Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

MYELOPATHY, RADICULOPATHY, and PERIPHERAL ENTRAPMENT SYNDROMES

MYELOPATHY, RADICULOPATHY, and PERIPHERAL ENTRAPMENT SYNDROMES David H. Durrant, D.C., D.A.B.C.N. Neuro-Orthopedic Institute Elgin, Illinois

Jerome M. True, D.C., D.A.B.C.N. University Rehabilitation and Therapeutics Plantation, Florida

With

John W. Blum, Jr., D.C. J. Donald Dishman, D.C., M.Sc., D.A.B.C.N. P. Michael Leahy, D.C., C.C.S.P. Edwin P. Patrick, D.C., F.A.C.O. Clifford M. Shooker, D.C., D.A.B.C.N.

CRC PR E S S Boca Raton London New York Washington, D.C.

Library of Congress Cataloging-in-Publication Data Durrant, David H. Myelopathy, radiculopathy, and peripheral entrapment syndromes / David H. Durrant, Jerome M. True, with John W. Blum, Jr. … [et al.]. p.; cm. Includes bibliographical references and index. ISBN 0-8493-0036-3 (alk. paper) 1. Spinal cord—Diseases. 2. Nerves, Peripheral—Diseases. 3. Entrapment neuropathies. I. True, Jerome M. II. Title. [DNLM: 1. Spinal Diseases—diagnosis. 2. Diagnostic Imaging. 3. Nerve Compression Syndromes. 4. Radiculopathy. 5. Spinal Cord Diseases. 6. Spinal Cord Injuries. WE 725 D965m 2001] RC400 .D87 2001 616.8¢7—dc21 2001035203

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Visit the CRC Press Web site at www.crcpress.com © 2002 by CRC Press LLC No claim to original U.S. Government works International Standard Book Number 0-8493-0036-3 Library of Congress Card Number 2001035203 Printed in the United States of America 2 3 4 5 6 7 8 9 0 Printed on acid-free paper

“Many a man has the eyes of a hawk and the vision of a clam.”

— B.J. Palmer, D.C., Ph.C. ( As a Man Thinketh )

Dedication To my loving wife Christine, for her unconditional support and encouragement, which has empowered me to pursue the desires of my heart, and to my beautiful daughter Amanda, who inspires me each day with her abundant love and energy.

To my parents, Richard and Patricia Durrant, for their enduring love and guidance throughout the years, which will forever motivate me to pursue my dreams.

In memory of my friend Jean Ryan, whose courage, independence, and accomplishments, despite her physical limitations, continue to serve as a source of inspiration. — DHD

In Memory of My Father, Martin Austin True “Knowledge comes, but wisdom lingers.” — Alfred, Lord Tennyson And a dedication to my loving wife, for her support, trust and patience. — JMT

Foreword It isn’t often that a textbook appears that so clearly delineates the relationship between neurology and functional musculoskeletal diagnosis. This text represents an extensive diagnostic guide for neurological disorders from the “neck down” to the extremities. It is the first time I have ever seen such a definitive correlation between orthopedic signs/tests and possible neurological involvements. Tables, which assemble and organize information from many studies, permit the practitioner to proceed to an accurate diagnosis in an orderly and efficient way. A few examples I have found beneficial to my own diagnostic procedures are: “Checklist for Assessment of Patient with Spinal Cord Compromise,” “Methods of Quantifying Sensibility,” and “Classification of Spine Lesions by Anatomic Compartment.” The subject of neurology is indeed complex and difficult to retain in our everyday care of patients. Most of us retain a certain level of understanding, but with the

passage of time, details, especially of the neurological variety, begin to escape us. For the Doctor of Chiropractic and all types of physical medicine specialists dealing with the spine and extremity disorders, this textbook provides a complete description and review of what we must understand to adequately treat our patients. The illustrations, tables, and related text are excellent. They are designed so that the practitioner can move easily through them to support daily diagnosis and to help develop a treatment plan. The material covered in this landmark textbook should be part of the core curriculum for all doctors and health care professionals caring for the spine. Those of us in the healing arts owe a debt of gratitude to Doctors Jerry True and David Durrant. They have devoted the last 5 years to assembling and compiling the most recent neurological information in a form accessible and useful to us all. Warren Hammer

Authors’ Foreword It is a pleasure and a great relief to complete a large project, such as the first edition of this text. Countless late nights and early mornings have passed since the initial discussions of the outline topics and framework for this book in 1991 in Orlando, FL. We have met many times per year in Chicago and Fort Lauderdale to organize text, scout for references, and formulate chapter outlines and themes. During the editing process many of the contributing authors received daily phone calls from one or the other of us to discuss refinements or deadlines for their chapters. As any author knows, the contributors have all sacrificed weeks and months of their lives to support this project. Thousands of hours of computer time have gone into creation of the graphics for this text. The meticulous attention to detail should be apparent in our neuroanatomical pathways. The research needed to assemble the illustrations for the neuroanatomical section and the pathway illustrations totaled hundreds of hours per completed illustration, spanning the period between 1989 and 2000. We have made every attempt to accurately illustrate the pathway mechanisms and theories in this book with opinions

currently accepted in the scientific literature. We acknowledge in advance that inadvertent flaws and typos occur in all publications, as well as opposing or contrary views to the status quo. We encourage the reader to direct comments, criticisms, or corrections to the publisher and authors for consideration and review. As a consequence of the exponential growth in monthly scientific periodicals, it is often possible that research is uncovered that supports a different opinion or explains a previously unknown mechanