force of the blunt impact that is responsible for the observed head injuries." The child is likely first shaken and subsequently thrown, and the head strikes an object-the so-called shaken impact syndrome.13 The most common CT finding seen in child abuse on early-generation CT scanners was an acute interhemispheric SDH located in the parieto-occipital area (Fig. 9-47). The SDH is secondary to tearing of the bridging cerebral veins at their attachment to the falx. Infarction or cerebral swelling in the parieto-occipital lobes was a frequent associated a b n ~ r m a l i t y . ' ~The ~ J ~most ~ common finding observed on later-generation CT scanners is SAH.18 Other findings frequently seen include cerebral edema, intraparenchymal hemorrhage, SDH, infarction, and s M 1 fracture. It may sometimes be difficult to differentiate interhemispheric SDH from SAH, and in some instances, they may coexist.18 In children who are victims of strangulation, large infarctions and SDHs may be present, usually involving the supratentorial brain.16 Skull radiographs should be obtained in victims of child abuse because fractures may not be evident on CT scans. Radiographic features of skull fractures may allow the differentiation of the abused child from the child injured in an accident.81These features are multiple, bilateral fractures that cross suture lines. Focal or diffuse atrophy with sulcal and ventricular enlargement is evident on repeat CT scans in all patients; infarction is evident in some patient~.l*J~~ Although CT scans are performed in acutely injured patients to exclude a surgical lesion, MRI studies should

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be used when the clinical symptoms do not correlate with the CT findings. MRI is also more useful in the evaluation of subacute and chronic head injury because the technique is more sensitive than CT scans in the detection of small SDH, cortical contusion, and diffuse axonal injury. The advantage of MRI lies in the ability to determine the age of subdural blood on the basis of signal intensity. The presence of SDHs in various stages of evolution, signifying a difference in age, may be an indicator of child abuse.loO

Complications of Central Nervous System Trauma Hydrocephalus Hydrocephalus is a possible complication of head injury. Diffuse brain injury or obstruction of CSF pathways results in enlargement of the ventricular system. In the former, as diffuse edema resolves, there is a gradual enlargement of the ventricular system, which retains a normal configuration.* Noncommunicating hydrocephalus may be evident initially or shortly after injury, with intraventricular hemorrhage impedmg the outflow of CSF at the level of obstruct i ~ n Communicating .~~ hydrocephalus is the result of decreased absorption of CSF at the level of the arachnoid villi over the cerebral convexities. This may be observed as a gradual enlargement of the ventricular system on serial CT scan.66Enlargement of the ventricular system occurs in the majority of patients within 2 weeks of injury, however, it may rarely develop over several months to 1 year after injury?5 The clinical outcome in patients who experience

Figure 9-47. A and B, Child abuse. Axial CT scans show an acute posterior interhemispheric subdural hemorrhage in the occipital area (arrows).


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Axial CT scan shows ventricular enlargement with massive intraventricular hemorrhage. A shunt tube is present in the right lateral ventricle. Posterior interhemispheric subdural hematoma and frontal lobe contusions are present. B, Ten days later, the intraventricular hemorrhage has resolved, and the ventricles have decreased in size but remain enlarged.

aly is a cystic defect that may or may not communicate hydrocephalus is much worse than in those who do not, with the majority sustaining moderate to severe di~ability.~~with the ventricular system. In the communicating type, The CT appearance of communicating hydrocephalus the defect communicates with the ventricular system or is consists of dilatation of the ventricular system and effaceseparated from it by only a thin layer of tissue. In closed ment of the cortical sulci (Fig. 9 4 8 ) . In the acute stage, porencephaly, the cyst does not communicate with the decreased density representing transependymal fluid shift ventricular system. The CT appearance is that of a wellis present in the periventricular white matter. The transepdefined area of CSF density with no contrast enhanceendymal fluid shift is visible as a thin rim of hyperintensity ment." Shift of the midline structures and the ventricular in the periventricular white matter on proton-density and system is usually toward and rarely away from the defect. T2-weighted MR images. Other findings that may be obMRI studies demonstrate the porencephalic defect to be of served are dilatation of the anterior third ventricle, inferior CSF signal intensity on all pulse sequences. displacement of the hypothalamus, depression of the posterior fornix, and elevation of the corpus callosum-which are seen on sagittal TI-weighted images." Infarction The CSF flow void sign is from the turbulent flow of CSF and indicates the presence of flow in the aqueduct of Infarction may be a sequela of head trauma secondary Sylvius and third and fourth ventricle.lo6 Absence of the to vasospasm, vascular occlusion, or direct vessel damflow void sign in the aqueduct in the presence of hydroage.66 In the acute stage, decreased density or isodense cephalus is an indication of obstruction or stenosis at the cerebral swelling with mass effect and midline shift may level of the aqueduct.lo7Intraventricular hemorrhage within be seen on CT scans (Fig. 949).18.134The use of intravethe aqueduct results in absence of the flow void sign. The nous contrast material demonstrates luxury perfusion flow void sign is present in normal individuals as well around areas of infarction.I8 Focal encephalomalacia or as in patients with normal-pressure hydrocephalus, acute porencephaly with ventricular and sulcal dilatation are seen communicating hydrocephalus, and atrophy." Although the in the chronic stage.66 MRI is more sensitive than CT in flow void sign is present in all of these conditions, it is the detection of infarction. Brain swelling is seen on T1most evident in normal-pressure hydrocephalus and is not weighted images within several hours after the onset of as evident in atrophy and acute communicating hydrocephsymptoms, before any signal change is evident on T2a l ~ s . ~However, ' it cannot be used to differentiate acute weighted images.'" Hyperintense signal may be evident communicating hydrocephalus from atrophy.lo8 between 8 and 24 hours on T2-weighted images, whereas the CT scan may be normal up to 2 days after the onset of A trophy symptoms. Intravascular and meningeal enhancement may Areas of porencephaly may result from head trauma at be present within the first several days after administration the site of intracerebral hematoma or infarction. Porencephof gadopentetate di~neglumine.~~.~"


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Figure 9-49. A, Infarction secondary to assault with a hammer. Unenhanced CT scan shows acute left frontal lobe infarction in the distribution of the left anterior cerebral artery. B, CT scan with bone window reveals nondepressed fracture of the left frontal bone (arrowhead).

Post-traumatic Leak

Infection

A CSF leak indicates abnormal communication between the intracranial and extracranial environments. It most commonly occurs after penetrating injury or fracture along the skull base and usually involves the cribriform plate or the temporal bone. CSF leak indicates communication with the paranasal sinuses and, less likely, the mastoid air cells or the middle ear cavity. The clinical significance ranges from entirely benign, because it is frequently self-limited, to infection and brain abscess if it is associated with persistent extracerebral comm~nication.~~ The most common sites of fractures and CSF leaks are in the sphenoethmoid region of the anterior cranial fossa. Leakage may occur through the nose, mouth, or the middle ear and depends on the location of the fracture. Precise detection of the sites of leakage is difficult. An air-fluid level in the sphenoid sinus suggests a fracture of the cribriform plate, although a CSF leak from anywhere between the frontal sinus and sphenoid bone may result in retrograde flow of CSF into the sphenoid o s t i ~ r n . Most ~'~ CSF leaks are related to high-velocity trauma.68, 97 The demonstration of a post-traumatic leakage site requires thin-section, high-spatial r e s o l u t i ~ n ~g'~ direct ~ coronal scans. Such scans may demonstrate a bony dehiscence of the skull base near a sinus or an air cell and, thus, localize the level of air entry. A cisternogram may be of help if there is an active leak at the time of the study but is otherwise not necessary, particularly when highspatial-resolution, direct coronal scanning is performed (Fig. 9-50).77

Infection of the central nervous system may uncommonly occur as a complication of trauma associated with fracture. Direct extension of microorganisms through a

709

Figure 9-50. Post-traumatic cerebrospinal fluid leak. High-resolution direct coronal CT cistemogram demonstrates leakage of contrast material in the right ethmoid sinus (arrowhead) and the fracture site in the right cribriform plate (arrow).


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Figure 9-51. A, Cerebrit ixial -weighted image (TR = 2500 msec, TE = 80 msec) shows edema in the right frontal lobe. Small, bilateral, convexity subdural hematomas are present. B, Contrast-enhanced T1-weighted image (TR = 500 msec, TE = 15 msec) reveals focus of nodular enhancement (arrow).

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fracture site may result in meningitis, cerebritis, abscess, or, less commonly, subdural or epidural empyema. The initial CT scan is often normal with meningitis. A second CT scan may demonstrate hydrocephalus, effacement of the basal cisterns secondary to inflammatory exudate, and enhancement of the basal cisterns and meninges with intravenous contrast material.15Contrast-enhanced MRI is more sensitive than contrast-enhanced CT in detecting meningeal e n h a n ~ e m e n t Cerebritis .~~ is more readily demonstrated with MRI than with CT.47J0L Hyperintense edema is evident on T2-weighted images, where& nodular enhancement can be seen on contrast-enhanced TI-weighted images (Fig. 9-51). Contrast-enhanced CT and MRI depict intraparenchymal abscess as a ring enhancing mass with surrounding edema (Fig. 9-52).

Tension Pneumocephalus Air may enter the cranial cavity through a fistulous connection in sufficient amounts to cause mass effect?, 32.9' Its mechanism is poorly understood. This is a rare complication usually caused by trauma or surgery to the skull base, it has also been described after infection with gas-forming organisms or congenital defects of the skull base.76

References

Figure 9-52. Abscess secondary to right temporal bone fracture. Contrast-enhanced CT scan shows ring enhancing abscess caused by Staphylococcus in the right temporal lobe.

1 . Ambrose J: Computerized transverse axial scanning (tomography). Part 2: Clinical application. Br J Radiol46:1023-1047. 1973. la. Adams WM, ~ a %RD,Jackson A: The role of MR angiography in the pretreatment assessment of intracranial aneurysms: A comparative study. AJNR Am J Neuroradiol 21:161&1628, 2000. 2. Amendola MA, Osmm BJ: Diagnosis of isodense subdural hematomas by cornput+ tomography. AJR 129693-697, 1977.


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60. Katz DI,Alexander MP, Seliger GM, Bellas DN: Traumatic basal ganglia hemorrhage: Clinicopathologic features and outcome. Neurology 39:897-904, 1989. 61. Kaufman HH, Singer JM, Sadhu VK, et ak Isodense acute subdural hematoma. J Comput Assikt Tomogr 4557-559, 1980. 62. Kelly AB, Zimmerrnan RD,Snow RB,et al: Head trauma: Comparison of MR and CT--experience in 100 patients. AJNR Am J Neuroradio1 9699-708, 1988. 63. Kim KS, Hemmati M, Weinberg PE: Computed tomography in isodense subdural hematoma. Radiology 128:71-74, 1978. i l l K, Hoare R: Growing fractures of the skull. J 64. Kingsley D, T Neurol Neumsurg Psychiatry 41 :312-3 18, 1978. 65. Kishore PRS, Lipper MH, Miller JD, et al: Post-traumatic hydrocephalus in patients with severe head injury. Neumradiology 16: 261-265, 1978. 66. Kon AH, LaRoque RL: Evaluation of head trauma by computed tomography. Radiology 123:345-350, 1977. 67. Lane JL, Flanders AE, Doan HT,Bell RD:Assessment of carotid artery parency on routine spin-echo MR imaging of the brain. AJNR Am J Neuroradiol 12:81%826, 1991. 68. Lantz ET, Forbes GS, Brown ML,Laws ER Jr: Radiology of cerebrospinal fluid rhinnorhea. AJR 135:1023-1030, 1980. 69. Lau LSW, Pike W The computed tomographic findings of peritentorial subdural hemorrhage. Radiology 146:699-701, 1983. 70. Leech PJ, Patterson A: Conservative and operative management for cerebrospinal fluid leakage after closed head injury. Lancet 1: 1013-1016, 1973. 71. Lende RA: Enlarging skull fractures of childhood. Neuroradwlogy 7:119-124, 1974. 72. Lindenberg R, Fischer RS, Durlacher SH, et ak Lesions of the corpus callosum following blunt mechanical trauma to the head. Am J Pathul31:287-317, 1955. 73. Lipper MH, Kishore PRS, Givendulis AK, et al: Delayed intracranial hematoma in patients with severe head injury. Radiology 133:645+9, 1979. 74. Lipper MH, Kishore PRS, Enas GG, et al: Computed tomography in the prediction of outcome in head injury. AJNR Am J Neuroradiol 6:7-10, 1985. 75. Luerssen TG. Heart injuries in children. Neurosurg Clin North Am 2399-410, 1991. 76. Lunsford LD, Maroon JC, Sheptak PE, Albin MS. et al: Subdural tension pneumacephalus. J Neurosurg 50:525-527, 1979. 77. Manelfe C, Cellerier P, Sobel D, et al: Cerebrospinal fluid rhinorrhea: evaluation with metrizamide cisternography. AJR Am J Roentgem1 138:471476, 1982. 78. Mathews VP, Kuharik MA, Edwards MK: Gd-DTPA enhanced MR imaging of experimental bacterial meningitis: Evaluation and comparison with (3T. AJNR Am J Neumradiol9:1045-1050, 1988. 79. McCluney KW, Yeakley JW, Fenstermacher MJ, et ak Subdural hygromas versus atrophy on MR brain scans: "The cortical vein sign." AJNR Am J Neuroradiol 13:1335-1339, 1992. 80. Mew PS, Mukem RV, Panych LP, Jolesz FA: Comparing the FAISE method with conventional dual-echo sequences. JMRI 1: 319-326, 1991. 81. Meservy CJ, Tabin R, McLaurin RL, et al: Radiographic characteristics of skull fractures resulting from child abuse. AJR 149:173175, 1987. 82. Messina AV, Chernik NL: Computed tomography: the "resolving" intracerebral hemorrhage. Radiology 118:609-613, 1975. 83. Meyer CA, Mirvis SE, Wolf AL, et al: Acute traumatic midbrain hemorrhage: Experimental and clinical observations with CT. Radiology 179:813-818, 1991. 84. Milo R. Razon N, Schiffer J: Delayed epidural hematoma: A review. Acta Neurochir (Wien) 84:13-23, 1987. 85. Moller A, Ericson K: Computed tomography of isoattenuating subdural hematomas. Radiology 130:149-152, 1979. 86. Moon KL Jr, Brant-Zawadzki M, Pitts LH, Mills CM: Nuclear magnetrc resonance imaging of CT-isodense subdural hematomas. AJNR Am J Neuoradiol5:319-322, 1984. 87. Morgan MK, Besser M, Johnston I, Chaseling R: Intracranial carotid artery injury in closed head trauma. J Neurosurg 66:192-197, 1987. 88. Nagib MG, Rockswold GL, Sherman RS, Lagaard MW: Civilian gunshot wounds to the brain: Prognosis and management. Neurosurgery 18:533-536, 1986. 89. Newton TH, Troost BT: Arteriovenous malformations and fistulae.

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In Newton TH, Potts DG (eds): Radiology of the Skull and Brain. St. Louis, CV Mosby, 1974. 90. Omar MM, Binet EF: Peripheral contrast enhancement in chronic epidural hematomas. J Comput Assist Tomogr 2332-335, 1978. 91. Osbom AG, Daines JH,Wing SD, Anderson RE: Intracranial air on computerized tomography. J Neurosurg 48:355-359, 1978. 92. Pang D, Horton JA, Herron JM, et al: Nonsurgical management of extradural hematomas in children. J Neurosurg 59:95&971, 1983. 93. Pozzati F,Tognetti F, Cavallo M, Acciani N: Extmdural hematomas of the posterior cranial fossa: Observations on a series of 32 consecutive cases txeated after the introduction of computed tomography scanning. Surg Neurol 32:30&303, 1989. 94. Ramsey RG, Huckman MS: Computed tomography of porencephaly and other cerebrospinal fluid-containing lesions. Radiology 123: 73-77, 1977. 95. Reed D, Robertson WD,Graeb DA, et al: Acute subdural hematomas: Atypical CT findings. AJNR Am J Neuroradiol 7:417-421, 1986. 96. Rengachary SS, Szymanski DC: Subdural hematomas of arterial origin. Neurosurgery 8: 166-171, 1981. 97. Robinson J, Donald PJ: Management of associated cranial lesions. In Pitts L, Wagner FC (eds): Craniospinal Trauma New York, Thieme Medical, 1989. 98. Rosenblum WI, Greenberg RP, Seelig JM, Becker DP: Midbrain lesions: Frequent and significant prognostic feature in closed head injury. Neurosurgery 9:613-620, 1981. 99. Ross JS, Masaryk TJ, Modic MT, et ak Intracranial aneurysms: Evaluation by MR angiography. AJNR Am J Neuroradiol 11:449456, 1990. 100. Sato Y, Yuh WC, Smith WL, et al: Head injury in child abuse: Evaluation with MR imaging. Radiology 173:653-657, 1989. 101. Schroth G, Kretzschmar K, Gawehn J, et al: Advantage of magnetic resonance imaging in the diagnosis of cerebral infections. Neuroradiology 29: 12&126, 1987. 102. Scotti G, Terbmgge K, Melancon D, Belanger G: Evaluation of the age of subdural hematomas by computerized tomography. J Neurosurg 47:311-315, 1977. 103. Seidenwurm D, Meng TK, Kowalski H, et al: Intracranial hemorrhagic lesions: Evaluation with spin-echo and gradient-refocused M R imaging at 0.5 and 1.5 T. Radiology 172: 189-194, 1989. 104. Servadei F, Faccani G, Roccella P, et al: Asymptomatic extradural haematomas: Results of a multicenter study of 158 cases in minor head injury. Acta Neurochir (Wien) 963945, 1989. 105. Shenkin HA: Acute subdural hematoma: Review of 39 consecutive cases with high incidence of cortical artery rupture. J Neurosurg 57: 254-257, 1982. JL, Citrin CM: Magnetic resonance demonstration of nor106. Shemal CSF flow. AJNR Am J Neumradiol7:3-6, 1986. 107. Sherman JL, Citrin CM, Bowen BJ, Gangarosa RE: MR demonseation of altered cerebrospinal fluid flow by obstructive lesions. AJNR Am J Neumradiol7:571-579, 1986. 108. Sherman JL, Citrin CM, Gangarosa RE, Bowen BJ: The MR appearance of CSP flow in patients with ventriculomegaly. AJR Am J Roentgen01 148:193-199, 1987. 109. Shoung HM, Sichez JP,Pertuiset B: The early prognosis of craniocerebral gunshot wounds in civilian practice as an aid to the choice of treatment. Acta Neurochir (Wien) 74:27-30, 1985. 109a. Singer MB, Atlas SW, Drayer BP: Subarachnoid space disease: Diagnosis with fluid-attenuated inversion-recovery MR imaging and comparison with gadolinium-enhanced spin-echo MR imaging--blinded reader study. Radiology 208:417-422, 1998. 110. Sipponen JT, Sepponen RE, Sivula A: Nuclear magnetic resonance (NMR)imaging of intracerebral hemorrhage in the acute and resolving phases. J Comput Assist Tomogr 7:954-959, 1983. 111. Sipponen ST, Sepponen RE, Sivula A: Chronic subdural hematoma: Demonstration by magnetic resonance. Radiology 150:79-85, 1984. 112. Smith AS, Hurst GC, Duerk JL, Diaz PJ: MR of ballistic materials: imaging artifacts and potential hazards. AJNR Am J Neuroradiol32: 567-572, 1991. 113. Smith WP Jr, Batnitzky S, Rengachary SS: Acute isodense subdural hematomas: a problem in anemic patients. AJNR Am J Neuroradiol 2:3740, 1981. 114. Sparacio RR, Khatib R, Chiu J, Cook AW Chronic epidural hematoma. J Trauma 12:435-439, 1972. 115. Strich SJ, Oxon DM: Shearing of nerve fibres as a cause of brain


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damage due to head injury: A pathological study of twenty cases. Lancet 2 : 4 4 3 4 8 , 1961. 116. Tamakawa Y, Hamfee WN: Cerebrospinal fluid rhinorhea: The significance of an air-fluid level in the sphenoid sinus. Radiology 135:101-103, 1980. 117. Tsai FY,Huprich JE:Further experience with contrastenhanced CT in head trauma. Neuroradiology 16:314-317, 1978. 118. Tsai FY, Teal JS, Q u h MJ?, et al: CT of brainstem injury. AJNR Am J Neuroradiol 1:23-29, 1980. 119. Tsai FY, Teal JS, Itabashi HH,et al: Computed tomography of posterior fossa trauma. J Comput Assist Tomogr 4291-305, 1980. 120. Tsai FY, Huprich JE,Gardner FC, et al: Diagnostic and prognostic implications of computed tomography of head trauma. J Comput Assist Tomogr 2:323-33 1, 1978. 121. Turski PA, Korosec F: Technical features and emerging clinical applications of phasecontrast magnetic resonance angiography. Neuroirnaging Clin North Am 2785-800, 1992. 122. Unger EC,Cohen MS, Brown TR:Gradient-echo imaging of hemorrhage at 1.5 Tesla. Magn Reson Imaging 7:163-172, 1989. 123. Van den Heever CM, Van der Merwe DJ: Management of depressed skull fractures: Selective conservative management of nonmissle injuries. J Neurosurg 71:186-190, 1989. 124. Weaver D, Pobereskin L, Jane JA: Spontaneous resolution of epidural hematomas: Report of two cases. J Neurosurg 54:248-251, 1981. 125. Wilberger J, Chen DA: The skull and meninges. Neurosurg CIin North Am 2:341-350, 1991. 126. Winston KR Beatty RM, Fischer EG: Consequences of dural defects acquired in infancy. J Neurosurg 59:83%846, 1983. 127. Yuh WTC, Crain MR, Loes DJ, et al: MR imaging of cerebral

ischemia: Findings in the first 24 hours. AJNR Am J Neuroradiol 12:621-629, 1991. 128. Zimmerman RA, Bilaniuk LT: Computed tomographic staging of traumatic epidural bleeding. Radiology 144:809-812, 1982. 129. Zimmerman RA, Bilaniuk LT, Gemarelli T Computed tomography of shearing injuries of the cerebral white matter. Radiology 127: 393-396, 1978. 130. Z i e r m a n RA, Bilaniuk LT, Dolinska C, et al: Computed tomography of acute intracerebral hemorrhagic contusion. Comp Ax Tomogr 1:271-279, 1977. 131. Zimmerman RA, Bilaniuk LT, Bruce D, et al: Computed tomography of pediatric head trauma: Acute general cerebral swelling. Radiology 1 2 6 4 0 3 4 8 , 1978. 132. Zimmerman RA, Bilaniuk LT, Gemarelli T, et al: Cranial computed tomography in diagnosis and management of acute head trauma. AJR 131~27-34, 1978. 133. Zimmerman RA, Bilaniuk LT, Bruce D, et al: Interhemispheric acute subdural hematoma: A computed tomographic manifestation of child abuse by shaking. Neuroradiology 1 6 3 9 4 0 , 1978. 134. Zimmerman RA, Bilaniuk LT, Bruce D, et al: Computed tomography of cmniocerebral injury in the abused child. Radiology 130:687690, 1979. 135. Zimmerman RA, Russell El, Yurberg E, Leeds NE, et al: Falx and interhemispheric fissure on axial CT. 11: Recognition and differentiation of interhemispheric subarachnoid and subdural hemorrhage. AJNR Am J Neuroradiol 3:635442, 1982. 136. Z i m m e m RA, Bilaniuk LT, Hackney DB, et al: Head injury: Early results of comparing CT and high-field MR. AJNR 7:757-764,1986. 137. Zimmerman RD, Heier LA, Snow RB, et al: Acute intracranial hemorrhage: Intensity changes on seauential MR scans at .ST. AJR 150:651461, 1988.


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Neurodegenerative Disorders Andrei I. Holodny, Ajax E. George, Mony J. de Leon, Sassan Karirni

Advances in magnetic resonance imaging (MRI) have significant1y improved the assessment of neurodegenerative disorders, including the dementias, hydrocephalus, and movement disorders. Often it is difficult to differentiate clinically between various neurodegenerative disorders and even between pathologic processes and the normal aging process. In recent years, specific and sensitive radiologic criteria have been developed to accurately establish the correct diagnosis in these disorders. MRI, with its ability to image the structure and function of the living brain, has become an invaluable tool. The value of understanding the MRI appearance of neurodegenerative disorders will increase as the population ages and as new therapies for these disorders are developed.

Normal Aging The brain changes that occur as part of normal aging include ventricular and sulcal dilatation due to cerebral atrophy (Fig. 10-1).21. 26. 27. 67. 88. 111 Despite these structural changes, cerebral metabolism, as measured by positron emission tomography (PET)with the glucose anaand carbon deoxylogues fluorine deoxyglucose (18-FDG) glucose ("C-2DG) does not decline with age." 25 The severity of normally occurring brain atrophy is variable, ranging from minimal to moderately severe. Sulcal dilatation is a prominent feature of the aging process, even in the absence of ventricular enlargement. Some subjects over 60 years of age show no ventricular enlargement and demonstrate only mild or no sulcal dilatation. These subjects may be more appropriately considered "supernormals" because of the minimal structural changes that are present despite their age. On average, ventricular volume increases approximately twofold between young (ages 20 to 30) and elderly (ages 60 to 80) nonnal subjects. The ventricular volume remains relatively stable up to age 60 years, after which time there is an accelerated increase in size. MRI quantification studies of this type have confirmed the findings reported in the literature on computed tomography (CT) showing that in young normal subjects sulcal volume is approximately equal to that of the ventricular system. In normal subjects over age 60, sulcal volume is greater than that of ventricular v01ume.~" MRI-based measurements have shown that in normal healthy volunteers the volumes of the hippocampus, amygdala, and temporal horn remain stable until age 60, with progressive volume loss seen with more advanced age.86

Dementia Dementia can be caused by myriad pathologic processes: (1) anatomic (e.g., tumor, subdural hematoma, or normal-pressure hydrocephalus), (2) physiologic (electrolyte imbalance), or (3) psychiatric (depression). It is often difficult to establish the cause by clinical examination alone. During radiologic assessment, it is imperative to rule out the presence of treatable causes of dementia. The advent of new pharmacologic agents and neurosurgical techniques has increased the number of dementias, which are at least potentially treatable, making the accurate radiologic assessment even more important.

Alzheimer's Disease Alzheimer's disease (AD)"' has been recognized as one of the most significant health problems of the 20th cenAD is estimated to afaict 10% of people over 65 t~ry.'~ years of age and 50% of individuals over age 85 years.37 It is the most common dementing disorder of the elderly.'19 According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)29 patients with AD present with "a multifaceted loss of intellectual abilities, such as memory, judgment, abstract thought, and other higher cortical functions, and changes in personality and behavior." However, these clinical findings are not specific for AD and often are seen with other causes of dementia. In up to 40% of cases, genetic factors have been implicated in the etiology of AD. Three genes, when mutated, have been identified to cause AD. Some cases of AD are inherited as autosomal dominant trait. In addition, sporadic cases have been identified and account for up to 20% of cases of AD.= A number of pharmacologic trials have been undertaken to improve or stem the advancement of the clinical symptoms of AD. Some have been encouraging. Cholinergic enhancement achieved by phannacotherapy improves cognitive and noncognitive abilities in a number of patients." With the introduction of CT in the 1970s,investigators tried to correlate the degree of cerebral atrophy to the degree of dementia in patients with AD. Several early studies reported ventricular and sulcal enlargement in association with AD.21. 26.27. 46. 75.79. 8a 111. 114 These aaophic changes, therefore, accentuate those of normal aging. However, there was a large overlap between patients with AD and normal age-matched controls. Some patients with severe cortical atrophy had normal cognition, whereas some patients with severe dementia had minimal cortical atrophy.


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Figure 10-1. A, T2-weighted transverse axial image at the level of the bodies of the lateral ventricles in a normal, elderly male volunteer. B, Negative angle (infraorbital-meatal plane) cut at the level of the temporal horns. C, Coronal T1weighted gradient-echo image at the level of the hippocampus. There is mild cortical atrophy. The lateral ventricles are not appreciably enlarged. The temporal lobes show minimal, if any, atrophy. Prominent perivascular (Virchow-Robin) spaces emanate from the lateral ventricles (A), representing a normal variant. Faint peritrigonal T2 hyperintensities in A indicate minimal microvascular disease.

Neuropatholonic evidence has shown severe focal cell loss and ieurofibrillary tangle formation of the subiculum and entorhinal cortex in AD.88The focal pattern of pathology in this region apparently isolates the hippocampal formation from much of its output and input, thereby contributing to the memory disorder characteristic of AD patients. The pathologic changes include senile plaques, neurofibrillary tangles, and granulovacuolar degeneration with progressive neuronal loss and atrophy of the hippocampal formation.'O. There are also neural transmitter deficits and a severe loss in the density of synaptic terminals." In view of the involvement of this region, AD has been characterized as a hippocampal dementia.1° In view of this neuropathologic evidence, imaging studies, including our own,21.26,27.46,75,76r79.80,111, 114 have focused on specific evaluation of the temporal lobes. These studies strongly suggest that AD may be diagnosed in life by MRI or (3. Thus, the role of neuroimaging and the diagnosis of this process, which has long been based on the method of exclusion, is now changing. The transverse fissure of Bichat separates the telencephalon from the diencephalon. A medial part separates the thalamus from the fornix and corpus callosum, and a lateral part is situated between the thalamus and the parahippocampal gyrus. Medially the transverse fissure communicateswith the perimesencephalic cisternm(Figs. 10-2 and 10-3). 74v

Figure 10-2. Normal anatomy of the brain Coronal pathologic section through the medial temporal lobe, including the hippocampus (H). The perihippocampal fissures, including the transverse fissure of Bichat (large arrow), the hippocampal fissure (small arrows), and the choroidal fissure (curved arrows) are seen. The transverse fissure of Bichat communicates with the perimesencephalic cistern (lower left). The choroid plexus and the fimbria (arrow with square) form a physical barrier between the temporal horn (TH) and the choroidal fissure. PH, parahippocampal gyrus. (From Holodny AI, George AE, Golomb J, et al: The perihippocampal fissures: Normal anatomy and disease states. Radiographics 18:653-665, 1998.)


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10-3. Normal brain anatomy. Coronal dia-

gram shows the medial temporal lobe structures, in-

cluding the perihippocampal fissures. The medial aspect is to the left and the lateral aspect is to the right. The perMppocampal fissures are visible but are not

nucleus; H, hippocampus; HF, hippocampal fissure; PMC, perhesencephalic cistern; S, subiculum; TFB, transverse Essure of Bichat. (From Holodny AI, George @, Golomb J, et al: The perihippocampal fissures: Normal anatomy and disease states. Radiographics 18:653'465, 1998.)

Temporal lobe changes are highly sensitive markers of AD.27.46.6 L The use of either CT or MlU negative-angle thin-section cuts that parallel the temporal lobes or corona thin-section MRI scans perpendicular to the axial plane maximizes the demonstration of temporal lobe pathology. Almost all patients with AD show at least a moderate degree of hippocampal atrophy as well as atrophy of the parahippocampal gyrus, dentate gyrus, and subiculum. These atrophic changes lead to enlargement of the transverse fissure of Bichat and the hippocampal and choroidal extensions as well as dilatation of the temporal horn (Fig. 104). Although high-resolution coronal images display this anatomy optimally, even mild hippocampal atrophy and the resultant dilatation of the perihippocampal fissures can be seen on standard MRI and CT imagesn (see Figs. 10-5 and 104). The longitudinal study of normal subjects and patients with AD for structural brain changes shows a greatly increased rate of change in the AD patients as compared with normal subjects.2641 We found that 90% of patients with AD showed progressive atrophy of the temporal lobes when they were longitudinally studied over a 3-year periodZ6(see Fig. 10-12). More important is that the presence of medial temporal lobe atrophy in individuals49 may represent a significant risk factor for the subsequent development of AD." In it appears that an hippocampus not only is a radiologic marker for the presence of AD but also may actually serve as a predictor for the future development of this disorder. In a landmark study by de Leon and coworker^,'^ 86 older adult patients who were either normal

figure 10-5. Clinical Alzheimer's disease. Reverse-angle CT Scan parallel to the hippocampus) an area of decreased density in the medial aspect of the temporal lobe (arrow). The density of this area approaches that of cerebrospinal fluid. This corresponds to dilatation of the perihipp~ampalfissures and is an accurate indicator of hippocampal atrophy. (From Holodny AI, George AE, Golomb J, et al: The perihippocampal fissures: Normal anatomy and disease states. Radiographics 18: 653-665, 1998.)

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Figure 10-6. Presumed Alzheimer's disease in a 60-year-old woman. A, Coronal TI-weighted MR image demonstrates severe atrophy of the hippocampus and dilatation of the perihippocampal fissures. B and C, Reverse-angle axial T2-weighted images in the same patient. These images demonstrate tbe importance of evaluating for prominence of the perihippocampal fissures and hippocampal atrophy in the correct plane. B is inferior to C. In B, the left medial temporal lobe demonstrates prominent perihippocampal fissures (the area of increased signal intensity between the temporal horn and the pons). The right medial temporal lobe on image B fails to demonstrate this area of increased signal intensity. This is because the patient is slightly tilted and one is actually scanning through the area of the parahippocampal gyrus (see Fig. 10-I), not the atrophic hippocampus. An analogous situation exists in C. The dilated perihippocampal fissures are seen on the right. The scanning plane on the left side is directed superior to the perihippocampal fissures and therefore does not demonstrate the area of increased signal intensity associated with dilated perihippocampal fissures. (From Holodny AI, George AE, Golomb J, et al: The perihippoc&pal fissures: Normal anatomy and djseas; states.'~adio~ra~hics 18: 652665, 1998.)


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or who had minimal cognitive impairment were monitored for four years. Dilatation of the perihippocampal fissures at the time of entry into the study was a predictor of future deterioration and development of AD, with a sensitivity of 91% and a specificity of 89%.

Hydrocephalus Classification

1

Hydrocephalus, from the Greek hydro (water) ancl cephalus (brain) is an abnormal accumulation of intracranial fluid (i.e., water on the brain) resulting from a structural or functional block to the normal flow of cerebrospinal fluid (CSF). The ventricles may become significantly enlarged. The diagnosis of hydrocephalus in patients under age 60 years is usually straightforward. In patients over age 60, however, often confounding superimposed changes of atrophy are caused by normal aging and possible coexisting AD.48Hydrocephalus is initially associated with increased intracranial pressure, but it may later reach a state of equilibrium known as arrested, or normal-pressure, hydrocephalus. When the block to the flow of CSF occurs along the ventricular system, the condition is known as obstructive hydrocephalus. Since all hydrocephalus is obstructive, the term intraventricular obstructive hydrocephalus has been proposed as a more accurate description for this type of obstruction. If the block to CSF is distal to the ventricular system, either at the base of the skull or as distal as the level of the pacchionian granulations, the hydrocephalus is described as communicating (i.e., the ventricular system communicates with the extraventricular subarachnoid space). A more accurate term for this condition would therefore be extraventricular obstructive hydrocephalus. The term hydrocephalus ex vacuo is sometimes used tc refer to cerebral atrophy; this term is best a\;oided, how ever, because of its confusing implications. The terms communicating hydrocephulus and noncommunicating (or obstructive) hydrocephalus have prevailed since the early days of neuroradiologic diagnosis. Dandy and BlackfanZ3introduced a color dye (phenolsulfonphthalein) by ventricular catheter into the hydrocephalic ventricular system. If the color dye could be extracted by lumbar

Figwe 10-7. ~ n & h & ~m egain hydrocephalus.

there is dilation of the temporal horn of the lateral ventricle. The hippocampus is displaced medidy, and the perihippocampal fissures are compressed. The choroid plexus (Cb)and the fimbria (F) form a physical barrier between the temporal horn fTH) and the choroidal fissure (CT).CN, caudate nucleus; H, h i p p campus; HF, hippocampal fissure; PMC, perimesencephalic cistern; S, subicalum; TFB, transverse fissure of Bichat. (From Holodny AI, George AE, Golomb J, de Leon MJ, W n AJ:The perihippocam4 fissures: Normal anatomy and disease states. Ra-

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spinal tap within 2 to 3 minutes, the hydrocephalus was then described as "communicating." If the dye did not appear on spinal tap or was greatly delayed, the hydrocephalus was considered obstructive, or "noncommunicating." The CT and MRI features of communicating hydrocephalus are as follows:

1. Early dilatation and rounding of the temporal homs. These features may be the earliest manifestation of ventricular obstruction and may be seen before obvious enlargement of the bodies of the lateral ventricles. In contradistinction, temporal horn dilatation as a manifestation of temporal lobe atrophy occurs later in the progression of a degenerative brain disease and is invariably associated with the presence of enlargement of the perihippocampal fissures (the transverse fissure of Bichat, and the choroidal and hippocampal fissures). The cisternal spaces and their extensions (the perihippocampal fissures) do not communicate with the temporal lobe; therefore, the dilatation of the temporal horn caused by obstructive hydrocephalus may actually displace the hippocampus medially and cause compression of the perihippocampal fissures59(Figs. 10-7 and 10-8). 2. Rounding and enlargement of the frontal horns. Figure 10-8 shows the MRI scan of a 47-year-old woman with hydrocephalus. The scan shows severe lateral and third ventricular dilatation. The frontal horns are ballooned, and the angle formed by their medial walls (the septal angle) is acute. In atrophy, the frontal horns are typically enlarged but not ballooned. The septal angle is often obtuse. 3. Enlargement and ballooning of the third ventricle. In atrophy, the third ventricle tends to enlarge by increasing the distance between its walls, which tend to remain parallel to each other. Ballooning and rounding of the third ventricle are characteristic of hydrocephalus. In the sagittal projection, the roof of the third ventricle may be flattened by the often huge lateral ventricular bodies. 4. Severe dilatation of the bodies of the lateral ventricles and increased height of the ventricles. The degree of dilatation of the lateral ventricles in hydrocephalus is typically notably greater than that occurring secondary to atrophy. The corpus callosum is thinned and bowed, forming an arch. Interpeduncular height may be decreased.35 Typically, a patient with severe ventricular

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Ffgure 10-8. Hydrocephalus in a 47-year-old patient. A, Sag., TI-weighted image demonstrates dilatation of the lateral, third, and fourth ventricles. There is bowing of the corpus callosum. B, Axial fluid-attenuated inversion recovery (FLAIR) image demonstrates marked dilatation of the ventricles out of proportion to the sulci. C and D, Coronal TI-weighted images demonstrate marked dilatation of the lateral ventricles, including the temporal horns. There is no hippocampal atrophy. E, Hydrocephalus is confirmed on this axial T2-weighted image. (From Holodny AI, George AE, Golomb J: Newodegenerative disorders. In Edelman R, Hesselink JR (eds): Clinical Magnetic Resonance Imaging, 2nd ed. Philadelphia, WB Saunders, 1996.)


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dilatation caused by hydrocephalus may show a minimal cognitive deficit. In contrast, a patient with comparably severe ventricular dilatation caused by atrophy usually shows profound cognitive impairment. Note the relatively modest ventricular enlargement in patients with severe dementia. A motoric deficit, especially gait impairment, is a characteristic feature of hydrocephalus. The motoric deficit may be severe to the point that patients may be wheelchair-bound or bed-bound. Ventricular shunting in these patients may have dramatic results, with significant improvement in gait and motor function. 5. Enlargement of the fourth ventricle. This finding presupposes that the hydrocephalus is communicating. In chronic obstructive hydrocephalus, however, the fourth ventricle may also enlarge secondarily from incisural obstruction created by the enlarged ventricles, dilated temporal horns, and swollen temporal lobes, which tend to herniate into the incisural notch. When present, dilatation of the fourth ventricle can be helpful in establishing the diagnosis of hydrocephalus. However, fourthventricular enlargement may be absent or minimal despite the presence of definite hydrocephalus. 6. Sukal efacement. When present, sulcal effacement is usually diagnostic of hydrocephalus in the elderly age group because cortical atrophy is almost invariably present as part of the normal aging process. Hydrocephalus, however, may coexist with large sulci and, in particular, with large sylvian fissures. This occurs when the block is at the level of the high convexity or the pacchionian granulations. Consequently, the sulci and fissures dilate because of the damming of fluid proximal to the block. In effect, the sulci and fissures dilate in the same way as the ventricular system because of the distal obstruction. In such patients, ventricular shunting may lead to collapse of the sylvian fissures, the sulci, and other convexity CSF collecti~ns.~~ 7. Pen'ventricular edema. This finding is seen especially in the periventricular white matter of the frontal horns in acute and subacute phases of hydrocephalus. In older people, however, it is usually not possible to distinguish between periventricular T2 changes resulting from microvascular parenchymal disease (see later) and the periventricular edema of hydrocephalus. In fact, hydrocephalus may lead to chronic microvascular changes, as shown in animal hydrocephalus models.s9It was initially thought that MRI might help identify ventricular enlargement due to hydrocephalus by the presence of a periventricular high-signal halo on T2-weighted images. Because periventricular high-signal changes as a result of microvascular disease are also seen, the finding is therefore nonspecific and not h e l p f ~ lFurthermore, .~ in chronic stages of hydrocephalus, periventricular edema resolves and is not visualized by either CT or MRI.

Obstructive Hydrocephalus The sites where the ventricular system is normally narrow (i.e., the foramina) are particularly vulnerable to obstruction. Causes of intraventricular obstruction at the level of the foramen of Monro include (1) colloid cyst of the

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third ventricle, (2) ependymoma, (3) teratoma, (4) congenital atresia, and (5) involvement by adjacent glioma. The posterior third ventricle may be obstructed by pinealomas and aneurysms of the vein of Galen. Aqueductal obstruction can also occur in association with aqueductal stenosis, periaqueductal gliomas, arteriovenous malformations, and cysts of the quadrigeminal region.

Communicating Hydrocephalus Communicating hydrocephalus may result from previous infection such as meningitis or may be secondary to previous hemorrhage caused by trauma, surgery, or rupture of an aneurysm with subarachnoid hemorrhage. It is also seen in association with Arnold-Chiari malformation and in the presence of subarachnoid seeding of tumor (meningiocarcinomatosis). A functional hydrocephalus in the presence of elevated CSF protein is seen in association with spinal cord tumors, typically ependymomas. Overproduction of CSF caused by choroid plexus papilloma or carcinoma may also result in hydrocephalus.

Normal-Pressure Hydrocephalus An idiopathic form of communicating hydrocephalus, usually seen in older adults and known as normal-pressure hydrocephalus (NPH), was described originally by Adarns and Hakim and their colleag~es.~. 56 These authors reported a clinical triad of gait impairment characterized as magnetic gait, dementia, and urinary incontinence. Symptoms can be relieved by ventricular shunting, with the most dramatic improvement usually seen in gait. The typical patient with NPH who is likely to respond rn a shunt exhibits a mild cognitive impairment along with a significant gait disturbance. Differentiating NPH fiom cerebral atrophy can be extremely difficult. Initial enthusiasm for the concept of NPH as a treatable cause of dementia and gait impairment resulted in shunt procedures in patients who either failed to respond or showed an initial improvement but subsequently continued to deteriorate. Because of these discouraging results, the number of shunt procedures for NPH in the elderly has significantly decreased. The failure of patients to respond to the shunt procedure probably resulted from erroneous diagnosis of hydrocephalus in patients who were suffering from degenerative brain disease such as cerebral atrophy associated with AD. This has led to more stringent criteria to identify potential shunt candidates. These criteria (2) continuous include (1) radioisotope ci~temography,~ intracranial pressure recor~lings,~~ (3) spinal effusion,g0and (4) CT cisternography with intrathecal iodinated contrast material.36Despite these criteria, a reliable study predicting shunt outcome has not been established. In terms of MRI, two approaches can be used to differentiate NPH from cerebral atrophy: the anatomic approach and the functional approach. Anatomically, in patients with AD, volume loss of the hippocampus develops and resultant dilatation of the perihippocampal fissures ensues (see Fig. 10-4). Patients with NPH have dilation of the temporal horn (Fig. 10-7).61Although the hippocampus and the


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Figure IU-Y. L a Alzneuner s alsease m a woman. KeVerSedisease in a 73 u-old patient. angle axial TI-, Jted MR image ( ~ l ~ b~a l ~ t ~ scale f i ~ Figure ~ ~ t10-10. i ~ Alzheimer's ~ Axial n-weightd images angled parallel to the hippocampi = 5). There is decreased signal intensity between the temporal demonstrate marked of the hippocm~usand marked horns and the perimesencephalic cistern. This represents dilatation dilatation of the pefihippocm~alfissures. BY comparison, the of the perihippocampal fissures (PHFs) and atrophy of the strucventricles and cortical sulci are only mildly dilated. Compare tures of the temporal lobe, including the hippocampus. with Figures 10-11 and 10-12. (From Holodny AI, waxman R, The size of the PHFs was assessed as moderately dilated. CornGeorge AE, et al: MR differential diagnosis of normal-pressure pare with Figures 10-11 and 10-12. (From Holodny AI, Waxman hydrocephalus and Alzheimer disease: Significance of the perihipR,G~~~~~AE, et al: MR differential diagnosis of nomal-pressure p0cmpd fissures. kTNR Am J Neuroradiol 19:813-819, 1998.) hydrocephalus and Alzheimer disease: Significance of the perihipp-ocampa fissures. A M Am J ~euroradiol19:813-819,-1998.)

Figure 10-11. Reverse-angle axial TI-weighted MR image of normalpressure hydrocephalus in a 72-year-old man who improved after the placement of a ventriculoperitoneal shunt. There is no abnormally decreased signal intensity of the structures of the medial temporal lobes; therefore, there is no dilatation of the perihippocampal fissures or atrophy of the structures of the medial temporal lobe, including the hippocampus. The size of the perihippocampal fissures was graded as normal. This is in contrast to the patients from the group with Alzheimer's disease in Figures 10-9 and 10-10. There is dilatation of the temporal horns to a degree similar to patients from the Alzheimer group. (From Holodny AI, Waxman R, George AE, et al: MR differential diagnosis of normal-pressure hydrocephalus and Alzheimer disease: Significance of the perihippocampal fissures. N N R Am J Neuroradiol 19:813-819, 1998.)


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perihippocampal fissures are best seen in the coronal plane on MRI, it is important to stress that the anatomic changes occurring in NPH and AD can be appreciated to a large degree on axial MRI and CT (Figs. 10-9 to l&12)?9 Occasionally, patients with NPH present with dilated sylvian fissures and rarely with focally dilated cortical s ~ l c i . ~In" a number of cases of shunt-proven NPH, there was actually paradoxical decrease in the size of the dilated cortical fissures and sulci that paralleled the decrease in the size of the lateral ventricles following successful shunting. Therefore, sulcal dilatation (especially when focal) should not be taken to imply cortical atrophy, and the maxim that hydrocephalus is defined as ventricles dilated out of proportion to the sulci does not always apply (Figs. 10-13 and 10-14). Because AD is rather prevalent in the elderly, it can occasionally coexist with NPH. Earlier literature suggested that patients with dementia due to AD are not candidates for intraventricular shunting. However, more recent work suggests that for patients with accurately diagnosed NPH, concomitant AD does not strongly influence the clinical response to shunt p l a ~ e m e n t . ~ Another MFU approach to the diagnosis of NPH is the quantification of CSF flow in the aqueduct. Work by Bradley and coworkers14 has demonstrated that in patients with shunt-proven NPH, the CSF stroke volume and CSF velocity in the aqueduct are both increased. However, the presence or absence of a flow void in the aqueduct does not appear to be an accurate predictor of shunt res onse l4

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In summary, using the combination of radiologic and clinical criteria in conjunction with the results of measurements of cerebral blood flow and cerebral metabolism, we may more reliably and with greater accuracy identify patients with hydrocephalus who are likely to respond to shunt. Functional MRI techniques now becoming available may noninvasively provide similar functional information as that derived from PET and single photon emission computed tomography (SPECT). As a result of these advances, interest has been renewed in the surgical management of patients with hydrocephalus.

Pick's Disease

Pick's disease, another cause of dementia in adults, was first described in 1892.97The onset of dementia is often in the presenile age group, and a familial occurrence has been rep0rted.5~Pick's disease is much less prevalent than AD. The clinical presentation in most patients is suggestive of frontal lobe damage. There is an insidious deterioration in intellectual capacity and difficulty in concentration and memory. There is a slow but steady progression to marked dementia, which is usually more rapidly progressive than with AD. On pathologic examination, there is atrophy of the brain, particularly of the frontal lobes and the anterior aspects of the temporal lobes. The parietal and occipital lobes are usually spared. Histologically, there is an intense loss and L&-:l.-iJ misalignment of neurons as well as subcortical gliosis in T $ ' * . ; the affected areas of the brain. Many of the remaining neurons are small and contain characteristic intracytoplasmic, argentophilic inclusion bodies (Pick's bodies), which are well seen with, Bielschowsky silver stain and antibody imrn~nostaining.~, Prior to the aifv'e'i ' of cross-sectional imaging, Pick's disease could be definitively diagnosed only at autopsy; however, the introduction of CT and MRI has allowed for the accurate diagnosis of Pick's disease in vivo and to differentiate it from other neurodegenerative disorder^.^^ Radiographically, Pick's disease parallels the findings seen on pathologic studies, and marked atrophy of the anterior temporal and frontal lobes are characteristics. The sulci of these lobes become so atrophic that they have been described as icicle-like. There is usually a sparing of the posterior aspect of the superior frontal gyrus and the brain posterior to it.33

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Leukoencephalopathy of Aging, Multi-Infarct Dementia, and Binswanger's Disease Figure 10-12. Reverse-angle axial TI-weighted MR image of a

patient with normal-pressure hydrocephalus. There is a mild degree of decreased signal intensity of the structures of the medial temporal lobes. Therefore, the size of the perihippocampal fissures was graded as mildly dilated. Compare with Figures 10-9 and 10-10. (From Holodny AI, Waxman R, George AE, et al: MR differential diagnosis of normal-pressure hydrocephalus and Alzheimer disease: Significance of &e perihip&xamial fissures. AJNR Am J Neuroradiol 192313-819, 1998.)

MRI is exquisitely sensitive to the detection of white matter disease. As in the atrophic changes described in the first part of this chapter, understanding the MIU characteristics and the underlying pathophysiology can allow one to arrive at the accurate diagnosis. Since this chapter focuses on neurodegenerative diseases, it covers only the limited number of white matter diseases that apply to this category. Long repetition time (TR) (T2, proton-density) and fluidattenuating inversion recovery [FLAIR] hyperintensities are common in the elderly.45 These white matter lesions


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Figure 1&13. Shunt-proven normal-pressure hydrocephalus in a patient with prominent focal sulcal dilatation. Axial CT scans through the bodies of the lateral ventricles (A) and third ventricle (B) and midsagittal MR image (C) demonstrate marked dilatation of the lateral ventricles. The temporal horns are moderately enlarged. The tlrird ventricle is severely dilated and rounded. There is marked dilatation of the following sulci: the sylvian fissures bilaterally, the centtal sulci bilaterally, the anterior aspect of the interhemispheric fissure, the left parieto-occipital fissure and the left calcarine fissure. In addition, there is marked focal dilatation of the cingulate sulcus on the right, the precentral sulcus on the left, and the frontal sulci bilaterally. There is also dilatation of the suprasellar and quadrigeminal plate cisterns. The remaining sulci are compressed. There is no evidence of dilatation of the choroidal and parahippocampal fissures, hippocampal atrophy, or cerebellar or brain stem abnormalities. (From Holodny AI, George AE, de Leon MJ, et al: Focal dilatation and paradoxical collapse of cortical fissures and sulci in patients with normal-pressure hydrocephalus. J Neurosurg 89:742-747 1998.)

are typically patchy or punctate and involve the peritrigonal region preferentially. The second most common area involves the white matter adjacent to the frontal horns. Brain stem lesions are less common. Typically, this process spares the arcuate fibers and the corpus callosum. Variously termed leukoencephalopathy, l e ~ k o a r a i o s i s , 'deep ~ - ~ ~white matter ischemia, or white matter hyperintensities of aging,

the lesions are strongly related to age and have increasing prevalence in individuals over age 60 year^.^ It is also seen earlier and to a greater degree in patients with microvascular diseases, such as diabetes and hypertension. White matter is more susceptible than gray matter to chronic ischemic changes because it is supplied by long, smallcaliber vessels, which are affected these diseases.


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Figure 10-14. Normal-pressure hydrocephalus in a 68-yeru-old man with paradoxical collapse of the sylvian fissures. A k d B, Axial TI-weighted imaget? demonstrate enlarged lateral ventFicles, including the te~lkporalhorn as well as moderately distended sylvian fissures. Several months after successful shunting, the patient returned with recurrePlt symptoms. C, A CT scan demonstrated evidence of shunt failure with distention of the lateral ventricles. Sxlrian fissure dilatation was also present. D,Wowing shunt revision, a CT scan demonstrated a decmme in the size of the lateral ventricles as well as a decrease in the size of the sylvian fissures. (From Holodny AL George AE, de LRon hU, et al: Focal dilatation and paradoxical collapse of cortical fissures and sulci in patients with normalpressure hydrocephalus. J Neurasurg 89:742-747,1998.) .

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Leukoencephalopathy cannot be considered a benign entity.16 We and others have found that these brain changes are related to gait disturbances and increased incidence of falls in the deficits of fine motor coordination,"' and an increased frequency in cerebral infarcts. ". 69-In The increased incidence of falls is particularly of concern in older people.83The microvascular lesions themselves are not associated with dementia; however, the cognitive deficit associated with preexisting AD or other dementing disorders may be potentiated by the presence of the white matter lesion." Autopsy work, including our own, has shown changes of the hypertensive type in the white matter associated wit11 hyalinosis of arterioles and rarefaction of the white matter.19."-52* loo In addition, mild gliosis, increased interstitial fluid, and "myelin pallor" are seen. Frank infarction occurs in more advanced cases and can be seen as welldefined areas of decreased signal intensity on the T1weighted images. The T1 characteristics allows one to differentiated leukoencephalopathy from frank infarction. Multiple-infarct dementia (MID) is the second most common cause of dementia in the elderly representing 10% to 20% of cases in patients over 65 years old.IZ1Clinically, these patients present with a sudden onset of dementia, day-to-day fluctuation, and spontaneous improvement early in the disease. These patients present radiographically with focally dilated fissures and multiple areas of focal cortical volume loss. Multiple subcortical infarcts and infarcts involving certain strategic structures (e.g., parts of the thalamus, caudate, or genu of the internal capsule) can also result in dementia.8' In 1894, Binswangef described a slowly progressive disease characterized by loss of memory and intellectual impairment associated with recurring neurologic deficits. Binswanger was apparently describing a type of multiinfarct dementia with severe hypertensive type microvascular changes, multiple subcortical infarcts, and dementia. The presence of periventricular T2 hyperintensities on MRI scans should not prompt a diagnosis of Binswanger's disease or multi-infarct dementia unless evidence clearly shows that infarcts are also present and that dementia is clinically present. Multiple infarcts, whether cortical or subcortical and especially when bilateral, may be associated with dementia. One should also keep in mind that even numerous subcortical infarcts may lead to only mild dementia. Because periventricular white matter hyperintensities are widely prevalent, especially in the elderly, the terms multi-infarct dementia and Binswanger 's disease should not be used to describe these radiologic findings." 45s

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Creutz er&t-~akob .-. Disease Creutzfeldt-Jakob disease (CJD) is a rare cause of rapidly progressive dementia and is one of several associated neurodegenerative illnesses whose pathogenesis is related to a small, nonviral, 30- to 35-kD proteinaceous infectious particle known as a prion. The loci of pathology involve the cerebral and cerebellar cortices as well as the basal ganglia, where neuronal loss, reactive astrocytosis and the formation of cytoplasmic vacuoles within the glia and neurons give the tissue a characteristic spongiform appear-

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ance on light microscopy. All of these changes occur in the absence of an inflammatory response. The clinical syndrome is typically one of rapid cognitive decline, often with psychosis and delirium. Motor abnormalities of cerebellar dysfunction can appear, and almost all patients evidence pronounced myoclonus prior to the final phase of deepening umesponsiveness and coma. The time course of the disease from presentation until death is usually less than 1 year. In the very early stages of the disease, CT and even MRI findings may be normal.L* Early changes are symmetrical increased signal intensity in the basal gangliaIJ.30. s5. l i 8 and occasionally in the white matter.l3l Occasionally, the changes in the basal ganglia occur before the typical clinical and neurophysiologic signs of CJD de~elop.'~' In three patients, cortical diffusion-weightedimaging abnormalities were reported to occur before the onset of abnormal signal in the basal ganglia on routine sequences. The year 1986 heralded the appearance of a new form of CJD-bovine spongiform encephalitis (BSE), or "mad cow disease." This new variant (nvCJD) was first detected in humans in 1996. The possibility of direct transmission of BSE from cows to humans has raised serious concerns, especially in nvCJD tends to affect a younger population, with a median age at death of 29 years.129The earliest MRI lindings are abnormal signal intensity on the 132 long TR-weighted images of the pul~inar.'~~. During the late stages of the disease, significant atrophy develops and progresses rapidly.'25Symmetrical increased T2 signal abnormality with mass effect in the occipital cortex, predominantly in a gray matter distribution, has been reported.38 A study using magnetic resonance spectroscopy (MRS) detected a decrease in N-acetylaspartate (NAA) and other metabolites in late CJD.53

Huntington's Disease Huntington's disease (HD) is a degenerative neurologic disease that is inherited in an autosomal dominant fashion with complete penetrance. It is determined by a gene localized to the short arm of chromosome 4. Patients usually become symptomatic before age 50 and tend to present with abnormalities of affect and personality. Within time, dementia becomes evident, accompanied by gradual disintegration of motor control and the emergence of choreoathetoid movements. Occasionally, rigidity rather than chorea is the most salient motor abnormality (Westphal variant). Neuropathologically, the most conspicuous finding in patients with HD is atrophy of the basal ganglia, generally proceeding medial to lateral and dorsal to ventral.5899. Degenerative changes can also affect the frontal and temporal cortices. The degenerative process is accompanied by diminished neurotransmitter concentrations of acetylcholine and gamma-aminobutyric acid (GABA). In early cases, neuronal loss is generally first appreciated in the head of the caudate.'26 This has been confirmed by a number of MRI studies showing atrophy of the basal ganglia in patients with HD,which is most prominent in the head of the caudate, appearing as focal enlargement of frontal horns on imaging. The atrophy of these structures worsens as the disease progres~es.~ MRS studies indicate a decrease in


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Figure 10-15. Huntington's disease in a 33-year-old man. Axial proton-density (A) and T2-weighted (B) images demonstrate abnormal signal intensity in the putamen and caudate nuclei. (From Sclar G, Kennedy CA, Hill JM: Cerebellar degeneration associated with HIV infection [letter]. Neurology 54:1012-1013, 2000.)

NAA and creatine in the basal ganglia of 60% in symptomatic patients and a decrease of 30% in presymptomatic gene carriers.114 A number of investigators have reported that in addition to atrophic changes, patients with I-ID present with areas of abnormal T2 signal hyperintensity in the basal ganglia (Fig. 10-15). Two groups have reported that such changes are present in all patients with the rigid form of HD but only occasionally in the classic hyperkinetic form.". lo7 More advanced cases of HD present with atrophy of other parts of the central nervous system, including the olives, pons, and cerebellum108;the thalamus, mesial temporal lobe and white matter tracts70; and the cerebral cortex.IlS Cortical atrophy, as seen on the MRI scan, has been shown to correlate well with specific neuropsychological deficits.lI5

Parkinsan's Disease Parkinson's disease (PD) affects approximately 1% of the population over 50 years of age and is perhaps the most common neurologic explanation of progressive motor impairment among older adults. Onset of symptoms is typically seen between 40 and 70 years of age. The disease is caused by an acceleration of the normal agedependent depletion of dopamine synthesizing pigmented cells within the pars compacta of the substantia nigra. The loss of dopaminergic input to the striatum caused by this cell loss produces a characteristic syndrome, of which the most salient features are progressive bradykinesis, rigidity,

masked facies, hypophonia, festinating gait with stooped posture, and a coarse resting tremor. Dementia may occur in up to 30% of patients, which may reflect the concomitant presence of AD. In addition to the substantia nigra, patients at autopsy reveal a loss of pigmented cells within the locus ceruleus and the dorsal motor nucleus of the vagus. These regions exhibit reactive astrocytosis, and some of the remaining neurons contain eosinophilic cytoplasmic inclusions called Lewy bodies. Radiographs show a significant narrowing of the pars compacta of the substantia nigra, best visualized on T2weighted sequences. Multiple studies have demonstrated very little overlap between patients with PD and normal age-matched controls.15." Early PD has been reported to show a loss of signal in a lateral to medial gradient of the pars compacta, thereby indicating the potential for detecting presymptomatic disease.63 The diagnostic role of MRI in patients with suspected PD is to exclude other neurodegenerative syndromes with a clinical presentation similar to that of PD.17.110 With the advent of deep brain stimulator (DBS) implants, which have been successful in treatment of medically refractory tremor, MRI plays an important role in targeting the nucleus ventralis intermedius (Vim) of the thalamus during the stereotactic implantation of the device.5

Multiple-System Atrophy In contrast to PD, in which extrapyramidal clinical manifestations result from a loss of dopaminergic input to the


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striatum, other diseases produce progressive motor dysfunction by means of primary degenerative processes that simultaneously affect groups of several subcortical anatomic structures. This group of disorders has been referred to by the clinical term Parkinson's plus syndrome or by the anatomic term multiple-system atrophy (MSA). Various forms of MSA can present with a clinical picture similar to that of PD. These two disorders can be especially difficult to differentiate clinically early on in the presentation. Neurologically, MSA is suspected when patients presumed to have PD do not respond to L-dopa therapy. Anatomically, the patient's disease is due to the involutional change undergone by various combinations of striatal, cerebellar, pontine, brain stem, and spinal cord nuclei. With the growing ability of MRI to show detailed anatomy, a number of recent investigators have demonstrated the atrophic and signal abnormality changes in patients with the various forms of MSA, which allows differentiation from PD. One neuropathologic pattern of MSA is termed striatonigral degeneration (SND). In patients with this condition, a PD-like syndrome results from a progressive atrophy and neuronal depletion of the putamen and caudate, accompanied by cell loss within the zona compacta of the substantia nigra without Lewy body deposition. Radiographically, patients with SND also exhibit thinning of the pars compacta of the substantia nigra, a presentation similar to that seen in PD.8. 116 This is expected from the histopathology of the disease. However, SND also exhibits a number of specific findings that allows one to differentiate it from PD radiographically. The most prominent distinguishing feature of SND is the presence of hypointensities in the p~tamen,'~.~.117.1w lu thought to be due to increased iron depo~ition.~~.Focal atrophy in the quadrigeminal plate1" and putarnenw has also been reported. These findings are not seen in PD. When MSA patients present with herniparkinsonism, MRI findings have consistently demonstrated abnormalities, including (1) T2 hypointensity of the posterior lateral putamen and (2) atrophy of the putarnen, caudate nucleus, and pars compacta of the substantia nigra on the contralateral ~ide.7~. 78 Another form of MSA is olivopontocerebellar atrophy (OPCA) in which degeneration involves the pontine nuclei, transverse pontine fibers, middle cerebellar peduncles, cerebellar cortex, and inferior olives. Clinically, the syndrome results in progressive ataxia and bulbar dysfunction. OPCA is typically a disorder of adult onset and can be both familial (usually autosomal dominant) as well as sporadic. Radiographically, patients present with atrophy of the transverse fibers of the pons, ~erebellum,8~, Iz0 and middle cerebellar peduncleslo6 (Fig. 10-16). There is a mild decrease in the width of the pars compacta of the substantia nigra? The T2 hypointensity seen in SND is not seen in OPCA.lZ3These radiographic findings are in concert with the histopathology. They appear to be specific for the disease and should be identified before the diagnosis of OPCA is made. Other cases have been identified in which the anatomic loci of degenerative change are even more widespread and involve brain stem motor nuclei, corticospinal pathways, and such spinal cord structures as the dorsal columns,

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anterior horns, and spinocerebellar tracts. OPCA can occur independently or in tandem with SND. Many patients with MSA undergo cell loss within the autonomic intermediolateral nuclei of the spinal cord, producing symptoms of orthostatic hypotension, anhidrosis, incontinence, and sexual dysfunction in addition to the those of MSA. This is known as Shy-Drager syndrome (SDS). MRI findings reflect the atrophic changes and T2 abnormalities seen in MSA.%,loS

Progressive Supranuclear Palsy Progressive supranuclear palsy (PSP) is a neurodegenerative disorder without known familial predilection that affects middle-aged and older adults. The pathologic changes involve neuronal loss and astrocytosis within the globus pallidus, dentate nucleus, and several diencephalic structures, including the subthalarnic nucleus, periaqueductal gray matter, and pretectal regions. Singlestranded neurofibrillary pathology is a distinctive histopathologic feature of this condition. The clinical presentation is characterized by pseudobulbar signs, supranuclear oculomotor disturbances, axial dystonia, gait dysfunction, and dementia. Radiographically, patients with PSP present with atrophy of the pretectum, dorsal pons, tectum and midbrain.4 In addition, decreased T2 relaxation times have been reported in the superior colliculi, globus pallidus, and putamen, which are more pronounced than in patients with MSA.33 These radiographic findings are confirmed by the histopathology of the disease and are useful in distinguishing PSP from clinically similar entities such as PD.33-lo9

Friedreich's Ataxia Friedreich's ataxia (FA) is a progressive spinocerebellar degeneration transmitted both by autosomal dominant and recessive modes of inheritance that affect both children and young adults. Spinal cord degeneration involves the dorsal columns, lateral corticospinal tracts, Clarke's column, and spinocerebellar tracts. Degeneration also occurs within the dorsal root ganglia, dentate nucleus, cerebellar vermis, and inferior olive. Children typically present with ataxia and are often incapable of walking by 5 years of age. Later, bilateral Babinski signs with areflexia, tremor, slurred speech, and nystagmus appear. Other associated abnormalities include pes cavus deformity, kyphoscoliosis, and cardiomyopathy. Radiographic findings include FA spinal cord atrophy, which is often severelZ8and which is seen even in early cases.89Moderate cerebellar or bulbar atrophy is occasionally seen.128In advanced cases, atrophy of the cerebellar vermis and medulla has been reported (Fig. 10-17)." :

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Amyotrophic Lateral Sclerosis Amyotrophic lateral sclerosis (ALS), is the most common form of a broader class of motor system diseases characterized by primary degeneration of the motor neurons within the brain, brain stem, and spinal cord. Patients


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Figure 10-16. Olivopontocerebellar atrophy in a 57year-old woman who presented with slight unsteadiness 2 years earlier. The symptoms have since progressed. At the time of this MRI study, she was experiencing swallowing difficulties, abnormal eye movements, and severe 'ifficulty walking. Sagittal TI-weighted (A)), axial TIreighted (B), and two axial T2-weighted (C and D) images demonstrate atrophy of the transverse fibers of "le pons, the cerebellum, the middle cerebellar peduncles, nd the inferior olives. E, Axial T2-weighted image lrough the lateral ventricles fails to demonstrate atrophy r hydrocephalus. (From Holodny AI, George AE, Go)mb J: Neurodegenerative disorders. In Edelrnan R, Hes:link JR [eds]: Clinical Magnetic Resonance Imaging, *nd ed. Philadelphia, WB Saunders, 1996.)

typically present with progressive muscle weakness and limb and truncal atrophy combined with signs of spacticity. Mean age at the time of diagnosis is 55 years, and the incidence of new cases is 1 per 100,000 population.I8 Familial transmission is seen in 10% of the cases as both

autosomal dominant and recessive traits and sporadic in the remaining 90% of the cases.Il2 Prognostically, about 50% of patients die within 3 years and 90% die within 6 years following onset of symptoms. In ALS, both anterior horn neurons in the spinal cord


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Figure 10-17. gressive Friedreich's ataxia in a 4-year-old girl. Two sagittal (A and B) and two axial (C and D) TI-weighted images demonstrate severe atrophy of the cerebellum. (From Holodny AI, George AE, Golomb J: Neurodegenerative disorders. In Edelman R, Hesselink JX [eds]: Clinical Magnetic Resonance Imaging, 2nd ed. Philadelphia, WB Saunders, 1996.)

as well as pyramidal Betz cells within the primary motor cortex @recentral gyms) undergo progressive involutional change. Histopathologic features include astrocytosis, lipofuscin deposition, and, occasionally, the accumulation of intracytoplasmic inclusion bodies. Secondary degeneration of the descending corticospinal fibers occurs with variable demyelination and lipid-filled macrophage buildup. Corticospinal tract involvement is most evident within the lateral and anterior columns of the lower spinal cord but can also affect the cerebral white matter of the internal capsule, corona radiata, and centrum semiovale. MRI reveals abnormal signal intensity along the motor pathways. In the precentral gyms (i.e., the location of the perikarya of the motor neurons, which are affected by ALS), T2 hypointensity is thought to represent increased deposition of iron.g1.130 In the subcortical white matter tracts, patients with ALS typically demonstrate abnormal hyperintensity on long TR images (T2, proton-density, and FLAIR). These areas of signal abnormality extend from the motor cortex to the centrum semiovale, the corona

radiata, the posterior third quarter of the internal capsule, and the pons.'. lZ4 Radiologic-pathologic studies have shown that these signal abnormalities represent degeneration of the corticospinal tract and myelin pallor.65 These signal abnormalities are distinctly different from normally appearing areas of hypointensity on T1 and hyperintensity on T2, which represent normal fibers of the corticospinal tract traversing the internal capsule. Similar areas of T2 hyperintensity have been identified in the corticospinal tracts in the spinal cord.39 MRI shows an increase in the mean choline and myoinositol and a decrease in glutamine and N-acetyl in the precentral gyrus.13 Magnetization transfer measurements have also been reported to be sensitive in the early identification of ALS.71 51s

References 1. Abe K, Yorifuji S, Nihikawa Y: Reduced isotope uptake restricted to the motor area in patients with amyotrophic lateral sclerosis. Nemradiology 35:410-411, 1993.


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Chapter 10

2. Adams JH, Duchen LW: Greenfield's Neuropathology. New York, Oxford University Press, 1992. 3. Adams RD,Fisher CM, Hakim S: Symptomatic occult hydrocephalus with "normal" cerebrospinal fluid pressure: A treatable syndrome. N Engl J Med 273:117-126, 1965. 4. Aiba I, Hashizume Y, Yoshida M, et al: Relationship between brainstem MRI and pathological findings in progressive supranuclear palsy--study in autopsy cases. J Neurol Sci 152:210-217, 1997. 5. Alteman RL, Reiter GT, Shils J, et ak Targeting for thalamic deep brain stimulator implantation without computer guidance: Assessment of targeting accuracy. Stereotact Funct Neurosurg 72150153, 1999. 6. Alzheimer A: b r eine eigenartige Erkrankung der Hinuinde. Allg Z Psychiatr Psych Med 64:146, 1907. 7. Alzheimer A: Uber eine eigenartige Erkrankung der Hirnrinde. Zentralb gesamte Neurologie Psychiatrie, 18:177-179, 1907. 8. Aotsuka A, Shinotoh H, Hirayama K, et al: Magnetic resonance imaging in multiple system atrophy. Rinsho ~ h h k e i ~ a k32(8): u 815-821. 1992. 9. Aylward EH, Li Q, Stine OC,et ak Longitudinal change in basal ganglia volume in patients with Huntington's disease. Neurology 48:394-399, 1997. 10. Ball MJ. Fishman M, Hachinski V, et ak A new definition of Alzheimer's disease: A hippocampal dementia. Lancet 1:14-16, 1985. 11. Barboriak DP, Provenzale JM, Boyko OB: MR diagnosis of Creutzfeldt-Jakob disease: Significance of high signal intensity in the basal ganglia. AJR Am J Roentgenol 162137-140, 1994. 12. Baron SA, Jacobs L, Kinkel W: Changes in size of normal lateral ventricles during aging determined by computerized tomography. Neurology 26101 1-1013, 1976. 13. Bowen BC, Pattany PM, Bradley BG, et al: MR imaging and localized proton spectroscopy of the precentral gyrus in amyotrophic lateral sclerosis. AJNR Am J Neuroradiol 21:647458, 2000. 14. Bradley WG, Scalzo D, Queralt J, et al: Normal-pressure hydrocephalus: Evaluation with cerebrospinal fluid flow measurements at MR imaging. Radiology 198:523-529, 1996 15. Braffman BH, Grossman RI, Goldberg HI, et ak MR imaging of Parkinson's disease with spin-echo and gradient-echo sequences. AJR Am J Roentgenol 152159-195, 1989. 16. Briley DP, Haroon S, Sergent SM, Thomas S: Does leukoaraiosis predict morbidity and mortalitv? Neurology 5490-94, 2000. 17. Brooks DJ: ~ o & h o l o ~ i c aadd l function2 imaging studies on the diagnosis and ~roeression of Parkinson's disease. J Neurol 247 (suipl 2):IIll-Ih8:2000. 18. Brown RH: Amyotrophic lateral sclerosis: Insights from genetics. Arch Neurol541246-1250, 1997. 19. Burger PC, Burch JG, Kunze U: Subcortical arteriosclerotic encephalopathy (Binswanger's disease): A vascular etiology of dementia. Stroke 7:626-631, 1976. 20. Cala LA, Thickbroom GW, Black JL, et al: Brain density and cerebrospinal fluid space size: CT of normal volunteers. Am J Neuroradiol 2:4147, 1981. 21. Convit A, de Leon MJ, Golomb J, et al: Hippocampal atrophy in early Alzheimer's disease: Anatomic specificity and validation. Psychiatr Q 64:371-387, 1993. 22. Cruts M, Van Broeckhoven C: Molecular genetics of Alzheimer's disease. Ann Med 30:560-565, 1998. 23. Dandy WE, Blackfan DK: An experimental and clinical study on internal hydrocephalus. JAMA 61:2216, 1913. 24. de Leon MJ, George AE, Fems SH, et al: Positron emission tomography and computed tomography assessments of the aging human brain. J Comput Assist Tomogr 8:88-94, 1984. 25. de Leon MJ, George AE, Tomanelli J, et al: Positron emission tomography studies of normal aging: A replication of PET III and 18-FDG using PET VI and 1lC-2DG. Neurobiol Aging 8: 319-323. 1987. 26. de Leon MJ, George AE, Reisberg B, et al: Alzheimer's disease: Longitudinal CT studies of ventricular change. AJNR Am J Neuroradi01 10:371-376, 1989. 27. de Leon MJ, Golomb J, George AE, et al: The radiologic prediction of Alzheimer disease: The atrophic hippocampal formation. AJNR Am J Neuroradiol 14897-906, 1993. 28. De Volder AG, Francart J, Laterre C, et al: Decreased glucose utilization in the striatum and frontal lobe in probable striatonigral degeneration. AM Neurol26239-247, 1989.

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57. Hamos JE, DeGennaro W ,Drachman DA: Synaptic loss in Alzheimer's disease and other dementia. Neurology 39:355-361, 1989. 58. Harris GJ, Pearlson GD, Peyser CE, et al: Putamen volume reduction on magnetic resonance imaging exceeds caudate changes in mild Huntington's disease. Ann Neurol 31:69-75, 1992. 59. Holodny AI, George AE, Golomb J, et al: The perihippocampal fissures: Normal anatomy and disease states. Radiographics 18: 653-665, 1998. 60. Holodny AI, George AE, de Lean MJ, et al: Focal dilatation and paradoxical collapse of cortical fissures and sulci in patients with normal-pressure hydrocephalus. J Neurosurg 89:742-747, 1998. 61. Holodny AI, Waxman R, George AE, et al: MR differential diagnosis of normal-pressure hydrocephalus and Glzheimer disease: Significance of the perihippocampal fissures. AJNR Am J Neuroradiol 19:813-819, 1998. 62. Hughes CP, Gado M: Computed tomography and aging of the brain. Radiology 139:391-396, 1981. 63. Hutchinson M, Raff U: Structural changes of the substantia nigra in Parkinson's disease as revealed by MR imaging. AJNR Am J Neuroradiol 2 1:697-701, 2000. 64. Hyman BT, Van Horsen GW, Damasio AR, Barnes CL: Alzheimer's disease: Some specific pathology isolates the hippocampal fonnation. Science 22:1168-1170, 1984. 65. Ishikawa K, Nagura H, Yokota T, Yamanouchi H: Signal loss in the motor cortex on magnetic resonance images in amyotrophic lateral sclerosis. Ann Neurol 33:218-222, 1993 66. Iwasaki Y, Kinoshita M, Ikeda K, et al: MRI in patients with amyotrophic lateral sclerosis: Correlation with clinical features. Int J Neurosci 59:253-258, 1991. 67. Jack CR Jr, Peterson RC, O'Brien PC, Tangalos EG: MR based hippocampal volumetry in the diagnosis of Alzheimer's disease. Neurology 42: 183-188, 1992. 68. Jacoby RJ, Levy R, Dawson JM.Computed tomography in the elderly: I. The normal population. Br J Psychiatry 136:249, 1980. 69. Janota I: Dementia, deep white matter damage and hypertension: "Binswanger's disease." Psycho1 Med 11:3948, 1981. 70. Jernigan TL,Salmon DP, Butters N, Hesselink JR: Cerebral structure on MRI: Part 11. Specific changes in Alzheimer's and Huntington's diseases. Biol Psychiatry 2968-81, 1991. 71. Kato T, Kume A, Ito K, et al: Asymmetrical FDG-PET amd MRI findings of striatonigral system in multiple system atrophy with hemiparkinsonism. Radiat Med 10:87-93, 1992. 72. Kato Y, Matsumura K, Kinosada Y, et al: Detection of pyramidal tract lesions in amyotrophic lateral sclerosis with magnetization transfer measurements. AJNR Am J Neuroradiol 18:1541-1547, 1997. 73. Katzman R: Alzheimer's disease. N Engl J Med 314964-973, 1986. 74. Kemper T: Neuroanatomical and neuropathological changes in normal aging and in dementia. In Albert ML (ed): Clinical Neurology of Aging. New York, Oxford University Press, 1984, pp S 5 2 . 75. Kesslak JP, Nalcioglu 0 , Cotman CW: Quantification of magnetic resonance scans for hippocampal and parahippocampal atrophy in Alzheimer's disease. Neurology 41:51-54, 1991. 76. Kido DK, Caine ED, LeMay M, et al: Temporal lobe atrophy in patients with Alzheimer disease: A CT study. AJNR Am J Neuroradiol 10:551-555, 1989. 77. Kluger A, Gianutsos J, de Leon MJ, et al: Significance of agerelated white matter lesions. Stroke 191054-1055, 1988. 78. Kume A, Shiratori M, Takahashi A, et al: Hemi-parkinsonism in multiple system atrophy: A PET and MlU study. J Neurol Neurosurg Psychiatry 521221-1227, 1989. 79. LeMay M: CT changes in dementing diseases: A review. Am J Neuroradiol 7:841-853, 1986. 80. LeMay M, Stafford JL,Sandor T, Albert M, et al: Statistical assessment of perceptual CT scan ratings in patients with Alzheimer type dementia. J Comput Assist Tomogr 10:8021809,1986. 81. Loeb C, Meyer JC: Vascular dementia. J Neurol Sci 143:31-40, 1996. 82. Lotz PR, Ballinger WE Jr, Quisiling RG: Subcortical arteriosclerotic encephalopathy: CT spectrum and pathologic correlation. Am J Neuroradiol7:817-822, 1986. 83. Masdeu J, Lantos G, Wolfson L: Penventricular white matter lesions correlate with falls in the elderly. Acta Radio1 Suppl 369:392, 1986. 84. McCullough DC,Harbert JC, Di Chiro G, Ommaya AK: Prognostic criteria for cerebrospinal shunting from isotope cisternography in communicating hydrocephalus. Neurology 20:594-598, 1970.

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85. Milton WJ, Atkas SW, Lavi E, Mollman JE: Magnetic resonance imaging of Creutzfeldt-Jakob disease. Ann Neurol 29:438-440, 1991. 86. Mu Q, Xie J, Wen 2,et al: A quantitative study of the hippocampal formation, the amygdala and the temporal horn of the lateral ventricle in healthy subjects 40 to 90 years of age. AJNR Am J Neuroradi0120:207-211, 1999. 87. Mukai E, Makino N, Fujishiro K: Magnetic resonance imaging of parkinsonism. Rinsho Shinkeigaku 29720-725, 1989. 88. Narkiewicz 0, de Leon MJ, Convit A, et al: Dilatation of the lateral part of the transverse fissure of the brain in Alzheimer's disease. Acta Neurobiol Exp 53:457-465, 1993. 89. Nicolau A, Diard F, Fontan D, et al: Magnetic resonance imaging in spinocerebellar degenerative diseases. Pediatric 42:359-365, 1987. 90. Nosaka Y: Hydrocephalus associated with subarachnoid hemorrhage: Clinical study of computed tomography, radioisotope cisternography and constant infusion test. Acta Med Okayama 35:45-60, 1981. 91. Oba H, Araki T, Ohtomo K, et al: Amyotrophic lateral sclerosis: T2 shortening in motor cortex at MR imaging. Radiology 189: 843-846, 1993. 92. O'Brien C, Sung JH,McGeachie RE, Lee MC: Striatonigral degeneration: Clinical, MRI and pathological correlation. Neurology 40: 710-711, 1990. 93. Oliva D, Carella F, Savoiardo M, et al: Clinical and magnetic resonance features of the classical and akinetic-rigid variants of Huntington's disease. Arch Neurol50:17-19, 1993. 94. Ormerud IE, Harding AE, Miller DH, et al: Neuropsychological deficits accompanying striatonigral degeneration. J Clin Exp Neuropsychol 13:773-788, 1991. 95. Pantoni L, Garcia m. The significance of cerebral white matter abnormalities 110 years after Binswanger's report: A review. Stroke 26: 1293-1301, 19%. %. Pastakia B, Palinsky R, Di Chiro G, et al: Multiple system atrophy (Shy-Drager syndrome): MR imaging. Radiology 159:499-502, 1986. 97. Pick A: Ueber die Benziehungen der senile n Himat ophiel zur Aphasie. Prager Med Wochenschr 17:165, 1892. 98. Pickard JD: Adult communicating hydrocephalus. Br J Hosp Med 27:35-40, 1982. 99. Roos RAC, Pruyt JFM,de Vries J, Bots GTA: Neuronal distribution in the putamen in Huntington's disease. J Neurol Neurosurg Psychiatry 48:422-425, 1985. 100. Rosenberg GA, Kornfeld M, Stouring J, Bicknell JM: Subcortical arteriosclerotic encephalopathy (Binswanger): Computerized tomography. Neurology 29: 1102-1 106, 1979. 101. Rother J, Schwartz A, Harle M, et al: Magnetic resonance imaging follow-up in Creutzfeldt-Jakob disease. J Neurol239:404-406, 1992. 102. Rusinek H, de Leon MJ, George AE, et al: Alzheimer disease: Measuring loss of cerebral gray matter with MR imagmg. Radiology 78:109-114, 1991. 103. Rutledge JN,Hilal SK, Silver AJ, et al: Study of movement disorders and brain iron by MR. AJNR Am J Neuroradiol 8:397-411, 1987. 104. Sanchez-Pemaute R Garcia-Segura JM, del Barrio Alba A, et al: Clinical correlation of striatal 1H MRS changes in Huntington's disease. Neurology 53:806-812, 1999. 105. Savoiardo M, Strada L, Guotti F, et al: MR imaging in progressive supranuclear palsy and Shy-Drager syndrome. J Comput Assist Tomogr 13:555-560, 1989. 106. Savoiardo M, Strada L, Girotti F, et al: Olivopontocerebellar atrophy: MR diagnosis and relationship to multisystem atrophy. Radiology 174693696, 1990. 107. Savoiardo M, Strada L, Ollva D, et al: Abnormal MRI signal in the rigid form of Huntington's disease. J Neurol Neurosurg Psychiatry 54:888-891, 1991. 108. Sax DS, Bird ED, Gusella JF, Myers RH: Phenotypic variation in 2 Huntington's disease families with linkage to chromosome 4. Neurology 391332-1336. 1989. 109. Schrag A. Good CD, Miszkiel K, et al: Differentiation of atypical parkinsonian syndromes with routine MRI. Neurology 54:697-702, 2000. 110. Schultz JB, Skalej M, Wedekind D, et al: Magnetic resonance imaging-based volumetry differentiates idiopathic Parkinson's syndrome from multiple system atrophy and progressive supranuclear palsy. Ann Neurol45:65-74, 1999.


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111. Seab JP, Jagust WS, Wong SFS, et al: Quantitative NMR measurements of hippocampal atrophy in Alzheimer's disease. Magn Reson 8:20&228, 1988. 112. Siddique T, Nijhawan D, Hentati I: Familial amyotrophic lateral sclerosis. J Neural Trans Supp149:219-233, 1997. 113. Soininen R, Puranen M, Riekkinen PJ: Computed tomography findings in senile dementia and normal aging. J Neurol Neurosurg Psychiatry 4550-54, 1982. 114. Squire LR, Amaral DG,Press GA: Magnetic resonance imaging of the hippocampal formation and mammillary nuclei distinguish medial temporal lobe and diencephalic amnesia. J Neurosci 10:3106 3117, 1990. 115. Starkstein SE, Brandt J, Bylsma F, et ak Neuropsychological comlates of brain atrophy in Huntington's disease: A magnetic resonance imaging study. Neuroradiology 34:487489, 1992. 116. Stem MB, Braffman BH, Skolnick BE, et al: Magnetic resonance imaging in Parkinson's disease and parkinsonian syndromes. Neurology 39: 1524-1526, 1989. 117. Sullivan EV, De La Paz R Zipursky RB,Pfefferbaum A: Neuropsychological deficits accompanying striatonigral degeneration. J Clin Exp Neuropsychol 13:773-778, 1991. 118. Tartaro A, Fulgente T, Delli Pizzi C, et al: MRI alterations as an early finding in Creutzfeldt-Jakob disease. Eur J Radio1 17: 155-158, 1993. 119. Teny RD: Senile dementia of the Alzheimer type. Ann Neurol 14: 497-506, 1983. 120. Testa D. Savoiardo M, Fetoni V, et al: Multiple system atrophy. Clinical and MR observations on 42 cases. Ital J Neurol Sci 14: 211-216, 1993. 121. Tomlinson BE, Corsellis JAN: Ageing and dementias. In Adams JH,

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Conellis JAN (eds): Greenfield's Neuropathology, 4th ed. New York, LW Duchen Wiley, 1984, pp 951-1025. 122. Tomonaga M, Hiioski Y, Tohgi H: Clinicopathologic study of progressive subcortical vascular encephalopathy (Binswanger type) in the elderly. J Am Geriatr Soc 30:524-529, 1982. 123. Tsuchiya K: High-field MR findings of multiple system atrophy. Nippon Igaku Hoshasen Gakkai Zasshi 50:772-779, 1990. 124. Udaka F, Sawada H, Seriu N, et ak MRI and SPECT findings in amyotrophic lateral sclerosis. Neuroradiology 343389-393, 1992. 125. Urchino A, Yoshinaga M, Shiokawa 0,et al: Serial MR imaging in Creutzfeldt-Jakob disease. Neuroradiology 33:364-367, 1991. 126. Vonsattel JP, Meyers RH,Steven TJ: Neuropathologic classification of Huntington's disease. J Neuropathol Exp Neurol 44559-577, 1985. 127. Weber T, Otto M, Bodemer M, Zerr I: Diagnosis of CreutzfeldtJakob disease and related human sponflorm encephalopathies. Biomed Pharmacother 51:381-387, 1997. 128. Wessel K, Schroth G, Diener HC, et al: Significance of MRIconfirmed atrophy of the cranial spinal cord in Friedreich's ataxia. Eur Arch Psychiatry Neurol Sci 238:225-230, 1989. 129. Will RG, Zeidler M, Stewart GE, et al: Diagnosis of new variant Creutzfeldt-Jakob disease. Ann Neurol 47:575-582, 2000. 130. Yagashita A, Nakano I, Oda M, Hirano A: Location of the corticospinal tract in the internal capsule at MR imaging. Radiology 191: 455460, 1994. 131. Yamamoto K, Morimatsu M: Increased signal in the basal ganglia and white mater on magnetic resonance imaging in CreutzfeldtJakob disease. Ann Neurol 32: 114, 1992. 132. Zeidler M, Sellar RJ,Collie DA, et al: The pulvinar sign on magnetic resonance imaging in variant Creutzfeldt-Jakob disease. Lancet 355: 1412-1418, 2000.


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Brain Magnetic Resonance Spectroscopy Jay J. Pillai, Lester Kwock

A Brief History Magnetic resonance spectroscopy (MRS) is a means of noninvasive physiologic imaging of the brain that measures relative levels of various tissue metabolites. Absolute quantitation of these metabolites is also possible, although in standard clinical practice ratios are commonly used to describe relative concentrations of these metabolites. MRS enables evaluation of metabolic derangements that are specific to certain central nervous system (CNS) diseases or categories of disease. Thus, MRS may aid in the diagnosis of various CNS diseases when standard structural magnetic resonance imaging (MRI) findings may be nonspecific. MRS may also be used to monitor therapy and to provide prognostic information in certain conditions. This chapter presents the basic principles of MRS, followed by a discussion of basic clinical applications. The discovery of the phenomenon of nuclear magnetic resonance (NMR) can be traced to Purcell and coworkers and Bloch and coauthors in 1946, who found that magnetic dipoles of atomic nuclei resonated when placed in an external magnetic field and demonstrated nuclear induction (induction of an electromotive force in a surrounding recording coil)." Is5 MRS, in the 1970s, involved phosphorus (31P)spectroscopy in animals, including evaluation 1'6*16L Human of red blood cells and rat leg muscle tissue.'O1~ applications became possible in the early 1980s, when larger-bore magnets became available; applications in the extremities were followed by applications in the CNS.'I6 The first human brain applications involved 3'P spectroscopy in infants.32-99, "6. lg7 Bottomley and Radda and their coauthors then described applications of in vivo 3'P spectroscopy in the adult brain, followed in 1985 by the earliest 'I6. lS6 in vivo brain hydrogen ('H) spectroscopic studies." With the advent of technical advances that allowed for improved spatial localization and water suppression, MRS has rapidly progressed in clinical utility and acceptance in the late 1980s to near its current status. Today MRS-in particular, IH MRS-has become a valuable physiologic imaging tool with wide clinical applicability.

Technical Considerations Basic Principles What is the difference between MRS and MRI? The answer to this most frequently asked question is that basi-

cally there is no difference, because both techniques are governed by the same physical principles of magnetism. MRS and MRI differ only in the manner in which the data are processed and presented. With MRI, the data collected are analyzed in the time domain (free induction decay [mD] signal) to obtain information about the nuclear relaxation time (namely, T1 and T2), which is processed to generate an anatomic image. In MRS, time domain information is converted to frequency domain information via Fourier transformation of the mD time domain signal. What is the frequency domain, and why do the protons of water resonate at a different frequency (H20, 4.7 parts per million at pH = 7.4) from that of the protons located in other metabolites, such as the following? 1. The N-acetyl methyl group of N-acetylaspartate (CH3C==NH-R; 2.0 ppm). 2. The N-methyl groups of choline ((CH3),N-); 3.2 ppm). 3. The N-methyl group of creatine (CH3--NH-R). As resented in a number of reviews. NMR is based on the principle that some nuclei have associated magnetic spin properties that allow them to behave like small magn e t ~ . ' ~20a,~ 213 . In the presence of an externally applied magnetic field, the magnetic nuclei interact with that field and distribute themselves to different energy levels. With protons having a magnetic spin number of 112, the nuclei distribute themselves into two energy states. Conceptually, these energy states correspond to the proton nuclear spins, either aligned in the direction of (low-energy spin state) or against the applied magnetic field (high-energy spin state). If energy is applied to the system in the form of a radiofrequency (RF) pulse that exactly matches the energy between both states. a condition of resonance occurs. That is, nuclei in the lower-energy state can absorb this energy and are promoted to the higher-energy state. The Larmor frequency equation describes this phenomenon:

where coo is the Larmor precessional frequency (cycleslsecond [Hz]) h is Planck's constant y is the gyromagnetic ratio for that nucleus (MHztTesla [TI> B, is the applied magnetic field (T) This equation states that the resonance frequency of a

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Brain and Meninges

magnetic nucleus (the RF needed to excite a given nucleus to the higher spin state) is directly proportional to the magnetic field environment it experiences. Chemical elements having different atomic numbers such as hydrogen ('H)and phosphorus (31P)resonate at different Larmor RFs because of the differences in the magnetic properties in the nucleus of these atoms; that is, at 1.5 T the Larmor RF for 'H is 63.86 MHz; for 31Pit is 25.85 MHz. This difference in the Larmor RF has been used to identify magnetic nuclei having different atomic numbers. Even for a given magnetic nucleus having the same atomic number, however, chemical compounds containing this nucleus can have slightly different Larmor RFs. The reason for this is due to the electrons (negatively charged subatomic particles) that surround the nucleus of the atom. The circulating electrons form an "electron cloud" that surrounds the nucleus. Like Drotons and neutrons in the nucleus of the atom, electrons have magnetic spin properties. Thus, when exposed to an externally applied magnetic field, electrons precess and produce a small magnetic field, B*, around the nucleus. These local magnetic fields generated by the electrons (normally in the range of parts per million of B,) can add or subtract from the applied magnetic field, Bo. Consequently, the nucleus of the atom experiences a slightly different magnetic field from Bo. This field is defined as B, and is equal to (B, - B*). Because of this small change in the local magnetic field, the nucleus of the atom resonates at a shifted Larrnor RF; i.e.,

AE = h 2 / ~(Bo - B*) = h ( ~ 0- u*) This phenomenon is called the chemical shift and is the basis of MRS.

Single- Volume versus Multivolume MRS Techniques Single-Volume Proton Magnetic Resonance Spectroscopy At present, two single-volume proton localization techniques are employed in clinical MRS studiesm: Stimulated echo acquisition mode (STEAM) Point-resolved spectroscopy (PRESS) Both methods are highly effective, each with its advantages and disadvantages.

Advantages of STEAM STEAM enables observation of proton metabolites that have short T2 relaxation processes, such as myo-inositol (MI), glutamate (Glu), and glutaxnine (Gln), because echo times (TEs) less than 20 msec can be used; with PRESS, they cannot. STEAM also affords more effective suppression of the water resonance signal because water suppression chemical shift-selective (CHESS) pulses can be placed not only at the preparation phase of the volume localization pulse sequence but also within the localization sequence (at the TM phase of the STEAM sequence) without penalty to the TE being used. This is a major advantage, especially when short TEs ( disease (subacute necrotizing encephalomyelopathy) is a rare, inherited disorder in which multiple biochemical defects are found. The most striking neuropathologic change is symmetrical vacuolation of the basal ganglia, the brain stem, the cortex, ~ d , J o a l e s ~ e degree, r


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I

Figure 13-38. Fi (Alexander's disease), early stage. This child was 7 months old at the time of her first CT scan: she had been in good health until 5 months of age, at which time left focal seizures began, associated with occasional absence spells and generalized lethargy. A, Initial CT scan with paradoxically increased density of the medial frontal white matter. B and C,Significant contrast enhancement in the basal ganglia, frontal white matter, and periventricular brain substance. The external capsule is hyperlucent. This unusual pattern of enhancement is identical to that reported in a biopsy-proven case of fibrinoid leukodystrophy. D and E, Follow-up CT study 8 months later, during which time the child regressed neurologically and her seizures became refractory to treatment. Contrast-enhanced sections document significant cerebral atrophy in the interim, with less contrast enhancement.


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Chapter 13

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Leukoencephalopathiesand Demyelinating Disease

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rrgure AMY. l a m al9estse Qexosammaase deficiency) in a 3-year-old girl with rnegalencephztly. A, TI-weighted sagittal MR image shows generalized whi& matter hypoattenuation and extreme hypogemis of the corpus callosurn (a nonspecific finding). B, T2weighted axial MX shows extreme demyelination of virtually all white matter as well as characteristic T2 prolongation in thalami and lenticular nuclei.

the white matter. Low attenuation in the basal ganglia, brain stem, or central white matter may be seen on CT scans but is much better delineated on T2-weighted MR images (Fig. 13-40).15.", 86 The most characteristic foci of demvelination are in the lentiform nuclei. the cerebral ped;ncles, the periaqueductal gray matter, the pons, and the medulla. Contrast enhancement may be seen in the acute stages. Other mitochondrial cytopathies that have shown abnor-

malities on imaging are MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokes), MERRF (myoclonic epilepsy with ragged red fibers), and Keams-Sayre syndrome pigs. 13-41 and 13-42).73999

Aminoacidopathies Aminoacidopathies constitute another class of neurodegenerative disorders. Heritable disorders of amino acid

Figure 1340. Leigh's Qsease (subacute necrobzmg encephalomyelopathy) in a 10-year-old girl with developmental delay and slow neurologic deterioration. A and B, Initial MR scans. C and D, Follow-up scan 3 years later. A, T2-weighted axial MR image at the level of the midbrain. Hyperintensity of the entire mesencephalic tectum is visible, with lesser involvement of the cerebral peduncles. B, Postgadolinium-enhanced,TI-weighted image at the same level demonstrates symmetrical enhancement just anterior to the aqueduct.

Illustration continued on following page


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Figure 13-40. Continued. C, T2-weighted axial image at the midbrain level. The previously seen hyperintensities have resolved almost completely, leaving only small periaqueductal foci. D, There is residual persistent hyperintensity in the putamina bilaterally.

Figure 13-41. Mitochondria1 depletion syndrome in an 8-month-old boy with hypoglycemia, liver failure, and pancreatic insufficiency. A and B, Cranial MR axial T2-weighted images. There is hyperintensity of virtually the entire cerebral white matter, including internal

and external capsules, compatible with severe hypomyelination and demyelination.


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Figure 13-42. Myopathic camitine deficiency in a 10-year-old boy with myopathy. Non-contrast-enhanced CT scans show diffuse,

widespread, symmetrical lucency of the white matter, suggestive of demyelination.

metabolism may be accompanied by neurologic dysfunction, ranging from mild to severe, acute or chronic. Some affected infants die of edema brought on by hyperammonemia or anoxia; others have been shown at autopsy to have spongy degeneration of the white matter, demyelination, or hypomyelination. The more well-known aminoacidopathies include maple syrup urine disease (MSUD), phenylketonuria, the ketotic hyperglycinemias, urea cycle enzyme errors (ornithine transcarbamylase deficiency or citrullinemia), and nonketotic hyperglycinemias. More than 50 subtypes have been described. Depending on the time of imaging, an affected child with one of these aminoacidopathies may show cerebral edema, hypomyelination, or diffuse white matter atrophy (Fig. 1343)." 51 A characteristic diagnostic feature is the demonstration of white matter edema in the neonatal period, since this excludes most classic leukodystrophies.

Wilson's Disease Wilson's disease is a rare autosomal recessive disorder of copper metabolism. Although basal ganglia are predominantly affected, white matter tract abnormalities have been routinely characterized by MRI.90

Mucopolysaccharidoses Six well-recognized syndromes are caused by enzyme defects resulting in accumulation of glycosaminoglycans in many organs. Hurler's syndrome is the prototype. Although demyelination is not a prominent neuropathologic feature, diffuse white matter changes simulating demyelination have been reported (Fig. 13-44).40. 58

Multiple Sclerosis The most common demyelinating disease seen in adult neurologic practice is MS. Clinically, it may present in acute, chronic, or relapsing forms. The common neurologic signs are optic neuritis, paralysis, numbness, ataxia, and tremor. Repeated remissions and exacerbations are characteristic, and the average duration of disease is many years.67.95 The gross pathologic features of MS have been well documented over many decades. The in vivo demonstration of demyelinated plaques was k s t made possible with the advent of CT, but MRI is clearly the imaging method of choice, with superior sensitivity, specificity, and characterization of the disease p r o ~ e s s76. ~In many studies, MRI not only is the most accurate imaging method but also is even more sensitive than other nonimaging tests such as oligoclonal bands, somatosensory evoked potentials, and visual evoked potential^.^^ The sensitivity of MRI has been as high as 85% in patients with clinically definite MS, and the figure is probably even higher if serial studies are performed.59CT, however, has probably less than half the sensitivity of MRI; nonetheless, a brief description of CT abnormalities is in order, if only for historical interest. Three CT features are typical of MS: 1. Most characteristic is focal decreased attenuation in the periventricular white matter. 2. Another type of focal abnormality in CT scans of MS is contrast-enhancing plaque. These enhancing lesions have been shown to correspond to the acute phase of demyelination, and the blood-barrier breakdown resolves within a few weeks (Fig. 13-45).57 The contrast enhancement may be ameliorated or abolished by the administration of corticosteroids, although the long-term


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Figure 13-43. Maple syrup urine disease (MSUU) in a 10-month-old boy with feeding difficulties and developmental delay. When admitted, he was obtunded and his urine smelled faintly of maple syrup. A-C, Three representative sections from the unenhanced CT scan show diffuse, moderately low density of the cerebral white matter. Mild, diffuse cerebral atrophy is apparent on all sections. Lucency of the temporal lobe (A), the internal capsule (B), and the splenium of the corpus callosum (C) is prominent.


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Figore 13-44. Mucopolysaccharidosis (Hurler's syndrome) in a 7-year-old girl with mild macrocephaly. CT scan demonstrates the multiple periventricular cysts, characteristic of this disease, as well as more subtle generalized white matter hypodensity. Unusual skull defects with brain herniations are also shown.

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Figure 1 3 4 5 . ML ,le sclerosis, acute phase, in a 19-year-old woman with extremity numbness. difficulty in walking, blurred vision. and slurred speech. A-C, Precontrast CT sections are abnormal, with diffuse. patchy hypodensity of the white matter. Illustrcltion continued on follo\ving pcige


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Corresponding sections after administratio11 ~f intravenous contraw. ~ ~ l is~ prominent l e patchy Figure 13-45. Continued. enhancement of the periventricular white matter bilaterally. Occasionally, as in this case, a few contrast-enhancing plaques may be found in the cerebral cortex, but the periventricular lesions predominate.


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Figure 13-46. Multiple sclerosis in 50-year-old woman with previous optic neuritis and relapsing-remitting symptoms. A, T2-weighted cranial MR axial image demonstrates several deep white matter plaques and periventricular lesions. B and C,Proton-density axial images. The periventricular and corpus callosum lesions are visualized more clearly on the proton-density image.

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course of the disease does not appear to be altered by this regimen. 3. A less common CT finding in MS is cerebral atrophy, caused by large-scale white matter shrinkage. This results in generalized ventricular and sulcal dilatation. The foregoing discussion notwithstanding, MRI is the imaging method of choice in cases of suspected MS of the brain and spinal cord. The emphasis is not only on supporting the diagnosis of MS but on the fact that MRI is effective in differentiating MS from other processes, such as slowly growing tumors, brain stem vascular malformations, and vasculitis. The most widely used sequences for detection of MS are the T2-weighted and proton-density sequences. These are rapidly being supplemented by fast spin-echo imaging. Other techniques that may prove to be extremely useful are magnetization transfer; FLAIR; and, possibly, high-dose contrast-enhancement scheme^.^' Although magnetic resonance spectroscopy is beyond the scope of this chapter, it is evident that it is a powerful technique for the study of MS and other white matter diseases.= On standard =-weighted sequences, MS plaques appear as high-intensity lesions, usually ovoid, elongated, or round. The protondensity and FLAIR scans are very useful because high-signal plaques adjacent to ependymal surfaces may be obscured by high-signal cerebrospinal fluid on standard T2-weighted images (Figs. 1 3 4 6 to 13-49).81 In general, TI-weighted images are much less sensitive, but it is noteworthy that chronic plaques of MS are often

Figure 13-47. Multiple sclerosis (MS), as shown on a fluidattenuated inversion recovery (FLAIR) MR image; the patient is a 36-year-old woman with relapsing-remitting MS. Note the conspicuity of the numerous bilateral periventricular white matter lesions.

Figure 13-48, Multiple sclerosis (MS). Fluid-attenuated inversion recovery (FLAIR) parasagittal MR image depicts the extensive demyelinated plaques of progressive MS.

well shown, especially in the corpus callosum, on T1weighted sequences, appearing as low-signal lesions surrounded by a very thin halo of mildly increased signal intensity (Fig. 13-50). Hemorrhage is not seen in MS lesions; edema and mass effect are distinctly uncommon (see later). The most characteristic diagnostic feature of MS plaques on MR images is not their signal intensity but their anatomic distribution. There is a predilection for periventricular distribution and ependymal surfaces, especially along the occipital horns and, to a lesser degree, the frontal horns. If not pathognomonic, corpus callosum lesions are so characteristic of MS as to be almost specific?' Other MS sites commonly affected are the corona radiata, internal capsule, and centrum semiovale. In the posterior fossa, MS plaques are quite common, with a predilection for the surface of the pons, especially near the fifth cranial nerve entry zone, the middle cerebral peduncle (brachium pontis), the floor of the fourth ventricle, and the colliculi. Contrast enhancement is an important part of MRI techniq~e.~" It is known that acute lesions of MS are accompanied by transient breakdown of the blood-brain barrier, which may be demonstrated with use of gadolinium contrast enhancement. While TI-weighted images are the standard practice, magnetization transfer may show greater detectability of these lesions because of its background suppression (Fig. 13-51; see Fig. 1349). 2' Serial studies have demonstrated that contrast enhancement in acute lesions of MS may persist for 6 to 8 weeks after acute demyelinati~n.~ The enhancement may be punctate, nodular, or ringlike. In rare cases, there may be single or multiple large foci of MS with mass effect and significant contrast enhancement simulating a tumor (Fig. 13-52).52.101 Although many cases of MS have these characteristic imaging features, rendering differential diagnosis relatively unimportant, MS lesions may occur anywhere in the CNS, including the cortex and other gray matter nuclei. The lesions may be few or may be present in otherwise uncharacteristic locations. A differential diagnosis in these


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Fire 1349. MRI ft I a 32-y( )Id womi spin: ~dcerebral multiple sclerosis (MS). A, Parasagittal fluid-attenuated inversion recovery ( ~ , A I K ) sequence. Numerous hypermtease plaques are clustered on the inferior surface of the corpus callosum, highly correlated with the diagnosis of MS. B, Contrast-enhanced, TI-weighted, magnetization-transfer coronal image; two enhancing plaques are visible, indicating active demyelination: one in the corona radiata, the other in the brachium pontis. C, Sagittal T2-weighted, fast spinecho MRI of the cervical spinal cord. Numerous plaques are visible, some with evident swelling (edema). D,Fat-suppressed, contrast-enhanced image at the same level as in C; one of the lesions has ringlike enhancement.

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Figure 13-50. Multiple sclerosis (MS) in 29-year-old woman with severe relapsing-remitting symptomatology, cranial M R images. A, Parasagittal TI-weighted image, with multiple callosal hypointense plaques. B and C, Transaxial T2-weighted images at the level of the pons. Multiple scattered hyperintense plaques of MS, bordering predominantly on the fourth ventricle or pontine surface. C, Lesions are grouped bilaterally around the fifth cranial nerve entry zor

Figure 1S51. Multiple sclerosis (MS) in 37-year-old woman presenting with thoracic myelopathy. A and B, Cranial T2-weighted axial MR images show multiple, hyperintense plaques distributed bilaterally in the centrum semiovale and periventricular regions and especially grouped around the trigones. Note especially the characteristic corpus callosum lesions.


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1 Figure 13-51. Continued. C, Postgadolinium-enhanced, TI-weighted axial image, with several enhancing plaques in the deep white matter. D,Postcontrast magnetization transfer (MT) image demonstrates more conspicuous enhancement of additional lesions than the standard TI-weighted se:nce. E, Postcontrast midsagittal MR image of the cervicothoracic cord. There are two typical contrast-enhancing MS plaques: one in the anterior cervical cord and one in the posterior thoracic cord at the T2 level. (Incidentally visible is a moderate C5-6 disk protrusion.) Despite the multiple intracranial enhancing MS lesions, this patient had only spinal cord symptomatology.

cases must include demyelination secondary to AREM, vasculitis, Lyme disease, sarcoidosis, ischemic disease, and, in rare cases, tumors. As previously described, multiple ischemic white matter foci are usually seen in older patients, are associated with cardiovascular risk factors, are not located in the immediate periventricular white matter in most cases, and rarely involve the corpus callosum. Also, infratentorial ischemic lesions tend to have a different distribution than does MS in the pons and cerebellum. Despite all of these clues, some MR images are indeterminate, and the final diagnosis must await clinical confirmation or serial studies.

Spinal Cord Multiple Sclerosis Some of the false-negative MRI diagnoses of MS are attributable to cases with only spinal cord involvement.

The spinal cord is much more of a challenge in MRI diagnosis, but newer techniques are yielding more rapid and detailed examinations of such cord lesions. These include multiarray receiver coils, fast spin-echo imaging, and the FLAIR sequence. Reports suggest that cord lesions may be detected in a majority of MS patients using such techniques. Characteristically, the cord lesions of MS appear as high signal intensity on T2-weighted sequences, with the cervical cord involved about twice as often as the thoracic cord. The lesions range from a few millimeters to extension over one or more vertebral segments (Fig. 13-53; see Figs. 13-49 and 13-51). The most common location is lateral and posterior in the cord, but MS may involve both gray and white matter and may occupy the entire transverse diameter. Swelling of the cord is reported in a minority of cases, with diminished signal intensity on TI-weighted images sometimes


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Figure 13-52. Demyelinating disease presenting as a mass. A, 7'2-weighted cranial MR axial image. There is a hyperintense masslike lesion in the left parieto-occipital lobe, surrounded by edema. A few scattered pexiuen$rieular and deep white matter lesions are also visible bilaterally. B, PosQadolinium-enhanced, TI-weighted coronal MR image. Incomplete ringlike enhancement outlines the lesion. Biopsy showed nonspecific demyelination. Follow-up MR several months later showed almost complete spontaneous resolution of this mass. (From Jordan JE, Lane B: MRI characteristics of demyelinating disease mimicking brain tumor. Appl Radiol, December 1992, pp 36-38.)

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Figure 13-53. Multiple sclerosis (ma) in a 26ye&-old woman with myelopathy. A, Fast spinecho, midsagittal T;?-weighted cervicothoracic MR image shows extensive, high-intensity demyelination involving the cervical and thoracic spinal cord. The cord appears mildly swollen. B, Axial TI-weighted cervical cord MR image at the C2-3 level. The spinal cord appears mildly enlarged. C, Postgadolinium-enhanced, TI-weighted MR image at the C2-3 level shows extensive plaque enhancement in the posterior spinal cord. The clinical diagnosis is MSI

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visible. Gadolinium enhancement parallels that of MS brain lesions. The differential diagnosis includes transverse myelitis, other inflammations, and intrinsic cord tumor. The final diagnosis is accomplished, preferably, by serial imaging studies and clinical correlation rather than by biopsy.

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55. Melhem E, Loes D, Georgiades S, et al: X-linked adrenoleukodystrophy: The role of contrast-enhanced MR imaging in predicting disease progression. AJNR Am J Neuroradiol21:839, 2000. 56. Miller GM, Baker HL Jr, Okazaki H, et al: Central pontine myelinclysis and its imitators. Radiology 168:795, 1988. 57. Morariu MA, Willcins DE, Patel S: Multiple sclerosis and serial computed tomography: Delayed contrast enhancement of acute and early lesions. Arch Neurol 37:189, 1980. 58. Murata R, Nakajima S, Tanaka A, et al: MR imaging of the brain in patients with mucopolysaccharidosis. AJNR Am J Neuroradiol 10:1165, 1989. 59. Mushlin AI, Detsky AS, Phelps CE,et al: The accuracy of magnetic resonance imaging in patients with suspected multiple sclerosis. JAMA 269:3146, 1993. 60. Olsen WL, Longo FM, Mills CM, et al: White matter disease in AIDS: Findings at MR imaging. Radiology 169:445, 1988. 6 1. O'Neill BP, Forbes GS: Computerizd tomography and adrenoleukomyeloneuropathy: Differential appearance in disease subtypes. Arch Neurol 38:293, 1981. 62. Pederson H, Clausen N: The development of cerebral CT changes during treatment of acute lymphocytic leukemia in childhood. Neuroradiology 2279, 1981. 63. Penn RD, Trinko B, Baldwin L: Brain maturation followed by computed tomography. J Comput Assist Tomogr 4614, 1980. 64. Penner MW,Li KC, Gebarski SS, et ak MR imaging of PelizaeusMerzbacher disease. J Comput Assist Tomogr 11:591, 1987. 65. Peters AC, Versteeg J, Bots GT, et al: Progressive multifocal leukoencephalopathy. Arch Neurol 37:497, 1980. 66. Picard L, Claudon M, Roland J, et ak Cerebral computed tomography in premature infants, with an attempt at staging developmental features. J Comput Assist Tomogr 4435, 1980. 67. Poser CM: Exacerbation, activity and progression in multiple sclerosis. Arch Neurol 37:471, 1980. 68. Ragland RL, Duffis AW, Gendelmal S, et al: Central pontine myelinolysis with clinical recovery: MR documentation. J Comput Assist Tomogr 13:316, 1989. 69. Rail RL, Perkin GD: Computerized tomographic appearance of hypertensive encephalopathy. Arch Neurol37:310, 1980. 70. Ramsey RG, Geremia GK: CNS complications of AIDS: CT and MR findings. A.TR 151:449, 1988. 71. Reik L Jr: Disseminated vasculomyelinopathy: An immune complex disease. Ann Neurol 7:291, 1980. 72. Reisner T, Maida E: Computerized tomography in multiple sclerosis. Arch Neurol37:475, 1980. 73. Rowland LP: "Ophthalmoplegia plus" or Kearns-Sayre syndrome. Arch Neurol 37:256, 1980. 74. Rowley HA, Dillon WP: Iatrogenic white matter diseases. Neuroimaging Clin North Am 3:379, 1993. 75. Ruiz-Martinez J, Martinez Perez-Basal A, Ruibal M, et al: Marchiafava-Bignami disease with widespread extracallosal lesions and favourable course. Neuroradiology 41:40, 1999. 76. Runge VM, Kirsch JE, Lee C, et al: MRI of multiple sclerosis in the brain. MRI Decisions 6(4):2, 1992. 77. Saito H, Endo M, Takase S, Itahara K: Acute disseminated encephalomyelitis after influenza vaccination. Arch Neurol 37:564, 1980. 78. ScanbergerA, Tomaiuolo F, Sabatini U, et al: Dernyelinating plaques in relapsing-remitting and secondary-progressive multiple sclerosis: Assessment with diffusion MR imaging. AJNR Am J Neuroradiol 21:862, 2000. 79. Shah M, Ross J: Infantile Alexander disease: MR appearance of a biopsy-proved case. AJNR Am J N m r a d i o l 11:1105, 1990. 80. Sheldon JJ, Siddharthan R,Tobias J, et ak MR imaging of multiple sclerosis: Comparison with clinical and CT examination in 74 patients. Am J Neuroradiol6:683, 1985.

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81. Simon JH, Holtas SL, Schiffer RB, et al: Corpus callosum and subcallosal-periventricular lesions in multiple sclerosis: Detection with MR. Radiology 160:363, 1986. 82. Statz A, Boltshauser E, Schinzel A, Spiess H: Computed tomography in Pelizaeus-Merzbacher disease. Neuroradiology 22:103, 1981. 83. Steingart A, Hachinski VC, Lau C, et al: Cognitive and neurologic findings in demented patients with diffuse white matter lucencies on computed tomographic scan (leukoaraiosis). Arch Neurol 44: 36, 1987. 84. Stovring J, Fernando LT: Wallerian degeneration of the corticospinal tract region of the brain stem: Demonstration by computed tomography. Radiology 149:717, 1983. 85. Thompson DS, Hutton JT,Stears JC, et al: Computerized tomography in the diagnosis of central and extrapontine myelinolysis. Arch Neurol 38:243, 1981. 86. Topcu M, Saatci I, Apak A, et al: Leigh syndrome in a 3-year-old boy with brain MR imaging and pathologic findings. AJNR Am J Neuroradiol 21:224, 2000. 87. Tsuruda JS, Kortman KE, Bradley WG, et al: Radiation effects on cerebral white matter: M R evaluation. AJNR Am J Neuroradiol 8: 431, 1987. 88. Uchimaya M, Hata Y, Tada S: MR imaging in adrenoleukodystrophy. Neuroradiology 3325, 1991. 89. Valentine AR, Moseley IF, Kendall BE: White matter abnormality in cerebral atrophy: Chicoradiological correlations. J Neurol Neurosurg Psychiatry 43139, 1980. 90. van Wassenaer-van Hall H, van den Heuvel G, Jansen G, et al: Cranial MR in Wilson disease: Abnormal white matter in extrapyramidal and pyramidal tracts. AJNR Am J Neuroradiol 16:2021, 1995. 91. Vaughn DJ, Jarvik JG, Hackney D: High-dose cytarabine neurotoxicity: MR findings during the acute phase. AJNR Am J Neuroradiol 141014, 1993. 92. Walker DL: Progressive multifocal leukoencephalopathy. In Vinken PJ, Bruyn GW, Klawaus HL (eds): Handbook of Clinical Neurology. New York, Elsevier, 1985, p 503. 93. Walsh PJ: Adrenoleukodystrophy: Report of two cases with relapsing and remitting comes. Arch Neurol 37448, 1980. 94. Waltz G, Harik SI, Kaufrnan B: Adult metachromatic leukodystrophy. Arch Neurol44:225, 1987. 95. Waxman S: The demyelinating diseases. Ln Rosenberg RN ( 4 ) : The Clinical Neurosciences, vol 1. New York, Churchill Livingstone, 1983. %. Weingarten KL,Zimmerman RD, Pinto RS, Whelan MA: Computed tomographic changes of hypertensive encephalopathy. Am J Neuroradio1 6:395, 1985. 97. Whiteman MLH, Post MJD, Berger JL, et al: Progressive multifocal leukoencephalopathy in 47 HIV-seropositive patients: Neuroimaging with clinical and pathological correlation. Radiology 187:233, 1993. 98. Wolf R, Zimmerman R,Clancy R, Haselgrove J: Quantitative apparent diffusion coefficient measurements in term neonates for early detection of hypoxic-ischemic brain injury: Initial experience. Radiology 218:825, 2001. 99. Wray S, Provenzale J, Johns D, Thulbom K: MR of brain in mitochondrial myopathy AJNR Am J Neuroradiol 16:1167, 1995. 100. Yamamoto T, Ashikaga R, Araki Y, Nishimura Y: A case of Marchiafava-Bignami disease: MRI findings on spineecho and fluid attenuated inversion recovery (FLAIR) images. Eur J Radio1 34141,2000. 101. Yetkin FZ, Haughton VM: Common and uncommon manifestations of MS on MRI. MRI Decisions 6: 13, 1992. 102. Young RSK, Osbakken MD, Alger PM, et ak Magnetic resonance imaging in leukodystrophies of childhood. Pediatr Neurol 1:15, 1985. 103. Zeumer H, Schonsky B, Sturm KW: Predominant white matter involvement in subcortical arteriosclerotic encephalopathy (Binswanger disease). J Comput Assist Tomogr 414, 1980.


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The Orbit

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Jon Mark Fergenson, Neal Mandell, James J. Abrahams

Magnetic resonance imaging (MRI) and computed tomography (CT) have revolutionized diagnostic imaging of the orbit and its contents. With its superb soft tissue contrast and ability to image in multiple planes, MRI provides excellent rendering of the orbital anatomy. CT also shows the soft tissues within the orbit very well and is best at displaying anatomy and pathology of the bony orbit. The fine structures within the orbit require more attention to imaging protocol than many other regions of the body to ensure optimal diagnostic information. This chapter discusses technique for the more commonly used imaging issues, presents an overview of pertinent anatomy, and touches on a cross-section of orbital pathology, including some familiar and some unusual lesions.

Anatomy The anatomy of the orbit consists of a bony cavity within which the globe, muscle cone, optic nerve-sheath complex, lacrimal apparatus, and various vascular and nerve structures are packed into a cushion of fat. The bony orbit is a conical structure that consists of the orbital plate of the frontal bone, the maxilla, the greater and lesser wings of the sphenoid bone, the ethmoid bone, and the lacrimal bone. The inferior and medial walls are quite thin and prone to fracture. The medial wall is named the lamina papyracea, in recognition of its paper-thin nature. Multiple foramina transmit vessels and nerves. The most prominent among these include the superior and inferior orbital fissures, the optic canal, the infraorbital and supraorbital foramina, and the lacrimal duct foramen. Other tiny foraminal spaces are not usually appreciated in imaging because of their size. The contents of the major foramina are listed in Box 14-1. Box 14-1. Major Foramina of the Orbit Optic Canal

Optic nerve Ophthalmic artery Superior Orbital Fissure

Ill, IV, VI, V, cranial nerves Lacrimal and frontal nerves Superior and inferior ophthalmic veins Inferior Orbital Fissure

V, cranial nerve lnfraorbital vessels, zygomatic nerve

The muscle cone consists of seven extraocular muscles: the superior, medial, lateral, and inferior recti as well as the superior and inferior obliques, and the levator palpebrae superioris. All but the inferior oblique muscle originate at the orbital apex at Zim's ring and pass anteriorly to form tendinous attachments to the globe. The inferior oblique muscle originates on the inferomedial aspect of the orbit and passes in a somewhat lateral course to attach to the posterolateral aspect of the globe. The cone of the muscle has been designated a relative boundary or demarcation in addressing the position of several pathologic processes, with the orbit divided into intraconal and extraconal spaces. In general, processes involving the intraconal space require surgical attention, whereas extraconal processes are often amenable to medical management. The globe is approximately spherical, with only a few readily visualized structures: the cornea, lens, anterior chambers, vitreous, and the retina-sclera-choroid complex. None of the conventional imaging modalities is able to visualize the retina from the choroid separately in the healthy patient. When an intervening process does occur, it causes separation of these thin membranes. Proptosis is evaluated by axial scanning, with a line connecting the lateral orbital walls at the level of the lens and with the imaging specialist measuring from that line to the anterior aspect of the globe.31This measurement should not exceed 21 mm.'l The optic nerve-sheath complex consists of the optic nerve, its surrounding meningeal sheath, and the cerebrospinal fluid (CSF), which separates them. The sheath extends from the optic canal to the globe. The normal diameter of the nerve is up to 4 rnrn. The diameter of the complex may vary from 4 to 6 mm. The amount of visualized subarachnoid fluid is also variable. Occasionally, the presence of CSF makes it possible to determine whether a tumor arises from the sheath or from the nerve itself. Tumors arising from the sheath, such as meningiomas, form a "tram track" appearance in which the outer layer is thickened but remains separated from the normal-sized nerve by a layer of fluid. Because the nerve takes a sigmoid course from apex to globe, coronal imaging is essential for assessing the optic nerve-sheath complex. The lacrimal apparatus consists of the lacrimal gland, its secretory duct, and the ductal system, which drains these secretions into the nasal cavity. The gland lies in the superolateral aspect of the orbit. The draining ductal system lies near the medial canthus and consists of the suuerior and inferior puncta, their associated ducts, the 1acrimAl sac, lacrimal duct, and the valve of Hasner, a draining orifice inferolateral to the inferior nasal turbinate. The anterior border of the orbit is formed by the orbital


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Figure 14-1. A, Coronal CT scan: normal anatomy. Lateral rectus (a), superior rectus (b), medial rectus (c), superior oblique (d), levator palpebrae superioris (e), lacrimal gland (f), inferior oblique (g). B, Medial rectus (a), superior oblique (b), ophthalmic artery

(c), superior rectusflevator palpebrae superioris complex (d), dural sheath (e), superior ophthalmic vein (f), subarachnoid space (g), optic nerve (h), inferior rectus (i), lateral rectus (i). septum, a fibrous structure adherent to the inner margin of the orbital rim with central portions that extend into the tarsus of the eyelids. Although there are a few orifices for passage of vessels, nerves, and ducts, the septum forms an effective barrier to prevent superficial processes from extending into the orbit proper. A pathologic process such as cellulitis may be designated preseptal or postseptal.

Technique Computed Tomography Intraorbital fat provides a natural source of contrast on CT scans. Most lesions within the orbit, whether inflammatory, infectious, or neoplastic, are relatively radiodense in comparison to the surrounding fat, and they are easily distinguished by CT. CT is rapid, and the images are obtained incrementally. Therefore, patient cooperation is less crucial than in MRI. Commonly accepted protocols call for both axial and coronal images with the potential for multiplanar reconstruction. For most orbital studies, 3-mm sections in the axial and coronal planes are adequate. Coronal sections

should be initiated at the lateral orbital rim (to lessen exposure to the radiosensitive lenss0)and continued to the posterior aspect of the optic canals, with the anterior clinoid or dorsum sella used as landmarks. The axial sections should include images of the entire brain, specifically to include the retro-orbital optic apparatus, with additional retrospective magnified views of the orbits. Coronal images are especially important in that crosssectional evaluation of all of the intraorbital structures is optimal (e.g., extraocular muscles, optic nerve-sheathnasal complex, vessels, and globe) (Fig. 14-1). This plane is also imperative for assessing spread of processes from surrounding structures (e.g., paranasal sinuses, trauma, tumor). The prone patient position is ideal, especially with , ~ supine positioning is also acceptsinus-related d i s e a ~ ebut able. Occasionally, a patient may be unable to tolerate positioning for direct coronal imaging. This occurs most commonly with elderly patients with severe degenerative disease of the cervical spine and in the setting of acute trauma. Recent developments in multislice CT technology allow for faster thin-slice imaging. As a result, axial thin-section images can be obtained for coronal reconstruction in these patients (Fig. 14-2).

Figure 14-2. A, Coronal CT scan in a patient whose extensive dental hardware obscures detail in the orbits. B, Reformatted coronal view shows enlargement of the extraocular muscles on the left side. In view of the patient's known hyperthyroidism, this finding was thought to represent Graves' disease.


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Figure 1&3. A, Axial CT scan: normal anatomy. Lens (a), lid (b), lacrimal gland (c), medial rectus (d), optic nerve-n-sheath complex (e), lateral rectus (f), superior orbital fissure (g). B, Axial CT scan: normal anatomy. Superior ophthalmic vein (arrow),globe (g).

Intravenous (IV) contrast material is a necessary addition to most orbital examinations, although it is not necessary in the setting of trauma. IV contrast can increase the sensitivity and sometimes specificity of distinguishing between various entities-whether inflammatory, infectious, neoplastic, or vascular. The contrast agent can be administered by either IV drip or by mechanical injector. A single dose (e.g., 150 mL) can be used, or split doses, one for each plane or section, depending on the lesion. Windowing is also critical to assessing pathologic changes and should include both soft tissue and bone windows (Fig. 14-3). Thin-section CT may be performed following the administration of contrast material into the nasolacrimal duct to evaluate patency. These CT dacrocystograms are often performed in conjunction with an ophthalmologist, who cannulates the duct and administers the contrast agent. Coronal reconstructions of the axial data can be helpful (Fig. 14-4).

Magnetic Resonance Imaging Although MRI is relatively new, compared with CT, this modality has rapidly gained ground in the assessment of

orbital disease. The capacity to produce images without ionizing radiation and in any plane of section without a change in patient position has made MRI an important tool in orbital imaging. The absence of bony artifact is an advantage over CT, especially in the orbital apex, optic canal, and parasellar regions. MRI uses the physical properties of the proton, the hydrogen atom's nucleus, to generate imaging data. Because hydrogen is an abundant component of the water and the macromolecules in all tissues, MRI can be used to examine any body part. The patient is placed in a strong unidirectional magnetic field, and a small population of protons become aligned with that field. The region of interest is subjected to pulsed radiofrequency (RF) energy. This serves to change the orientation of the spinning proton. The natural tendency of the perturbed proton is to realign with the overall magnetic field. This is referred to as the TI characteristic of the tissue. By definition, T1 is that time for which protons in a particular tissue have regained approximately 63% of the original alignment. When the protons are "tipped" by the RF pulse, they

Figure 14-4. A, Coronal reformatted image from a CT dacrocystogram shows dilation of the lacrimal duct. The nasal septum and inferior turbinate are deviated leftward and cause obstruction at the valve of Hasner. B, The obstruction is only partial, as evidenced by the presence of contrast material in the posterior nasopharynx.


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are initially "in phase," or are spinning together coherently in the 90-degree frame of reference. Over time, they lose cohesion and become "out of phase," called T.2 relaxation. T1 and T2 are inherent tissue characteristics and are not produced by the magnetic resonance itself. One uses the T1 and T2 of various tissues being imaged to enhance and accentuate contrast differences between those tissues. Magnetic gradients are superimposed on the overall magnetic field to spatially "encode" the position of each spinning proton in space. One can obtain spatial information using the frequency of the spinning protons or their relative phase. The most commonly used protocols today involve (1) spin-echo imaging and (2) gradient-echo imaging. Spin-echo imaging involves an additional 180-degree pulse to "rephase" the protons to produce an "echo" at a specified time: TE, or echo time. The sequence is repeated as many times as needed to obtain information about the anatomic area of interest. TR, or reperition time, refers to those repeated intervals. For a more detailed review of MRI physics, see References 3, 15, 22, 45, 53, and 71. Gradient-echo imaging involves the actual reversal of the image gradients used for spatial encoding in the region of interest. Acquisition imaging data can be obtained rapidly, either in a slice-by-slice format or volumetrically. Shallow flip angles ( -41 .- - T 4 t lv

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On the other hand, Aspergillus infection usually Occurs in otherwise healthy patients and has no relationship to pulmonary aspergi~bsis,which is known to occur in debilitated patients. The radiographic appearance, however, is similar to other fungal infections with ~pacificationof a single paranasal sinus, a hyperdense paranasal sinus on CT scans, hypointense signal -on T2-weighted MRI studies from heavy metal, and osseous destruction mimicking aggressive tumor in the later stages. Although less aggressive

than mucormycosis, Aspergillus infection may cause a vasculitis that results in cerebral thrombosis as well.

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Various granulomas produce diseases that may involve the sinonasal cavities. These include granulomas caused by organisms such as Nocardia and infectious diseases such as


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a~pergillosis,2~ actinomyc~ses,~~ tuberculosis, and syphili~.~ Granulomas can be caused by autoimmune or collagenvascular diseases such as Wegener's granulomatosis,3' lymphoma or lymphatoid diseases such as midline granuloma, and processes such as sarcoidosis. In addition, granulomas may be the result of exposure to irritants such as beryllium and chromium. In general, granulomatous diseases affect the paranasal sinuses first by causing a nonspecific inflammatory type of reaction with mucosal thickening and increased secretion~.~' The nasal septum may exhibit focal thickening, or septal erosions may-be found. The paranasal sinuses are usually involved secondary to nasal cavity involvement. The maxillary and ethmoid sinuses, as with inflammatory diseases. are most often affected. When the sinuses are involved, a nonspecific inflammatory reaction is seen. Airfluid levels are usually not present. Bony changes of the nasal cavity and paranasal sinuses may include thickened and sclerotic walls and septa. This is from the chronic inflammatory reaction (Fig. 16-14). Wegener's granulomatosis is fundamentally a necrotizing granulomatous vasculitis that initially involves the respiratory tract and eventually spreads to include the kidneys as well as other organs. When the sinonasal cavity is involved, the nasal septum is affected initially with diffuse thickening followed by septal perforation. A more aggressive and idiopathic granulomatous process is so-called idiopathic midline granuloma,13 which is characterized by a necrotizing inflammatory reaction involving the sinonasal cavities and midline of the face as well as the upper res~iratorvtract. This is a more localized disease with the luigs a n i kidneys unaffected. Tuberculosis may involve the paranasal sinuses secondary to pulmonary infection. The sinus disease is again nonspecific. Another granulomatous disease involving the paranasal sinuses is actinomycosis, which only rarely involves the paranasal sinuses and is usually the result of direct extension from the mandible.

Fire 16-14. Wegener's granulomatosis. Granulomatous disease within the paranasal sinuses may be manifested as linear enhancement (arrow) or nodule enhancement. Destruction of 0sseous structures out of proportion to soft tissue thickening should lead one to think of a granulomatous process or lymphoma.

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Mucoceles Mucoceles are the most common expansile lesions of the paranasal ~inuses.4~ A mucocele develops from obstruction of a sinus o~tium.~O The continued secretions of the sinus mucosa cause expansion and remodeling of the bony margins. Expansion of the sinus cavity causes erosion of internal septa and displacement of adjacent organs such as the intraorbital structures (Fig. 16-15). The frontal sinuses are most commonly affected, accounting for approximately 60% of all rnu~oceles.4~ The ethmoid sinuses account for approximately 25% of all mucoceles. The maxillary sinuses account for approximately lo%, and the remaining 1% or 2% are the rare sphenoid sinus m ~ c o c e l e sThe . ~ ~ presenting symptoms are those of mass effect with proptosis or cosmetic deformity. Pain is rare unless the mucocele is infected, in which case it is referred to as a mucopyocele. On CT scans, a mucocele appears as an expanded sinus filled with homogeneous material of fairly low attentuation (-15 HU) (Fig. 16-16). As one would expect, on MRI studies most mucoceles are isointense to soft tissue such as adjacent brain on TI-weighted images and show increased signal on T2-weighted images because of their high water content. However, a mucocele that has been present for many months may be of low signal on T2-weighted images and may even produce a signal void. This may be because of the high concentration of proteinaceous secretions and the slow resorption of water through the mucosa.'. 39940

Neoplastic Processes Papillomas (Fig. 16-1 7) The mucosa of the sinonasal cavity is ciliated columnar epithelium containing mucus-secreting glands called Bowman's glands. This unique mucosa is of ectodermal origin and gives rise to a distinct class of lesions with a hyperplastic zone of basement membrane enclosing epithelium that in some patients falls inward on itself, forming a polyp with an irregular or vemcose surface. These lesions are known as papillomas and are important to differentiate from simple cysts and polyps of the sinonasal cavity because of the possibility of malignant degeneration within the papillomas.245Fungiform papillomas make up approximately half of all papillomas. These nearly always arise from the nasal septum, are usually solitary and unilateral, and may have an irregular surface much like that of other papillomas but are not considered premalignant. Fungiform papillomas must therefore be differentiated from inverted papillomas or endophytic papillomas, which make up approximately 50% of all sinonasal papillomas. These tend to occur in middle-aged men, characteristically arise from the lateral nasal wall in the region of the root of the middle turbinate, and may extend laterally into the paranasal sinuses, especially the maxillary sinus. The most common presenting symptoms are nonspecific, including nasal obstruction, epistaxis, and anosmia. The rate of malignancy associated with inverted papillomas is approximately 15%. Although inverted papillomas most often have degenerated into squamous cell carcinomas, other tumors such as mucoepidermoid and adenocarcinomas have been reported.


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Figure 16-15. Mucocele. Sixty percent of mucoceles occur in the frontal sinus. A, An expansile mass is shown arising from the left frontal sinus with destruction of the lateral wall of the left frontal sinus (arrow).B, A slightly more superior image in the same patient depicts dehiscence of the posterior wall of the left frontal sinus (arrow), which is also the anterior wall of the anterior cranial fossa. C, An anterior ethmoid mucocele is shown with lateral expansion into the right orbit and dehiscence of the right medial orbital wall (large arrow). There is medial displacement of orbital contents such as the medial rectus (small arrow), leading to diplopia. Mucoceles may be the result of sinus obstruction from either inflammation or tumor. D, Postcontrast sagittal T1-weighted image (TR500,TE32) in the midline. There is solid enhancement in the region of the ethmoid air cells (long arrow), peripheral enhancement with central secretions within the sphenoid sinus (short arrow), and a mucocele with linear peripheral enhancement secondary to sinus obstruction from tumor.

Carcinoma

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. I

Squamous cell carcinoma of the sinonasal cavity arises most commonly from the maxillary sinus. This structure is involved in at least 80% of all patients with squamous cell carcinoma at some point in their c o u r ~ e .These ~ lesions occur primarily in men in the 6th and 7th decades of life. Most are low-grade tumors that arise from the nasal septum near the mucocutaneous junction. Because of the paucity of symptoms or mild symptoms, these tumors are often misdiagnosed or go undiagnosed with such chronic complaints as sinusitis, polyposis, and lacrimal duct obstruction until a mass in the oral cavity or cheek is noticed. The 5year survival is approximately 25% to 30%.3The main cause of unsuccessful response is local recurrence. When examining post-treatment patients, one may encounter radiation-induced changes. These can be differentiated from local recurrence (Fig. 16-18). The primary pathologic and therefore imaging feature of these lesions is propensity to destroy bone even in the presence of a relatively small demonstrable mass. Because of the similarity in density of squamous cell

carcinoma and other carcinomas to adjacent secretions within obstructed sinuses, a small region of bony abnormality and apparent destruction is important for the early imaging diagnosis of carcinoma, especially squarnous cell carcinoma. The use of IV contrast injection for CT scanning is rarely useful for differentiating tumor from inflammatory conditions or masses within the sinuses. The tumors themselves tend to enhance very little, whereas inflammatory mucosa may sometimes enhance brightly. However, the data suggest that enhanced (gadolinium [GdDTPA]) MIU examinations may be most useful for differentiating neoplastic from inflammatory masses within the paranasal sinuses when this diagnosis is in doubtI7 (Fig. 16-19). Approximately 10%of tumors of the sinonasal tract are glandular in origin. These include tumors that arise from minor salivary glands such as adenoid cystic carcinomas and mucoepidermoid carcinomas. They also include adenocarcinoma^.^ 3*45 Adenoid cystic carcinomas are unusual because of their course. Many tend to recur many years following their initial diagnosis and treatment. These lesions also tend to spread along perineural sheaths and to


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Figure 16-16. Im ers. A, Sagit 'I-weighted (TR500,TE? mage in the midline. Increased signal is seen overlying the frantal sinus (arrow). This may represent fat, hemorrhage, or a paramagnetic substance in a metastatic tumor such as a melanoma. The accompanying coronal CT image (B) shows a nonpneumatized and nmdeveloped right frontal sinus. The marrow signaI from this right frontal sinus was thought to produce the abnormal signal on the MRI study in A. C, Non-contrast-enhanced axial CT scan through the maxillary sinuses in a patient with sickle cell disease. The speckled pattern overlying the maxillary sinuses proved to be hyperactive marrow within the maxillary sinuses.

Figure 1617. Papillomas. A, Polypolid soft tissue mass is shown based on the nasal septum (arrow), which proved to be a fungiform papilloma on biopsy. B, Polypoid soft tissue mass is shown based on the lateral nasal wall (arrows). This is a biopsy-ptouen inverted papiIloma. Distinguishing lzetween these two lesions is important because of the malignant potential of the inverted papilloma.


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Figure 16-18. Radiation changes. These are MR images through the brain of a patient 18 months after radiation therapy for carcinoma in the paranasal sinuses. The T2-weighted image (A) reveals the presence of abnormal increased signal (arrow) in the frontal lobe white matter. The corresponding TI-weighted contrast-enhanced images (B and C) reveal nodular enhancement bifrontally (arrows).PET scans were negative. These lesions represent radiation-induced demyelination.

Figure 16-19. Squamous cell Carcinoma. A, On this coronal T2-weighted image (TR3000,TE60),structures containing water, such as cerebrospinal fluid and inflammatory polyps, in the left maxillary sinus are of increased signal intensity. More cellular masses such as skeletal muscle and the mass within the inferior meatus on the left (arrow) are of more intermediate signal intensity. Cellular masses within the nasal cavity and sinonasal tract should be suspected of being neoplasms. B, The accompanying post-contrast-enhanced T1weighted image (TR500,TE32)shows the expected surface linear enhancement on the inflammatory polyps in the left maxillary sinus (arrow).The turbinates and normal nasal mucosa enhance brightly inhomogenwusly. The suspected nasal mass enhances somewhat less intensely than the normal turbinates. This is a biopsy-proven squamous cell carcinoma.


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leave normal skip areas between the primary lesion and a local metastatic site along a nerve. This is often the case when a tumor arising in the maxillary sinus gains access to the mandibular nerve and extends toward the skull base. At the time of radical antrectomy, the surgeon may be informed that the frozen sections showed no evidence of tumor. Some studies indicate that in many cases there has already been distant regional metastasis into the cavernous sinus at the time of surgery with an intervening normal segment of the trigeminal nerve. It has become the role of the imaging specialist, therefore, to evaluate the cavernous sinus and the more proximal portions of the trigeminal nerve in such patients to establish proper staging before radical and disfiguring surgery is undertaken. Most adenocarcinomas arise from the ethmoid air cells and are especially common in hardwood workers and Bantu Indians. A biopsy specimen revealing adenocarcinoma must be considered to represent a metastasis to the head and neck from kidney, lung, breast, or digestive tract until a metastatic workup is negative.

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philosophy now dictates that a craniofacial resection should be performed as the initial procedure in all patients. With this protocol, cure rates have approached the 90% survival mark. Before this approach, recurrence neared 50%, with metastasis in approximately a third of patients (Fig. 16-20).

Lymphoma Lymphomas represent the most common sarcomas involving the sinonasal tract.9 The majority of these are non-Hodgkin's types of lymphomas. Non-Hodgkin's lymphoma is the second most common malignancy of the head and neck following squamous cell carcinoma. It is important to try to recognize lymphoma as distinct from squamous cell carcinoma because of its different clinical course and the marked radiosensitivity of lymphomas relative to squamous cell carcinoma. Grossly, these tend to be bulky soft tissue masses that may enhance following gadolinium injection and tend to remodel bone and occasionally erode bone rather than destroy bone.lg The nasal cavity and maxillary sinus are the most common sites of origin.

Olfactory Neuroblastoma"* The olfactory neuroblastoma or esthesioneuroblastoma is an uncommon tumor that originates from neural crest cells and arises from the olfactory mucosa. The incidence curve for this disease has a bimodal shape, with the first peak in the 2nd decade and the 2nd peak in the 6th decade. This polypoid tumor may be soft or firm but may be friable and bleed profusely. A unique feature regarding olfactory neuroblastomas and the importance of these lesions to the imaging physician concerns its unique site of origin and pathway of spread. The mass may be relatively slow-growing for a malignant tumor and may cause some expansion and remodeling of bony structures. It may therefore be mistaken for benign disease. On the other hand, the tumor has a propensity for intracranial extension through the dura in the region of the cribriform plate. A change in surgical

Benign Tumors One of the most important benign tumors of the sinonasal structures-although by no means the most common benign tumor in this region-is the juvenile angiofibroma or nasopharyngeal angiofibroma (Fig. 16-21). This is a highly vascular and nonencapsulated polypoid mass that is histologically benign but highly aggre~sive.~ It occurs almost exclusively in males in the second decade of life, who present with nasal obstruction and severe epistaxis as well as facial deformity and proptosis. The site of origin is thought to be the nasopharyngeal region at the pterygopalatine fossa or sphenopalatine foramen. Involvement of the pterygopalatine fossa is seen in approximately 90% of patients as asymmetry in the size or widening of this structure and an absence of the normal fat plane between

Fgule 16-20. Esthesioneuroblastoma. This unique tumor arises from the olfactory mucosa in young adults, It typically spreads anteriorly into the orbital apices and posteriorly into the suprasellar region. The left carotid artery is encased (A)(arrow).There is also inferior extension into the nasal cavity as seen in the post-contrast-enhanced coronal image (B) (arrow).


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Figure 16-21. Juvenile angiofibroma. Axial post-contrast-enhanced CT scan (A) through the paranasal sinuses reveals an enhancing mass within the infratemporal fossa (arrows) that extends into and expands the pterygopalatine fissure (arrhwhead). In the coronal view (B) there is extension into the nasal cavity with destruction of the pterygoid plates and extension into the sphenoid sinus. There is also lateral extension into the region of the cavernous sinus with bone destruction (arrow). These masses are usually supplied by terminal branches of the sphenopalatine artery (C, long arrow). In this particular patient, because of the extension intracranially, there is supply from dural vessels such as the middle meningeal artery (C, short arrow). In addition, there is also supply from other external carotid branches such as the ascending pharyngeal (D). In patients with intracranial extension or with extension into the clivus, there may be supply from branches of the internal carotid artery (E, arrow).

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the pterygoid plates and the back of the maxillary sinus.46 Because of the extreme vascularity of the tumor and The tumor may extend anteriorly and superiorly into the propensity for profuse hemorrhage, the imaging physician maxillary and ethmoid sinuses or superiorly into the cranial must recognize this entity when it occurs and should fossa. There is also the possibility of extension superiorly strongly discourage biopsy. Ultimately, an arteriogram through the inferior orbital fissure into the orbit and then should be performed to demonstrate the major feeding through the superior orbital fissure into the brain. -vessels, which are most often the internal maxillary artery


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Chapter 16

and ascending pharyngeal artery. Preoperative embolization of these branches of the external carotid artery may greatly reduce blood loss at surgery, allowing for a more careful dissection and, therefore, complete resection in addition to minimizing the risk of multiple transfusions. Contrastenhanced CT or MRI examination reveals a polypoid and infiltrating enhancing mass that involves the nasopharynx and pterygopalatine fissures and extends anteriorly into the nasal cavity, maxillary sinuses, and ethrnoid sinuses.4s Again, the orbits and cavernous sinuses may be involved. The treatment of choice is surgical resection. The role of radiation therapy is not clear, although control of tumor growth has been reported. The use of estrogen therapy is also re~ommended.~ Many of these tumors begin to involute toward the end of puberty, and the goal of therapy is to minimize facial deformitv and bone destruction and to fatal epistaxis, until the tumor begins to involute and fibrose as part of its natural history. nere is no premalignant potential.

Neurogenic Tumor34 Schwannomas are benign, encapsulated, slowly growing tumors of the nerve sheath that occur in patients from the 4th to 7th decades. Few have been reported within the sinonasal cavity, although a fairly sizable proportion do occur in the head and neck. These are slow-growing expansile lesions that are important for one to recognize as differential diagnostic possibilities when faced with a similar sinonasal mass. Most importantly, they may mimic juvenile angiofibromas by bowing forward the posterior wall of the maxillary sinus. They do not, however, usually involve the pterygopalatine fissure and by that observation may be differentiated from juvenile angiofibromas in younger patients. Neurofibromas also occur in the head and neck. These are hamartomatous lesions associated with neurofibromatosis I. Some of these may not be differentiable from schwannomas in the head and neck. When plexiform neurofibromas arise from the soft tissues or subcutaneous tissues, they may infiltrate from superficial to deep within the paranasal sinuses. At times these may be aggressive and destructive and mimic malignant tumors.

Fibro-osseous lesions are probably the most common noninflarnmatory benign masses of the sinonasal region. Of all the nonepithelial tumors of the paranasal sinuses, approximately 25% are thought to be fibro-osseous in origin. One of the more common incidental findings, which is a fibro-osseous lesion, is the osteoma (Fig. 16-22). This benign proliferation commonly occurs within the frontal sinus and may cause obstruction or directly erode from the frontal or ethmoid sinus into the cranial cavity, causing a spontaneous cerebrospinal fluid (CSF) leak. These are often described as "ivory" or highly dense bone, which is obvious on both plain film and CT examinations. Osteomas

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at the base of the left frontal sinus (arrow) is an osteoma. This is a common benign tumor within the anterior ethmoids or inferior frontal sinuses and may cause spontaneous cerebrospinal fluid rhinorrhea.

may be small incidental findings on plain film or CT scans but may obstruct the frontal sinuses and again cause CSF rhinorrhea. When multiple osteomas are seen--especially when the skull and mandible are primarily involved--one should entertain the diagnosis of Gardner's syndrome, and investigation of the gastrointestinal tract should be undertaken in a search for intestinal polyps (Box 16-5). Fibrous dysplasia6 is an idiopathic disorder in which the medullary bone is replaced by a poorly organized and loosely woven bone that is also expanded compared with normal adjacent bone (Fig. 16-23). The monostotic type is the most common, involving approximately 75% of all patients. In approximately 25% of the patients, bones of the head and neck are involved, with the maxilla and mandible being the most common sites. Polyostotic fibrous dysplasia accounts for approximately one quarter of all cases of fibrous dysplasia. There is a small potential for

Figure 16-23. Fibrous dysplasia. Polyostotic or monostotic fi-

brous dysplasia frequently occurs in the facial bones. This axial CT scan through the skull base shows monostotic fibrous dysplasia affecting the pterygoid bones on the right (arrow).

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Box 16-5. Syndromes Affecting the Paranasal Sinuses Gardner's Syndrome

Cystic Fibrosis

Osteoma (sinus) Cysts and skin tumors Intestinal polyposis

Nasal polyposis Sinusitis Mucoceles

Kartagener's Syndrome

Louis-Bar Syndrome (Ataxia-Telangiectasia)

Chronic sinusitis Bronchiectasis Situs inversus

Cerebellar ataxia Pulmonary infection Sinus infection

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Basal Cell Nevus Syndrome

Wegener's Granulomatosis

Basal cell carcinoma Dermal pits Calcification of dural structures Cysts in mandible and maxilla Axial skeleton and rib abnormalities

Granulomatous sinuses and respi~;p,x ;trgL Vasculitis Wl r r 1 ' w Glomerulonephritis -1 )

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Figure 16-24. Osteopetrosis. A, A frontal radiograph of the sinuses in a 1-year-old girl reveals the classic sclerotic and chalky appearance of the facial bones and orbits. B and C,Axial and coronal CT scans also show the typical appearance of this rare disease with thickened sclerotic bone and secondary obstruction of the sinuses.


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Chapter 16

Figure 16-25. Ossifying fibroma. An expansile mass with calcified matrix forming arches or rings is indicative of a benign primary bone tumor. With expansion and destruction, a more aggressive process must always be suspected such as a chondrosarcoma or osteogenic sarcoma. I

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malignant transformation (-0.5% of patients). This most often occurs in the polyostotic form. Radiographically, the affected bones are noted to be abnormal because of their texture. There is a ground-glass or ivory appearance of the affected bone with expansion of the middle table blending into the inner and outer tables. Osteopetrosis rarely occurs in the paranasal sinuses (Fig. 16-24). The ossifying fibroma, unlike fibrous dysplasia, contains a lamellar rather than woven pattern of bone and has a normal number of osteoblasts and osteoclasts (Fig. 16-25). Internal regions of disorganization with discrete zones contain either osseous issue or fibrous tissue. Pathologically, the differential diagnosis from fibrous dysplasia is difficult, whereas from an imaging standpoint the differential diagnosis is often much easier. Giant cell tumors43or osteoclastomas make up approximately 5% of all primary bone lesions. Most of these are located in the epiphyseal regions of the long bones, especially around the knee. Approximately 2% of all giant cell

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tumors, however, occur in the head and neck. These may be located in the region of the sphenoid temporal bone or ethmoid sinuses. Approximately 10% to 15% of giant cell tumors have histologic evidence of malignancy, and these lesions should be irradiated following complete surgical excision. From an imaging point of view, these tumors are lytic lesions with narrow zones of transition. A high index of suspicion is necessary on the part of the imaging physician to raise this diagnosis early so that aggressive surgery and radiation therapy can be ~ndertaken?~ Odontogenic tumors that arise from the alveolar ridge may extend to the maxillary sinus.37Approximately 10% to 15% of all maxillary sinus inflammatory and neoplastic diseases have an odontogenic origin. A high index of suspicion is required on the part of the imaging physician when confronted with a suspicious mass within the maxillary sinus; coronal examinations should be done to evaluate the possibility of extension of a cyst or mass from the alveolar ridge into the maxillary sinus (Fig. 16-26). The most common odontogenic lesions involving the maxillary sinus are odontogenic cysts.26 These fall into three broad categories. Primordial cysts represent approximately 5% of odontogenic cysts and are thought to arise from a supernumerary tooth germ in a patient with an otherwise normal complement of teeth. These are cystic masses that expand from the alveolar ridge superiorly into the maxillary sinus. They are unassociated with either normal or abnormal tooth buds. Dentigerous cysts represent approximately 95% of follicular cysts and are thought to arise from an unerupted tooth after the crown of the tooth has been devel~ped."~ The crown of the affected tooth projects into the cystic mass, and the roots of the unerupted tooth project centrifugally from it. These are unilocular and grow slowly, loosening and disrupting the relationship of adjacent teeth. They may also present as cystic masses within the maxillary sinus. These periodontal or radicular cysts are also known as periapical abscesses or granulomas and are the result of inflammatory changes at the tooth root associated with dental caries. Other unusual tumors of the upper molar teeth include

Figure 16-26. Odontogenic mass. On the Waters view of the paranasal sinuses, a teardrop-shaped density was identified in the right maxillary sinus (A, arrow). The accompanying coronal CT image (B) revealed an expansile mass containing multiple teeth.


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established that the patient can cooperate for coronal examination and is stable regarding other injuries that may have been sustained, axial and coronal noncontrast CT examination through the paranasal sinuses is recommended in all instances.

Nasal Bone

Figure 16-27. Inferior orbital wall fracture. Coronal CT scan reveals a fracture in the inferior wall of the right orbit with downward displacement of the fragment (curved arrow) but without herniation of .the orbital contents. --

, multilocular ameloblastoma and the highly dense cementoma. These are beyond the scope of this chapter.

Because of extensive overlying edema, hemorrhage, and soft tissue injury, the deformity of the underlying facial skeleton is often concealed at the time of presentation to the emergency department following trauma. There may be subtle clinical signs such as palpable stepoff of the orbital rim, hypertelorism, midface elongation, or CSF rhinorrhea Radiographic examination is key to the diagnosis of facial and orbital fractures on a timely basis so that these lesions can be treated along with other potentially life-threatening injuries.J5.32 Before imaging evaluation of the patient with suspected facial fractures, or to rule out such fractures, one should evaluate the cervical spine for fracture andlor instability on both a clinical and imaging protocol. When it has been

Fractures of the nasal bone are the most common fracture of the facial skeleton.36 These may be isolated or associated with other injuries. Plain film examination with oblique cone-down views of the nasal bones is the most sensitive study for identifying and mapping these lesions. In children, when the intranasal suture is not yet ossified, dislocation of the cartilaginous portion of the nose is more common. In adults, when the nose is struck, linear fracture traversing the long axis of the nose is the expected lesion. 8

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A blow to the orbit most often strikes the inferior orbital rim. It is now thought that the relatively thick rim of the orbit has elastic properties that allow it to bend posteriorly and rebound anteriorly following trauma. During this posterior excursion of the inferior orbital rims, however, there may be wrinkling and then crumbling of the floor of the orbit.12 There is a groove within the floor of the orbit (the groove for the infraorbital nerve) that acts as a fault line, allowing orbital floor fractures to occur as the most common isolated fracture of the orbit. With more extensive force, there may be fracture of both the inferior orbital rim and the orbital floor. The former lesion is known as a "pure" blowout fracture, whereas the latter lesion, involving the inferior orbital rim,is known as a "impure" blowout fracture (Fig. 16-27). Although the medial orbital wall the lamina papyracea, is the thinnest bone in the body, it is supported by laterally and medially running septa of the ethrnoid air cells. These act as struts between free segments of the lamina papyracea to prevent medial orbital blowout. Fractures through the

Figure 16-28. Trimalar fracture. On the axial view the tnmalar fracture (A, arrow) is manifested as fractures of the anterior sinus wall and posterior sinus wall. B, Fracture of the ipsilateral zygomatic arch is shown. , - . . . . .


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Figure 16-29. Le Fort fractures. The unifying fracture among all types of Le Fort fractures is fracture through the pterygoid plates (A, arrow). Le Fort I fractures are rare. With Le Fort I1 types, the medial orbital wall (B, long arrow) is fractured, with continuation of the fracture line through the floor of the orbit and into the pterygoid plates. A Le Fort ID fracture (B, short arrow) extends from the medial

wall of the orbit to the lateral orbital wall and then inferiorly through the pterygoid plates. medial orbital wall still occur either through transmission from direct trauma to the nose or from increased intraorbital pressure. Blowout fractures of the orbital roof also occur. Again, these may be caused by transmitted force through the superior orbital rim. More often they are the result of extension of fracture elsewhere in the skull into the superior orbital rim.

The Le Fort III fracture also begins as a fracture through the base of the nose or glabella and extends along the medial wall of the orbit, much as the Le Fort I1 fracture does. Rather than extending into the floor of the orbit, however, there is extension of the fracture line along the lateral wall of the orbit, inferiorly through the maxillary sinus and then posteriorly through the pterygoid plates (Fig. 16-29).

Side of the Face

References

Trauma to the side of the face or lateral orbital rim may result in the familiar tripod or trimalar fracture28 (Fig. 16-28). This is a complex fracture involving the floor of the orbit, the anterior and posterior walls of the maxillary sinus, the zygomatic arch, the zygomaticofrontal suture, and the posterior wall of the orbit. Although it actually has at least four points, in any single plane it may appear as a three-pointed fracture fragment; thus, the eponyms are tripod and trimalar.

1. Babbel R, Hamsberger HR, Nelson B, et al: Optimization of techniques in screening CT of the sinuses, AJNR Am J Neuroradiol 12: 849-854, 1991. 2. Bames L, Verbin RS, Gnepp DR: Diseases of the nose, paranasal sinuses and nasopharynx. In Barnes L (ed): Surgical Pathology of the Head and Neck, vol 1. New York, Marcel Dekker, 1985, pp 403-451. 3. Batsakis JG: Tumors of the Head and Neck: Clinical and Pathological Considerations. In Baltihouse Z ( 4 ) : Baltimore, Williams & Wilkins, 1979, pp 177-178. 4. Bryan N, Sessions RB,Horowitz BL: Radiographic management of juvenile angiofibromas. AJNR Am J Neuroradiol 2157-166, 1981. 5. Chapnick JS, Bach MC: Bacterial and fungal infections of the maxillary sinus. Otolaryngol Clin North Am 9:43, 1976. 6. Dehner LP: Fibro-osseous lesions of bone. In Ackerman LU, Spjut HJ, AbeU MR (4s): Bones and Joints. International Academy of Pathology, Monograph No. 17. Baltimore, Williams & Wilkins, 1976, pp 209-235. 7. Dilon WP, Som PM, Fullerton GD: Hypointense MR signal in chronically inspissated sinonasal secretions. Radiology 174:73078, 1990. 8. Dodd GD, Jing BS: Radiology of the Nose, Paranasal Sinuses and Nasopharynx. Baltimore, Williams & Wilkins, 1977. 9. Duncavage JA, Campbell BH, Hanson GH: Diagnosis of malignant lymphomas of the nasal cavity, paranasal sinuses and nasopharynx. Laryngoscope 93:1276, 1983. 10. Evans FO, Sydnor JB,Moore WEC, et al: Sinusitis of the maxillary antnun. N Engl J Med 293:735, 1976. 11. Goss CM: Gray's Anatomy of the Human Body, 27th ed. Philadelphia, Lea & Febiger, 1963, pp 1167-1176. 12. Hamrnerschlag SB, Hughes S, O'ReiUy GV, et al: Another look at blow out fractures of the orbit. AJNR Am J Neuroradiol 3: 331-335, 1982. 13. Harrison DFN: Midline destructive granuloma: Fact or fiction? Laryngoscope 97:1049, 1987. 14. Kennedy DW, Zinreich SJ, Rosenbaum AE, et al: Functional endoscopic sinus surgery. Arch Otolaryngol 111:576-582, 1985. 15. Kreipke DL, Moss JJ, Franco JM,et al: Computed tomograpy and

Le Fort Fractures The unifying feature of Le Fort fractures is disruption Because of the associated disrupof the pterygoid ~lates.3~ tion of the pterygoid venous plexus, it is important to recognize these fractures as potentially life-threatening because of the relatively large nasopharyngeal hematoma that sometimes occurs. There are three types of Le Fort fractures: The LQ Fort I fracture is a horizontal fracture above the hard palate with separation of the hard palate and lower portion of the pterygoid plates from the rest of the facial infrastructure. The Le Fort II fracture begins at the bridge of the nose and extends laterally along the medial wall of the orbit and then inferiorly along the inferior wall of the orbit, through the anterior wall of the maxillary sinus, and then posteriorly through the alveolar recess of the maxillary sinus into the pterygoid plates.


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thin-section tomography in facial muma. AJNR Am J Neuroradiol 5:423, 1984. 16. Lanzieri CF, Levin HL,Rosenbloom SA, et al: Three dimensional surface rendering of nasal anatomy for CT data. Arch Otolaryngol 115:1444-1446, 1989. 17. Lanzieri CF, Shah M, Krauss D, et al: Use of Gd-DTPA enhanced MRI for differentiating mucoceles from neoplasms in the paranasal sinuses. Radiology 178:425-428, 1991. 18. Last RJ: Anatomy Regional and Applied, 6th ed., London, Churchill Livingstone, 1978, pp 398406. 19. Lee YY, et al: Lymphomas of the head and neck: CT findings at initial presentation. AJNR Am J Neuroradiol 8:665, 1987. 20. Levine HL:The sphenoid sinus, the neglected sinus. Arch Otolaryngo1 104:585-587, 1978. 21. Maffe MF. Endoscopic sinus surgery: Role of the radiologist. AJNR Am J Neuroradiol 12855460, 1991. 22. Maresh MM:Paranasal sinuses from birth to late adolescence. Am J Dis Child 60:58, 1940. 23. McGill TJ, Simpson G, Healy GR: Fulminant aspergillosis of the nose and paranasal sinuses: A new clinical entity. Laryngoscope 90: 748, 1980. 24. Modic MT, Weinstein MA, Berlin J, et al: Maxillary sinus hypoplasia visualized with CT. Radiology 135383-385, 1980. 25. Moore KL: The special sense organs. In The Developing Human. Philadelphia, WB Saunders, 1973, pp 335-349. 26. Mourshed F: A roentgen study of dentigerous cysts. Oral Surg 18: 47-61, 1964. 27. Myerowitz RL,Guggenheimer J, Barnes L:Infectious diseases of the head and neck. In Barnes L (4): Surgical Pathology of the Head and Neck, vol 2. New York, Marcel Dekker, 1985, pp 1771-1822. 28. Nalcamura T,Gross CW:Arch Otolaryngol97:28&290, 1973. 29. Osborn AG: The nasal arteries. AJNR Am J Neuroradiol 130:89, 1978. 30. Paff GH: Anatomy of the Head and Neck. Philadelphia, WB Saunders, 1973, pp 183-203. 31. Paling MR, Roberts HL,Fauci AS: Paranasal sinus obliteration in Wegener's granulomatosis. Radiology 144:539, 1982. 32. Pathria MN, Blaser SI: Diagnostic imaging of craniofacial fractures. Radio1 Clin North Am 27:839-853, 1989. 33. Postic WP, Wetmore RF: Pediaeic rhinology. In Goldman JL (ed): The Principles and Practice of Rhinology. New York, John W~ley& Sons, 1987, pp 801-845. 34. Richtsmeier WJ, Johns ME: Actinomycosis of the head and neck. In Batsakis J, Savory J (4s): Critical Review in Clinical Laboratory Sciences, vol 11. Boca Raton, Fla, CRC Press, 1979, pp 175-202. 35. Rogers LF: Radiology of Skeletal Trauma, vol 1. New York, Churchill Livingstone, 1982.

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16. Schultz RC, Oldham RT: An overview of facial injuries. Surg Clin North Am 57:987-1010, 1977. 37. Shafer WG,Hine WK, Levy BM: A Textbook of Oral Pathology. Philadelphia, WB Saunders, 1974. 38. Smith GA, Ward PH: Giant cell lesions of the facial skeleton. Arch Otolaryngol 104:186, 1978. 39. Som PM, Dillon WP, Curtin HD,et al: Hypointense paranasal sinus foci: Diierential diagnosis with MRI in relation to CT findings. Radiology 176:777-781, 1990. 40. Som PM, Diion WP, Fullerton GD, et al: Chronically obstructed sinonasal secretions observations on T1 and 72 shortening. Radiology 172515-520, 1989. 41. Som PM, Dillon WP, Sze G, et al: Benign and malignant sinonasal lesions with intracranial extension: Differentiation with MRI. Radiology 172763-766, 1989. 42. Som PM, Lawson W, Biller H, et al: Ethmoid sinus disease: CT evaluation in 400 cases. Radiology 159:591-597, 1986. 43. Som PM, Lawson W, Cohen BA: Giant cell lesions of the facial bones. Radiology 147:129-183. 44. Som PM, Shapiro MD, Biller HF, et al: Sinonasal tumors and inflammatory tissues: Differentiation with MRI. Radiology 167:803808, 1988. 45. Som PM: Sinonasal cavity. In Som PM, Burgeron RT (eds): Head and Neck Imaging, 2nd ed. St. Louis, Mosby-Year Book, 1991, pp 51-276. 46. Som PM, Cohen BA, Sacher M, et al: The angiomatous polyp and the angiofibroma: Ttvo different lesions. Radiology 144:324, 1982. 47. Swischuk LE,Hayden CK, Dillard RA: Sinusitis in children. Radiographics 2241-252, 1982. 48. Temer F, Weber W, Rue fen acht D, et al: Anatomy of the ethmoid: CT endoscopic and macroscopic. AJNR Am J Neuroradiol 6:77-84, 1985. 49. Towbin R, Dunbar JJ: The paranasal sinuses in children. Radiographics 2253-280, 1982. 50. Van Tassel P, Lee YY, Jing BS, et al: Mucoceles of the paranasal sinuses. AJNR Am J Neuroradiol 10:607412, 1989. 51. Williams HG: Nasal physiology. In Paparella MM, Shumrick DA (4s): Otolaryngology: Basic Science and Related Disciplines, vol 1. Philadelphia, WB Saunders, 1973, pp 329-346. 52. Zinreich SJ, Kennedy DW, Kumar AJ, et al: MRI of the nasal cycle. J Comput Assist Tomogr 121014, 1988. 53. Zinreich SJ, Kennedy DW, Malat J, et al: Fungal sinus~tis:Diagnosis with CT and MRI.Radiology 169:439-444, 1988. 54. Z i i c h SJ, Kennedy DW, Rosenbaum A& et al: Paranasal sinuses: (3imaging. Requirements for endoscopic surgery. Radiology 163: 769-775, 1987.


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Cervical Adenopathy and Neck Masses Roy A. Holliday, Deborah L. Reede

High-resolution computed tomography (CT) and magnetic resonance imaging (MU) have proved to be invaluable tools for evaluating the soft tissue structures of the neck. Although many imaging modalities are available for the evaluation of a neck mass, including radiography, ultrasonography, angiography, and radioisotope imaging, CT and MRI provide anatomical detail that cannot be obtained with these other modalities. CT and MRI demonstrate both the precise location of a neck mass and its relationship to adjacent vascular, muscular, and neural structures. In addition to providing this anatomical detail, CT and MRI frequently are able to characterize the vascularity and internal architecture (solid versus cystic) of a neck mass. The combination of soft tissue characterization and anatomical localization afforded by CT and MRI allows radiologists to make a substantial contribution to the preoperative assessment of the patient with a neck mass. Although an exact tissue diagnosis is not always possible, careful analysis of the imaging features of a neck mass in combination with clinical history and physical examination produce a reasonably short differential diagnosis in nearly every case.

Imaging Technique CT imaging of the neck is performed with the patient supine on the scanner gantry. Contiguous 5-mm-thick axial images are usually obtained from the level of the superior orbital rim to the lung avex. Care must always be taken to avoid image degradation by dental amalgam.-one common solution is to acquire images from the superior orbital rim to the hard with the-use of gantry Ggulation parallel to the central skull base. Images from the alveolar ridge of the mandible to the lung apex are then obtained with a gantry angulation parallel to the body of the mandible. If the patient's chin is fully extended, this latter series may be obtained with a 0-degree gantry angulation. Intravenous contrast enhancement is essential for CT examinations of the soft tissue of the neck, to facilitate both tissue characterization of neck masses and separation of neck masses from normal vascular structures. Most investigators recommend an initial rapid bolus of approximately 50 mL of contrast material administered over 1 to 2 minutes before image acquisition, followed by a steady rapid drip infusion of the remaining 100 to 150 mL during scanning. Power injectors, commonly used for abdominal or thoracic CT scanning, can be readily adapted for neck CT examinations. Contrast administration should be interrupted during changes in gantry angulation.

Optimal MRI of the neck requires the use of surface coils. Images of the suprahyoid neck may be obtained by placement of the patient well inside many standard head surface coils. Images of the infrahyoid neck require dedicated anterior neck surface coils, because the use of posteriorly placed cervical spine surface coils results in suboptimal images owing to signal drop-off. Current MRI techniques involve acquisition of T1weighted images in sagittal, axial, and coronal projections with corresponding T2-weighted images obtained in the projection that best depicts the lesion. Slice thicknesses of 4 to 6 mm with 1- to 2-mm intervals between slices are commonly used. The prolonged scan times of axial T2weighted images often result in images of diminished diagnostic quality owing to gross patient motion as well as artifacts produced by swallowing, respirato~ymotion, and cardiac pulsations. To overcome these problems, rapid spinecho techniques are often used to obtain T2-weighted images in shorter scan times.49 Contrast administration is not essential in MRI of neck masses. The use of multiple pulse sequences and multiple projections is usually sufficient to differentiate neck masses from adiacent vascular structures. When contrast enhancement isrequired for tissue characterization, fat-suppressed TI-weighted images are commonly used, particularly in the assessment of cervical aden~pathy.~'

Choice of Imaging Modality MRI and CT should be considered complementary, rather than competitive, modalities for imaging neck masses. The advantages MRI offers over CT in imaging other parts of the body (multiplanar capability, lack of ionizing radiation, safer contrast agents) also apply to imaging the soft tissues of the neck. By comparison, CT examinations offer the advantages of superior assessment of osseous integrity, shorter examination time, wider patient access, and lower cost.'2 The authors prefer to use contrast-enhanced CT as the initial study to assess neck masses in adults. In children and in adults whose clinical status precludes the use of iodinated contrast material, MRI is the study of choice, although a limited noncontrast CT study may be required for the evaluation of osseous integrity. The remainder of this chapter reflects this preference and emphasizes the normal and abnormal CT appearance of the soft tissues of the neck.


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Normal Gross Anatomy The neck is composed of the posteriorly located nucha and the anteriorly located cervix. The nucha, which consists primarily of the vertebral column and its associated musculature, is discussed in detail in Chapter 19. For practical purposes, the cervix (which also means neck) can be thought of as a cylinder of soft tissue whose superior extent is a line connecting the occiput and the tip of the chin and whose inferior extent parallels the course of the first rib at the thoracic inlet.I3 The most important landmark to identify when one is studying the neck in any plane is the sternocleidomastoid muscle. The sternocleidomastoid muscle takes its origin from the mastoid tip and digastric notch at the skull base and extends anteriorly, inferiorly, and medially, spiraling across the anterior aspect of the neck on each side to insert as two heads on the medial third of the clavicle and the manubrium. The course of the sternocleidomastoid muscle is the basis for the division of the soft tissues of the neck into two paired spaces, the anterior and posterior triangles (Fig. 17-1). The sternocleidomastoid muscle forms the posterior border of the anterior triangle and the anterior border of the posterior triangle. All structures located anterior to the sternocleidomastoid muscle lie within the anterior triangle; those deep as well as posterior to it are in the posterior triangle.32 It is important to remember that no septum or fascial plane physically separates the anterior from the posterior triangle. The anterior triangles have a common side, abutting each other in the midline. Their borders are the sternocleidomastoid muscle posteriorly, the mandible superiorly, and the midline medially. The hyoid bone divides this triangle

Figure .'-7l the neck. Anterior of the digastric muscle; 2, posterior belly of the digastric muscle; 3, superior belly of the omohyoid muscle; 4, inferior belly of the omohyoid muscle; 5, sternocleidomastoid muscle; 6 , trapezius muscle. A, Submental triangle; B, submandibular triangle; C, carotid triangle; D, muscular triangle; E, occipital triangle; F, subclavian triangle. (From Reede DL, Whelan MA, Bergeron RT: CT of the soft tissue structures of the neck. Radio1 Clin North Am 22:239, 1984.)

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into a suprahyoid portion and an infrahyoid portion, each of which has two subdivisions. The suprahyoid division contains the laterally located submandibular triangles and the medially located submental triangles. Superiorly these triangles are separated from the oral cavity by the mylohyoid muscle. This muscle forms a sling connecting the two inner surfaces of the mandible with the hyoid bone. By definition, structures above the mylohyoid muscle are in the oral cavity; those below are in the neck. The base of each submandibular triangle is formed by the ramus of the mandible. The other two sides of each submandibular triangle are formed by the anterior and posterior bellies of the digastric muscle. The digastric muscle takes its origin from a depression on the skull base between the mastoid tip and the styloid process known as the digastric notch. The posterior belly of the digastric muscle extends anteriorly, inferiorly, and medially from the digastric notch to the greater cornu of the hyoid bone. The anterior belly of the digastric muscle extends from the greater cornu anteriorly, superiorly, and medially to insert on the anterior border of the mandible, inferior to the attachment of the mylohyoid muscle. The major structures contained within the submandibular triangle are numerous small lymph nodes and the submandibular salivary glands. The anterior surface of the submandibular gland abuts the posterior free margin of the mylohyoid muscle, so a small portion of each submandibular gland lies within the posterior oral cavity but the majority of the gland lies within the suprahyoid neck. The base of the submental triangle is formed by the hyoid bone. The other two sides of the submental triangle are formed by the anterior bellies of the digastric muscles. No major anatomical structures are located in this triangle except for a few small lymph nodes and branches of the facial artery and vein. The infrahyoid division of the anterior triangle is divided by the superior belly of the omohyoid muscle into two parts, the carotid triangle superolaterally and the muscular triangle inferomedially. The infrahyoid portion of the anterior triangle contains the larynx, hypopharynx, trachea, esophagus, lymph nodes, and thyroid and parathyroid glands. The two sides of each posterior triangle are the sternocleidomastoid muscle anteriorly and the trapezius muscle posteriorly. The base of each triangle is formed by the clavicle. The inferior belly of the omohyoid muscle crosses the inferior aspect of the posterior triangle and divides it into two unequal parts, the occipital triangle anteriorly and the subclavian triangle inferiorly. The major structures located within the occipital triangle are the spinal accessory nerve (cranial nerve XI) and its associated chain of lymph nodes. The major structures located within the subclavian triangle are the transverse cervical vessels and their associated chain of lymph nodes. Also present within the posterior triangle are the exiting cervical nerve roots, the cervical components of the brachid plexus, and nutrient vessels. The internal jugular vein and its associated chain of lymph nodes closely parallel the deep surface of the anterior margin of the sternocleidomastoid muscle, thereby bridging the anterior and posterior triangles. The arterial and neural components of the carotid sheath, the common


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Chapter 17

carotid artery, the internal carotid artery, and the vagus nerve, also traverse the neck within the anterior triangle.32 -syi wal

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muscle comes a change in relative sizes of the anterior and posterior triangles. Superiorly the anterior triangle occupies the majority of the cross-sectional area of the neck because there is little space between the sternocleidomastoid and trapezius muscles. Inferiorly the posterior triangle occupies the majority of the cross-sectional area of the neck because there is little space between the anterior surface of the sternocleidomastoid muscle and the midline. The mylohyoid muscle, the major landmark separating the oral cavity from the suprahyoid neck, is readily identified on both coronal and axial images. On axial images (Fig. 17-24 and B), the muscle appears in cross-section as

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Normal Sectional Anatomy o

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The sternocleidomastoid muscle is a constant landmark that can always be identified on axial CT scans or MR images through the neck. As one progresses from superior to inferior, the location of the sternocleidomastoid muscle moves from a far lateral position to a paramedian position. With this change in position of the sternocleidomastoid

Figure 17-2. Normal sectional anatomy at the junction of the oral cavity and neck. A, Contrast-enhanced CT image at the level of the mandible. The sternocleidomastoid muscle is posterior to the parotid gland. B, TI-weighted MR image at a similar level in a different patient. Note the greater tissue contrast between the mylohyoid muscle and the submandibular gland on MRI. Coronal CT scan (C) and coronal TI-weighted MR image (D) demonstrate the anterior belly of the digastric inferior to the sling-shaped mylohyoid muscle. 1, Sternocleidomastoid muscle; 2, mylohyoid muscle; 3, submandibular gland; 4, internal jugular vein; 5, internal carotid artery; 6, posterior belly of digastric muscle; 7, parotid gland; 8, anterior belly of digastric muscle; 9, longus colli muscle.


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Figure 17-3. Normal axial anatomy of the suprahyoid neck. T1weighted MR image in same patient as Figure 17-2B. The sub-

mental triangle is located between the two anterior bellies of the digastric muscle. 1, Sternocleidomastoid muscle; 2, mylohyoid muscle; 3, submandibular gland; 4, internal jugular vein, 5, internal carotid artery; 6, posterior belly of digastric muscle; 8, anterior belly of digastric muscle; 9, longus colli muscle.

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two separate muscle bundles medial to the mandible. As axial images are obtained from superior to inferior, the distance between the separate bundles decreases. The superior aspect of the submandibular gland is identified on axial images at the posterior margin of the mylohyoid muscle. On coronal images, the muscle has the configuration of a hammock suspended from the medial (lingual) surface of the mandible (Fig. 17-2C and D).lZ Immediately inferior to the mylohyoid muscle, the anterior bellies of the digastric muscle can be identified (Fig. 17-3). Depending on the degree of angulation used on axial imaging, varying amounts of mylohyoid muscle can be seen projecting between the anterior bellies of the digastric muscle. The cervical portion of the submandibular gland lies lateral to each anterior belly of the digastric muscle. The posterior belly of the digastric muscle can usually be identified medial and posterior to the parotid gland, separating the gland from the contents of the carotid sheath.32 The hyoid bone is the major bony landmark of the anterior neck (Fig. 174). The hyoid is best identified on axial CT images, where its central body and greater horns (cornua) appear in the midkine as an "inverted U" approximately at the level of the C3-4 disk space. The carotid bifurcation is typically located at or near the level of the hyoid bone. The thyroid cartilage has an inverted V appearance on axial images. The superior third of the cartilage is not fused in the midline at the level of the thyroid notch. Immediately superficial to the two halves of

Figure 17-4. Normal axial anatomy at the level of the hyoid bol 1, Contrast-enhanced CT scan. Note that the normal retrofacial vein or proximal external carotid artery might be mistaken for a lymph node or other mass on a noncontrast examination. B, T1weighted MR image demonstrates the same soft tissue and vascular anatomy without intravenous contrast. 1, Sternocleidomastoid muscle; 3, submandibular gland; 4, internal jugular vein; 5, internal carotid artery; 6, external carotid artery; 7,retrofacial vein; 9, longus colli muscle.


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Figure 17-5. Normal axial anatomy at the level of rhe thyroid cartilages. A, CT scan. B; TI-weighted MR image. Mote how the anterior margin of the sternocleidomastoid muscle is located anterior to the vertebral body. Compare with Figure 17-2B. 1, Sternocleidomastoid muscle; 2, strap muscle; 3, internal carotid artery; 4, internal jugular vein; 9, longus colli muscle.

the thyroid cartilage are the strap muscles (sternohyoid, sternothyroid, thyrohyoid, and superior belly of the omohyoid). The degree and pattern of ossification of the cartilages vary with the age and sex of the patient. Separation of nonossified cartilage from the overlying strap muscles is accomplished more easily with MRI than CT. At the level of the thyroid cartilage (Fig. 17-5), the carotid sheath structures are situated along the anterior surface of the sternocleidomastoid muscle or slightly deep to it, posterior and lateral to the thyroid cartilage. The superior cornua of the thyroid cartilage are easily identified as paired calcified structures located lateral to two of the extrinsic muscles of the spine, the longus colli muscles. The inferior cornua of the thyroid cartilage articulate with the posterior aspect of the cricoid cartilage. The cricoid c p l a g e has a characteristic circular appearance on axial imaging. As with the thyroid cartilage, the degree of ossification of the cricoid varies with age. In adult patients, the cricoid cartilage appears on CT scans as a thin rim of calcification surrounding a lucent medullary center.32On TI-weighted MR images, the cricoid appears as a ring of tissue isointense to fat. At approximately the level of the cricoid cartilage (Fig. 17-6), the superior pole of the thyroid gland appears on axial images as a triangular soft tissue structure situated between the cricoid cartilage medially and the carotid sheath structures laterally. The normal gland enhances uniformly with iodinated intravenous contrast material.32On noncontrast TI-weighted images, the gland is homogeneous in appearance and slightly hyperintense to skeletal muscle. The level of the cricoid cartilage also marks the point at which the omohyoid muscle crosses over the internal jugular vein. Images at the level of the first tracheal ring (Fig. 17-7) demonstrate the lower poles of the thyroid gland and the adjacent carotid sheath structures. The sternocleidomastoid muscles have a paramedian position just superior to their insertions on the sternum and clavicle. The esophagus is

usually collapsed, lying posterior to the trachea and usually just to the left of the midline. The posterior triangle of the normal supracricoid neck appears as a fat-filled cleft containing a few small soft tissue structures representing nutrient vessels, lymph nodes, and nerves.32Beginning at the level of the cricoid cartilage, the anterior scalene muscle can be identified in the medial aspect of the posterior triangle, posterior to the carotid sheath structures. The anterior scalene, which arises from the transverse processes of C3 through C6 and inserts on the superior and posterior surfaces of the medial first rib, lies directly anterior to the exiting trunks of the brachial plexus. At the level of the ii~-sttracheal ring, the brachial plexus is identified as a heterogeneous low-density or lowsignal-intensity focus immedia tely posterior to the anterior scalene muscle.

Evaluation of Cervical Adenopathy Enlarged cervical lymph nodes are the most common cause of a neck mass in an adult. In patients older than 40 years, the enlarged nodes are most often secondary to metastatic carcinoma, usually from a primary neoplasm of the aerodigestive tract. In patients between the ages of 21 and 40, the enlarged nodes are most often secondary to lymphoma.37 The optimal evaluation of cervical lymph nodes requires close attention to radiographic detail as well as an understanding of basic anatomical and pathologic principles of otolaryngology.

Anatomic Principles Approximately 300 lymph nodes are located in the head and neck. The French anatomist R ~ u i v e r edivided ~~ these nodes into the following 10 principal groups (Fig. 17-8)? 1. Occipital nodes.


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Figure 17-6. Normal axial anatomy at the level of the cricoid cartilage and inferior comua of the thyroid cartilage. A, CT scan. The asymmetry in the diameters of the internal jugular veins is a normal variant. B, TI-weighted MR image. 1, Sternocleidomastoid muscle; 2, thyroid gland; 3, internal carotid artery; 4, internal jugular vein; 8, trapezius muscle; 9, longus colli muscle.

2. 3. 4. 5. 6. 7.

8. 9. 10.

Mastoid nodes. Parotid nodes. Facial nodes. Submandibular nodes. Submental nodes. Sublingual nodes. Retropharyngeal nodes. Anterior cervical nodes. Lateral cervical nodes.

The first six groups form a lymphoid collar at the junction of the head and neck. Each group is responsible for the primary lymphatic drainage of a different region of the neck, as follows: Occipital: Scalp and subcutaneous tissues of the occiput and superior neck. Mastoid: Parietal scalp and auricle. Parotid: Forehead, temporal scalp, lateral face, posterior cheek, lateral gingiva, buccal mucous membrane, exterior auditory canal, and parotid gland. Facial: Lateral eyelids, anterior cheek, midface.

Submandibular: Lateral chin, lower and upper lips, lower cheek, anterior nose, medial eyelids, gingiva, anterior tongue, floor of the mouth, and submandibular and sublingual glands. Submental: Central chin, lower lip, anterior gingiva, anterior floor of mouth, and tip of tongue. The sublingual nodes also drain the tongue and floor of mouth but are not always identifiable as a separate group. The retropharyngeal nodes are further divided into medial and lateral groups. The medial group lies in the midline of the suprahyoid neck directly posterior to the pharynx. Enlargement of the medial group of retropharyngeal nodes is most commonly seen in neonates and young children. The lateral group is located anterior to the longus colli and longus capitus muscles, medial to the internal carotid artery, in both the suprahyoid and the infrahyoid neck. The retropharyngeal lymph nodes primarily drain the nasopharynx and posterior oropharynx as well as the paranasal sinuses, middle ear, posterior palate, and nasal cavity. The anterior cervical nodes are toward the midline of the infrahyoid neck, located between the two carotid



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Figure 17-7. Normal axial anatomy at the level of the first tracheal ring. A, CT scan. B, TI-weighted MR image. Note the relative sizes of the fat-filled posterior triangles and the anterior triangle between the right and left sternocleidomastoid muscles. Compare with Figures 17-2B and 17-5B. 1, Sternocleidomastoid muscle; 2, thyroid gland; 3, internal carotid artery; 4, internal jugular vein; 5, anterior scalene muscle; 6, esophagus; 9, longus colli muscle.

Facial nodes Jugulodigastric node

Submandibular nodes Submental nodes External carotid artery

Spinal accessory nerve Greater auricular nerve

Internal iugular chain (common carotid artery, internal iugular vein, vagus nerve)

Spinal accessory chain External jugular vein ransverse cervical chain

Anterior jugular chain

Figure 17-8. Nodal chams of the neck. (From Reede DL, Bergeron RT: CT of cervical lymph nodes. J Otolaryngol 11:411, 1982.)

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sheaths. There are two divisions to this nodal group. The superficial division lies on the anterior surface of the strap muscles, following the course of the anterior jugular vein, The deep division of the anterior cervical nodes (also known as the juxtavisceral nodes or anterior compartment nodes) is located anterior to the larynx, thyroid gland, and trachea as well as in the tracheoesophageal groove. Included in the deep division is the Delphian node, located in the cricothyroid membrane of the larynx. The deep division drains the supraglottic and infraglottic larynx, piriform sinuses, thyroid gland, trachea, and esophagus. The lateral cervical group constitutes the primary nodes of clinical interest in head and neck malignancies because it serves as a common route of drainage for all of the major regional structures. Similar to the anterior cervical nodes, the lateral cervical nodes are divided into superficial and deep divisions. The nodes in the superficial division follow the course of the external jugular vein. The deep division of lateral cervical nodes is further subdivided into the spinal accessory, internal jugular, and transverse cervical chains. The spinal accessory chain of nodes follows the course of the spinal accessory nerve (cranial nerve XI) in the posterior triangle of the neck, deep to the sternocleidomastoid muscle. The spinal accessory chain receives drainage from the occipital and mastoid nodes as well as the lateral portions of the neck and shoulders. The internal jugular chain of nodes follows the course of the internal jugular vein. At the superior aspect of this chain under the skull base, it is impossible to separate the internal jugular chain from the superior aspect of the spinal accessory chain. As the internal jugular vein descends in the neck, it is crossed by two muscles, the posterior belly of the digastric muscle superiorly and the omohyoid muscle inferiorly. At each junction of muscle and vein, a single lymph node, larger than adjacent nodes, is present. The jugulodigastric node (also known as the sentinel or tonsillar node) receives the lymphatic drainage from the submandibular nodes as well as the palatine tonsil and lateral oropharyngeal wall. The jugulo-omohyoid node receives all of the lymphatic drainage of the tongue. The internal jugular nodes (also known as the deep cervical nodes) are arranged either in series or in parallel interconnecting rows adjacent to the vein. The nodes drain the parotid, submandibular, submental, retropharyngeal, and some anterior chain nodes. Nodes superior to the point where the omohyoid muscle crosses the internal jugular vein are usually located anterolateral to the vein. Nodes inferior to this point may be located anterior, medial, or posterior to the vein. This infraomohyoid node also receives lymphatic drainage from the arm and superior thorax. Among the most inferior of the internal jugular nodes are the nodes of Virchow. The transverse cervical chain of nodes (also known as the supraclavicular nodes) follow the course of the transverse cervical vessels. The nodes in this chain connect the inferior aspects of the spinal accessory, internal jugular, and anterior jugular chains. The transverse cervical chain also receives drainage from the subclavicular nodes, the skin of the anterolateral neck, and the upper chest wall.

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Figure 17-9. Simplified nodal classification. Diagram of the head and neck in left anterior oblique projection. Palpable nodes are indicated with use of a simplified nomenclature of Roman numerals I through VII. See text for explanation. (From Som PM: Lymph nodes of the neck. Radiology 165:596, 1987.)

In an attempt to eliminate the variations in nodal terrninology, a simplified nodal classification was proposed in 1981.36This classification divides the clinically palpable cervical nodes into seven groups, each designated by a roman numeral (Fig. 17-9), as follows: Level I: Submandibular and submental lymph nodes. Level LI: Internal jugular chain from the skull base to the level of the carotid bifurcation. Level 111: Internal jugular chain from the level of the carotid bifurcation to the level of the intersection of the chain with the omohyoid muscle. Level IV: Infraomohyoid portion of the internal jugular chain. Level V: Posterior triangle lymph nodes. Level VI: Nodes related to the thyroid gland. Level VII: Nodes in the tracheoesophageal groove and superior mediastinum. It is important to remember that this system does not include all the cervical lymph nodes. Retropharyngeal nodes and transverse cervical nodes are not included. The system, however, is easily transferred to sectional imaging (Fig. 17-10). Because the carotid bifurcation is typically located at or near the level of the hyoid bone and the level of the intersection of the internal jugular chain with the omohyoid muscle is at the level of the cricoid cartilage,


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Figure 17-11). Sectional imaging using simplified nodal classification. A, Axial contrast-enhanced CT scan demonstrates bilateral lymph nodes (curved white arrows) anterior to each submandibular gland. They are level I (submandibular triangle) lymph nodes. Note the lucent zone of fat eccentrically located in each node. These zones represent prominent nodal hila. Compare with Figures 17-12 and 17-26. B, Axial contrast-enhanced CT scan demonstrates a homogeneous 2.5-cm diameter lymph node (asterisk) in the left posterior triangle deep to the sternocleidomastoid muscle (s) and separate from the internal jugular vein (v), internal carotid artery (a), and posterior belly of the digastric muscle (d). This is a level V (spinal accessory chain) lymph node. Asymmetry in the appearance of right and left digastric muscles is secondary to slight skewing of the patient's head within the scanner gantry.

the following axial levels may be used in staging nodal disease at imaging (Fig. 17-1 Axial level II: Suprahyoid internal jugular chain. Axial level HI: Lnfrahyoid internal jugular chain above the cricoid cartilage. Axial level IV: Infracricoid internal jugular chain. Patients referred for imaging of cervical lymph nodes typically can be assigned to one of three categories. The first is a patient with a known malignancy of the head and neck in whom nodal staging is required. The second is a patient with a neck mass, already demonstrated by aspiration cytology to be metastatic squamous cell carcinoma, in whom no primary head and neck malignancy is identified. The third is a patient with a neck mass of uncertain origin.

Modal Staging CT remains the standard for assessing palpable and nonpalpable nodal metastases in patients with tumors of

the head and neck. Based on the work of MancusP3' and others, the following criteria have been adopted by most centers: 1. Normal lymph nodes are often invisible on CT. When present, these nodes have an ovoid (lima bean) shape and are of homogeneous soft tissue density. Normal lymph nodes typically measure less than 1.0 cm in diameter. 2. Any node measuring more than 1.5 cm in diameter is abnormal. Reactive as well as neoplastic nodes may produce this pattern. Reactive adenopathy is most commonly encountered in submandibular and jugulodigastric nodes. 3. Any node with a central lucency, regardless of size, is abnormal (Fig. 17-12). Nodes with this CT appearance, often referred to as necrotic, are focally or completely replaced with tumor (typically, metastatic squamous cell carcinoma). Actual necrosis of nodal tissue is not commonly seen on pathologic examination. Care must be


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Figure 17-11. Internal jugular chain lymph nodes. A, Axial contrast-enhanced CT scan at the level of the hyoid bone demonstrates a 2-cm-diameter lymph node (asterisk) medial to the left sternocleidomastoid muscle (s) and lateral to the left internal jugular vein. This lymph node is present at the junction of axial levels I1 and III. B, Axial contrast-enhanced CT scan at the level of the cricoid cartilage demonstrates a 2-cm-diameter lymph node (asterisk) immediately posterior to the left internal jugular vein (v). This lymph node is present at the junction of axial levels 111 and IV.

taken not to mistake the fatty hilum of a normal node for the abnormal lucency. The fatty hilum is located at the periphery of the node (see Fig. 17-10A). 4. Obliteration of fascial planes surrounding a node is abnormal. The CT appearance of "dirty fat" surrounding a node may be seen in cases of extranodal spread of tumor or inflammation as well as after surgery or radiation therapy to the neck. In general, extranodal spread of tumor tends to cause a more focal obliteration of fascial planes than the other processes. Correlation with clinical history is essential (see Fig. 17-26).3' Many centers with active head and neck tumor services have more stringent criteria for assessing nodal size. Expounding on the pathologic studies of van den Brekel, these centers consider all lymph nodes with a short axis greater than or equal to 1.2 cm significa~t.4~ An alternative system is to maintain the size criterion of 1.5 cm for submandibular and jugulodigastric nodes but to consider nodes at other levels that measure 1.0 cm or larger to be significant." When these criteria are used, approximately 80% of the enlarged (homogeneous) nodes are secondary to metastatic disease, and 20% are caused by reactive hyperpla~ia.~'

When the extranodal changes described here obliterate fascial planes between a lymph node and adjacent structures (muscles, vessels), there may be clinical fixation of the node to these structures. The amount of fixation is subjective, depending on the individual examiner. It is difficult to predict solely on the basis of CT findings whether clinical fixation exists. The only sure sign of nodal fixation is if the structure in question is completely surrounded by a nodal mass. This point is particularly important in evaluation of the internal or common carotid artery." Loss of definition of the vessel wall, with visualization of an otherwise normal lumen, is consistent with infiltration of the vessel wall (Fig. 17-13). The utility of spin-echo MRI in evaluation of noda disease remains limited. TI-weighted images usually provide good differentiation between intermediate signal nodes and the surrounding high-intensity fat, allowing for accurate measurement of nodal size. Assessment of central nodal necrosis is more difficult on MRI than on CT. Tumor cells within nodes tend to produce intermediate signal on TI-weighted and T2-weighted images, whereas areas of actual nodal necrosis usually appear as areas of low signal on TI-weighted images and of high signal on T2-weighted


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Chapter 17

Figure 17-12. Metastases to small lymph nodes. Axial contrastenhanced CT scan obtained at a level between the hyoid bone and the cricoid cartilage demonstrates two lymph nodes (white arrows) in the left internal jugular chain, each measuring 1 cm in diameter with central hypodensity not equal to that of fat. Each of these level III lymph nodes demonstrates a necroric center: Multiple small nodes deep ta the Left sternocleidomastoid muscle (s) have a homogeneous appearance.

1

Figure 17-13. Extranodal spread of tumor. Axial contrast-enhanced CT scan demonstrates an irregular interface between the large left necrotic nodal mass and the cervical fat. Anteriorly, the overlying platysma is thickened and irregular (curved white arrows). Posterolaterally, there is extension through the platysma into the subcutaneous fat (straight arrows). This nodal mass was immobile or "fixed" on physical examination. Note how the mass engulfs the arteriosclerotic left internal carotid artery (open . . . black arrow). . . L.. ' I I+ * . I .h , I . i tiz-d.i t,;trfl L , . . 1 > I 4

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images."' One practical solution is to consider any lymph node that is heterogeneous in appearance abnormal, but even this alternative can fail if the dynamic gray scale of the images is limited or the signal-to-noise ratio low."

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Level I: Oral cavity, submandibular gland. , Level 11: Nasopharynx, oropharynx, parotid gland, supraglottic larynx. Level 111: Oropharynx, hypopharynx, supraglottic larynx. Level IV: Subglottic larynx, hypopharynx, esophagus, thyroid. Level V: Nasopharynx, oropharynx. Levels VI and VII: Thyroid, larynx, lung. I

The Unknown Primary Approximately 5% of all patients with carcinoma and 12% of patients with head and neck carcinoma have nodal metastases as the sole presenting ~omplaint."~ In cases in which a head and neck malignancy is not appreciated by the otolaryngologist on initial clinical examination, knowledge of the pathways of nodal drainage, in combination with the ability of CT to detect nonpalpable pathologic lymph nodes, allows the radiologist to identify potential sites of neoplasm, particularly when the tumor is predominantly submucosal in nature.

Bilateral nodal disease is particularly common in tumors of the soft palate, tongue, epiglottis, and nasopharynx. Isolated nodal disease in the su~raclavicularfossa is unlikely to be secondary to a maligiancy of the aerodigestive tract; more likely sites are lung, breast, stomach, and thyr0id.4~ .

m -

Figure 17-14. The unknown primary. Axial contrast-enhanced CT scan demonstrates a clinically palpable pathologic lymph node in level m of the right internal jugular chain (asterisk). Flexible nasopharyngoscopy failed to demonstrate a primary neoplasm. CT examination demonstrates asymmetrical soft tissue density in the right paralaryngeal space. Direct laryngoscopy confirmed the diagnosis of squamous cell carcinoma of the

laryngeal ventricle.

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Figure 17-15. Hodnkin's disease. Axial c o d

trGt-enhanced C T scan at the level of the 6rst tracheal ring demonstrates multiple enlarged homogeneous lymph nodes filling the left posterior triangle. Lymph nodes adjacent to the internal jugular vein (V) are level IV nodes. Lymph nodes adjacent to the trapezius muscle (T) are level

Neck Masses Isolated nodal masses may mimic a wide variety of lesions in the neck. including masses of congenital. neural. and infectious origins. hi key to limitiig differentii diagnosis is correlation with clinical history. Multiple masses in the neck are most likely secondary to nodal enlargement. Although aspiration cytology or excisional biopsy is necessary to confirm the diagnosis of nodal disease, identification of certain CT patterns of nodal disease facilitates clinical evaluation, as follows: 1. Large homogeneous lymph nodes are most commonly encountered in lymphoma, sarcoid, and infectious mononucleosis. CT cannot reliably differentiate Hodgkin's from non-Hodgkin's lymphoma (Fig. 17-15).3L 2. Total or relatively uniform enhancement of an enlarged node is usually encountered in inflammatory processes. Exceptions to this rule include nodal involvement by Kaposi's sarcoma, thyroid carcinoma, and renal cell carcinoma (Fig. 17-16). 3. Calcification within lymph nodes is unusual. Most commonly, the calcific deposits are the result of prior granulomatous d i ~ e a s e .Metastatic ~ papillary carcinoma of the thyroid is the most common cause of neoplastic nodal ~alcifications.4~ In rare instances, metastatic or lymphomatous nodes may calcify after irradiation or chem~therapy.~.~ 4. The presence of multiple nodes with a variety of CT appearances (homogeneous, necrotic, enhancing, and calcified) is most compatible with granulomatous disease of cervical lymph nodes. In urban centers, tuberculosis is the most common cause (Fig. 17-17).28 Thyroid carcinoma may also produce this 'pectrum of CT appearances."

Evaluation of Non-Nodal Neck Masses The CT and MRI appearances of nodal and non-nodal neck masses often overlap. Careful attention to imaging

Figure 17-16. Kaposi's sarcoma. Axial contrast-enhanced CT at the level of the anterior bellies of the digastric muscles demonstrates multiple, uniformly enhancing masses in the antenor and posterior triangles of the neck bilaterally, the largest identified in the left spinal accessory chain (asterisk). Multiple oropharyngeal lesions are also present (K'r


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Figure 17-18. Type I1 second branchial cleft cyst. Axial contrastenhanced CT scan demonstrates a unilocular cystic mass with minimal rim enhancement along the anterior margin of the left sternocleidomastoid muscle (s) displacing the left submandibular

Figure 17-17. Tuberculous ade ;. Axial contrast-enhancedcT scan at the level of the thyroid cartilage demonstrates nodes that are variably homogeneous (asterisk), necrotic arrow), enhancing (curved white arrow), and calcified (s white arrow). The patient, who is 12 years old, has little ossificat . . . ,.:.. tion of the thyroid cartilage- Y. m,-nl ,, r r .,. .,, . . . !. ...

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The most common developmental mass identified on imaging is the branchial cleft cyst. This lesion is the result of incomplete obliteration of the first, second, third, or fourth branchial apparatus. The majority of these lesions arise from the second branchial apparatus, which forms the facial muscles, styloid process, pinna, and portions of the ossicular chain and muscles of the middle ear.* The second branchial cleft cyst most commonly identified at imaging is the Bailey type 11cyst, which is secondary to persistence of the embryologic cervical sinus.2 These type 11 second branchial cleft cysts often manifest as painless fluctuant masses along the course of the anterior margin of the sternocleidomastoid muscle. They most commonly manifest in patients between the ages of 10 and 40 years but may become clinically obvious at any age.33 On contrast-enhanced CT (Fig. 17-18), a type I1 second branchial cleft cyst characteristically appears as a wellcircumscribed, unilocular, low-density mass adjacent to the anterior margin of the sternocleidomastoid muscle. CT attenuation measurements of these and other cystic masses range from 10 to 25 HU." On MRI (Fig. 17-19), the contents of the cyst are usually isointense with cerebrospinal fluid on T2-weighted images. On TI-weighted images, the cyst contents are usually hyperintense to cerebrospinal fluid and may even be hyperintense to skeletal muscle.18 The extent of rim enhancement of branchial cleft cysts is variable. Thick rim enhancement and indistinctness of fascia1 margins may occur if the cyst becomes infected.

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Septations are uncommon and are usually found only in cases of previous infection or needle aspiration. Infected cysts may mimic necrotic jugular chain-lymph nodes or cervical abscesses on both CT and MRI. If sufficiently large, the type 11 second branchial cleft cyst displaces the carotid artery and jugular vein medially or posteromedially. In contrast, the type I11 second branchial cleft cyst courses between the external and internal carotid arterie~.~ Cystic hygroma is the most common form of lymphagiomatous malformation occurring in the neck. Although there are multiple theories of pathogenesis for lymphagiomas, most experts believe that cystic hygromas form because the primordial lymphatic sacs failed to drain into the veins, resulting in hugely dilated cystic lymphatic spaces.46 Seventy-five percent of cystic hygromas occur in the neck, and 20% in the axilla. Cystic hygromas are usually isolated malformations in patients in whom the remainder of the lymphatic system is normal. They may occasionally be associated with a more generalized failure of lymphatic system development, as seen in cases of the 45,X chromosome karyotype (Turner's ~ y n d r o m e ) . ~ In contrast to branchial cleft cysts, cystic hygromas typically manifest at or shortly after birth. The clinical presentation is often characteristic: a painless, easily compressible mass that may transilluminate on physical examination. Patients are usually asymptomatic, unless there is Cervical cystic hygromas significant airway obstr~ction.~~ are most commonly found in the posterior triangle but can also occur in the floor of mouth, submental triangle, and submandibular triangles. Because up to 10% of cervical cystic hygromas may extend into the mediastinum, imaging is performed to assess the extent of the lesion and its relationship to adjacent structures before surgical resection. On contrast-enhanced CT (Fig. 17-20), cystic hygromas are low density in appearance without peripheral rim enhancement. Larger lesions may be multiloculated and are

RoshanKetab Medical Publishers 588 Part III 1 Imaging of the Head and Neck

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Figure 17-19. Type I1 second branchial cyst. A, Sagittal TI-weighted MR image demonstrate3 a well-circumscribed anterior triangle mass (asterisk) mildly hyperintense to muscle along the anterior margin of the sternocleidomastoid muscle (s). B, Axial T2-weighted MR image demonstrates a hyperintense mass along the anterior margin of the left sternocleidomastoid muscle (s). Compare with Figure 17-18. 4 I I - l r i 11 I I J I . !I !mfi r l t l r s r c l ~ l m lo;' , ,,i ' '. )I , I. I t : ,r 83rlC: h tra L 30 1 +I I i e a r 11 t

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often poorly circumscribed. In contrast to other cysticappearing masses in the neck, cystic hygromas typically insinuate themselves between adjacent structures rather than displace vascular or muscular structures.33 The multiplanar capability of MRI makes it the ideal imaging modality for evaluating cystic hygromas (Fig. 1721). On T2-weighted images, the hygromas are isointense with cerebrospinal fluid. Their appearance on TI-weighted images is more variable, either hypointense or hyperintense to skeletal muscle, depending on the relative protein concentration of the lymph fluid and prior episodes of trauma or Thyroglossal duct cysts are the result of incomplete involution of an embryologic tract, the thyroglossal duct.

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It is through the duct that the thyroid gland passes during its migration from the foramen cecum in the tongue to its final position in front of the trachea. If any portion of this epithelium-lined duct persists after birth, a cyst may develop. The hyoid bone is intimately associated with the thyroglossal duct during its development; a thyroglossal duct cyst may be located anterior to, posterior to, or within the hyoid bone." Thyroglossal duct cysts account for approximately 70% of all congenital neck masses, with the overwhelming majority occurring in the pediatric age group. Routine sectional imaging of thyroglossal duct cysts is not performed in children because the clinical presentation (a painless midline neck mass that moves on swallowing) is so typi, ,..

Figure 17-20. Cystic hygroma. Axial contrast enhanced CT scan at the level of the first trachea ring demonstrates a multilocular cystic mas without rim enhancement occupying the entirc right posterior triangle extending toward the right axilla. S, Sternocleidomastoid muscle. L a-


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Figure 17-21. Cystic hygroma. A, Sagittal TI-weighted MR image demonstrates a lobulated posterior triangle mass (asterisk) that is moderately hyperintense to muscle and located deep to the posterior margin of the sternocleidomastoid muscle (s). Note how the hygroma tracks posterior to the internal jugular vein (V). B, The hygroma appears virtually isointense to fat in the right posterior triangle (PT),owing to window width and level.

~ a l . ' Ultrasonography ~ or radioisotope scanning may be performed to confirm a normal position of the thyroid before surgery. Cl' or MRI is usually performed preoperatively in cases of suspected thyroglossal duct cyst in adults to confirm the diagnosis and to exclude other nodal masses. On contrastenhanced CT, a well-circumscribed, lowdensity mass is present (Fig. 17-22).30 Peripheral rim enhancement or internal septations are occasionally seen. The MRI signal characteristics of thyroglossal duct cysts are the same as those of branchial cleft cysts or small cystic hygromas.

Figure 17-22. Thyroglossal duct cyst. Axial contrast-enhanced CT scan at a level immediately inferior to the hyoid bone demonstrates a cystic anterior triangle mass with peripheral rim enhancement (asterisk) embedded within the strap muscles to the right of midline. M, Left strap muscles; S, right sternocleidomastoid muscle.

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Suprahyoid thyroglossal duct cysts are midline in location. The more common infrahyoid thyroglossal duct cysts often have both midline and off-midline components, the latter being embedded in the strap muscles. It is the location of an infrahyoid thyroglossal duct cyst in the strap muscles, not its signal or attenuation characteristics, that allows for a definitive radiographic diagnosis.30The presence of a solid mass along the thyroglossal duct should raise suspicion of ectopic thyroid tissue, in which occult malignancy is more likely. Dermoid cysts are the rarest of the congenital neck


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Figure Der d cyst. Axial contrast-enhanced CT scan demonstrates a mass with peripheral rim enhancement in the submental triangle. The mass contains a fatty component ankriorly and a fluid component posteriorly. D, Anterior bellies of the digastric muscles. The central portion of the hyoid bone is absent because of previous surgery to remove a thyroglossal duct cyst. prom Reede DL, et al: Nonnodal pathologic conditions of the neck. In Sorn PM, Bergeron RT (eds): Head and Neck Imaging, 2nd ed. St. Louis, CV Mosby, 1991.)

lesions. Only 7% of all dermoid tumors occur in the head and neck. The majority of head and neck dermoids occur in the orbit, nasal cavity, or oral cavity; true cervical dermoids are rare. The term demzoid cyst has been used to include the following three types of cysts: (1) epidermoids or epidermal cysts, (2) dermoids, and (3) teratoid cysts."33 These three types of congenital cysts can be differentiated histologically by the presence or absence of an epithelial lining and the cyst contents. Differentiation among the three types of dermoid cysts by sectional imaging is often impossible. Most cervical dermoid cysts occur in the midline or just off-midline and are usually present at birth. In contrast to thyroglossal duct cysts, dermoid cysts typically do not move with swallowing. On CT,the presence of fat within the mass suggests a diagnosis of dermoid rather than epidermoid (Fig. 17-23. In the absence of demonstrable fat, epidermoids and dermoids cannot be distinguished by CT or MRI.

Masses of Inflammatory Origin It is often difficult to determine clinically whether a patient with an erythematous, painful, and swollen neck has a simple cellulitis or a potentially life-threatening deep

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neck abscess. With sectional imaging, it is possible not only to diagnose an abscess but also to differentiate it from cell~litis.'~.~~ The CT characteristics of neck infections have been well described. Abscesses appear as single or multiloculated, low-density masses that conform to fascial spaces. When intravenous iodinated contrast agent is administered, abscesses demonstrate peripheral rim enhancement. Cutaneous and subcutaneous manifestations of infection are also seen. The manifestations include enlargement of adjacent muscles (myositis), thickening of the overlying skin, prominent linear densities within the subcutaneous fat, and enhancement of fascial planes. The presence of these cutaneous and subcutaneous manifestations without a low-density collection is consistent with cellulitis (Fig. 17-24).'2.33 A "characteristic" appearance of cervical infections on MRI has yet to be defined. In general, abscesses appear as single or multiloculated masses that are hypointense to skeletal muscle on TI-weighted images and markedly hyperintense on T2-weighted images. The use of MRI contrast agents should demonstrate an enhancing rim in a mature abscess. Differentiation of abscesses from other noninfectious masses on MRI requires careful attention to variations in the dynamic gray scale. Particular attention must be paid to window and level settings because subtle changes in cervical fat may be obscured by the hyperintense signal of cervical fat on TI-weighted images (Fig. 17-25). No studies have yet compared CT and MRI in the evaluation of cervical infection. Several problems have been noted by investigators using MRI to evaluate inflammatory disease: First, the cutaneous manifestations of infection are not obvious on MR images; second, subcutaneous manifestations of infection may be obscured on MR images if imaging parameters are not carefully monitored; third, after intravenous administration of contrast agent, the enhancing rim may become isointense with surrounding fat, limiting detection or delineation of the abscess unless fat-suppression techniques are used; fourth, areas of abscess formation and cellulitis both tend to be hyperintense on T2-weighted images, hampering differentiation between the two proce~ses.'~.~~ The authors prefer the use of contrast-enhanced CT to assess suspected inflammatory disease in adults. In children and in adults whose clinical status precludes the use of iodinated contrast material, MRI is the study of initial choice, although a limited noncontrast CT study may be required for evaluation of osseous integrity. If MRI is not available, ultrasonography is an alternative modality for localizing suspected collections for surgical drainage. Regardless of the modality used, the following important principles must be remembered:

1. Radiographic changes in the skin, fat, and fascial planes of the neck are not pathognomonic for an infectious process. Inflammatory reactions after radiotherapy or surgery can mimic cervical infections. 2. Radiographically, a necrotic tumor, nodal disease with extension into the adjacent soft tissues, and a thrombosed vessel may all mimic an abscess on sectional images (Fig. 17-26). Clinical correlation is essential. 3. Not every infectious process demonstrates the radio-


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Figure 17-24. Abscess versus cellulitis.A, Axial contrast-enhanced CT scan demonstrates a lowdensity collection (A) in the anterior triangle surrounded by an irregular rim of contrast enhance ment (arrows) consistent with abscess. B, Axial contrast-enhanced CT scan in a different patient demonstrates irregular linear densities in h e fat of the anterior triangle (C). There is thickening of the platysma muscle (black arrows) and the skin (white arrow). No fluid collections are present. This image is compatible with cellulitis. (From Holliday RA, Prendergast NC: Imaging inflammatory processes of the oral cavity and suprahyoid neck. Oral Max Surg Clin North Am

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graphic changes listed here. Granulomatous infections with Mycobacterium and occasionally Actinomycosis species often appear as "bland" masses, without central necrosis or peripheral cellulitic changes. 4. Inflammatory lesions are always in a state of evolution. It is possible that a patient may be studied before a cellulitis has "ripened" to a frank collection of pus. If a diagnosis of cellulitis is made and the patient shows no response to appropriate antibiotic therapy, a second examination should be performed to ensure that an a a abscess cavity has not f~rmed.lZ'~ 4 Once a diagnosis of cervical abscess is established, it is important to "map out" the sites of abscess accurately to ensure proper surgical drainage. Cervical infections frequently spread along the fascial planes within the neck. Abscesses are often located within a single compartment or "space" within the neck. The following summary of fascial anatomy is designed to facilitate mapping of cervical infections. It must be acknowledged that any classification of fascial anatomy is somewhat arbitrary because fasciae are simply the more obvious layers of the general connective tissue packing with the body. Nevertheless, the

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following definitions are stressed in both the anatomical and the surgical literature (Figs. 17-27 and 17-28). Two cervical fasciae exist, the superficial and the deep.'O. 17* 23, 26,41 The superficial cervical fascia is a layer of connective tissue that surrounds the head and neck, encircling the platysma muscle. The fascia also contains blood vessels, lymphatic channels, cutaneous nerves, and hair follicles. Its primary function is to allow the skin to glide easily over the deeper structures of the neck. Infections that track along the superficial cervical fascia are often secondary to skin infections and rarely track deeper into the neck. The deep cervical fascia consists of three layers: the superficial layer, known as the investing fascia; the middle layer, known as the visceral fascia; and the deep layer, which has two divisions separated by a potential space-the alar layer anteriorly and the prevertebral layer posteriorly. The investing fascia surrounds all the important structures of the neck. The visceral fascia surrounds the aerodigestive tract. The deep layer surrounds the vertebral column and paravertebral muscles. All three layers are closely


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Figure 17-25, Abscess. A, A X I ~ I I L-weighted MR image demomtrates a mass (asterisk) in the right submandibbla triangle that is hypointense to the anterim bellies of the di~astricmuscles. B, Correspo&g axial T2-wei&bd MR image demon8trates hyperintense signal within the mass (asterisk). Note that inflammatory changes in the fat l a t d to the abscess (arrows) are not as easily appreciated as on CT scans. (From Holliday RA, Prendergast NC? Imaging inflammatory processes of the oral cavity and mpdtyoid neck. Oral Max Surg Clin North Am 4:215, 1992.)

Figure 17-26. Metastatic lymph node mimicking abscess. Axial contrast-enhanced CT scan demonstrates a low-density right submandibular triangle mass (asterisk) surrounded by an irregular rim of contrast enhancement. The overlying platysma muscle is thickened. The patient, who was afebrile, had a history of treatment for squamous cell carcinoma of the right oropharynx 2 years before this examination. Needle aspiration of the mass yielded atypical squamous cells.


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Figure 17-27. The layers of deep cervical fascia and the cervical spaces, sagittal view. Solid line, investing fascia; dotted line, visceral fascia; broken line, prevertebral fascia. 1 , Suprasternal space of Bums; 2, visceral space; 4a, retrovisceral component of the retropharyngeal space; 4b, danger space; 5, prevertebral space. M, mylohyoid muscle; THY, thyroid gland. (Adapted from Smoker WRK, Harnsberger HR: Normal anatomy of the neck. In Som PM,Bergeron RT (eds): Head and Neck Imaging, 2nd ed. St. Louis, Mosby Year Book, 1990, pp 498-518.)

associated in the anterolateral neck, where they all contribute to the formation of the carotid sheath, which surrounds the carotid artery, internal jugular vein, and vagus nerve. The investing fascia is attached posteriorly to the ligamentum nuchae and the spinous processes of the cervical vertebral bodies. As it extends anteriorly, the fascia splits to envelope the trapezius and sternocleidomastoid muscles, forming the roof of the posterior triangle. In the suprahyoid neck, the fascia also splits to surround the parotid and submandibular glands before attaching to the body of the hyoid bone and the inferior surface of the mandible. In the infrahyoid neck, the investing fascia splits to surround the strap muscles anterior to the larynx and trachea. The fascia also invests the omohyoid muscle, holding the muscle close to the clavicle, so contraction of the muscle results in a downward rather than a lateral pull on the hyoid bone. The investing fascia is attached superiorly to the external occipital protuberance, the mastoid process, and the skull base. It is attached inferiorly to the clavicle, the acromion, and the anterior and posterior surfaces of the sternum. The visceral fascia extends from the central skull base to the mediastinum, encircling the pharynx, esophagus, larynx, and trachea. In the mediastinum, the visceral fascia blends with the pericardium, forming the anterior border of the retropharyngeal space. In the infrahyoid neck, the

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Figure 17-28. The layers of deep cervical fascia and the cervical spaces of the infrahyoid neck, axial view. Solid line, investing fascia; dotted line, visceral fascia; broken line, prevertebral fascia. 2, Visceral space; 3, carotid space; 4, retropharyngeal space; 5, prevertebral space. CCA, common carotid artery; E, esophagus; IJV, internal jugular vein; SCM,sternocleidomastoid muscle; STR, strap muscles; THY, thyroid gland; TR, trachea; TRP, trapezius muscle. (Adapted from Smoker WRK, Harnsberger HR: Normal anatomy of the neck. In Som PM, Bergeron RT (eds): Head and Neck Imaging, 2nd ed. St. Louis, Mosby Year Book, 1990, pp 498-518.)

fascia is attached anteriorly to the cricoid and thyroid cartilages and splits to form the capsule of the thyroid gland. The deep layer of the deep cervical fascia, like the investing fascia, begins in the posterior midline. The deep layer forms the floor of the posterior triangle, covering the paraspinal and scalene muscles. The deep layer is attached laterally to the transverse processes of the vertebral bodies, where it then splits into the anterior J a r and posterior prevertebral layers as they extend anterior to the vertebral body. The alar and prevertebral layers have different craniocaudad extensions; although both attach superiorly at the skull base, the alar layer blends with the visceral layer along the posterior margin of the esophagus at the level of approximately T2, whereas the prevertebral layer extends more inferiorly anterior to the anterior longitudinal ligament. The three layers of the deep cervical fascia delineate spaces in and through which bacterial infections can spread in the infrahyoid neck. The visceral space includes all structures within the confines of the visceral fascia and is continuous with the anterior mediastinum. The retropharyngeal space is situated in the midline directly posterior to the pharynx. The anterior boundary of the retropharyngeal space is formed by the visceral fascia, and the posterior boundary is formed by the deep layer of the deep cervical fascia. The retropharyngeal space can be further divided by the alar layer into the retrovisceral space anteriorly and the danger space posteriorly. Depending on its location, infection in the retropharyngeal space can extend inferiorly in


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the retrovisceral space to the level of approximately T3 (where the alar layer and the visceral layer fuse) or in the danger space inferiorly to the level of the diaphragm. Because it is impossible to separate these two smaller spaces radiographically, the retropharyngeal space may be considered as a single radiographic space, with the recognition that all infections in the retropharyngeal space must be evaluated in full, and scans of either the superior mediastinum or entire chest may be necessary. Infections of the retropharyngeal space in children are usually secondary to infection of the medial retropharyngeal lymph nodes. In adults, retropharyngeal space infection is most commonly the result of perforation of the posterior wall of the pharynx or esophagus. Infections of the parapharyngeal space or posterior pharyngeal wall, if unchecked, may penetrate the visceral fascia and involve the retropharyngeal space.I2 Regardless of their origin, retropharyngeal space abscesses have a characteristic "bow tie" appearance on axial images that facilitates identificatiom7 Sagittal MR images are ideal for definition of the superior and inferior extension of retropharyngeal abscesses before surgical intervention (Fig. 17-29). The prevertebral space includes those structures (verte-

Figure 17-29. Retropharyngeal space abscess. Sagittal T2weighted MR image demonstrates a hyperintense mass in the retropharyngeal space (asterisks) with anterior displacement of the airway. The abscess extends inferiorly to the level of the third thoracic vertebra (T3),implying involvement of the retrovisceral space rather than the danger space. (From Holliday RA, Prendergast NC: Imaging inflammatory processes of the oral cavity and suprahyoid neck. Oral Max Surg Clin North Am 4:215, 1992.)

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bra1 bodies, paravertebral and scalene muscles, vertebral arteries) that are surrounded by the deep layer of the deep cervical fascia. Lying posterior to the retropharyngeal space, the prevertebral space may be further divided into anterior and posterior compartments by the attachment of the deep layer of deep cervical fascia to the transverse processes. Infections of the prevertebral space are usually secondary to vertebral infection (osteomyelitis) or posterior extension arising in the retropharyngeal space. The carotid space is a potential space w i t h the carotid sheath. Because little areolar tissue is present within the sheath, actual infection of the carotid space is rare. The carotid sheath, however, with its contributions from all three layers of the deep cervical fascia, is a conduit of infection from one space to another. Septic or reactive thrombosis of the internal jugular vein may produce swelling within the carotid space.12

Masses of Vascular Origin Asymmetry in the diameter of the internal jugular veins is a normal variant and should not be confused with a mass (see Fig. 17-6). Tortuous arterial vessels may manifest as a pulsatile mass in the supraclavicular fossa or neck. Masses lying in close proximity to the internal or common carotid arteries may transmit normal arterial pulsations. Sectional imaging can differentiate between these "pulsatile" masses and aneurysms of the cervical arterial system. Internal jugular vein thrombosis, most commonly secondary to central venous catheterization or intravenous drug abuse, is readily diagnosed on sectional imaging. On contrast-enhanced CT, the central portion of the thrombosed vessel is usually less dense than contrast-enhanced blood. Enhancement of the wall of the vein is often present and may extend into surrounding fascia1 planes.' A number of lesions may mimic a thrombosed vein on one or more sequential CT scans. Lesions that may be confused with a thrombosed vessel include necrotic lymph nodes, cervical abscesses, infected branchial cleft cysts, and thrombosed carotid arteries (Fig. 17-30). In most cases, careful analysis of sequential images and correlation with clinical history can distinguish venous thtombosis from other lesions.33 In the evaluation of venous patency with MRI, care must be taken not to confuse flow-related enhancement with thrombosis. The MRI diagnosis of venous thrombosis often requires partial flip angle imaging or phase imaging to confhn findings identified on spin-echo sequences4 Paragangliomas, commonly known as glomus tumors, are neoplasms of neural crest cell origin that arise within the adventitial layer of blood vessels at multiple sites in the head and neck, including the middle ear (glomus tympanicum), paraphqngeal space (glomus jugulare), and larynx. The two most common paragangliomas to present as a neck mass arise at the carotid bifurcation (carotid body tumor) and along the nodose ganglion of the vagus nerve (glomus vagale). Such a mass typically manifests as a painless slow-growing mass in the anterior triangle of the suprahyoid neck. The mass is commonly pulsatile, and a bruit may be auscultated over it.33 The most constant feature of the glomus vagale or


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Figure 17-30. Internal jugular vein thrombosis. A, Axial contrast-enhanced CT scan at the level of the cricoid cartilage demonstrates hypodensity with peripheral rim enhancement (curved white arrow) lateral to the right common carotid artery (A). 3, Left common carotid artery; UV, left internal jugular vein. B, Axial contrast-enhanced CT scan at the level of the jugular vein (curved white arrow) and the necrotic left internal jugular chain lymph node (white arrow) metastatic from the left supraglottic carcinoma (white arrowheads). Arteriosclerotic change is present in the common carotid arteries bilaterally (A).

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carotid body tumor on CT scans is intense enhancement after intravenous contrast administration. Dynamic CT scanning after bolus contrast administration has been reported as a reliable method of differentiating paragangliomas from schwannomas, because the former have a vascular flow curve but the latter do not.43 MRI has all but replaced dynamic CT in the imaging evaluation of suspected glomus or carotid body tumors. Paragangliomas more than 1.5 cm in diameter should demonstrate curvilinear areas of signal void representing areas of high vascular flow (Fig. 17-31).25Schwannomas, which classically are avascular lesions on angiography, do not demonstrate areas of signal void.33 Identifying areas of signal void within a neck mass on MRI allows the confident diagnosis of paraganglioma only

if the mass is present in the correct location. Carotid body tumors arise in the juxtahyoid neck and separate the internal and external carotid arteries on sectional imaging. Glomus vagale tumors arise in the suprahyoid neck and displace the internal carotid artery anteromedially and the internal jugular vein posterolaterally. Other neck masses with areas of signal void on MRI, such as nodal metastases from renal cell or thyroid car~inoma,"~ do not demonstrate these vascular displacements. This MRI appearance is not pathognomonic for paraganglioma and may be seen in a variety of high-flow lesions. An imaging diagnosis of paraganglioma should prompt a careful search for additional lesions because multiple glomus tumors occur in up to 10% of the general population and in up to 33% of patients with a family history of paragangli~ma.~'

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Figure 17-31. Carotid body tumor. A, Sagittal TI-weighted MR image demonstrates a heterogeneous mass (arrow) at the bifurcation of the common carotid artery (c) splaying the external (e) and internal (i) carotid arteries. B, Axial T1-weighted MR image at the level of the hyoid bone in the same patient demonstrates a right anterior triangle mass (large black arrow) with multiple internal areas of relative signal void (small black arrows).

Masses of Neural Origin Schwannomas and neurofibromas are the most common types of neurogenic tumors found in the head and neck. Common sites for schwannomas and neurofibromas in the neck are the vagus nerve (cranial nerve X), the ventral and dorsal cervical nerve roots, the cervical sympathetic chain, and the brachlal plexus. Associated motor dysfunction and pain in the distribution of a sensory nerve are inconstant clinical findings.15 Without a clinical history of neurofibromatosis, it is impossible to distinguish between these two neural masses on sectional imaging. Most neural tumors appear hypodense or isodense to skeletal muscle on noncontrast CT. These tumors tend to be hypointense or isointense to skele-

tal muscle on TI-weighted MR images and variably hyperintense on 7'2-weighted images. Variations in the CT or MRI appearance of masses of neural origin are commonly thought to be secondary to variations in cellularity or lipid content. The enhancement pattern of neural tumors is highly variable. Intense, uniform enhancement, inhomogeneous enhancement, and lack of enhancement have all been reported. It is not unusual for an isolated schwannoma to be mistaken for a nodal mass on sectional imaging (Fig. 17-32).11. 18,29,42 The correct imaging diagnosis of a neural tumor requires a thorough knowledge of the normal anatomy of the major nerves in the neck. A tumor arising from the vagus nerve manifests as a mass in the anterior triangle, displacing the internal or common carotid artery anteromedially and the

Figure 17-32. Schwannoma. Axial contrast-enhanced CT scan at the level of the hyoid bone demonstrates a heterogeneous mass (curved white arrow) deep to the right sternocleidomastoid muscle. An initial radiographic diagnosis of nodal metastases was offered because of the location of the mass posterior to the internal jugular vein (v) and the patient's history of prior right facial melanoma,

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Figure 17-33. Vagal schwannoma. Axial contrast-enhanced CT scan at the level of the thyroid notch demonstrates a predominantly low-density mass (curved white arrow) deep to the anterior margin of the right sternocleidomastoid muscle (s) that is splaying the intemal jugular vein (v) and the internal carotid artery (I). e, External carotid artery.

internal jugular vein posterolaterally (Fig. 17-33).14 Neoplasms of the cervical nerve roots manifest a mass in the posterior triangle, which may extend into one of the neural foramina of the cervical spine (Fig. 17-34). Sympathetic chain tumors demonstrate a constant relationship with the longus colli muscles. Brachial plexus schwannomas and neurofibromas in the infrahyoid neck often displace the anterior scalene muscle a n t e r i ~ r l y . ~ ~

Masses of Mesenchymal Origin Lipomas are the most common cervical neoplasms of mesenchymal origin. They typically manifest as painless, slow-growing masses, occurring most commonly in the midline of posterior neck or the posterior triangle. Their CT appearance-a homogeneous, nonenhancing mass isodense with subcutaneous fat-is diagnostic (Fig. 17-35).33,MThe overwhelming majority of lipomas identified on MRI are isointense to subcutaneous fat on all pulse sequences. Lipomas may or may not have a demonstrable capsule on sectional images. Liposarcomas arise from totipotential mesenchymal cells and are rarely encountered in the head and neck. Liposarcomas occur de novo and are not the result of malignant degeneration of preexisting lipomas. Liposarcomas are differentiated from lipomas on the basis of their faster growth rate and the presence of soft tissue and mucoid elements admixed with fat on sectional imaging. None of the remaining mesenchymal tumors can be confidently diagnosed by sectional imaging alone. These rare lesions tend to appear largely isodense or isointense to skeletal muscle on noncontrast CT or TI-weighted MR images. Inhomogeneous contrast enhancement is usually observed. Rhabdomyosarcoma and other malignant mesenchymal tumors tend to destroy bone and distort soft tissue planes.16 Desmoids and other benign mesenchymal tumors tend to have sharply circumscribed borders and typically do not infiltrate adjacent soft tissue or destroy bone? The primary role of imaging is one of lesion localization, not lesion characterization.

Masses Arising from the Aerodigestive Tract Masses may be detected on sectional images of the neck that represent cervical extensions of diseases arising within the oral cavity, larynx, or hypopharynx. A ranula is a mucous retention cyst that arises from an obstructed sublingual or minor salivary gland in the floor of the mouth. Simple ranulas are limited to the sublingual space and are seen as intraoral mass lesions. Diving (or plunging) ranulas herniate through or around the mylohyoid muscle and extend into the submandibular triangle. Diving ranulas have been likened to pancreatic pseudoceles because they both contain proteolytic enzymes that allow the mass to infiltrate adjacent tissues. On CT, ranulas are thin-walled unilocular homogeneous cystic lesions. As with congenital cystic masses, prior infection or surgical intervention results in septations or irregular rim enhancement (Fig. 17-36)> On MRI, ranulas are typically hypointense to skeletal muscle on T1weighted images and isointense to cerebrospinal fluid on T2-weighted images. An imaging diagnosis of diving ranula should be considered only when the lesion abuts or involves the sublingual space. The multiplanar capacity of MRI may facilitate documentation of a tail of tissue within the floor of mouth.18 A laryngocele is an abnormal dilatation of the saccule (appendix) of the laryngeal ventricle. Although a small proportion of laryngoceles are congenital, the majority are the result of chronic increases in intralaryngeal pressure. Neoplasms or localized inflammation and edema may partially obstruct the ventricle. The resulting ball-valve mechanism traps air within the saccule. Mucus produced by the respiratory epithelium of the ventricle may result in a fluidfilled laryngocele (laryngeal mucocele). Internal laryngoceles are limited to the paralaryngeal space. External or combined internal and external laryngoceles extend from the paralaryngeal space into the anterior triangle of the neck via fenestrations in the thyrohyoid membrane.g On CT or MRI, the external component of a laryngocele appears as


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Figure 17-34. Dorsal cervical nerve root schwannoma. A, Axial contrast-enhanced CT scan at the level of the thyroid cartilages demonstrates a rimenhancing solid posterior triangle mass (mterisk)deep to the left s t e m 0 c l e i d o ~ toid muscle (S). On this single image, differentiation of neural tumor fiom enhancing lymph node would be impossible. B, Axial contrast-enhanced CT soan at tke level of the hyoid bone demrmstrates that the mass (wterirk)involves the neural foxamen (amws), allowing the correct radiologic diagnosis of neural tumor.

Figore 17-35. Lipoma. Axial contrast-enhand C T m e at thr, 1&el of the thymid notch in an adoleseent patient demawtmtm a uniform-fatdensity mass in she: mt&ox Lriwgle Q, sup&cial to the right sttap muscles {S).Imaging was peaformed to exclude the pmibility of thyroghisal duct cyst Compare wiSh

~~ 17-22.



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Figure 17-36. Ranula. A, Axial contrast-enhanced CT scan at the level of the thyroid cartilage demonstrates a unilocular cystic anterior triangle mass deforming the anterior margin of the right sternocleidomastoid muscle (S). On the basis of this single image, differential diagnosis would include second branchial cleft cyst, lymphangioma, and necrotic lymph node. Thyroglossal duct cyst should be excluded from the differential diagnosis because the mass is extrinsic to the strap muscles (asterisks). B, AxiaI contrast-enhanced CT lmage at the level of the mandible demonstrates the origin of the ranula in the posterior oral cavity, medial to the enhancing mylohyoid muscle (arrows). M, Right mylohyoid muscle; G, right submandibular gland.

a thin-rimmed, fluid-filled or air-filled mass directly lateral to the thyrohyoid membrane. Continuity with the internal component can be demonstrated on axial or direct coronal images (Fig. 17-37). A pharyngocele is an abnormal dilatation of the piriform sinus, which may also herniate through the thyrohyoid membrane to manifest in the anterior triangle. The less common pharyngocele is differentiated from a laryngocele by the demonstration of continuity with the piriform sinus rather than the laryngeal ventricle. Neoplasms or abscesses involving the apex of the piriform sinus may extend into the anterior triangle of the infrahyoid neck through the cricothyroid membrane.3s

References

Figure 17-37. Combined laryngocele. Axial contrast-enhanced CT image at the level of the hyoid bone demonstrates a thinwalled, air-filled, right anterior triangle mass (white arrows) in direct continuity with the left paralaryngeal space. Curved arrow. right paralaryngeal space.

1. Albertyn LE, Alcock MK: Diagnosis of internal jugular vein thrombosis. Radiology 162502, 1987. 2. Benson MT, Dalen K, Marcuso AA, et al: Congenital anomalies of the branchial apparatus: Embryology and pathologic anatomy. Radiographics 12:943, 1992. 3. Bertrand M, Chen JT, Lipshitz HL: Lymph node calcification in Hodgkin's disease after chemotherapy. AJR 129:1108, 1977. 4. Braun IF, Hoffman JC Jr, Malko JA, et al: Jugular venous thrombosis: MR imaging. Radiology 157:357, 1985. 5. Brereton ND, Johnson RE: Calcification in mediastinal lymph nodes after radiation therapy of Hodgkin's disease. Radiology 112:705,

1973. 6. Coit WE, Harnsgerger HR, Osborn AG, et al: Ranulas and their mimics: CT evaluation. Radiology 163:211, 1987.


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4s WL, Haxnsberger HR, Smoker WR, et al: Retropharyngeal Evaluation of normal anatomy and diseases with CT and MR imaging. Radiology 17459, 1990. Egund N, Ekeland L, Sako M, Persson B: CT of soft tissue tumors. AJR 137:725, 1981. Glazer HS, Mauro MA, Aronberg DJ, et al: Computed tomography of laryngoceles. AJR 140:549, 1983. Grodinsky M, Holyoke EA: The fasciae and fascial spaces of the head, neck and adjacent regions. Am J Anat 367, 1938. Hamsberger HR, Mancuso AA, Muraki AS, et al: Branchial cleft anomalies and their mimics: computed tomographic evaluation. Radiology 152:739, 1984. Holliday RA, Prendergast NC: Imaging infiammatory processes of the oral cavity and suprahyoid neck. Oral Max Surg Clin North Am 4215, 1992. Hollinshead WH: Textbook of Anatomy, 3rd ed. New York, Harper & Row, 1974. Jacobs JM, Hamsberger HR, LufXn RB, et al: Vagal neuropathy: Evaluation with CT and MR imaging. Radiology 164:97, 1987. Katz AD, Passy V, Kaplan L: Neurogenous neoplasms of the major nerves of face and neck. Arch Surg 10251, 1971. Latack JT,Hutchinson RJ, Heyn RM:Imaging of rhabdomyosarcomas of the head and neck. AJNR 8:353, 1985. Levitt GW. Cervical fascia and deep neck infections. Otol Clin North Am 9:703, 1976. Mancuso AA, Dillon WP:The neck. Radiol Clin North Am 27: 407, 1989. Mancuso AA, Hanafee WN: Oral cavity and oropharynx including tongue base, floor of the mouth and mandible. In Computed Tomography and Magnetic Resonance Imaging of the Head and Neck, 2nd ed. Baltimore, Williams & W i s , 1985. Mancuso AA, Hamsberger HR,Muraki AS, et al: Computed tomography of cervical and retropharyngeal lymph nodes: Normal anatomy, variants of normal and applications in staging head and neck cancer. I: Normal anatomy. Radiology 148:709, 1983. Mancuso AA, Harnsberger HR,Muraki AS, et al:Computed tomography of cervical and retropharyngeal lymph nodes: Normal anatomy, variants of normal and applications in staging head and neck cancer. 11: Pathology. Radiology 148:715, 1983. New GB, Erich JB: Dermoid cyst of the head and neck. Surg Gynecol Obstet 65:38, 1937. Nyberg DA, Jeffrey RB, Brant-Zawadzki M, et al: Computed tomography of cervical infections. J Comput Assist Tomogr 9:288, 1985. Ogura JH, Biller HF:Head and neck-surgical management. JAMA 221:77, 1972. Olsen WL,Dillon WP,Kelly WM,et al: MR imaging of paragangliomas. AJR 148:201, 1987. Paonessa DF, Goldstein JC: Anatomy and physiology of head and neck infections. Otol Clin North Am 9:561, 1976. Pratt LW: Familial carotid body tumors. Arch Otolaryngol 97:334, 1973. Reede DL, Bergeron RT Cervical tuberculous adenitis: CT manifestations. Radiology 154:701, 1985.

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29. Reede DL, Bergeron RT: CT of cervical lymph nodes. J Otolaryngol 11:411, 1982. 30. Reede DL, Bergeron IYT, Som PM.Cl' of thymglossal duct cyst. Radiology 157:121, 1985. 31. Reede DL, Som PM: Lymph nodes. In Som PM, Bergeron RT (4s): Head and Neck Imaging, 2nd ed. St. Louis, 1991, CV Mosby. 32. Reede DL, Whelan MA, Bergeron R'T? CT of the soft tissue structures of the neck. Radiol Clin North Am 22239, 1984. 33. R&e DL, et al: Nonnodal pathologic conditions of the neck. In Sorn PM, Bergeron RT (4s): Head and Neck Imaging, 2nd ed. St. Louis, CV Mosby, 1991. 34. Rouviere H: Lymphatic system of the head and neck. In Anatomy of the Human Lymphatic System (transl. M Tobias). Ann Arbor, MI. Edwards Brothers, 1938. 35. Schwartz JM, Holliday RA, Breda SB: CT diagnosis of piriform sinus perforation. J Comput Assist Tomogr 12869, 1988. 36. Shah JP, Strong E, Spiro RH, V i i B: Surgical grand rounds, neck dissection: Current status and future possibilities. Clin Bull 11: 25, 1981. 37. Shumrick DA: Biopsy of head and neck lesions. In Paparella MN, Shumrick DA (eds): Otolaryngology, vol 1. Philadelphia, WE3 Saunders, 1973. 38. Siege1 UT, Glazer HS, St Amour TE, et al: Lymphangiomas in children: MR imaging. Radiology 170:467, 1989. 39. Silver AJ, Mawad ME, Hilal SK, et al: Computed tomography of the carotid space and related cervical spaces. Part 11: Neurogenic tumors. Radiology 150:729, 1984. 40. Simpson G T The evaluation of neck masses of unknown etiology. Otol Clin North Am 13:489, 1980. 41. Smoker WRK, Harnsberger HR: N o d anatomy of the neck. In Som PM, Bergeron RT (eds):Head and Neck Imaging, 2nd ed. St. Louis, CV Mosby, 1991. 42. Som PM: Review: Detection of metastasis in cervical lymph nodes: CT and MR criteria and differential diagnosis. AJR 158:961, 1992. 43. Som PM, Biller HF, Lawson W,et al: Parapharyngeal space masses: An updated protocol based on 104 cases. Radiology 153:149, 1984. 44. Som PM, Scherl MP,Rao VM, Biller J3F, et al: Rare presentations of ordinary lipomas of the head and neck. AJNR 7:657, 1986. 45. van den Brekel MHW, Stel HV,Castelijns JA, et al: Cervical lymph node metastasis: Assessment of radiologic criteria. Radiology 177: 379. 1990. 46. Weingast BR: Congenital lymphangiectasia with fetal cystic hygroma: Report of two cases with coexistent Down's syndrome. J Clin Ultrasound 16:663, 1988. 47. Yousern DM, SOM PM, Hackney DB, et al: Central nodal necrosis and extracapsular neoplastic spread in cervical lymph nodes: MR imaging versus CT.Radiology 182:753, 1992. 48. Zadvinskis DP, Benson MT, Kerr HH,et al: Congenital malformations of the cervicothoracic lymphatic system: Embryology and pathogene sis. Radiographics 12:1175, 1992. 49. m k i GH. Mackev JK. Arzai Y. et al: Head and neck: Initial clinical experience G t h fast spin-echo MR imaging. Radiology 188: 323, 1993.


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The Larynx Hugh D. Curtin

Imaging of the larynx can be an extremely difficult endeavor. The anatomy is complex. The target moves with every breath and every swallow. In certain situations, however, imaging addresses questions that the clinician has difficulty in answering and can make a considerable difference in treatment planning. Imaging must be considered in light of the capabilities of modern endoscopy.l. lo. l8 AS the technology of imaging has progressed, so too has the instrumentation available for direct visualization. The mucosa can be examined thoroughly. To be relevant, imaging must provide information that cannot be obtained by direct visualization. Thus, the usual intent of the radiologist is to evaluate the deeper tissues. In some cases, a bulky lesion of the upper larynx may block the view of the lower larynx, and imaging may assist in defining caudal extent of disease. The radiologist seeking to assess laryngeal pathology obviously must be familiar with the anatomy. The disease processes and their behavior are important. The radiologist must also be familiar with the available therapeutic options to emphasize the information that will be important in making clinical decisions. This chapter begins with a discussion of anatomy, including the normal appearance in the various imaging planes. A brief mention of technical considerations in applying magnetic resonance imaging (MRI) and computed tomography (CT) scans to the task of examining the larynx is followed by descriptions of imaging of various pathologic conditions. The important clinical considerations in each disease are stressed.

Anatomy The larynx is a system of mucosal folds supported by a cartilaginous framework.ls Tension and movement of the mucosal folds are accomplished by the actions of small muscles pulling against the cartilaginous framework. The clinical organization of the larynx emphasizes the mucosal anatomy, making the mucosa a good starting point for the present discussion. This concept is particularly important to the radiologist because descriptions of tumors must encompass the relationship to the landmarks on the mucosal surface. From the superior view (the view of the endoscopist), the first landmark seen is the epiglottis. The upper edge of the epiglottis represents the most superior limit of the larynx. The epiglottis is the anterior boundary of the entrance into the larynx. Anteriorly, two small sulci-the valleculae-separate the free portion of the epiglottis from the base of the tongue (Fig. 18-1). From the lateral margin of the epiglottis, the aryepiglottic (AE) folds curve around

to the small interarytenoid notch. Together these structures complete the boundaries of the airway at the entrance into the larynx. The inner mucosal surface of the larynx, or endolarynx, can be thought of as the working part of the organ. Two prominent parallel folds stretch from front to back along the lateral aspect of each side of the airway (Figs. 18-2 and 18-3; see also Fig. 18-1). These are the true and false vocal cords or folds, and they are in the horizontal plane. The true cord (the glottis) is the key functional component in the generation of voice and has a fine edge at the medial margin. The more superiorly placed false vocal fold has a more blunted medial edge. Separating these two folds is one of the most important landmarks in the larynx. The ventricle is a thin cleft between the true cord and the false cord, stretching from the most anterior limit of the cord almost to the posterior limit of the larynx. Above the false cord the mucosa sweeps upward and outward to the aryepiglottic (AE)folds. Inferiorly, the mucosa covering of the true cord sweeps outward into the subglottic area, eventually merging smoothly with the mucosa of the trachea. A final important mucosal landmark is the anterior cornmissure, the point where the true vocal cords converge anteriorly to attach to the inner (posterior) surface of the anterior angle of the thyroid cartilage. The three ~arallelstructures-the true cord. the false cord, and the ventricle-rganize the larynx 'into three regions: the supraglottis, the glottis, and the subglottis. The true cord is the glottis. The glottic region of the larynx extends from the upper surface of the true cord to a line somewhat arbitrarily chosen as being 1 cm below the level of the ventricle. The subglottic region is between this arbitrary line and the inferior edge of the cricoid cartilage, the lower margin of the larynx. There is no defined mucosal structure representing the exact boundary or separation of the glottic and subglottic regions. The supraglottic region is the part of the larynx that is above the ventricle. This region includes the false cords, the epiglottis, and the AE folds.

Laryngeal Skeleton The laryngeal cartilages are the supporting framework of the larynx. The major cartilages include the cricoid, the thyroid, the arytenoid, and the epiglottic. The smaller cartilages, the corniculate and the cuneiform, reside in the aryepiglottic fold and are not of particular importance to the radiologist. The cricoid cartilage is the foundation of the larynx and


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Figure 18-2. Sagittal T1-weighted MRI study. This sagittal slice is just off midline. The slice shows the anterior part of the true cord (1) and false cord (2) separated by the low signal intensity of the laryngeal ventricle (arrowhead). The axial image plane should be along the ventricle, as indicated by the white line. The preepiglottic fat is shown by an a m w . E, epiglottis; H, hyoid. (From Curtin HD: MR and CT of the larynx. In Thrall JH [ed]: Current Practice of Radiology, 3rd ed. St. Louis, Mosby-Year Book, 1994.)

Figure 18-1. The larynx is split sagittally, with a view of the lateral wall of the airway. The mucosa over the true cord (1) has been removed to show the thyroarytenoid muscle (TAM), which extends from the arytenoid to the thyroid cartilage. The upper edge of the muscle (arrow) indicates the level of the ventricle. The false cord (2) is just above the ventricle. E, epiglottis; F, preepiglottic fat; H, hyoid; T, thyroid cartilage; V, vallecula. (From Curtin HD: The larynx. In Som PM, Bergeron RT [eds]: Head and Neck Imaging, 2nd ed. St. Louis, Mosby-Year Book, 1991.)

is the only complete ring. The posterior part is larger than the anterior, giving the cartilage the appearance of a signet ring facing posteriorly. The lower margin of the cricoid cartilage represents the lower margin of the larynx. The thyroid and the arytenoid cartilages articulate with the cricoid. The thyroid cartilage is large and can be thought of as forming a shield for most of the inner larynx. The arytenoid cartilages perch on the superior edge of the posterior cricoid. The arytenoid cartilage spans the ventricle. The upper arytenoid is at the level of the supraglottic larynx. The lower arytenoid has a pointed process anteriorly, called the vocal process. Because of its characteristic shape and position, the arytenoid cartilage can help localize the ventricle on axial scanning. This is most helpful on CT scans, where the vocal process may be directly visualized. The upper margin of the arytenoid is at the level of the lower false cord just above the ventricle. The vocal process is at the level of the true cord just below the ventricle. Indeed,

Figure 18-3. Coronal T1-weighted image. This slice would be perpendicular to the white line in Figure 18-2 at the level of 1 and 2. The thyroarytenoid muscle (1) makes up the bulk of the true cord. The paraglottic space at the level of the false cord (2) is filled predominantly with fat. The ventricle is the air-filled slit (arrowhad) between the two. T, thyroid cartilage. (From Curtin HD: MR and CT of the larynx. In Thrall JH [ed]: Current Practice of Radiology, 3rd ed. St. Louis, Mosby-Year Book, 1994.)


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Chapter 18

the vocal ligament, which represents the medial margin of the true cord, attaches to the vocal process. The epiglottic cartilage, except for its superior tip, is totally contained within the external framework of the larynx. This cartilage is made up of elastic fibrocartilage and does not calcify. Grossly, this cartilage has multiple perforations resembling more a mesh than a solid plate, and the epiglottic cartilage is thus not a major barrier to tumor spread. Inferiorly, the epiglottic cartilage is connected to the inner surface of the anterior part nf the thyroid cartilage by the thyroepiglottic ligament.

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surface of the ring as well. This membrane or fascial layer merges with the anterior cricothyroid ligament in the anterior midline. A similar structure is seen in the supraglottic larynx. A thin ligament called the ventricular ligament is found in the lower margin of the false cord and the quadrangular membrane sweeps superiorly from the ventricular ligament terminating in the AE fold. The fan-shaped hyoepiglottic ligament stretches from the epiglottis to the hyoid bone and divides the supraglottic larynx into a superior (suprahyoepiglottic) and an inferior (infrahyoepiglottic) area.27

Muscles ana ~igaments The cartilages are connected by a system of muscles and ligaments. Several muscles are mentioned in the remainder of the chapter. One deserves special attention. The thyroarytenoid muscle (TAM) stretches from the arytenoid cartilage to the inner surface of the anterior thyroid cartilage (Fig. 18-4; see Fig. 18-1). This muscle parallels the true cord and makes up the bulk of the true cord. The cricothyroid and thyrohyoid ligaments span the greater part of the intervals between the cricoid cartilage, the thyroid cartilage, and the hyoid bone and represent, along with the cartilages, the outer limits of the larynx. Two membranes are found just deep to the mucosa. The conus elasticus (also called the cricovocal ligament or lateral cricothyroid ligament) stretches from the vocal ligament to the upper margin of the cricoid cartilage. Some descriptions indicate the membrane attaching to the inner

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The paraglothc space and the preepiglottic space are situated between the mucosal surface and the cartilaginous outer limit of the larynx. The paraglottic space is found laterally and represents much of the soft tissue wall of the larynx (Figs. 18-5 and 18-6). Although descriptions of the paraglottic space vary, I am using Tucker and Smith's original description^,^^ with the medial boundary represented by the conus elasticus and quadrangular membrane. The lateral boundary is the external skeleton of the larynx, formed predominantly by the inner cortex of the thyroid cartilage. At the level of the supraglottic larynx, the paraglottic space is filled mostly with fat. Below the ventricle, the TAM fills the paraglottic region. A small recess of" e ventricle, called the laryngeal saccule or appendix, extends upward into the p&glottic space of the supraglottic larynx. This structure is within the paraglottic fat lateral to the quadrangular membrane. The preepiglottic space is between the epiglottis posteriorly and the thyroid cartilage and thyrohyoid membrane anteriorly. The hyoepiglottic ligament forms the roof of the preepiglottic and paraglottic spaces.

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Imaging Considerations

Figure 1 8 4 . View from above, looking down at the skeletonized larynx. The thyroarytenoid muscle (M) is seen stretching from the arytenoid to the thyroid cartilage. Arrow indicates the point where paraglottic spread of tumor is expected to intersect the lateral cord. The opposite side shows the vocal ligament stretching from the vocal process of arytenoid to the thyroid cartilage. A, arytenoid; C, cricoid. (From Curtin HD: MR and CT of the larynx. In Thrall JH [ed]: Current Practice of Radiology, 3rd ed.

St. Louis, Mosby-Year Book, 1994.)

Although CT scanning is limited to the axial plane, it has the advantage of fast imaging speed. The advent of multidetector CT represents a significant improvement in the application to the l a r y n ~The . ~ scan is faster and thus allows the entire larynx to be covered in a single breathhold. The thinner-slice thickness allows multiplanar reformatted images comparable in quality to direct imaging. At present, magnetic resonance imaging (MRI) is better at differentiating various soft tissues compared with CT. MRI may allow better analysis of potential cartilage invasion or improved definition of the tumor muscle interface. Motion artifact is a significant problem in imaging of the larynx. CT scanning tries to avoid the problem by its use of fast imaging. The spiral acquisition may cover the larynx in 10 to 20 seconds. The examination can be performed during slow, shallow respiration, or the scan can be done with the breath held. More elaborate schemes are required for MRI studies.


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Figure 18-5. Axial CT through the larynx, with contrast from superior to inferior. A, Supraglottic larynx (level of the upper thyroid cartilage). dost of the wall of the larynx is fat density. E, epiglottis; C, arotid artery; J, jugular vein; PES, preepiglottic space). B, Supraglottic larynx inferior to that shown in A. The laraglottic space (arrow) is filled with fat density. An arrowlead represents the aryepiglottic fold. SCM, sternocleidomas3id muscle; T, thyroid cartilage. C, Just above the ventricle (level of the false cord). The laraglottic space is filled with fat (arrow). The upper arytenoid artilage (A) is visible. D, True cord level. The thyroarytenoid muscle (TAM) fills the paraglottic space. The cricoarytenoid joint is shown by an arrowhead. The upper margin of the cricoid cartilage is visible. E, Subglottis. The mucosa is tightly applied to the inner surface of the cricoid ring (C) without intervening soft tissue.

At our institution, before the examination begins, usually before the patient is placed on the table, the patient practices breathing with the abdominal muscles rather than with the chest muscles. Surface coils, a necessity in laryngeal MRI studies, are positioned so that any chest movement does not bump the coil. Although speed of imaging is always an advantage, some have recommended using up to multiple excitations on the TI-weighted sequence. This gives longer imaging times but averages out some of the

motion. Fast spin-echo imaging also shortens imaging times. The use of contrast agents is controversial. At our institution, contrast material is usually used for tumor imaging. Gadolinium, combined with fat suppression, has given good preliminary results. Imaging emphasizes the importance of the ventricle, and axial images are taken along the plane of the ventricle. The position of the ventricle is estimated in axial images by the


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Chapter 18

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Figure 18-6. Reformatted coronal image through the larynx (multidetectorCT). The patient is holding his breath. The position of the closed airway is represented by the dashed line. Note the density of fat in the paraglottic space at the supraglottic level (arrow). The thyroarytenoid muscle (arrowhead) forms the bulk of the true cord (glottic level). The thyroid cartilage and cricoid cartilage are also visible. H, hyoid bone; T, thyroid gland.

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bility of these therapies depends on the origin and the extent of the tumor. The following discussion of imaging of carcinoma of the larynx is organized according to the tumor's site of origin.

Supraglottic Tumors The usual voice-sparing surgical option for supraglottic squamous cell carcinoma is the supraglottic laryngectomy (Fig. 18-7). The resection is made along the ventricle, and the surgeon removes the entire supraglottic larynx, leaving at least one-and usually botharytenoid cartilages.'. lo. The patient retains the true cords and can thus generate voice in the usual manner. The protective function of the supraglottic larynx, particularly the epiglottis, is lost, and the patient must learn how to swallow without aspirating. Tumor crossing the ventricle is the primary contraindication for the supraglottic laryngectomy (Box 18-1). The incision passing along the ventricle would cut through tumor. Tumor growing along the mucosa to reach the true cord may be obvious at direct visualization. In a smaller lesion, the tumor may invade into the deeper tissues and follow the paraglottic space around the ventricle into the lateral edge of the true cord. This type of spread is unusual

appearance of the cartilages or by the transition from the fat to muscle in the paraglottic region. In MRI studies, the coronal images are perpendicular to the ventricle. Even if the ventricle is not actually visible, its position can be predicted by the transition from fat to muscle in the paraglottic space.

Pathology Most laryngeal imaging is performed in order to evwuate patients with tumors of or trauma to the laryn~."-'~~ 23. 24 The tumors can be mucosal or submucosal. In most instances, the larynx is visualized directly-if not by endoscopy, at least by mirror-and the radiologist should emphasize information that is not obtainable by direct visualization. 2'e

Mucosal Tumors Most tumors that come to imaging are squamous cell carcinomas arising from the mucosa of the larym2 With the possible exception of rare tumors arising deep within the ventricle, these tumors are detected before imaging. Indeed, imaging currently cannot rule out a small malignancy and thus is not a substitute for direct visualization. The otolaryngologist can assess smaller lesions completely. The margins of a small tumor may be readily visible, with no further information required. Alternatively, a patient with a large tumor may obviously require a total laryngectomy, and imaging may not add significant information. Imaging is most important for the patients with moderate-sized tumors in whom some sort of voicesparing procedure is considered. Such treatment options include partial laryngectomies and radiotherapy. The feasi-

Figure 18-7. Diagram of a supraglottic laryngectomy. The dotted line shows the incision of a supraglottic laryngectomy and passes along the ventricle between the true cord and the false cord (2). AE, aryepiglottic fold; C, cricoid cartilage; E, epiglottis; T, thyroid cartilage. (From Curtin HD: Imaging of the larynx: Current concepts. Radiology 173: 1-11, 1989.)


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as an isolated phenomenon but should be checked during ;: m&a imaging of a supraglottic tumor. . r d

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Box 18-1. Contraindications to Supraglottic Laryngectomy Tumor extension onto the cricoid cartilage Bilateral arytenoid involvement Arytenoid fixation Extension onto the glottis or impaired vocal cord mobility Thyroid cartilage invasion Involvement of the apex of the piriform sinus or postcricoid region Involvement of the base of the tongue more than 1 cm posteriorly to the circurnvallate papillae -1

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From Lawson W, Biller HF, Suen JY: Cancer of the larynx. In Suen JY, Myers E (edr): Cancer of the Head and Neck. New York, Churchill Livingstone, 1989, DD 533-591.

Axial imagirig parallels the ventricle and, therefore, is somewhat limited in its ability t~ identify the level of this key s@ucture. The paraglottic space of the false cord level is predominamtly fat, but at the true cord level it is predominantly muscle. The transition between the two represents the approximate level of the ventticle. If a normal slice can be found below the tumor but still within the supraglottic larynx, the supraglottic laryngectomy is technically possible pig. 18-8). If the tumor can be identified at the level of the cord as well as in the supraglottis, the decision is again made and the patient cannot have the usual supraglottic resection. If surgery is chosen as the therapy* the patient must have a total 1aryng-m~. On axial images, the lateral edge of the TAM should be carefully examined for the earliest evidence of transglottic spread. k narrow extension of the paraglottic fat is often 'preadSeen the Outer mar* of the ing around the ventricle will grow into this fat and eventu.

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Figure 18-8. CT scan of a supraglottic tumor separated m from the ventricle. A, Axial slice shows the tumor (T) at the level of the hyoid bone. Note the metastatic nodes

(N). The left node shows considerable irregularity, indi- , r . cating extracapsular tumor spread. B, The axial slice, slightly lower than in A, is normal. The normal para- u t glottic fat (arrowhead) indicates that the slice is at the IL" supraglottic level and thus between the tumor and the ventricle. C, A slice through the true vocal cord would show the normal muscle density (arrowhead).The vocal fc2 21 process is represented by an arrow. r-;

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1 Figure 18-9. Supraglottic tumor with paraglottic spread into the lateral edge of the true cord. A, Axial slice through the supraglottic level shows the tumor (T). Note the interface of tumor with fat in the preepiglottic space (arrowhead) and the normal paraglottic fat (arrow) on the opposite side. B, Axial slice at the level of the cord shows a small amount of tumor (arrow) prying its way between the thyroid cartilage (T) and the thyroarytenoid muscle (TAM) (open arrow). This is at the true cord level below the level of the ventricle. A, arytenoid. (B, From Curtin HD: MR and CT of the larynx. In Thrall JH [ed]: Current P a r f i c p of Radiology St. Louis, Mosby-Year Book, 1994.)

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ally will appear to "pry" the muscle away from the thyroid cartilage. Tumor can be distinguished readily from the fat in the supraglottic paraglottic space. The interface between tumor and muscle at the true cord level is more difficult to visualize. MRI offers the advantage of better tissue differentiation because of its various pulse sequences, but this advantage can be realized only if the patient is able to control motion (Fig. 18-9). Coronal images are perpendicular to the ventricle and may also be helpful in showing the relationship between tumor and the lateral aspect of the true cord (Figs. 18-10 d 18-11). Midline tumor can cross the level of the ventricle to involve the anterior commissure. This area can be difficult to evaluate either by direct visualization or by imaging. If there is deep growth from the anterior commissure into the attachment of the cord or through the cricothyroid membrane, imaging may detect tumor that is unappreciated clinically (see "True Cord"). Anterior growth from a supraglottic carcinoma brings the tumor into the preepiglottic space (see Figs. 18-8 and 18-9). The preepiglottic space as well as the paraglottic space has a rich lymphatic drainage, and tumor invasion heightens the concern regarding nodal metastases. Invasion is easily appreciated on axial imaging because the tumor is contrasted against the fat. Such involvement is not a contraindication to a supraglottic laryngectomy. Thyroid cartilage invasion is usually considered a contraindication t~ the supraglottic laryngectomy. such invasion is Llncommon unless the tumor is large and has crCL%ed the ventricle.16 In such a case, the patient would be excluded as a candidate on the basis of ventricular involvement. Involvement of the epiglottic cartilage is not a contraindication. (Cartilage assessment is discussed in the text on true cord lesions.) h14 -* a

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The supraglottic partial laryngectomy is the most accepted surgical therapy for tumors limited to the area above the ventricle. More extensive resections have been used for lesions extending beyond the boundaries of supraglottic larynge~tomy.'~ Pearson's near-total laryngectomy is done for supraglottic cancer extending to one cord. The resection

Figure 18-10. Supraglottic carcinoma extending around the ventricle into the lateral cord. The tumor (T) is readily visible to the endoscopist. A small amount of tumor (arrow) is seen extending around the lateral of the ventricle into the supnolateral mar& of the thyroarytenoid muscle The mucosa at the me cord level was Thyroid cartilage is represented by a white (From curtin HD: MR and CT of the larynx. Thrall JH [ed]: C-nt &actice of Radiology, 3rd ed. St. Louis, Mosby-Year Book, 1994.)

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Figure 1tL11. Transglottic tumor, reformatted coronal image (multidetector). A, The tumor follows (arrow) the paraglottic space around the ventricle widening the cord as the tumor infiltrates. An arrowhead represents the approximate level of the ventricle. B, Note the relationship of the tumor to the arytenoid cartilage (arrow), the thyroid cartilage (T) (immediately lateral), and the cricoid (C). N, metastatic node. ,-, , m

is continued to include the cord and to take the upper margin of the cricoid. The supracricoid partial laryngectomy with cricohyoidopexy takes the anterior cords to the level of cricoid. Minor involvement of the thyroid cartilage is not a contraindication. In either of these approaches, the inferior extent remains the most important assessment at imaging. An alternative to the partial laryngectomies already mentioned is endoscopic laser surgery.26 Lesions of the suprahyoid epiglottis, the AE fold, and the false cord are more appropriate for this type of surgery compared with lesions of the laryngeal surface of the epiglottis. The latter tumors are partially hidden by the epiglottis and thus are less accessible to endoscopic resection. Radiation therapy is also performed for supraglottic cancer. The same landmarks and considerations for supraglottic laryngectomy pertain to assessment for radiation therapy. The bulk of the tumor is also a prognostic factor. Patients with larger tumors fare worse than those with smaller tumors. One study used a 6-mL volume as a separation, with larger tumors carrying a much worse prognosis than smaller ones.20 Nodal metastases are very common in supraglottic tusesatsM atm & e'rof can,be b$a,tq@l-- .-

lage. The lesion can cros; the anterior commissure and involve the anterior one third of the opposite cord and still be treatable by vertical hernilaryngectomy. The incision through the thyroid cartilage is moved laterally toward the opposite side. Contraindications for vertical hemilaryngectomy are listed in Box 18-2. The most important assessments done at imaging concern inferior extension of the tumor, deep invasion at the anterior commissure, and cartilage invasion. Submucosal superior extension crossing the ventricle into the supraglottic larynx is a problem only occasionally. Box 18-2. Contraindications t o Vertical Frontolateral Hemilaryngectomy* Tumor extension from the ipsilateral vocal cord across the anterior commissure to involve more than one third of the contralateral vocal cord Extension subglottically >I0 mm anteriorly and >5 mm posterolaterally Extension across the ventricle to the false cord Thyroid cartilage invasion Impaired vocal cord mobility a relative contraindication

7

True Cord There are several options for therapy of glottic carcinoma, including simple resection, laser resection, and radiotherapy. Vertical hemilaryngectomy may be considered for a lesion involving the true cord. In this procedure, the surgeon removes the true and false cord on one side of the larynx using a vertical incision through the thyroid carti-

*This technique can still be used if the vocal process and anterior surface of the arytenoid are involved, but involvement of the cricoarytenoid joint, interarytenoidarea, opposite arytenoid, or rostrum of the cricoid is a contraindication. From Lawson W, Biller HF, Suen JY: Cancer of the larynx. In Suen JY, Myers E (eds): Cancer of the Head and Neck. New York, Churchill Livingstone, 1989, pp 533-591.

Inferior extension is quantified relative to the cricoid cartilage. The cricoid cartilage is the f~undationof the


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the membrane should be examined closely on the axial image. Cartilage invasion (discussed next) is considered a contraindication for vertical hemilaryngectomy. Minor thyroid cartilage invasion has been treated with supracricoid partial laryngectomy with cricohyoepiglottopexy.19In this procedure, more of the supraglottic larynx is removed and the cricoid cartilage is then suspended from the remaining supraglottic tissues and hyoid bone.

Cartilage Invasion

Figure 18-12. Vocal cord lesion with subglottic extension. T1weighted MRI study. The patient presented with a lesion of the true cord (not shown). The tumor (T) is within the ring of the cricoid cartilage (C). Note the intact fat planes (arrowheads)just anterior to the cricothyroid membrane. SCM, sternocleidomastoid. (From Curtin HD: Imaging of the larynx: Current concepts. Radiology 173: 1-11, 1989.)

larynx, and most surgeons suggest that even partial resections of this important cartilage are not possible. At imaging, if the tumor can be identified within the ring of the cricoid cartilage, the standard vertical laryngectomy cannot be done and laryngectomy is usually recommended (Fig. 18-12). Deep invasion at the anterior commissure may involve the thyroid cartilage or the cricothyroid membrane (Fig. 18-13; see Fig. 18-12)." The subtle fat plane anterior to

Figure 18-13. Tumor of the anterior commissure extending anteriorly. A small tumor was seen at the anterior commissure (white arrow). Anterior extension carried the tumor through the thyroid cartilage (arrowheads) with a prominent nodule in the anterior soft tissues (black avow). N, metastatic node. (From Curtin HD: The larynx. In Som PM,Bergeron RT [eds]: Head and Neck Imaging, 2nd ed. St. Louis, Mosby-Year Book, 1991.)

Cartilage invasion is considered a contraindication to both the standard supraglottic and vertical hemilaryngectomies. The subject is discussed here because such invasion is more of a concern in lesions involving the true cord. With both CT and MRI studies, the most reliable sign of cartilage involvement is identification of tumor on the extralaryngeal or outer surface of the cartilage. Minor degrees of cartilage invasion can be difficult to detect. The variability of ossification of the major cartilages can lead to problems in detecting cartilage invasion. The nonossified part of the cartilage can have approximately the same appearance as tumor on CT scans. MRI has the advantage of better tissue discrimination, and although there are no large series available, early results suggest that tumor can be differentiated from nonossified cartilage based on the intensity of the If signal is bright on the TI-weighted image, that part of the cartilage can reliably be considered normal. The high signal represents fat in ossified cartilage, and carcinoma is never that bright. On TI-weighted images, tumor and nonossified cartilage are usually dark. The nonossified cartilage may be slightly darker than tumor. Regions that are dark on TI-weighted images are examined on the long repetition time (TR) sequence. Nonossified cartilage remains relatively dark on long TR sequence images. Tumor tends to be significantly brighter than nonossified cartilage (Figs. 18-14 and 18-15). One cannot rely on the long TR image alone because fat may be fairly bright, even though the sequence is T2-weighted. Indeed, the tumor may have the same signal as the fat on T2-weighted images particularly if fast spin-echo sequences are used. Tumor, then, is dark or intermediate on TI-weighted images and usually relatively brighter on T2-weighted images. =-weighted images show tumor as intermediate to bright. This signal pattern does not definitely indicate tumor. Edema, fibrosis, or even red marrow have also been described with this pattern5 Edema is of particular concern because squamous cell carcinoma often has a peritumoral inflammatory response. Edema may be slightly brighter than tumor on T2-weighted images, but more experience is needed before a definite statement can be made regarding separation of tumor and edema. Edema of the cartilage presumably means that tumor is at least very close. In my experience, at least the perichondrium has been invaded if edema is present in the cartilage. At CT, irregularity of the inner cortex may suggest that tumor is eroding; however, this sign is questionable because of the variability of ossification. The cortex may be interrupted normally. Asymmetric sclerosis, particularly of


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Figure 18-14. Supraglottic tumor without cartilage invasion. A, Short TR, short TE. The tumor (arrow) abuts an area of the cartilage (arrowhead) that has the same signal intensity. On the opposite side, a normal ossified thyroid lamina with bright signal of medullary fat (open arrow) is identified. B, Long TR, short TE. The tumor (arrow) is significantly brighter than the nonossified cartilage (arrowhead). (From Curtin HD: MR and CT of the larynx. In Thrall JH [ed]: Current Practice of Radiology, 3rd ed. St. Louis, Mosby-Year Book, 1994.)

the thyroid and cricoid cartilages, may indicate tumor.4 Tumor may obliterate the medullary fat within the cartilage. Further study regarding the significance of various signal patterns and CT findings is needed. For instance, the effect of the various imaging findings on prognosis of various therapies, particularly radiotherapy, may potentially change management?

Subglottic Tumors Subglottic tumors are rare. When they do occur, the only surgical option is almost always a total laryngectomy because of the proximity to the cricoid cartilage.

Hypopharynx Although the hypopharynx is not actually part of the larynx, it is so intimately associated that discussion is warranted here. Decisions about potential surgical resection usually relate to the proximity of the tumor to landmarks within the larynx, and the assessment is thus quite similar to that of lesions within the larynx itself. Two regions of the hypopharynx have important relationships to the larynx: the pirifomz sinuses and the postcricoid region. The pirifonn sinuses indent the posterior wall of the

s tumor (T) against a Figure 18-15. Tumor involving tilage, axial MRI study. A, Short TR, short TE TI-weighted image s suspicious area of cartilage (sm~..~rrowheads).The cartilage has a more intermediate signal rather than ,, high signal of fat. A normal thyroid lamina is seen on the opposite side (open arrow). B, Long TR, long TE T2-weighted image shows significant "brightening" compared with that in A. The behavior of this area is the same as that of the tumor. Nonossilied cartilage remains as a dark linear structure within the higher-intensity tumor. (From Curtin HD:MR and CT of the larynx. In Thrall JH [ed]: Current Practice of Radiology, 3rd ed. St. Louis, Mosby-Year Book, 1994.)


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the esophagus and in the upper mediastinum become a significant concern.

Radiation Therapy

Figure 18-16. Tumor (T) of the piriform sinus. The lesion pro-

trudes through the thyroarytenoid gap between thyroid cartilage and arytenoid (arrow). The tumor thus invades the paraglottic space (arrowhead) of the supraglottic larynx. Compare with the fat in the paraglottic space on the normal side. C, carotid artery.

larynx. The anterior wall of the piriform sinuses represents the posterior wall of the paraglottic space. The piriform sinus makes up the lateral aspect of the AE fold. If a tumor is localized to the upper piriform sinus, a supraglottic resection may be considered along with resection of the tumor. A tumor that invades the paraglottic region of the larynx can follow the paraglottic pathway to reach the level of the cord, and in these patients a total laryngectomy is usually required (Fig. 18-16). The postcricoid region is that area of the lower hypopharynx that covers the posterior aspect of the cricoid cartilage. To achieve an appropriate margin, the surgeon must usually remove the cricoid and then perform a total laryngectomy. In these patients, the inferior extension within the pharynx should be estimated to help the surgeon decide the appropriate method of reconstructing the food passage.

Lymph Nodes Metastasis to the lymph nodes is a major consideration in carcinoma of the larynx. The subject of lymph nodes is covered elsewhere in this book, but brief comments about major pathways of spread are appropriate. Nodal metastases are a major concern with supraglottic tumors. Spread to the jugular nodes occurs very frequently because of the rich lymphatic drainage. The margin of the true cord does not have any lymphatics; therefore, tumors of the true cord do not spread to the lymph nodes unless there is deep invasion or, alternatively, unless the tumor has grown along the mucosa to involve the subglottic region. Because the subglottic mucosa does have lymphatic drainage, a primary tumor arising in this location or a glottic tumor extending into the area secondarily can metastasize to the nodes. In these patients, the nodes along

From a surgical perspective, the evaluation of patients uses landmarks that are slightly more precise, but many of the same findings are appropriate when radiotherapy is chosen as the treatment. The dimensions of the tumor in the axial plane are relevant, since they reflect the bulk of the tumor and relate to the depth of invasion into the soft tissues. The vertical extent of the tumor should be estimated, although the precision relating to the ventricle is less crucial. Extension into the subglottic area is very important because the treatment portals may be changed to include the paratracheal and upper mediastinum regions. Formerly, cartilage involvement was considered a contraindication to radiation therapy. Tumor recurrence is more frequent, as is radiation chondritis and chondronecrosis. More recently, however, some have expressed the opinion that relatively subtle involvement is not an absolute contraindication.

Other Mucosal Tumors Many benign lesions, such as polyps and papillomas, arise from the mucosa of the larynx. These lesions are seldom evaluated by CT or MRI studies. Submucosal tumors can ulcerate through the mucosa (see "Submucosal Tumors7' next). Although almost all malignancies arising from the mucosa of the larynx are squamous cell carcinoma, occasional malignancies arise from the minor salivary glands with histologies such as adenocarcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma. Verrucous carcinoma is an exophytic, slow-growing variant of squamous cell carcinoma. It does not usually metastasize, but it can be locally aggressive. There are no particular imaging features, but the lesion has a typical exophytic "warty" appearance on direct inspection.

Submucosal Tumors Lesions presenting beneath an intact mucosa usually arise from the nonepithelial elements of the larynx.13 Such tumors include chondroid lesions, hemangiomas, neurogenic tumors, and rare lesions such as leiomyoma, rhabdomyoma, and lipomas. Sarcomas arising from the same various mesenchymal elements are often submucosal, but with increasing size they can lead to mucosal ulceration. In rare instances, a squamous cell carcinoma can appear to be entirely submucosal. Such a lesion arises in the ventricle or ventricular saccule (appendix). The tumor expands upward into the paraglottic space and downward into the m e cord rather than medially toward the lumen of the larynx. A submucosal tumor represents a different problem. Unlike the squamous cell carcinoma, in which the actual tumor can be seen and is easily accessible for biopsy, the submucosal tumor presents as a bulge beneath an intact mucosa. In these patients, imaging is used not only to show


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Figure la-11. ~nonaroidlesion of the cricoid cartilage. The

lesion (arrow)expands the cricoid cartilage. The apparent origin in the cartilage suggests the diagnosis. A higher slice showed calcifications.

the extent of the lesion but also to help identify the type of tumor. With certain tumors, the findings are characteristic enough that the diagnosis can be predicted accurately. When the diagnosis is not definitive after imaging, certain findings can still be helpful to the otolaryngologist. The first question is whether the tumor is a chondroid lesion. Chondrosarcomas and chondromas arise from the cartilaginous framework of the larynx (Figs. 18-17 and 18-18); most arise from the cricoid. The thyroid cartilage is the second most common site of origin. Differentiation

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between benign -an1 malignant c a n i e ~ c u l even t at histopathologic examination. These tumors can compromise the airway, and treatment is usually surgical. A partial laryngectomy can be curative if the entire lesion is resected. If the cricoid cartilage is extensively involved, a total laryngectomy may be considered because of the key role of this cartilage in maintaining a patent airway. With either CT or MRI, the cricoid origin may be obvious and may give a clue as to the identity of the lesion (see Fig. 18-17). The cartilage may be expanded, indicating a lesion arising within the cricoid rather than eroding into the cartilage from a more superficial mucosal origin. The cartilaginous matrix is the most characteristic finding at imaging (see Fig. 18-18). CT scans are better than MRI studies at demonstrating the calcifications within the matrix of the tumor. Such calcifications are extremely rare in other lesions. Relapsing polychondritis can have fairly extensive calcification; however, this is extremely rare and should not involve the larynx exclusively. If the lesion does not have the imaging characteristics of a cartilage lesion, the radiologist tries to determine whether the lesion is vascular. Hemangiomas and paragangliomas enhance intensely on CT scans if a bolus or rapid drip of intravenous contrast material is used. The knowledge that a tumor is vascular has obvious implications if biopsy or resection is planned. Most of the other tumors mentioned have no specific identifying characteristics. They do not have a cartilaginous matrix and do not enhance brightly. The absence of these two imaging characteristics is useful information in limiting the diagnostic possibilities. Cysts also present as submucosal masses and are described next.

cysts Three types of cysts arise within or in intimate association with the larynx: The saccular cyst (laryngocele) and the mucosal cyst arise within the larynx, and the thyroglos-


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Mucosal Cyst A mucosal cyst is considered to be an obstructed mucous gland and can present anywhere mucosa is present. The benign nature of this cyst may be suggested by the smooth appearance, and this diagnosis is considered when a cystic-appearing mass is found on a mucosal surface.

Thyroglossal Duct Cyst

Figure 18-19. Diagram of a laryngocele. Coronal section through the larynx shows the ventricle (arrow)and the ventricular appendix (arrowhud)on the normal side. When this appendix is obstructed, it dilates (i.e., it fills with either fluid or air) to form a saccular cyst or laryngocele. In the diagram, the lateral extent of the saccular cyst protrudes through the lateral cricothyroid membrane. (From Curtin HD: The larynx. In Som PM, Bergeron RT [eds]: Head and Neck Imaging, 2nd ed. St. Louis, MosbyYear Book, 1991

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sal duct cyst arises just outside the larynx in close association with the strap muscles.

Saccular Cyst (Laryngocele) The saccular cyst, or laryngocele, represents a dilatation of the ventricular saccule or appendix (Fig. 18-19). Strict terminology refers to the abnormality as a saccular cyst if it is fluid-filled and as a laryngocele if it is air-filled. Many simply refer to the lesions as air-filled or fluid-filled laryngoceles. The laryngocele is a supraglottic abnormality, and the true cord is normal. Either presents as a submucosal mass or bulge in the supraglottic larynx (Figs. 18-20 to 18-22). The air or fluid withln is readily identifiable, and the extent can be determined. A small cyst or laryngocele may be confined to the supraglottic paraglottic space and is referred to as "internal." A larger lesion may protrude laterally through the thyrohyoid membrane just anterior to the upper horn of the thyroid cartilage. Any component outside the membrane is referred to as "external" (see Fig. 18-21). A pure external laryngocele is rare. The external component is seen in combination with an internal component. This is called a mixed laryngocele. When the external component is large, the laryngocele can present as a neck mass. Laryngoceles and saccular cysts are benign. However, these abnormalities can occur when tumor in the ventricle causes obstruction of the laryngeal saccule; therefore, both the radiologist and the endoscopist must carefully examine this key area (see Fig. 18-22).

The thyroglossal duct cyst arises from the remnant left as the thyroid gland descends to the appropriate position in the lower neck. The cyst can arise above or below the hyoid bone. A cyst that arises below the hyoid bone is usually found just off midline in the region of the strap muscles anterior to the larynx (Fig. 18-23). The appearance of the thyroglossal duct cyst is characteristic and should not be confused with saccular cyst arising within the larynx itself. A thyroglossal duct cyst in rare circumstances may bulge over the anterior notch of the thyroid cartilage but should not pass through the lateral aspect of the thyrohyoid membrane. The paraglottic mace should not be involved.

Post-therapy Appearance of the Larynx Both surgery and radiotherapy significantly distort the normal appearance of the larynx. After a total laryngectomy, the food passage may dilate to mimic an airway, but the laryngeal landmarks are no longer seen. Lower CT or MRI slices show the tracheostomy site. The appearance of the glottic and subglottic levels is unchanged by a supraglottic laryngectomy. With the supraglottic larynx removed, the characteristic landmarks of the paraglottic and preepiglottic spaces are not identified. Usually, the hyoid bone is removed. The major portion of the thyroid cartilage above the level of the cords is also removed. The vertical hemilaryngectomy can produce a variable appearance. One cord is removed, leading to significant asymmetry at the glottic level. Part of the upper larynx is removed on the ipsilateral side. The position of the original lesion dictates the position of the cuts through the thyroid cartilage, resulting in significant variability in appearance among patients with vertical hemilaryngectomies. At times, the surgeon may attempt to reconstruct the cord using a small slip taken from the strap muscles. This can lead to significant soft tissue that cannot be readily distinguished from tumor. Radiotherapy can cause characteristic apparent swelling of the soft tissues over the arytenoid cartilage and supraglottic region. Subtle reticulation or stranding of the supraglottic fat is seen. Initially, this represents local idammation and edema, but small-vessel changes make the appearance more permanent.

Trauma Direct trauma can result in fractures or dislocations of the cartilages in the larynx. Soft tissue injuries such as


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Figure 18-20. Saccular cyst (laryngwele

stgal I TI-weighted axial i e th $I th )per epiglottis shows the cyst (C). B, Slightly lower image shows the C ~ J L(L,~n thb yrua51dti~space at the f a l s ~ r l de ~ ~The l . ~ l l ~ c o (arrowhead) sa is intact. C, Axial image through the true cord level shows no evidence of tumor. A, arytenoid; T, thyroid. The thyroarytenoid muscle (TAM)is shown by an arrow. D, Coronal image shows the lower margin of the lesion (arrow) above the upper edge of the TAM (arrowhead); thus, the cyst is above the ventricle.


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Figure 18-21. Saccular cyst (laryngocele). A, The cystic structure has both an internal and external component. The s a c c u l ~cyst (C) protrudes through the thyrohyoid membrane, approximately at the arrowheads. Note the sharp margin of the cyst. B, Slightly lower slice shows the dilated appendix (arrow) just above the ventricle. Again, note the sharp margin. The fat in the paraglottic space indicates that this is still above the ventricle. A normal appendix is on the opposite side (arrowhead).

Figure 18-22 tar cyst I aV%ocf h e saccl (L) is seen ~gthe paraglottic space at the level of the false cord. NLatact mu,,, , arrow).,,' y,,glottic f;. , ,normal side ,,.rowhead) remains of high signal intensity. Fat is shown in the thyroid cartilage (black arrow). B, Slightly lower slice shows a tumor (T) filliig the ventricle and causing the obstruction of the ventricular appendix, causing the saccular cyst. (From Curtin HD: MR and CT of the larynx. In Thrall JH [ed]: Current Practice of Radiology, 3rd ed. St. Louis, Mosby-Year Book 1 QQA

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The cricoid fracture & &aracmkw9 a double break Fig. 18-25). The forcrt rrf fha blaw arch posteriorly, f r w ;fhe ring in The ring coIlapses inward. There is swin the subglottic soft tissum, giving apparent aft tissue against the inner surface of the cricoid M t d g e , whw zmmaliy the mucosa is very thin or almost in-* at hmgin~~~ Compromise of tha ahmy is. a cawem. Any inward displacement reduces the lmen of the h y . Equally of conem is the possibility of a tear of the mswsa. A fracture b mucosil eften results in fragment protruding through t chondzitis and 4chondronecrosiswith l%&erairway restriction. If there is any suspicion of the airway, direct vim-on, exploration, is indicated for a thioraqh imesment of the mucosa. If there is sufficienf fime ;Eo fhe thyroid cartilage, the lower epiglstth G@ b tom sa avulsed. This situation can be seen, pzutlp:&& d t l r h&mntal fi-actures where the fragments ate pushed p1mtee1y, creating a shearing force across the lower epiglo&f%. Because the abnormality is epiglottis does not calcify significantly, not detectable by CT scans. The only finding may be hematoma obscuring the fat in the preepiglonic space. The arytenoid cartilage is not often fractured, but the cricoarytenoid joint can be dislocated (Fig. 18-26). This can occur with fairly minimal trauma to the lateral larynx or may result from more severe insult associated with fractures of the major cartilages. The arytenoid is normally perched just off midline. The radiologist tries to verify that the cartilage is in the normal position or grossly displaced. Currently, a subtle displacement cannot be confidently excluded. The lower horns of the th@d cartilage articulate with the lateral cricoid ctld8ge Thk e r i d y r o i d joint can theoretically.be dislocated, u w 4 y in assatiation with fractures of either the thyroid or Criwid cartilagas. Because the attachment of the horn rn fo aicoid c d l a g e is fairly strong, a fracture of the bmr horn is common. One must be ,eamful in m&hg this diagnosis, since slight obliquity sf &le s1lm can muse apparent asymmetry of the space beween thb two cartdages. Each of the inferior horns must be followed d m to the point of articulation.

~~

Figure 18-23. Thyroglossal duct cyst. The cystic structure (arrow) is seen on the outer surface of the thyroid cartilage intimately associated with the strap muscles. Note that the paraglottic fat (arrowhead) remains clear.

mucosal tears and hematomas can occur in isolation but are often seen in conjunction with fractures. CT scanning is usually used because of the ability to visualize the calcified cartilage and because of the speed of imaging. The fragile airway is more easily managed and monitored in the CT scan than in the more confined area of the MRI study. In young patients, the cartilage may not be calcified but it can often be seen as slightly increased density against the contiguous soft tissues. Fractures usually affect the thyroid or cricoid cartilage. The thyroid cartilage can have vertical or horizontal fractures (Fig. 18-24). Vertical fractures are easily detected in the axial, scan plane, but horizontal fractures may be undetectable unless there is some displacement of the fracture fragments. Reformatted images may help to define horizontal fractures.

Fignre 18-24. Vertical fracture of the larynx; axial CT. The arrow indicates a fracture.

cle enlarges into the volime vaca& by the atrophied muscle so that air can be seen where there should be


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Chapter 18

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The Larynx

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Figure 18-25. Fracture of the cricoid cartilage; the ring has been fractured. Fragments from the anterior ring (arrowheads) have been pushed back into the airway. These fragments would be in danger of perforating the mucosa. The lamina of the cricoid (arrow) is not fractured. Note the air in the soft tissues and the soft tissue within the ring of the cricoid cartila1 (FromCurtin HD:MR and CT of the larynx. In Thrall JH [ed]: Current Practice of Radiology, 3rd ed. St. Louis, Mosby-Year Book, 1994.) rrg- I 4 , x n!

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muscle. The vocal ligament remains, and the arytenoid cartilage may be in a fairly normal position or may be tipped slightly. The piriform sinus on the affected side often enlarges as well. The posterior cricoarytenoid muscle is very thin, but since the axial plane provides a perfect cross-section, atrophy of this muscle may also be a~preciated.~~ In this case, fat appears to be closely applied to the posterior surface of the cricoid cartilage instead of the typical muscle density. In most instances, atrophied muscle is seen in patients with known paralysis. If the cause of the paralysis is not known, the course of the vagus nerve and the recurrent laryngeal nerve is examined. CT scanning is usually performed because of the distance that must be covered and because bone detail is important at the level of the jugular foramen in the temporal bone. The nerve is just posterior

to the carotid artery and jugular vein on transit through the neck. Lower in the neck, the nerve moves forward with respect to the carotid artery. The left nerve loops around the aortic arch, and the right nerve loops around the subclavian artery. The nerve on both sides ascends along the tracheoesophageal groove to reach the larynx. A lesion at any level can involve the nerve and cause paralysis. Superior laryngeal nerve paralysis is much less common, and characteristic radiographic findings have not been described. An extremely rare paralysis is "adductor paralysis." In this form, all muscles innervated by the recurrent laryngeal nerve are affected except the posterior cricoarytenoid. This muscle, unopposed, rotates the arytenoid and the cord laterally. This rare form of paralysis is not as well understood as the other more common paralyses but is thought to be related to an intracranial pathologic process.

Figure 18-26. Arytenoid dislocation. A, CT axial slice through the level of the cricoarytenoid joint. There is a normal configuration on the right. The arytenoid cartilage (arrow) articulates normally with the small articular surface of the cricoid (arro~vhead)on the superior edge of the cricoid cartilage. The arytenoid on the left is not identified in a normal position. B, Higher slice shows the dislocated arytenoid (arrow) in the supraglottic area.


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Stenosis Subglottic stenosis and tracheal stenosis can be evaluated by plain films, but imaging can give information about the cross-sectional area of the remaining airway. CT can show narrowing or stenosis of anterior and posterior commissures. The position of the cartilage relative to the airway can also be visualized. CT scans can determine whether the cartilage has collapsed into the airway or whether the cartilage remains in the normal position with the stenosis related only to soft tissue. Such narrowing can be congenital or may be the result of trauma. Granulation tissue can develop after tracheostomy. The length of the narrowing and the relationship to the vocal cords should be estimated. Plain films can be very helpful in estimating the length of the abnormality.

Granulomatous Disease Granulomatous disease, either of infectious or noninfectious etiology, can involve the larynx. Although rare, it can involve any of the mucosal surfaces and can be mistaken for tumor. The findings at imaging are nonspecific.

Rheumatoid Arthritis Rheumatoid arthritis can involve the cricoarytenoid joint. This process is not usually evaluated radiologically.

Polychondritis Relapsing polychondritis is a rare disease of unknown etiology. The cartilages of the larynx and trachea (among others) become inflamed, with edema of surrounding tissues. Calcifications of the abnormal tissue are characteristic and can be highly prominent. If calcifications are particularly prominent, the increased soft tissues and calcifications can mimic chondroid lesions.

Summary CT or MRI can be done for tumor imaging. One approach is to do CT as a first step, reserving MRI for answering specific questions remaining after CT. MRI is then done in a small fraction of cases. At our institution we begin with MRI in those cases where supraglottic laryngectomy is contemplated. This is because of a preference for MRI when looking at the region of the ventricle and the thyroarytenoid muscle. Contrast-enhanced CT scans are preferred for imaging of submucosal masses. CT scans are done without enhancement in trauma cases.

References 1. Bailey BJ, Biller HF (eds): Surgery of the Larynx. Philadelphia, WB Saunders, 1985. 2. Barnes L, Gnepp DR: Diseases of the larynx, hypophary~ an*

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esophagus. In Barnes L (4) Surgical : Pathology of the Head and Neck, vol 1. New York, Marcel Dekker, 1985, pp 141-226. 3. Becker M, Moulin G, Kurt AM, et al: Non-squamous cell neoplasms of the larynx: Radiologic-pathologic correlation. Radiographics 18: 1189-1209, 1998. 4. Becker M, Zbaren P, Delavelle J, et al: Neoplastic invasion of the laryngeal cartilage: Reassessment of criteria for diagnosis at CT. Radiology 203:521-532, 1997. 5. Becker M, Abaren P, Laeng H, et al: Neoplastic invasion of the laryngeal cartilage: Comparison of MR imaging and CT with histopathologic correlation. Radiology 194:66 1-669, 1995. 6. Blurting R Sturm C, Hong C, et al: The diagnosis of stages T1 and T2 in laryngeal carcinoma with multislice spiral CT. Radiologie 39: 939-942, 1999. 7. Castelijns JA, Gemtsen GJ, Kaiser MC, et ak Invasion of laryngeal cartilage by cancer: Comparison of (JT and MR imaging. Radiology 166:199-206, 1987. 8. Castelijns JA, Gerritsen GJ, Kaiser MC, et ak MRI of normal or cancerous laryngeal cartilages: Histopathologic correlation. Laryngoscope 97:1085-1093, 1987. 9. Castelijns JA, van den Brekel MW, Smit EM et al: Predictive value of MR imaging-dependent and non-MR imaging-dependent parameters for recurrence of laryngeal cancer after radiation therapy. Radiology 196:735-739, 1995. 10. Cummings CW,Fredrickson JM,Harker LA, et ak OtolaryngologyHead and Neck Surgery, 3rd ed, vol 3. St. Louis, Mosby-Year Book. 1998. 11. curti" HD: Imaging of the larynx: Current concepts. Radiology 173: 1-11, 1989. 12. Curtin HD: The larynx. In Som PM, Curtin HD (eds): Head and Neck Imaging, 3rd ed, vol 1. St. Louis, Mmby-Year Book, 1996, pp 6 12-707. 13. Curtin HD: Imaging of the larynx. In Valvassori GE. Mafee MF, Carter BL (eds):Imaging of the Head and Neck. New York, Thieme, 1995, pp 366-389. 14. Gion J, Joffre P, Serres-Cousine 0 , et ak Magnetic resonance imaging of the larynx: Its contribution compared to x-ray computed tomography in the pre-therapeutic evaluation of cancers of the larynx. Apropos of 90 surgical cases. Ann Radiol (Paris) 33: 170-184, 1990. 15. Gray H, Williams PL, Bannister LH: Gray's Anatomy: The Anatomical Basis of Medicine and Surgery, 38th ed. New York, Churchill Livingstone, 1995. 16. Kirchner JA: n o hundred laryngeal cancers: Patterns of growth and spread as seen in serial seaion. Laryngoscope 87:474-482, 1977. 17. Kolbenstvedt A, Charania B, Natvig, et al: Computed tomography in T1 carcinoma of the larynx. Acta Radiol 30:467469, 1989. 18. Lawson W, Biller HF, Suen JR: Cancer of the larynx. In Suen JY, Myers EN (eds): Cancer of the Head and Neck. New York, Churchill Livingstone, 1989, pp 533-556. 19. Levine PA, Brasnu DF, Ruparelia A, et al: Management of advancedstage laryngeal cancer. Otolaryngol Clin North Am 30:lOl-112, 1997. 20. Mancuso AA, Mukherji SK, Schmalfuss J, et al: Preradiotherapy computed tomography as a predictor of local control in supraglottic carcinoma. J Clin Oncol 17:631-637, 1999. 21. Phelps PD: Review: carcinoma of the larynx: The role of imaging in staging and pretreatment assessments. Clin Radiol 46:77-83, 1992. 22. Romo LV, Curtin HD:Atrophy of the posterior cricoarytenoid muscle as an indicator of recurrent laryngeal nerve palsy. AJNR Am J Neuroradiol20:467-471, 1999. 23. Sakai F, Gamsu G, Dillon WP, et al: MR imaging of the larynx at 1.5 T. J Comput Assist Tomogr 14:60-71, 1990. 24. Teresi LM, Luflcin RB, Hanafee WN: Magnetic resonance imaging of the larynx. Radiol C l i North Am 27:393-406, 1989 25. Tucker GF, Smith HR: A histological demonstration of the development of latyngeal connective tissue compartments. Trans Am Acad Ophthal Otol 65303-318, 1962. 26. Zeitels SM: Surgical management of early supraglottic cancer. Otolaryngol Clin 30:5%78, 1997. 27. Zeitels SM, Kirchner JA: Hyoepiglottic ligament in supraglottic can-


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Nasopharynx and Oropharynx

I

Sherif Gamal Nour, Jonathan S. Lewin

The pharynx is a fibromuscular tube that forms the upper part of the aerodigestive tract. It extends from the skull base down to the C6 vertebral level, serving as a conduit that conveys both air and food to the respiratory and alimentary tracts, respectively. The nasopharynx, oropharynx, and hypopharynx (laryngopharynx) are the three classic pharyngeal subdivisions that lie directly on the spine behind the nose, oral cavity, and larynx, respectively. The nasopharynx and oropharynx constitute the suprahyoid part of the pharynx. Formed of a thin muscle layer, the pharyngeal wall is lined by a mucous membrane and covered by loose fascia that permits pharyngeal movement during deglutition.lt3. A diverse range of pathologic conditions may involve the nasopharynx and oropharynx. These may occur primarily within the layers of the pharyngeal wall or in the deep suprahyoid neck spaces adjacent to the pharynx, or they may protrude from the nose or skull base to hang in the airway as pharyngeal masses. In addition, pharyngeal disease may be a consequence of functional rather than anatomic derangement. Prior to the modem imaging era, few tools were available for investigating pharyngeal disease. Having no more than a lateral plain x-ray, a conventional tomogram, or a contrast laryngopharyngogram, the radiologist had to depend on such signs as soft tissue fullness, intralurninal fihng defects, and abnormalities in the pharyngeal margins imaged in profilet45;all of these signs constituted indirect evidence of pathology, yet no means existed to visualize the actual disease process. Although amenable to clinical inspection, pharyngeal mucosal lesions may be difficult to evaluate because of anatomic variations and patient ~ompliance.'~~ A mucosal lesion, as detected by endoscopy, may represent no more than the "tip of an iceberg," with the exact deep extent always remaining uncertain to the endoscopist. Moreover, associated cervical lymph nodes, unless of palpable size, may be overlooked in the clinical setting. The advent of cross-sectional imaging exemplified in computed tomography (CT), then magnetic resonance imaging (MRI), has revolutionized the diagnosis of pharyngeal and deep neck disease. For the first time, the radiologist was able to gain true insight into the actual pathology, to define its exact site of origin, to map out its extent, and to study its effect on vital neighboring neck structures. With this wealth of information, the radiologist could interact with the clinician in a more effective manner and could make invaluable contributions to treatment decision making.

The improved understanding of the complex suprahyoid neck anatomy offered by these modern imaging modalities has led to the development of a new approach to the diagnosis of pathologic conditions involving this region that utilizes the concept of fascially defined spaces rather than the classic pharyngeal subdivisions. As CT and MRI have become the basic tools for evaluating nasopharyngeal and oropharyngeal pathology, the current classifications of nasopharyngeal and oropharyngeal carcinomas adopted by the International Union Against Cancer (UICC) and the American Joint Committee on Cancer (AJCC) are now based on cross-sectional imaging findings. The continuing evolution of MRI has gone beyond the mere imaging of anatomic changes to approach near realtime recording of the functional status of the pharynx, and the time is not far before the radiologic focus of interest broadens to include disorders of pharyngeal function, such as obstructive sleep apnea. Finally, interventional MRI is a rapidly growing part of current radiologic practice and has been successfully applied to the pharynx and adjoining deep neck spaces to guide biopsies and minimally invasive therapeutic procedures.

Anatomy The topics to be discussed are summarized in Box 19-1.

Traditional Classification Classically, the suprahyoid head and neck region is divided into the nasopharynx, oropharynx, and oral cavity (Fig. 19-l), with the exact contents of each compartment dependent on how much of the adjoining deep tissues are in~luded.~.lZ8 653

Nasopharynx The nasopharynx is the uppermost part of the aerodigestive tract. It measures approximately 2 X 4 cm in anteroposterior and craniocaudal diameters, respectively. It is bounded posterosuperiorly by the basisphenoid, basiocciput, and upper two cervical vertebrae as well as by the Iz8 prevertebral muscles.65 Anteriorly, it communicates with the nasal cavity through the choana. Inferiorly, it is in direct continuity with the oropharynx, and the plane of division is a horizontal line drawn along the hard and soft palates and passing


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Box 19-1. Anatomy I. Traditional Classification A. Nasopharynx . . B. Oropharynx I II. Spatial Approach A. Superficial fascia ' 1. B. Deep fascia 1. Superficial layer (investing fascia) a. Description b. Spaces included (1) Masticator space (2) Parotid space (3) Submandibular and sublingual spaces (4) Muscular space ( 5 ) Suprasternal space (of Burns) 2. Deep layer (prevertebral fascia) a. Description b. Spaces included (1) Perivertebral space, , (2) Danger space 3. Middle layer (visceral fascia) a. Description (1) Buccopharyngeal fascia Cloison sagittale ' (2) (3) Fascia of tensor veli palatini b. Pharyngobasilar fascia (pharyngeal aponeurosis) c. Spaces included (1) Pharyngeal mucosal space (2) Retropharyngeal space (3) Parapharyngeal space (a) Prestyloid (b) Retrostyloid

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open mouth). It is separated from the oral cavity by the circumvallate papillae of the tongue, the anterior tonsillar pillars, and by the soft palate. The posterior third of the tongue and lingual tonsil are therefore considered to be within the oropharynx and not in the oral cavity.65 Posteriorly, the superior and middle constrictor muscles separate the oropharynx from the prevertebral muscles overlying the second and third cervical vertebrae. Superiorly, the oropharynx communicates with the nasopharynx. Inferiorly, it is separated from the hypopharynx by the pharyngoepiglottic fold and from the larynx by the epiglottis and glossoepiglottic fold.6s.'I9. '28 The features of the lateral oropharyngeal walls include two faucial arches: 1. The anterior (palatoglossus muscle) arch. 2. The posterior (palatopharyngeus muscle) arch. Between them lies the tonsillar fossa, which contains -the palatine tonsil on each side.ug fi ' -c

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Spatial Approach

posteriorly to the Passavant's ridge (a ridge of pharyngeal musculature that opposes the elevated soft palate).65.Io8. 142 The features of the lateral nasopharyngeal walls are discussed later. r

*

Although the classic classification of nasopharynx, oropharynx, and hypopharynx is quite effective in regard to superficial mucosal lesions, such as squamous cell carcinoma, this "non-fascially based" classification is much less helpful to the radiologist attempting to accurately localize deeply seated head and neck lesions as evaluated on crosssectional imaging.4.65 The traditional classification of the suprahyoid head and neck into the nasopharynx, oropharynx, and oral cavity has thus been largely replaced by a somewhat complicated, yet more useful scheme that divides this region into multiple spaces, defined by the layers of cervical fascia. Such a "spatial approach" provides a satisfactory means of localizing the space of origin of a suprahyoid lesion and, consequently, helps to limit the differential diagnosis to a unique set of pathologic processes specific to each anatomic space.4+ 65. 67. 128+L62 Moreover, it utilizes surgically and pathologically defined terminology, thereby creating a "common language" for the radiologist-yd the referring surgeon.65 409

Oropharynx The oropharynx is the part of the aerodigestive tract that lies behind the oral cavity (it can be seen through the

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Chapter 19


62 1

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Figure 19-2. Diagrammatic layout of the suprahyoid neck spaces and their fascial boundaries at the level of the nasopharynx (A), &tail of the nasopharynx (inset), and the oropharynx (B).

Crucial to an appreciation of suprahyoid neck spaces is a proper understandmg of the fascial framework of the head and neck (Fig. 19-2; see Figs. 19-5 and 19-6). For the sake of completeness, each of these spaces is addressed here, with particular emphasis given to those most relevant to the subject of this chapter. Basically, two major compartments constitute the head and neck fasciae: the superficial and deep layers.

Superficial Fascia

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Superficial Layer of the Deep Fascia (Investing Fascia) Descrl~tlon The superficial layer forms a complete collar around the neck and is attached superiorly to the lower border of the mandibular body back to its angle and more posteriorly to the mastoid processes, the superior nuchal line, and to the external occipital protuberance. Inferiorly, this layer attaches to the acromion and spine of the scap;la, to the clavicle, and to the manubrium st&. The two halves of the investing fascia attach posteriorly to the ligarnentum nuchae and cervical spinal processes. Anteriorly, they are continuous and are attached to the hyoid bone, where they converge with the middle (visceral) layer of the deep fascia, dividing the neck into suprahyoid and infrahyoid portions?'. 113 '

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The investing fascia splits to enclose number of structures within the neck, thereby forming the following fascia1 spaces:

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Masticator Space. Above the attachment to the lower border of the mandible, a part of the investing fascia continues upward to enclose the muscles of mastication and the mandible (ramus and posterior body) by splitting into a superficial and a deep layer. The superficial layer covers the masseter muscle and then attaches to the zygomatic arch (this is continuous with the fascia covering the parotid gland forming the parotid-masseteric fascia). The deep layer runs deep to both pterygoid muscles to attach to the skull base, separating the masticator from the prestyloid compartment of the parapharyngeal space (PPS).40. 64. O' Parotid Space. The parotid space is formed as the investing fascia splits between the mastoid process and the angle of the mandible to enclose the gland, forming its capsule.14l6 The medial aspect of the parotid space, which contains the deep lobe of the parotid gland, extends through the stylomandibular tunnel (the gap between the styloid process and the posterior margin of the mandible) for a variable distance before it meets the prestyloid compartment of the PPS?' Submandibular and Sublingual Spaces. A layer of the investing fascia splits to line the undersurface of the submandibular gland before reattaching to the mandible at the rnylohyoid line, thereby forming the capsule of the gland. In the radiologic literature, the term submandibuhr space is given to the entire area superficial to the rnylohyoid muscle down to the superficial layer of investing fascia as it extends from the hyoid bone to the mandible. The sublingual space is the area deep to the mylohyoid muscle, up to the mucosa of the mouth floor. The relevance of these spaces to this chapter is their free communication with the prestyloid compartment of the PPS." 87

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skull base to the coccyx and is tight enough to resist the superoinferior spread of infection or ne0p1asms.l~~

Danger Space. This thin potential space lies between the prevertebral fascia posteriorly and the alar fascia anteriorly. The space is named as such because it extends from the skull base to the level of the diaphragm and is filled with loose areolar tissue, which provides a ready conduit for the spread of infe~ti0n.l~~ Middle Layer of the Deep Fascia (Visceral Fascia) Description There has been considerable confusion in the literature concerning the layers composing the visceral fascia, with most of the anatomic references focusing mainly on the pretracheal fascia in regard to the fascial layers between the investing and prevertebral fasciae.61.I l 3 However, to give the reader a full understanding of the spatial anatomy of this region, it would be more appropriate in this context to stress the layers relevant to the suprahyoid neck. The following basic fascial planes comprise the visceral fascia above the hyoid bone.

Bumpharyngeal Fascia. This fascia is a thin layer of loose connective tissue that covers the pharyngeal constrictor muscles and permits pharyngeal movement. It attaches superiorly to the skull base, having the same attachment as the pharyngobasilar fascia (see later), and is continuous anteriorly over the buccinator m u s ~ l e70. . ~ .'I9.lZ8 The buccopharyngeal fascia is not visible on CT scans or MR images.83

Cloison Sagittale. These bilateral, small, sagittally oriented fascial slips extend from the buccopharyngeal fascia anteriorly to the prevertebral fascia posteriorly, near its Muscular Spaces. Muscular spaces are formed as the attachment to the transverse processes of the cervical vertefascia splits to enclose the trapezius, the sternocleidomasbrae. The importance of these tiny fascial slips is that they toid, and the inferior belly of the omohyoid m u s ~ l e s . ~ l . ~ ~separate the medially positioned retropharyngeal space (RPS) from the laterally positioned retrostyloid compartSuprasternal Space (of Burns). This shallow space is ments of the PPS8' These slips are sometimes also called formed just above the manubrium sterni as the investing the alar fascia, but this tern is better avoided to prevent fascia splits to attach to the anterior and posterior borders confusion with the alar fascia described earlier.87 of the jugular n~tch.~~.'O Fascia of Tensor Veli Palatini. This relatively thick Deep Layer of the Deep Fascia (Prevertebral Fascia) fascial sheet envelops the styloid process and its musculaDescription ture and extends anteromedially to merge with the fascia associated with the tensor veli palatini muscle. It then The deep layer encircles the vertebral column as well continues further anteriorly to fuse with the pterygomanas the paraspinal and prevertebral muscles, with a firm insertion on the spinous and transverse processes of the dibular raphe and the buccopharyngeal f a s ~ i aIs8. ~ This fascial layer divides the PPS into anterolateral (prestyloid) vertebral column. The prevertebral fascia extends from the Is8 and posteromedial (retrostyloid) ~ornpartments.~. skull base down to the third thoracic vertebra, where it fuses with the anterior longitudinal ligament in the postePharyngobas~larFascia (Pharyngeal Aponeurosis) rior mediastin~rn.~' Some authors have described a slip of the prevertebral fascia, the alar fascia, which is immediThis important fourth fascial sheet lies between the ately anterior to it and has a similar coronal plane of superficial and the deep layers of the deep fascia, but it is 0rientation.6~. usually considered to be separate from the middle layer. As a tough membrane, it forms an almost closed, very Spaces resistant chamber that determines the configuration of the nasopharyn~.~~. '42 It attaches superiorly to the skull base Perivertebral Space. The perivertebral space (PVS) is from the medial pterygoid plates, passing posteriorly to the enclosed by the circumferential prevertebral fascia and is petrous bones just anterior to the carotid foramina, where divided by the fascial attachment to the cervical transverse it reflects medially on either side to be continuous over the processes into the anterior prevertebral and posterior paralongus capitis and rectus capitis muscles. The fascia despinal ~ornpartments.6~128 This space extends from the 673


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Chapter 19

scends from the skull base, forming an elongated ring that closes the gaps above the superior constrictor muscle of the pharynx bilaterally. References on anatomy describe the fascia to then continue lining the inner surface of the pharyngeal musculature, thereby supporting the mucous membrane of most of the nasal portion of the pharynx, then it becomes much thinner below, at about the level of the soft 113- l L 9 , Iz8 From the functional and imaging perspectives, the most relevant portion of the pharyngobasilar fascia is that above the superior constrictor muscle, hence the name the pharyngeal aponeurosis (see Fig. 19-5). Formed of dense fibrous tissue, the pharyngobasilar fascia shows up on MRI images as a low-intensity line extending from the medial pterygoid plate to the carotid foramen medial to the tensor palatiniS3 Thus, the constrictor muscles of the pharynx are "sandwiched" between the pharyngobasilar fascia (inside) and the buccopharyngeal fascia (outside). Above the upper edge of the superior constrictor muscle (between it and the skull base), the two fascial layers blend to form, along with the lining mucosa, the thin wall of the lateral pharyngeal reAnterior to these cesses (fossae of R~senmiiller).~~*%. recesses, a natural defect in the pharyngobasilar fascia (sinus of Morgagni) exists on each side, transmitting the eustachian tubes and levator veli palatini muscles from the skull base to the pharyngeal mucosal space (PMS).Q %. lI9* Iz8 The torus tubarius, the most prominent anatomic landmark on the lateral nasopharyngeal walls, is a ridge lying between the orifice of the eustachian tube anteroinferiorly and the fossa of Rosenmiiller posterosuperiorly on each side. It is formed by the levator veli palatini muscle together with the cartilaginous eustachian tube and the ~~. overlying m u ~ o s a .%969

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Spaces

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,,.- - - . The deep face and neck spaces, defined by the justdescribed layers of visceral fascia, are presented next. L

Pharyngeal Mucosal Space. The PMS is the area of the nasopharynx and oropharynx on the inner (airway) side of the buccopharyngeal fascia. The latter separates the PMS from the PPS laterally and the RPS posteriorly. The PMS is thus composed of the five layers forming the pharyngeal wall. From internal to external, they are as f0ll0ws~~~: 1. Mucous membrane. The upper part of the nasopharynx is lined by respiratory epithelium (pseudostratified ciliated columnar). Inferiorly, where food contact is more of an issue, the epithelium changes to a stratified squamous tv~e.% , 2. Submucosa. The submucosa contains minor salivary glands and prominent lymphoid tissue of Waldeyer's ring (adenoids, palatine tonsils, lingual tonsils, and submucosal lymphatics). Lymphoid tissue may also normally be present in the epithelium (lymphoepithelium).65.%, 128 .- . 3. Dense pharyngobasilar fascia. . 4. Superior constrictor muscle of the pharynx. Above this muscle, layers 3 and 5 are adherent and are pierced by the eustachian tube (cartilaginous end) and the levator palatini muscle, which are considered within the PMS. 5. Thin buccopharyngeal fascia. This fascia forms the outer confinement of the PMS. &

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Nasopharynx and Oropharym

623

Retropharyngeal Space. The RPSS7.128 is a small, potential space that is bounded as follows: 1. Anteriorly by the buccopharyngeal fascia, separating it from the PMS. 2. Posteriorly by the prevertebral fascia, separating it from the perivertebral space. 3. Laterally by the cloison sagittale, separating it from the retrostyloid compartment of the PPS on each side.87 4. Superiorly by the skull base. 5. Inferiorly by the fusion of the buccopharyngeal and prevertebral fasciae between the T2 and T6 spinal leve l ~ . ~ ~

The RPS normally contains a small amount of fat and, in the suprahyoid region, the lateral (nodes of Rouviere) and medial retropharyngeal lymph nodes.". The medial retropharyngeal lymph nodes are located near the midline and are seldom seen unless they are pathologically enlarged.39.45 The lateral retropharyngeal (LRP) lymph nodes are found immediately medial to the internal carotid artery, adjacent to the longus capitis muscle, and are usually most prominent at the C1-C2 level but can occasionally be visualized down to the level of the ~ a l a t e . ~lol~The . ~ ~LRP , nodes are usually identified on MR images and, to a lesser extent, on CT scans. In adults, the nodes are usually smaller than 3 to 5 mm, but nodes of up to 1 cm can be considered normal if they are homogeneous.45* lol In children, the LRP nodes may be as large as 2 cm in size, particularly if the adenoids are prominent.39This lymph node chain provides drainage for the nasopharynx, oropharynx, middle ear, nasal cavities, and paranasal sinuses.39.132

Parapharyngeal Space. The PPS is an anatomic recess, shaped like an inverted pyramid with its base at the base of the skull and its apex at the greater cornu of the hyoid bone. It occupies the space between the muscles of mastication and the deglutitional muscle^.^^^ 67, 1 3 1 9 156. 158 It has the following boundaries and relations: 1 . Laterally a. Antemlaterally; separated from the masticator space by the layer of investing fascia covering the medial 158 aspect of the medial pterygoid muscle. ~ 3 %. , b. Posterolaterally; separated from the parotid space by the layer of investing fascia covering the deep lobe lS8 However, this is a sparse of the parotid gland.119. fascial layer that does not present a barrier to the spread of disease." 2. Medially; separated from the PMS by the buccopharyngeal fascia, while its extreme posterior part is separated from the RPS by the cloison sagittale.Io3.lZa. 158 3. Posteriorly; separated from the perivertebral space by the prevertebral fascia.Io3. 158 4. Anteriorly a. Antemsuperiorly (at the level of the pterygomandibular raphe); closed by the convergence of the buccopharyngeal fascia with the fascia covering the medial aspect of the medial pterygoid m u s ~ l eI .l 9~ b. Anteroinferiorly (at the level of the mylohyoid muscle); PPS is often continuous with the sublingual and submandibular spaces, thereby allowing lesions to


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pass from one space to another without crossing a fascial bounda~-y.36.'O 5. Inferiorly: PPS is generally described as extending down to the hyoid bone; however, the fusion of multiple fascial layers and muscle sheaths near the angle of the mandible limit the caudal extent of the s p a ~ eand , ~ the styloglossus muscle can be considered the functional inferior boundary of the PPS.87 The PPS, as just defined, is a larger area of the deep face than the fatty triangles seen Qn either side of the 659

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pharynx. This definition, which is supported by most authors, implies the division of the PPS by the fascia of tensor veli palatini (see earlier) into the 1. Prestyloid PPS, anterolateral to the fascia. 2. Retrostyloid PPS, posteromedial to the fascia. This is the suprahyoid extension of the carotid space (carotid sheath and its contents). The contents of the suprahyoid neck spaces along with the common disease processes involving each space are listed in Table 19-1. .' ,.-41.,- . ,i

Table 19-1. Anatomic Spaces of the Suprahyoid Neck: Their Contents and Common Disease Processes Pharyngeal mucosal space (PMS)

Contents

Differential Diagnosis of Lesions

1. Mucosa 2. Submucosa containing a. Minor salivary glands b. Lymphoid tissue (adenoids, palatine, and lingual tonsils) 3. Pharyngobasilar fascia 4. Superior and middle constrictor muscles 5. Buccopharyngeal fascia (enclosing layer)

Psardo~lass

+ Cartilaginous eustachian tube + Levator veli palatini muscle

Asymmetric fossae of Rosenmiiller Pharyngitis Infectious pobdiation ' I ' CongenitaI ;I' . a ' +b Thornwaldt's cyst ' ' " '

.

A'L

t

.4-

} ::%EMS~ystmphic caicification Retention cyst L:

!

H..

Plwmorphic adenoma (belugn mixed tumor) of minor salivarv glands

;Minor s&vary gl&d

malignancy ~habdom~os&%ma (pediitric) -

Prestyloid parapharyngeal space (PPPS)

1. 2. 3. 4. 5.

Fat Pterygoid venous plexus Internal maxillary artery Ascending pharyngeal artery Branches of the mandibular division (V3) of trigeminal nerve

Pseudomass 2nd branchial cleft cyst from adjacent spaces

,adenoiditis, tonsillitis, peritonsillar abscess, retromandibular vein thrombosis PS: parotid calculus disease, deep lobe parotid '- , abscess MS: dental infection, 3rd upper molar extraction with violation of pterygomandibular raphe Infection secondary to penetrating trauma to the lateral pharyngeal wall Benign tunror *I ' Pleomorphic ahnoma (benign mixed tumor) Extending from deep lobe of parotid gland Arising from salivary gland rests in PPS Lipoma

-

MaEgnmt tumor Mucoepidermoid carcinoma Adenoid cystic carcinoma Malignant mixed aunor from

1

of salivary gland rest in PPS

"-

Adjacent spaces PMS: squamous cell carcinoma, non-Hodgkin's lymphoma, minor salivary gland malignancy PS: mocoepidennoid carcinoma, adenoid cystic carcinoma I? MS: sarcoma Skull base tumor

.

. I , . - . ,

I

f

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,tTable contimed on following page


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Chapter 19

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625

Table 19-1. Anatomic Spaces of the Suprahvoid Neck: Their Contents and Common Disease Processes Continued Contents Retrostyloid parapharyngeal space (RPPS) Carotid space (CS)

1. Internal carotid artery 2. Internal jugular vein 3. Lower 4 cranial nerves (IX-XII) 4. Sympathetic chain 5. Lymph nodes (deep cervical chain)


wirss

Carotid space cellulitis or abscess Spread from adjacent spaces Breakdown of infected internal jugular lymph nodes Vme~ulnr

Benign tumor ?e -i;-*.

Glomus jugulare Glomus vagale Carotid body tumor Nerve sheath tumor * $€?l-w**Neurofibroma Meningioma (of jugular foramen) aligna ant tumor -

+t.@M-m@-

Direct invaston by pnmary squamous cell carcinoma

Retropharyngeal space (RPS)

.. .,.

2. Lymph nodes a. Lateral retropharyngeal (of Rouviere) b. Medial retropharyngeal

Pseudomuss Tortuous internal carotid artery Edema fluid or lymph spilling into RPS secondary to venous or lymphatic obstruction Congenital Hemangioma Lymphangioma ZnRhmmaton

Benign hrmor

Thyroid carcinoma

Masticator space (MS)

1. Mandible (ramus + posterior body) 2. Muscles of mastication a. Lateral pterygoid b. Medial pterygoid c. Masseter d. Temporalis 3. Inferior alveolar and lingual nerves (branches of the mandibular division V3 of trigeminal nerve)

4~ceWO.@?-yH

,Benign &g@e&q ~ ~ ~ @ f k @ @ e r a l d b i ( a p e m l 2

Mandibular nerve (cranial nerve V3) denervabon atrophy Congenital Hemangioma Lymphangioma

~ a n d b u l a osteomyelitis r Benign tumor Osteoblastoma Leiomyoma Nerve sheath tumor (schwannoma-neurofibroma) Malignant tumor f +chondrosarcoma, osteosarcoma, soft tissue sarcoma Malienant schwannoma ----.----

---

- - ~ ----

~~

cer of lung, breast, Table continued on folbwing page


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626

Table 19-1. Anatomic Spaces of the Suprahyoid Neck: Their Contents and Common Disease Processes . 1 i T Continued

Parotid space (PS)

.

a L

4.

i

Contents


1. Parotid gland

Congenital 4 r 1st branchial cleft cyst Hemangioma (pediatric) Lymphangioma (pediatric) ZnJlammatory Cellulitis/abscess Benign lymphoepithelial lesions (AIDS) o Reactive adenopathy Benign tumor ~ l g @ ~ p h icidekma c fberiign m i x & i . ~ r ) vauhin) ' m r Ipn&ma@sum] Oncocytoma Lipoma Facial nerve schwannoma or neurofibroma Malianant tumor

- 2. Facial nerve V1I

'.3. External carotid artery (ECA) (terminating in

parotid gland into internal maxillary and superficial temporal arteries) ' 4. Retromandibular vein 5. Intraparotid and per~parotldlymph nodes L

h

.

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+. '

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,

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.,'$

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Acinous cell Squamous cell Non-Hodgkin's lymphoma Malignant @mixededtumor L~ (within proti2 &) qnamouS-cell- c eJirnanm of scalp homa

LkaszUei Perivertebral space (PVS)

. .. -

1. 2. 3. 4. 5.

Prevertebral muscles Scalene muscles Vertebral arteries and veins Brachial plexus Phrenic nerve

Pseudomass %

k q e b q l body rgsfe~pAj4 Anterior d ~ s kherniation ... - Cellulitis, abscess

-

Vascular Vertebral artery dissection, aneurysm, or pseudoaneurysm Benign tumor Schwannoma/neurofibroma (cervical nerve roots, brachial plexus) Vertebral body benign bony tumors Malignant tumor Primary Whoiao~ Non-Hodgkin's lymphoma Vertebral body primary malignant tumor Metastatic

I'

Direct invasion of sqwunous cell carcimnta Nore: Shaded entries indicate the most common lesions. AIDS, acquired immunodeficiency syndrome. Data from Barakos, 1991"; Curtin, 1987"'; Harnsberger, 1991" and 19!B6-'; Lewin, 1995"; Norbesh, 1996'*; and Silver et al, 1984.Is

-.-

'

3

Normal Imaging Anatomy The anatomy of the normal suprahyoid neck, as seen with CT and MRI, is demonstrated in Figures 19-3 to 19-6.

lmaging Rationale and Techniques CT and MRI are currently the primary modalities for investigating the suprahyoid neck region. This region,

which extends from the skull base to the hyoid bone, is surrounded. for the most Dart, by bones that limit external clinical examination. In addition, while the superficial extent of mucosal lesions can be readily identified by the examining physician, their deep extent as well as lesions confined to the deep spaces are almost totally inaccessible for clinical or endosco~icevaluation. In many cases of suprahyoid neck masses, MRI offers benefits over CT because of its higher soft tissue contrast resolution, multiplanar capability, and superiority in detecting perineural tumor spread and intracranial invasion.65


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Chapter 19

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Figure 19-3. A-G, Normal imaging anatomy of the nasopharynx and oropharynx on a contrast-enhanced axial CT scan (5-mrnslice thickness). 1 Nasopharyngeal airway 2 Tensor veli palatini muscle 3 Levator veli palatini muscle 4 Temporalis muscle (deep = medial head) 5 Temporalis muscle (superficial = lateral head) 6 Coronoid process of mandible . 1,;.- ..--. 7 Lateral pterygoid muscle 8 Condylar process of mandible 9 Internal carotid artery in vertical segment of petrous 10 Pterygopalatine fossa (basal part) 11 Pterygomaxillary fissure 12 Pterygoid fossa between medial and lateral pterygoid plates 13 Medial pterygoid muscle 14 Internal maxillary vessels 15 Fat in prestyloid compartment of parapharyngeal 16 Parotid gland (superficial lobe) 17 Facial nerve surrounded by fat in stylomastoid foramen 18 Internal jugular vein . lll.II+ .. 19 Internal carotid artery 20 Eustachian tube orifice 21 Torus tubarius overlying levator veli palatini muscle r% > 1 cm in diameter) can be seen, keeping the configuration of normal nodes (oval or kidney-shaped) and usually presenting a homogenous texSuppurative Lymphadenitis. Suppurated lymph nodes appear enlarged and demonstrate central low attenuation on CT or fluid signal intensity on MRI.". However, these central changes can also be seen in early liquefying nodes without complete suppuration. Frankly suppurated nodes can be identified by their enhancing rims (Figs. 19-21A) and by the associated edema of the RPSa Retropharyngeal Cellulitis or Abscess. The most common finding in patients with infection of the RPS is that of cellulitis localized to the RPS at the level of the nasopharynx or 0ropharynx.4~It is seen as diffuse thickening (>75% of anteroposterior diameter of vertebral body2) and as enhancement of the retropharyngeal soft tissues (see Fig. 19-21). When an abscess forms, it appears as an area of fluid collection marginated by an enhancing rim, with possible air or air-fluid level seen ~ i t h i n . 4AS ~ stated, it starts at the region of lateral retropharyngeal nodes (Fig. 19-22) but may spread to involve the entire RPS (see Fig. 19-21B), where it may attain a characteristic "bowtie" appearan~e.~' Significant mass effect is often present,llg and the degree of pharyngeal airway compromise should always be sought. It is also important to distinguish a true retropharyngeal abscess, which necessitates surgical drainage, from both suppurative adenitis (with surrounding edema) and cellulitis, because the latter two conditions may respond to conservative treatment without the need for inter~ention.~~. 'I9


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v. a L

Figure 19-21. Retropharyngeal infection in a 5-year-old boy presenting with left upper neck swelling. A, Postcontrast CT scan reveals enlarged, left-sided lateral retropharyngeal lymph node (of Rouviere) (N), displaying central low attenuation and thick enhancing margin, a picture consistent with suppurative lymphadenitis (intranodal abscess). The associated enlargement of palatine tonsils (arrowheads) indicates the source of infection. Note the integrity of the ipsilateral prestyloid parapharyngeal space (arrow). B, Section at a lower level in the same patient shows low fluid attenuation casting the entire retropharyngeal space. The presence of a thin, enhancing rim marginating the collection suggests a retropharyngeal abscess (caused by rupture of another suppurated lymph node), rather than a mere associated edema, and necessitates the establishment of drainage. Note the bilateral posterior cervical space lymphadenopathy (arrows).

Complicated Retropharyngeal Abscess. The parapharyngeal fat may appear dense as a result of associated inflammation (see Fig. 19-21). When suppuration extends into this space, however, external drainage (rather than the transoral approach used with most retropharyngeal abscesses) is indicated.I6" Although axial CT usually demonstrates the full extent of retropharyngeal infection, sagittal MlU may occasionally

be helpful to better define the superoinferior extent of disease and associated displacement or compression of the pharynx, larynx, trachea, or e s ~ p h a g u s . ' ~ ~ Extension of RPS infection into the danger space cannot be differentiated from an RPS process unless abscess or cellulitis extends below the T2 to T6 vertebral level. Benign Tumors Retropharyngeal Lipoma Benign tumors of the RE'S are rare, although lipoma has been rep0rted.4~This tumor is readily identifiable on both CT and MRI as a retropharyngeal soft tissue mass with characteristic low CT density ( - 50 to - 100 HU), bright T1 signal, and diminished signal on T2-weighted images. Malignant Tumors Malignant tumors of the RPS are much more common than benign tumors and are usually secondary to the following5:

Figure 19-22. Retropharyngeal infection. Axial contrast-enhanced CT scan through the oropharynx demonstrates enhancing, thickened retropharyngeal soft tissue consistent with cellulitis (thin white arrow) and a low attenuation collection on the right suggesting abscess formation (thick white arrow) that causes significant airway compromise. Note the abscess starting at the region of the lateral retropharyngeal lymph node (of Rouviere). Associated inflammation results in increased attenuation of the prestyloid parapharyngeal fat on the right (black arrow).

1. Direct extension of primary squamous cell carcinoma of the nasopharynx, posterior oropharyngeal wall, or hypophary~. 2. Metastatic involvement of retropharyngeal lymph nodes. a. Most commonly, from a nasopharyngeal primary squamous cell carcinoma but may also be seen with an oropharyngeal carcinoma.45Enlarged nodes may show central necrosis. b. Metastases from other areas, such as thyroid carcinoma and malignant melan0ma.4~ Involved nodes may present bright TI-weighted signals, in melanotic melanoma resulting from the paramagnetic effect and in thyroid carcinoma resulting from the high protein (thyroglobulin) content.65 In addition, the retropharyngeal lymph node chains may


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Chapter 19

be involved by non-Hodgkin's lymphoma, either as an initial site or as a part of a multiple chain involvement. Involved nodes initially appear unilateral and homogeneous, but later extranodal progression may cause the lymphomatous tissue to fill the entire RPS.6S

Lesions of the Prestyloid Parapharyngeal Space Pseudotumor Asymmetrical Pterygoid Venous Plexuses Occasionally, the pterygoid venous plexus of one side (overlying the inner surface of the lateral pterygoid muscle) is larger than that of the other side. The vascular nature of this anatomic variant can be depicted by its racemose enhancement on postcontrast CT scans and on contrastenhanced, fat-suppressed, axial TI-weighted MR images.65 Congenital Lesions Atypical (Parapharyngeal)Second Branchial Cleft Cyst The lower face and neck are formed from six pairs of branchial arches. Between them lay five endodermal pharyngeal pouches on the inner aspect and five ectodermal clefts on the outer aspect.'O- l6 The second pharyngeal pouch forms the tonsillar fossa and palatine tonsils, whereas the second branchial cleft (together with the third and fourth clefts) forms an ectoderm-lined tract, called the cervical sinus,% which is obliterated at a later stage of development. Failure of the cervical sinus to become completely obliterated results in a second branchial cleft sinus, a fistula, or, more commonly, a cyst anywhere along a line from the oropharyngeal tonsillar fossa to the supraclavicular region of the neck.@ Although the most common location for a second branchial cleft cyst is the submandibular space,36 the cyst can atypically present in the PPS, arising from the parapharyngeal portion of the embryonal tract.%

Clinical Presentation. Although congenital, these cysts most commonly present in young adults and are often precipitated by respiratory tract infection or trauma.@Small cysts are asymptomatic. Patients with a large cyst in the parapharyngeal location may present with parotid gland On examinabulge, dysphagia, or vague neck discomf~rt.'~ tion, the posterolateral oropharyngeal wall appears to be bulging intern all^.^^ Imaging Features. In its atypical (parapharyngeal) location, the cyst appears on CT and MRI as a thin, smoothwalled structure of fluid attenuation or signal intensity extending from the deep margin of the palatine tonsil into the parapharyngeal fat toward the skull ba~e.6~ Occasionally, T1 hyperintensity may result from high protein content or intracystic hemorrhage.15 When infected, the cyst wall may become thickened and irregular, and the surrounding fat planes may become o b s ~ u r e d . ~ As mentioned, the most common site of a second branchial cleft cyst is within the submandibular space, characteristically displacing the submandibular gland anteriorly, the sternocleidomastoid muscle posterolaterally, and the carotid sheath p~sterornedially.~~ At this location, it is important to consider cystic metastasis of papillary thyroid

1


65 1

carcinoma in the differential diagnosis. An enhancing soft tissue nodule in cystic metastasis may provide a clue to the diagnosis. Other cystic lesions of the submandibular space (but rarely giving the characteristic pattern of displacement of adjacent structures) include submandibular gland cysts, lymphangiomas, necrotic or cystic nerve sheath tumors, and epidermoid or dermoid cysts.% Inflammatory Conditions Parapharyngeal Space Infection Infection of the prestyloid compartment of the PPS most commonly arises from spread of peritonsillar abscesses, retrotonsillar vein thrombopheblitis, third molar extractions with violation of the pterygomandibular raphe, penetrating injury to the lateral pharyngeal wall, or extension of deep lobe parotid abscesses or as a complication of local anes' ~ Inflammathesia for tonsillectomy or dental ~ u r g e r y . 179 tion may also spread from the submandibular glands, branchial cleft, or thyroglossal duct cysts or from temporal bone infections through petrous apex air ~ e 1 l s . l ~ ~ Patterns of spread of inflammatory changes within the PPS and the adjacent spaces depend on individual differences in fascial anatomy that may arise from normal variation, previous trauma, surgery, infection, or radiation thera p ~ . The ' ~ ~virulence and antibiotic sensitivity of the invading organism, as well as the general health and immunologic status of the host, may also affect the spread of infection.132Once inside the prestyloid PPS, infection can readily extend into the parotid, masticator, submandibular, or retrostyloid compartment of the PPS.lM

Clinical Presentation. Clinical presentation of the PPS and the adjacent spaces includes the sudden onset of fever and chills. Dysfunction of cranial nerves IX through XII or the sympathetic plexus may also occur with extension into the retrostyloid compartment, and trismus may occur with masticator space involvement. Painful swelling of the gingival tissues of the maxilla and of the cheek on the involved side may also be noted.'79 On clinical examination, a medial bulge of the lateral pharyngeal wall is commonly seen.lM.179 Complications of PPS infection include erosion of the adjacent carotid artery with fatal hemorrhage or pseudoaneurysm formation as well as extension to the RPS with possible asphyxia or dysphagia from the resulting mass effect and inflammation. 179 Paranasal sinus and orbital involvement, intracranial extension, and osteomyelitis may also result.52 Imaging Features. Imaging of the PPS and the adjacent spaces may be of great assistance in detecting complications of deep neck infections and determining the optimal timing and approach for surgical drainage.164Imaging is most useful when infection is complex, widespread, or difficult to assess clinic all^.^^ On CT, cellulitis may present as a soft tissue mass with obliteration of adjacent fat planes. The mass is often ill defined, enhancing, and extending along fascial planes (Fig. 19-23) and into subcutaneous tissues.52. Involved muscles may enhance and appear enlarged, and overlying subcutaneous tissues often demon-

652


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into the PPS through the stylomandibular However, salivary gland tumors can also arise primarily within the prestyloid compartment from congenital rests of salivary gland t i s s ~ e .162 ~.

Clinical Presentation. The patient typically presents with a painless mass, since benign salivary gland tumors seldom result in other symptoms.68

Figure 19-23. Prestyloid compartment parapharyngeal space infection from spread of tonsillitis. Axial contrast-enhanced CT scan at the level of the oropharynx demonstrates enlargement of the right faucial tonsil with obliteration of the prestyloid parapharyngeal fat on the right. One small area of decreased attenuation is noted within the inflammatory process, which may represent a small abscess cavity (black arrow). Fat planes surrounding the contents of the retrostyloid compartment of the parapharyngeal space remain intact (white arrow).

strate linear or mottled increased attenuation beneath thickened skin.179 Abscesses of the deep neck spaces, reported to represent up to 9% of masses within the PPS, often appear as unilocated or multiloculated cystic lesions with air or fluid attenuation centers. They may have somewhat irregular, enhancing walls or surrounding tissue edema and may conform to the surrounding fascia1 boundaries.'03. 164. 179 Occasionally, pus formation is incomplete or may be delayed by antibiotic therapy, and an area of low attenuation on CT,suggesting an abscess cavity, may not yield pus on aspiration or expl~ration."~ Although axial and coronal CT may determine the extent of disease and presence of complications, MRI often provides superior localization because of its multiplanar capabilities and better soft tissue contrast resolution. Inflammatory exudate is of low to intermediate signal intensity on T1-weighted images and is often isointense with adjacent muscle.179Both cellulitis and abscess cavities exhibit increased signal intensity on T2-weighted images. Gadolinium contrast agents may help to differentiate abscess from cellulitis by demonstrating an enhancing abscess wall. Neither MRI nor CT findings can typically differentiate a bacterial from a granulomatous origin of inflamrnati~n.'~~

Benign Tumors Most prestyloid PPS tumors are benign. Of these, the majority are of salivary gland origin, with pleomorphic adenoma representing the most common hi~tology.~ Benign Mixed Salivary Gland Tumor (Pleomorphic Adenoma) Salivary gland tumors in the prestyloid PPS commonly arise from the deep lobe of the parotid gland and extend

Imaging Features. The CT appearance of a benign salivary gland tumor is usually that of an ovoid soft tissue mass. When small, the tumor is typically homogeneous; when larger, it may show variable areas of low attenuation that represent sites of cystic degeneration or seromucinous collections. Focal areas of high attenuation representing calcification may also be present.'62 The MR appearance of a benign salivary gland tumor is that of a well-defined mass with low to intermediate signal intensity on TI-weighted and intermediate-weighted (long TR, short TE) images and intermediate increased signal on T2-weighted images (Fig. 19-24). Smaller lesions are typically homogeneous in appearance, whereas lesions greater than 2.5 cm in diameter are often heterogeneous on all pulse sequences and may have internal foci of low signal or signal void, corresponding to areas of calcification or fibrosis (see Fig. 19-24).162Areas of high signal intensity on TI-weighted and intermediate-weighted MR images may also occur in larger tumors and correspond to areas of local hem~rrhage.'~~ With the prevalence of such findings, mass heterogeneity is not a useful predictor of a benign versus a malignant neoplasm.162The best predictors of a benign pleomorphic adenoma are the presence of dystrophic calcifications, best detected with CT,or a well-defined, highly lobulated tumor contour, best seen with MRI.162 The site of origin of prestyloid compartment salivary neoplasms is of importance in the surgical management of these patients, because a lesion arising within the deep lobe of the parotid gland is usually treated with operative control of the facial nerve in order to prevent nerve damage, whereas a lesion totally confined to the prestyloid PPS without connection to the parotid gland may be treated with little concern for facial nerve injury.ls9 At some institutions, a submandibular approach without control of the facial nerve is also used for deep lobe parotid masses when the tumor does not approach the stylomandibular tunnel. For an accurate diagnosis of an extraparotid origin of a prestyloid parapharyngeal tumor, an intact fat plane between the posterolateral margin of the tumor and the deep portion of the parotid gland must be clearly demonstrated. Careful attention is necessary because this connection may be a very thin isthmus of tissue that is best detected on high-resolution, thin-section, axial TI-weighted MR images. When lesions are greater than 4 cm in diameter, the intervening fat plane may be obliterated by mass effect alone and distinguishing between intraparotid and extraparotid origin may be impossible (see Fig. 19-24).162In such cases, the surgical approach for a tumor of parotid origin is often used in order to minimize the risk of facial nerve damage.159.162 Parapharyngeal Lipoma Parapharyngeal lipomas are uncommon lesions that are readily identified by their characteristic low attenuation on


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Figare 19-24. Pleomorphic adenoma. A, Nonenhanced, T1-weighted axial image (TR = 500 msec, l% = 12 msec) dimbhstrates a well-defined mass of lower signal intensity than adjacent muscle, replacing the prestyloid parapharyngeal fat with minimal residual fat displaced medially (straight white arrow) and the internal carotid artery displaced posteriorly (straight black arrow). No intact fat plane can be demonstrated between the lesion and the deep lobe of the parotid gland (open arrow). B, Intermediate-weighted (TR = 2500 msec, TE = 30 msec) coronal image demonstrates the mass as relatively homogeneous, of increased signal intensity relative to adjacent muscles and lymphoid tissue, and well defined. The oropharyngeal mucosa is displaced medially. The left medial pterygoid muscle is compressed and displaced superolaterally (arrows). C, Contrast-enhanced, TI-weighted (TR = 500 msec, TE = 15 msec) sagittal image demonstrates marked heterogeneity of the mass, with multiple low-signal-intensity regions that may represent areas of calcification or fibrosis. Both sagittal and coronal images are useful in revealing the craniocaudal extent of the lesion, which fills most of the prestyloid parapharyngeal space (arrows). The mass is inseparable from the deep lobe of the parotid gland and must be considered as arising from the deep lobe for surgical planning. However, the deep lobe of the parotid gland has been compressed and displaced laterally, with no visible connection to the mass at surgery. 0

i'

1. .j

canand by their Characteristic dgnal intensib, which pardlels that of fat on all MRI pulse sequences. , -

-

Malignant Tumors J -11 Malignant tumors of the prestyloid compartment of the PPS are much less common than benign lesions. These tumors include malignancies of salivary gland origin (e.g., mucoepidermoid, adenoid cystic, and acinic cell carcinomas) along with direct invasion of malignancies of the adjacent spaces.'". 162 Differentiation from benign tumors may be difficult because approximately two thirds of salivary gland malignant tumors have smooth, well-defined However, the presence of an irregular, ill-defined margin or infiltration of surrounding tissues may be z

present, suggesting a more aggressive lesion. Unfortunately, an inflammatory reaction surrounding a benign tumor may occasionally result in a similar appearance.16'

I

Lesions Arising Outside the Pharynx and Bulging into the Pharyngeal Airway Antrochoanal Polyps An antrochoanal polyp is a benign antral polyp that expands, widens the sinus ostium, and prolapses into the nasal cavity. When the polyp is large, it fills the ipsilateral nasal fossa and extends backward through the choana into


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Figure 19-25. Basal cephalocele. Coronal nonenhanced CT scan shows a large midline, isodense nasopharyngeal soft tissue mass that is significantly compromising the airway in a child. The obvious associated midline skull base defect represents the persistent hypophyseal (craniopharyngeal) canal and suggests that the postnasal mass is actually a herniated pituitary gland. Note the consequent downward traction of the suprasellar cistern into the basal defect.

the nasopharynx. Occasionally, it becomes large enough to hang down into the oropharynx. Antrochoanal polyps represent 5% of all nasal polyps."

Clinical Presentation. The patient is typically a teenager or a young adult. A history of allergy is present in 15% to 40% of cases, with an incidence of additional nasal polyps in 8%.427I6O Imaging Features. A large antrochoanal polyp appears as a smoothly outlined mass within the nasopharyngeal airway; it is continuous into the nasal cavity and maxillary antrum on one side. The maxillary ostium is widened, yet the sinus itself is not expanded. There is no bone erosion. Absence of bone erosion is a distinguishing feature from juvenile nasopharyngeal angiofibroma. An antrochoanal polyp typically presents as a homogenous, low-mucoidattenuation (10 to 18 HU)mass on CT,but older lesions develop fibrous stroma, resulting in a higher attenuation. On MR images, these polyps display low to intermediate TI-weighted and T2-weighted signal intensity. Postcontrast studies show mucosal enhancement on the surface.42. 97. 133, 160

Sphenochoanal Polyps Sphenochoanal polyps are rare, with an etiology similar to that of antrochoanal polyps. They arise in the sphenoid sinus and extend through the sphenoid ostium and sphenoethmoidal recess into the nose, then backward through the choana into the nasopharynx. Identification of the sinus of origin (sphenoid and not maxillary) is important in order to determine the surgical approach.Is1

Persistent Hypophyseal (Craniopharyngeal) Canal Persistent hypophyseal canal is a rare congenital defect of the skull base that is worthy of mention. The canal connects the pituitary fossa to the nasopharynx, allowing the pituitary gland to herniate downward into the nasopha-

ryngeal airway and to present as a midline nasal polyp that might cause significant airway obstruction in ne0nates.7~ Because acquired polyps are almost unknown in children younger than 2 years of age, it is necessary to interpret, with a high index of suspicion, midline nasal polyps in young children, particularly when the polyp is coupled with hypertelorism. In these cases, it is always best to ascertain that the sellar floor is completely intact and that the pituitary gland is normally located within its fossa. Coronal CT or MRI is best suited for such e ~ a l u a t i o n . ~ ~ Picking up these rare cases is crucial in order to prevent inadvertent hypophysectomy and consequent panhypopituitarism. Occasionally, a persistent hypophyseal canal may be wide enough to allow a large basal cephalocele to form in the postnasal space (Fig. 19-25).74

Nasopharyngeal and Oropharyngeal Trauma The suprahyoid portions of the pharynx (i.e., nasopharynx and oropharynx) are less vulnerable to trauma than the infrahyoid pharynx (hypopharynx) or the larynx1Ig;most radiologically documented nasopharyngeal or oropharyngeal injuries are described in the literature as case reports.* The clinicopathologic outcome and the imaging findings expected after trauma to this part of the pharynx, to a large extent, are dictated by the mechanisms of trauma. By convention, these are classified into blunt (closed) and penetrating (open) types.

Blunt Trauma Blunt head and neck trauma, such as that caused by motor vehicle accidents, may result in the formation of retropharyngeal hematoma, a condition that may progress rapidly into a life-threatening airway o b s t r u c t i ~ n45. ~ ~ ~ *See references 43, 75, 104, 106, 114, 129, 135, 137, 153, 157, 169, 170, and 175.


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Once post-traumatic, prevertebral soft tissue fullness is seen on the emergency radiographs, the primary concern should be directed toward securing and maintaining the patient's followed by a CT scan to evaluate for potential cervical spine fractures. CT sections should start as high as the skull base to detect possible occipital condyle fractureslWand should cover as low as the inferior extent of the hematoma, which may reach down to the mediastinum. Retropharyngeal hematomas have also been reported following minor blunt minor hyperextension injuries,lZ9 and airbag deployment in minor motor vehicle accidents.I7O Nontraumatic causes of retropharyngeal hematoma include anticoagulant therapy and complications of aneurysms, tumors, and infe~ti0ns.I~~

Penetrating Trauma Trauma leading to pharyngeal perforation may be accidental or iatrogenic. Accidental perforations usually involve the oropharynx and may be caused by foreign bodi e ~ fish , ~bones,169 ~ gunshots,162and direct injury by intraoral sharp objects, as when, for example, a child falls with a toothbrush in the mouth.137Iatrogenic perforations more commonly involve the nasopharynx and may complicate upper gastrointestinal endoscopy,17' assisted ventilation:' neonatal pharyngeal suction catheters, and nasogastric or tracheal intubation during resuscitation of newborns. 135 Pharyngeal perforation may result in any or a combination of the following problems: 1. Surgical emphysema. Emphysema may be caused by air dissecting its way through the tom pharyngeal wall. Retropharyngeal free air is the most common sequela of perforation and is readily identified on CT. Occasionally, large amounts of interstitial air may cast multiple deep fascial spaces and may extend downward, giving rise to pneumomedia~tinum.~~~ 143. 17' 2. Retropharyngeal abscess. Abscess occurs less often and is due to the spread of organisms from the oral bacterial flora. Uncontrolled infection may spread into the deep fascial planes, resulting in fascitis or parapharyngeal abscessu9; may extend downward along the RPS to cause mediastinitis; and may even enter the danger space to reach down to the diaphragrn.ln The imaging features of retropharyngeal abscess have been described earlier. 3. Vascular injury. Internal carotid artery thrombosis and cerebral ischemia may complicate posterolateral oropharyngeal injury, particularly when a child falls with a sharp object in the mouth. Typically, the internal carotid artery is injured 1 to 3 cm above the common carotid bifurcation, where it is separated from the oropharyngeal airway only by the tonsil and the superior constrictor muscle. The patient classically presents after a lucid interval of occasionally more than 24 hours, with disturbed consciousness, hemiplegia, and possibly expressive aphasia if ischemia involves the dominant cerebral hemisphere.137

Carotid artery thrombosis has also been reported following blunt intraoral1I4and minor pharyngeal injuries.153

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655

Obstructive Sleep Apnea Syndrome Obstructive sleep apnea syndrome is an episodic upper airway obstruction during sleep, most commonly occurring at the pharyngeal level.102The condition may be considered, in part, a neuromuscular disorder. Normally, the neural output to the pharyngeal muscles decreases with the onset of sleep, thus reducing their tone. With inspiration, the negative pressure created in the upper airway has the potential to collapse the hypotonic pharyngeal wall if the pharyngeal airway is originally smaller or more compliant than normal.57

Clinkal Presentution. Obstructive sleep apnea is most common amone obese males. The incidence also increases with age, snoring, tobacco and alcohol use, and the use of sedatives as well as with genetic and familial risk factors.Im The repetitive episodes of apnea during sleep, lasting from 10 to more than 60 seconds,'02 result in arterial oxygen desaturation and recurrent awakening, leading to the syndrome, which is characterized by daytime sornnolence, morning headache, and poor c~ncentration.'~Other conditions that have been linked to the syndrome include gastroesophageal reflux, impotence, cardiac arrhythmias, hypertension, and increased risk of stroke and myocardial infar~tion.~~ . d

Role of Imaging. The diagnosis of obstructive sleep apnea is a clinical one that is supported by (1) overnight polysomnography (continuous recording of relevant physiologic changes during sleep) to determine the physiologic severity, and by (2) transnasal jiberoptic endoscopy to estimate the actual grade of airway narrowing.lo2 With the emergence of new imaging technology, dynamic imaging of the pharynx in near real-time has become a reality, permitting the noninvasive assessment of functional pharyngeal abnormalities. Many reports have described the use of ultrafat CT (electron beam CT)12.'O. 51. 57* and MR fl~oroscopy~~~ L44 I5O, l5I. 168 for the dynamic evaluation of upper airways in these patients. Ultrafast CT scanning utilizes an electron gun to produce a fast-moving electron beam that hits multiple detector rings in the gantry, permitting the simultaneous acquisition of multiple image sections. This results in a superior temporal resolution, and images can be obtained in as little as 50 to 100 msec?' Other than its use of ionizing radiation, the disadvantage of selecting ultrafast CT in evaluating patients with obstructive sleep apnea is the inability to obtain primary images in the midsagirtal plane.78 The term MR fluoroscopy has been introduced with the development of numerous rapid gradient-echo sequences capable of acquiring MR images as fast as 0.3 to 7 seconds per frame.8893Fluoroscopic MR imaging has been used for functional imaging of the upper airways utilizing GRASS (gradient-recalled acquisition in the steady state78. Is1 and FLASH (fast low-angle shot) sequence^.^^ 168 Images are obtained in the sagittal and axial planes during quiet nasal respiration, simulation of snoring, and performance of the Miiller maneuver (inspiratory effort with the mouth and nose closed).78Axial scans are obtained at the levels of the oropharynx and velopharynx (the lowest part of nasopharynx opposite the soft palate, which is one of the narrowest sites in patients experiencing obstructive sleep apnea).14


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Two fundamental imaging abnormalities are sought in evaluation of these patients5'- 78: 1. Narrowing of the luminal cross-sectional area of the pharynx, as seen on axial images. The length of narrowing is determined on sagittal images. 2. Increased compliance of pharyngeal walls. The mobility of the uvula, tangue base, and posterior pharyngeal wall is assessed on sagittal images, whereas the mobility of the lateral pharyngeal walls is assessed on axial images.

Suprahyaid Neck Biopsy and lnterventional MRI Interventional MRI is the use of MR techniques to guide radiologic interventions, including both diagnostic and minimally invasive therapeutic procedures. In areas of complex anatomy, the tissue contrast, spatial resolution, and multiplanar capabilities peculiar to MRI provide the obvious advantages for its use to guide interventional procedures. This is particularly true for sampling suprahyoid neck 92, an endeavor in which CT guidance is limited by several factors, including the following: 1. The inability to maintain a confident localization of the vascular anatomy throughout the procedure. 2. The inability to go beyond a single imaging plane (usually axial). 3. The frequent improper definition of pharyngeal submucosal lesions on CT.

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4. The beam-hardening artifacts inherent in CT at the skull base. On the contrary, the major benefits of using MRI for procedure guidance in this region (Fig. 19-26) are as followS88.92. 109: 1. The ability to continuously visualize the internal carotid, vertebral, and major branches of the external carotid arteries during the entire needle insertion procedure. The high vascular conspicuity is due to flow-related enhancement effects inherent in the gradient-echo sequences used for procedure guidance. 2. The multiplanar imaging capabilities that ensure precise needle centralization along the axial as well as the craniocaudal dimensions of the lesion. In addition, imaging in any arbitrary plane allows the needle trajectory to be tailored according to the individual case. 3. The ability to guide needle insertion with continuous, near real-time imaging so that the needle can be redirected in order to avoid critical structures in a timeefficient manner. 4. The ability to shift between TI-weighted and T2weighted contrast during the procedure to maximize lesion conspicuity. T2-weighted techniques also allow sampling of the non-necrotic regions of complex masses, thus increasing the diagnostic tissue yield. An additional use of the interventional MRI techniques that form the basis for biopsy guidance is application of these methods for the monitoring of direct intralesional drug injection, including injection for sclerotherapy of vascular malformations. The same rapid image updates used

Figure 19-26. Interventional near-real-time, MR-guided suprahyoid neck biopsy. Images from continuous series obtained at 7 seconds per image with fast imaging with steady-state precession (FISP) sequence (TR = 18 msec, TE = 7 msec, 4 signal averages, flip angle = 90 degrees) obtained during guidance of needle insertion in a 68-year-old man with a C1-2 vertebral and prevertebral mass. A previous attempt at surgical transoral biopsy had been unsuccessful. A, Image obtained early, during needle insertion, demonstrates the needle tip passing through the left parotid space. An ill-defined mass can be seen in the prevertebral space. High vascular conspicuity resulting from 2D Fourier transform technique allows ready visualization of flow-related enhancement within the internal carotid (arrowhead) and vertebral (curved arrow) arteries. The needle tip (straight arrow) can be interactively directed to avoid these major vascular structures. B, The needle is redirected more anteriorly once it is safely beyond the internal carotid artery (ICA). The location of the needle's side notch is shown as an area of thinning of the distal needle tip (between arrowheads). Histologic examination revealed chronic osteomyelitis and cellulitis, and the offending organism was successfully isolated.


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Chapter 19

1


657

Figure 19-27. Intementional MRI suite setup for radiologic intervention has an open magnet design to provide easy patient access and a video camera sensor array (curved arrow) to detect the location and orientation of a hand-held probe (black arrow). The system automatically acquires continuous MR images based on the probe position and automatically updates display of four images on shielded liquid crystal diode monitor adjacent to the scanner (arrowhead). A computer mouse on the LCD console and foot pedals (not shown) allow the scanner to be operated by the radiologist throughout the procedure.

for interactive needle placement can be used to monitor the injection of sclerosing agents for the treatment of lowflow vascular malformations?' The multiplanar images obtained with MRI allow the injection of alcohol or other sclerosing agents to be monitored during administration to ensure filling of the entire targeted portion of the malformation and to exclude extravasation or dissipation of the agent through venous The accuracy and safety of MRI-guided procedures depend on proper needle visualization. Achieving this task requires a sound understanding of a number of user-defined imaging parameters as well as needle trajectory decisions, 90.93. '09 which are beyond the scope of this Three basic components combine to form the foundation of the modem interventional MRI suite: 1. The availability of an "open" magnet imaging system to facilitate the patient access necessary for performing the procedures (Fig. 19-27). 2. The application of new, fast gradient-echo pulse sequences that allow a wide range of tissue contrast in a time frame sufficient for device tracking (between 0.3 and 7 seconds per image), even at the low field strengths of open magnets and with the suboptimal coil position sometimes required to access the puncture site.35.48. 933

98, 109

3. The ability to view images in near real-time at the scanner side through an in-room high resolution radiofrequency-shielded monitor (see Fig. 19-27).88* 93. la6 With these three components, the entire procedure can be performed with the operator sitting next to the patient and without the need to remove the operator's hand from the interventional device at any time. This manner of intervention, analogous to an angiographic or sonographically guided procedure, is well suited to the skill set developed by radiologists during more conventional types of imageguided intervention.

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15. Cerezal L, M o d e s C, Abascal F, et al: Pharyngeal branchial cyst: Magnetic resonance findings. Eur J Radiol 29:l-3, 1998.

47. Dillon WP, Mills CM, Kjos B, et al: Magnetic resonance imaging of the nasopharynx. Radiology 152:731-738, 1984.

16. Chandler JR, Mitchell B: Branchial cleft cysts, sinuses, and fistulas.

48. Duerk JL,Lewin JS, Wendt M, Petenilge C: Remember true FISP?

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25. 26. 27. 28. 29. 30. 31. 32.

33. 34. 35. 36. 37. 38. 39. 40.

41. 42. 43. 44. 45.

46.

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A high SNR, near 1-second imaging method for T2-like contrast in interventional MRI at .2 T. J Magn Reson Imaging 8:203-208, 1998. 49. Easton JM, Levine PH, Hyarns VJ: Nasopharyngeal carcinoma in the United States: A pathologic study of 177 U.S. and 30 foreign cases. Arch Otolaryngol 106:88-91, 1980. 50. Ell SR, Jolles H, Galvin JR: Cine CT demonstration of nonfixed upper airway obstruction. AJR Am J Roentgenol 146:669-677, 1986. 51. Ergun GA, Kahrilas PJ, Lin S, et al: Shape, volume, and content of the deglutitive pharyngeal chamber imaged by ultrafast computerized tomography. Gastroenterology 105:1396-1403, 1993. 52. Faerber EN, Swartz JD: Imaging of neck masses in infants and children. Crit Rev Diagn Imaging 31:283-314, 1991. 53. Finkelstein Y, Malik 2, Kopolovic J, et al: Characterization of smoking-induced nasopharyngeal lymphoid hyperplasia. Laryngoscope 107:1635-1642, 1997. 54. Fischbein NJ, AAssar OS, Caputo GR, et al: Clinical utility of positron emission tomography with L8F-fluorodeoxyglucosein detecting residuallrecurrent squamous cell carcinoma of the head and neck. AJNR Am J Neuroradiol 19:1189-1196, 1998. 54a. Fleming I, Cooper J, Henson D, et al (4s): Manual for Staging of Cancer, 5th ed. American Joint Committee on Cancer. Philadelphia, Lippincott-Raven, 1997. 55. Franco RA, Har-El G: Cancer of the head and neck. In Lucente FE, Har-EL G (eds): Essentials of Otolaryngology, 4th ed. Philadelphia, Lippincott Williams & Wilkins, 1999, pp 326-335. 56. Gale DR: CT and MRI of the oral cavity and oropharynx. In Valvassori GE, Mafee MF, Carter BL (eds): Imaging of the Head and Neck. Stuttgart, Thieme, 1995, pp 445474. 57. Galvin JR,Rooholamini SA, Stanford W: Obstructive sleep apnea: Diagnosis with ultrafast CT. Radiology 171:775-778, 1989. 58. Gates GA, Avery CA, Prihoda TJ: Effect of adenoidectomy upon children with chronic otitis media with effusion. Laryngoscope 98: 5-3, 1988. 59. Gates GA, Avery CA, Prihoda TJ, Cooper JC Jr: Effectiveness of adenoidectomy and tympanostomy tubes in the treatment of chronic otitis media with effusion. N Engl J Med 317:144&1451, 1987. 60. Govrin-Yehudain J, Moscona AR, Calderon N, Hirshowitz B: Treatment of hemangiomas by sclerosing agents: An experimental and clinical study. Ann Plast Surg 18:465469, 1987. 61. Gray H: Muscles and fasciae. In Clemente CD (ed): Gray's Anatomy, 30th American Edition. Philadelphia, Lea & Febiger, 1985, pp 429-605. 62. Gromet M, Homer MJ, Carter BL: Lymphoid hyperplasia at the base of the tongue: Specmm of a benign entity. ~ a d i o l o144: ~~ 825-828, 1982. 63. Gullane PJ, Davidson J, O'Dwyer T, Forte V: Juvenile angiofibroma: A review of the literature and a case series report. ~ G n ~ o s c o ~ e 102:92&933, 1992. 64. Hardin CW, Harnsberger HR, Osborn AG, et al: Infection and tumor of the masticator space: CT evaluation. Radiology 157:413417, 1985. 65. Hamsberger HR: Head and neck imaging. In Osborne AG, Bragg DC (4s): Handbooks in Radiology (series), 2nd ed. St. Louis, Mosby-Year Book, 1995. 66. Hamsberger HR, Mancuso AA, Muraki AS, et al: Branchial cleft anomalies and their mimics: Computed tomographic evaluation. Radiology 152:739-748, 1984. 67. Harnsberger HR, Osborn AG: Differential diagnosis of head and neck lesions based on their space of origin: Part 1. The suprahyoid part of the neck. AJR Am J Roentgenol 157:147-154, 1991. 68. Heeneman H, Maran AG: Parapharyngeal space tumours. Clin Otolaryngol 4:57-66, 1979. 69. Hillsamer PJ, Schuller DE, McGhee RB Jr, et al: Improving diagnostic accuracy of cervical metastases with computed tomography and magnetic resonance imaging. Arch Otolaryngol Head Neck Surg 116~1297-301, 1990. 70. Hollinshead WH,Rosse Cornelius. Pharynx and larynx. In Textbook of Anatomy, 4th ed. Philadelphia, JB Lippincott, 1985, pp 987-1006. 71. Huda W, Slone RM: Computers and computed tomography. In Review of radiologic physics. Philadelphia, JB Lippincott, 1995, pp 93-109.


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72. Hudgins PA, Burson JG, Gussack GS, Grist WJ: CT and MR appearance of recurrent malignant head and neck neoplasms after resection and flap reconstruction. AJNR Am J Neuroradiol 15: 1689-1694, 1994. 73. Hudgins PA, Jacobs IN, Castillo M: Pediatric airway disease. In Som PM, Curtin HD (4s): Head and Neck Imaging, 3rd ed. St. Louis, Mosby-Year Book, 1996, pp 545411. 74. Hughes ML, Carty AT, White FE: Persistent hypophyseal (craniopharyngeal) canal. Br J Radiol 72204-206, 1999. 75. Hung T, Huchzermeyer P, Hinton AE.Air rifle injury to the oropharynx: The essential role of computed tomography in deciding on surgical exploration. J Accid Emerg Med 17:147-148, 2000. 76. Hunink MG, de Slegte RG, Gemtsen GJ, Speelman H: CT and MR assessment of tumors of the nose and paranasal sinuses, the nasopharynx and the parapharyngeal space using ROC methodology. Neuroradiology 32226225, 1990. 77. Ikushima I, Korogi Y, Makita 0 , et al: MR imaging of Thornwaldt's cysts. AJR Am J Roentgenol 172:1663-1665, 1999. 78. Jager L, Gunther E, Gauger J, Reiser M: Fluoroscopic MR of the pharynx in patients with obstructive sleep apnea. AJNR Am J Neuroradiol 19:1205-1214, 1998. 79. Kao CH, ChangLai SP, Chieng PU, et al: Detection of recurrent or persistent nasopharyngeal carcinomas after radiotherapy with 18fluoro-2-deoxyglucose positron emission tomography and comparison with computed tomography. J Clin Oncol 16:3550-3555, 1998. 80. King AD, Kew J, Tong M, et al: Magnetic resonance imaging of the eustachian tube in nasopharyngeal carcinoma: Correlation of patterns of spread with middle ear effusion. Am J Otol 20:69-73, 1999. 81. King AD, Lam WW, Leung SF, et al: MRI of local disease in nasopharyngeal carcinoma: Tumour extent vs tumour stage. Br J Radiol 72:734-741, 1999. 82. Laine FJ, Braun IF, Jensen ME, et al: Perineural tumor extension through the foramen ovale: Evaluation with MR imaging. Radiology 174:65-71, 1990. 83. Lanzieri CF, Lewin JS: Ompharynx and nasopbarynx. In Stark DD, Bradley WG (4s): Magnetic Resonance Imaging, 3rd ed. St. Louis, Mosby, 1999. 84. Lawson VG, LeLiever WC, Makerewich LA, et al: Unusual parapharyngeal lesions. J Otolaryngol 8241-249, 1979. 85. Lenz M, Greess H, Baum U, et al: Ompharynx, oral cavity, floor of the mouth: CT and MRI. Eur J Radiol 33:203-215, 2000. 86. Leslie A, Fyfe E, Guest P, et ak Staging of squamous cell carcinoma of the oral cavity and oropharynx: A comparison of MRI and CT in T- and N-staging. J Comput Assist Tomogr 23:43-49, 1999. 87. Lewin JS: Imaging of the suprahyoid neck. In Valvassori GE, Mafee MF, Carter BL (eds): Imaging of the Head and Neck. Stungart, Thieme, 1995, pp 3-23. 88. Lewin JS: Interventional MR imaging: Concepts, systems, and applications in nemradiology. AJNR Am J Neuroradiol 20:735-748, 1999. 89. Lewin JS, Curtin HD, Ross JS, et al: Fast spin-echo imaging of the neck: Comparison with conventional spin-echo, utility of fat suppression, and evaluation of tissue contrast characteristics. AJNR Am J Neuroradiol 15:1351-1357, 1994. 90. Lewin JS, Duerk JL, Jain VR, et al: Needle localization in MRguided biopsy and aspiration: Effects of field strength, sequence design, and magnetic field orientation. AJR Am J Roentgenol 166: 1337-1345, 1996. 91. Lewin JS, Merkle EM. Duerk JL, Tam RW: Low-flow vascular malformations in the head and neck: Safety and feasibility of MR imaging-guided percutaneous sclerotherapy-preliminary experience with 14 procedures in three patients. Radiology 211:566-570, 1999. 92. Lewin JS, Nour SG, Duerk TL: Magnetic resonance imageguided biopsy and aspiration. Top Magn Reson Imaging 11:173-183,2000. 93. Lewin JS, Petersilge CA, Hatem SF, et al: Interactive MR imagingguided biopsy and aspiration with a modified clinical C-arm system. AJR Am J Roentgenol 170:1593-1601, 1998. 94. Loevner LA, Ott IL, Yousem DM, et ak Neoplastic fixation to the prevertebral compartment by squamous cell carcinoma of the head and neck. AJR Am J Roentgenol 170:1389-1394, 1998. 95. Lufkin RB, Wortham DG, Dietrich RB, et al: Tongue and oropharynx: Findings on MR imaging. Radiology 161:69-75, 1986. 96. Mafee MF. Nasophatym, parapharyngeal space, and skull base. In Valvassori GE, Mafee MF, Carter BL (eds): Imaging of the Head and Neck. Stuttgart, Thieme, 1995, pp 332-363.

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radiation therapy alone? AJNR Am J Neuroradiol 16: 655-662, 1995. 121. Mukheji SK, Weeks SM, Castillo M, el al: Squarnous cell carcinomas that arise in the oral cavity and tongue base: Can CT help predict perineural or vascular invasion? Radiology 198:157-162, 1996. 122. Mulliken JB, Glowacki J: Hemangiomas and vascular malformations in infants and children: A classification based on endothelial characteristics. Plast Reconstr Surg 69:412-422, 1982. 123. Muraki AS, Mancuso AA, Harnsberger HR, et al: CT of the oropharynx, tongue base, and floor of the mouth: Nonnal anatomy and range of variations, and applications in staging carcinoma. Radiology 148: 725-731, 1983. 124. Nee1 HB, Slavitt DH: Nasopharyngeal cancer. In Baily BJ (ed): Head and Neck Surgery: Otolaryngology. Philadelphia, JB Lippincott, 1993, pp 1257-1260. 125. Ng SH, Chang JT, KO SF, et al: MRI in recurrent nasopharyngeal carcinoma. Neuroradiology 41:855-862, 1999. 126. Ng SH, Chang TC, KO SF, et al: Nasopharyngeal carcinoma: MRI and CT assessment. Neworadiology 39:741-746, 1997. 127. Ng SH, Chong VF, KO SF, Mukheji SK: Magnetic resonance imaging of nasopharyngeal carcinoma. Top Magn Reson Imaging 10:290-303, 1999. 128. Norbash AM: Nasopharynx and deep facial spaces. In Eldman RR, Hesselink JR, Zlatkin MB (4s): Clinical Magnetic Resonance Imaging, 2nd ed. Philadelphia: WB Saunders, 1996, pp 1079-1109. 129. O'Donnell JJ, Birkinshaw R, Harte B: Mechanical airway obstruction secondary to retropharyngeal haematoma. Ew J Emerg Med 4: 166-168, 1997. 130. Olmi P, Fallai C, Colagrande S, Giannardi G: Staging and follow-up of nasopharyngeal carcinoma: Magnetic resonance imaging versus computerized tomography. Int J Radiat Oncol Biol Phys 32:795800, 1995. 131. Olsen KD:Tumors and surgery of the parapharyngeal space. Laryngoscope 104:1-28, 1994. 132. Paonessa DF, Goldstein JC: Anatomy and physiology of head and neck infections (with emphasis on the fascia of the face and neck). Otolaryngol Clin North Am 9:561-580, 1976. 133. Phelps PD: The pharynx and larynx: The neck. In Sutton D ( 4 ) : Textbook of Radiology and Imaging, 6th ed. New York, Churchill Livingstone, 1998, pp 1273-1295. 134. Potsic WP: Assessment and treatment of adenotonsillar hypertrophy in children. Am J Otolaryngol 13:259-264, 1992. 135. Pumberger W, Bader T, Golej J, et al: Traumatic pharyngo-oesophageal perforation in the newborn: A condition mimicking oesophageal atresia. Paediatr Anaesth 10:201-205, 2000. 136. Radkowski D, McGill T, Healy GB, et al: Angiofibroma: Changes in staging and treatment. Arch Otolaryngol Head Neck Surg 122: 122-129, 1996. 137. Rayatt SS, Magennis P, Harnlyn PJ: Carotoid artery thrombosis following a penetrating oro-pharyngeal injury of unusual aetiology. Injury 29:320-322, 1998. 138. Reede DL, Holliday RA, Som PM, Bergeron RT: Non-nodal pathologic conditions of the neck. In Som PM, Bergeron RT (eds): Head and Neck Imaging. St. Louis, Mosby-Year Book, 1991. 139. Robertson RL, Robson CD, Barnes PD, Burrows PE: Head and neck vascular anomalies of childhood. Newoimaging Clin North Am 9: 115-132, 1999. 140. Robinson JD, Crawford SC, Teresi LM, et al: Extracranial lesions of the head and neck: Preliminary experience with Gd-DTPAenhanced MR imaging. Radiology 172:165-170, 1989. 141. Rossiter JL, Hendrix RA, Tom LW, Potsic WP: Intramuscular hemangioma of the head and neck. Otolaryngol Head Neck Surg 108: 18-26, 1993. 142. Ryan SP, McNicholas MMJ (eds): Head and neck. In Anatomy for Diagnostic Imaging. London, WB Saunders Company, Ltd, 1994, PP 1-44. 143. Schoem SR, Choi SS, Zalzal GH, Grundfast KM: Management of oropharyngeal trauma in children. Arch Otolaryngol Head Neck S W 123:1267-1270, ~ 1997. 144. Schoenberg SO, Floemer F, Kroeger H, et al: Combined assessment of obstructive sleep apnea syndrome with dynamic MRI and parallel EEG registration: Initial results. Invest Radiol 35267-276, 2000. 145. Seaman WB: Pharynx: Radiology. In Margulis AR, Bwhenne HJ (eds): Alimentary Tract Radiology, 3rd ed. St Louis, CV Mosby, 1983; pp 491-518.

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146. Sham JS, Cheung YK, Choy D, et al. Nasopharyngeal carcinoma: (3evaluation of patterns of tumor spread. AJNR Am J Neuroradiol

12:265-270, 1991. 147. Sham JS, Choy D: Prognostic value of paranasopharyngeal extension of nasopharyngeal carcinoma on local control and short-term survival. Head Neck 13:29&310, 1991. 148. Sham JS, Wei WI, Kwan WH, et al: Nasopharyngeal carcinoma: Pattern of tumor regression after radiotherapy. Cancer 65:216-220, 1990. 149. Shanmugaratnam K, Sobin LH: Histologic typing of upper respiratory tract tumors. In International Histologic Classification of Tumors. No. 19. Geneva, World Health Organization, 1978. 150. Shellock FG. Schatz CJ, Julien PM, et al: Dynamic study of the upper airway with ultrafast spoiled GRASS MR imaging. J Magn Reson Imaging 2:103-107, 1992. 151. Shellock FG, Schatz CJ, Julien P, et al: Occlusion and narrowing of the pharyngeal airway in obstructive sleep apnea: Evaluation by ultrafast spoiled GRASS MR imaging. AJR Am J Roentgenol 158: 1019-1024, 1992. 152. Sheman U:Diseases of the oropharynx. In Lee KJ ( 4 ) : Textbook of Otolaryngology and Head and Neck Surgery. New York, Elsevier, 1989, pp 407414. 153. Sidhu MK, Shaw DW, Roberts TS: Carotid artery injury and delayed cerebral infarction after rmnor pharyngeal trauma. M R Am J Roentgenol 167:1056, 1996. 154. Sievers KW, Greess H, Baum U, et al: Paranasal sinuses and nasopharynx CT and MRI. Ew J Radiol 33:185-202, 2000. 155. Sigal R, Zagdanski AM, Schwaab G, et al: CT and MR imaging of squamous cell carcinoma of the tongue and floor of the mouth. Radiographics 16:787-810, 1996. 156. Silver AJ, Mawad ME, Hilal SK, et al: Computed tomography of the carotid space and related cerv~calspaces: Part I. Anatomy. Radiology 150:723-728, 1984. 157. Siou G, Yates P: Retropharyngeal abscess as a complication of oropharyngeal trauma in an 18-month-old child. J Laryngol Otol 114:227-228,2000. 158. Som PM, Biller HF, Lawson W: Tumors of the parapharyngeal space: Preoperative evaluation, diagnosis and surgical approaches. Ann Otol Rhino1 Laryngol Suppl 90:3-15, 1981. 159. Som PM, Biller HF, Lawson W, et al: Parapharyngeal space masses: An updated protocol based upon 104 cases. Radiology 1533149156, 1984. 160. Som PM, Brandwein M: Sinonasal cavities: Inflammatory diseases, tumors, fractures, and postoperative findings. In Som PM, Curtin HD (4s): Head and Neck Imaging, 3rd ed. St. Louis, Mosby-Year Book, 1996, pp 126-315. 161. Som PM, Braun IF,Shapiro MD, et al: Tumors of the parapharyngeal space and upper neck: MR imaging characteristics. Radiology 164:823-829, 1987. 162. Som PM, Sacher M, Stollman AL, et al: Common tumors of the parapharyngeal space: Refined imaging diagnosis. Radiology 169: 81-85, 1988. 163. Stein MG, Gamsu G, de Geer G, et al: Cine CT in obstructive sleep apnea. AJR Am J Roentgenol 148:1069-1074, 1987. 164. Stiernberg CM: Deep-neck space infections: Diagnosis and management. Arch Otolaryngol Head Neck Surg 1121274-1279, 1986. 165. Su CY, Hsu SP, Chee CY: Electromyographic study of tensor and levator veli palatini muscles in patients with nasopharyngeal carcinoma: Implications for eustachian tube dysfunction. Cancer 71: 1193-1200, 1993. 166. Su CY, Lui CC: Perineural invasion of the trigeminal nerve in w e n t s with nasopharyngeal carcinoma: Imaging and clinical correlations. Cancer 78:2063-2069, 1996. 167. Sugimura K, Kuroda S, Furukawa T, et al: Tongue cancer treated with irradiation: Assessment with MR imaging. Clin Radiol 46: 243-247, 1992. 168. Suto Y, Matsuo T, Kato T, et al: Evaluation of the pharyngeal airway in patients with sleep apnea: Value of ultrafast MR imaging. AJR Am J Roentgenol 160:311-314, 1993. 169. Tenofsky PL, Porter SW, Shaw JW: Fatal airway compromise due to retropharyngeal hematoma after airbag deployment. Am Surg 66: 692694, 2000. 170. Tsai YS, Lui CC: Retropharyngeal and epidural abscess from a swallowed fish bone. Am J Emerg Med 15:381-382, 1997. 171. Unger JM: The oral cavity and tongue: Magnetic resonance imaging. Radiology 155:151-153, 1985.


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172. Ungkanont K, Byers RM, Weber RS, et al: Juvenile nasopharyngeal angiofibroma: An update of therapeutic management. Head Neck 18:60-66, 1996. 173. Ungkanont K, Yellon RF,Weissman JL,et al: Head and neck space infections in infants and children. Otolaryngol Head Neck Surg 112: 375-382, 1995. 174. Union Internationale Contre le Cancer: In Sobin L, Wittekind C (eds): TNM Classification of Malignant Tumors. 5th ed. New York, Wiley-Liss, 1997. 175. Verron P, Grandpierre G, Vergeau B, et al: Nasopharyngeal perforation: An exceptional accident during digestive endoscopy. Ann Otolaryngol Chir C e ~ c o f a c115:27-28, 1998. 176. Vogl TJ, Dresel SH: New developments in magnetic resonance imaging of the nasopharynx and face. Curr Opin Radiol 3:61-66, 1991. 177. Vogl T, Dresel S, Bilaniuk LT, et al: Tumors of the nasopharynx and adjacent areas: MR imaging with Gd-DTPA. AJR Am J Roentgenol 154585-592. 1990. 178. Wakisaka M, Mori H, Fuwa N, Matsumoto A: MR analysis of nasopharyngeal carcinoma: Correlation of the pattern of tumor extent at the primary site with the distribution of metastasized cervical lymph nodes-preliminary results. Eur Radiol 10:970-977, 2000. 179. Weber AL, Baker AS, Montgomery W W Inflammatory lesions of

180. 181. 182. 183. 184. 185. 186.

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the neck, including fascial spaces: Evaluation by computed tomography and magnetic resonance imaging. Isr J Med Sci 28:241-249, 1992. Weissleder R, Rieumont MJ, Wittenberg J (4s): Head and neck imaging. In Primer of Diagnostic Imaging, 2nd ed. St. Louis, Mosby-Year Book 1997, pp 547-94. Weissman JL, Tabor EK, Curtin HD:Sphenochoanal polyps: Evaluation with CT and MR imaging. Radiology 178:145-148, 1991. Wong DS, Fuller LM, Butler JJ, Shullenberger CC: Extranodal nonHodgkin's lymphomas of the head and neck. Am J Roentgen01 Radium Ther Nucl Med 123:471-481, 1975. Yakes WF, Haas DK, Parker SH, et al: Symptomatic vascular malformations: Ethanol embolotherapy. Radiology 170: 1059-1066, 1989. Yousem DM, Chalian AA: Oral cavity and pharynx. Radiol Clin North Am 36:967-981, 1998. Yousem DM, Hatabu H, Hurst RW, et al: Carotid artery invasion by head and neck masses: Prediction with MR imaging. Radiology 195: 715-720, 1995. Yu ZH, Xu GZ, Huang YR, et al: Value of computed tomography in staging the primary lesion (T-staging) of nasopharyngeal carcinoma (NPC):An analysis of 54 patients with special reference to the parapharyngeal space. Int J Radiat Oncol Biol Phys 11:2143-2147, 1985.


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20 Thyroid and Parathyroid Glands

Theodore C. Larson 111, Michelle M. Smith, Wui K. Chong, William H. Martin

Thyroid Gland The shield-shaped thyroid gland is normally positioned anterior and lateral to the cricoid cartilage, although its position may be located more superiorly, anterior to the thyroid cartilage, or more inferiorly, anterior to the trachea. The thyroid contains two lobes, each with a superior and inferior pole; an isthmus; and, in 50% to 80% of patients, a pyramidal lobe that originates from the isthmus or the medial aspect of either lobe. The pyramidal lobe develops along the distal embryonic thyroglossal duct, which explains its location. Similarly, thyroid tissue may be ectopically located anywhere along its developmental migration track (i.e., as a lingual thyroid at the base of the tongue, within a vestigial thyroglossal duct cyst, or further caudally within the mediastinurn) (Fig. 20-1). The superficial location of a normally positioned thyroid gland makes imaging easily accomplished with ultrasonography. Using a 7.5- to 10-MHz linear-array transducer provides 2-mm spatial resolution, although penetration depth and range of view are somewhat curtailed. The normal thyroid gland is homogeneous and more echogenic than muscle but less echogenic than fat. The standard

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rn Figure 20-1. Axial TI-weighted MR postgadolinium image with fat suppression shows ovoid enhancing tissue (arrow) anterior to

the larynx. The tissue, which shows the same signal intensity and enhancement as the enlarged right thyroid lobe (t), represents pyramidal lobe tissue involved by goiter (same patient as in Figure 20-27).

examination provides transverse and longitudinal planar images with evaluation of regional cervical lymph nodes. Ultrasonography is often the first modality used to image the thyroid gland because it is convenient, inexpensive, quick, and easy to perform. Ultrasonography readily identifies and distinguishes between cystic and solid lesions without using ionizing radiation, although thyroid disorders and diseases that are purely cystic are uncommon. Ultrasonography typically detects more thyroid masses than does computed tomography (CT), magnetic resonance imaging (MRI), or scintigraphy because of its greater spatial resolution. Limitations of ultrasonography include difficulties in evaluating ectopically located thyroid tissue, predicting the functional status of thyroid nodules, and surveying the neck for metastatic lymphadenopathy. Radiopharmaceuticals used in evaluating the thyroid include technetium 99m-pertechnetate ( T c ) , iodine 123 ('=I), iodine 131 (13'1), thallium 201 (ZolTl),-Tc-sestamibi (MIBI [methyl-isobutyl-isonitrile]), fluoro-18-deoxyglucose (18FDG), gallium 67 (67Ga),indium 111 (I1'In)octreotide, and '3LI-metaiodobenzylguanidine (mIBG). '=I is the preferred agent for imaging substernal thyroid glands, and 1311is preferred for detecting metastases after thyroid ablation. CT evaluation of the thyroid is performed in the axial plane, usually after the intravenous (IV) administration of iodinated contrast material. The performance of CT and scintigraphic examinations must be coordinated because the administration of N contrast material for a CT examination interferes with thyroidal uptake of radioiodine and 99Tc for 4 to 6 weeks. An advantage of CT is that the entire neck as well as the mediastinum can be surveyed for metastatic lymphadenopathy and ectopic thyroid tissue; CT also permits the detection of any unassociated concomitant conditions (Fig. 20-2). CT is excellent at characterizing the density of a thyroid lesion, thus defining the presence of calcification, cysts, or hemorrhage. The borders of a thyroid mass are usually well delineated by CT; thus, invasion of adjacent structures such as the trachea, larynx, and vascular structures of the carotid sheath can be identified. MRI of the thyroid, like CT, can be used to evaluate the contents of the entire neck. Advantages of MRI over CT include improved soft tissue discrimination and lack of beam-hardening artifacts; however, MRI is not superior in Differthe identification of malignant 1ymphaden0pathy.l~~ entiation between hemorrhagic lesions and lesions of increased protein content such as colloid-containing masses can be difficult, both being of either bright or dark signal

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20-2. Axial postcontrast CT scan performed in a patient after thyroidectomy for papillary carcinoma. The heterogeneously enhancing mass (arrow)in the left neck lateral to the left common carotid artery (c) is consistent with a diagnosis of nodal metastasis.

intensity on TI-weighted and n-weighted images. MRI also demonstrates well the relationship of thyroid lesions to adjacent structures, which assists in determining whether local invasion is present. In most instances, fine-needle aspiration of palpable suspected thyroid masses can be accomplished freehand without imaging assistance; biopsy of small or nonpalpable lesions can be accomplished with the aid of ultrasonographic, CT, or MRI guidance.139.'51 Solid, hypoechoic thyroid nodules 8 rnm or larger are typically selected for nekdle aspiration. Smaller nodules can -be difficult to aspirate in a precise manner and are more often followed with serial ultrasonographic examinations. A 20- or 22-gauge needle is employed for sampling the solid portion of the mass, with imaging used to guide needle placement and avoid the common carotid artery and internal jugular vein (Fig. 20-3). Sensitivity and specificity for fine-needle aspirations are reported to be greater than 94%, but results are highly dependent on the expertise of the cytopathologist, and nondiagnostic material may be present in as many as 20% 28. 31. 43, 66, lS7 Fine-needle aspiration, with or of without imaging guidance, is the most cost-effective method of diagnosis of primary and recurrent thyroid malignancy.

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anaplastic carcinoma, about 5%, and the remaining malignancies together, about Imaging of thyroid neoplasms using any of a number of modalities is typically not specific for malignancy, since benign processes often simulate malignant tumors. Nodules with irregular margins or masses that invade normal local structures revealed on any imaging examination suggest a malignant process. Irregular borders are visualized in approximately 60% of thyroid malignancies, yet are also seen in approximately 45% of benign thyroid tumors.130 Multiple small, highly echogenic foci (with or without shadowing) on sonography strongly suggest the presence Coarse or of microcalcifications within malignancie~.~~ peripheral (eggshell) calcification, visualized on CT or with sonography, suggests a benign nodule (Fig. 204).lWOverall, calcification is found in 13% of thyroid masses, including l7% malignancies and 11% benign Thyroid masses with hemorrhage; cysts; diminished density, isodensity, or increased density (or signal intensity); contrast enhancement; and well-circumscribed margins examined on ultrasonography, CT, or MRI may be benign or malignant.w*159 Cystic elements are found in 38% of thyroid malignancies but also in 62% of benign thyroid entities.IM Although most thyroid carcinomas are hypoechoic at sonography, most hypoechoic nodules are benign because benign thyroid nodules are much more common than malignant thyroid nodules. S o n o g r a ~ h i c d ~75% , of thyroid

139v

Pathologic Thyroid Conditions Thyroid Malignancies Malignant thyroid neoplasms constitute the most common endocrine cancer. These include the well-differentiated papillary and follicular carcinomas as well as a mixed papillary-follicular variety. Less common but more aggressive malignancies include medullary carcinoma, anaplastic lymphoma, metastatic disease* and other rare such The most these is papillary carcinoma, which accounts for approximately 70% of all thyroid malignancie~.~~.139 Follicular carcinoma comprises about 10%; medullary carcinoma, 5%;

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Figure &3, Ultrasound-guidd, fine-needleaspiration of a thymid mass. A 22-gauge needle (curved arrow) is being inserted

into a left thyroid lobe mass (straight arrow) under real-time sonographic guidance. Cytologic examination revealed a follicular adenoma.


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Chapter 20

I

Thyroid and Parathyroid Glands

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to as great as 50% if the patient has had earlier neck irradiation.Il6 The role of imaging includes the following: 1. Evaluation of thyroid capsule transgression. 2. Detection of neoplastic infiltration into adjacent structures, including prevertebral and local musculature, the carotid sheath, and the aerodigestive tract (Fig. 20-5). 3. Identification of malignant lymphadenopathy. Enlarged lymph nodes, nodes demonstrating extracapsular spread, and clustered nodes suggest pathologic involvement but are not specific findings of malignant lymphadenopathy.I3l.'39 None of the imaging modalities can reliably predict malignant thyroid histology. Figure 2 0 4 . Axial CT scan through the lower neck shows peripheral coarse calcifications (arrowheads) in an adenoma within

an enlarged, goitrous thyroid gland. This peripheral calcification may also be thin and eggshell-like.

carcinomas are hypoechoic, 23% are isoechoic, and only 2% are hyperechoic.I3OPurely cystic or completely hyperechoic nodules are very rarely malignant. Benign nodules may coexist with malignant nodules, however. For instance, 33% of thyroidectomy specimens containing papillary carcinoma also harbor benign nodules.46 Color Doppler imaging demonstrates the vascularity of malignant and benign thyroid nodules, with malignant nodules typically showing central intranodular vascularity and benign lesions being characterized by peripheral perinodular vascularity.lx There is considerable overlap, however, and the distribution of vessels on color Doppler imaging is not a reliable means of differentiating benign from malignant nodules.lx More than 99% of "hot" thyroid masses on scintigraphy are benign, typically representing hyperplastic or adenomatous nodules.28. A "cold" nodule is associated with a 15% to 25% incidence of malignancy, which increases .i- t

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7

Papillary Carcinoma Papillary carcinoma is characterized histologically by psammoma bodies, "ground-glass" nudear material, and a ~ ~ cyst formation is fibrovascular papillary ~ t r o m a .When present, the carcinoma is termed a cystadenocarcinoma. Papillary carcinomas are often encapsulated, and they are bilateral or multifocal in 10% to 15% of cases.1s2 The incidence of malignant lymphadenopathy is approximately 50%,67 and 22% of cases of malignant lymphadenopathy arise from occult thyroid tumors.4 Malignant nodes may be cystic, necrotic, hemorrhagic, or calcified, and they may contain colloid (Fig. 20-6).'31. 132 In approximately 5% of patients, distant metastases occur to lungs, skeleton, or central nervous system.67With adequate resection, 13'1therapy, and chronic suppressive therapy with thyroxine (T,), the 20-year survival rate is reported to be 94%.78Tumors with both papillary and follicular components behave like purely papillary carcinomas. Imaging of papillary carcinoma typically demonstrates a solid, hypoechoic (77%) or isoechoic (14%) thyroid mass, often with associated microcalcifications (Fig. 20-7).I3O The lesions most commonly appear to be hypofunctioning (cold) using 99mTc-pertechnetateand radioiodine (Fig. WmT~2C-8) but may demonstrate increased uptake of 20LT1, MIBI, or 18FDG.

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Figure 20-5. A, Axial postcontrast CT shows a heterogeneously enhancing mass (arrowheadr) within the right thyroid lobe, with invasion of the cricoid ring and submucosal extension of tumor (arrow). e, esophagus. B, CT image in the same patient at a lower level shows the mass invading the trachea and esophagus (e). Papillary carcinoma was found at surgery.


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Papillary carcinoma with nodal metastases. A, Axial postcontrast CT shows a heterogeneous, multilobular mass involving the right thyroid lobe without tracheal invasion. A peripherally calcified lymph node (arrow) is seen in the right tracheoesophageal groove. B, CT in the same patient at the level of the mandible shows two enlarged, enhancing lymph nodes (arrows) within the right posterior triangle and one along the left jugular chain. Normal submandibular glands (s).

F i g . l l ~20-6. ~

Radioiodine uptake by functioning thyroid carcinomas and their metastases is usually less than 10% that of normal thyroid tissue. Therefore, distant and nodal metastases may not be visualized by radioiodine scanning prior to the ablation of any postoperative thyroid remnant.17 Optimal 13'1 uptake by neoplastic tissue is also dependent on thyroid-stimulating hormone (TSH). Adequate endogenous TSH levels of greater than 40 p,U/mL can be attained 2 weeks after thediscontinuance of exogenous liothyronine (T,) therapy or 4 to 6 weeks after the discontinuance of levothyroxine (T,) therapy.', Preliminary experience indicates that the use of recombinant human TSH as a method of stimulating radioiodine uptake in patients taking exogenous thyroid hormone (TH) replacement yields a detection rate for metastases nearly equal to that seen following thyroid hormone withdrawal.59 Thyroglobulin is an iodinated glycoprotein synthesized

by both benign and malignant thyroid tissue. Approximately 90% of patients with metastases demonstrate an elevated serum thyroglobulin Following surgery and 13'1 ablation, it should be undetectable (,Dt ,

I,..,

Bacterial thyroiditis may be spontaneous, may arise from hematologic seeding, may occur in an immune-compromised host, may result from a cervical puncture wound, may develop because of an infected third or fourth 44 or may arise branchial cleft cyst (usually left-~ided),~ from an aerodigestive tract or thyroglossal duct fistula.53It typically follows a fulminant course. MRI or CT scans of acute bacterial thyroiditis are sometimes used to evaluate airway compromise, associated lymphadenopathy, carotid sheath inflammation (including jugular vein thrombosis), and associated congenital cysts) and to idenhfy fistulous tracts and abscesses.16

De Quervain's Thyroiditis De Quervain's thyroiditis (or subacute granulomatous thyroiditis) is a subacute condition that usually presents with a diffusely tender thyroid in middle-aged women following a viral respiratory tract infection. Coxsackievirus, adenovirus, echovirus (enteric cytopathogenic human orphan virus), influenza virus, and mumps virus have been implicated as causative '49 Approximately 50% of patients present with mild, transient, destruction-induced hyperthyroidism followed by mild hypothyroidism, eventually returning to euthyroidism over a period of 6 to 9 months. lo6. I I 9 Sonographically, the thyroid gland appears hypo-

Figure 20-30. Diffusely increased radionuclide uptake m d e n larged gland is typical of Graves' disease. Background activity is €.absent and the isthmus is thickened.

.::

Uptake of radioiodine (or %Tc-pertechnetate) is heterogeneous and initially low (0% to 5%); it later becomes elevated before returning to normal. On ultrasonography, MRI, CT, or nuclear scintigraphy, the end-stage thyroid gland may be atrophic, although this is rare. More than 90% of patients with subacute thyroiditis have a normal thyroid gland with normal function and normal appearance on any imaging test at long-term follow-up.

Hashimoto's Thyroiditis Hashimoto's thvroiditis is a chronic lvm~hocvticinfiltration of the thyrbid. It is the most conknin o i the thyroiditides, it primarily occurs in women between ages 40 and 60 years, and it is the most common thyroiditis in children.'58The disease is caused by an autoimmune response to thyroglobulin, colloid, or other thyroid antigens. Other autoimmune diseases may be associated, such as adrenal insufficiency, pernicious anemia, and systemic lupus erythematosus. More than 50% of patients with Hashimoto's thyroiditis are hypothyr~id.'~~ There is also a predisposition for development of non-Hodgkin's lymphoma.I4' The radionuclide scan may be normal, may reveal a homogeneously enlarged gland, or may demonstrate diffuse heterogeneous activity; in some patients, a solitary region of photopenia may be seen. Radioiodine uptake may be normal, low, or high.25The affected gland frequently accumulates 18FDG or 67Ga.154 At ultrasonography, the thyroid gland is enlarged and diffusely hypoechoic or multinodular (Fig. 20-31).lS6 Calcification may be seen on CT or ultrasonography (Fig. 20-32). On T2-weighted MR images, Hashimoto's thyroiditis typically demonstrates increased signal intensity, sometimes with linear, low-signal-intensity strands, possibly representing fibrosis.30,'"

Figure 20-29. With technetium 99m-pertechnetate, a solitary

large focus of increased activity is identified in the left neck. The lack of contralateral thyroid activity and the virtual absence of background activity are consistent with a diagnosis of solitary toxic adenoma. The suprasternal notch is identified with a cobalt marker (arrow).

Riedel's Thyroiditis Riedel's thyroiditis, also termed stnuna thyroiditis, is a rare chronic inflammatory condition of the thyroid gland. The gland enlarges and may demonstrate regional mass effect with hoarseness and dysphagia caused by the extensive associated neck fibrosis. The condition is more com-


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Thyroid and Pmtftymid Glads

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Figme 20-31. A, Sagittal ultrasound image of the right thyroid lobe shows an enlarged lobe with homogeneous, slightly hypoechoic echotexture. No focal nodulw, cysts, or calcifications are noted in this patient with Hashimoto's thyroiditis. B, Transverse ultrasound image shows homogeneous, hypoechoic parenchyma with enlargement of the thyroid isthmus (i) as well as both lobes. The centrally located trachea (t) demonstrates artifact posterior to it generated by internal air.

mon in women. It may affect one or both thyroid lobes and typically causes hypothyroidism. At imaging, the thyroid appears enlarged and homogeneously hypoechoic on ulmonography and hypodense to isodense on CT.". Io4 Riedel's thyroiditis may mimic malignancy with local infiltration, and it often calls for surgery for definitive diagnosis and relief of compressive symptoms. Diminished signal intensity on TI-weighted and T2weighted MR images is thought to be caused by chronic fibrosis.'" Riedel's thyroiditis may be associated with other fibrotic conditions such as retroperitoneal fibrosis, mediastinal fibrosis, sclerosing cholangitis, and orbital pseudotumor? - . .:,'

Figure 20-32. Unenhanced CT scan shows a diffusely enlarged, homogeneous thyroid gland in a patient with Hashimoto's thyroiditis. No focal masses or calcifications are noted.

Miscellaneous Thyroid Conditions Other inflammatory but rare thyroid conditions include tuberculosis, sarcoidosis, fungal diseases, and opportunistic organisms, especially in patients with acquired immunodeficiency syndrome (AIDS). Amyloidosis and hemochromitosis m y replace thyroid parenchyma and may cause decl?eased signrml intensity on T2-weighted MR images.'" Radiation receivexi from external beam or radioactive iodine therapy may lead to fibrosis and atrophy of the thyroid gland.

Developmental Thyroid Anomalies Lingual Thyroid Lingual thyroid results from arrest of migration of the thyroid anlage at the foramen cecum in the base of the tongue to its normal location in the anterior neck. The condition occurs in one in 3000 patients with thyroid disease, and it is the most common form of functioning ectopic thyroid tissue (90% of case^)."^ Arrest of migration may be complete or incomplete, typically occurring in the midline of the tongue base between the circumvallate papillae and the epiglottis. Rare cases may involve the entire tongue. Thyroid tissue in its normal location in the neck is absent in ?o% to 80% of case~,3~, H 9 and most of these patients are hypothyroid. Ectopic thyroid tissue is more common in women than men (7: 1) and may present as an enlarging mass at puberty or during pregnancy secondary to hormonal changes.158 Malignancy in lingual thyroid tissue occurs in 2.8% of cases." Radionuclide 99mTc-pertechnetate,'=I, or l3]I scintigraphy demonstrates avid tracer uptake within the midline of


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iodinated wntsast material, the lingual thyroid densely and homogeneously enhances (Fig. 20-34). MJU shows lingual thyroid tissue to be isointense to normal thyroid tissue on TI-weighted images and hyperintense on T2-weighted images.38 The mass enhances strongly after administration of gadolinium-based contrast material. Additional thyroid tissue lower in the neck may 1 be identified with either CT or MRI.

Thyroglossal Duct Cyst

Figme 20-33, Lingual thyroid. Frontal projection of a tshe tium 99m-perhzhnetate thyroid scan shows prominent upfake d radiotracer in the base of the tongue ( a m h e & ) . Tracer uptake is absent where it would be expected in the thyroid tissue in the lower neck. Normal uprake is noted in the parotid (arrows)and submandibular (open arrows) glands.

the tongue base if a lingual thyroid is present pig. 20-33). If surgery is contemplated, radionuclide evaluation with '"1 or Tc-pertechnetate is recommended to detect additional functioning thyroid tissue in the neck. Unenhanced CT

&.

The thyroglossal duct cyst (TDC) is the most common congenital cystic aeck mass, accounting for 70% of nonodontogenic congenital neck abnmdities. The thyroglossal duct is the embryologic tract along which the thyroid anlage c o r n as it descends from the foramen cecum in the tongue base to its normal location in the bw anterior neck. TlXk may occur anywhere along the course of the duct but typically occur &ut the hyoid bone. The majority of cysts (65%)ate located within the thyrohyoid membrane and are infrahyoid in 10cation.~Fifteen percent of TDCs are at the level of the hyoid, and 20% are supral~yoid.~ Suprahyoid TMJs are more likely to be at the midline, imbedded between the anterior bellies of the digastric muscles. Infrahyoid lesions are paramedian and tend to be located within the strap musculature. Two percent are completely intdngual. Most TDCs present in young adulthood, with 50% occurring before age 10 years and 70% before age 30. Rarely, they may present in older adults. There is no known sex

Figure 20-34. A, Enhanced CT image at the level of the oropharynx shows a well-circumscribed, homogeneously enhancing mass (arrows) in the tongue base, consistent with a diagnosis of ectopic lingual thyroid tissue. B, CT scan in the same patient at the expected level of the thyroid gland demonstrates no paratracheal thyroid tissue (arrowheads).


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Figure 20-35. Thyroglossal duct cyst. A, Axial postcontrast CT scan at the level of the hyoid bone shows a multilobulated low-density mass traversing the hyoid bone. A component of the lesion is deep to the hyoid within the pre-epiglottic fat (arrow), and the remainder is seen anterior to the hyoid (white arrowheads). The bone defect can be seen within the central aspect of the hyoid bone (black arrowhead). Note also the submandibular glands (s). B, Axial CT scan in the same patient 5 mm caudal to A shows two low-attenuation components of the mass (asterisks) and their relationship to the hyoid bone. Submandibular glands are normal.

predilection. Coexisting carcinoma, usually of the papillary type, occurs in 1% of patients with TDC3.45. 47 Follicular carcinoma, adenocarcinoma, and squamous cell carcinoma have been reported. Ectopic thyroid tissue is present within the wall of TDC in fewer than 5% of case^.^.^^ CT demonstrates a unilocular or multilocular low-density mass, usually 2 to 4 cm in diameter, present anywhere from the tongue base to the supenor margin of the thyroid gland. When located within the hyoid bone, a defect in the bone itself may be apparent on CT (Fig. 20-35). TDC contents may be isodense to hyperdense because of increased protein content or hemorrhage. The capsule of the lesion may uncommonly enhance unless the patient has a history of trauma or current or previous infection. Prior or active superinfection is seen in approximately 60% of patients. Enhancement of the surrounding musculature and obscuration of facial planes indicate TDC superinfection and overlying cellulitis (Fig. 20-36). Nodules of enhancing tissue within the cyst raise the possibility of concurrent malignancy but may represent only ectopic thyroid tissue. MRI signal characteristics vary, depending on the protein content of the fluid within the cyst. TDCs most commonly show low to intermediate signal intensity on TI-weighted images, increased signal intensity when proteinaceous, and high signal on T2-weighted images (Fig. 20-37). With both CT and MRI, enhancing ectopic thyroid tissue may be seen along the course of the thyroglossal duct. Scintigraphy is more sensitive in the detection of these ectopic thyroid rests. Ultrasonography of a TDC displays an anechoic, cystic mass with through-transmission. Inter-

nal echoes within the cyst may be caused by increased protein content or hemorrhage. Both ultrasonographic and nuclear medicine imaging can confirm the presence of a normal thyroid gland before TDC r e s e c t i ~ n . ~ ~

Parathyroid G 1ands Typically, four parathyroid glands are present (two superiorly and two inferiorly) along the of

Figure 20-36. Infected thyroglossal duct cyst. Axial postcontrast CT scan at the level of the upper thyroid cartilage demonstrates an enhancing, slightly heterogeneous soft tissue mass (arrow) within the anterior cervical space. Stranding within the fat surrounding the lesion suggests infection.


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Figure 20-37. Thyroglossal duct cyst. A, Axial TI-weighted MR image just inferior to the hyoid bone shows a rounded, low-signalintensity mass (black arrow) in the anterior pre-epiglottic fat at the superior margin of the thyroid cartilage. The normal epiglottis (white arrow) is demonstrated. B, Axial T2-weighted image slightly inferior to A shows the lesion (arrow) extending anterior to the thyroid cartilage (arrowheads) between the strap muscles. The lesion shows increased signal intensity on the T2-weighted sequence.

both lobes of the thyroid; however, the location of the inferior parathyroid glands may vary. In approximately 20% of patients, they are located anywhere from the carotid bifurcations to the upper mediastinurn as well as within the 35* 92, Io6 Ten thyroid or behind the trachea or esophagu~.~. percent to 25% of patients have more than four parathyroid glands, with the supernumemy glands most often found in the upper mediastinurn."- 68 Parathyroid pathology may be detected by radionuclide scintigraphy, ultrasonography, CT, MRI, angiography, and venous sampling. The success of all of these techniques, except venous sampling, depends, to a varying degree, on the size of the abnormal gland. The radiopharmaceutical of choice for imaging parathyroid enlargement is Tc-MIBI, employing a double-phase protoc01.~.6z,n, 84 T c - M I B I accumulates in both parathyroid and thyroid glands but is retained longer in pathologic parathyroid tissue. Imaging 2 to 3 hours after T c - M I B I injection allows physiologic washout of thyroid radioactivity but persistent accumulation within the abnormal parathyroid tissue (Fig. 20-38).lM Increased mitochondrial content in parathyroid adenomas is believed to be responsible Because of the high for the observed MIBI concentrati~n,~~ sensitivity of MIBI scintigraphy (80% to 90%) in detecting parathyroid aden~rnas,~~. loo. '40 9A"TcPOLTIsubtraction imaging is used only rarely in current clinical practi~e.'~ Oblique planar views and single photon emission computed tomography (SPECT)have been reported to improve sensitivity and localization of abnormal parathyroid glands.86. los. Subtraction of thyroid activity with '*I may be used with MIBI and can be useful when concomitant thyroid disease is suspe~ted.~ Ultrasonographic evaluation of the parathyroid gland employs a 7- to 10-MHztransducer and adequately delineates parathyroid gland enlargement when the glands are located in characteristic parathyroid locations. Normal parathyroid glands are not detected. When parathyroid gland enlargement is not found in the region of the thyroid, the entire anterior neck from mandible to suprasternal notch

is examined sonographically, including the retrotracheal region via a lateral approach; however, ectopic parathyroid gland location in the neck may escape ultrasonographic detection. Ultrasonography cannot be used to identlEy mediastinal parathyroid adenomas. Parathyroid masses within a goitrous thyroid or surgical bed are difficult to discern. Thyroid nodules (particularly when posteriorly located) and cervical lymph nodes (especially within the tracheoesophageal groove) may mimic parathyroid pathology.60

933

Figwe 20-38. With dual-phase technetium 99m-MIBI ~maging, an immediate anterior view of the neck reveals a focus of increased activity ia the upper pole of the right thyroid lobe. On the 2-hour delayed image, the thyroid activity has washed out to a large degree; the persistent fixus of increased activity in the upper right neck (arrow) was further confirmed on a 4.5-hour delayed scan, at which point there was additional thyroid washout. At surgery, a solitary parathyroid adenoma was resected.


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Chapter 20

Lymph nodes can sometimes be distinguished from parathyroid adenomas by a hyperechoic central fatty hilum and absence of the vascularity commonly seen with color Doppler imaging within parathyroid a d e n ~ m a s Thyroid .~~ nodules appear less vascular than parathyroid adenomas and more often demonstrate calcification, cystic changes, and heterogeneous echogenicity. A hyperechoic capsule favors a parathyroid adenoma. These sonographic features are inconsistent, however, and differentiating abnormal parathyroid glands from lymphadenopathy and thyroid masses is not always possible. An advantage of CT is its ability to evaluate the entire neck and the mediastinum from the skull base to the aortic arch. Distinguishing lymphadenopathy from parathyroid adenomas with CT is problematic, as it is with ultrasonography. The use of CT requires the administration of N contrast material, but only 25% of parathyroid adenomas enhance (Fig. 20-39) CT evaluation of parathyroid adenomas may produce false-negative or false-positive results as a result of artifactual obscuration of parathyroid adenomas that may be caused by patient or respiratory motion, shoulder underpenetration or beam-hardening artifact, suboptimal technical factors, or inherently poor soft tissue differentiation. Identifying parathyroid adenomas may be especially challenging in the postoperative neck, where normal tissue planes are distorted and metallic clips generate streak artifact. MRI evaluation of the neck employs standard T I weighted, TZweighted, and postcontrast TI-weighted imaging. Normal parathyroid glands are not visualized by MRL60 Parathyroid adenomas and parathyroid hyperplasia are typically bright on T2-weighted images, show soft tissue signal intensity on TI-weighted images, and enhance with contrast material; however, approximately 40% of abnormal glands have atypical MRI signal characteristiCS.42.51. 56. W. 61.90. 102 121. 134 Pathologic parathyroid glands may contain fat, hemorrhage, sclerosis, or fibrosis, which may alter the expected MFU signal intensity.@ Contrast-enhanced TI-weighted images should be performed with fat suppression to allow the enhancing adenoma to be differentiated from dark neck


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fat.".48 MRI features are not specific for parathyroid adenomas, however, and cannot differentiate adenomas from other neck masses and lymphaden~pathy.~~. '37 High-resolution MRI scanning is currently performed with surface coils, which may have a limited region of coverage. Multiple surface coils may be necessary to evaluate the neck together with the upper mediastinum. MRI is also susceptible to artifact degradation, particularly from patient and respiratory motion, flowing blood, or cerebrospinal fluid pulsation. Several different imaging modalities may be combined to improve the sensitivity and specificity of parathyroid adenoma and hyperplastic gland identification in the virgin neck, the previously operated neck, and in ectopic locat i o n ~ . MRI ~ ' is particularly useful for identifying abnormal ectopic parathyroid glands.51. 79' 137 Fine-needle biopsy employing ultrasonographic, CT, or MRI guidance may be used to sample parathyroid gland enlargement.ll4.128. L29 Cytology, immunocytochemistry, and radioimrnunoassay for parathyroid hormone (PTH) may be conducted to evaluate the aspirated material. 79s

Pathologic Parathyroid Conditions Hyperparathyroidism Hyperparathyroidism is a common endocrinopathy manifested by hypercalcemia and elevated circulating levels of PTH, with or without associated urinary, cardiovascular, GI, skeletal, or psychiatric abnormalities." The solitary parathyroid adenoma is most often found along the inferior pole of a thyroid lobe158and is responsible for primary hyperparathyroidism in 80% of patients.% 35. IM. 145 HYperplastic parathyroid glands (lo%), multiple parathyroid adenomas (2% to 5%), and parathyroid carcinoma (1%) 145. 147 In 10% to 20% make up the remainder.34. lM. of patients, parathyroid adenomas are ectopic in locationan.35,92,1M Therapy for primary hyperparathyroidism is usually surgical resection of the abnormal gland or glands, especially in view of growing evidence of adverse cardiac and skeletal effects of chronic hyperparathyroidism.39.74* 136 The use of routine preoperative imaging for patients with uncompli"'* 146 cated primary hyperparathyroidism is controver~ial.~~. Some surgeons recommend no preoperative imaging of patients with hyperparathyroidism,reporting a 90% to 95% cure rate in previously unoperated patients.". log. The success rate of finding a hyperplastic parathyroid gland or adenoma at surgery, however, is less than 70% if the pathologic parathyroid gland is in an ectopic location?'. 35a

144, 158

Some authors have justified routine preoperative imaging with claims of improving operative success rates, decreasing the risk of recurrent laryngeal nerve and normal parathyroid gland injury, and lowering cost, operating time, and blood 10~s.~'. Is. 75, '13, 'I7 With the emergence of minimally invasive parathyroidectomy performed using local anesthesia and a hand-held gamma probe intraoperatively, preoperative radionuclide localization is becoming standard practice.% In addition, preoperative imaging can identify concomitant thyroid pathology in up to 50% of patiena.29v63, 108, 153 369

Figure 20-39. Axial postcontrast CT at the level of the clavicles shows an enhancing parathyroid adenoma (arrow)in the right tracheoesophageal groove. Goitrous enlargement of the right lobe of the thyroid can be visualized (curved arrow).


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87' 9 9 ~loo. IN 99"Tc-MIBI and lead to a false-positive Many of these false-positive results can be reduced by the use of subtraction techniques with '23L49 Patients who are not candidates for surgical resection of parathyroid adenomas may be treated with percutaneous alcohol injection using ultrasonographic, CT, or MRI guida n ~ e . This ' ~ ~ is a minimally invasive procedure with few risks if care is taken to avoid vascular structures during needle puncture. With a 22-gauge needle, 0.5 to 1 mL of 98% dehydrated alcohol is injected in multiple locations in the adenoma. Monitoring of serum calcium levels indicates success of the technique, and repeated percutaneous alcohol injections may be performed if necessary.

Parathyroid Adenomas

The identification of parathyroid adenomas has been evaluated using multiple imaging modalities with a range of specificities and sensitivities. Ultrasonographic identification of parathyroid adenomas is reported to have a sensitivity of 64% and a specificity of 94%.'69 lo8 The detection rate significantly improves when the parathyroid adenomas are large.lo8At sonography, parathyroid adenomas are typically homogeneously hypoechoic, sometimes with a hyperechoic capsule (Fig. 2WO).36s'O8, 135 Adenomas may be partially cystic or inhomogeneous with foci of hypoechogenicity or hyperechogenicity. Color Doppler imaging reveals parathyroid adenomas to be uniformly hypervascular, which may help distinguish Parathyroid Hyperplasia them from other neck ma~ses.7~ CT is reported to have a sensitivity of 70% and a Parathyroid hyperplasia may be primary, secondary, or specificity of 90% for parathyroid adenoma dete~ti0n.l~~tertiary. Secondary and tertiary hyperparathyroidism are MRI has accuracy and sensitivity rates of 74% to 92% for caused by chronic renal failure and are complicated by a identifying parathyroid adenomas (Fig. 2041).61.79. 134. 13' variable degree of associated renal osteodystrophy. *"TcwTc-MIBI imaging has a reported sensitivity rate of 82% MrSI scanning is the imaging examination of choice to to 100% and is generally considered the standard initial evaluate secondary and tertiary hyperparathyroidism, alimaging modality to identify a parathyroid adenoma.18. though only a minority of these patients require preopera77, 99, loo, It can detect not only the typical cervical tive imaging. It is also the preferred imaging study for single adenoma or rare dual adenomas but also ectopic and parathyroid hyperplasia evaluation, with a reported detecmediastinal adenomas (Fig. 2042). tion rate as high as 75% (Fig. 20-43).34936*61.f7, 92. W,loo. The fusion of metabolic sestamibi SPECT images with False-negative MIBI results therefore occur in at least 25% CT images offers optimized localization of a mediastinal of cases. Ultrasonography has been reported to have a adenoma for surgical planning and guidance, with or withsensitivity rate of 30% to 69%, CT 45% to 88%, and MRI 40% to 74%.34935. 79. lo2. lo6* 13" Some hyperplastic out the use of an intraoperative handheld gamma probe. Concomitant benign or malignant thyroid abnormalities parathyroid glands may calcify.lZ8Imaging cannot differen(e.g., thyroid adenomas) may cause increased uptake of tiate parathyroid hyperplasia from parathyroid adenomas, and no modality typically identifies all four parathyroid glands. Patients who are not surgical candidates may be treated by percutaneous alcohol ablation of hyperplastic parathyroid glands with the use of image guidance techniques similar to those used for adenoma reduction.12s.Iz9 In approximately 30% of patients, primary parathyroid hyperplasia is familial rather than sporadic, a component of MEN svndrome. MEN-1. also termed Werner's svndmme, is & autosomal dornihant disorder with high pinetrance. The locus for this genetic syndrome is on chromosome 11. In addition to primary parathyroid hyperplasia, patients with MEN-1 have pancreatic islet cell tumors such as insulinomas, gastrinomas (Zollinger-Ellison syndrome), pancreatic polypeptide-producing tumors, glucagonomas, or vasoactive intestinal peptide tumors (VIPomas), and pituitary adenomas. Thyroid disorders, including goiter, adenomas, or thyroiditis; adrenal adenomas or carcinomas; and carcinoid tumors have also been reported. Parathyroid hyperplasia is also a component of MEN-2A and, occasionally, MEN-2B (or MEN-3) syndrome (see earlier discussion of medullary thyroid carcinoma). 368

Persistent or Recurrent Hyperparathyroidism Figure 20-40. Parathyroid adenoma. Transverse sonographic image shows a hypoechoic mass (arrow) inferior to the right lobe of the thyroid (asterisk). A, right common carotid artery.

A

,

Persistent or recurrent hyperparathyroidism after attempted surgical cure presents a serious challenge. In approximately 50% of cases, reoperation reveals abnormal parathyroid glands in a perithyroidal location that were missed at the initial s ~ r g e r y .So, ~ .I1O Other parathyroid ade-


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Figure 2041. Surg y PI rathyroid adenoma. A, Axial T2-weighted MR image shov n ovoid mas! row) of increased T2-weighted signal posterior LU UCI tight lobe of the thyroid and adjacent to the esophagus ast ten^^). B, Axial TI-weighted MR image demonstrates that the mass (arrow) is isointense to thyroid parenchyma. Flow voids can be seen in the right common carotid artery (asterisk) and right internal jugular vein (open arrow). C, Axial T1-weighted MR image after gadolinium contrast administration demonstrates enhancement within the lesion (arrow). D,Axial postcontrast CT image shows a homogeneously enhancing ovoid mass (arrow) in the right tracheoesophageal groove.

Figure 20-42. A, An anterior image of the neck and thorax immediately following technetium 99m-MIBI injection demonstrates physiologic thyroid activity (curved arrow) with a single focus of increased activity in the chest to the left of midline (arrow).B, Most of the thyroid activity has faded by 2 hours on the delayed images, thus accentuating the persistent mediastinal abnormality (arrow). At surgery, a rnediastinal parathyroid adenorna was resected, resulting in postoperative eucalcemia.


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Figure 20-43. Dual-phase technetium-99m-MIBI imaging-immediate

(A) and 2-hour-delayed (B) acquisitions-of a patient with chronic renal failure. Imaging reveals four persistent foci of increased activity on the delayed images (B), consistent with parathyroid hyperplasia.

noma locations, however, include the anterior mediastinurn, deep in the tracheoesophageal groove, and deep cervical, intrathyroidal, and parathymic 10cations.~~~ 11° Imaging can assist the surgeon in preoperatively identifying a persistent or ectopic parathyroid adenoma or parathyroid hyperplasia, increasing surgical success from 60%to 79. lo6 99mTc-MIBI imaging is the mainstay for identifying the source of persistent hyperparathyroidism; it has a sensitivity of 80% to 90% (Fig. 2044).61. 73+ 150 Persistent postoperative thyroid MIBI uptake due to suspected thyroiditis may obscure residual parathyroid adenoma or hyp e r p l a ~ i a .Ultrasonography, ~~ CT, and MRI have variable sensitivities of between 25% and 90% for the detection of '9% 135 Some auresidual parathyroid tissue." 51. 82s

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thors recommend MRI as a complementary imaging modality to 99mTc-MIBIs~intigraphy.~". 98 Although the success of 18FDGPET imaging of parathyroid adenomas has been variable, carbon 11 ("C) methionine PET imaging is reported to be more successful than CT or ultrasonography in patients requiring either primary or reoperative resection."- L38 In the patient with persistent or recurrent hyperparathyroidism, most investigators recommend initial functional imaging with 99mTc-MIBI,complemented by anatomic imaging with MRI or CT,ultrasonography plays a limited role in these patienk9* 18FDG or llC-methionine PET may be attempted in patients without localization after %Tc-MIBI scintigraphy. Other approaches include parathyroid venous sampling


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yields a characteristic clear watery fluid with high PTH and low thyroglobulin content and may be curative if combined with a sclerosing agent.14

Parathyroid Carcinoma Parathyroid carcinoma is a rare cause of hyperparathyroidism, with an incidence of 1% to 2% and no sex preference.lS9 Thirty percent of patients present with metastatic lymphadenopathy; distant metastases are seen in approximately 25%.Is9Approximately 90% of parathyroid carcinomas cause hyperparathyr~idism.~'. Parathyroid carcinomas are indistinguishable from parathyroid adenomas in all imaging studies except when local invasion of neighboring structures is present.= %Tc-MIBI and I8FDG PET may be 94 used to detect local and distant metastase~.~~. 733

References

Figure M 5 . v l g l w buvuacrion angiographic image in AP projection. Left superior thyroidal artery injection shows a homogeneously enhancing mass consistent with a parathyroid adenoma (arrow) within the low left neck. (Courtesy of M. Mazer, M. D.)

and arteriography (Fig. 20-45).U) These invasive procedures have sensitivities of 50% to 80%". but may be valuable in selective cases, particularly in previously operated patients who have fibrotic scar tissue, abnormal tissue planes, postoperative inflammation, or enlarged reactive lymph nodes, which may lead to false-negative or falsepositive results with other imaging studies.

Other Parathyroid Masses Parathyroid Cysts Parathyroid cysts are rare, comprising only 0.6% of all thyroid and parathyroid lesions,159but they may be large at presentation. Most present in middle-aged women.68Parathyroid cysts may develop from pharyngeal pouch remnants or may represent degenerated parathyroid adenomas.15sAlmost all are found caudal to the inferior margin of the thyroid, and most are associated with the inferior parathyroid glands.'59 Mimics include thyroid or thymic cysts and necrotic lymph nodes.71 Symptoms may be secondary to tracheal, esophageal, or laryngeal nerve compression or from cyst hemorrhage and subsequent pain.ls9 Ultrasonography demonstrates an anechoic mass in a typical parathyroid gland location. CT demonstrates a well-circumscribed, low-density parathyroidal mass. MRI may demonstrate bright signal intensity on T1-weighted images if the contents of the cyst have an increased protein content or hemorrhage. 99mTc-MIBImay demonstrate a photopenic focus. Fine-needle aspiration

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47. Hays LL, Marlow SF Jr: Papillary carcinoma arising in a thyroglossal duct cyst. Laryngoscope 78:2189-2193, 1968.

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Chapter 20

1


689

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Pediatric Head and Neck Imaging John C. Egelhoff

Head and neck pathology in children encompasses diseases that are both unique to the pediatric age group as well as processes that occur in adults. The diseases that cross age barriers may have a different biologic behavior pattern or clinical presentation when they occur in children. Fortunately, most pediatric head and neck pathology is composed of benign tumors, congenital masses, and inflammatory lesions. In contrast to the situation with adults, primary malignancies are a less frequent occurrence in children. To approach the imaging algorithms and differential diagnoses in a logical method, imaging specialists should have a basic knowledge and understanding of the pathology that occurs in the head and neck in children. The topic of the head and neck pathology in children represents a vast spectrum of diseases. This chapter focuses on extracranial disease processes of the head and neck, specifically the most common congenital masses, benign and malignant tumors, neurogenic masses, vasoformative lesions, and masslike conditions, including inflammatory processes related to adenitis. Additional topics in head and neck pathology are presented in other chapters.

Imaging The imaging modality of choice in children with head and neck pathology depends on the clinical findings, the patient's age, and the location of the mass. Generally, the initial imaging study in the young child is sonography. The ability to perform this examination without giving sedation and the lack of ionizing radiation are primary advantages. Sonography is excellent in differentiating solid from cystic masses and is useful in defining the location and extent of these masses. Ultrasound may be helpful in the differentiation of phlegmon from abscess in cases of suppurative adenitis. Color-flow Doppler imaging can be used to assess vascular patency when masses involve the vascular bundle and to demonstrate the appearance of intralesional and perilesional vascularity. Computed tomography (CT) enables an accurate diagnosis in most cases of extracranial head and neck pathology in children. In addition to the obvious advantage of evaluating bony involvement, CT can assess the location and extent of masses, the internal attenuation values and enhancement characteristics, and the relationship of masses to critical adjacent structures. The full extent of masses and inflammatory processes is better delineated by CT compared with sonography. With newer scanners, multiplanar reconstruction (MPR) is helpful in further defining

pathology. The speed of the new multidetector scanners should significantly decrease the need for sedation in the pediatric patient. In our experience, CT is the mainstay of imaging of pediatric head and neck pathology because of the speed and ease of the study as well as the useful diagnostic information obtained for the clinician. Magnetic resonance imaging (MRI), with its multiplanar capabilities, is very helpful in the evaluation of skull base masses for the detection of intracranial extension. Flowsensitive techniques and magnetic resonance angiography (MRA) are useful in assessing involvement of the vascular bundle by tumor, vascular patency, and, in rare cases, intralesional vascularity. In some cases, soft tissue signal characteristics of tumors on MRI give a more definitive diagnosis. In our experience, MRI is usually reserved as a secondary study because of the longer imaging time, necessitating the need for additional sedation; this liability also dictates the need for dedicated nursing support and monitoring equipment, which may not be available at all facilities. Conventional angiography is used primarily in the evaluation of vascular masses that are potentially amenable to embolization. Embolization can be used as a primary means of therapy in lesions such as vasoformative masses or as an adjunctive treatment before surgery in lesions such as juvenile nasopharyngeal angiofibroma.

Congenital Masses of the Neck The most common benign congenital masses of the neck in children include thyroglossal duct cysts (72%) and anomalies of the branchial apparatus (24%). Thymic cysts, dermoid and epidermoid cysts, and teratomas are less common congenital masses of the head and neck in the pediatric age group.lgl

Thyroglossal Duct Cyst Thyroglossal duct cysts (TDCs) are the second most common benign cervical mass in children after reactive lymphaden~pathy,~ comprising ~ ~ . ~ ~ ~ approximately 70% of congenital neck masses in children.244At approximately 3 weeks of gestation, the thyroid gland begins to develop as a midline endodermal diverticulum from the floor of the pharynx, between the tuberculum impar and copula. Over the following 4 weeks of embryonic development, the primitive thyroid gland enlarges to form a bilobed divertic-


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ulum that will descend caudally along the epithelial-lined thyroglossal duct. This duct extends from the foramen cecum at the tongue base (at the junction of the anterior two thirds and posterior one third of the tongue) to the lower neck (at the future location of the pyramidal lobe of the thyroid gland). As the diverticulum descends, it remains ventral to all arch derivatives caudal to the first arch. Thus, the path of the primitive thyroid gland courses over the anterior and inferior aspects of the hyoid bone (with a small posterior loop behind the hyoid), thyroid cartilage, and cricoid cartilage. Caudal migration leaves a connecting tract (thyroglossal duct) between the foramen cecum and pyramidal lobe of the thyroid gland. In the usual course of events, the duct involutes between 8 and 10 weeks of gestation. Thyroglossal duct cysts or fistula form when any part of the duct fails to involute, thus leaving functioning secretory epithelium behind.97. 191.2.44 Thyroglossal duct cysts usually present in the first 5 years of life, with approximately 66% noted before age 7 years. Males and females are equally affected. The cysts Unless infection are more commonly found in Cau~asians.~ is a complicating factor, patients with thyroglossal duct cysts typically present with a nontender, mobile, 2- to 4cm, subcutaneous midline neck mass of variable firmness. Occasionally, there is a history of fluctuating size; more commonly, however, the cyst demonstrates an abrupt or gradual increase in size with time. Complications of infection, fistula formation, or rupture of the mass can also lead 229 Fistulous openings are almost to clinical pre~entation.~~ always secondary to infection associated with spontaneous or surgical drainage.5 Coexisting carcinoma in the wall of the cyst is reported in fewer than 1% of patients with TDC. This typically occurs in adults and is thyroid in origin.5.193 34.45

Microscopically, TDC is lined by simple columnar or squarnous epithelium. Infrequently, inflammatory changes can distort the usual mucosal findings with variable amounts of fibrous tissue in the cyst wall. This usually

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forces the pathologist to make a presumptive diagnosis based on clinical and surgical evidence. Thyroid tissue is uncommonly found in thi wall of the cyst, gccounting for 177,242 the rare occurrence of thyroid Thyroglossal duct cysts are classified by location as follows: infrahyoid (65%), suprahyoid (20%), and at the level of the hyoid (15%).201164, 193, 244 Initial imaging evaluation is often performed with ultrasound, which demonstrates a well-defined, thin-walled, midline, or paramedian mass with increased through transmission and variable internal echogenicity. Infected cysts typically have a thicker wall with variable increased internal echogenicity. Thus, the pattern of internal echogenicity in these cysts may not be helpful in distinguishing infected from noninfected 1esi0ns.I~~~ 253 TJIC appears as a mass of relatively decreased attenutation to muscle with variable rim enhancement on CT (Fig. 21-1). Cysts below the level of the hyoid are almost always embedded in the strap muscle.193 Infection or hemorrhage alters these imaging characterist i c ~ (Fig. ' ~ ~ 21-1). The primary differential considerations by imaging include: dermoid and epidermoid cysts, branchial cleft cysts (if TDC is paramedian in location), or rarely, sebaceous cysts.I7' Historically, preoperative nuclear medicine imaging of the thyroid was performed to document normal functioning thyroid tissue, because the only functioning tissue was occasionally located within the thyroglossal duct cyst.lp6 More recently, reports indicate that preoperative identification of a normal thyroid gland by ultrasound confirms the presence of a source of thyroid hormone separate from the thyroglossal duct cyst, precluding additional imaging studies.I4' The treatment (the Sistrunk procedure) is surgical, with removal of all tissue along the course of the duct as far as the foramen cecum. Removal of the central portion of the hyoid bone as well as the tract coursing behind the hyoid has led to a decreased rate of recurrence (-3% to 50/0).177,229

Figure 21-1. Thyroglossal duct cyst. A, Axial postcontrast CT scan demonstrates a midline mass of decreased attenuation (arrows) at the level of the thyroid gland. Minimal rim enhancement is present. B, Coronal fast spin-echo (FSE) MRI scan shows an oval-shaped mass of slightly hyperintense signal at the base of the tongue, in the area of the foramen cecum (arrowhead) in this infected cyst.


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Chapter 21

Anomalies of the Branchial Apparatus A basic knowledge of the normal embryogenesis of the branchial apparatus and the derivatives is helpful in the understanding the imaging appearance of these anomalies.IQ. 1 4 ~ . 19'.223 The branchial apparatus is a complex structure derived from neural crest cells. It develops between the 2nd and 7th weeks of gestation. This embryonic structure can be subdivided into five pairs of mesodermal arches that lie between five paired ectodermal branchial clefts (grooves) externally andfour endodermal pharyngeal pouches internally.'48 The fifth arch lies buried near the site of the laryngotracheal outgrowth and by convention is called the sixth arch. These &e the primitive structures that give rise to the muscles, bones, and ligaments of the face and neck as well as their nerve and blood supply.19' After 4 weeks of gestation, at which time-the branchial arches are well defined, the first and second arches begin to thicken and enlarge. This thickening and enlargement of the first and second arches joins with the third and fourth arches and their intervening closing membranes to form a shallow ectodermal pit called the cervical sinus of His. The second and fifth clefts then merge with each other, obliterating the cervical sinus. The first and second pouches merge to form the tubotympanic recess that further develops into the middle ear and eustachian tube. The ventral portion of the second branchial pouch gives rise to the tonsillar fossa. The inferior parathyroid, thymus, and piriform sinus are formed by the third pouch and the superior parathyroid gland and apex of the piriform sinus by the fourth pouch. The first branchial cleft is the only cleft to give rise to an adult structure, the epithelium of the external auditory ~ a n a 1 . l ~ ~ Although the cause of branchial anomalies is controversial, current theories include (1) an origin as vestigial remnants secondary to incomplete obliteration of the branchial apparatus and (2) structures that arise from "buried" epithelial cell rests. In the vestigial remnant theory, incomplete obliteration of any portion-of a branchial cleft, pouch, or the cervical sinus of His can lead to formation of a sinus, fistula, or cyst. In the cell rest theory, trapped cells located anywhere in the branchial apparatus a r e thought to be capable of forming branchial cysts later in life.". 148 Anomalies of the branchial apparatus are classified as fistula, sinus, or cyst. If there is persistence of both a branchial cleft and a corresponding pharyngeal pouch, a communication in the form of a fistula can develop. In this case, an epithelium-lined tract connects the skin to the lumen of the foregut (pharyngeal mucosa). A branchial sinus is an incomplete tract that usually opens externally to the lateral skin surface of the neck. Communication with an associated cyst is variable. Both fistulas and sinuses can be lined by squamous, ciliated, or columnar epithelium. Congenital cysts of branchial origin have no internal or external communication with the skin or pharynx. The cysts are thin-walled and lined with squarnous or columnar epitheli~rn.'~ 148

First Branchial Anomalies First branchial apparatus anomalies account for 5% to 8% of all branchial anomalies, and are usually in the form

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of a cyst or sinus?5 Although both Arnotga and Workm attempted to classify first branchial anomalies into two distinct subtypes, Olsen found this scheme difficult in the lSO An uncategorization of all first branchial an~malies.~'. derstanding of these anomalies is not intuitive; thus, a grasp of the regional embryology appears to be more helpful rather than an attempt to subclassify them. The first branchial apparatus gives rise to portions of the middle ear, external auditory canal, eustachian tube, mandible, and maxilla. The formation of these structures is completed by 6 and 7 weeks of gestation. The parotid gland and facial nerve form and migrate between 6 and 8 weeks of gestation. First branchial apparatus anomalies present in a variable relationship to the parotid gland and facial nerve. They can arise anywhere along the nasopharynx, middle ear cavity, external auditory canal, superficial or deep lobes of the parotid gland, superficial to the parotid gland, angle of the mandible, or anterior or posterior to the pinna." Although this anomaly occurs in childhood, it is more commonly encountered in middle-aged women who present with recurrent abscesses or inflammatory processes at the angle of the mandible or ear. If the anomaly is related to the parotid gland, the patient often presents with recurrent parotid abscesses, which are unresponsive to therapy. Refractory cases, associated with facial nerve palsy, can mimic a parotid neoplasm clinically.242If the cyst drains into the external auditory canal, the initial presentation may be otorrhea. On ultrasound, CT, and MRI, a first branchial cyst appears as a typical cystic mass that may be located within, superficial, or deep to the parotid gland and near the external canal of the ear or angle of the mandible (Fig. 21-2). Infected cysts have variable wall thickness and enhancement characteristics. When the anomaly is located in the parotid gland, imaging findings are nonspecific and do not allow this mass to be differentiated from other cystic masses of the parotid gland.I2'

Second Branchial Anomalies Approximately 95% of all branchial anomalies are related to the second branchial apparatus. The most common

Figure 21-2. First branchial apparatus cyst. Axial postcontrast CT scan. A nonenhancing, kidney-shaped mass is seen superficial to, but contiguous with, the parotid gland (curved arrow).

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location of this anomaly is the submandibular space; however, occurrence may be anywhere from the oropharyngeal fossa to the supraclavicular region of the neck.'" Three fourths of these anomalies are cysts.'27Fistulas or sinuses usually present before age 10 years, whereas cysts are more common between ages 10 and 40 years.ls8,231 There is no gender predile~tion.~~ Bailey classified second branchial cysts into four subtypes based on location12-162-175. 215: Type I cysts lie deep to the platysma muscle and the overlying cervical fascia, and anterior to the sternocleidomastoid muscle. These cysts are thought to represent a remnant of the tract between the sinus of His and skin. Type II cysts, thought to be the result of persistence of the sinus of His, are the most common. They are located posterior to the submandibular gland, anterior and medial to the sternocleidomastoid muscle and anterior and lateral to the carotid space. Type III cysts course medially, between the internal and carotid arteries? and may extend the lateral Figure 21-3. Second branchial apparatus cyst. Axial postcontrast wall of the pharynx or skull base. These cysts are CT scan. A rounded, nonenhancing mass is present in the typical to arise from a dilated pharyngeal pouch. position of a Bailey type TI cyst. The cyst lies posterior and Type N cysts arise from a remnant of the pharyngeal pouch lateral to the submandibular gland, anterior and medial to the sternocleidomastoid muscle, and lateral to the carotid space. and lie in the mucosal space of the pharynx, adjacent to the pharyngeal wall. Second branchial cleft cysts most commonly present as second most common congenital lesion of the posterior a fluctuant, nontender mass at the lateral aspect of the cervical space after lymphatic malformation.183Anomalies mandibular 231 If the cyst becomes infected, of the fourth branchial apparatus usually appear as a sinus patients seek medical attention with a clinical history of a rather than a cyst or fistula. The majority of third and slowly enlarging, painful mass.231If a fistula is present, an fourth anomalies are found on the left.49 ostium is usually noted at birth at the anterior border Because the dorsal aorta between the third and fourth of the junction of the middle and inferior third of the arches involutes, a third branchial apparatus anomaly origisternocleidomastoid muscle. The associated tract courses nates in the posterior cervical space.24Third branchial cleft deep to the platysma muscle, ascends laterally along the cysts must be located posterior to the common or internal carotid sheath, and continues above and lateral to the hypocarotid artery, and between the hypoglossal nerve (below) glossal and glossopharyngeal nerves. It then passes beand glossopharyngeal nerve (above). If the anomaly is in tween the internal and external carotid arteries before terthe form of a fistula, it will have a cutaneous opening minating in the region of the palatine tonsillar fossa.12." similar to a second branchlal fistula (i.e., anterior to the Because these cysts usually present as a neck mass in lower sternocleidomastoid muscle). It then courses postethe young child, sonography is often the initial imaging rior to the common or internal carotid artery, anterior to study. The cysts range in size from 1 to 10 cm.s8.243 If the the vagus nerve, and between the hypoglossal and glossoanomaly is uncomplicated, the sonographic appearance is pharyngeal nerves. The fistula pierces the thyrohyoid memtypical for a cyst (i.e., a sharply marginated, anechoic, brane and enters the piriform sinus anterior to the internal compressable mass with increased through transmissi~n).~~~ pharyngeal nerve. A well-circumscribed, thin-walled mass of decreased attenA third branchial cleft cyst often presents as a painless, uation is present on CTuO(Fig. 21-3). On MRI, the fluid fluctuant mass in the posterior triangle of the neck after a within the cyst varies from hypointense to slightly hyperinviral upper respiratory infection. On imaging, the cyst most tense to muscle on T1-weighted images and is usually commonly appears as a unilocular mass with variable wall hyperintense to muscle on T2-weighted i1nages.9~When thickness and enhancement characteristic^.^^^ the cyst is infected, it can demonstrate increased echogeniFistulas of the fourth branchial apparatus have not been city on a sonogram, relatively increased attenuation on a reported.49Anomalies related to the fourth branchial cleft CT scan, and relatively hyperintense MRI signal, with are in the form of a sinus tract. The tract arises from the variable contrast enhancement and edema of surrounding piriform sinus and pierces the thyrohyoid membrane. It t i s s ~ e95.. ~162, 242 Occasionally, the "beak sign," pathogthen descends along the tracheoesophageal groove and connomonic of a Bailey type I11 second branchial cyst, is tinues into the mediastinurn, following a course under the present. In this case, the medial aspect of the cyst is aortic arch on the left and ascending into the neck, anterior compressed and forms a beak as it extends between the to the common or internal carotid artery. This is in contrast internal and external carotid arteries on axial CT or MRI?3 to third branchial remnants, which course posterior to the Third and Fourth Branchial Anomalies carotid artery (Fig. 21-4). Rarely, the tract may descend Both third and fourth branchial anomalies are rare.49In on the right coursing under the subclavian artery.24 spite of the rarity of third branchial cysts, they are the Differentiating third from fourth branchial anomalies on


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and anywhere from the level of the hyoid to the superior mediastinum.17 Because the thymus reaches its greatest relative size at 2 to 4 years of age and its greatest absolute size at puberty, most thymic cysts are detected in childhood.82l k o thirds of thymic cysts are detected in the first decade of life (most commonly, at 3-8 years of age), with the remaining one third detected in the second and third decades.33.93Seventy-three percent of thymic cysts are found in 23J9256

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Figure 21-4. Fourth branchial apparatus sinus. Axial noncontrast CT after the patient had ingested oral contrast medium. Barium is present in a sinus tract (arrow)that lies anterior to the thyroid

gland on the left. The tract arose from the piriform sinus and continued into the mediastinum.

imaging is problematic. Key relationships include the carotid artery and the superior laryngeal nerve. Third branchial anomalies lie posterior to the carotid artery, whereas fourth branchial anomalies are anterior to it. Those anomalies above the superior laryngeal nerve are third branchial origin, whereas those below the nerve are related to the fourth branchial apparatus.49On imaging, both third and fourth branchial anomalies related to the piriform sinus may appear similar to external laryngoceles."

Cervical Thymic Remnants Cervical thymic remnants are rare lesions derived from the third and fourth pharyngeal pouches. During the 6th week of gestation, thymic primordia (endoderm) develops from lateral and ventral diverticula of the third pharyngeal pouch, with a small contribution from the fourth pharyngeal pouch. These hollow outgrowths, which are connected to the pharynx by the thymopharyngeal ducts, begin to elongate in a caudal plane. At the end of the 6th week, the diverticula are obliterated secondary to epithelial proliferation. These two solid masses join in the midline before their final descent into the anterior mediastinum at the 9th week of gestation. In the 10th week of gestation, lymphocytes invade the endodermal structure to form lymphoid tissue in the thymus. The superior thymic primordia usually regresses.l 7 256 Currently, two main theories have been reported to explain the etiology of thymic remnants. The congenital theory, favored by the most authorities, states that these cysts arise secondary to persistence of thymopharyngeal duct remnants. Progressive, cystic degeneration of thymic (Hassall's) corpuscles, primitive endodermal cells, lymphocytes, and the epithelial reticulum of the thymus have been proposed as the origin in the acquired theory.15- 266 AS related to the embryologic development, these cysts may be located beneath or medial to the sternocleidomastoid 659

Most patients are asymptomatic, with 80% to 90% presenting with a slowly enlarging, painless neck mass near the thoracic inlet, anterior or deep to the sternocleidomas254 Hoarseness, dysphasia, toid m u s ~ l e . ~67.~ ~ stridor, and dyspnea in the newborn may occasionally be seen as the initial complaint secondary to the mass effect. Infection, hemorrhage, or Valsalva maneuvers can cause rapid enlargement of the cyst.l5% Seventy percent of thymic cysts are left-sided, 23% are right-sided, and the remaining 7% are midline or pharyngeal in l ~ c a t i o n . ~ ~ . ~ ~ Cervical thymic remnants may be found anywhere along the path of the thymopharyngeal duct, which courses along the carotid sheath, from the level of the angle of the mandible to the superior mediastinum. The lesions vary in size (1 to 17 cm) and shape (round to e l ~ n g a t e d ) . ~ ~ ~ ~ ~ ~ Most cysts are unilocular and have a smooth li11ing.3~.65' lm, lgl A connection between the cervical thymic anomaly and the mediastinal thymic gland may persist in the form of direct extension or a remnant of the thymopharyngeal duct in 50% of cases.38.52' 247 A fibrous strand may also remain between the cervical thymic cyst and the thyroid gland.65 Cervical thymic cysts are often associated with thyroid and parathyroid inclusion cysts.15 Grossly, thymic cysts are well defined, thin-walled, uniloculated, or multiloculated masses. They are lined by stratified or pseudostratified, cuboidal, or columnar epithelium with pathognomonic Hassall's corpuscles within the wall.15,I6O The wall may also contain lymphoid tissue or giant cells with cholesterol clefts and granuloma^.^^^^^^^^ 160 Thymic tissue must be present within the lesion for the pathologic diagnosis. Occasionally, thyroid or parathyroid tissue is also found within the cyst or cyst As derivatives of the third and fourth branchial clefts, thymic cysts can extend through the thyrohyoid membrane and into the piriform sinus.'j8 There have been no reports of malignant degeneration of thymic cysts in children or the development of myasthenia gravis or immunologic deficiencies following excision of a thymic cyst. However, malignant degeneration has been documented in ectopic solid thymic tissue.'". '74 Because most ectopically located thymic masses are primarily cystic, sonography usually shows a large, welldefined unilocular or multilocular cyst parallel to the sternocleidomastoid muscle with hypoechogenicity and increased through-transmission. A homogeneous, near-water attenuation, uniloculated or multiloculated, nonenhancing mass is seen located along the course of the carotid sheath on C P *33, ll4. 140.161 (Fig. 21-5). MRI of thymic cysts demonstrates a fluid-filled mass with signal characteristics isointense to hyperintense to water.149If hemorrhage or infection is present, imaging characteristics vary accordi n g l ~ ?231 ~. 174s

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Epidermoid cysts are rarely found in the head and neck. When they occur, they are usually present in infancy.u0 There is no gender predilection with dermoid or epidermoid cy~ts.~"~.=~ Dermoid cysts typically become clinically apparent in the second or third decades of life.104,231 They most commonly present as a soft, slowly growing, suprahyoid, midline neck mass. Size is variable, from a few millimeters to 12 cm. A rapid increase in size can be seen secondary to association with a sinus tract, pregnancy, or increasing desquamation of skin appendage p r o d u ~ t s . ' ~LRsions ~.~~ lying in the floor of the mouth, in the sublingual space, are often clinically inapparent or exhibit minimal mass effect. If located in the submandibular space, the lesion usually presents with a more obvious swelling or mass e f f e ~ t . ' ~ , ~ ~ In contrast to thyroglossal duct cysts, which move with protrusion of the tongue because of their association with the hyoid bone, dermoid cysts are nonrnobile with this maneuver.'82 On pathologic examination, dermoid cysts are welldefined, encapsulated masses lined with squamous epithelium. They may contain skin appendages in the form of sweat or sebaceous glands or hair follicles. Inclusion of Figure 21-5. Thymic cyst. Axial postcontrast CT scan. A large, skin appendages can lead to the formation of keratin and round, nonenhancing mass is present in a position similar to a sebaceous material and, occasionally, hair.m The incidence second branchial apparatus cyst; however, the sternocleidomastoid of malignant degeneration into squamous cell carcinoma is muscle lies in a more lateral position. approximately 5%. Epidermoid cysts lack skin appendages but otherwise are similar in histologic appearance to derm~ids.~O The main differential consideration of thymic remnants Because dermoid cysts typically present in older chilis a second branchial cleft cyst. A true thymic cyst passes dren, CT is often performed as the initial imaging study. posterior to the carotid bifurcation and terminates in the Dermoid cysts appear as a thin-walled, unilocular mass piriform sinus, whereas a second branchial cleft cyst passes with homogeneously decreased attenuation, with CT meabetween the internal and external carotid arteries and ends surements in the negative numbers (0to - 18 HU)'08 (Fig. in the superior tonsillar pillar. Fifty percent of cervical 21-6). ~ccasionall~, a "sac of marbles" appearance, reprethymic cysts extend into the superior mediastinurn, whereas senting multiple, small fatty nodules within the fluid, is mediastinal extension with branchial cleft anomalies does seen within the cyst. This appearance is virtually pathognot If a mass is located in the area of the nomonic of a dermoid cyst. A more heterogeneous appearinferior pole of the thyroid gland, a thymic origin should ance can be present secondary to a difference in composibe ~0nsidered.I~~ Other differential considerations would tion of the v&ous skin appendage components. ~luid-fluid include thyroglossal duct cyst, lymphatic malformation, levels are a rare finding. After administration of contrast cystic neuroblastoma, lympadenopathy, external laryngomedium, thin, peripheral enhancement is often p r e ~ e n t . ~ cele, and vallecular ~ y s t s . ~ ~ , " ~ On MRI, signal changes are variable and dependent on the composition of the cyst. TI-weighted signal can be hyperintense secondary to lipid concentration or isointense Dermoid and Epidermoid Cysts to muscle; T2 signal is usually hyperintense to m u ~ c l e . ~ " a ~ When dermoids are located in the floor of the mouth, The terminology and classification of dermoid, epideraccurate localization by imaging is important for surgical moid, and teratoids cysts of the head and neck can lead to planning. Most commonly, dermoids in the floor of the confusion because of overlapping features. All of these mouth lie above the mylohyoid muscle, which places them cysts can be considered in the spectrum of teratomas. The in the sublingual space. These cysts are amenable to an masses share a common feature of containing tissue that is intraoral surgical approach. Cysts that lie below the myloforeign to the body part from which it originates. Dermoids hyoid muscle are localized to the submandibular space, and epidermoids are ectoderm-lined inclusion cysts, with necessitating an external, submandibular approach. Coronal dermoids containing skin appendages, and epidermoids CT or MRI is the optimal imaging plane for localization lacking these elements. Teratoid cysts may be composed of these masses into the appropriate space.230 of tissues of other organ systems.Io8 Epidermoid cysts most commonly have homogeneously Dermoid cysts of the neck commonly occur near middecreased attenuation on CT, with hypointense T1line, along lines of embryonic fu~ion."~ In the neck, the weighted and hyperintense T2-weighted signal to muscle most common location is the floor of the mouth, accounting on MRI closely following water signal. With this imaging for 11.5% of all derm~ids.~'~ Other locations in the head and neck include the anterior neck, tongue, and ~alate.'~2"~ appearance, it is difficult to distinguish epidermoid cyst


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three germ layers, with differentiation to enable recognizable organs by histologic examination. 4. Epignathi-masses containing elements of all three g e m layers, with differentiation greater than true teratoma, usually incompatible with life.

Cervical Teratoma Grossly, cervical teratomas are encapsulated, partially cystic masses with a variegated appearance on cut section. These tumors contain diverse histopathologic findings with variable degrees of maturation. Mature elements are derived from ectodenn, mesoderm, and endodem; immature tissue arises mostly from neuroectoderm. Neuroectodermal elements (both mature and immature) tend to predominate in cervical teratomas. Although cells in this tumor can be found in any stage of differentiation, the degree of histologic maturity should not be equated with malignant potentia1.9.66" Clinically, teratomas are divided into (1) those present at birth or in early childhood and (2) those presenting in the first decade of life. The clinical presentation is variable and depends on the size and location of the tumor. Congenital tumors (presenting in the first 60 days of life) tend to have a benign clinical behavior, but they exhibit a high mortality rate secondary to airway compression with pulmonary compromise. Tumors that present later are usually smaller but carry a higher incidence of malignancy.200True Figure 21-6. Derrnoid cyst. Axial postcontrast CT scan. A wellcervical teratomas are large and can lead to obstetric comdefined mass of decreased attenuation lies in the anterior neck, plications, such as difficult labor with malpresentation, slightly off midline (curved arrow). Attenuation values were 0 to premature labor, stillbirth, and acute respiratory distress.35 - 5 Hounsfield units (HU). Extensive unilateral or more diffuse cervical swelling is often present.= 228 Maternal polyhydramnios has been-reported in 18% of patients with cervical t e r a t o m a ~ . ~ ~ . ' ~ ' . ~ ~ ~ Because of the frequent use of ultrasonography in obfrom uncomplicated cystic lesions in the floor of the mouth, such as a lymphatic malformation or r a n ~ l a . ~ ~ stetrics, the diagnosis is often made antenatally. On sonograms, teratomas demonstrate heterogeneous echogenicity with multiloculated areas of cystic and solid regions, angulated cyst walls, and acoustic shadowing from calcificaTeratoma tions. The mass mav amear well defined or. less commonly, infiltrative.md~f&rbirth, the patients are usually Teratomas constitute approximately 9% of all pediatric referred for CT. head and neck neoplasms, with fewer than 5% of all Imaging characteristics directly reflect the pathologic Il5 In the teratomas occurring in the head and makeup of the tumor, often demonstrating a heterogeneous pediatric population, most teratomas are extragonadal in location, with 82% found in the sacrococcygeal area.L4.240 attenuation pattern and appearing primarily cystic, solid, or multicystic. Most cervical teratomas are large, measuring Locations in the head and neck include the neck, orbit, up to 12 cm in size, with approximately 50% containing nasal cavity, paranasal sinus, oral cavity, oropharynx, nasoc a l c i f i ~ a t i o n(Fig. ~~~ 21-7). ~ Both CT and MRI are helppharynx, temporal bone, and ear.l.60. 97. 239 Teratomas are ful in delineating the extent of the tumor and the degree of thought to arise from misplaced, pleuripotential, primordial The MRI appearance is a mass of airway cornpr~mise.'~~ germ cells. They are classified as "true neoplasms" beheterogeneous signal on all pulse sequences with the fatty cause of their biologic behavior of progressive and invasive component, hyperintense on T1-weighted sequences, and growth patterns.200 areas of calcification, hypointense or hyperintense on T1Teratomas have been subclassified by Ewing and Arnold weighted images. Attenuation values and signal characterisinto four typePa 203: tics of fat and bone, in a mass of the head and neck in a 1. Dermoids-masses of ectodermal and mesodermal eleyoung child, is nearly pathognomic of teratoma. Variable ments, composed mostly of adipose tissue with fragenhancement is present on both CT and MRI after contrast ments of muscle, cartilage, or bone. administration. Intubation is commonly required in these 2. Teratoids-masses containing elements of all three germ patients before s ~ a n n i n g . ~ layers, differing from true teratomas because of their The primary differential consideration of a cervical terapoor histologic differentiation. toma is lymphatic malformation, which more closely fol3. True teratomas-masses containing elements of all lows water signal on all pulse sequences on MRI. Other 473


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Figure 21-7. Cervical teratoma. Axial postcontrast CT scan. The majority of the anterior neck is involved with an extremely large, heterogeneous mass with mild enhancement. The vascular bundle on the right is not visualized secondary to tumor involvement. The infant required intubation because of mass effect on the airway.

differential considerations include thyroglossal duct cyst, branchial cleft cyst, goiter, hemangioma, and external laryng~cele.~~ Despite the appearance of teratomas on CT and MR, cervical teratomas do not typically infiltrate surrounding tissue; thus, complete surgical resection is usually possible.200Surgery is mandatory for congenital cervical teratomas, as the mortality rate is 80% to 100% secondary to airway complications, if the tumor is left untreated. Thus, differentiating this tumor from other congenital space-occupying masses of the neck is crucial. The incidence of true malignancy of congenital teratoma is low (roximately 50 to 100 HU, which is somewhat denser than the surrounding ligaments and much denser than epidural fat and the fluid-filled thecal sac. This makes the disk easily distinguishable from neighboring structures, particularly in the case of disk herniation. On TI-weighted MR images, the disk is a fairly homogeneous structure, isointense to muscle. On images with a long repetition time (TR), the disk becomes brighter because of its water content. On T2-weighted images, the nucleus pulposus, which is more hydrated than the annulus fibrosus, becomes even brighter than the annulus.

Pathogenesis The pathogenesis of disk degeneration is complex and not well understood. End-plate and disk degeneration is probably a normal consequence of the aging process. By age 50 years, 85% to 95% of adults show evidence of degenerative disk disease at autopsy.63 The cartilaginous end plate becomes thinner. The nucleus pulposus and, to a lesser degree, the annulus fibrosus lose up to 70% of their water content. The disk tissue also undergoes biochemical changes with respect to its collagen and proteoglycan content. The entire volume of the disk decreases with aging.', l 6 Annular fibers become stretched, leading to disk bulging (which is usually not significant unless the canal is already small). These changes occur most frequently in the parts of the lumbar spine most subjected to mechanical stresses (i.e., L4-5 and L5-Sl). Whether normal disk aging plays a predisposing role is unclear, but the sequence of events in disk herniation appears to be as follows. The annulus becomes frayed during repeated flexional and rotational forces, resulting in radial and concentrically oriented fissures in the annulus. This then predisposes the nucleus to further degeneration and subsequent herniation into and then through the annular fibers.51Although central disk herniations are by no means rare, disks tend to herniate posterolaterally because the posterior longitudinal ligament and annular fibers are thickest and strongest in the midline and thinner laterally.

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Figure 22-15. Type I end-plate changes. A, T1-weighted MR image shows hypointensity of the inferior L2 and superior L3 end plates (arrows). 3,T2-weighted MR image shows thaf the end plates have become hyperintense. This is the earliest stage of disk degeneration. The lower lumbar disks are dark on the T2-weighted scan because they have became dehydrated from degeneration. Note small SchmorI's nodes (asterisks).

64) and fast spin&,

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fast s p b e h o , n-weighted images.

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T2-weighted images, the fatty end plates thus become slightly darker.) Qpe I1 changes tend to remain stable with time. Type III changes, or the final stage if it occurs, are represented by low signal intensity on both T1-weighted and T2-weighted images (Fig. 22-17). This stage correlates with bony sclerosis seen on CT scans and plain films of severely degenerated end plates. This is the only endplate change visible on CT scans or radiographs. Whether these end-plate changes have any prognostic significance has not been established; however, they are part of the normal aging process and must not be confused with other pathologic processes, such as tumor and infection (Fig. 22-1 8).

Bulging and Herniated Disks

Figure 22-17. Type III end-plate changes. TI-weighted (A) and T2-weighted (B) MR images show hypointensity of the inferior L3 and superior LA end plates on both sequences (arrows).

Radiographic Changes The earliest radiographically visible changes of intervertebral disk degeneration are those that occur at the end plate. These are best seen on MRI. Three types of endplate changes have been Type I changes demonstrate low signal intensity on T1weighted images and high signal intensity on T2weighted images (Fig. 22-15). This stage is believed to reflect replacement of the end-plate marrow with vascular fibrous tissue in response to chronic "injury." Type II changes, the next stage, show high signal intensity on TI-weighted and on FSE T2-weighted images (Fig. 22-16). This stage represents replacement of the endplate marrow with fatty tissue. (On standard spin-echo,

Figure 22-18. TI-weighted (A) and T2-weighted (B)

MR images show end-plate changes of varying stages. The resulting marrow heterogeneity is easily confused with bone metastases.

Classification The most important step in the analysis of the degenerative lumbar spine-after the vertebrae, end plates, ligaments, and joints-is the disk itself. As mentioned, the intervertebral disk is made up of a jelly-like nucleus pulposus, surrounded by a tough, fibrous annulus fibrosus. Unfortunately, no universally accepted classification of disk herniation exists. The one presented here5' may differ from those offered by other texts and institutions.47* 49 Abnormal disks can be classified as bulging or herniated. A herniated disk can be subclassified as (1) protruded, (2) extruded, or (3) sequestered. Bulging Disk An annular bulge represents an extension of the disk margin beyond the confines of the adjacent vertebral end plate. The annular fibers are stretched but intact. The disk bulges diffusely around the posterior (and sometimes lateral) aspects of the end plate (Figs. 22-19 and 22-20). This does not usually lead to clinical symptoms unless the spinal canal is already congenitally small or narrow owing to spondylosis. Protruded Disk When some of the inner fibers ol u~t:annulus tear but the outer layers remain intact, the nucleus can focally


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PROTRUSION

Figure 22-19. Illustration of a bulging disk. The disk bulges diffusely beyond the vertebral body margin. The annular fibers are stretched but completely intact. (Modified from Modic MT: Magnetic Resonance Ima$j?g-of ,theuspine. St.- Louis, Mas!: Year Book, 1989.)

herniate through the inner tear. This is the simplest (and probably earliest) type of disk herniation and is called a disk protrusion (Fig. 22-21). Disk herniation is distinguished from annular bulge by its focality. Whereas a disk usually bulges fairly uniformly along its margins, a disk herniates through one particular spot--the annular tear. The signal intensity (on MRI) and density (on CT scans) of the protruded segment are generally, but not invariably, the same as those of the nonherniated portion. Extruded Disk

A disk extmsion occurs when the nucleus pulposus herniates through a complete tear of the annulus fibrosus and is contained only by the posterior longitudinal ligament (Fig. 22-22). The herniated segment, however, remabjs attached to the parent disk but may extend cephalad or caudad. It can be difficult to differentiate between a disk I

Figure 22-21. Illustration of disk protrusion. A portion of nl cleus pulposus herniates focally through a rent in the inner ann~ lar fibers. The outer annular fibers are intact. (Modified from Modic MT: Magnetic Resonance Imaging of the Spine. St. Louis, Mosby-Year Book, 1989.)

protrusion and extrusion when the amount of herniated disk is small. This distinction, however, is not clinically significant; it is more important to recognize that these are simply different degrees of herniation and that the significance of a herniated disk is its effect on the spinal canal and nerve roots (Figs. 22-23 and 22-24). Sequestered Disk

Finally, when an extruded nucleus breaks free of the parent disk, it is termed a sequestered disk orfree fragment (Fig. 22-25). The sequestered portion may or may not be confined by the posterior longitudinal ligament. In fact, it may migrate inferiorly or superiorly to a different interspace or, in rare cases, may even penetrate the dura. Free fragments also tend to resemble the parent disk on both CT scans and on short TR MR images (Fig. 22-26). On long TR or gradient-echo MR images, sequestered disks may be of higher signal intensity than the disk of

Figure 22-20. Disk bulge. Postmyelogram CT scan (A) and TI-weighted (B) MR image show disk margins (long arrows) diffusely bulging beyond the bone margins (short arrows).


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origin. The most important distinction, however, is the lack of a connection between the extruded component and the --.u-: parent disk. This is better appreciated on MR sagittal views ' than on axial views. On CT scans, sagittal reconstructions are often necessary to confirm the presence of a free fragment. Because there is no connection to the parent disk, free fragments can be confused with neoplasm, abscess, or postoperative epidural fibrosis.

Clinical Considerations EXTRUSION Figure 22-22. Illustration of disk extrusion. herniated through a complete annular tear but to the parent disk. (Modified from Modic M nance Imaging of the Spine. St.

The clinical presentation of disk herniation is different than that of nondiskogenic spinal stenosis, in that it tends to be acute and occurs in younger individuals between ages 30 and 45. The inciting event is usually a fall, sudden lifting, or rotation. Sometimes it occurs spontaneously. The pain usually begins in the lower back, and the patient flexes anteriorly or laterally to reduce the pain. Pain is exacerbated by standing, sitting, or by increased CSF pressure induced by coughing, sneezing, or bowel movements. Because the most commonly compressed roots are

Figure 22-23. Various disk herniations on a postmyelogram CT scan. A, Small disk herniation (arrows) impinging on the spinal canal. Note focality. B, Larger herniation (arrows) with mass effect on the canal. C, Larger herniation encroaching on right neural foramen (white arrows). An osteophyte (black arrow) is encroaching nn the left foramen.


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Figure 22-24. Various disk herniations as shown with MRI. A, Sagittal TI-weighted MRI in a patient with a right param& disk herniation (arrows). B, Sagittal T2-weighted MRI of the same patient. Disk herniation (arrow) and displacement of the posterior longitudinal ligament (arrowheads) by the disk. C, Axial T1-weighted scan of the same patient. Amws indicate the herniated disk. D, Axial T2-weighted scan in the same patient. Note displacement of the right S1 nerve mot (closed a m w ) by the disk. The open a m w indicates the normal left S1 nerve root.


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~agitfal(tII I I ~ IUC ~ . rlght LA5 foramen and nerve root (arrow in E) are crowded by an L4-5 disk herniation. Note how the L1-2 herniation extends superiorly behind the posterior longitudinal ligament (arrow in F). G, Axial TI-weighted view of L4-5 herniation. The disk presses on and displaces the inadoraminal right LA root. The herniated disk and G,displaced root form a large soft tissue mass (white arrow). Note the normal left LA root (black arrow) with surrounding fat. H and I, Sagittal (H) and axial (I) T2-weighted MR images of a huge herniated disk lying behind the LA vertebral body. The disk is so large that one cannot tell if it emanates from the L3-4 or the L4-5intenpace. The disk is probably sequestered, or broken off from the native disk.

E 4 ,Multiple disk herniations in a different patient. T2-weighted right parasagittal (E) m u lllidh;


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vertebral body lamina is removed (Fig. 22-28). Sometimes the exposure is widened by removal of a variable amount of facet joint for better visualization and decompression. In a laminotomy, only a small amount of lamina is removed near a herniated disk for adequate exposure. On CT and MRI, laminectomy sites are fairly obvious because of the bone removal involved. In a microdiskectomy, however, only a tiny bit of lamina is removed and sometimes the operative site is difficult to locate on CT scans or MR images. Before the advent of MFU, contrastHERNIATION enhanced CT scans were the preferred method of evaluating the postoperative spine." This method has essentially Figure 22-25. Illustration of a sequestered disk. Disk material has herniated through a complete annular tear and has broken off been replaced by MRI because of its superior ability to from the parent disk. The disk fragment can migrate freely. differentiate postoperative soft tissue changes (e.g., scar(Modified from Modic MT: Magnetic Resonance Imaging of the ring versus recurrent disk hemiation),67 its multiplanar Spine. St. Louis, Mosby-Year Book, 1989.) capability, and the use of relatively safe contrast agents. MIU changes in the postoperative spine are now well described13. 70*71 and are summarized here. L5 and S1, pain radiates down the lower extremity in these In the immediate postlaminectomy period, the signal radicular distributions (Fig. 22-27). Paresthesias may also from normal bone and ligament is replaced by edema at be a feature. The radiculopathy has both a mechanical the resection site. This is heterogeneously isointense to component, owing to compression by the herniated disk, muscle on TI-weighted images and increased on T2and an inflammatory component, owing to nerve root weighted images. In a purely decompressive laminectomy edema. without diskectomy, significant mass effect on the thecal Medical treatment, usually with steroids, anti-inflammasac is unusual unless a hematoma is present. Between 6 toIy agents, and a regimen of physical therapy, can reverse weeks and 6 months after surgery, the postoperative edema the inflammatory component and alleviate symptoms. If is replaced by scar tissue posterior to the thecal sac. The pain persists as a result of the mechanical component, ., ,.pear appearance can range from low to high signal intensity surgery may be necessary>7 ,,' F n 72-weighted images (Fig. 22-29). If a diskectomy is performed with the laminectomy, ditional changes related to the diskectomy are appreciIn the early postoperative period, there is edema in Postoperative Lumbar Spine epidural space in addition to disruption of the Imaging of Complications margin due to disk curettage. On T1Scarring and Recurrent Disk Herniation !$lpeiphted images, this is reflected by anterior epidural interA variety of surgical techniques are available for treat- .r' :,mediate signal intensity that may blend with the remaining ment of spinal stenosis and disk disease. The surgeon p;?native disk. On T2-weighted images, this area may be may remove a variable amount of bone from the posterior ~4 . .$variably hyperintense. This probably results from edema67 and possibly even blood.6 elements to expose an area for diskectomy, spinal canal decompression, or both. In a larninecfomy, much of the $bj The imaging specialist must therefore exercise care in 67v

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Figure 22-26. Sequestered disk. A, Sagittal MR image shows an LA-5 disk fragment (arrow) lying posterior to the LA body. B, Axial MR image shows the fragment (arrows) obliterating the LA root in the right lateral recess and pressing on the thecal sac. See also Figure 22-24H and I.


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Figure 22-27. Illustration of lower extremity radiculopathies resulting from common disk herniations.

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Figure 22-28. ~ a n u n d o m ~ . scan shows resection of spinous process and both laminae (arrows). B, Axial postcontrast TI-weighted MR image shows enhancing posterior scar (black arrows) replacing both laminae, which have been resected. There is also an enhancing anterior epidural scar (white arrows). C, Laminotomy. Most of the left lamina has been resected. Note the scar (arrow) replacing it.

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Figure 22-29. Laminectomy. A, Sagittal unenhanced, TI-weighted MR image shows an isointense, posterior epidural scar (black arrow). The anterior e~iduralscar from this LA-5 diskectomy is also seen (white arrow). Note resection of L5 svinaus Drocess. B, T2weighted MR image shows the scar (arrows) as hyperintensebut heterogeneous. A small, f d fluid collection (Ateriskj is also visible.

This is a normal postoperative finding.

m!i

interprednx-early postoperative changes because this normal mass effect on the thecal sac may mimic recurrent or residual disk herniation (Fig. 22-30). Furthermore, confusing areas of gadolinium enhancement may be seen in the normal early postoperative spine, including the paraspinal muscles, facet joints, and nerve rook6 Therefore, gadolinium cannot be used for the evaluation of scar versus recurrent disk herniation in the early postoperative period. The reasons for all of these normal early postoperative changes have not been completely worked out. Therefore, MRI should probably not be used in the early postoperative period unless other complications, such as hematoma, pseudomeningocele, and infection, are suspected. By 6 weeks after surgery, the edema and mass effect subside and the thecal sac margin returns to normal. In a patient with late postsurgical recurrent back pain, the distinction between recurrent disk herniation and scarring must be made because reoperation on a scar may lead to a poor result with the formation of more scar tissue. Noncontrast MRI is at least equivalent to contrast CT

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s c m g in aisnngmsning scar Irom disk,13 with a 79% accuracy rate for noncontrast MRI and a 71% accuracy rate for contrast @r scans in one s t ~ d y . 7 ~ Scar tissue tends to conform to the shape of, and often to enwrap, the dural sac and exiting nerve roots, and it does not have a definable margin (Fig. 22-3 1). Mass effect on the thecal sac may or may not be present; however, the dura may actually retract toward the scar. On non-contrast-enhanced MR images, anterior epidural scar tissue is generally hypointense to isointense to disk on TI-weighted sequences and hyperintense on T2-weighted sequences. Lateral and posterior scar tissue may be somewhat more variable. Herniated disks tend to be contiguous with the native disk space (unless sequestered) and have a definable margin (see Fig. 22-24). Mass effect on the thecal sac is present. Herniated disks tend to be of low signal intensity on all pulse sequences but large, extruded, and sequestered disks can be hyperintense on T2-weighted sequences, making distinction between a disk, a scar, and CSF difficult.48Morphology, rather than signal characteris-


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Figure 22-32. Sagittal TI-weighted postoperative MR image shows an apparent recurrent disk herniation (arrow) at L4-5.With contrast enhancement, this proved to be scar tissue.

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tics, is therefore probably a more useful method of distinguishing a scar from a disk on the noncontrast MRI.30967 Even so, well-defmed scar tissue can mimic a disk herniaF w r e 22-30. Early view of the postoperative spine. T2- 1 tion on unenhanced MR images Fig. 22-32). Gadolinium-enhanced MRI has met with considerable weighted image shows apparent severe canal stenosis (asterisk) from a soft tissue structure (arrowhead), which probably represuccess in differentiating postoperative scarring from recursents soft tissue swelling and blood, but mimics the appearance rent disk herniation. Accuracy of contrast-enhanced MRI of disk herniation. Note subligamentous edema (arrows), also a has been r e p o d to be as high as 96%,31.74 Scar tissue normal postoperative finding. The patient was asymptomatic at consistently enhances postoperatively (Fig. 22-33) this particular level. continues to enhance months to years after surge~y.~' herniated disk should not enhance (Fig. 22-34). One caveat: Even though anterior epidural scar mvanably shows this pattern of consistent enhancement, posterior epidural scar may not. In fact, posterior epidural scar may show a rapid decline in enhancement over a period of months,3'- although the reason for this is not known. As noted previously, a herniated disk does not enhance in the immediate postinjection period. If delayed images are obtained, contrast medium may diffuse into the herniated disk from adjacent scar tissue, causing disk enhancement as well. Therefore, care must be taken to complete the enhanced portion of the examination no more than 30 minutes after injection. Gadolinium is particularly useful when a mixture of scar and recurrent disk herniation is found; the enhancing scar can be separated from the nonenhancing, low-signal recurrent disk herniation (Fig. 22-35). However, an enhancing, inflammatory reaction around a herniated disk is a common occurrence, even in the absence of prior surgery. This peridiskal reaction may actually be prominent enough to obscure a small herniation that it surrounds, thus masking it and mimicking pure scar tissue. -. ' These enhancement characteristics generally apply to 9t2; patients in the late postoperative period (>6 weeks after surgery). Scar tissue has been shown to enhance in the early postoperative p e r i ~ d As . ~ mentioned, however, differFigure 22-31. MR image shows an epidural entiation of this enhancement from the myriad normal immediate postoperative changes may be difficult. The scar (arrows) pamauy encircling and compressing the thecal sac. The posterior margins of the scar are ill defined. enhancement of epidural scar is probably related to "leaky

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Elgum 22-33. Same patient as in E p 22-32. A, Axial nrneahanced TI-weighted MR m e shows an apparent recurrent disk herniation (anow). B, After &okium administration, the scar tissue (arrow) enh;ances intensely, e n p s the left L5 root, and compmses the thecal sgc. No evidence of demcm&ate postoperative scar (&rows) in can be seen only dfrer contrast administration. This is a common postoperative k-,

Figure 22-34. Postoperative disk herniation. A, Sagittal unenhanced MR image shows major disk herniation. B, Axial MR image after gadolinium administration shows no disk enhance-


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Figure 22-35. Disk herniation. A, Postoperative sagittal unenhanced, TI-weighted MR image. Recurrent disk herniation (arrow) is indistinguishable from scarring (arrowheads). B, Nonenhancing recurrent disk herniation (arrow) now stands out from the surrounding postoperative scar (arrowheads).The intensely enhancing bright rim around the disk is not a postoperative scar but, instead, peridiskal inflammation, whlch can be seen even on nonoperated disk herniations. n, nerve root. C,Axial enhanced TI-weighted MR image in the same patient shows recurrent disk herniation with inflammation (closed arrows). Open arrows

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va~cularity,"~~ which can persist years after s q e r y ; in contrast, the herniated disk is avascular. A In summary, a recurrent herniated disk is an avascular, well-defined, low-intensity mass that does not enhance on early postinjection images. It has a well-defined margin and is usually located in the anterior epidural space contiguous with or near the native disk space. An epidural scar

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is a vascular structure with ill-defined margins that tends to circle the thecal sac and roots. Anteriorly, it consistently enhances even years after surgery. Posterior epidural enhancement may decline over time. Whereas morphology d enhancement are quite reliable in differentiating a disk from a scar, signal characteristics and mass effect may overlap and should be used only as secondary signs.


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Disk space infection Epidural abscess Bony Stenosis Bony stenosis may account for up to 60%of failed back surgery cases.80Osteophytes and hypertrophic bone vary in MRI signal appearance, depending on degree of marrow content. CT, particularly with intrathecal contrast material, is especially helpful in evaluating canal narrowing resulting from postoperative bone overgrowth (Fig. 22-36).

Figure 22-36. Postoperative bone overgrowth. Postrnyelogram CT scan shows severe hypertrophy of posterior elements compressing the spinal canal.

Other Complications Aside from recurrent disk herniation, several postoperative complications may occur, including: Bony stenosis Pseudomeningocele Arachnoiditis

Pseudomeningocele A pseudomeningocele is a localized collection of fluid communicating with the thecal sac. This results from an iatrogenic dural tear during surgerya1Whereas small postoperative fluid collections along the soft tissues of the incision site may be a normal finding, a pseudomeningocele is not. MRI and CT scans show a saclike area of fluid intensity adjacent to the dura (Fig. 22-37). Blood or debris may be present within the fluid. Differentiation between abscess, postoperative fluid collection, and pseudomeningocele may be difficult. However, pseudomeningocele is likely if a communication between the thecal sac and the collection can be demonstrated, or if, on CT myelography, contrast medium enters the fluid Arachnoiditis Arachnoiditis represents an inflammatory reaction in which nerve roots adhere to the thecal sac and to each

Figure 22-37. Pseudomeningocele. A, Postsurgical sagittal T2-weighted MRI shows large pseudomeningocele (PM). The communication (between the arrows) between the pseudomeningocele and the canal (C) is quite large. Compare with small, normal postoperative fluid collection shown in Figure 22-27, B, Axial postoperative CT scan in a different patient shows a large amount of intrathecally injected contrast pooling in a pseudomeningocele. Demonstrating the actual connection between the pseudomeningocele and the thecal sac can be difficult at times and could not be shown in this figure.


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other. This can occur after laminectomy and is one of the causes of failed back surgery.14 Normally, the nerve roots are symmetrically distributed within the dependent portion of the CSF (see Fig. 2 2 - 4 0 . In arachnoiditis, nerve roots clump together centrally or adhere to the dura peripherally. In advanced stages, the lumbar spinal canal is filled with inflammatory soft tissue. These changes are obvious on both MRP2 and on CT myelography (Fig. 22-38). Interestingly, enhancement is not a prominent feature.

Disk Space Infection Postoperative disk space infection and epidural abscess are uncommon but serious postlaminectomy complications. Although diskitis in adults is usually characterized by he-

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matogeneous spread, bacterial contamination from disk manipulation can occur. Disk space infection typically presents as hypointensity on TI-weighted images and as hyperintensity on T2weighted images in the disk and adjacent end plates, with poor definition of the end plates themselves. These signal changes reflect reactive edema. On TZweighted images, the internuclear cleft (the normal horizontal band of low signal intensity in the center of the nucleus pulposus) is lost. In disk space infection, the disk and adjacent end plates usually enhance with gadolinium administration (Fig. 22-39)? Despite the myriad early normal postoperative changes in the epidural space, generalIy no signal intensity or morphoiogic changes are found in the disk space itself or in the adjacent end plates after uncompli-

Figure 22-38. Arachnoiditis. A, Axial postoperative unenhanced TI-weighted MR image shows clumping of nerve roots (arrows) within the spinal canal. B, Enhanced scan in another postoperative patient shows the nerve roots adhering peripherally to the dura (arrows). Note that root enhancement is not a feature. C, Postmyelogram CT scan shows nerve roots adhering peripherally to the dura (arrows). This gives the appearance of an "empty" thecal sac. D, Postmyelogram CT scan shows advanced arachnoiditis. Most of the spinal canal is filled with inflammatory tissue (arrows), with only a small amount of contrast noted anteriorly.

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Figure 22-39. Postoperative infection. A, TI-weighted unenhanced MR image of LA-5 disk.itis/osteomyelitis. Dark signal (asterisk) denotes edema in the vertebral end plates and marrow. The infected disk is conforming to the shape of eroded end plates (closed arrows). Abnormal soft tissue is seen in the anterior epidural space (open arrow). B, T1-weighted enhanced MR image in the same patient. The margins of the disk enhance (closed armws) as does the infected anterior epidural soft tissue (open arrow). C, Short tau inversion recovery (STIR) sequence shows the bone edema (asterisks) markedly well. Note loss of the internuclear 'cleft in the infected disk (closed arrow) compared with a normal nondegenerated, noninfected disk (open arrow). ' D, Fast spin-echo, T2-weighted MR image does not show the edema nearly as well as the STIR sequence, which is indispensable --. --7-I.. -. ----, 'for evaluation of osteomyelitis. nsWb .duwt. mb-.*mit --Tub t g m + l i m m . $ rTrF , u w e ' I H . a ~ - ~ ~ - * I w ~ t wvlb

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Chapter 22

cated diskectomy.' Therefore, any disk space or end-plate abnormality in the postoperative period should be viewed with suspicion. Several problems occur, however, in differentiating both degenerated disks and normal postoperative disks from disk infection: 1. Type I degenerated end plates are also hypointense on TI-weighted images and hyperintense on T2-weighted images and may enhance with gadolinium. However, no change should occur in the appearance of the unenhanced disk after uncomplicated diskectomy. Comparison of preoperative and postoperative scans is thus important. Furthermore, the cortical margins should remain sharp after uncomplicated diskectomy, whereas the margins are indistinct in infection. 2. Type II degenerated end plates have high signal intensity on TI-weighted images and high to slightly lower signal intensity on T2-weighted images. This high T1 signal may mask the low T1 signal found in disk space infection. In this case, too, it is important to look for abnormal disk signal, to compare preoperative and postoperative scans, and to evaluate cortical margins. 3. Infected disks and end plates usually enhance with gadolinium; uncommonly, however, the normal postoperative disk can enhance. Boden and colleagues7 observed that it is unlikely for normal postoperative patients to have all three abnormal findings (i.e., low disk/endplate signal on TI-weighted images, high disklend-plate signal on T2-weighted images, and diskfend-plate enhancement with gadolinium). This "triad" suggests disk infection in the symptomatic patient.

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both the upper and lower extremities, symptoms referable to arms, legs, or both may occur. 2. Because the dimensions of even the normal cervical spinal canal are small relative to the lumbar, small spondylitic or disk changes may cause significant symptoms.

Anatomic Considerations

Although the basic anatomy of the cervical and lumbar vertebrae and diskovertebral junctions are similar, several important differences as they may relate to spondylosis warrant brief review. Unlike the more rounded configuration of the lumbar sac, the cervical spinal canal is triangular. The cervical spinal cord is oval (Fig. 2240). The canal decreases in size from C1 to C3 and is uniform from C3 to C7. The normal lower limit anternposterior diameter of the canal is 16 mm at C1, 15 mm at C2, and 12 mm in the lower cervical spine." The exiting cervical nerve roots travel in an inferior direction through the foramina at about 45 degrees with respect to the coronal plane (Fig. 22-41). This differs from the lumbar roots, which travel inferiorly but nearly parallel with the coronal plane. This makes sagittal imaging of the cervical nerve roots less optimal than in the lumbar spine. The cervical nerve roots exit above (not below, as in the lumbar spine) the pedicle of its corresponding vertebral body. Because there are eight cervical roots but only seven vertebrae, the relationship changes at the C8 root, which passes above the T1 pedicle. The T1 root then passes under MRI using fat suppression has made the diagnosis of the TI pedicle and the pattern is the same as in the lumbar postoperative diskitis/osteomyelitis easier. Short tau inverspine the rest of the way down. ad-. .-asion recovery (STIR) imaging shows disk and bone edema In addition to the body, laminae, pedicles, spmous, ana that may be difficult to visualize on TI-weighted and T2transverse processes, the cervical vertebrae have uncinate weighted images because of bright, fatty marrow obscuring processes, or joints of Luschka, paired bony ridges prothe edema (Fig. 22-390, jecting superiorly from the posterolateral margins of the vertebral bodies. They fit into notches on the posterolateral surfaces of the inferior end plates of the vertebral bodies Epidural Abscess above. On axial images, they can be seen indenting the Epidural abscess is also hypointense on TI-weighted posterolateral disk margin as they bridge the vertebral images and hyperintense on T2-weighted images and bodies (Fig. 22-42; see Fig. 2241). The uncinate procshows mass effect on the thecal sac. Because these changes esses contribute to the anterior walls of the neural forammay be masked by the similar signal of CSE gadolinium ina; if hypertrophied, they can cause foraminal stenosis. should be given when epidural abscess is suspected (Fig. Whereas the lumbar facet joints are fairly sagittally on22-3 9).76 ented, the cervical facets are obliquely positioned, their surfaces lying halfway between a coronal and axial plane (see Figs. 2 2 4 1 and 22-42). Cervical Spine The vertebral arteries pass through the bony transverse foramina, located on the lateral aspects of vertebrae C1 to After the lumbar spine, the cervical spine is next most C6 (see Fig. 22-40). The arteries can rarely be compressed commonly affected by spondylosis and disk herniati~n.~ by foraminal spurs. The most frequently involved interspaces are C4-5, C5-6, and C6-7. This may be due to the greater degree of motion at these levels.21Although many concepts of nondiskogenic Imaging Techniques and diskogenic degeneration (osteophyte formation, foraminal stenosis, spondylolisthesis, and disk herniation) are At our institution, CT scans of the cervical spine for much the same as in the lumbar canal, a couple of imdegenerative disease are usually done following myelograportant anatomic and clinical differences should be emphaphy (see Figs. 22-40 and 22-42). Investigators have found sized: that the increased sensitivity of CT myelography over stan1. Because the cervical spinal cord carries neurons from dard CT in the cervical spine is even greater than in the

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Figure 2240. Cervical images. A, Cervical postmyelogram CT scan. Note the triangular configuration of the spinal canal (arrows) and oval shape of the spinal cord (white asterisk). The nerve root sheaths (black asterisk) can be seen exiting through the neural foramina. B, Axial cervical TI-weighted MR i m a e c , ,s@~@c-anal; s, seinal cord. Arrows indicate n e w roots; arrowheads indicate vertebral arteries in the transverse foramina. , ~ f i W d d m ~ ~ b - f ~

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lumbar spine.12After myelography, 2-mm contiguous axial images through the levels of concern are obtained. Both bone and soft tissue windows are photographed. Unlike lumbar CT myelography, cervical CT myelography is done soon after the intrathecal injection because contrast mate-

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rial in the cervical canal tends to flow away from the cervical canal more quickly and the injection volume is generally smaller than in the lumbar canal (Box 22-3). As in the lumbar spine, numerous choices are available for MRI of the cervical spine. We obtain a set of fast spinecho, TI-weighted and T2-weighted sagittal images of the entire cervical region (Fig. 22-43). These images should include the cerebellar tonsils down to the first thoracic level. With the development of stronger x-y-z gradient coils,

Figure 2242. Cervical postmyelogram CT scan. The uncovertebra1 joints of Luschka are indenting the posterolateral disk (d) margins (arrows) (see Fig. 22-41). Note also the near-horizontal orientation of the facet joints (arrowheads) (see also Fig. 22-41).

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Box 22-3. Routine CT of Cervical Degenerative Disease Axial contiguous images from C2 t o T I Slice thickness = 2-3 mm, intersection gap = 2 mm Both wide and narrow window settings lntrathecal contrast preferable

matrices in the range of 300 to 600 can be obtained, greatly increasing image resolution. The stronger gradients also allow for shorter imaging times and larger fields of view (allowing inclusion of the upper thoracic spine in the cervical images-a request often made by referring physicians) with little or no decrease in image resolution. We also obtain a set of 2D gradient-echo as well as 3D (volume) gradient-echo axial images from the C3-4 interspace down to at least the C6-7 interspace. The T1-weighted images are used for evaluation of overall anatomy and marrow abnormalities. The gradient-echo images bring out the "myelographic effect," enhancing contrast between boneroot-cord and CSF (see Fig. 22-41). We use both 2D and 3D gradient-echo axial views because we find that overall image quality tends to be better with 2D sequences, but the thinner slices obtained with 3D sequences often help to detect small lesions. We apply a magnetization transfer pulse to the 3D images to help darken the cord and roots, thus increasing the myelographic contrast effect. Again, imaging sequences may vary widely among institutions. For instance, some centers routinely obtain T1weighted axial views, whereas we do not, except in the postoperative cervical spine. All 2D images are 3 to 4 mm

Figure 22-43. Sagittal fast spin-echo, T1weighted (A) and T2-weighted (B) cervical MR images. The field of view should include cerebellar tonsils to at least the first thoracic level. A large field of view helps to include the upper thoracic spin^ 'w;" ""v. -V 4AL'~'4l'ii~.l!J~ mL 4

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Box 22-4. Example of Routine MRI of Cervical Degenerative Disease 1. Sagittal fast spin-echo, T1-weighted image t o include cerebellar tonsils t o TI level a. Field of view = 26-28 cm, thickness = 3-4 mm, intersection gap = 1 mm, matrix = 256 x 512 2. Sagittal fast spin-echo, T2-weighted image t o include cerebellar tonsils t o T I level a. Field of view = 26-28 cm, thickness = 3-4 mm, intersection gap = 1 mm, matrix = 384 x 512 3. Axial 2D gradient-echo sequence t o cover at least C23 through C6-7 interspaces a. Field of view = 20 cm, thickness = 3 mm, intersection gap = 1 mm, matrix = 384 x 512 4. Axial 3D gradient-echo sequence contiguous to cover at least C2-3 through C6-7 a. Field of view = 20 cm, reconstructed thickness = 2 mm, matrix = 512 x 512 b. Apply magnetization transfer pulse 5. I f postoperative spine, substitute noncontrast T1weighted, fast spin-echo axial views for one of the gradient-echo sequences a. Field of view = 20 cm, thickness = 3 mm, intersection gap = 1 mm, matrix = 256 X 256

thick with a 1- to 1.5-mm gap (Box 224). Given the 45-degree angle of the exiting nerve roots, some authors advocate using sagittal oblique images (perpendicular to the foramina) rather than direct sagittal views for optimal foraminal imaging.55This, however, requires two separate sets of oblique images, one for each side, and is therefore more time-consuming. We occasionally make use of the

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sagittal oblique when there is obvious clinical radiculopathy without obvious MRI findings. The oblique images occasionally reveal small, but strategically located intraforaminal disk herniations. Because the cervical spine is small and "crowded," volume averaging, patient motion, flow and pulsation artifacts, and small-structure (e.g., foramina1 stenosis) evaluation are more problematic in the cervical than in the lumbar spine. More refined imaging techniques (e.g., volume imaging, fast spin-echo imaging, magnetization transfer, motion compensation) to alleviate these problems are evolving rapidly, and numerous new sequences and techniques

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Degenerative disease of the cervical spine is very common after age 40 and may, in fact, affect 70% of people

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older than age 7 0 . 43~ 6 ~ older individuals, facet hypertrophy and osteophytosis become more problematic than disk herniation; whereas osteophytes and facet disease worsen with age, disk material becomes harder, more immobile, and less likely to pr~trude.~ As in the lumbar spine, osteophytes can compress any portion of the neural canal and foramina (Fig. 2 2 4 ) . Ligamentum flavum hypertrophy can contribute to spinal and foraminal stenosis (see Fig. 2 2 4 ) . Unique to the cervical spine are the uncinate processes, or joints of Luschka, which contribute to the anterior wall of the neural foramina. Uncinate hypertrophy or osteophytosis, therefore, may lead to foraminal stenosis (Fig. 2245).45.58 Facet hypertrophy generally narrows the foramina (see Fig. 2245). CT is well suited for visualization of bone and facet fhsease. On MRI, osteophytes can be of high, intermediate, or low signal intensity on TI-weighted images, depending on their yellow marrow content.54Intermediate-signal and low-signal osteophytes may blend in with adjacent liga-

Figure 2244. A, Sagittal gradientecho MR image shows multiple osteophytes (small arrows) encroaching on the thecal sac. Ligamentous hypertrophy (large arrows) is also present posteriorly. B, Postmyelogram CT scan shows an osteophyte (arrow)

flattening the right aspect of the canal and cord. C,Postmyelogram CT scan shows posterior element osteophytes farrows).


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Figure 22-45. Postmyelogram CT scan (A) and axial gradient-echo (B) MR image show hypertrophied uncovertebral joint (closed arrows) narrowing the right neural foramen. Right-sided facet hypertrophy (curved arrows) contributes to this narrowing. Note also osteophytes (open arrows).

ments and CSF in the cervical region, where volume averaging is already a problem. As mentioned, we obtain gradient-echo images in the cervical region, which makes bone very dark regardless of marrow content. This stands out nicely against the myelographically bright CSF. One must beware, however, of the "blooming" effect, in which osteophyte size may be exaggerated on gradient-echo sequences owing to magnetic susceptibility. Thus, spinal stenosis secondary to osteophytes seen on gradient-echo sequences should be confirmed on T1-weighted images, whose magnetic susceptibility effects are not as prominent. Posterolateral bone, ligament, and facet disease, which impinge on the nerve roots, can lead to upper extremity radiculopathy. Central disease that compresses the cervical resulting in cord can produce myelopathy as we11,'0.28*59 lower extremity symptoms, including spasticity, weakness, 28 Clinically, this syndrome must be and gait di~turbance.~. differentiated from other forms of myelopathy, such as multiple sclerosis, spinal neoplasm, and various intrinsic spinal cord diseases. In addition, if large spurs compress the vertebral arteries, symptoms of vertebrobasilar insufficiency may occur.8 Although common in Japan, ossijication of the posterior longitudinal ligament (OPLL) is a fairly rare cause of spinal stenosis in the United States. There is no known etiologic mechanism. The ossified posterior longitudinal ligament can impinge on the spinal canal, resulting in nerve root or spinal cord compression. This entity is well visulaized on plain films as a vertical band of ossified tissue along the posterior margin of the vertebral bodies. On CT scans, the involved portion of the ligament is replaced by the high density of calcium. On MR images, the ossification is represented by low signal on short TR, long TR, and gradient-echo sequences (Fig. 2246). However, fatty marrow within the ossification can yield areas ,V of high signal intensity on

Diskogenic Spinal Stenosis Early in the course of cervical spinal osteoarthritis, the most common cause of pain is direct nerve-root compres. sion by a laterally herniated cervical disk, which ordinarily occurs without prior trauma. This results in neck and arm pain with paresthesias in a dennatomal distribution. Both sensory and motor abnormalities occur. Cervical disk herniations are most common in the second through fourth decades of life.8 These herniations are well seen on both CT myelography (Fig. 2247) and MRI (Fig. 2248) as extradural soft tissue masses contiguous with the parent disk and focally protruding posterolaterally into the canal andlor neural foramina. Central disk herniations are less common and can cause spinal cord compression, resulting in myelopathy as well as radiculopathy (Fig. 2248E).8

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Postoperative Cervical Spine Postoperative Changes Most decompressive procedures on me cervica splne are now performed via an anterior approa~h.'~? 34-65 With the Smith-Robinson technique, the disk and end-plate material are removed and are replaced with an osseous wedge from the iliac bone.65 During the Cloward technique, the surgeon removes posterior and posterolateral osteophytes, drills a hole into the disk space and end plates, and reinserts a prefitted piece of bone.15 Strut grafts are used for cervical stabilization after multilevel decompressive surgery is performed. The grafted bone bridges the involved vertebral bodies. Although these techniques are commonly used, many other approaches, both anterior and posterior, are available (Fig. 2249). In the immediate diskectomy-fusion postoperative period, the signal intensity of the intervertebral bone

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Figure 2246. Ossified posterior longitudinal ligament. Axial noncontrast CT scan (A) and axial gradient-echo MR image (B) show the ossified ligament (arrows) impinging on the spinal canal.

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F i m 2247. Pos ye ogram CT scans of cervical disk hekation. A. Lateral disk-herniation flattens the left side of the spi& cord (arrow). Note also osteophytes. B, Slightly lateral disk herniation (arrow). C, Central disk herniation (black arrow). These are somewhat less common in the cervical spine. Bilateral uncovertebral hypertrophy (white arrows) are also seen.


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Figare 2248. MR images of cervical && herniation. Sagittal fast spin-echo, TI-weighbed (A) and axial gradient-echo (B) images show a small central disk herniation (amws). In the mid spine, herniations can be quite snbtIe. Sagittal fast spin-echo, T1weighted (0a d T2-weighted (D)images of multiple disk herniations (amws) in a single patient

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Figure 2 2 4 8 Continued E-G, Axial gradient-echo images in a patient with multiple disk herniations. E, This centrally her-

niated disk severely narrows the canal at one level (arrow). E This laterally herniated disk severely narrows the left foramen (arrow) at another level. G, Osteophytes, which are much darker than disk herniations on gradient-echo imaging, are present as

grafts on MRI may be quite variable, according to whether the marrow is cellular or fatty and whether the bone is cancellous or compact- Adjacent end plates can have norma1 signal or signal that reflects postoperative Disk and end-plate changes in the late postoperative period are even more reflecting the the bone graft but also, possibly, the amount of revascularization> postoperative srresses, and inrraO~erativetrauma received by the end plate and graft?O. 73 Strut grafts are easily seen as long wedges of bone ridging the anterior aspects of the vertebral bodies. On h4R images, the signal of the bulk of the graft may be variable but low-signal cortex outlines the graft margins (see Fig. 2249). Solid bony fusions without replacement of disk by graft are seen as continuous marrow signal with no definable interspace (Fig. 22-49C). One of the most common types of procedures seen today involves anterior diskectomy, followed by interbody fusion with a piece of bone and placement of an anterior plate-screw device for maximum stability (Fig. 22490-G).

Cornplications Complications of cervical spine decompression are similar to those in the lumbar region, including (1) bony stenosis, (2) disk herniation, (3) pseudomeningocele, and (4) infection. There are, however, some differences. 1. Bony stenosis may be caused not only by osteophyte formation but also by uncovertebral hypertrophy or by overgrowth of the fusion mass itself. These can produce spinal as well as foramina1 stenosis. When one is looking at gradient-echo images of the cervical spine, the surgical material used may cause magnetic susceptibility "blooming" artifact and may mimic severe sp~nalstenosis when in fact no stenosis exists (see Fig. 2249D-G). It is important, therefore to examine all images carefully, especially the TI-weighted and T2-weighted sequences. These sequences (especially FSE) tend not to exaggerate the degree of spinal stenosis. We substitute a set of T1-weighted axial images for one of the gradient-echo axial views to mitigate these artifacts in the postoperative cervical spine (see Fig. 2 2 4 9 6 ) .

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Figure 2249. Various types of cervical fusions. A, Large fibular strut graft (black arrows) for multilevel fusion. Note early postoperative edema (white arrows) causing cord compression. B, Axial CT scan in a different patient shows a fibular strut graft (arrow) fusing C4-5. C, Solid (25-6 fusion. D-G, C4-6 fusion by means of plate-screw combination and interbody bone graft. D, TI-weighted image. Arrows indicate a platescrew device. Asterisk indicates interbody bone graft. No significant spinal stenosis post-grafting. Illustration continued on following page


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Figore 2249 Continued E, Fast spin-echo, T2-weighted sequences produces artifact from the metal portion of the graft (armws) but does not show significant spinal stenosis. Axial gradient-echo image. Artifact falsely suggests severe spinal stenosis. c, cord. G, Axial TI-weighted image shows the me, nonstenotic coconfigwation of the canal. B, bone graft.,C, cord; P, metal plate.

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2. Because most or all of a disk is removed and repfa&& a"nd rotational deformities as well as malalignment. in a cervical diskectomy and fusion, postoperative recurThese scans can also be performed in flexion and extension to demonstrate abnormal motion. Unfortunately, no rent disk herniations tend not to occur unless residual . , effective way of evaluating graft integrity by CT or disk material is inadvertently left behind. Graft extrusion, however, is an uncommon complication that can .! ..; MRI exists to date. mimic a herniated disk at the operative level. Cervical , disk herniations at nearby levels can occur from the . - . altered stresses within the spine.70 fhoracic Spine 3. Cervical spine instability can be a significant problem Both disk herniation and spinal stenosis of the thoracic in a patient's status after cervical lamine~tomy.~~ Both spine are less common than in the lumbar and cervical MRI and CT scans with sagittal or coronal reconstructions can demonstrate postoperative scoliotic, kyphotic, spine. The infrequency of thoracic spinal stenosis is proba-

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Figure 2251. Normal postmyelogram thoracic CT scan. Note the round shape of the normal thoracic cord and canal.

Figure 22-50. Sagittal fast spin-c , TI-weighted (A) and T2weighted (B) thoracic MR images. The entire thoracic spine as well as the cervical spine is easily included in the field of view.

bly due to the large size of the thoracic canal relative to the cord.5' To produce compressive symptomatology, bony or ligamentous hypertrophy must be fairly large. The incidence of thoracic disk herniation is also less than in the remainder of the spine. This is presumably due to the Limited mobility of the thoracic spine and because the weight-bearing axis does not intersect the posterior margins of the vertebral bodies.5. 66 Most patients with operated thoracic disks report an incidence of less than 2%, although autopsy series report an incidence of between 7% and 15%.2 With the emergence of MRI, these herniations are being recognized with increased frequency."

excluding other causes of thoracic disease, such as tumor or infection. At our institution, we obtain TI-weighted sagittal sequences, followed by FSE T2-weighted sagittal sequences (Fig. 22-50). These images are then inspected, and axial images are obtained through the level of concern as needed (Box 22-5). CT myelography complements MRI in evaluation of spinal stenosis caused by bony hypertrophy or ligamentous ossification owing to its superior ability to image calcium. Because of its length, covering the entire thoracic spine with CT using a reasonable number of slices is difficult. Therefore, if CT scanning is to be performed, it is probably best done after myelography or MRI to define the level of pathology (Fig. 22-51). CT images can then be obtained through the level of concern (Box 22-6). With modern, large field-of-view coils, MRI can be used to depict the entire thoracic spine in one shot (see Fig. 22-50), thus making MRI the preferred imaging modality for thoracic degenerative disease.

Imaging Techniques

Nondiskogenic Spinal Stenosis

MRI demonstrates both thoracic canal stenosis and thoracic disk herniitjons quite weU. MRI is also useful for

Acquired thoracic spinal stenosis can result from hypertrophy of the bony posterior elements.84Since the advent of CT scanning, hypertrophy or calcification of the posterior longitudinal ligament pig. 22-52) and degenerative ligamentum flavum hypertrophy are also being recognized with 50 increased frequency in the thoracic

Box 22-5. Example of Routine MRI of Thoracic Degenerative Disease 1. Sagittal T I to include entire thoracic spine a. Field of view = 40 cm, slice thickness = 3-4 mm, intersection gap = 1 mm, matrix = 512 x 512 2. Sagittal fast spin-echo, T2-weighted image to include entire thoracic spine a. Field of view = 40 cm, slice thickness = 3-4 mm, intersection gap = 1 mm, matrix = 512 x 512 3. Axial fast spin-echo, TI-weighted and T2-weighted images through areas of concern as needed

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Figure 22-53. Sagittal (A) and axial (B) T1-weighted MR images of central disk herniation (arrows). C, Postmyelogram CT scan of slightly lateral disk herniation (arrow).


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Diskogenic Spinal Stenosis Most thoracic disk herniations occur in the lower thoracic spine. T11 and T12 are the most common locations. Unlike the case with the rest of the spine, most thoracic herniations are centrally, rather than laterally, located (Fig. 22-53). Multilevel thoracic herniation is rare. Most patients with thoracic disk herniations are between 30 and 50 years of age.66 . p., l

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Box 22-7. Nondegenerative Causes of Spinal Stenosis A. Congenital-developmental stenosis 1. Idiopathic 2. Achondroplasia/hypochondroplasia 3. Hypophosphatemic vitamin D-resistant rickets 4. Morquio's disease 5. Congenital dysplasias associated w i t h lax atlantoaxial joints - '"'" .". . 6. Down's syndrome 7. Spondylolisthesis ;:, , ,, , y , .- , 8. Scoliosis .- - --.-K --& 7 ,.,,, 9. Spinal dysraphism ,-

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developmental narrowing of the spinal canal. This is probably due to inadequate development of the canal and foramina. Symptoms usually arise when degenerative changes of disks, facets, and ligaments are superimposed on an already small canal.25 Box 22-7 summarizes the nondegenerative causes of spinal stenosis.

References 1. Adams P, Eyre DR. Muir H: Biochemical aspects of development and aging of human lumbar intervertebral disks. Rheumatol Rehabil 16:22-29, 1977. 2. Arseni C, Nash F: Protrusion of thoracic intervertebral discs. Acta Neumhir 11:3-33, 1963. 3. Bamett GH, et al: Thoracic spinal canal stenosis. J Neurosurg 66: 338-344, 1987. 4. Bates DB, Rugiem P: Imaging modalities for evaluation of the spine. Radiol Clin North Am 29:675-690, 1991. 5. Blumenkopf B: Thoracic intervertebral disk herniations: Diagnostic value of magnetic resonance imaging. Neurosurgery 23:3640, 1988. 6. Boden SD, Davis DO, Dina TS, et al: Contrast-enhanced MR imaging performed after successful lumbar disk surgery: Prospective study. Radiology 182:59-64, 1992. 7. Boden SD, Davis DO, Dina TS, et al: Postoperative diskitis: Distinguishing early MR imaging findings from normal postoperative disk space changes. Radiology 184765-77 1, 1992. 8. Bohlman HH: Osteoarthritis of the cervical spine. In Osteoarthritis Diagnosis and Management. Philadelphia, WB Saunders, 1984, pp 443459. 9. Bowen V, Shannon R, Kirkaldy-Willis WH: Lumbar spinal stenosis: A review article. Child's Brain 4257-277, 1978. 10. Brain WR,Northfield DW, Wilkinson M: The neurological manifestations of cervical spondylosis. Brain 75:187-225, 1952. 11. Brown MD: The pathophysiology of disc disease: Symposium on disease of the intervertebral disc. Orthop Clin Noah Am 2359-370, 1971. 12. Brown BM, Schwartz RH, Frank E, Blank NK: Preoperative evaluation of cervical radiculopathy and myelopathy by surface-coil MR imaging. AJR Am J Roentgenol 151:1205-1212, 1988. 13. Bundschuh CV, et al: Epidural fibrosis and recurrent disk herniation in the lumbar spine: Assessment with magnetic resonance. AJNR Am J Neuroradiol 9:169-178, 1988. 14. Burton CV, Kirkaldy-Willis WH, Yong-Hing K, Heithoff KB:Causes of failure of surgery on the lumbar spine. Clin Orthop 157:191-199, 1981. 15. Cloward RB:The anterior approach for removal of ruptured cervical discs. J Neurosurg 15:602414, 1958. 16. Coventry MB:Anatomy of the intervertebral disk. Clin Orthop 67: 9-15, 1969. 17. de Roos A, Krossel H, Spritzer C, Dalinka M: MR imaging of m m w changes adjacent to end plates in degenerative lumbar disk disease. Am J Roentgenol 149:531-534, 1987. 18. Donvart RH,Volger JB III, Helms CA: Spinal stenosis. Radiol Clin North Am 21:301-325, 1983. 19. Dublin AB, McGahan JP, Reid MH: The value of computed tomographic metrizamide myelography in the neuroradiologic evaluation of the spine. Radiology 146:79-86, 1983. 20. Epstein NE, Epstein JA, Cmas R, Hyman RA: Far lateral lumbar disc herniations and associated structural abnormalities: An evaluation in 60 patients of the comparative value of CT, MRI, and myelo-CT in diagnosis and management. Spine 15:534-539, 1990. 21. Epstein BS, Epstein JA, Jones MD: Cervical spine stenosis. Radiol Clin North Am 15:215, 1977. 22. Epstein BS, Epstein JA, Jones MD: Lumbar spinal stenosis. Radiol Clin North Am 153227-239, 1977. 23. Frymoyer JW, Cats-Baril WL: An overview of the incidences and costs of low back pain. Orthop Clin North Am 22, 1991. 24. Frymoyer JW, Pope MI-I, Ciements JH, et al: Ricks factors in low back pain: An epidemiological survey. J Bone Joint Surg Am 65: 213-218, 1983. 25. Gaskill IvIF, Lukin R, Wiot JG: Lumbar disc disease and stenosis. Radiol Clin North Am 29:753-764, 1991. 26. Goldberg AL, Soo MS, Deeb ZL,Rothfus WE: Degenerative disease


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Spinal Tumors Donna M. Plecha Progress continues to be made in the evaluation of extramedullary spinal tumors. Magnetic resonance imaging (MRI) is usually the imaging modality of choice for evaluating the spine if there is clinical concern for tumor. Although MRI is not usually helpful in determining the specific diagnosis or for grading neoplasms, it is excellent for determining the extent of involvement as well as anatomic detail such as spinal cord compression, and it may help to limit the diagnostic possibilities. It has also facilitated the determination of whether a tumor is extradural, intradurd extramedullary, or intramedullary.

Extradural Tumors of the Spine Extradural tumors of the spine are the most common of all spinal tumors. Most extradural tumors of the spine are metastatic lesions because the vertebral bodies are highly vascularized. The thoracic spine is most commonly involved. Spinal cord compression is seen in 5% of cancer Metastatic lesions in the patients with bone meta~tasis.~ epidural space usually result from direct extension of vertebral body metastasis. Otherwise, there can be epidural involvement from hematogenous spread through the epidural and paravertebral venous plexus.13 Most metastatic lesions of the spine originate from breast, lung, or prostate cancer.24The most common initial symptoms include local pain and radicular pain. With more advanced disease, motor dysfunction and/or sphincter dysfunction may occur. Therapies include surgery and radiation, or 4.41 and preoperative transarterial embolization of the spinal metastasis. The latter is safe and effective; it can limit blood loss during surgery and aid in more complete tumor resection.39Outcome is related to the patient's condition at diagnosis, radiosensitivity of the tumor, Early initiation of therapy is important and tumor bi~logy.~' to preserve motor f~nction.~' Bach and colleagues4 found that 79% of patients who could walk at diagnosis were still ambulatory after treatment, but only 18% of nonambulatory patients were able to walk after therapy. Therefore, timely initiation of therapy is critical. Spin-echo (SE) TI-weighted sequences are excellent for determining the extent of metastatic disease because of their high signal-to-noise ratio. Also, the high fat content of the bone marrow contributes to excellent contrast (Fig. 23-1). The metastatic lesions alter the usual fat content within the vertebral bodies, thereby causing a decrease in signal intensity on TI-weighted SE images. T2-weighted SE sequences are also helpful as abnormal bone marrow usually demonstrates increased signal intensity on T2-

weighted images. In addition, fat saturation techniques offer potential advantages for increasing the conspicuousness of bone marrow lesions. T2-weighted fat-saturated fast spin-echo W E ) and short TI inversion recovery (STIR) sequences have also been used to increase lesion conspicuity.26.32 Abnormal bone marrow signal intensity on any imaging sequence is nonspecific and does not always mean that a patient has metastatic disease. Kim and colleagues attempted to differentiate between hematopoietic malignancies and metastasis.16 They assessed lymphoma, leukemia, and multiple myeloma lesions in an attempt to distinguish them from metastasis using the following criteria: pattern of involvement, signal change of the vertebral body, location of the paraspinal mass, cortical destruction, contour change, and compression fracture. Although the two categories overlapped, diffuse involvement was more commonly seen in hematopoietic malignancies than in metastasis, and cortical destruction was more commonly seen in metastasis that in hematopoietic malignancies. The other parameters examined failed to show any statistically significant difference between the two groups.16 The authors found that it was difficult to evaluate young patients because of persistent red marrow. Patients with metastatic disease often present with compression fractures. When a patient does not have widespread metastatic disease, it is sometimes difficult to differentiate between pathologic and benign compression fractures of the spine, and various MRI sequences have been used in an attempt to differentiate between them. Baker and colleagues5examined 53 patients with a total of 34 benign compression fractures and 27 pathologic fractures. The authors used a presaturation technique, suppressing either fat or water signal with a presaturation pulse, to obtain "fat" and "water" images. STIR and SE images were also used. Most compression fractures more than 1 month old showed marrow signal isointense to that of the surrounding normal vertebral bodies. When the fracture was acute, however, the edema caused signal intensity changes similar to vertebral bodies involved with tumor. Only seven patients had acute benign fractures less than l month old. All showed high signal intensity on T2-weighted images and low signal intensity on TI-weighted SE images. In five of the patients, the water images and the =-weighted images of the problematic vertebral bodies showed heterogeneous patterns. In the other two patients, the involved vertebral bodies showed diffusely homogeneous increased signal intensity throughout. Another seven patients had pathologic compression fractures, all of which showed homogeneous diffuse decreased


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Figure %I. A, Sagittal TI-weighted image of the thoracic spine demonstrating multiple areas of abnormal bone marrow signal intensity. This patient has diffuse metastatic disease. B, TI-weighted axial image shows a right-sided metastatic mass causing mass effect on the spinal cord and thecal sac.

signal intensity on the TI-weighted images and increased signal intensity on the T2-weighted, STIR, and water images, The fat images showed a complete absence of fatty marrow signal intensity. Therefore, the patterns of signal intensity changes between the two groups did overlap. Because each group was composed of only seven patients, it is difficult to determine whether the findings are statistically significant. Another difference between the benign and malignant acute fractures was that the pathologic fractures tended to have convex outward anterior and posterior margins compared to the more sharply angulated borders of the acute benign fractures. Baur and colleagues7 assessed MR diffusion-weighted imaging (DWI) for its ability to distinguish between malignant and benign causes of spinal compression fractures. When they studied DWI of bone marrow, they found that acute benign compression fractures either showed lower signal intensity than normal bone marrow or were isointense with normal bone marrow. They thought that this difference was caused by free extracellular water in the bone marrow edema andlor hemorrhage. When DWI is used, increased signal intensity is seen where diffusion of water is decreased or restricted, such as in vertebral bodies invaded by tumor cells. Baur and coworkers7demonstrated that the pathologic bctures showed increased signal intensity within the bone marrow; this corresponded to a decrease in the apparent diffusion coefficient. MR DWI does have drawbacks, however. For example, it has low spatial resolution and a low signal-to-noise ratio. In an editorial, Le Bihanm argued that it is more difficult to separate the effects of T1 and T2 from diffusion effects with the steady-state free precession (SSFP)diffusion se-

quence than with an SlEbased diffusion sequence. SSFP diffusion-weighted imaging needs to be studied further to establish its usefulness in distinguishing pathologic from benign vertebral fractures. Percutaneous vertebroplasty has been used in patients with compression fractures (Fig. 23-2). This procedure, developed in France, involves injection of polymethylmethacrylate cement into the collapsed vertebra. The stabilization and reinforcement provided by the cement can alleviate pain. Barr and colleagues6 performed percutaneous vertebroplasty in 47 patients (eight of whom had tumor involvement in the spine) for stabilization of the spine. Only 50% of the patients experienced significant pain relief. Possible complications of this procedure include cement extravasation and asymptomatic epidural venous filling.

Multiple Myeloma As stated, multiple myeloma can appear similar to metastatic disease on spine images. Usually, compressive lesions involve the spine. When the disease is isolated to a single vertebral body, it is called a plasmacytoma. When multiple bones are involved, the term multiple myeloma is used. Multiple myeloma is more common in men and is usually seen in the sixth decade of life. The tumor is composed of monoclonal B cells within the bone marrow. The lesions show decreased signal intensity on TI-weighted images and increased signal intensity on T2-weighted images (Fig. 23-3). A study examining


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Figure 23-2. A, Axial CT image with needle in place through the pedicle of a metastatic vertebral body during percutaneous vertebroplasty. B, Axial CT image after injection of polymethylmethacrylatecement.

Figure 2S3. A, Axial CT image through the TI1 vertebral body shows a destructive lesion with a soft tissue component, which proved to be multiple myeloma. B, Sagittal TI-weighted image through the lumbar spine shows compression and bone mamw replacement of the TI1 vertebral body with associated spinal cord compression. There is also abnormal signal intensity in the surrounding vertebral bodies. C. TI-weighted axial image demonstrating significant spinal cord compression secondary to multiple myeloma mass invalving T11. The abnonnal signal intensity of the mass is isointense to muscle.

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the MRI characteristics of mu~tiplemyeloma round that of veneDral Domes without altering the shape of these these lesions were better identified with T2-weighted imvertebral bodies. This sign was found in patients with ages than with TI-weighted images in 65% of p a t i e n t ~ . ~ lymphoma but not in those with metastatic disease or with Another study found that STIR and T2-weighted images multiple myeloma.29 were better than TI-weighted images for detecting lesions and that contrast enhancement did not increase lesion dete~tion.~~ Primary Tumors of the Spine Various patterns of involvement of spinal multiple myeloma have been described. Focal lesions, diffuse involveOther extradural tumors include primary tumors of the ment, and a heterogeneous pattern of tiny lesions on a spine, which occur much less frequently than does metanormal marrow background were described in a study of static spinal disease. However, when a patient presents 29 patients." It was noted that diffuse and focal marrow with a solitary lesion, a primary tumor of the spine should patterns of involvement were associated with more abnorbe considered. Both benign and malignant tumors can be mal serum hemoglobin levels and a higher percentage of seen in the spine. Patients usually present with nonspecific marrow plasmacytosis. A similar study showed similar back pain. results: the diffuse pattern corresponded to patients with higher marrow plasmacytosis, higher cellularity, higher seOsteoid Osteoma rum calcium, higher P,-microglobin levels, and lower hemoglobin levels.21 The lumbar spine is the most common site of osteoid Another classification scheme was presented in a study osteomas, followed by the cervical, thoracic, and sacral of 61 patients.I9 The MRI patterns noted were described as spine.30Patients present with the classic symptoms of paindiffuse, nodular, diffuse and nodular, and normal. More ful scoliosis, focal or radicular pain, gait disturbance, and patients showing the normal and nodular MRI patterns of muscle atrophy. The pain is worse at night, and salicylates bone marrow signal intensity survived than patients showusually helpemVertebral posterior elements are usually ining the diffuse and the diffuse and nodular patterns.19 volved. Even though contrast-enhanced MRI was not found to Plain films reveal a round to oval area of lucency with be helpful in the initial detection of lesions in patients with surrounding sclerosis. Associated scoliosis may be found, multiple myeloma, it may be helpful for following their with the lesion located at the concave apex of the curve. responses to therapy. Patterns of complete response to CT, the study of choice for evaluating osteoid osteoma," treatment included resolution of the marrow abnormalities reveals an area of low attenuation with surrounding scleroseen before treatment and of persistent abnormality with sis (Fig. 23-6) and sometimes a central calcification. MRI peripheral rim enhancement. Signs of partial response inusually shows a nidus reflecting low to intermediate signal cluded conversion of a diffuse pattern of involvement to a intensity on TI-weighted images and intermediate to high variegated or focal pattern, and a decrease of the marrow signal intensity on T2-weighted images. Any associated involvement seen on MRI with persistent enhan~ernent.~~sclerosis or calcification shows low signal intensity on all A similar study of 18 patients demonstrated patterns of pulse sequences.30 response that included rim enhancement, no enhancement, and early enhan~ement.~~

Osteoblastoma

Lymphoma Lymphoma within the spine can present in several different ways. There can be extension from primary involvement in adjacent paravertebral lymph nodes into the neuroforamen and spinal canal. prima6 involvement can also occur within the highly vascular vertebral body, and it commonly extends into the epidural space, causing mass effect on the spinal cord and exiting nerve roots. Lymphoma can also arise in the epidural space along the leptomeninges and, rarely, in the intramedullary space, as is seen in 0.1% to 6.5% of patients with non-Hodgkin's lymphoma (Figs. 23-4 and 23-5).37 Marrow involvement occurs in 4% to 14% of patients with Hodgkin's lymphoma, and the percentage is much higher in patients with non-Hodgkin's lymphoma.29MRI is the imaging modality of choice because it is sensitive in picking up marrow involvement and in detecting mass effect on the spinal cord and spread into the epidural space and paraspinal soft tissue. Moulopoulos and colleagues describe a "wrap-around sign": tumor envelops the cortex

Osteoblastoma is another benign tumor of the spine; it has no predilection for any particular location in the spine.I7 Patients usually present with dull pain, paresthesias, paraparesis, and paraplegia. Scoliosis can be associated with osteoblastoma, although less frequently than with osteoid osteomas, and it may be convex toward the side of the lesion.'O Most commonly, osteoblastomas are expansile with small calcifications and a sclerotic rim.18 The second most frequent radiographic appearance of osteoblastoma is that of a central radiolucent area with surrounding sclerosis that can have central calcification. This is similar in appearance to osteoid osteoma, yet the clinical presentation and curve of the scoliosis may help to differentiate between the two. Also, ostwblastomas are usually bigger and they more commonly extend into the vertebral body. A third possible radiographic appearance of osteoblastoma is that of more aggressive bone destruction, with expansion and extension into adjacent soft tissues.'O CT commonly shows expansile lesions with associated sclerosis; these lesions may also have a chondroid matrix. MR imaging is usually nonspecific yet it is helpful in deterrnining mass effect on the adjacent spinal cord and thecal sac.


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Figure 2 3 4 . A, Sagittal MRI fast spin-echo T2-weighted image through the lumbar spine. A mass is seen posterior to the L4 vertebral body. The mass was biopsied and proved to be lymphoma. B, MRI sagittal spin-echo TI-weighted image through the lumbar spine following the intravenous administration of Gadoteridol. The mass enhances within the spinal canal. C, Axial TI-weighted image through the mass, which is extradural in location, causing mass effect on the adjacent thecal sac. D,Axial TI-weighted image through the mass, after the intravenous ad mini st ratio^ of Gadoteridol.

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Figure -5. A, TI-weighted sagittal hARI image through the lumbar spine showing a Iarge mass anterior ta the spine from TI1 to LA. There is destruction and replacement of the TI1 vertebral body. B, TI-weighted sagittal imm through the thoracic spine showing a large mass anterior to the mid and lower thorack vertebral bodies, which turned out to be lymphoma C, TI-weighted axial image demonstrating an extradural mass that is causing mass effect on the thecal sac on the right. D,TI-weighted &a1 image showing Iymphoma surrounding the vertebral body and extending into the epidural space that surrounds the thecal sac.


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Aneurysmal Bone Cysts

Figure 23-6. Axial CT image showing a lucency of the lamina of TI with surrounding sclerosis, which proved to be an osteoid osteoma.

Aneurysmal bone cysts are seen most commonly in the thoracic spine, followed by the lumbar and cervical spine. Symptoms, including pain and neurologic deficits, are usually associated with mass effect on the spinal cord. Radiographs, CT, and MRI demonstrate an expansile lesion centered in the posterior elements that commonly extends into the vertebral bodies. This lesion is usually lytic as well as expansive, with eggshell-like peripheral calcification (Fig. 23-10). ABCs can cross disk spaces and extend into adjacent structures. Both CT and MRI can evaluate for fluid-fluid levels. MRI is, however, better at showing both the extent of the mass and the mass effect on the spinal cord and nerve roots. A soft tissue rim is often seen on CT. It appears as a rim of decreased signal intensity on all MRI sequences. This rim is a thickened periosteal membrane, which, together with septations, can enhance with gadolinium. Complete resection is the treatment of choice, but it is not always possible because of tumor location and size. Radiation and embolotherapy have also been used as treatment.30

Osteochondromas Signal intensity is usually low to intermediate on TIweighted and intermediate to high on T2-weighted images (Figs. 23-7 and 23-8).** l7

Giant Cell Tumors Giant cell tumors (GCT) in the spine usually involve the sacrum, followed by the thoracic, cervical, and lumbar areas.30 Pain is the most common presenting symptom; however, pain can be accompanied by neurologic deficits.38 GCT usually presents as a large mass with bone destruction and bony expansion. When the sacrum is involved, the sacroiliac joint can be crossed. Within the spine, vertebral bodies are most commonly involved, although giant cell tumors can cross disk spaces and extend into the posterior elements, and they can be associated with vertebral collapse.30 CT reveals a soft tissue attenuation mass, which may have a rim of sclerosis (Fig. 23-9). If hemorrhage is involved, however, a mixed attenuation mass, or possibly fluid-fluid levels, may be seen. MRI usually shows a mass with mixed signal intensity.=. 30 Fluid-fluid levels of various signal intensities may be seen if hemorrhage is present. The signal intensity depends on the age and state of the blood: it may be high on both TI-weighted and T2-weighted images if blood is present. In the absence of hemorrhage, GCTs may have low to intermediate signal intensity on both TI-weighted and T2-weighted images; this may help to differentiate them from other tumors, which usually have increased signal intensity on T2-weighted images.30 Complete resection is the treatment of choice for GCT, yet it is not always possible. Adjuvant radiotherapy is also used. It has been argued that radiation therapy should be used for patients with incomplete excision or for those with 38 local recurren~e.'~.

Osteochondromas of the spine are uncommon. They usually occur within the cervical spine, especially at C2, and like most benign spinal lesions they usually occur in the posterior elements. CT imaging with thin slices is the modality of choice to evaluate osteochondromas. Continuity of the cortex and the marrow between the lesion and the vertebra is visible on CT (Fig. 23-11).30 MRI can also be helpful in identifying mass effect on the spinal canal. Central yellow bone marrow shows high signal intensity on TI-weighted images because of its fat content, and the corresponding signal intensity on T2-weighted images is intermediate (Fig. 23-12).30 Surgical resection is the treatment of choice.

Chordoma Chordoma is an uncommon malignant tumor of the spine arising from a remnant of the notochord. It usually occurs at the sacrococcygeal region or at the skull base. Because it is a slow-growing tumor, chordoma usually presents as a large destructive lesion with an associated large soft tissue mass. Calcifications are commonly seen within the mass on radiographs and CT, and they usually occur peripherally. Attenuation in the center of the mass is low, and it may be higher peripherally.30* 36 Coronal CT images are optimal for evaluating foramen and sacroiliac joint involvement. Advances in multidetector CT and in three-dimensional reconstructive capabilities may be helpful in evaluating the extent of disease. For determining the extent of disease in surrounding soft tissue, however, MRI is superior.35On TI-weighted images, chordoma usually shows low to intermediate signal intensity, and it shows high signal intensity on T2-weighted images because of its high water content (Fig. 23-13).30 Complete excision of the chordoma is necessary because of its poor sensitivity to radiotherapy and chemotherapy, but complete resection is not always possible. Preoperative MRI may help to determine the amount of involvement in the adjacent gluteal muscles; this may be important when Text continued on page 778


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Figure 23-7. A, Sagittal CT reconstructed image demonstrates a lytic lesion of the L3 vertebral body. This lesion proved to be an osteoblastoma. B, Axial CT postmyelogram image in the same patient, showing an expansile lesion of L3 ,olving the pedicle, vertebral body, and lamina of L3. There also associated mass effect on the adjacent thecal sac. C, -weighted sagittal image demonstrating the osteoblastoma th increased signal intensity involving the L3 vertebra. D, -weighted axial image demonstrating the mass, which is intense to muscle. The extension of the osteoblastoma into canal is clearly demonstrated, the image shows the mass ect on the thecal sac.


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Rigure23-S.A,AxialCI C7 dem ratin 1 expansile osteoblastom myelogram through C7 showing the mass involving the vertebral artery foramen on the left. C,T1-weighted sagittal image after injection of contrast material with the enhancing mass involving the left (37 facet. D,T1-weighted axial image throu& xhe osteoblastoma involving the C7 facet and lamina


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Figure 2S9. A, Frontal view of the lumbosacral junction showing giant cell tumor causing bone destruction of the left proximal sacrum and mass eff& on the thecal sac, pushing it to the left. B, Axial CT image after myelogram, demonstrating a destructive soft tissue mass involving the posterior elements of the sacrum and causing mass effect on the thecal sac. C,TI-weighted sagittal image of the lumbar spine clearly demonstrates the giant cell tumor involving the posterior aspect of the sacrum. The mass has mixed signal intensity. Evidence of hemorrhage or fluid-fluid levels is not seen. D, T2-weighted sagittal image of the same giant cell tumor, demonstrating mixed signal intensity. Again, evidence of fluid-fluid levels is not seen. E, TI-weighted axial image of giant cell tumor of the sacrum demonstrating signal intensity that is mixed but higher than that of muscle.


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Figure 23-10. A, Axial CT image demonstrating an expansile aneurysmal bone cyst (ABC) of the L5 vertebral body with some rimlike calcification. The extension of the mass into the spinal canal is not well delineated. B, TI-weighted sagittal image through the lumbar spine, demonstrating the ABC that involves the L5 vertebral body. The mass is mixed in signal intensity and extends into the spinal canal. C, T2-weighted sagittal image of the lumbar spine. The ABC has increased signal intensity, with areas of lower signal intensity within it. D, TI-weighted axial image through the L5 vertebral body after administration of contrast material. An enhancing, expansile ABC with pockets of nonenhancing fluid signal intensity extends into the spinal canal and posterior lateral soft tissues. The septations are enhanced. as stated in the text.


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Figure 23-11. Axial CT image through an osteochonuroma involving the spinous process and lamina of a vertebral body. This image demonstrates continuity of the cortex and marrow between the lesion and the vertebra.

Figure 23-12. A, Axial CT image demonstrating an ostwchondroma that involves the posterior elements of the L1 vertebral body. This mass is not in the typical C2 location, and it is larger than usually seen. There is no definite continuity of cortex and marrow between the mass and L1.B, Axial CT image of L1, showing the same mass with scalloping of the right aspect of the spinous process and calcification within the mass. C, TI-weighted sagittal image to the right of midline. The osteochondroma is mixed in signal intensity. D, T2-weighted image of the lumbar spine shows the same mass having mixed signal intensity. This is a nonspecific appearance. E, T1-weighted axial image of the lumbar spine showing that the mass has mixed signal intensity and does not involve the spinal canal.


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Figure 23-13. A, Plain film AF' d e w of the s m . There is destruction of the inferior and left aspect of the sacrum. B, Lateral plain film of the sacrum demonstrating destruction of the inferior sacrum. C,Axial CT image of the sacrum. The soft tissue mass that is destroying the sacnun has proved to be a cbordoma. This mass is in the usual sacrococcygeal region of the spine. D,T1-weighted sagittal image (with contrwt enhancement) of the sacrum nicely demonstrating the extent of the soft tissue tumor, which exhibits mild enhancement. The mass is causing anterior displacement of the rectum. E, T1-weighted axial image of the sacrum demonstrating the chordoma and its effects on the surrounding tissues.


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chordoma infiltrating the gluteal muscles may account for local recurrence^.^^

present with radicular pain, possible gait disturbance, and sphincter dysfunction. The pain experienced results from the fact that the tumors usually arise on the dorsal sensory nerve root. Neurofibromas and schwannomas are both deChondrosarcoma also ~ h ~ is most~commonly d seenr in the ~thoracic~ rived ~ from ~Schwann ~ cells;~however, ~ neurofibromas ~ have and spine, but it is also found within the posterior elements or Patients with neurofibromatosis type 1 (NF-1) usually the vertebral body. Patients usually have a good prognosis, have intraforaminal nerve sheath tumors extending into the because spinal chondrosarcoma is usually low grade.30 spinal canal in a dumbbell-shaped configuration. Only CT is a sensitive modality for revealing the chondroid matrix characteristic of chondrosarcomas, the bone desmcabout 1.6% of patients with N P I have symptomatic spinal Patients with NF-2 usually have intraspinal intration, and the soft tissue component.^ onCT,the soft tissue and 30% to 40% these patients have component can have decreased attenuation because its waneurologic deficits and symptoms." ter content is higher than that of muscle. which are nonspecific* may show enlargeMRI is helpful for evaluating any associated mass effect ment of the neuroforamen (Fig* 23-14). MRI is the study on the spinal cord and/or extension across disk spaces, of choice for evaluation of these tumors associated with which is seen in 35% of cases.30, 40 B~~~~~ of the water the spine. On TI-weighted images, nerve sheath tumors content of this tumor, signal intensity within the soft tissue component is decreased on ~ 1 - ~ ~ i images g h ~ d are typically isointense to muscle. Increased signal intensity on T2-weighted images is typical for nerve sheath tumors and increased on nmweighted images. me matrix shows whether using conventional SE or FSE imaging.43Postgaddecreased signal intensity on all imaging sequences.30 olinium imaging is commonly used to increase conspicuity W K . of lesions. Nerve sheath tumors commonly enhance Osteosarcoma -"*-,Ls brightly, thereby increasing detection (Figs. 23-15 and 23Osteosarcoma in the spine is rare; it is most cornrno 16). Fat-saturation techniques following administration of seen in the lumbosacral region and usually involves contrast material are also helpful for lesion detection.12 vertebral body eccentrically. On plain films, osteos Total resection of nerve sheath tumors is needed to presents with a 'lense matrix; an ivory vel-tc?bral bo prevent recmence. Neurofibromas have nerve fibers passbe seen. MRI is helpful in determining the extent ing through them and are therefore difficult to remove soft tissue component and its effect On surrounding smc- completely. Schw-omas are usually eccentric in location, tures. If the matrix exhibits dense mineralization, it may making total resection easier. appear to have decreased signal intensity on all MRI sequences. Patients with primary osteosarcoma of the spine have a very poor prognosis, with death usually ensuing paragang/iomaS within 2 years of the diagn0sis.3~ Extra-adrenal paraganghomas are rare, onglnating trom cells of neural crest origin. Usually these tumors are located Ewina's Sarcoma and Permeative at the glomus jugulare or near or within the carotid body. ~euroectodermalTumor Spinal paragangliomas are rare and can be seen in the Ewing's sarcoma and permeative neuroectodermal tuintradural, extramedullary compartment, usually in the lummor (PNET) are radiographically very similar and are usubar spine in the area of the cauda equina.' Rarely, they are ally seen within the sacrococcygeal region. Presenting also seen in the cervical and thoracic spine. symptoms include pain and often bowel and bladder dysParagangliomas of the spine are predominantly of the function. Metastatic foci are more common, yet primary sympathetic type. Patients usually present with symptoms lesions are also seen. These tumors usually occur in parelated to spinal cord or nerve root compression. MRI tients between 10 and 30 years of age.30 The lesion is findings, which are nonspecific, reveal an enhancing lobuusually centered in the vertebral body, and a soft t i s ~ lated or ellipsoid mass that is encapsulated and usually component is commonly present. found in the intradural extramedullary space. ParaganglioMRI is the modality of choice to determine both tuniof mas are usually isointense to the spinal cord on T1extent and involvement of surrounding tissue. The appearweighted imaging and nonhomogeneous on T2-weighted ance of the tumor on MRI, however, is nonspecific. Signal imaging. Generally, paragangliomas are slow growing and intensity is intermediate on TI-weighted images and interbenign.42 m.1 , mediate to high on T2-weighted images.2. l4 Immunohistochemical studies are used-to distinguish between PNET and Ewing's sarcoma. lntradural Extramedullary Metastases Chemotherapy and radiation are the treatments of choice Various types of intradural extramedullary metastases for both entities:~ occur. Drop metastases originate from central nervous system primary neoplasms, such as cerebral glioblastoma, posterior fossa medulloblastoma, anaplastic astrocytoma, lntradural Extramedullarv Tumors &d ependymoma. These are seeded through the cerebrospiNerve Sheath Tumors nal fluid (CSF) from the head. Thev are most commonlv Nerve sheath tumors make up the majority of extramedseen in th;? lu&bar location in the area of the conus rneduiullary tumors within the dural space. Patients commonly laris or the cauda equina. -6

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Chapter 23

Figure 23-14. A, Lateral plain @a of the. cervi

myelography, showing an e x t r a d &ass that is causing mass effect on the sphlal cmd on the hc~ft and extending into the neurofonmm on the l& , C, Gross specimen photograph of a smodh, bilobed schwannoma.

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Nonvisceral neoplasms with CSF seeding include mela noma, lymphoma, and leukemia.47Systemic malignancies such as breast and lung cancer, metastasize to the subarach noid space. When these patients are diagnosed with intradural extramedullary spinal canal metastases, they usually have widespread disease and a very poor prognosis.'O Most of the metastatic lesions are found on the conus medullaris and the cauda equina. Whatever their source, the intradural extramedullary metastatic lesions are usually best seen on postcontrast, T1-weighted MR images of the spine. The lesions are not as well seen on either precontrast TI-weighted images or T2-weighted images; however, these sequences are helpful in evaluating for spinal bone metastasis and spinal cord compression. Therefore, a combination of precontrast and postcontrast images is used to evaluate the spine in patients with suspected intradural extramedullary metastatic dis-

ease. The metastatic lesions are usually seen as nodular enhancing lesions on the conus medullaris and the cauda equina, yet they can occur anywhere along the intradural space of the spinal canal. Abnormally thin extramedullary areas of enhancement may also indicate metastatic disease.1° An intraspinal meningioma can present as an intradural extramedullary mass. As in the head, this mass is isointense to the cord on MRI TI-weighted and T2-weighted images, and it homogeneously enhances after the administration of contrast medium. Enhancement of the adjacent meninges is known as the dural tail sign. Quekel and V e r ~ t e e g e ~ ~ argue that to evaluate spinal meningiomas for the dural tail sign, sagittal, axial, and coronal planes should all be obtained following the administration of gadolinium. The dural tail sign is very suggestive of meningioma. reported on a patient who had Weil and


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Figure 23-15. A, TI-weighted post-contrast-enhanced sagittal image of the cervical spine, demonstrating an enhancing extra-axial mass posterior to C 2 4 3 in a patient with known neurofibromatosis type 1. B, TI-weighted sagittal post-contrastenhanced image through the thoracic spine, with enhancing neurofibromas in the lower thoracic spine. C,TI-weighted axial image showing extra-axial enhancing neurofibromas.


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Figure 2346. A, T1-weighted off-center sagittal image of the cervical spine showing multiple intradural extra-axial neurofibromas. This patient has known neurofibromatosis l. B, T1weighted coronal image of the cervical spine clearly shows multiple extramedullary tumors of the cervical spine. C, TI-weighted postcontrast-enhanced axial image through the Cl-CZ level, demonstrating bilateral enhancing extramedullary neurofibromas in a patient with known neurofibromatosis type 1, #*:* I 4 w r r $., . .. ,.

concurrent intradural and extradural meningiomas in the cervical spine. They recommend that when an epidural meningioma is found on MRI, special attention should be paid to the intradural space to find the high incidence of a concurrent meningioma.

Summary Extramedullary tumors of the spine are usually best imaged with MRI, although CT can sometimes be helpful.

Although the diagnosis is not always apparent, the radiologist can provide vital pretreatment information about the extent of disease and its effects on the spinal cord and nerve roots.

References 1. Aggarwal S, Deck JHN, Kucharczyk W. Neuroendocrinetumor (paraganglioma) of the cauda equina: MR and pathologic findings. AJNR Am J Neuroradiol 14:1003-1007, 1993.


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26. Mirowitz S, Apicella P, Reinus W, Hammerman A: MR imaging of 2. Baba Y, Ohkubo K, Seino N, et al: Osseous primitive neuroectodermal tumor: A case report. Radiat Med 16:297-300, 1998. bone marrow lesions: Relative conspicuousness on TI-weighted, fat3. Bach F, Agerlin N, Sorenson JB, et al: Metastatic spinal cord cornsuppressed T2-weighted, and STIR images. AJR Am J Roentgen01 pression secondary to lung cancer. J Clin Oncol 10:1781, 1992. . 162215-221. 1994. 4. Bach F, M e n BH. Rhode K, et al: Metastatic spinal cord compres27. Moulopoulos LA, Varma DG, Diopoulos MA, et al: Multiple mysion: Occurrence, symptoms, clinical presentations and prognosis in reloma: Spinal MR imaging in patients with untreated newly diagnosed 398 patients with spinal cord compression. Acta Neurochir (Wien)' disease. Radiology 185:833-840, 1992. 107:37, 1990. 28. Moulopoulos LA, Dimopoulos MA, Alexanian R, et al: Multiple 5. Baker L, Goodman S, Perkash I, et al: Benign versus pathologic myeloma: MR patterns of response to treatment. Radiology 193: compression fractures of vertebral bodies: Assessment with conven441446, 1994. tional spin-echo, chemical-shift, and STIR MR imaging. Radiology 29. Moulopoulos LA, Dimopoulos MA, Vourtsi A, et al: Bone lesions 174:495-502, 1990. with soft-tissue mass: Magnetic resonance imaging diagnosis of lym6. Barr J, Barr M, Lemley T, McCann R: Percutaneous vertebroplasty phomatous involvement of the bone marrow versus multiple myeloma for pain relief and spinal stabdimtion. Spine 25:923-928, 2000. and bone metastases. Leuk Lymphoma 34: 179-184, 1999. 30. Murphey M, Andrews C, Flemming D, et ak From the Archives 7. Baur A, Stabler A, Broning R, et al: Diffusion-weighted MR imaging of the AFIP. Primary tumors of the spine: Radiologic-pathologic of bone marrow: Differentiation of benign versus pathologic compression fractures. Radiology 207:349-356, 1998. correlation. Radiographics 16:1131-1158, 1996. 8. Crim JR, Mirra JM,Eckardt JJ, Seeger LL:Widespread inflammatory 31. O'Connor MI, Cunier BL: Metastatic disease of the spine. Orthoperesponse to osteoblastoma: The flare phenomenon. Radiology 177: dics 15:611, 1992. 32. Pui M, Chang S: Comparison of inversion recovery fast spin-echo 835-836, 1990. 9. France1 PC: Exhinsic spinal cord mass lesions. Pediatr Rev 19: (FSE) with T2-weighted fat-saturated FSE and T1-weighted M R imaging in bone marrow lesion detection. Skeletal Radio1 25:149389-395, 1998. 10. Frey I, Le Breton C, Leflcopoulos A, et al: Intradural extramedu~aryE 152, 1996. spinal canal secondary neoplasms: MR findings in 30 patients. Eurb . 33. Quekel LG, Versteege CW: The "dural tail sign" in MRI of spinal Radio1 €21187-1192, 1998. meningiomas. J Compvt Assist Tomog 19890-892. 1995. 11. Gamba JL, Mnninez S, Apple J, et ak Computed tomography of axialf I - 34. Rahmou" A, Divine M, Mathieu D. et al: Detection of multiple skeletal osteoid osteomas. Am J Roentgen01 142769-772, 1984. '? ! myeloma involving the spine: Efficacy of fat-suppression and con12. Georgy BA, Hesselink JR:MR imaging of the spine: Recent advances~. trast-enhanced MR imaging. AJR Am J Roentgen01 160:1049-1052, in pulse sequences and special techniques. AJR Am J Roentgen018 . 1993. 162:923, 1994. 35. Rahmouni A, Divine M, Mathieu D, et al: MR appearance of multiple 13. Gilbert RW, Kim JH,Posner JB: Epidural spinal cord compression myeloma of the spine before and after treatment. AJR Am J Roentfrom metastatic tumor: Diagnosis and treatment. Ann Neurol 3:40, genol 160:1053-1057, 1993. 1978. . Rosenthal DI, Scott JA, Mankin HJ,et al: Sacmoccygeal chordoma: 14. Hashimoto M, Akabane Y, Tete E: Ewing's sarcoma of the sacrum. Magnetic resonance imaging and computed tomography. Am J RoentRadiat Med 17:451-453, 1999. genol l45:143-147, 1985. 15. Khan DC, Malhotra S, Stevens RE, Steinfeld AD: Radiotherapy for 137. Salvati M, Cervoni L, Artico M, et al: Primary spinal epidural nonthe treatment of giant cell tumor of the spine: A report of six cases Hodgkin's lymphoma: A clinical study. Surg Neurol 46:339-343, and review of the literature. Cancer Invest 17:llO-113, 1999. :a1996. ' 16. Kim J, Ryu K, Choi W, et al: Spinal involvement of hematopoietic 38. Sanjay BK, Sim FH,Unni KK, et al: Giant-cell tumours of the spine. J Bone Joint Surg Br 75:148-154, 1993. malignancies and metastasis: Differentiation using MR imaging. Clin Imaging 23: 125-133, 1999. 39. Shi HB, Suh DC, Lee HK, et al: Preoperative transarterial emboliza17. Kroon HM, Schunnans J: Osteoblastorna: Clinical and radiologic ',?' tion of spinal tumor: Embolization techniques and results. AJNR Am findings in 98 new cases. Radiology 175:783-790, 1990. JJ Neuroradiol20:2009-2015, 1999. 18. Kumar R, Guinto FC, Madewell JE,et al: Expansile bone lesions of by, 40. Shives TC, McLeod RA, Unni KK,Schray % Chondrosarcoma of the spine. J Bone Joint Surg Am 71:1158-1165, 1989. the vertebra. Radiographics 8:749-769, 1988. $ 19. Kusumoto S, Jinnai I, Itoh K, et al: Magnetic resonance imaging 41. Simeone FA: Spinal cord tumors in adults. In Youmans JR (ed): patterns in patients with multiple myeloma. Br J Haematol 99:649. b;srNeurological Surgery, 3rd ed, vol 5. Philadelphia, WB Saunders, 655, 1997. , 1990, p 3531. 20. Le Bihan D: Differentiation of benign versus pathologic compression ,:42. Sundgren P, Annertz M, Englund E, et ak Paragangliomas of the fractures with diffusion-weighted MR imaging: A closer step toward spinal canal. Neuroradiology 41:788-794, 1999. the "Holy Grail" of tissue characterization? Radiology 207:305Sze G, Memam M, Oshio K, et al: Fast spin echo imaging in the evaluation of intradural disease of the spine. AJNR Am J Neuroradiol 307, 1998. 21. Lecouvet FE, Vande Berg BC, Michaux L, et al: Stage Jll multiple 13:1383, 1992. myeloma: Clinical and prognostic value of spinal bone marrow MR 44. Thakkar SD, Feigen U, Mautner VF: Spinal tumours in neurofibroimaging. Radiology 209653-660, 1998. matosis cype 1: An MRI study of frequency, multiplicity and variety. Newradiology 41:625629, 1999. 22. Libshia HI, Malthouse SR, Cunningham D, et al: Multiple myeloma: :,i Appearance at MR imaging. Radiology 182833437, 1992. 1' 45. Weil SM, Gewirtz RJ, Tew JM Jr: Concurrent intradural and extra23. Mautner VF, Lindenau M, Hazim W,et al: The newimaging and dural meningiomas of the cervical spine. Neurosurgery 27:629-631, 5; 1990. clinical spectrum of NF2. Neurosurgery 38:880-886, 1996. 24. McLain RF, Weinstein JN: Tumors of the spine. Semin Spine Surg 46 Yonemoto T, Tatezaki S, Takenouchi T, et al: The surgical manage2: 157, 1990. ment of sacmoccygeal chordoma. Cancer 85:878-883, 1999. 25. Meyers SP, Yaw K, Devaney K: Giant celI tumor of the thoracic @Yousem DM. Patrone PM, Grossman RI: Leptomeningeal metastases: spine: MR appearance. AJNR Am J Neuroradiol 15:962-964, 1994. MR evaluation. J Comput Assist Tomogr 14255-261, 1990.

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24 The Spinal Cord Jeffrey L. Sunshine, Scott Kolodny

Classically, evaluation of lesions within the spinal neural axis has been made on the basis of anatomic location. Lesions can be divided into extradural, intradural-extramedullary, and intrmedullary. Intramedullary lesions of the spinal cord, in turn, can be subdivided according to their etiology into (1) ischemic disease; (2) vascular malformations: (3) neoplastic processes; and (4) infectious, inflammatory, and demyelinating diseases. After a brief review of spinal cord anatomy, this chapter focuses on the intramedullary lesions of the spinal cord and their appearances on magnetic resonance imaging (MRI) and, to a lesser extent, on computed tomography (CT) scans.

Anatomy The spinal cord represents a caudal extension of the medulla oblongata; it terminates in the conus medullaris, typically at or just below the thoracolumbar junction in adults. The cord is slightly flattened along its anterior and posterior surfaces and is enlarged in two regions. The cord widens first for the brachial plexus at C3 to T2,then for the lumbar plexus at T9 to T12. The filum terminale represents extension from the conus to the coccyx, and the cauda equina refers to the extension of spinal nerve roots caudally from the conus within the lumbar subarachnoid space. The three-layered meningeal covering of the central nervous system (CNS) is contiguous with the spinal cord, and all lie within the bony spinal canal. The innermost layer, the pia mater, is adherent to the surface of the cord and extends from the lateral surface of the cord to a dural arachnoid membrane, forming the dentate ligaments. The arachnoid membrane remains closely adherent to the outer layer, the dura mater, allowing for a potential subdural space between the two layers. The subarachnoid space remains filled with cerebrospinal fluid (CSF) and is contiguous with the intracranial subarachnoid space. The dura extends to the S2 level, forming the dural (thecal) sac, which is surrounded externally by epidural fat to fill the remainder of the volume of the spinal canal. The gray matter of the spinal cord is located internally, in contradistinction to the gray matter of the brain, and is surrounded by white matter tracts; the proportion of gray matter increases in the cervical and lumbar regions. Both dorsal (sensory) and ventral (motor) roots arise along the entire length of the cord and these unite to form a total of 31 paired spinal nerves. There are 8 cervical, 12 thoracic, 5 lumbar, and 5 sacral roots. The arterial supply to the spinal cord, although variable, can be divided into three major regions.74Branches of the intracranial vertebral artery, cervical vertebral arteries, and cervical trunks produce radicular arteries that form the

predominant blood supply to the ce~icothoracicregion, generally ending after the first several thoracic vertebral segments. A single radicular artery, usually located at approximately the 7'7 level, supplies the midthoracic cord. This represents the smallest territorial division and typically extends from T4 through T8. The artery of Adamkiewicz, which arises from a low thoracic or upper lumbar artery, supplies the final thoracolumbar region. This important artery usually arises from an intercostal branch in the region of T9 to T12. In a few people, it may arise from a branch at a higher level but then the conus medullaris can be additionally supplied from a lower and smaller radicular artery. Least often, the artery of Adamkiewicz arises from the upper lumbar arteries. At the levels of the spinal cord, radicular branches enter the spinal canal through the neural foramina and lead to the anterior as well as to the paired posterior spinal arteries on the cord surface. These spinal arteries in turn generate a rich anastornotic arcade, with the anterior artery supplying the central gray matter and the posterior arteries feeding the dorsal columns and posterior peripheral white matter. Modem MRI machines and the newer gradient sequences allow excellent anatomic depiction of the arteries and veins of the spinal cord without the need to rely solely on catheter-based conventional angiograms.ll

Ischemia Spinal cord ischemia can arise and lead to infarction for a variety of reasons, including trauma to or dissection of the arterial supply, atherosclerotic and embolic disease, hypotension (e.g., cardiac arrest), complications of thoracoabdominal surgery or spinal angiography, vasculitis, hypercoagulation diseases, and spontaneous idiopathic incidence. More rarely, cord ischemia and infarcts arise or to hypercoasecondary to vascular malformations10z108 gulation diseases as in patients harboring antiphospholipid antibodies.'" Spinal cord infarction can be iatrogenic, resulting from neurosurgical procedures performed with the patient in a sitting positiong0or as a result of wayward migration of embolic materials during endovascular interventions." In addition to dissection of direct arterial supply to the cord, dissection or high-grade stenoses involving larger proximal vessels, such as the vertebral artery, have In patients who have underalso caused cord infar~tion.4.'~' gone trauma, the presence of intramedullary hemorrhage (Fig. 24-1) portends less chance of recovering motor activation and a good functional o ~ t c o m e . ~ ' . ~ ~ Spinal cord ischemia has been described in four progres-


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Figure %I. Spinal cord trauma with intramedullary hemorrhage. A, Axial CT section reveals the comminuted fracture of the vertebra and posterior elements with compression of the spinal canal. B, Sagittal CT reconstruction shows the anterior fracture of C5 and the posterior displacement of bone into the spinal canal. C,TI-weighted sagittal MR demonstrates the abnormal hypointense marrow signal in C5 from edema as well as the mild loss of height and again the posterior extension. No definite cord abnormality is seen. D, This axial FLASH (fast low-angle shot) TZweighted section reveals two foci of abnormal hypointense regions within the cord from acute blood products.

sive patterns, best seen on T2-weighted axial MR images. The most descriptive and smallest insult produces hyperintensity limited to the paired anterior horns of the central gray matter in a pattern that has been descriptively labeled "owl's eyes."74 Next, the paired posterior horns of the gray matter are involved in a pattern reminiscent of a butterfly

(Fig. 24-2). When the insult becomes more severe, the damage extends laterally to involve the corticospinal tracts. Finally, in the worst situations, the entire area of the cord can be homogeneously affected (Fig. 24-3). Insults that cause a change of signal intensity limited to the anterior horns most often have a better functional outcome, and


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Chapter 24

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Figure 24-2. Cord infarction. A, T1weighted sagittal MR image shows no definite intramedullary abnormality. B, TZweighted sagittal MR image reveals marked focal hyperintensity along the central and posterior cord centered at C5. C, A gradient-echo, FLASH (fast low-angle shot), T2-weighted axial section demonstrates the butterfly pattern of cord infarction involving the bilateral anterior and posterior horns of the gray matter.

indeed embolic events to spinal arteries arising during catheter angiography have been reported to resolve span@ neo~sly.~~ TI-weighted images best demonstrate associated swelling, particularly the associated enlargement of the cord.47 Gadolinium-enhanced TI-weighted images show disruptior, of the blood-brain barrier in the late acute and subacute phases of infarction. This disruption tends to involve thc peripheral margins of the central gray matter, whereas in anterior cord syndrome the ventral margins tend to be involved more than the peripheral, probably as a resul of the posterior collateral ~ u p p l y . ~MRI, ' . ~ ~ especially T2weighted images, demonstrates associated abnormalities of the aorta and of adjacent vertebral b ~ d i e s . ~ ~ . ' ~ '

Vascular Malformations Vascular malformations of and around the spinal cord have been variously classified as (1) dural arteriovenous

fistulas (AVFs), (2) perirnedullary intradural or cord AWs, (3) cavernous angiomas, and (4) spinal cord arteriovenous malformations (AVMs). Diagnosis of these malformations has been improved tremendously with the application of MRI techniques that enable the reliable demonstration of the primary vascular lesion and the secondary cord edema and myelopathy. Until very recently, diagnosis required c o n ~ a t i o by n demonstration of the primary vasculopathy with conventional spinal angiograms, but the advent of contrast-enhancedMR angiography has invasive demonstration of the lesion^.^, 9. lop 72 71v

Spinal Cord Arteriovenous Malformations Cord AVMs are congenital in origin and are%~~osed of the typical xiidus of abnormal vessels arising I I U ~arterial feeders that then lead directly to hypertensive "arterialized" venous drainage. Those with a typically compact, wholly intramedullary nidus have been termed glornus


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Figure 24-3. Cord infarction. A, T1-weighted sagittal h& image shows cord expansion begin& at C< and extending to C7. B, The nweighted sagittal MR image demonstrates the expansion as well as increased signal centrally at the same levels. C-E, Sequentially lower sections though the infarct show the n o d cord (C); the widened cord (DLand the homogeneous hv~erintensity of the central 'g& matter (E) o i these &H, T2weighted axial slices.


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Figure 24-4. Intramedullary glomus arteriovenous malformation. A, TI-weighted sagittal MR image shows conus expansion around a central hypointensity that demonstrates heterogeneous signal. B, T2-weighted sagittal MR image demonstrates a greater heterogeneity and the more inferior extension of an enlarged curvilinear flow void probably representing a dilated draining vein. C, Angiographic image reveals the serpentine arterial input that enters the nidus from above and the dilated curvilinear draining vein below.

AVMs (Fig. 24-4), and those with a looser configuration that often extends into the extramedullary spaces have been labeled juvenile-type AVMS.~In rare instances, these malformations occur in conjunction with vertebral angiomas and skin nevi, all at the same metarneric level; this is called the Cobb syndrome.80 AVMs present a risk of hemorrhage and ensuing complications as well as effects of venous hypertension, which may include spinal cord edema, ischemia, or infarct. Indeed, this is the only subset of vascular malformations that show associated spinal artery aneurysm formation, most likely the result of long-standing high flow. When such aneurysms occur, they frequently hem~rrhage.~ MRI can often be used to detect spinal AVMs when the effects of high flow, signal changes about the nidus, hemorrhage, and edema are readily apparent6' In addition, the telltale curvilinear filling defects can be seen on CT

rnyel~graphy.~~ Spinal AVMs that occur within the cord substance can be complicated by associated infarct that appears bright on T2-weighted images and enhances with gad~linium.'~~ If spinal AVMs spontaneously thrombose (Foix-Alajouanine syndrome), an associated cord ischemia can occur, leading to cord infarct.lo2Even greater sensitivity for the lesions, and in particular for the shunt, is gained through application of dynamic MRI using a T2-weighted sequence and tracking of a gadolinium Spinal AVFs are the more common spinal cord vascular malformations; they are subdivided into malformations involving only the dural branches of a radicular artery (dural AVFs) and those arising directly from the spinal arteries (intradural AVFs), Dural AVFs are probably acquired, whereas intradural AVFs are thought to be congenital. The larger congenital lesions often present in childhood with hemorrhage of focal neurologic deficits.lw


Dural Arteriovenous Fistulas

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Dural AVFs, whose point of shunt is within the dural surface, comprise the majority of all spinal vascular malformation~?~ The resultant venous engorgement can produce venous hypertensive changes in the spinal cord, often in the midthoracic to upper lumbar region, that in turn induce cord myelopathy. The myelopathic changes, both clinically and on MR images, can occur distal to the level of the fistula; this can become particularly disorienting near the cervicomedullary junction, where the fistula can be intracranial but the myelopathy cervical to thoracic or vice versa.s- I*. 33' 92 Disruption of such a fistula can produce subarachnoid hemorrhage at a distance from the lesi0n.4~ MRI typically shows hyperintensity on T2-weighted images, possible cord enlargement, and, at times, cord enhancement secondary to infarct.@The high vascular flow usually produces the expected flow voids in the vicinity of the fistula on MR images or dilated vessels on m y e l o r phy.4' Of interest, a surrounding peripheral rim of hypo tensity on T2-weighted images has been reported with these fistulas, which may be specific in the absence of CT can be used to evaluate these associated hem~rrhage?~ fistulas immediatelv after endovascular embolization to confirm occlusion of the entire shunt.20

lntradural Arteriovenous Fistulas Intradural AVFs lie on the cord surface, where they are further subdivided by size: type I, small; type 11, larger, with dilatation of the artery and vein; and type 111, largest, with multiple feeders and marked venous dilatati~n.~ A variant on this classification defines type I as those draining only to meningeal veins, type II to meningeal veins and then retrograde to subarachnoid veins, and type 111 to subarachnoid veins only.' On MRI examinations, these lesions often appear with cord enlargement, edema, hyperintense signal on T2-weighted images, areas of enhanceIz2 Spiral or multislice ment, and abnormal flow CT scanners enable precise localization of the fistula, which allows a greater degree of treatment planning, particularly demonstrating the relationship to surrounding bone.48

Cavemous Angiomas Cavernous angiomas are most often intramedullary, and the risk to the patient is of hemorrhage into functioning tissues. Cavemous angiomas can be found at any cord level, and they are multiple in a significant minority of cases.22.Iz7 These angiomas show a typical reticulated pattern of heterogeneous signal intensity on all MR sequences, producing the classic "popcorn" appearance best demonstrated on T2-weighted sequences.I5This pattern, in association with a family history, other lesions in the neural axis, and a tendency toward diminished signal intensity over time, can confirm the diagnosis.'=

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Intramedullary neoplasms consist of (1) primary cord neoplasms (e.g., ependymomas and astrocytomas) and, to

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1 lesser extent, (2) hemangioblastomas, (3) intramedullary metastases, and (4) other even less common entities (e.g., intramedullary lipomas). In adults, intramedullary neoplasms comprise 7% to 22% of all spinal neoplasms and include, in decreasing order of frequency, ependymomas (65%); astrocytomas (25%); glioblastoma (7.5%); and rare hemangioblastomas, oligodendrogliomas, and metastases?'. '05. '09. "3 Intrarnedullary metastases are usually not neural in origin; lung cancer is the most common primary tumor to metastasize to the cord, followed by breast cancer. Lymphoma, colon and renal tumors, head and neck carcinoma, and melanoma also metastasize to the cord but less comm ~ n l y .a~ ~ ~43. In children, intramedullary lesions account for one third of spinal neoplasms and include astrocytomas (58%), ependymomas (28.5%), teratomas, and dermoid or epidermoid tumors (5.8%). Hemangioblastomas and intramedullary metastases, such as glioblastoma, primitive neuroectodermal tumor, r Wilms' tumor, occur infrequently in the spinal cords

Diffuse fusiform or focal expansion of the cord with loss of the normal cord contour and resultant distortion of the surrounding subarachnoid space is the hallmark of intramedullary tumors on MR images as they are on CT myelograms. Differentiation between the white matter tracts and the butterfly or H-shaped central gray matter may often be obtained with high-resolution MRI."2 MRI can also be used to demonstrate the longitudinal extent of abnormal signal and enhancement as well as the internal derangement of spinal parenchymal architecture. These abilities have established the superiority of MRI over other neuroimaging techniaues in the evaluation of intramedullary processes. Traditionally, CT myelography demonstrated intramedullary masses as expansile lesions of the spinal cord, displacing the intrathecal contrast material within the subarachnoid space peripherally; occasionally, however, intramedullary lesions are not shown to expand the cord. One series noted a normal myelographic appearance in 42% of patients with intramedullary neopla~ms.4~ Abnormal signal on standard or fast spin-echo n-weighted images and abnormal contrast enhancement confirm the presence of intramedullary neoplasms on MRI despite lack of cord expansion.li8 Exophytic growth of intramedullary lesions, most commonly in the region of the conus medullaris, may result in both focal cord expansion and cord displacement by the exophytic process. Exophytic growth of intramedullary lesions has been described in astrocytomas, mixed ghomas, ependymomas, and hemangioblastomas. With early imaging and contrast enhancement, it is possible to locate intramedullary parenchymal lesions within specific quadrants of the spinal cord or within the central canal of the cord. Intrarnedullary neoplasms, however, are usually relatively large when initially imaged, and they distort the parenchyma of the cord over the length of several segments. Signal intensity changes of most intramedullary processes are nonspecific, and it is often impossible on unenhanced MRI to differentiate neoplasm from associated edema or postoperative gliosis because of similar nonspecific T1 anhT2_ kpgthening,". 94, "0, lZ9 Tnmx


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Ependymomas appear isodense to hypodense on nonenand edema have similar MRI characteristics, whereas asso nced spinal CT and enhance after the intravenous (IV) ciated cysts may become more hyperintense on T2administration of contrast material. Although calcification weighted sequences than the adjacent abnormal cord. Feahas been reported to be common in posterior fossa and tures that help distinguish tumor-related cysts from syringes supratentorid ependymomas, it has not been commonly include abrupt changes in diameter and position of the cyst, uneven thickness of the surrounding cord, increased T2- observed in spinal cord ependymomas. Ependymomas of the cauda equina are reasonably characteristic, usually apweighted signal of tumor cysts, and pathologic enhancepearing as a spherical mass centrally within the spinal ment.Io6.lZ6 Cystic lesions associated with tumor, however, canal. After administration of a water-soluble contrast mav not be well defined without contrast administrati~n.'~*~~ agent, myelographic and postmyelographic CT scans demh e r administration of contrast, there is striking and onstrate the nerve roots of the cauda equina above and immediate enhancement of most intramedullary neoplasms below the tumor mass, thus delineating the conus as sepaon both CT scans and MR images. The focus of enhancerate from the mass. ment is usually smaller than the region of abnormal signal The MRI appearance of spinal ependymomas is variand spinal cord enlargement defined on the unenhanced able, depending on the location within the spinal cord. In ~ "I"~ views, helping to localize the actual neoplastic f o ~ u s . 79+ the cervical and thoracic regions, they appear as expansile ~ccasiona~l~,~lesions fail to enhance and may be identified lesions of the cord in the sagittal and axial planes and are by abnormal signal intensity only. slightly hypointense on TI-weighted images and hyperinUnfortunately, enhancement patterns are nonspecific, altense on T2-weighted images. In addition, intratumoral cyst though astrocytomas tend to enhance in a more irregular cavities have occasionally been reported in these locamanner compared with ependymomas or hemangioblastot i o n ~ .In ' ~the ~ cauda equina region, the tumors are typically mas and are often eccentrically located. Cystic degeneraspherical masses witk signal intensities similar to those tion tends to indicate astrocytoma, whereas signal changes consistent with pigment or fatlcalcium tend to indicate found elsewhere (Fig. 24-5). Because of possible episodes melanoma or teratoma, re~pectively.~~ of rebleeding from the fibrovascular stroma, however, reEpendymomas and peated episodes of subarachnoid hemorrhage may lead to hemangioblastomas both enhance homogeneously and are hemosiderin deposition within the subarachnoid space. This more likely to be associated with cysts and syringes. Up to appears as areas of marked hypointensity on T2-weighted 75% of hemangioblastomas are cystic, and draining veins images.'32Gadolinium enhancement is generally in a homoand cord edema, probably secondary to vascular shuntgeneous, well-circumscribed pattern, renderin the lesion related congestionLmay also be seen in hemangioblastomas.2L44. 89. Heterogeneous signal on T1-weighted and more conspicuoug ---I .>I + 1 - 'I.~II T2-weighted images, hypointensity at the tumor margins .:I It. I ., resulting from firm pseudocapsule formation, and intratuAstrocytomas moral hypointensity from hemorrhage suggest ependyr n ~ m a .86~ ~ . Astrocytomas represent one third of intramedullary gliomas and may occur at any location along the cord. They are most common between 20 and 50 years of age and are slightly more common in men. Seventy-five percent of these tumors are low-grade (grade I or 11). Astrocytomas tend to occur in the cervical i d thoracic segments, where Ependymomas represent 65% of spinal cord neoplasms. they have an incidence equal to or greater than that of They are found more commonly in men and usually present ependymomas. In children, the proportional incidence of between 20 and 60 years of age. They represent the most astrocytomas to ependymomas is higher than that in common glial tumor of the lower cord. Three quarters are adults.'32 myxopapillary subtypes and arise within the conus or filum Intratumoral cysts within astrocytomas, as well as syrinterminale, and the remainder are found in the cervical gomyelia at one or both ends of the cord associated with and thoracic cords. Ependyrnomas within the cervical and astrocytomas, occur with variable incidences. Most astrocythoracic cords are generally indistinguishable from astrocytomas are solitary tumors, but they can be multiple in the tomas; however, astrocytomas are far more common in the case of neurofibromatosis. Histologically, the low-grade cervical cord and slightly more common in the thoracic tumors are fibrillary astrocytomas with Slocytic features. cord than ependym0mas.7~ On noncontrast CT scans, astrocytomas of the spinal cord ~ ~ e n d y m o m are a s usually histologically benign and appear as hypointense to isointense lesions.85After adminslowly growing, which generally allows them to reach a istration of IV contrast material. these lesions often enlarge size by the time they manifest clinically. They may hance heterogeneously, with nonenhancing portions of tuspan one to five vertebral body segments and are highly mor representing intratumoral cyst ca~ities."~ Water-soluble vascular, often resulting in intratumoral hemorrhage that myelographic scans demonstrate fusiform enlargement of can be visualized on imaging.'32They may be large enough the spinal cord, with focal nodules or abrupt changes in to produce marked expansion of the spinal canal, and the size indicating the likelihood that the cord mass represents vertebral bodies on either side of the-disk may be excaa tumor and not a syrinx. Syringes at either end of the vated, with the pedicles and neural arches eroded. Smaller tumor generally have a sausage-like appearance, being uniependymomas tend to displace nerve roots, whereas larger formly expanded and lacking any focal nodules. Calcificatumors tend to engulf adjacent nerve roots and may become tion within astrocytic tumors of the spinal cord is not indistinguishable from them. common.132

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Figure 2 4 5 . Conus myxopapilk oma. A, T1-weighted sagittal MR image shows a hypointense expansion of the conus. B, T2-weighted sagittal MR image demonstrates an exophytic cystic lesion of the conus that contains a fluid-fluid level.

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MRI is the best way to demonstrate enlargement of the spinal cord by an astrocytoma (Fig. 24-6). Sagittal and axial plane images demonstrate expansion of the cord. TIweighted images demonstrate astrocytomas to be low in signal intensity whereas proton-density-weighted and T2weighted images show them to be high in signal intensity.107.129 Intratumoral cysts are irregular areas; their contents reflect a signal intensity similar to that of CSF. Syrinxes at either end of the tumor demonstrate parallel walls, and their contents also demonstrate signal intensity similar to that of CSF. Axial images demonstrate the asymmetrical expansion of the cord by tumor tissue. Astrocytomas tend to enhance more heterogeneously than ependymomas, partly because of the high incidence of intratumoral cysts, and N gadolinium administration aids in the detection and characterization of astrocytomas."

Hemangioblastomas Hemangioblastomas are uncommon tumors of the spinal cord, representing 1.6% to 3.6% of spinal cord tumors; they are most often found in association with von HippelLindau disease.132They are usually found in middle-aged adults, demonstrate no sexual predilection, and are solitary in 80%of cases. Although they are usually solitary, hemangioblastomas may be multiple in von Hippel-Lindau dis-

ease. Approximately 50% of hemangioblastomas are cystic with a mural tumor nodule. The cysts are often high in protein content and are suggestive of prior episodes of The tumors may arise in the cervical or thoracic cord, usually causing diffuse focal widening of the cord. On nonenhanced CT scans, the tumor nidus appears isodense to slightly hyperdense in attenuation, and after administration of N contrast material, the tumor markedly enhances; the enhancing tumor nodule appears distinct from the associated cyst. On contrast myelographic scans, the spinal cord appears enlarged with multiple serpentine filling defects from arteries and veins that result from this relatively vascular tumor.132 MR images demonstrate an enlarged, infiltrated spinal cord, and in half the cases a cyst containing a mural nodule can be identified. A large syrinx may also accompany the tumor, helping to support the diagnosis.94 Gadolinium enhancement (Fig. 24-7) is the most useful technique to differentiate the mural tumor nidus from the associated reactive, cystic changes.". I16. II-~IL.. i A 4

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Figure 24-5. Continued, C. A postcontrast T1-weighted sagittal MR iniage shows the sharp rim enhancement of the tumor. D and E, A postcontrast T1-weighted axial section demonstrates compression of the conus by the enhancing cystic mass. I&=

rare, even when there are metastatic lesions to other spinal structures, such as the vertebral bodies and the epidural space.= Of the tumors of non-neurogenic origin metastasizing to the cord, lung carcinoma is the most common (Fig. M ) ,and breast carcinoma is the second most common. Other reported primary tumors are much less common; they include lymphoma, melanoma, colorectal carcinoma, Hodgkin's disease, head and neck carcinoma, and leukemia.99 Drop metastases from primary brain tumors can seed down the central canal of the spinal cord and produce an appearance similar to that of an intrarnedullary metastasis. These metastases are usually from malignant gliomas, ependymomas, medulloblastomas, and pineal tumors. Although apparent on CT myelograms, these, like other lesions, are best detected by MRI with contrast enhancement.% In most instances, the intramedullary metastatic lesion

is small and does not produce significant mass effect. Therefore, a discernible change in the size of the spinal cord cannot be noticed on either contrast-enhanced myelographic or postmyelogram CT scans.'" In a few instances, focal enlargement of the cord may be sufficient to be seen by either modality. MRI is the best technique for evaluating intsamedullary spinal cord metastatic lesions. Enlargement of the spinal cord, even when subtle, is best seen on TI-weighted images in the sagittal plane and is the first indication of an intramedullary lesion. Lesions are hyperintense on T2-weighted images and generally enhance heterogeneously after IV gadolinium administration (Fig. 24-9). T2-weighted signal intensity changes and abnormal enhancement can be seen in the absence of cord enlargement.99 Subsequent to the intramedullary metastasis, a blockage and then dilatation of the central canal can occur, producing a typical syrinx in association with the Text continued on page 796

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Fignre 24-6. Cord astrocytoma. A, TI-weighted sagittal MR image shows marked expansion of the cervical cord by a large cystic lesion. B, T2-weighted, fast spin-echo, sagittal MR image confirms the cystic nature of the mass and better demonstrates the long inferior extent of the associated cystic syrinx. C, Postcontrast TI-weighted sagittal MR image reveals the heterogeneous nodular enhancement within the larger cervical cyst. D,Postcontrast TI-weighted axial section demonstrates the homogeneous enhancement of the solid comnonent. E, T1-weighted axial section lower in the cord confirms the central svrinx.


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tiit JI& ~ ~ d s?(ndtome. a 4 u P&trast ~ ~ s@ttaL - image af w &e ~ e d c~ a l s p h S$QW~S~& p@Tj~@ pXiphBrd & & i % ~ a n o % k k at the f26-7 b e l . B, Postwatmst Tl-wei&td sagittal M R image of rfie lurmb-ar spine Ide!m~mmresan enhancing nodule &She: tip d thr:wm. C,PQS%OUtrast T I - w e i w d-OII reveals the solid enhan&le .within the peripheral substance of the conas meduIlaris.

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Figure 24-9. Hematogenous metastasis to the conus medullaris from lung carcinoma. A, TI-weighted sagittal MR image shows expansion of the inferior cord. B, T2-weighted sagittal MR image demonstrates abnormal hyperintense signal in the conus and a more focal area of greater signal intensity. C,Postcontrast TI-weighted sagittal MR image shows heterogeneous enhancement extending over the length of more than one vertebral body of the lower cord. D, A gradient-echo, FLASH (fast low-angle shot), TZ-weighted axial section confirms cord expansion and the cenfxd signal intensity abnormality. E, Postcontrast TI-weighted axial section highlights a focal area of ater enhancement.

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Infection, Inflammation, and Demyelination Infectious diseases typically occur around the spinal :ord, as in osteomyelitis, diskitis, and epidural abscesses, but more rarely they can involve the intramedullary substance. Cord infection can be expected to produce decreased signal with T1 weighting, increased intensity on -weighted images, and early variable enhancement with adolinium, representing myelitis or abscess.83 These le$ions occur as a result of hematogenous dissemination and x-' .:-' , can arise, for example, from typical pyogenic bacteria, ' #I4-. :- . ' in syphilis or in tuberculo~is.~~. s4 The myelitis can have " associated enhancement that may resolve after successful antimicrobial therapy, whereas frank abscesses can show typical rim enhan~ement.~'.84 A congenital lesion, such as , , a dermal sinus, can allow formation of an unusually high I number of intramedullary abscesses.= Intramedullary involvement in the prototypical granuloatous diseases, tuberculosis and sarcoidosis, is rare. When the cord is involved in tuberculosis, an enhancing intramedullary tuberculoma is expected, but fewer than 150 examples have been reported among patients with normal immune systems.'01In patients with acquired immunodeficiency syndrome (AIDS), this entity may arise slightly more often, but the tuberculoma has a nonspecific appearance, its signal intensity is decreased on TI-weighted images and increased on T2-weighted images, and peripheral or nodular enhancement is seen.76 Very rarely, a frank abscess within the cord arises, at times in association with . j eningitis of t~berculosis."~ CNS involvement in systemic sarcoidosis occurs in - y about 5% of patients, but direct primary cord lesions have

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been reported in fewer than 100 cases. In the cord, this disease also has a nonspecific appearance, with cord en. largement and multifocal patchy areas of enhancement, again frequently in association with meningiti~.~'These lesions should resolve, however, after appropriate steroid therapy, perhaps with the exception of infrequently reported I* central ~alcifications.9~. Parasitic myelitis can produce a similar appearance ir association with a CSF e~sinophilia.~~ Although rare, typi. cal parasitic diseases have been reported to involve thc spinal cord: schisto~omiasis,2~ toxoplasmosis in patient! with lo3 and cysticercosis. When schistosomiasi~ invades the cord, it can cause a nonspecific myelitis, or tht ova can induce formation of granulomas that can be identified on CT myelogra~ns.~~ In patients with cysticercosis, syringomyelia or cystic intramedullary lesions can be present and are associated with brain parenchymal lesions.68 Involvement of the spinal cord as a direct result of fu I disease occurs only rarely and typically only in those witk significant immune compromise. Aspergillosis is the mos common fungal disease of the cord, typically presenting as a myelopathy but also reported as occluding principally thc anterior spinal artery.59.% Cord abscesses caused by Can. dida, Coccidioides, and Nocardia have been reported. " Similarly, cord granulomas caused by Cryptococcus anc Histoplasma have been described in isolated reports.55.'I4 Viral infections of the spinal cord are encountered mos often among patients with immune compromise. In patient: with AIDS, intramedullary infection with human immuno deficiency virus type I (HIV-1) causes a vacuolar myelopa thy that shows nonspecific hyperintensity on T2-weightec images.3.124 Herpes zoster typically affects the skin but car produce a myelitis that shows cord enlargement, hyperin

Figure 24-10. Degenerative changes of the spine with cord effect. A, T2-weighted FLASH (fast low-angle shot) axial section demonstrates a posterior disk-osteophyte complex impressing upon the thecal sac and the central cord. B, T2weighted fast spin-echo sagittal MR image confirms the degenerative changes along the posterior vertebral line and demonstrates nonspecific abnormal hyperintensity within the substance of the cord at the C6 level.

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tensity on T2-weighted images, and variable enhancement.38.5L Cord involvement by the Epstein-Barr virus has been reported as either encephalomyelitis or isolated myelitis, demonstrating the same nonspecific findings as the preceding viral di~orders.'~.~~ Degenerative and demyelinating disorders can cause an acute transverse myelitis, or myelopathy. When the spinal canal narrows because of degenerative changes in the bones, joints, and disks, pressure to the cord can occur that will cause myelopathic changes visible on MR images (Fig. 24-10). The causes are uncertain and may include edema, idammation, ischemia, or gli0sis.7~ The lesions of multiple sclerosis, the prototypical demyelinating disease, tend to be located at the cervical level, although they can be found throughout the medullary substance, whereas the lesions of idiopathic myelitis tend to appear at the thoracic level^.'^.^^ The lesions of multiple sclerosis often demonstrate multiplicity within the CNS, underscoring the need for separation in time and space to diagnose this multiphasic disease. In contrast, acute disseminated encephalomyelitis arises as a monophasic illness after exposure to a viral vaccine; multifocal plaques may appear, but they do not recur after improvement, which is slow." In the rare instances when these plaques do recur in the absence of a diagnosis of multiple sclerosis, other autoimmune disorders, perhaps

Figure 24-11. Multiple sclerosis plaque. A, A FLAIR (fluid-attenuated inversion recovery) sagittal MR image shows the lesion within the anterior cord centered at the third thoracic vertebra. B, The same lesion is even better demonstrated by the fast spin-echo T2-weighted sequence, and its appearance is not significantly diminished because of the high signal from the surrounding cerebrospinal fluid.

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involving the presence of anti-cardiolipin antibodies, may be considered.I4 A delayed postradiation myelopathy can occur, but the diagnosis remains one of exclusion, with nonspecificity of the signal changes and enhancement on MR images.58Collagen vascular diseases, in particular in 1%to 2% of patients with systemic lupus erythematosus, can also cause a transverse myelitis that rarely affects the entire ~ o r d . ~ ~ . ~ ~ Unfortunately, the lesions of all these disorders have a similar appearance: hyperintense plaques within the cord substance on T2-weighted images, possible cord enlargement, and possible enhancement. Only the spinal cord enlargement can be well seen on CT scans; thus, the modality of choice is MRI, in which the absence of cord expansion has become the best predictor of a non-neoplastic cause to an unknown cord le~ion.~',~~ These lesions are best depicted with fast STIR (short tau inversion recovery) sequences, and in contrast to similar lesions in the brain, they are not well demonstrated by FLAIR (fluid-attenuated inversion recovery) sequences (Fig. 24-1 in multiple sclerosis, the most common source of myelitis seen in the United States, lesions tend to occur in multiples (Fig. 24-12), to be eccentrically located (Fig. 24-13), to involve less than half the cross-sectional area of the cord, and to extend less than two vertebral bodies in length.120


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Figure 24-12. Multiplicity of multiple sclerosis plaques. A and B, These fast spin-echo, =-weighted MR images reveal a larger ovoid area of hyperintensity centered at C5 (A), and a second smaller, rounded lesion more superiorly at the level of C2C3. C, An axial FLASH (fast low-angle shot) gradient-echo sequence produced this axial image showing two side-by-side lesions, the larger to the patient's right.

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Figure 24-13. Eccentricity of multiple sclerosis plaques. A. A STIR (short tau inversion recovery) sagittal MR image shows a broad ovoid hyperintensity along the anterior cord at C4. B, The postcontrast TI-weighted ' sagittal MR image reveals eccentric anterior rim a hancement. C, The postcontrast T1-weighted axial section demonstrates a low level of rim enhancement eccentrically positioned in the right anterior quarter of the cord.

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Figure 24-14. Systemic lupus erythematosus. A, TI-weighted sagittal MR images demonstrate cord enlargement at the conus. B, FLASH (fast low-angle shot) gradient-echo axial section shows abnormal hyperintense signal of the central gray matter consistent with cord ischemia secondary to a lupus vasculitis. C,A high 'l2weighted axial section from the cervicomedullary junction shows similar abnormal signal in the bilateral posterior substance

The relevance of enhancement depends on the underlying cause. In infection, it represents a more mature myelitis moving toward abscess; in demyelination, it represents acuity of the process with concurrent active destruction of m ~ e l i nSome . ~ ~ have reported an increased specificity when diagnosing lesions after gadolinium enhancement in multi-

ple sclerosis.121Yet, any or all of these findings, including abnormal signal, cord thickening, and enhancement, can be seen in each of these disorders, even the more rare manifestations such as lupus'00; indeed, some, as in lupus, may even appear indistinct from other causes of spinal cord infarct on MR images (Fig. 24-14).


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References 1. Banuelos AE Wffliams PI,, Johnson RH, et al: Central nervous system abscesses due to Coccidioides species. Clin Infect Dis 22: 240-250. 1996. Bao YH, Ling F: Classification and therapeutic modalities of spinal vascular malformations in 80 patients. Neurosurgery 40:75-81. 1997. 3. Barakos JA, Mark AS, Dillon WP,Norman D.MR imaging of acute transverse myelitis and AIDS myelopathy. J Comput Assist T o m 14:45-50, 1990. 4. Bergqvist CA, Goldberg HI, Thomensen 0,Bird SJ: Posterior cervical spinal cord infarction following vertebral artery dissection. Neurology 48: 1112-1 115, 1997. Binkert CA, Kollias SS, Valavanis A: Spinal cord vascular disease: Characterization with fast threedimensional contrastenhanced MR angiography. AJNR Am J Neuroradiol 20:1785-1793, 1999. Biondi A, Merland JJ, Hodes JE,et al: Aneurysms of spinal arteries associated with intramedullary arteriovenousmalformations: I. Angiographic and clinical aspects. AJNR Am J Neuroradiol 13:913922, 1992. Borden JA, Wu JK, Shucart WA: A proposed classification for spinal and c m a l dural arteriovenous fistulous malformations and implications for treatment [published erratum appears in J Neurosurg 82705-706, 19951. J Neurosurg 82166-179, 1995. Bousson V: Inmacranial dural fistula as a cause of diffuse MR enhancement of the cervical spinal cord. J Neurol Neurosurg Psychiatry 67:227-230, 1999. 9. Bowen BC: Spinal dural arteriovenous fistulas: Evaluation with MR angiography. AJNR Am J Neuroradiol 1632029-2043, 1995. 10. Bowen BC: MR angiography of the spine. Magn Reson Imaging Clin North Am (5165-178, 1998. 11. Bowen BC: Vascular anatomy and disorders of the lumbar spine and spinal cord. Magn Reson Imaging Clin North Am 7555-571, 1999. 12. Brunberg JA, Dietro MA, Venes JL, et ak Intramedullary lesions of the pediatric spinal cord: Correlation of findings from MR imaging, intraoperative sonography, surgery, and histologic study. Radiology 181:573-579. 1991. 13. Caldas C: Case repart: Transverse myelitis associated with EpsteinBarr virus infection. Am J Med Sci 30T45-48, 1994. 14. Campi A, Filippi M, Comi G. Scotti G: Recurnot acute transverse myelopathy associated witb anticardiolipin antibodies. AIM Am J Neuroradiol 19:781-786, 1998. 15. Chabert E: Intramedullary cavernous malfomations. J Neumdiol 26962-268, 1999. 16. Chamberlain MC, Sandy AD, Prtss GA: Spinal cord tumors: Ciadoliniurn-DTPA-enhanced MR imaging. Neuroradiology 33:469-474. 1991. 17. Chang WT, Chen HC, Peng HC: Solitary spinal cord metastasis of Wilms' tumor. J Pediatr Surg 25:550-552, 1990. 18. Chen CJ. Chen CM,Lin TK. Enhanced cervical MRI in identifying intracranial dural arteriovenous fistulae with spinal perimedullary venous drainage. Neuroradiology 40:393-397, 1998. 19. Choi KH. Lee KS, Chung SO, et al: Idiopathic transverse myelitis: MR characteristics [see comments]. AJNR Am J Neuroradiol 17: 1151-1160, 1996. 20. Cognard C: The role of CT in evaluation of the effectiveness of embolisation of spinal dural arteriovenous fistulae with N-butyl cyanoacrylate. Neuroradiology 38:60348, 19%. Colombo N. Kucharczyk W, Brant-Zawadzki M, et al: Magnetic resonance imaging of spinal cord hemangioblastoma. Acta Radiol Suppl 369:734-737, 1986. 22. Cosgrove GR, Bemand G. Fontaine S, et ak Cavernous angiomas of the spinal cord. J Neumurg 68:31-36. 1988. 23. Costigan DA, Wdelman MD: Intramedullary spinal card metastasis: A clinicopathological study of 13 cases.- J ~ e u r o s u 62227r~ 233, 1985. 24. David P: MRI of acute disseminated encephalomyelitis after coxsackie B infection. J Neuroradiol20:258-265, 1993. 25. Dev R, Husain M, Gupta A, mpta RK: MR of multiple intraspinal abscesses associated with congenital dermal sinus. AJNR Am J Neuroradiol 18:742-743, 1997. 26. Di Lorenzo N: Primary spinal neoplasms in childhood: Analysis of 1234 published cases (including 56 personal cases) by pathology, sex, age and sitc+differences from the situation in adults. Neurochirurgia (Stuttg) 25: 153-164, 1982.

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27. Dion WP, Nonnan D, Newton TH. et al: Intradural spinal cord lesions: Gd-DTPA-enhanced MR imaging. Radiology 170:229-237. 1989. 28. Donovan WD: Case report: MRi findings of severe Epstein-Barr virus encephalomyelltis. J Comput Assist Tomogr 20:1027-1029, 1996. 29. Dupuis MJ, Atrouni S, Dooms GC, Gonsette RE: MR imaging of schistosomal myelitis. MNR Am J Neumradiol 11:782-783, 1990. 30. Edelson RN, Deck MD, Posner JB: Intramedullary spinal cord metastases: Clinical and radiographic findings in nine cases. Neurology 221222-1231, 1972. 31. Elksnis SM, Hogg JP,Cunningham ME: MR imaging of spontaneous spinal cord infarction. J Comput Assist Tomogr 15:22&232. 1991. 32. Epstein F, et al: Intramedullary tumors of the spinal cord. In Pediatric : Neurosurgery: Surgery of the DevelMcLawin RL (4) oping Nervous System, 2nd ed. Philadelphia, k n e & StIauon, 1989, pp 428-442. 33. Emst RJ: Cervical myelopathy associated with intracranial dural arteriovenous fistula: MR findings before and after treatment. AJNR Am J Neuroradiol 18:1330-1334, 1997. 34. Faig J: Vertebral body infarchon as a confirmatory sign of spinal cord ischemic stroke: Report of three cases and review of the literature. Stroke 293239443, 1998. 35. Flanders AE, Spettell CM, Friedman DP, et al: The relationship between the functional abilities of patients with cervical spinal cord injury and the severity of damage revealed by MR imaging. AJNR Am J Newradio1 20:926934, 1999. 36. Flanders A@, Spettell CM,Tartaglino LM,et al: Forecasting motor recovery after cervical spinal cord injury: Value of MR imaging. Radiology 201:64%55, 1996. 37. Forbes G, Nichols DA, Jack CR Jr, et al: Complications of spinal cord arteriography: Prospective assessment of risk for diagnostic procedures. Radiology 169:479-484, 1988. 38. Friedman DP: Herpes zoster myelitis: MR appearance. AJNR Am J Neuroradiol 13:1404-1406, 1992. 39. Friedman DP, Flanders AE: Enhancement of gray mauer in anterior spinal infarction. AJNR Am J Neuroradiol 13:983-985. 1992. 40. Friess HM, Wasenko JJ: MR of staphylococcal myelitis of the cervical spinal cord. AJNR Am J Neuroradiol 1R455-458, 1997. 41. Gilbertson JR, Miller GM. Goldman MS, Marsh W R Spinal dural arteriovenous btulas: MR and myelographic findings. AJNR Am J Neumradiol 16:2049-2057, 1995. 42. Goy AM, Pinto RS. Raghavendra BN, et al: Intramedullary spinal cord mnors: MR imaging, with emphasis on associated cysts. Radiology 161:381-386, 1986. 43. Grem JL,Burgess J, Trump DL: Clinical features and natural history of intramedullary spinal cord metastasis. Cancer 56:2305-2314, 1985. 44. Hackney DB: Neoplasms and related disorders. Top Magn Reson Imaging 4:37-6 1, 1992. 45. Handel S, Grossman R. Sarwar M: Case report: Computed tomography in the diagnosis of spinal cord asmytoma. J Comput Assist Tomogr 2:226-228. 1978. 46. Haribhai HC, Bhigjee AI, Bill PL, et al: Spinal cord schistosomiasis: A clinical, laboratory and radiological study, with a note on therapeutic aspects. Bwin 114:709-726, 1991. 47. Hasegawa M. Spinal cord infarction associated with primary antiphospholipid syndrome in a young child: Case report. J Neurosurg 79:446-450, 1993. 48. Hasegawa M: The efficacy of CI'arteriography for spinal arteriovo nous fistula surgery: Technical note. Neuroradiology 4 1:9 15-9 19, 1999. 49. Hashimoto H: Spinal dural arteriovenous fistula with perimesencephalic subarachnoid haemorrhage. J Clin Neurosci 7:64-66, 2000. 50. Heinz R: Detection of cerebrospinal fluid metastasis: CT myelography or MR? AJNR Am J Neuroradiol 16:1147-1151. 1995. 51. Hirai T Case report: Varicella-zoster virus myelitis-serial MR findings. Br J Radiol 69:1187-1190, 1996. 52. Hittmair K: Spinal cord lesions in patients with multiple sclerosis: Comparison of MR pulse sequences. AJNR Am J Neuroradiol 17: 1555-1565, 1996. 53. Hurst RW Peripheral spinal cord hypointensity on T2-weighted MR images: A reliable imaging sign of venous hypertensive myelopathy. AJNR Am J Neuroradiol21:781-786, 2000.


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54. Keiper MD, Grossman RI, Brunson JC, Schnall MD: The low sensitivity of fluid-attenuated inversion-recovery MR in the detection of multiple sclerosis of the spinal cord. AJNR Am J Neuroradiol 18:1035-1039, 1997. 55. Kelly DR, Smith CD, McQuillen MP: Successful medical treatment of a spinal histoplasmoma. J Neuroimaging 4:237-239, 1994. 56. Keung YK: Secondary syringomyelia due to intramedullq spinal cord metastasis: Case report and review of literature. Am J Clin Oncol 20:577-579, 1997. 57. King SJ, Jeffree MA: MRI of an abscess of the cervical spinal cord in a case of Listeria meningoencephalornyelitis. Neu~oradiology35: 495-496, 1993. 58. Koehler PJ: Delayed radiation myelopathy: Serial MR-imaging and pathology. Clin Neurol Neurosurg 98:197-201, 1996. 59. Koh S: Myelopathy resulting from invasive aspergillosis. Pediatr Neurol 19:135-138, 1998. 60. Kohno M: Postmyelographic computerized tomographic scan in the differential diagnosis of radiculomeningeal arteriovenous malformation: Technical note. Surg Neurol 47:68-71, 1997. 61. Kohno M: Preoperative and postoperative magnetic resonance imaging (MRI) findings of radiculomeningeal arteriovenous malformations: Important role of gravity in the symptoms and MRI. Surg Neurol 48:352-356, 1997. 62. Kovacs B: Transverse myelopathy in systemic lupus erythematosus: An analysis of 14 cases and review of the literature. Ann Rheum Dis 59: 120-124.2000. 63. Kumar J, Kimm J: MR in Toxocara canis myelopathy. AJNR Am J Neuroradiol 15:1918-1920, 1994. 64. Lapointe JS, Graeb DA, Nugent RA, Robertson WD: Value of intravenous contrast enhancement in the CT evaluation of intraspinal tumors. AJR Am J Roentgenol 146:103-107, 1986. 65. Larsson EM, Desai P, Hardin CW, et al: Venous infarction of the spinal cord resulting fiom dural arteriovenous fistula: MR imaging findings. AJNR Am J Neuroradiol 12:739-743, 1991. 66. Larsson EM, Holtas S, Nilsson 0: Gd-DTPAenhanced MR of suspected spinal multiple sclerosis. AJNR Am J Neuroradiol 10: 1071-1076, 1989. 67. Lee M: Nonneoplastic intramedullary spinal cord lesions mimicking tumors. Neurosurgery 43:78&794, 1998. 68. k i t e CC, Jinkins JR,Escobar BE, et al: MR imaging of intramedullary and intradural-extramedullary spinal cysticercosis. AJR Am J Roentgenol 169:1713-1717, 1997. 69. Li MH, Holtas S: MR imaging of spinal intramedullary tumors. Acta Radiol 32505-513, 1991. 70. Lindner A: Magnetic resonance image findings of spinal intramedullary abscess caused by Candida albicans: Case report. Neurosurgery 36:411412, 1995. 71. Mascalchi M: MR angiography of spinal vascular malformations. AJNR Am J Neuroradiol 16:289-297, 1995. 72. Mascalchi M: Identification of the feeding arteries of spinal vascular lesions via phase-contrast MR angiography with threedimensional acquisition and phase display. AJNR Am J Neuroradiol 18:351358, 1997. 73. Mascalchi M: Posterior spinal artery infarct. AJNR Am J Neuroradiol 19:361-363, 1998. 74. Mawad ME, Rivera V, Crawford S, et al: Spinal cord ischemia after resection of thoracoabdominal aortic aneurysms: MR findings in 24 patients. AJNR Am J Neuroradiol 11:987-991, 1990. 75. Mehalic +IT,Pezzuti RT, Applebaum BI: Magnetic resonance imaging and cervical spondylotic myelopathy. Neurosurgery 26:217226, 1990. 76. Melhem ER,Wang H: Intramedullary spinal cord tuberculoma in a patient with AIDS. AJNR Am J Neuroradiol 13:98&988, 1992. 77. Merine D, Wang H, Kumar AJ, et al: CT myelography and MR imaging of acute transverse myelitis. J Comput Assist Tomogr 11: 606-608, 1987. 78. Miller GM, Forbes GS, Onofrio BM: Magnetic resonance imaging of the spine. Mayo Clin Proc 64:9861004, 1989. 79. Miyasaka K: Computed tomography and magnetic resonance imaging of intramedullary spinal cord tumors. Acta Radiol Suppl 369: 738-740, 1986. 80. Miyatake S, Kikuchi H, Koide T, et al: Cobb's syndrome and its treatment with embolization: Case r e p . J Neurosurg 72:497499, 1990. 81. Mock A, Levi A, Drake JM: Spinal hemangioblastoma, syrinx, and

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hydrocephalus in a two-year-old child. Neurosurgery 27:799-802, 1990. 82. Mukunda BN: Solitary spinal intramedullary abscess caused by Nocardia asteroides. South Med J 92:1223-1224, 1999. 83. Murphy KJ, Bmberg JA, Quint DJ, Kazanjian PH: Spinal cord infection: Myelitis and abscess formation [see comments]. AJNR Am J Neuroradiol 19:341-348, 1998. 84. Nabatame H, Nakamura K, Matuda M, et al: MRI of syphilitic myelitis. Neuroradiology 34105-106, 1992. 85. Nagakawa H, et al: Computed tomography of soft tissue masses related to the spinal column. In Post MJ (ed): Radiographic Evaluation of the Spine: Current Advances with Emphasis on Computed Tomography. New York, Masson, 1980, pp 320-352. 86. Nemoto Y, Inoue Y, Tashiro T, et al: Intramedullary spinal cord tumors: Si&cance of associated hemorrhage at MR imaging. Radiology 182793-796. 1992. 87. Nesbit GM, Miller GM, Baker HL Jr, et al: Spinal cord sarcoidosis: A new finding at MR imaging with Gd-DTPA enhancement. Radiology 173:839-843, 1989. 88. Neumann-Andersen G: Involvement of the entire spinal cord and medulla oblongata in acute catastrophic-onset transverse myeIitis in SLE. Clin Rheumatol 19: 156-160, 2000. 89. Neumann HP, Eggert HR, Scheremet R, et al: Central nervous system lesions in von Hippel-Lidau syndrome. J Neurol Neurosurg Psychiaay 55:898-901, 1992. 90. Nitta H: Cervical spinal cord infarction after surgery for a pineal region choriocarcinoma in the sitting position: Case report. Neurosurgery 40: 1082-1085, 1997. 91. Nittner K: Spinal meningiomas, neurinomas, and neurofibromas, and hourglass tumors. In Vinken PJ, Bruyn GW (4s): Handbook of Clinical Neurology. New York, Elsevier North-Holland, 1976, pp 177-322. 92. Oishi H: Successful surgical treatment of a dural arteriovenous fistula at the craniocervical junction with reference to pre- and postoperative MRI. Neuroradiology 41:463467, 1999. 93. Oldfield EH, Di Chiro G, Quindlen EA, et al: Successful treatment of a group of spinal cord arteriovenous malformations by intenuption of dural fistula. J Neurosurg 59: 1019-1030, 1983. 94. Parizel PM: Gd-DTPA-enhanced MR imaging of spinal tumors. AJR Am J Roentgenol 1521087-1096, 1989. 95. Pascuzzi RM,Shapiro SA, Rau AN, et al: Sarcoid myelopathy. J Neuroimaging 6:61-62, 1996. 96. Pfausler B: Syndrome of the anterior spinal artery as the primary W e s t a t i o n of aspergillosis. Infection 23:24&242, 1995. 97. Phuphanich S: Magnetic resonance imaging of syrinx associated with intramedullary metastases and leptomeningeal disease. J Neuroimaging 6:115-1 17, 1996. 98. Poon TP, Tchertkoff V, Pares GF, et al: Spinal cord Toxoplasma lesion in AJDS: MR findings. J Comput Assist Tomogr 16:817819, 1992. 99. Post MJ, Quencer RM,Green BA, et al: Intramedullary spinal cord metastases, mainly of nomeurogenic origin. AJR Am J Roentgenol 148:1015-1022, 1987. 100. Provenzale JM,Barboriak DP, Gaensler EH, et al: Lupus-related myelitis: Serial MR findings. AJNR Am J Neuroradiol 15:19111917, 1994. 101. Ratliff JK: Intramedullary tuberculoma of the spinal cord: Case report and review of the literature. J Neurosurg 90:125-128, 1999. 102. Renowden SA: Case report: Spontaneous thrombosis of a spinal dural AVM (Foix-Alajouanine syndrome)-magnetic resonance a p pearance. Clin Radiol 47:134-136, 1993. 103. Resnick DK, Comey CH, Welch WC, et al: Isolated toxoplasmosis of the thoracic spinal cord in a patient with acquired immunodeficiency syndrome: Case report. J Neurosurg 82493-496, 1995. 104. Ricolfi F: Giant perimedullary arteriovenous fistulas of the spine: Clinical and radiologic features and endovascular treatment. AMR Am J Neuroradiol 18:677-687, 1997. 105. Russell DS, Rubenstein LJ: Pathology of Tumors of the Nervous System. Baltimore, Williams & Wilkins, 1989. 106. Schubeus P, Schomer W, Hosten N, Felix R: Spinal cord cavities: Differential-diagnostic criteria in magnetic resonance imaging. Eur J Radiol 12219-225, 1991. 107. Scotti G, Scialfa G, Colombo N, Landoni L: Magnetic resonance diagnosis of intramedullary tumors of the spinal cord. Neuroradiology 29:130-135, 1987.


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Chapter 24

108. Sener RN, Larsson EM, Backer R, Jinkins JR: MRI of intradural spinal arteriovenous fistula associated with ischemia and infarction of the cord. Clin Imaging 17:73-76, 1993. 109. Shapiro R ( 4 ) : Tumors. In Myelography. Chicago, Year Book Medical Publishers, 1984, pp 345-421. 110. Slasky BS, Bydder GM, Niendorf IIP, Young I . : MR imaging with gadolinium-DTPA in the differentiation of tumor, syrinx, and cyst of the spinal cord. J Comput Assist Tomogr 112345-850, 1987. 111. Solomon RA, Stein BM: Unusual spinal cord enlargement related to intrmedullary hemangioblastoma. J Neurosurg 68:55&553, 1988. 112. Solsberg MD, Lemaire C, Resch L, Potts DG: High-resolution MR imaging of the cadaveric human spinal cord: Normal anatomy. AJNR Am J Neuroradiol 11:3-7, 1990. 113. Steinbok P: Intramedullary spinal cord tumors in children. Neurosurg Clin North Am 3:931-945, 1992. 114. Su MC, Ho WL,Cben JH. Intramedullary cryptococcal granuloma of spinal cord: A case report. Chung Hua I Hsueh Tsa Chih (Taipei) 53:58-61, 1994. 115. Suzuki K: Anterior spinal artery syndrome associated with severe stenosis of the vertebral artery. AJNR Am J Neuroradiol 19:13531355, 1998. 116. Sze G: Gadolinium-DTPA in spinal disease. Radiol Clin North Am 26: 1009-1024, 1988. 117. Sze G: Intramedullary disease of the spine: Diagnosis using gadolinium-DTPA-enhanced MR imaging. AJR Am J Roentgenol 151: 1193-1204, 1988. 118. Sze G, Merriam M, Oshio K, Jolesz FA: Fast spin-echo imaging in the evaluation of intradural disease of the spine. AJNR Am J Neuroradiol 13:1383-1392, 1992. 119. Tacconi L: Intramedullary spinal cord abscess: Case report. Neurosurgery 37:817-819, 1995. 120. Tartaglino LM, Friedman DP, Flanders AE, et al: Multiple sclerosis in the spinal cord: MR appearance and correlation with clinical parameters. Radiology 195:725-732, 1995.

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121. Tas MW, Barkhol F, van Walderveen MA, et al. The effect of gadolinium on the sensitivity and specificity of MR in the initial diagnosis of multiple sclerosis. AJNR Am J Neuroradiol 16:259264, 1995. 122. Tenvey B, Becker H, Thron AK, Vahldiek G: Gadolinium-DTPA enhanced MR imaging of spinal dural arteriovenous fistulas. J Comput Assist Tomogr 13:3&37, 1989. 123. Thorpe JW,Kendall BE, MacManus DG, et al: Dynamic gadolinium-enhanced MRI in the detection of spinal arteriovenous malformations. Neuroradiology 36:522-529, 1994. 124. Thumher MM, Post MJ, Jinkins JR: MRI of infections and neoplasms of the spine and spinal cord in 55 patients with AIDS. Neuroradiology 4255 1-563, 2000. 125. Turjman F, Joly D, Monnet 0 , et al: MRI of intramedullary cavemous haemangiomas. Neuroradiology 37:297-302, 1995. 126. Valk J: Magnetic resonance imaging in the differentiation of spinal cord tumours and hydromyelia. Acta Radiol Suppl 369242-244, 1986. 127. Vishteh AG, Zabramski JM, Spetzler RF. Patients with spinal cord cavernous malformations are at an increased risk for multiple neuraxis cavernous malformations. Neurosurgery 45:30-32, 1999. 128. Waubant E: MRI of intramedullary sarcoidosis: Follow-up of a case. Neuroradiology 39:357-360, 1997. 129. W i a m s AL, Haughton VM,Pojunas KW, et al: DiECerentiation of intramedullary neoplasms and cysts by MR. AJR Am J Roentgenol 149:159-164, 1987. 130. Winkelman MD, Adelstein DJ, Karlins NL: IntTamedullary spinal cord metastasis: Diagnostic and therapeutic considerations. Arch Neurol44:526-531, 1987. 131. Yuh WT,Marsh EE, Wang AK, et al: MR imaging of spinal cord and vertebral body infarction [see comments]. AJNR Am J Neuroradiol 13:145-154, 1992. 132. Zimmennan RA: Imaging of tumors of the spinal canal and cord. Radiol Clin North Am 26:%5-1007, 1988.


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25

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Magnetic Resonance Imaging of Infections of the Spine Charles F. Lanzieri

Because infections of the spine present with subtle and nonspecific symptoms, they represent a diagnostic problem, and imaging plays a key role in the initial diagnosis and subsequent management. Clinical symptoms, which commonly include fever, malaise, back pain, and focal tenderness, are often insidious in onset and can be attributed to a variety of common conditions. By the time focal neurologic findings such as extremity weakness or meningismus appear, the stage is set for rapid progression to permanent neurologic deficits at worst and a chronic state of osteomyelitis at best. The infection can rapidly spread to the epidural space with concomitant paraplegia. Delayed diagnosis increases the morbidity and mortality of spinal infections; diagnostic imaging is therefore critical. Infection of the spine initially involves either the disk space or the vertebral body, and spread occurs via the arterial or venous system or by direct inoculation during diagnostic procedures. Pyogenic infections evolve more rapidly than nonpyogenic infections, which have a more indolent course. Pyogenic infections are commonly caused by Staphylococcus aureus, which accounts for about 60% of this category of infection.%5. lZ The most common cause of the nonpyogenic infections is Mycobacterium tuberculosis. Specific pathogens are more common in patients with predisposing conditions. For example, Salmonella is a common cause of osteomyelitis in patients with sickle cell disease, and Serratia and Candida are commonly seen in patients using intravenous drugs. The course of nonpyogenic infections is even more insidious and has a slower evolution than that of pyogenic infections. Infections caused by the tubercle bacillus or fungus are very difficult to diagnose. Before cross-sectional imaging in the 1980s, radiologic diagnosis of disk space infections and vertebral osteomyelitis depended on interpretation of plain radiographs and radionuclide studies. Radiographs are usually unrevealing for the first 2 to 8 weeks of the disease process. Radionuclide studies have demonstrated incorporation of technetium Wm in 80% of infected bone sites by the 10th day of the infection.15 These examinations, however, have significant limitations, most notably false-positive results. Radionuclide bone scans cannot reliably differentiate cellulitis from osteomyelitis. False negatives also occur when the blood supply to the infected bone or disk space is impaired. The use of high-resolution computed tomography (CT)

was found to be very useful because of its ability to demonstrate bone destruction or focal osteopenia early in the course of the infection. Its ability to demonstrate prevertebral soft tissue swelling and cellulitis, however, was disappointing. Magnetic resonance imaging (MRI) quickly became the study of choice for evaluating patients with spinal complaints. Its advantages include multiplanar capability, superior soft tissue contrast resolution, and a unique ability to detect end-plate, disk space, and marrow changes. In addition, MRI can demonstrate subtle changes far earlier in the course of the disease than previously employed techniques. Finally, MRI is extremely useful for following patients with proven spinal infection and for planning aspirations or other interventions. This has a direct impact on patient management. MRI has dramatically changed the outcome of patients with spinal infections over the last 10 years.

~atho~h~siolo~~ Infectious processes can extend to the spine by several mechanisms. Direct extension occurs secondary to trauma or surgical intervention for reasons other than infection. Diagnostic lumbar punctures or epidural injections as well as surgery for herniated disks are common causes. Contiguous spread can occur from adjacent infected structures. Hematogenous spread can come from distant sites. A source of hematogenous dissemination can be found in up The most to half of the patients with spinal o~teomyelitis.~ common sources are the genitourinary tract, the skin, and the respiratory tract.18 The arterial system is thought to be a much more common route of spread to the spine, although extension via the epidural venous plexus occurs via the pelvic plexus of veins.19 A number of events occur during the first few weeks of infectious spondylitis. The organism commonly settles in the anterior portion of the subchondral bone marrow. The infection then spreads within the marrow space or into the adjacent intervertebral disk, causing osteomyelitis andlor diskitis. Nonpyogenic infection may spread into the subligamentous space, and from there it may penetrate the ligament and the adjacent soft tissues. Disk-sparing infections of adjacent vertebral bodies are a common sign of tubercle bacillus infecti~n.~ Both pyogenic and nonpyo-

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genic infections tend to remain within the vertebral body and disk spaces and do not usually involve the posterior elements and adjacent ligaments and soft tissues. This type of involvement is more typical of metastatic disease. Although pyogenic infections rarely involve the posterior elements, tuberculosis (TB) sometimes does. The level most often involved in TB spondylitis is L1, but the thoracolumbar junction is most affected in general. The cervical and lumbar levels are less frequently involved. Following successful therapy for infection, the reparative process can include partial or complete bony ankylosis of the disk space. Without adequate or proper therapy, bony lysis occurs, with subsequent collapse of the vertebral body. In nonpyogenic infections such as TB, anterior wedging with secondary kyphotic deformity occurs.

Pyogenic Disk Space Infections Pyogenic infections, which have a peak incidence in the sixth and seventh decades of life, are caused by both gram-positive and gram-negative bacteria. The dominant inflammatory cell is the polymorphonuclear leukocyte. Both the vertebral body and the adjacent disk space become involved. The cancellous bone adjacent to the cartilaginous end plate is richly vascular throughout adulthood, which makes it a common site for visitation from hematogenously borne pathogens. The infection then spreads across the disk to involve the adjacent vertebral body. Most of the time, the infection is limited to the disk space and the two adjacent vertebral bodies. In about 25% of cases, multiple

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Infectious agents settle in the most levels are invol~ed.~ vascular spaces in the spine. In children, who have a rich vascular supply in and around the disk spaces, infections can spread directly to the disk.5 In adults, the disk space is nearly avascular; therefore, infections begin in the subchondral bone adjacent to the end plate, which is very vascular throughout adulthood. Pyogenic infections are often self-limited in children and may be cured with bed rest and antibiotics. The population most commonly affected by vertebral osteomyelitis consists of adults in the sixth to seventh decade of life. The lumbar spine is the site most commonly affected, followed by the thoracic and cervical spine. Men are affected more often than women, at a ratio of two to one. Treatment with parenteral antibiotics for about 6 weeks is usually required for cure. Surgical intervention is necessary when there are neurologic findings and an epidural mass is identified, or when there is secondary instability and fusion needs to be performed. Radiographic findings are usually subtle and may not appear until relatively late in the process (Fig. 25-1). The hallmark of disk space infection on plain radiographic examination is disk space narrowing. This is followed by erosion of the adjacent end plates. It may be several days or weeks before these findings are evident. The characteristic findings of disk space narrowing and end-plate irregularity may not be seen until the fourth week of the infection. Prominence of the retropharyngeal soft tissues is a variable finding. Plain films cannot demonstrate the important intraspinal complications of infection that are ultimately responsible for neurologic symptoms. CT is very useful in

Figure 25-1. Lumbar disk space infection with osteomyelitis. A, T1-weighted sagittal MR image through the lumbar spine. The arrow indicates g'ksk spa& infection at the L1-2 level. The normal cortical dark line along both articular surfaces, especially along the inferior surface of L1, is not visible. A decrease in the signal coming from the marrow fat in both vertebrae indicates the presence of marrow edema. B, l2-weighted image in the same location shows edema in the marrow and slightly increased signal in the interspace. Although the disk space at L1-2 is not brighter than the adjacent disk spaces, the normal internuclear cleft is lost. In addition, a much lower signal would be expected in a partially collapsed and degenerated disk. C,Post-contrast-enhanced image in the same location. Although the disk space itself does not show enhancement, the vertebral bodies do. The arrow indicates loss of the anterior cortical margin of L1, a sign of upward spread of infection.


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Chapter 25

these patients because it is more sensitive than plain film. In addition, the soft tissue changes begin to become evident. MRI offers the best opportunity to image and confirm vertebral infections early in their course. The first MR findings reflect the replacement of normal bone marrow by inflammatory tissue and edema in association with structural changes such as disk space narrowing.'O The sensitivity of MRI for disk space infections is the same as that of radionuclide studies and the specificity is much higher. Even early studies using nonenhanced MRI showed a sensitivity of 96%, a specificity of 92%, and an accuracy of 92%.1° Evidence of vertebral osteomyelitis appears at about the same time on MRI as it does on gallium or technetium 99m radionuclide studies.I0 Marrow replacement first appears as decreased signal on TI-weighted images because of edema or infiltration of fat in the bone marrow. On T2-weighted images, marrow

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edema is reflected as increased signal because of the additional water content in the marrow. A band of increased signal in the subchondral bone marrow is highly suggestive of pathologic change in the adjacent disk space. Unfortunately, this change is somewhat nonspecific and can be seen in a variety of conditions including recent trauma and early degenerative disease. Changes in the disk space are seen on both T1-weighted and T2-weighted images. On the TI-weighted images, narrowing of the interspace with slight loss of signal can usually be visualized. The most dramatic, recognizable, and reliable sign of disk space infection on MRI is the increased signal seen on T2-weighted images. In adults, this is accompanied by loss of the normal band of decreased signal that represents what is referred to as the intranuclear cleft. These findings may be supported by the observation of swelling and edema in the adjacent soft tissues (Fig. 25-2). When the

Figure 25-2. Lumbar disk space infection with osteomyelitis and paraspinal cellulitides. A and B, Sagittal T2-weighted images through the lumbar spine. Bright signal is associated with the L2-3 intervertebral disk. This is the hallmark of diskitis on an MRI scan (arrow). C,Post-contrast-enhanced axial TI-weighted image. Enhancement can be visualized in and around the L2-3 interspace, as well as in the paraspinal soft tissues and within the spinal canal. These represent paraspinal and epidural cellulitides. If left untreated, they could progress to abscess formation. :+-rp~r r ~ r ~ 7 ~ r~ ~~ a,~m m


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bony cortex of the vertebral body becomes involved, the normally dark cortical margin on all MRI sequences can no longer be visualized. This implies osteomyelitis. If intravenous contrast material is given, enhancement within the disk space and in the adjacent vertebral bodies usually increases diagnostic confidence.13 Some pitfalls exist in diagnosing disk space infections using MRI. The intermediate changes seen in degenerative disk disease may mask the early changes of a disk space infection. Both processes produce low signal on T1weighted images. In the case of degenerative disease, the infiltration of fat into the subchondral portion of the vertebra is an intermediate change that increases the T1 signal intensity. Since infection lowers the degree of T1 signal, a canceling effect occurs that potentially masks the edema. The =-weighted images should be reviewed carefully to search for edema in suspected infections. Occasionally, a degenerated disk transiently contains cystic areas. This causes increased signal on =-weighted images and mimics one of the hallmarks of diskitis, a bright interspace. Although many disk space infections represent hematogenous seeding, a significant number are secondary to surgery involving the disk space. Disk space infections follow up to 3% of surgical procedures on the pine.^ Clinical

Figure 25-3. Cervical disk space infection. Disk space infections and diskitis are unusual occurrences in the cervical spine. T2weighted sagittal image shows increased signal in the C3-4 intervertebral disk space and edema in the adjacent bone marrow fat (arrow).The cortical margins remain intact and there is no evidence of a paraspinal abscess. Increased signal in the adjacent spinal cord represents the presence of myelomalacia from chronic cord compression. Although this patient had not had previous surgery, the same appearance is seen following cervical diskectomy.

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suspicion is raised when, in the first few postoperative weeks, patients present with back pain radiating to the extremities and signs of infection such as elevated white blood cell count, an elevated sedimentation rate, and fever. Because signal changes in the vertebral bodies, disk spaces, and adjacent soft tissues occur following surgery, the diagnosis of postoperative infection is difficult. Cervical vertebral osteomyelitis and diskitis are usually diseases of older people, but they occur frequently in younger patients who are intravenous drug abusers (Fig. 25-3).16

Epidural Abscesses Epidural abscesses can occur either spontaneously or secondary to disk space infection and osteomyelitis. Imaging greatly improves patient outcome because a specific diagnosis based only on clinical signs and symptoms is impossible and early treatment is important. MRI is the study of choice when an epidural abscess is suspected and results are positive before radionuclide scanning.' Clinical signs and symptoms include back and radicular pain, stiffness, and cramping. Rapid expansion can result in permanent neurologic deficits, the result of direct cord or root compression in most cases, with secondary white matter injury. Vascular thrombosis and direct infiltration of the cord or roots are less common. Although MRI and myelograjhc CT are similar in sensitivity for identifying epidural abscesses,1° MRI offers the ability to distinguish between causes of epidural masses. Thus MRI can differentiate epidural abscess from hematoma, tumor, or disk fragment (Fig. 25-4). Because it is noninvasive, it is the obvious first choice for imaging. Epidural abscesses appear as isointense masses on T1weighted images, and the intensity is frequently increased on =-weighted images.I2 Patients with epidural abscess almost always have accompanying meningeal thickening and enhancement. Without contrast injection, any fluid collection in, or necrotic portion of, the subarachnoid or epidural space can be overlooked. Although not necessary for the diagnosis of disk space infections, contrast-enhanced MRI is essential for the accurate diagnosis of abscess collections in the epidural space (Fig. 25-5). With contrast injection, epidural abscesses are easily demonstrated. Homogeneous enhancement of the mass is seen, with central necrosis indicating a focal fluid collection. Most abscesses occur adjacent to an infected interspace and generally spread to between two and four vertebral levels. Rarely, extension may involve the entire length of the spine.14

Tuberculosis Tubercle bacillus infections are more insidious than pyogenic infections of the spine. As in pyogenic infections, the initial symptoms are nonspecific and early diagnosis is


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Figure 25-4. Cervical disk space infection with epidural abscess. A, T2-weighted sagittal image through the cervical spine. The C5-5 intervertebral disk space has increased signal, indicating the presence of diskitis. Although there is no evidence of adjacent marrow edema and the cortical margins are intact, a region of increased signal in the paraspinal soft tissues anterior to the interspace (arrow) indicates the presence of paraspinal cellulitis. B, T1-weighted sagittal image reveals contrast enhancement of the interspace, which confirms disk space infection. Thickening and enhancement of the meninges in the cervical spine and a small epidural fluid collection in the epidural space (arrow) indicate the presence of an epidural abscess.

difficult. In the case of TB, the symptoms may last for months or years prior to diagnosis. lhberculous vertebral osteomyelitis remains a significant medical problem in developing countries. The skeleton is the most common extrapulmonary site of involvement, and spinal TB occurs in 50% of the cases of skeletal TB. Vertebral osteomyelitis is estimated to occur in 0.03% of all TB cases.7 The TB bacillus spreads to the vertebral body hematogenously and, like pyogenic organisms, lodges in the anterior and subchondral portion of the vertebral body. The granulomatous inflammatory response to the bacillus results in a tubercle, which then invades the surrounding soft tissues and forms a tuberculous abscess. As the abscess grows, the periosteum and the longitudinal ligaments of the spine are elevated and the abscess extends up and down the spine to involve adjacent vertebra. The thoracolumbar junction is most frequently involved; involvement of the cervical and thoracic spine is unusual. Classically, spinal tuberculosis initially involves the anterior and inferior portion of the vertebral body (Fig. 25-6). Extension to other vertebral bodies occurs beneath the anterior and posterior longitudinal ligaments and is referred to as subligamentous spread. The disk spaces usually remain relatively spared. Involvement of the posterior elements of vertebral bodies is more common in TB than in other forms of infection. Infection of multiple vertebral bodies and posterior elements is involved, with sparing of the disk spaces. This makes differentiation of TB from metastatic neoplasm difficult.17

Nontuberculous Granulomatous Spondylitis The granulomatous response is a nonspecific response to an antigenic stimulus, and it is observed in a variety of pathologic conditions, including infections, neoplasms, and autoimmune diseases. The pathologic hallmark is the presence of mononuclear phagocytic cells and multinucleated giant cells. Organisms that infect the spine and cause a granulomatous reaction include the tubercle bacillus, Brucella, and fungi. In endemic areas of the Middle East and Asia, granulomatous spondylitis is still quite common. Brucella is a small gram-negative coccobacillus common in cattle and swine. In the United States, the most common species are B. abortus and B. suis. When infecting humans, the organism often affects the lumbar spine. The disk space is usually spared and vertebral osteomyelitis may be accompanied by soft tissue fibrosis. The morphology of the vertebral body is preserved despite evidence of infection. The posterior elements are typically spared and the disk space is slightly reduced despite being involved with infection. Fungal infections of the spine include coccidioidomycosis (most frequently encountered in the southwestern United States), blastomycosis (found in the central and southeastern states), and actinomycosis. The findings in fungal infections are not specific to the infecting agent. Multiple vertebral bodies are involved but the disk spaces are spared. On plain radiographs, lytic lesions with sclerotic margins are seen. Lytic bony lesions with sclerotic margins are frequently seen with sparing of the interspace. Epidural


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Figure 25-5. Retropharyngeal abscess with extension to the spine. Although retropharyngeal abscesses can progress to involve the adjacent spine, the opposite can also happen. A, T2-weighted sagittal image reveals the presence of multilevel diskitis and osteomyelitis. Vertebral bodies C4 through T1 have increased signal, and the cortical margins are lost. There has been collapse of C4 and C6 and the (24-5and C6-7 interspaces are obliterated from previous surgery and ongoing infection. A multilevel larninectomy has been performed as part of this patient's cervical decompression. B, Post-contrast-enhanced and fat-suppressed TI-weighted image shows enhancement within the vertebral bodies and paraspinal soft tissues anterior to the spine. A focal region of nonenhancement just anterior to C5 (arrow) represents the presence of a small abscess in the paraspinal soft tissues. Images C and D were obtained several days later when the patient had failed to improve on antibiotic therapy. C, Post-contrast-enhanced TI-weighted image through ~ 6The . asterisk lies within a large retropharyngeal abscess that is contiguous with the C6 vertebral body. The curved arrow points to the thickened and enhancing meninges. The straight arrow indicates the presence of a fluid collection within the epidural space. This is an epidural abscess. D, Sagittal image also shows the retropharyngeal and paraspinal abscess (asterisk) and the epidural abscess (curved arrow).

and meningeal involvement is seen with all of these types of infections, but the degree of involvement is usually somewhat less than that seen with TI3 abscess of a similar size.

is rare.6 m the spine, where it is most often seen in the thoracolumbar region, it usually manifests as leptomeningeal thickening, and enhancement is seen after injection of contrast material. Mixed lytic and sclerotic changes have been seen in single or adjacent vertebrae. The intervertebral disks are spared.

Sarcoidosis Sarcoidosis is a noncaseating granulomatous condition that affects multiple organs in adults in the third through t of patients have central nervous fifth decades. ~ b b u 5% system involvement. Involvement of the vertebral bodies

1,,tramed llarycord 1,,fections The human immunodeficiency virus (HIV) causes a vacuolar degeneration of the central nervous system. In


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Figure 254. Tuberculous spondylitis frequently mimics metastatic disease. A, TI-weighted sagittal image demonstrates well-defined marrow replacement posteriorly and inferiorly in the L3 vertebral body (arrow). B, On the axial image, a slightly sclerotic, superior border is better appreciated (arrow). This degree of new bone formation would be unusual in metastatic disease unless it had been treated. The sclerotic margin suggests a chronic inflammatory process such as tuberculosis. C,Post-contrast-enhanced image shows that the infection has crossed the interspace to involve the adjacent LA vertebral body. Subligamentous spread is classic for tuberculous spondylitis.

the brain, this feature of the acquired immunodeficiency syndrome (AIDS) is recognized as focal frontal lobe atrophy or volume loss. In the spinal cord, increased signal can be seen within a short segment of the cord. This carries the general name of transverse myelitis (Fig. 25-7), and it is caused by other infectious agents as well. In patients who have transverse myelitis but are negative for HN,other viral infections such as herpes zoster should be considered. A variety of noninfectious causes also exist, including nutritional deficiencies, toxins, and drug^.^.^ Common autoimmune and demyelinating diseases, such as multiple sclerosis and lupus erythematosus, also cause transverse myelitis. The spinal cord itself can sometimes become infected,

and a cord abscess may form." The symptoms of cord infection are indistinguishable from those of an epidural abscess. Sources of cord infection include hematogenous spread, which is known to be a complication of congenital dermal sinuses, and bacterial endocarditis. It has been suggested that the pathophysiology of cord infection is similar to that of cerebral infection. In the initial myelitis phase, cord edema and enlargement are observed. At approximately 1 week, a poorly defined ring of enhancement begins to appear. This results in the formation of an abscess cavity, which is relatively isointense on TI-weighted images and hyperintense on =-weighted images. Cord abscesses are less well defined and less intensely enhancing than brain abscesses. This may be

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Figure 25-7. Transverse myelitis. T2-weighted sagittal image through the cervical spine demonstrates the presence of increased signal in the dorsal columns of the spinal cord. This appearance is nonspecific and can be caused by a demyelinating process or infarction. In this instance, it was associated with a transient myelitis.

Figure 25-8. Meningeal infection, with subtle enhancement of the meninges covering the lumbar nerve roots. A. Post-contrast-enhanced T1weighted image. he end of the conus medullaris at T12 is a flame-shaped structure that is slightly hypointense relative to the enhancing meninges and nerve roots. B and C,Axial contrast-enhanced images below the conus show that the nerve roots are thickened and enhancing. This nonspecific finding is compatible with meningitis and other disease processes.

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because the cord is relatively hypovascular compared with the brain. Bacterial abscess of the spinal cord has been thought to occur as a result of ba~teremia.~ Recently, cord abscesses have been reported in patients in whom the source of infection was not found.lL

Meningeal Infection Many infectious agents gain access to the central nervous system by first infecting the meninges. When encountered on MR images, meningeal infections produce a vague and subtle enhancement of both the dura and the leptomeninges (Fig. 25-8). Like transverse myelitis, this is a nonspecific finding; it can be caused by trauma, recent lumbar puncture, and various vascular malformations. For detecting meningeal infection, analysis of the cerebrospinal fluid is much more sensitive and specific, and much cheaper to perform, than any imaging procedure.

References 1. Angtuaco W.Mccomell JR, Chadduck WM,Flanigan S: MR imaging of spinal epidural sepsis. AJR AM J Roentgen01 149:12491253, 1987. 2. Baby R, Jafer JJ, Hray PP, et al: Intramedullq abscess associated with spinal cord ependymoma. Neurosurgery 30:121-124, 1992. 3. Barakos JA, Mark AS, Dillon WP, et al: MR imaging of acute transverse myelitis and AIDS myelopathy. J Comput Assist Tomogr Comput 14:45, 1990. 4. Brant-Zawadole M: Infection. In Newton TH, POUSDG (eds): Com-

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puted Tomography of the Spine and Spinal Cord. San Anselmo, Calif, Clavadel Press, 1983, p 205. 5. Enzmann DR: Infection/iiflammation. In Enzmann DR, De La Paz RL, Rubin J (eds): Magnetic Resonance of the Spine. St. Louis, Mosby-Year Book, 1990, p 260. 6. Kenney CM 3rd. Goldstein SJ: MRI of sarcoid spondylodiskitis. J Comput Assist Tomogr 16:66@-662, 1992. 7. Lin-Greenberg A, Cholankeril J: Vertebral arch destruction in tuberculosis: CT features. J Cornput Assist Tomogr 14300-302, 1990. 8. Malawski SK: Pyogenic infection of the spine. Int Orthop 1:125, 1977. 9. Merine D, Way H, Kumer AJ, et al: CT myelography and MRI of acute transverse myelitis. J Comput Assist Tomogr 11:606, 1987. 10. Modic MT, Feiglin DH, Piraino DW, et al: Vertebral osteomyelitis: Assessment using MR. Radiology 157:157-166, 1985. 11. Murphy KJ, Brunberg JA, Quint DJ, et al: Spinal cord infection: Myelitis and abscess formation. AJNR Am J Neuroradiol 19:341348, 1998. 12. Post MJD, Quencer RM, Montalvo BM, et al: Spinal infection: Evaluations with MR imaging and intraoperative ultrasound. Radiology 169:765, 1988. 13. Post MJD, Sze G, Quencer RM,et al: Gadolinium-enhanced MR in spinal infection. J Comput Assist Tomogr 14:721, 1990. 14. Post MJD,Bowen BC, Sze G: Magnetic resonance imaging of spinal infection. Rheum Dis Clin North Am 17:773-794, 1991. 15. Rinsley L, Gonis ML, Shurman DJ, et al: Technetium bone scanning in experimental osteomyelitis. Clin Orthop 128:361, 1977. 16. Ross PM, Fleming k Vertebral body osteomyelitis: Spectrum and natural history: A retrospective analysis of 37 cases. Clin Orthop 118: 190-198, 1976. 17. Smith AS, Weinstein MA, Lanzieri CF, et al: Tuberculous spondylitis: A contradiction of the MR characteristics of vertebral osteomyelitis. AJNR Am J Neuroradiol 10:619-625, 1989. 18. Waldvogel FA, Papageorgiou PS: Osteomyelitis: The past decade. N Engl J Med 303:360, 1980. 19. Wdey AM, Trueter J: The vascular anatomy of the spine and its relationship to pyogenic vertebral osteomyelitis. J Bone Joint Surg 413:796, 1959.


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Image-Guided Spinal Interventions Wade H. Wong, Huy M. Do, Barton Lane

Spine Biopsies Biopsies of the spine can play an important role in determining the correct diagnosis because imaging, although sensitive, is often nonspecific. When the patient may have an infection, a prompt biopsy can help the clinician define the organism and determine the optimal antibiotic sensitivity for early treatment. A spinal biopsy can provide a pathologic diagnosis that is critical to staging and treatment planning of neoplasms. Image guidance for biopsies of the spine is commonly provided with fluoroscopy or computed tomography (CT) scanning. In unique situations, image guidance with magnetic resonance imaging (MRI) might be provided.

average-sized adult. The view taken from this posteriorlateral approach is similar to that for a facet injection or for a diskogram (Fig. 261). Use of this approach permits a favorable trajectory to the center of the spine while avoiding the thecal sac if the operator should direct the needle too far posteriorly or avoiding the bowel or other internal abdominal viscera if the operator should direct the needle too far laterally. Final needle placement is confirmed through visualization of the needle position on the anterior-posterior plane as well as on the lateral plane. This helps to confirm the needle position and depth. An alternative to the posterior-lateral approach is the

Fluoroscopy Biopsies of the lumbar spine are readily and efficiently performed with fluoroscopic guidance. C-arm fluoroscopy is preferable to single-plane fluoroscopy because it allows the patient to remain in a stationary position while multiplanar relationships of the biopsy needle relative to the target are rapidly determined. The technique of fluoroscopic needle biopsy of the lower lumbar spine begins as follows. The patient is positioned isocentrically within the C-ann fluoroscope in such a way that the target area within the patient is centered in the rotational axis of the C-arm fluoroscope. This can be rapidly accomplished by first positioning the target in the lateral view and then adjusting its location so that it is centered on the anteroposterior view. Most biopsies of the spine can be performed with local anesthesia, although conscious sedation is sometimes helpful. After the patient is prepared and draped, an anesthetic needle is used to anesthetize the skin with a rather generous wheal, so that if the point of entry must be moved, it can be done so without having to reanesthetize the skin. Leaving the anesthetic needle in the skin by detaching the syringe from the needle with the needle along the intended trajectory course saves time in subsequent needle placements. With the initial anesthetic needle serving as a relative directional marker both on images and on the skin, longer needles can subsequently be placed with positional readjustments as necessary, so that the final needle can be placed in tandem (or coaxial) fashion relative to the target zone. Most biopsies of the lumbar spine (from about L2 to L5) can be performed from a posterior-lateral starting point, usually about 10 cm lateral to the spinous processes on an

Figure 26-1. ~luorosco~icall~ guided biopsy of L3 vertebra from a posterior-lateral approach starting about 10 cm lateral to the spinous processes in an average-size patient. This approach pro-

vides a clear view of the articular facet joints and would be the same for a facet injection or for a lumbar diskograrn. When the bone is entered, anterior and lateral views should be obtained to determine the correct depth of placement in the vertebra. An 11-gauge core biopsy needle was used, and the diagnosis was staphylococcal osteomyelitis.


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Chapter 26

Figure 2&2. Fluoroscopically guided needle biopsy of the L5S1 disk using a curved needle from a posterior-lateral starting point. The needle was passed over the iliac crest and then down to the level of the L5-S1 disk, at which point the needle was rotated medially to enter the disk. This is the same technique that would be used for a diskogram at the L5-S1 level. The diagnosis was diskitis due to Streptococcus viridaw.

transpedicular approach, in which the needle is passed through the pedicle. With this approach, the needle can be angled slightly superiorly or inferiorly but movement medially or laterally is somewhat limited. For the transpedicular approach, the operator should avoid entering too far medially or inferiorly on the pedicle as this runs the risk of injury to the nerve root either in the lateral recess or at the neural foramen. Fluoroscopically guided biopsies of the inferior margin of L5, the L5-S1 intervertebral disk, and the superior margin of S1 may be difficult from a posterior-lateral approach unless a curved needle is used to pass the needle over the intervening iliac crest and then down into the target area (Fig. 26-2). This technique is similar to performing an L5S1 diskogram from the posterior-lateral approach.59 In all other areas of the spine, CT may be the preferred method of biopsy unless a transpedicular approach is taken with fluoro~copy,~. " In the upper lumbar and thoracic regions, CT provides a means of visualizing the adjacent lung and other posteriorly located visceral organs, such as the kidneys, in the case of a high lumbar target. In the cervical region, CT may also be the preferred method of image guidance for biopsies because it can be used to define the positions of the jugular vein, carotid artery, vertebral artery, and pharyngeal and esophageal structures more accurately than fluoroscopy can (Fig. 26-

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3). Furthermore, to perform cervical biopsies with fluoroscopy, the operator may have to place his or her fingers in such a way as to deviate the carotid sheath laterally and the pharyngeal structures medially. This still poses the risk of inadvertent perforation of the esophagus, pharynx, or one of the major blood vessels that have been fixed in position. In addition, fluoroscopically guided needle biopsies of the cervical spine may subject the operator's hands to radiation while the fingers are pressing between the carotid sheath and the pharynxlesophagus. For paraspinous soft tissue biopsies, fluoroscopy is at a great disadvantage, compared with CT, in that it is difficult to visualize a paraspinous soft tissue target under fluoroscopy, whereas these areas become apparent under CT (Fig. 26-4). If CT is chosen for image guidance for spine biopsy, the area of concern should first be localized with a scout film. We often place a V-shaped reference marker over the area of concern (see Fig. 26-3A). This marker consists of a polyethylene catheter that is bent at an acute angle and taped over the target zone. The marker helps to localize the level at which the optimal target will be found by providing a measurement of the distance between the limbs of the V, and we can confirm the location through localization with the laser light. From one of the limbs of the V marker on the patient, a starting point can be measured on the CT scanner and duplicated on the patient's skin surface. We then prepare the patient. We use progressively longer anesthetic needles and deliver local anesthetic agent with a very large skin wheal. We leave the anesthetic needles in place, after they are disconnected from the syringe, along the anticipated trajectory for the biopsy needles. We scan and then readjust the trajectory of the anesthetic needles accordingly and place progressively longer anesthetic needles to the target, correcting the course trajectory as necessary. When we finally reach the periosteum along the optimal trajectory, we direct a bone biopsy needle into the bone and into the target zone, usually from a tandem technique. If a smaller bone biopsy needle is used (e.g., a 17-gauge needle), a larger coaxial guiding needle can be used for multiple passes. The advantage of using a coaxial system is that the operator can easily perform multiple biopsies along an intended trajectory. The disadvantage is that most bone biopsy needles are quite large, often 13 and 11 gauge, and a considerably larger guiding needle is necessary for coaxial passage. The advances of slip ring technology with a continuously rotating x-ray tube, x-ray tubes with improved heat capacity, more sensitive semiconductor detectors, new imaging reconstruction algorithms, and high-speed parallelarray processor systems for real-time raw data reconstruction and display allowed the eventual development of realtime CT fluoroscopy." Helical CT scanners with CT fluoroscopy are widely available. Depending on the vendor, frame rates vary from two to eight frames per second, and the continuous CT fluoroscopy time varies from 40 to 100 seconds. The main advantage of CT fluoroscopy guidance, compared with conventional CT guidance, is the decreased time needed for the procedure; the operator can see in real


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Figure 26-3. CT-guided b~opsyof the cervical spine. A, Lateral scout view of the cervical spine with an overlying V-shaped polyethylene marker for reference (whrte arrows). Measurement of the distance between the V can help to confirm the location from which biopsy samples are to be taken and can provide a reference mark for measurement to the starting point. B, The V-shaped catheter on this patient's slun surface is outlined (white arrows), and the level to be targeted is confirmed by matching the distance between the V-shaped catheter at this level with what is seen on the scout view. Black arrowheads denote the needle course taken posterior to the jugular vein and anterior to the vertebral artery. C, B~opsyis performed with a lightweight 17-gauge EZEM bone biopsy needle under CT guidance along the intended trajectory course. This needle has no heavy handles to throw it off course if it is unsupported when directed under CT guidance.

time the movements of the biopsy needle (Figs. 26-5 and 26-6). The disadvantage is increased radiation exposure to the operator,l1, 33* 36 which should improve with the developments of special needle holders and even more sensitive semiconductor detectors, permitting improved image quality with lower milliampere doses.l1-32. 33 For CT needle guidance in the thoracic region, the usual trajectory is between the rib head and vertebral body (costovertebral approach). This approach avoids placement of the needle through the lung or through the exiting nerve root at the neural foramen. This technique usually allows 32p

good angulation when other various zones of the vertebral body are targeted. The alternative approach to thoracic biopsies is a transpedicular approach, which provides limited medial or lateral angulation for targets throughout the vertebral body. A transpedicular approach can be used under either CT or fluoroscopic guidance (Fig. 267). For cervical biopsies, most patients tolerate being on a side (lateral) position for longer periods of time than they would in a prone position, which often results in claustrophobia. The trajectory chosen should avoid the carotid sheath, pharynx, esophagus, vertebral artery, and spinal


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Figure 2 6 4 . CT-guided needle biopsy of a painful paraspinous muscle mass. This lesion could not be seen fluoroscopically, and CT guidance was therefore necessary. A 25-gauge needle easily yielded cytologic samples to make the diagnosis of a metastatic transitional cell carcinoma to the psoas muscle before the primary malignancy site was discovered.

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Figure 26-5. Multiple images from noncontrast CT (A) and CT fluoroscopy (B and C) sequences during a biopsy of a mixed lytic and sclerotic lesion in T12 vertebra. These images demonstrate the successful biopsy of this small lesion (A) (arrows). Note that the needle angle trajectory avoids the left kidney, rib, and pedicle (arrows). The cytologic diagnosis was metastatic adenocarcinoma consistent with a breast origin.

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Figure 26-6. Biopsy of a left paraspinal soft tissue mass. CT fluoroscopy images demonstrate advancement of biopsy needle with changes in needle orientation and depth from A to B (arrows). CT fluoroscopy allows the changes to be made in real time. The pathologic process was bacterial osteomyelitis. . .

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Figure 27-37. Subpleural distributions. A, Early CT evidence of pulmonary damage resulting from bleomycin toxicity is seen in the subpleural zones (arrows). Increased reticular markings parallel the pleural surfaces and are most prominent posteriorly. (From Kuhlman

neycombing usually demonstrate the most severe damage the periphery of the lung, in the subpleural zone, and at e lung bases. (From Kuhlman JE: CT of diffuse lung sease. Appl Radio1 20: 17-21, 1991.)

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and disorders treated with bone marrow traniclantation (Fig. 27-38) (see Figs. 27-20, 27-22, 27-32).27. 97. loo. '033 lW- lo7- 'I0 HRCT aids in the early detection of lung infection in these patients. CT patterns and signs help to characterize the nature of the infection and direct invasive biopsy proced u e s to areas of the lung most affected. CT is also helpful in monitoring response of lung infection to appropriate therapy and in detecting relapse of infection.

Acquired Immunodeficiency Syndrome When routine chest films fail to reveal a cause of unexplain4 fever or respiratory symptoms in a patient with AIDS, CT plays an important diagnostic and management role (see Fig. 27-38). CT can detect early or subtle lung infection when chest films remain negative or equivocal. In the patient with AIDS who may have many reasons to have fever or symptoms, the ability of CT to confirm the presence or absence of significant lung infection is critical in expediting the diagnostic workup. CT patterns of parenchymal lung involvement may suggest the most likely diagnosis, and CT can be used to select the diagnostic approach most likely to yield a positive culture specimen.

P. carinii Pneumoniae Infection PCP is still one of the most common llreulreatening lung infections to occur in patients with AIDS in industrial30. 31' 46.93.99. 105. 164 pCp ized have a variety of presentations, from acute fulminant respiratory failure to a more insidious onset with nonspecific symptoms of nonproductive cough, malaise, and low-grade fe~er.9~ In a patient with AIDS, this more insidious presentation is more common. The classic chest film findings of PCP are well known and include bilateral ground-glass infiltrates in a perihilar or sometimes upper lobe distribution.', 31.46 The diagnosis is straightforward in patients who demonstrate these findings. Early in the course of infection, however, the chest film may appear normal or show only minimal increased lung markings, and a reported 10% of patients with documented PCP have normal or equivocal chest films.46In this setting, CT can be used to confirm or exclude the presence of parenchymal lung infiltrates. CT patterns of PCP are varied, but the most common pattern is of diffuse or patchy, ground-glass infiltrates that do not obscure bronchovascular margins (Fig. 27-39).110 Increased interstitial markings can also be seen, particularly


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Figure 27-38. bnexp~aneaIever m a pauenr wlrn acqulred immunodeficiency syndrome (AID>). A, Lnesr film shows central venous line but no obvious infiltrates. B, CT identifies multiple inflammatory nodules with feeding vessels (arrows), compatible with a diagnosis of septic emboli. The source of the septic emboli was found to be the central venous catheter that had become infected. (B, From Kuhlman JE, Fishman EK, Burch PA, et al: Diseases of the chest in ADS: CT diagnosis. Radiographics 99327-857. 1989.)

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-E, From Kuhlman JE: CT of the immunocomprom&ed andacutely ill patient. In %rhouni EA [ed]: CT and MRI of the Thorax. New York, Churchill Livingstone, 1990; F, From Kuhlman JE, Fishman EK, Burch PA, et al: Diseases of the chest in AIDS: CT diagnosis. Radiographics 9:827-857, 1989; G, From Kuhlman JE: AIDS-related diseases of the chest. In Kuhlman JE [ed]: CT of the Immunocompromised Host. New York, Churchill Livingstone, 1991.) H, Solitary pulmonary nodule, an unusual manifestation of PCP seen in a few patients with AIDS.

in patients who have had repeated Pneumocystis infections (20% to 40% of patients), because of the interstitial fibrosis that develops as the infection heals. Another CT pattern of PCP, which is quite different in appearance. occurs with the cystic form (Fig. 2740).* On CT scans, the cystic form of PCP is characterized by one or more thin-walled cysts or cavities that are somewhat irregular in shape and may be coarse or delicate in appearance. Surrounding ground-glass inliltrates are often present. This form of PCP may also be associated with CT manifestations of disseminated infection, including enlarged lymph nodes with calcifications found in the mediastinum and abdomen, and other calcifications in the liver, spleen, and kidneys (Fig. 27-41).99.lS3 Many patients with cystic PCP or lymph node and visceral calcifications caused by Pneumocystis infection were reported to be receiving aerosolized pentamidine for prophylaxis against PCP. The aerosolized drug may par*See References 13, 30, 41, 53, 83, 92, 105, 125, 149, 193, 203, and 222.

t i d y clear or partially suppress the pulmonary infection, but it may not attain high-enough concentrations in the blood to prevent dissemination of the Pneumocystis organism. The chronic infection that remains in the lung may predispose to cystic cavity formation. More recently, aerosolized pentamidine has been less often used as a prophylactic agent, having been replaced by other, more effective drugs. Despite this change, the cystic form of PCP continues to be seen and some report an increasing frequency of this pattern of pre~entation.~ A rare CT presentation of PCP is the solitary pulmomry nodule.13> 'lo A nodule may form in those individuals positive for the human immunodeficiency virus (HIV) who have less severe immunosuppression and can still mount a granulomatous response to the infection (see Fig. 27-390). Pleural effusions are an uncommon finding in uncomplicated PCP. Rare cases of pleural effusions caused by disseminated Pneumocystis infection have been reported, and More often pleural calcifications may be dem~nstrated.~~ in the patient with AIDS, the cause of a pleural effusion is a bacterial, fungal, or mycobacterial infection; lymphoma;

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Figure 2741. Disseminated Pneumocystis carinii pneumonia (PCP) infection. A, CT shows characteristic enlarged lymph nodes with calcifications. (From Kuhlman JE: CT evaluation of the chest in AIDS. In Thrall J [ed]: Current Practice in Radiology. St. Louis, Mosby-Year Book, 1993.) B and C, Calcifications caused by disseminated PCP can also be seen in the spleen (arrow in B), abdominal lymph nodes (arrows in 0, liver, and kidneys (arrowheads in C) in patients with disseminated PCP infection. Low-attenuation splenic lesions in C are the result of PCP splenic abscesses. (B, From Kuhlman JE: AIDS-related diseases of the chest. In Kuhlman JE [ed]: CT of the Irnmunocompromised Host. New York, Churchill Livingstone, 1991.) -1

or Kaposi's sarcoma. Although less well recognized, PCP infection can also cause airway abnormalities, including bronchiolitis and bronchiolitis ~ b l i t e r a n s . ~ ~ Several ancillary CT findings may be identified in patients with PCP or HIV disease. Apical and paraseptal bullae and spontaneous pneumothoraces are often noted in these relatively young patients (Fig. 2 7 4 2 and see Fig. 27-40).15 139. lg5 In a patient with AIDS, pneumothoraces are often difficult to resolve because of persistent air leaks. They may require more invasive procedures than simple chest tube placement, including pleurodesis, lung stapling, or pleurectomy to reexpand the lung.

Fungal Infection In patients with AIDS, fungal infections involving the lungs usually present as multiple nodules or cavities (Fig. 27-43).%. 90. 105. When present, fungal lung infection usually suggests disseminated disease. Other nonpulmonary manifestations of fungal disease, such as CT findings of esophagitis with esophageal wall thickening or focal lesions in the liver, may be the first indication of a disseminated fungal infection both in patients with AIDS and in other immunocompromised hosts (Figs. 27-44 and 27-45). Any number of fungal species may cause pulmonary infection in the AIDS patient, including Candida albicans, Coccidioides immitis, Histoplasma capsulatum, and Cryptococcus neoformuns. Infections caused by Aspergillus oc-

_

cur in patients with AIDS but much less frequently than they occur in other immunocompromised patients such as those with leukemia and prolonged neutropenia. This is because the body's immune response to Aspergillus infection requires only intact neutrophils and macrophages rather than healthy T cells or antibodies. Neutrophil function is relatively preserved in AIDS patients until end stages of the disease. Aspergillus infections are seen, however, in AIDS patients who are taking corticosteroids or multidrug regimens that suppress neutrophil counts. Cryptococcus is the most common fungal pathogen to affect the lungs in patients with AIDS, almost always (>go% of cases) in conjunction with infection of the central nervous system. Z

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Nocardial Infection Nocardia is yet another opportunistic organism that is increasingly being recognized in the patient with AIDS.%. 99* IoS On CT scans, Nocardia infection may start out as a small inflammatory nodule but eventually develops into a cavitary mass or more extensive cavitary pneumonia involving one or more segments or lobes of the lung (Fig. 2746). Although the unusual opportunistic infections are usually emphasized in regard to pulmonary infections in AIDS, it is important to keep in mind that bacterial infections, often severe, aggressive, and recurrent ones, occur fre-


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~3gure2742. A-G;-ApicaI and -pa sll (arrows) in a patient with acquired i m m u n o d e f i c i ~s w m (AIDS) and repeated Pneumocystis infdom. Wrn KWm8n JE,Kavura M, Fishman EK, Siegelman SS: Pnemcysris e a W pimatmania: Spectrum of parenchymal CT findbe. Radiology 1753'11-7 14, I%.)

nodules found in miliary TB,8. the nodular opacities seen in bronchogenic spread are nonuniform in size and unevenly distributed. Various terms have been used to describe these nodular opacities, including acinar nodules, acinose lesions, acinar Tuberculosis shadows, and tree-in-bud opacities.*Oa Pathologically, the Of increasing concern is the resurgence of TB as a lesions seen on CT scans correspond to peribronchiolar significant communicable pulmonary infection in the foci of infection and granulomatous reaction that are cenUnited States, resulting in part from tbe AIDS e p i d e m i ~ . ~ ~tered around the terminal respiratory bronchioles and their Emergence of multiresistant strains poses an ever-growing 167. lS2 In cases of suspected TB, surrounding threat to public health on a global scale. CT can be used to identify a small or occult cavity that is CT manifestations of pulmonary TB depend to a large the source of the bronchogenic spread and to demonstrate extent on the health of the individual's immune system the full extent of the infection, which is often widely (Figs. 27-47 to 27-55). In the immunocompetent host, scattered in both lungs. cavitation is one of the hallmarks of reactivation TB.56.167 If the host's immune system and the ability to mount a Cavities develop when centers of granulomatous reaction granulomatous response are intact, the reactivated infection to the TB bacillus undergo caseation necrosis. On CT is often contained and healing begins with the deposition of scans, cavities owing to TB can be thick-walled or thincollagen and scar tissue around areas of caseous necrosis! walled and are indistinguishable from those caused by Eventually, dystrophic calcifications form within granu167, 238 other atypical mycobacterial species6. ", lomatous nodules, lymph nodes, and fibrotic strands, and Often with the development of tuberculous cavitation, the lung assumes the characteristic appearance of chronic the necrotizing process erodes into the tracheobronchial fibrocalcific TB. Further scarring leads to lung distortion, tree and the expelled tuberculous material spreads by the bronchiectasis, volume loss, and cicatrization atelectasis endobronchial route to other parts of the lung. and compensatory emphysema. Fibrotic, masslike lesions may form in the lung apices and may be difficult to Typical CT features of bronchogenic spread include distinguish from apical lung cancers or scar carcinomas on patchy areas of air space disease consisting of poorly the basis of CT appearances alone.u8 defined nodular opacities measuring from 3 to 10 mm in Text continued on page 878 diameter.s6.59+ 8oa, 167 Compared with the smaller discrete

quently in patients with AIDS, including those caused by Streptococcus pneumoniae, Staphylococcus pneumoniae, and Haemophilus influenzae.

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Figure 27-43. Disseminated cryptococcal infection. Chest film (A) and CT (B, C ) show multiple pulmonary nodules.

Figure 274. Cytomegaloviral esophagitis. Marked thickening of the esophageal wall is evident on the CT scan. Oral contrast material is retained within the dilated, inflamed esophagus. (From Kuhlman JE: AIDS-related diseases of the chest. In Kuhlman JE [ed]: CT of the Immunocompromised Host. New York, Churchill Livingstone, 1991.)

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Figure 27-45. Disseminated candidiasis. CT shows multiple filling defects in the liver caused by fungal abscesses (arrows). (From Kuhlman JE:CT of the immunocompromised and acutely ill patient. In Zerhouni EA [edl: CT and MRI of the Thorax. New York, Churchill Livingstone, 1990.)

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Figure L/+b. Nocardiosis in a patient with acquired immunodeficiency syndrome (AIDS). A, Initial CT scan on a patient with positive status for human immunodeficiency virus (HIV) infection shows a small inflammatory nodule in the right lower lobe. B, Nocardia infection has progressed to a large necrotic cavity. C, Nocnrdin infection in another patient with AIDS presented as a multilobar cavitary pneumonia. (C, From Kuhlman JE: AIDS-related diseases of the chest. In Kuhlman JE [ed]: CT of the Immunocomprornised Host. New York, Churchill Livin sto?e, 1291.)

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Figure 27-47. A-C, Myc~bacterialinfections. Cavities may be thin-walled ( A ) or thick-walled ( B ) . (B, From Kuhlman JE, Deutsch JH, Fishman EK, Siegelman SS: CT features of thoracic mycobacterial disease. Radiographics 10:413-431, 1990.) C, Milia& taberculosis. CT reveals berinimerabletiny nodules distributed homogeneously throughout the lungs.

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Elgure LI-46. L l rei s or lchogenlc spread or mycobactend disease. A and B, LVl'scan shows a large cavity in the right upper lobe and a smaller c a on t :ft. Widely scattered areas of bronchogenic spread (arrows) are identified, demonstrating a "tree-inbud" pattern. The patient has a right-sided aortic arch.

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Figure 27-49. A and B, On these CT scans, areas of bronchogenic spread of tuberculosis appear as poorly marginated, "fluffy nodular densities of variable size.

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Figure 27-51. Ranke's complex. CT image shows the calcified parenchymal scar (Ghon's lesion) (arrow) and the calcified hilar nodes representing healed regional lymphatic involvement from the initial tuberculosis infection.

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Figure 27-52. Simon's foci, an example of healed sites of tuberculosis (TB) seeded to the lung apices at the time of the primary TB infection. The masslike opacity seen in the right apex was the result of healed TB in this case, but on the basis of the CT appearance alone, it is indistinguishable from that of lung cancer. Such opacities require close, serial follow-up to ensure stability in size over time or biopsy, in some cases, to exclude neoplasm. (From Kuhlman JE, Deutsch JH, Fishman EK, Siegelman SS: CT features of thoracic mycobacterial disease. Radiographics 10:413-431, 1990.)

Figure 27-53. A and B, Aspergillomas, growing in old tuberculous cavities, are identified on CT.

Figure 27-54. A and B, Tuberculosis in a patient with acquired immunodeficiency syndrome (AIDS). CT shows multiple inflammatory lung masses and bulky mediastinal nodes (arrows)resulting from tuberculosis (TB). Lymphadenopathy is the rule rather than the exception in patients with AIDS and TB.(From Kuhlman JE. CT evaluation of the chest in AIDS. In Thrall J [ed]: Current Practice in Radiology. St. Louis, Mosby-Year Book, 1993.)


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Figure 27-55. Tuberculosis in a patient with advanced acquired immunodeficiency syndrome (AIDS). A woman with status positive for human immunodeficiency virus (HIV) infection was shown at autopsy to have bilateral pulmonary infiltrates (A), extensive lymphadenopathy (B, arrows), and multiple lytic bone lesions (3 and C, arrowheads) caused by widely disseminated tuberculosis. (From Kuhlman JE: AIDS-related diseases of the chest. In Kuhlman JE [ed]: CT of the Imrnunocompromised Host. New York, Churchill Livingstone, 1991.)

Frequently on CT scans, evidence of earlier TB infection can be found in the form of old healed cavities or sequelae, .Yt such ass6.'02: .. 1. Ghon's lesion, the parenchymal scar or granuloma that occurs at the site of initial TB infection. This lesion is often calcified. 2. Ranke's complex, consisting of a parenchymal scar and the associated calcified lymph nodes in the pulmonary hilum or mediastinum. The presence of this complex suggests regional lymphatic spread. 3. Simon 'sfoci, or healed residua of TB seeded to the lung apices at the time of primary infection.

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serial chest films or serial CT scans. Follow-up CT exarninations have become an important adjunct to sputum cultures in assessing response to treatment in infected patients. In part because of the declining exposure rate of children to TB, a larger number of first-time exposures are occurring in adulthood, making cases of primary rather than reactivation TB in the adult more common than before. Mediastinal and hilar adenopathy is often an indication of primary TB infection?'. lu

Tuberculosis in Special Patient Populations A number of individuals are at increased risk for develChronic TB cavities may permanently scar the lung and opment of active TB, including older, debilitated, and malremain open even after sterilization. These chronic cavities nourished patients and patients with AIDS.56- 81. lS4, 16'. Ig4 may become complicated by superimposed infection or Special considerations also apply to patients with sarcoidocolonization with Aspergillus fungi that form m y c e t ~ m a s . ~ ~sis ~ and silicosis, in whom the prevalence of TB is increaSed.56. 81. 154. 167, 1%. 238 Although TB produces many chronic lung changes, disPatients with AIDS are particularly susceptible to mycoease activity cannot be determined on the basis of CT bacterial infections both from Mycobacterium tuberculosis appearances alone. Fibrotic areas of lung and cavities that and from other atypical organisms, such as M. aviumlook inactive on chest radiographs or CT may in fact intracellulare (MAI), M. avium complex (MAC), and M. harbor viable organisms.%,us The radiologic stability of TB-induced lung changes, however, can be assessed with k a n ~ a s i i .134 ~ ~In. 10% to 20% of patients with AIDS, M.


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avium-intracellulare infections are detected sometime durBleomycin ing their life from blood, sputum, or bone marrow cultures. In cases of bleomycin lung, HRCT has been more sensiAt autopsy, more than 50% of these patients are found to tive than chest radiographs in detecting early pulmonary be infected. Despite these statistics, pulmonary infiltrates toxicity, more accurate in quantifying the extent of pulcaused by M. avium-intracellulare are considerably less monary damage, and more helpful in monitoring disease common than those caused by TB.134 progression or res01ution.'~-l7 The extent of pulmonary The most common CT manifestation of M. aviumdamage, as seen on CT scans, correlates well with intracellulare infection is diffuse adenopathy. Regardless of measurements of impaired gas transfer and pulmonary mycobacterial species, however, the normal granulomatous function.16 l7 response to mycobacterial infection is poor or absent in the CT features of bleomycin lung toxicity include linear patient with AIDS, and disseminated disease is more reticulations, fibrotic bands, and nodular opacities that may common than in the immunologically competent h o ~ t .l" ~ ~ ~mimic ~ . pulmonary metastases or recurrent tumor (see Fig. The AIDS population is particularly vulnerable to the 27-%).I6. 163. These changes often appear first in the spread of TB. In some parts of Africa, the combination of periphery of the lung and at the lung bases, paralleling the AIDS and TB has become epidemic. Manifestations of pleural surfaces (see Fig. 27-37).16. 163, Is8 AS the pulmonary TB in the patient with AIDS depend on the degree of toxicity becomes more severe, the reticular and nodular immunosuppression. In a patient with early HIV infection opacities coalesce to form large confluent opacities. Diffuse and milder immunosuppression, TB presents in a more air space disease can also be seen with acute bleomycin classic fashion with cavitary disease and bronchogenic spread. TB that occurs in the setting of more severe immuRegardless of the offending agent, early CT findings of nosuppression or full-blown AIDS is more often atypical drug-induced pulmonary toxicity are often confined to the and aggressive in its manifestations, presenting in a manner subpleural zone. The apparent susceptibility of this region more reminiscent of primary TB, primary progressive TB, to lung toxicity may be related to the limited collateral or miliary TB.%.lM airflow within the region or to the increased pressure and In the patient with advanced AIDS, widely disseminated friction the zone experiences from the overlying pleura." and extrapulmonary disease and multiple pulmonary masses with significant adenopathy are not uncommon presentations of TB. Mediastinal and hilar adenopathy - - as a Amiodarone manifestation of TB in an AIDS patient is the rule rather Amiodarone is an antiarrhythmic agent that can cause than the exception. After administration of contrast rnatesignificant and potentially irreversible pulmonary toxicrial, tuberculous lymph nodes demonstrate characteristic ity.62.132. The drug is used primarily to treat refractory low-attenuation necrotic centers and rim enhancement on life-threatening arrhythmias. Early recognition of pulmoCT scans.!' 81. lS4 In addition, traditional tests for TB nary toxicity is important because prompt discontinuation exposure (e.g., the tuberculin skin test) are unreliable in 175 of the drug often results in resolution of patients with AIDS because most patients are anergic. Unfortunately, few radiographic or laboratory findings are specific for amiodarone toxicity. Symptoms are also nonspecific, making early diagnosis of pulmonary toxicity M . avium-intracellulare in Older Women on the basis of clinical evidence difficult. Onset of symptoms may be insidious, and symptoms caused by amiodarM. avium-intracellulare infection can also strike otherone toxicity, such as pleuritic chest pain, shortness of wise healthy, irnmunocompetent hosts. A distinct subtype breath, malaise, and low-grade fever, may be similarly has been reported in women between ages 50 and 90 years produced by cardiac decompensation, pneumonia, or pulwho have no underlying illness but present with a chronic, monary infarction, all common concurrent problems in persistent cough. This subtype has a fairly characteristic heart disease 175 Fortunately, because of its CT appearance, with scattered areas of mild tubular bronunique chemical composition (which contains three iodine chiectasis associated with nodular opacities and tree-in-bud moieties), amiodarone-when deposited in sufficient quanforms. Cavitation is less common than in TB?O",153a tities within the lung--can be recognized by its high CT attenuation, which aids in diagnosis (see Figs. 27-59 to 27-61).28. 115. 116. 172 187.209 Pulmonary Drug Toxicity On unenhanced scans, CT features of amiodarone lung Early detection of drug-induced lung toxicity is another toxicity include areas of consolidation or focal atelectasis application of HRCT that is under current investigation.* showing high CT attenuation in the range of 80 to 110 Patients with respiratory symptoms who are receiving bleoHU.28.lL5,ll6, lS7. The high-attenuation areas frequently mycin, methotrexate, amiodarone, or other potentially toxic abut the pleura, show adjacent pleural reaction, and may be agents to the lung benefit from CT evaluation (Figs. 27-56 wedge-shaped. Increased attenuation is also frequently demto 27-61). Early detection of drug-induced pulmonary damonstrated in the liver, spleen, thyroid gland, and occasionally age increases the likelihood that lung damage will be in the heart muscle. Nonspecific pulmonary infiltrates, interreversible when the drug is withdrawn. stitial infiltrates, mixed alveolar and interstitial disease, and conglomerate masses may also be 115172-187,m Nonenhanced CT findings of high-attenuation parenchy*See References 16, 17, 26, 28, 115, 116, 163, 172, 187, 188, and 209. mal abnormalities are thought to be related to the iodinated 1759237

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Figure 27-56. CT detection of drug-induced lung toxicity. Patient with recurrent lung cancer receiving ipomeanol, an investigational chemotherapeutic agentknown to cause potential lung toxicity. A, CT shows development of a band of increased attenuation in the subpleural region, not detected on plain films (arrow).B, After tinuation of the drug, the abnormality resolved.

*,

Figure 27-57. A and B, Methotrexate pulmonary toxicity. The patient, a 59-year-old woman who was taking methotrexate for treatmeh~ of severe psoriasis, experienced subacute onset of fatigue, shortness of breath, and a nonproductive cough. CT shows patchy "groundglass" infiltrates that were difficult to appreciate on chest radiographs. Cultures were negative for infection, and a lung biopsy specimen showed changes consistent with a diagnosis of methotrexate lung toxicity.


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Figure 27-58. Bleomycin lung toxicity, CT features. A and B, CT shows nodular opacities, which may be mistaken for tumor recurrence or' metastases but are actually caused by bleomycin toxicity, proven by biopsy. C, CT can be used to follow the progression or resolution of pulmonary toxicity. In this case. the nodular opacities progressed to larger areas of confluence. D, After discontinuation of the drug, a follow-up CT scan shows nearly complete resolution of the pulmonary lesions.

chemistry of the drug and its prolonged half-life within ported that occurred after pulmonary arteriography was the lung.* Amiodarone is known to accumulate in high attempted in patients who presented with pleuritic chest concentrations within the lung and the liver, where its halfpain caused by amiodarone lung toxicity. Performing pullife is 15 to 60 day^."^,'^^ Trapped by foamy macrophages, monary arteriography in these patients to the drug becomes incorporated within lysosomes, where nary infarction should be avoided if possible.'37 the cationic. amphophilic drug interacts with phospholipids to form a drug-lipid complex that resists biodegradation.? High-Attenuation Parenchymal Characteristic lamellar inclusion bodies form within the Abnormalities lysosomes and interfere with lipid degradation and surfactant turnover, ultimately inducing a fibrotic reaction within A few other disease processes can produce high-attenuathe lung. These unique properties of amiodarone and the tion parenchymal abnormalities on CT scans, as follows: use of CT to discriminate attenuation levels provide a as the means of iclentifying those patients with significant p u l m o ~ M e t a s r a t i cp L 1 l m o n a ~calc$cations -1 ' result of hyperparathyroidism from renal failure or from nary accun~ulationof the drug. RecogniLing amiodarone-induced lung changes in nond t h e infusion of large amounts of calcium salts in children with congenital heart disease can cause high-attenenhanced CT scans is particularly important in those paOn CT scans."3' "' tients who present with pleuritic chest pain. At least thremuation

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cases of acute pulmonary decompensation have been re Jr*a 2. Focal and multifocal, high-density lung opacities have I -been reported in cases of amvloid, probablv resulting from d;strophic calcification kithin'areas of amyloid "See References 9, 29, 39. 44, 67, 77, 85. 115, 116, 124. 137, I ~ L 187, 189. and 201. +See refe~cnces9, 29. 39.44. 62, 67, 77, 85, 124. 137, 162. and 189,

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Figure 27-55. .miodarone toxicity. A 69-year-old man with chronic obstructive pulmonary disease, ischemic cardiomyopathy, and ventricular arrhythmias required antiarrhythmic medication. He presented with a 2-week history of increasing shortness of breath and pleuritic chest pain. C ) -2 1 TJ A and B, Chest film shows ill-defined opacity or area of focal atelectasis (arrows) and left pleural effusioa,, rrrrb C and D, Nonenhanced CT scan shows the focal lung opacity demonstrating high attenuation on soft tissue window settings (arrow) compatible with a diagnosis of amiodarone toxicity. Bronchoscopy was negative for tumor and for infection and yielded abundant foamy macrophages. E and F; Other CT evidence of amiodarone exposure includes dense thyroid and dense liver resulting from the iodine content of the drug, which accumulates in these organc qcmL LIL I ~ , i v ~ ~ : ' C ~ . ~ , ~ ~ ~ u ~ . ~


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Figure 27-60. Aniiodarone toxicity. A and

-, The patient, a 40-year-old-wo~nanwith arrhythmias who had been taking arniodarone for 32 montlis. presented with pleuritic chest pain and shortness of breath. A. Noncontrast C T shows a large. wedge-shaped area of consolidation in the right lung base (or-robvs). A band of atelectasis is noted adjacent to the left heart border (ctrr-ott:hetrcl.s). B. Both areas demonstrate high attenuation on soft tissue window settings (nrro\v.s). The increased attenuation of the heart muscle is a result of JE. Tergen C. Ren H. et al: A~niodaronepullnonary toxicity: C T findings in amiodarone tieposition (arro~:l?etrtl.s).(From Kuhln syniptornatic patients. Radiology 177:121-125. 199b.l

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mitral stenosis can produce high-density air space opaci ties in the lung parenchyma.238a

Occupational Lung Disease

The use of CT, especially HRCT, in the evaluation f '. 86* lS4 occupational lung diseases is rapidly e~panding.~. A number of reports suggest that HRCT is superior to conventional radiographs and standard CT in the detection of pulmonary damage resulting from asbestosis and pneum~coniosis.-HRCT-~Sbeing ised to detect

occupational lung disease, to determine the extent of the damage, and to follow the disease progression. CT features of different types of pneumoconiosis are beginning to be recognized and characterized. HRCT findings that have been described in silicosis include micronodules, subpleural nodules, conglomerate masses, and focal emphysema (Fig. 27-62).lS4 CT has become an important adjunct to conventional radiographs in the evaluation of asbestos-related disease^.^^ 86 CT is more sensitive and specific than plain films and docymenting the presence59

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Figure 2741. High-density infiltrates on noncontrast CT, differential diagnosis. A, Highdensity atelectatic lung measuring 105 Hounsfield units because of arniodarone toxicity. (From Kuhlman JE, Teigen C, Ken H, et al: Amiodarone pulmonary toxicity: CT findings in symptomatic patients. Radiology 177:121-125, 1990.) B, High-density consolidation in the right middle lobe in this patient was the result of metastatic pulmonary calcification of chronic renal failure in an area of pneumonia. (From Kuhlman JE, Ren H, Hutchins GM, Fishman EK: Fulrninant pulmonary calcification complicating renal transplantation: CT demonstration. Radiology 173: 459-460, 1989.) --r.5~~+-P_II--


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Figure 27-62. A and B, CT findings in a patient with silicosis. The diffuse profusion of micronodules is caused by silicosis. (From Kuhlman JE: CT of diffuse lung disease. Appl Radio1 20:17-21, 1991.)


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plaques, pleural thickening, and pleural calc$cations, all of which are important markers of asbestos exposure (Fig. 27-63). Mimics of pleural plaques on plain films, such as rib companion shadows, extrapleural fat, and prominent intercostal muscles, are readily distinguished from pleural plaques by CT examination. CT is also helpful in evaluating other asbestos-related pleural changes, such as rounded atelectasis. Rounded atelectasis has a typical CT appearance that distinguishes it from an asbestos-related malignancy, such as lung cancer or mesothelioma (see "CT Signs of Focal Lung Disease" earlier and Fig. 27-23). HRCT is also used to search for evidence of interstitial fibrosis, which may indicate the presence of asbestosis. Findings such as thickened interlobular septa, honeycombing, and subpleural septa1 lines, although not specific for asbestosis, do indicate the presence of interstitial fibrosis and, when found in association with pleural plaques, are compatible with asbestos-induced parenchymal lung damage.3.s. =

Quantification of Lung Damage Emphysema Quantification of lung damage is another potential application for HRCT in the management of diffuse lung dis-

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Non-neoplastic Pare~chymalLung Disease

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ease. One such application is the assessment of the severity 63-148 and extent of pulmonary In emphysema, destruction of the alveolar wdls and the underlying elastic fiber network of the lung results in permanent enlargement of the air spaces distal to the terminal bronchiole? Involvement of the proximal portions of the acinus (the respiratory bronchioles) results in centrilobular emphysema (CLE) (Fig. 27-64), whereas enlargement of all elements, from the respiratory bronchioles to the terminal blind alveoli, results in panlobular emphysema (Fig. 27-65).7s Emphysema is thought to result from an imbalance in the elastase/antielastase activities within the lung. Alveolar wall destruction results from proteolytic destruction by elastin whenever there is a relative increase in elastase activity in comparison to antielastase forces, such as alpha,antitrypSin activity.58, 75.79, 119. 121. 1%. 199.233. 234 CT features of emphysema include intraparenchymal low-attenuation areas, pulmonary vascular pruning, pulmonary vascular distortion, and abnormal lung density gradients (see Figs. 27-64 and 27-65)." Visual grading systems as well as more sophisticated computer-generated attenuation maps of the lung can be used to grade pulmonary emphysema in both a qualitative and a quantitative fash-

Figure 27-64. Centrilobular emphysema: correlation between CT and pathology studies. A, C T scan of an inflated-fixed lung specimen demonstrates focal areas of nonperipheral low attenuation (long arrows) and small peripheral bullae (short arrows). B, Corresponding gross pathologic specimen. C, More severe centrilobular emphysema. CT of lung specimen shows more marked dilatation of the centrilobular air spaces (arrows) and large peripheral bullae (arrowheads). D, Matching gross specimen. (A-D, From Hruban RH, Meziane MA, Zerhouni EA, et al: High-resolution computed tomography of fixed-inflated lungs: Pathologic-radiologic correlation of centrilobular emphysema. Am Rev Respir Dis 136:935-940, 1987.)


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Figure 2745. A and B, Panacinar emphysema. Highresolution CT findings of panacinar bullous emphysema include intraparenchymal low-attenuation areas (lung dropout), pulmonary vascular pruning and distortion, abnormally low CT attenuation of the lung, and enlarged air spaces

ion."" These attempts to assess the extent and severity of emphysema using HRCT criteria have achieved a high degree of success, with emphysema scores correlating well with pulmonary function tests and measuregegs of jm-paired diffusing ~apacity.4~~ 63 CT provides more accurate assessments o!%&physema hi than conventional radiographs, and CT scores of centrilobular emphysema correlate well with the severity of disease demonstrated on pathologic examinations of inflated-fixed lung ~pecimens.4~. L48. HRCT has also been found to be accurate in evaluating experimentally induced emphyl~~ sema in pig lungs exposed to e 1 a ~ t a s e . Increasingly, HRCT is being used to assess the extent and severity of emphysema in clinical practice as well.lla~ss

portion to the abnormalities seen on conventional chest films, which may be remarkably normal. In more severe cases, chest radiographs may demonstrate hyperinflation, honeycombing, irregular opacities, coarse reticulations, chylous pleural effusions, and pneumothora~es.~~. 9s-'I8, lS6 The HRCT appearance of LAM is usually dramatic and characterized by bilateral, diffuse involvement of the lung with thin-walled, cystic air spaces (Fig. 2 7 4 ) . 1 1 8 . The cystic spaces generally measure less than 0.5 cm in mild disease but can be greater than 1 cm in diameter when more than 80% of the parenchyma is involved.lS6Most of the spaces have identifiable walls ranging from faintly perceptible to 2 mrn thick. Typically, the lung is involved uniformly, with no predilection for upper or lower lobes. Pathologically, LAM is characterized by widespread proliferation of atypical smooth muscle cells in the bronchial tree, alveolar septa, and pulmonary and lymphatic vessels (Fig. 2747).38.", 9s The pathogenesis of the cystic spaces seen on HRCT is not known. One theory suggests that obstruction of small airways by the proliferating smooth muscle cells causes distal air trapping and air cyst formation. Other evidence has shown there is an increased number of disrupted elastic fibers within the lungs of patients affected by LAM. Fukuda and colleaguess7postulate

","is

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Lymphangiomyomatosis Another pulmonary disease whose severity is more accurately depicted with HRCT than with conventional radiography is lymphangiomyomatosis (LAM).Il8. lS6 Patients with LAM present with symptoms of shortness of breath and dyspnea on exertion that resemble those of emphysema, but the disease occurs exclusively in women of child-bearing age. The symptoms are typically out of pro-

579


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Figure 27-66.2Yae patbat is rr 4%ym& msiw~with shortaas gf breath and mewrent pnemoxho~.4 Chest film&om h y p ~ t i o an8 n mmse re%&&-. was out of p p i i o a ,tg hchest abn;ormaWes, pegm me&y @fthe Kuhlman JE, Reyes BL,Hnrban RE& et al: AbnomaI air-filled spaces in the lung. Radiographics 13:47-75, 1993.) B, Hlgb-1.esolution CT shows extensive mpimrnent of mnnal lung anrhiitecture with innumerable thin-walled, dilated, cystic air spaces that resemble severe panacinar emphysema. In In& this patient has di&se lymphngiomyomatosis.

27-67. Pathology of lymphangiomyomatosis.A, Histologic specimen shows proliferation of smooth muscle fibers in the interstitiurn, and alveolar septa of the lung with remodeling of normal lung architecture. B, Low-power view of the lung shows replacement of the lung by cystic, dilated air spaces. (From Kuhlman JE, Reyes BL, Hruban RH,et al: Abnonnal air-filled spaces in the lung. Radiographics 13:47-75,1993.)

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888

Part V

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Figure 27-68. A and B, Early Langerhans' cell histiocytosis ~nvolvingthe lung. CT shows multiple, thin-walled regular cysts (arrows) and t ~ n ynodules (arrowheads). (From Kuhlman JE, Reyes BL, Hruban RH, et al: Abnormal am-filled spaces In the lung. Radiographics

13:47-75, 1993.)

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that the emphysema-like lesions seen in LAM on pathologic examination result from increased elastic fiber degradation caused by an upset of the elastaselantielastase balance within the lung.

Pulmonary Langerhans' Cell Histiocytosis (Histiocytosis X, Eosinophilic Granuloma) A lung disease whose radiographic and CT appearance resembles lymphangiomyomatosis is pulmonary Langerhans' cell histiocytosis (formerly, histiocytosis X and eosinophilic granuloma) (Figs. 27-68 to 27-71)?Ob Langerhans' cell histiocytosis is a granulomatous disease of unknown origin that may affect the lung exclusively or may affect multiple organ systems.L33It is in the spectrum of disseminated disorders, including Letterer-Siwe disease, Hand-Schiiller-Christian syndrome, and eosinophilic granu10rna.l~~Granulomas, in each case, are formed by eosinophils and cells of the monocyte-macrophage system, which are Langerhans' cells. Langerhans' cell histiocytosis

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affects mostly young and middle-aged adults, who present with complaints of cough, dyspnea on exertion, and sometimes chest pain from pneumothorax (20%) or bone i n v o l v e ~ n e n t 133 . ~ ~These ~ ~ patients are almost invariably (>go%) smokers?@' Findings on plain chest films include any combination of reticulation, nodules (2 to 5 mm),cysts (C1 cm), honeycombing, and emphysematous Is' The upper lung zones tend to be more involved and the costophrenic angles spared. Lung volumes are usually normal but sometimes increased. This has been attributed to the opposing effects of emphysema and the cicatricial fibrosis that occurs in this disease. HRCT demonstrates the extent and distribution of parenchymal lung damage in Langerhans' cell histiocytosis more accurately than conventional radiography.2s-u3 HRCT findings of pulmonary Langerhans' histiocytosis include small nodules (2 to 5 mm or less), cystic air spaces (usually C1 a)honeycombing, , and changes compatible with emphysema (see Figs. 27-68 and 27-70).". Is3 Much of what

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Figure 27-69. Histologic specimen of lung tissue affected by Langerhans' cell histiocytosis. A focus of manulomatous reaction farrows) has created a cystic space (arrowheads) throhgh retraction and remodeling of the lung architecture. (From Kuhlman JE, Reyes BL, Hruban KH, et al: Abnormal air-filled spaces in the lung. Radiographics 13:47-75, 1993.)


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889

Figure 27-70. Advanced Langerhans' cell histiocytosis. A, Chest film in a 19-year-old woman with diabetes insipidus and dyspnea. A right pneumothorax and increased reticulations are present. B, High-resolution CT more clearly shows that the lung has been replaced by cystic spaces of varying sizes, some of which have coalesced into bizarre shapes (arrow).(From Kuhlman JE, Reyes BL, Hruban RH, et al: Abnormal air-filled spaces in the lung. Radiographics 13:47-75, 1993.)

appears to be reticulation and emphysema on plain films can be shown to be discrete cystic air spaces with definable walls on HRCT.= Sometimes several cystic spaces coalesce to form bizarrely shaped air spaces on CT scans. CT also demonstrates more of the smaller ( Squamous ceU carcinoma Variants: papillary, clear cell, small-cell, basaloid ... Adenocarcinoma . . . Acinar adenocarcinoma , :' .. . Papillary adenocarcinoma f , . Bronchioloalveolar carcinoma -. Solid adenocarcinoma with mucin ... , I . . Adenocarcinoma with mixed subtypes -.+j-:Variants: fetal, clear cell, signet-ring, co 016 Large cell carcinoma Variants: clear cell, large-cell neuroendocrine, combined largecell neuroendocrine, basaloid, lymphoepithelioma-like carcinomas Adenosquamous carcinoma Small-cell carcinoma Variant: combined smallcell carcinoma Carcinomas with pleomorphic sarcomatoid or sarcomatous elements Carcinomas with spindle andlor giant cells (pleomorphic carcinoma, spindle cell carcinoma, giant cell carcinoma) Carcinosarcomas Pulmonary blastoma Carcinoid tumor Typical carcinoid Atypical carcinoid Carcinomas of salivary-gland type Mucoepidermoid carcinoma Adenoid cystic carcinoma 11. Mesenchymal k o r s Primary pulmonary sarcomas Vascular sarcomas (angiosarcoma, epithelioid, emangioendothelioma) Spindle cell sarcomas (malignant fibrous histiocytoma, hemangiopericytoma, fibrosarcoma, leiomyosarcoma, synovial sarcoma) III. Lympoproliferative Disorders Lymphoid interstitial pneumonia Nodular lymphoid hyperplasia Low-grade marginal-zone B-cell lymphoma of the mucosaassociated lymphoid tissue (MALT) Lymphomatoid granulomatosis IV. Miscellaneous Tumors Hamartoma Granular ceU tumors Sclerosing hemangioma Clear cell tumor V. firnor-like Lesions Hyalinizing granuloma Amyloid tumor

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Modified from Travis WD, Colby TV,Comn B, et al: Histological Typing of Lung and Pleural Tumors,3rd ed. Berlin, Springer-Verlag. 1999. -k

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however, are composed of more than one histologic type and are classified as combined tumors. Additionally, NSCLC are graded as well-differentiated, moderately differentiated, or poorly differentiated according to the least differentiated feature.227Exceptions to this grading classification are pleomorphic carcinoma, carcinosarcoma, and SCLC, all of which are poorly differentiated tumor^.^

Squamous Cell Carcinoma. Squamous cell carcinomas have been decreasing in relative incidence and now

Primary Pulmonary Neoplasms

905

constitute 25% of all lung cancers. They typically occur in central bronchi and frequently manifest as postobstructive pneumonia or atelectasis (Fig. 28-1).Ia9.202, 225 Mucoid impaction, bronchiectasis, and hyperinflation are uncommon radiologic manifestations (Fig. 2&2).un.2u9us Approximately one third of squamous cell carcinomas occur beyond the segmental bronchi and usually range in size from 1 to 10 cm (Fig. 28-3).% 225 Squamous cell carcinomas are more likely to cavitate than the other histo.~ occurs in 10% logic cell types of lung c a n ~ e rCavitation to 30% and is more common in large peripheral masses .~ is typically and poorly differentiated t ~ r n 0 r . s Cavitation eccentric with thick, irregular walls, although thin walls may occur in rare circumstances.* Most squamous cell carcinomas grow slowly, and extrathoracic metastases tend to occur late.*

Table 28-1. Histologic Classification of Lung Tumors

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1

Adenocarcinoma. Adenocarcinomas have increased in incidence and are now the most common cell type, compos-

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Figure 28-1. Squarnous cell lung cancer seen as a central endobronchial mass. A, Posteroanterior chest radiograph shows com-

plete atelectasis of the right upper lobe. Convexity in the lower portion of the atelectatic lung (arrows) is the result of a large central mass. B, CT confirms the large central mass in the region of the right upper lobe bronchus.


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Figure 28-2. Squamous cell lung cancer with obstructive h y p d a t i o n of the left upper lobe. A and B, GT scan shows hyperlucency of the left upper lobe and an endobronchial mass that completely occludes the left upper lobe bronchus (arrow in B).

ing 25% to 30% of all lung cancers.189Adenocarcinomas typically manifest as peripheral, solitary pulmonary nodules. Nodules can have an irregular or spiculated margin as a result of parenchymal invasion and an associated fibrotic response (Fig. 28-4).2029225 Lymphangitic carcinomatosis, although uncommon at presentation, occurs more frequently with adenocarcinomas and typically manifests radiologically as thickening of interlobular septa or multiple small pulmonary nodules (Fig. 28-5).lZ Intrathoracic metastases to hilar and mediastinal nodes are present in 18% to 40% and in 2% to 27% of patients, respectively, and tend to occur more often with more centrally located adenocarcinomas. 2Z. 261 Bronchioloalveolar cell carcinoma (BAC), a subset of adenocarcinoma, constitutes 0.5% to 10% of all lung canL89w

c e r . ~BAC . ~ ~ can be either solitary or multifocal at the time of initial presentation. To explain this difference, it has been proposed that the origin of BAC is either monoclonal (with multifocality due to dissemination by aerosolization, intrapulmonary lymphatics, and intra-alveolar growth) or polyclonal (with multifocality due to de novo tumor growth sites).119 88' 128. 138. ZTZ at The most common radiologic manifestation is a peripheral, solitary nodule that can remain stable in size for many Although cavitation in these years (Fig. 28-6).4 lo8, nodules is uncommon, the occurrence of multiple small, focal, low-attenuation regions (pseudocavitation) or airbronchograms within the nodule can occasionally be useful in suggesting the diagno~is.'~~~ I6*, 273 The diffuse form may present as multiple nodules (usually small, occasion25i9


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Figure 284. Adenocarcinoma manifesting as a pulmonary nodule. CT scan shows a nodule in the apical segment of the right upper lobe. The spiculated margin ir typical of lung cancer.

Figare 28-5. Adenccarcinoma of the lung appearing as lymphangitic carcinomatosis. A and B, Thin-section CT scan shows thickening of bronchial walls and interlobular septa (arrowheads) in the left lung. Nodularity of the septa is suggestive of malignancy.

Figure 28-45. B ~ o l o a l v e o l a rcell camham seen as a &obry p u h ~ m qnodule, A, Posteroanterior chest radiograph shows a nodule (arrow) in left upper lobe. B, CT scan reveals a spiculated margin suggestive of mahgnancy.


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6 3-

marginated masses greater than 7 cm in diameter (Fig. 28-10).2L,58, lS9. mL.m, u5 Although growth is typically rapid, cavitation is unc~mmon.~' Hilar and mediastinal adenopathy occurs in up to one third of patients at presentation, and early extrathoracic metastases are common?8.ml."m

Small-Cell Lung Cancer. SCLCs compose 20% to 25% of all lung ~ancers.5~ The primary tumor is typically small, is central in location, and is assmiated with marked hilar and mediastinal adenopathy and distant metastases to liver, bone marrow, adrenals, and brain (Figs. 28-11 and 28-12).58. ZS. 233 Pleural effusions occur in 5% to 40% of patients.17" ~ m . Approximately 2 ~ ~ 5% of SCLCs manifest as small, peripheral, solitary pulmonary nodules without intrathoracic adenopathy, disseminated extrathoracic dis233 ease, or pleural effusi0ns.7~.

Fgve 28-7. Bronchioloalveolar cell carcinoma PAC) manifesting as multiple pulmonary nodules. CT shows small, well-marginated pulmonary nodules with central areas of cavitation (the "Cheerio" sign of BAC).

ally cavitary), cc~und-glass"opacities, and opacities resembling pneumonia (Figs. 28-7 and 28-8).% ll. 4% FZ 13s.202 Most patients with the diffuse form of BAC have a combination of these findings (Fig. 28-9).2 Hilar and mediastinal adenopathy and pleural effusions are uncomrnOn.42.87. 162.202

Large-Cell Carcinoma. These lesions make up 19% to 20% of all lung cancers.58.202 Most are peripheral, poorly

Clinical Manifests tions Most patients are in their fifth and sixth decades of life and are symptomatic at presentati~n.~, 58, Symptoms are variable and depend on the local effects of the primary mass, the presence of regional or distant metastases, and the coexistem ,ofp,araneoplasticsyndromes. Central endobromhial carcinomas c m manifest as fever, dyqyea, hernpptysis, and cough.5 Cough productive of copious amounts of watery sputum (browhorrhea) typi~ally also occurs in patients with BAC and extensive pamnd~ymal ,disease, but this is rarely seenSmSymptoms that can occur as a result of local growth and invasion of adjacent m e s , vessels, and mediastinal s t r u c m include. 1. Chest pain (peribronchial nerve invol~ement);vocal cord paralysis and hoarseness (recurrent laryngeal nerve involvement) (Fig. 28-13); dyspnea due to diaphragmatic paralysis (phrenic nerve involvement) (Fig. 2814); Homer's syndrome--ptosis, mycosis, anhidrosis (sympathetic chain and stellate ganglion involvement by superior sulcus tumors) (Fig. 28-15).172 2. Facial swelling, headaches, enlarged collateral chest wall vessels (superior vena cava 3. Dysphagia (esophageal invasion).

Fgve 28-8. Bronchioloalveolar cell carcinoma appearing as homogeneous opacities mimicking pneumonia. A, Postemanterior chest radiograph shows diffuse, bilateral, homogeneous pulmonary opacities. Surgical clips are present in the medial aspect of the left hemithorax because of prior partial pulmonary resection. B, CT con6rms the diffusebilateral pulmonary consolidation and reveals a small left pleural effusion.

,


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Chapter 28

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Figure 28-9. Bronchioloalveolar cell carcinoma seen as nodules and consolidation. CT scan shows an opacity in the right lower lobe resembling pneumonia and a small nodule (arrow).Numerous small, well-circumscribed nodules were scattered throughout both lungs (not shown).

Figure 28-10. Large-cell lung cancer manifesting as a large cavitary mass. A, Postemanterior chest radiograph shows a large, lobular mass in the right upper lobe. Cavitation is present with an air-fluid level in the upper aspect of mass. B, CT shows a wellcircumscribed mass with eccentric cavitation and thick walls. Note Ehe nonenlarged, paratracheal and low left paratracheal lymph nodes (arrowheads).


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Figure 28-12. Small-cell lung cancer seen as intrathoracic adenopathy and atelectasis. A, Posteroanterior chest radiograph shows complete atelectasis of the right upper lobe with mild convexity of the distal aspect of the minor fissure (arrows)caused by an underlying right hilar mass. B, CT scan confirms marked hilar and mediastinal adenopathy and reveals occlusion of the right upper lobe bronchus.


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~ t hhoarseness caused by involvement of the recurrent laryngeal Figure 28-13. Small-cell lung cancer in a 76-year-old man presc nerve. A, Posteroanterior chest radiograph shows an aortopulmon,, .low mass. B, CT reveals mediastinal invasion with an extension of the mass into the aortopulmonary window (the anatomic location of recurrent laryngeal nerve).

.....

Figure 28-14. Small-cell lung cancer in a 50-year-old woman with diaphragmatic paralysis resulting from phrenic nerve involvement. A, Posteroanterior chest radiograph shows a large lobular mass in the left lower lobe and elevation of the left hemidiaphragm. B, CT reveals a necrotic mass in the left lower lobe and mediastinum (arrows)in the anatomic location of the phrenic nerve.

Figare 28-15. Non-small-cell lung cancer in a 54-year-old man with Pancoast's tumor and with a 2-month history of neck pain. A, Posteroanterior chest radiograph shows a left apical mass with destruction of the first rib (arrowheads). B, CT conlirms the left superior sulcus tumor and destruction of the left first rib.


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Many patients present with symptoms related to extrathoracic metastases, most commonly bone pain or central nervous system (CNS) abn~rmalities.~. loo Clinical signs and symptoms can also be caused by tumor excretion of a bioactive substance, or hormone, or as a result of an autoimmune phenomen~n.~. 17' These paraneoplastic syndromes occur in 10% to 20% of lung cancer patients and are Antidiuretic and usually associated with SCLC?. adrenocorticotropin hormones are the more frequently excreted hormones and can result in hyponatremia and serum hypo-osmolarity and in Gushing's syndrome (central obesity, hypertension, glucose intolerance, plethora, hirsutism), respe~tively.~? 40, 12'lS7,Ig9. 202 Other hormones that can be elevated are calcitonin; growth hormone; human chorionic gonadotropin; and, rarely, prolactin and serotonin.124 Neurologic paraneoplastic syndromes (Lambert-Eaton myasthenic syndrome, paraneoplastic cerebellar degeneration, paraneoplastic encephalomyelitis, paraneoplastic sensory neuropathy) are rare and are usually associated with SCLC.25.26. 28. 33. l13. 179 The neurologic symptoms typically lz49

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precede the diagnosis of lung cancer by up to 2 years, are incapacitating, and progress rapidly, although improvement can occur after treatment of the lung " cancer.33.]I3 Miscellaneous paraneoplastic syndromes associated with lung cancer include acanthosis nigricans, dermatomyositis, disseminated intravascular coagulation, and hypertrophic pulmonary osteoarthropathy (HPO). Of these, HPO is the most common, occurring in up to 17% of patients with adenocarcinoma (Fig. 28-16).143

Radiologic Evaluation Although imaging has an important role in the diagnosis, staging, and monitoring of patients with lung cancer, the role of imaging in screening for malignancy is not clearly defined. Screening

Because diagnosis of lung cancer at an early stage is associated with an improved prognosis, screening has been

Figure 28-16. Non-small-cell lung cancer in an asymptomatic 64-yearold woman. A, CT scan shows a large right upper lobe mass. B, Technetium 99m (99Tc)-labeled methylene diphosphonate (MDP)bone scintigraphy shows linear areas of increased radiotracer uptake in the

femurs and tibias. This appearance is characteristic of hypertrophic pulmonary osteoarthropathy.


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Chapter 28

advocated to detect lung cancer before clinical presentation. The ACS does not, however, recommend routine radiologic evaluation for the detection of lung cancer but instead advocates primary pre~ention?~ This recommendation is based on the results of four large randomized trials undertaken in the 1970s, which evaluated the utility of chest radiographs and sputum cytology in lung cancer screening. These triaIs showed that screening improved long-term survival rates without reducing mortality (considered the best evidence that screening is effective, as it is not affectedby lead-time bias, length bias, and overdiagnosis biaS).LZ 60, 105. 151. 218 A reanalysis of the data from these trials has suggested some justification for the use of chest radiography in lung cancer 2L7 Additionally, because of the concerns about design and methodology of the previous trials, together with improved detection of small lung cancers using computed tomography (CT), there has been a renewed interest in reevaluating screening. Consequently, new multi-institutional screening studies in the United States, supported by the National Cancer Institute as well as by other smaller trials in Japan and Germany, are being performed to reexamine the role of screening in lung cancer mmagement.83, 93. 161,207 Diagnosis Because most patients with lung cancer have advanced disease at presentation, diagnosis is usually not difficult. Nevertheless, 20% to 30% of patients with lung cancer present with a solitary pulmonary nodule, which may be difficult to differentiate from a benign nodule.242Certain morphologic and physiologic features, however, may suggest a diagnosis of lung cancer: 1. Size. The larger the nodule, the more likely it is to be malignant.76.86. n3 Small size, however, cannot be used to reliably exclude lung cancer, since up to 42% ofresected lung cancers are less than 2 cm in diarneter.203. 242.269 2. Margins. Lung cancers typically have irregular or spiculated margins?6*2M 225.269. 273 Although suggestive of lung cancer, these findings can occasionally be seen with benign nodule^.'^ 273 Furthermore, a smooth margin, a feature typical of benign nodules, cannot be used to exclude lung cancer, because 20% of malignant nodules have this appearance.*5 3. Internal morphology. Except for fat (attenuation, -40

Figore 28-17. Non-small-cell lung cancer manifesting as a

calcified mass. CT shows a large, right upper lobe mass with mediastinal invasion. Scattered areas of amorphous calcification in the mass are typical of, but not diagnostic for, malignancy.

1


913

to - 120 Hounsfield units [HU]) and calcification within a nodule, internal morphology is unreliable in distinguishing lung cancer from a benign nodule.76-lM), 204, 273 Calcification occurs histologically in up to 14% of lung cancers and may be detected by CT.'23.IS7 f i e calcification is typically amorphous in appearance (Fig. 28-17), unlike the diffuse solid, central punctate, laminated, or popcorn-like calcifications that are diagnostic of benign nodules. Amorphous calcification, however, is not diagnostic of lung cancer, because similar calcifications are occasionally detected in benign lesions. Cavitation occurs in benign nodules and lung cancer. Malignant nodules typically have thick, irregular walls, whereas benign nodules have smooth, thin walls.259.260. 273 These findings, however, are not specific, and wall thickness cannot be used to confidently differentiate benign nodules from lung cancer. 4. Growth. Lung cancers typically double in volume (an increase of 26% in diameter) between 30 and 400 days (average, 240 days).u9 Although absence of growth over a 2-year period is usually reliable for confirming that a nodule is 73.' I 8 it is difficult to reliably detect growth in small nodules because the small change in diameter associated with a doubling of volume may not be visible on radiographs. The use of CT can improve the accuracy of growth assessment. It has been reported that growth can be detected in lung cancers as small as 5 mm when CT imaging is repeated within 30 days.2M Furthermore, the measurement of serial volumes of small nodules (which increase proportionally faster than diameters), may be an accurate and potentially useful method for assessing the rate of At present, the determination of when and how to observe and image small nodules in the assessment of tumor growth rate has not been resolved. 5 . Blood supply. Blood supply to malignant pulmonary nodules is qualitatively and quantitatively different from the blood supply to benign nodules. Contrast-enhanced CT can be used to image this difference by determining nodule enhancement. Qpically, malignant nodules enhance more than 20 HU, whereas benign nodules enhance less than 15 HU (Fig. 28-18).u3 6. Metabolism. Metabolism of glucose is typically increased in lung cancer cells. Positron emission tomography (PET), using a D-glucose analog, 18F-2-deoxy-Dglucose (FDG), can be used in imaging this increase and in differentiating malignant from benign n0du1es.l~~


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Figure 28-18. Non-smd-cell cancer appearing as an enhancing nodule after administration ontrast material. A, Non-contrastenhanced CT scan shows a left l u g nodule with an attenuation value of 24 Hounsfield units mu). B, Contrast-enhanced CT scan shows nodule enhancement of 70 HU and central necrosis. Enhancement of more than 20 HU suggests malignancy. Resection revealed non-smaII-cell cancer. (Courtesy of Tom Hartman, M.D., Mayo Clinic, Rochester, Minn.)

Nodules as small as 1 cm can be imaged; if FDG uprake is low, the nodules are almost certainly benign?'. 'O1. [I4. 173.174 Nodules with increased FDG uptake are generally considered malignant (Fig. 28-19), although inflammatory and infectious processes (e.g., rheumatoid nodules, tuberculosis, histoplasmosis) may result in increased FDG upt&e.lO1. 173. 174, 238

tumor (T status), lymph nodes (N status), and metastases (M status) (Table 28-2).'45 The TNM descriptors can be determined clinically (history, physical examination, radiologic imaging) or by pathologic analysis of samples obtained by biopsy or surgery. In general, the clinical stage underestimates the extent of disease when compared with the pathologic

Primary %mar /T Status), The T status defines the size, location, and extent of the primary tumor. Because Non-Small-Cell Lung Cancer. Because treatment and the extent of the primary tumor determines therapeutic prognosis depend on the anatomic extent of NSCLC at management (surgical resection or palliative radiotherapy initial presentation, accurate assessment is i m p ~ r t a n t . l150~ ~ ~ or chemotherapy), imaging is often performed to assess the The International Staging System for Lung Cancer is used degree of pleural, chest waU, and mediastinal invasion. to describe the extent of NSCLC in terms of the primary CT is useful in confirming gross chest wall invasion Staging

Figure 28-19. Non-small-cell lung cancer seen as hypermetabolic nodule on a PET scan with 18F-fluorodeoxyglucose(FDG-PET). A, CT scan shows a nodule in the right upper lobe. The irregular margin suggests malignancy. B, Axial PET image with FDG shows increased uptake within the nodule (arrow)when compared to adjacent mediastinum. Findings suggest malignancy. Resection revealed squamous cell cancer. M, mediastinum; V, vertebral body.


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9 15

Table 28-2. International Staging System for Lung Cancer Prhnary b o r (T) Primary tumor cannot be assessed, or tumor proven by the presence of malignant ceUs in sputum or bronchial washings but not visualized by imaging or bronchoscopy No evidence of primary tumor TO Carcinoma in situ Tis Tumor 5 3 cm in greatest dimension, surrounded by lung or visceral ~leura,without bronchosco~icevidence of invasiokore proximal than the lobar bronchus* (i.e., not in the main bronchus) Tumor with anv of the following features of size or extent: >3 cm in &atest dimensionInvolves main bronchus, 2 2 cm distal to the carina Invades the visceral pleura Associated with atelectasis or obstructive pneumonitis that extends to the hilar reeion . but does not involve the entire lung T3 Tumor of any size that directly invades any of the following: chest wall (including superior sulcus tumors), diaphragm, mediastinal pleura, parietal pericardium; or tumor in the main bronchus

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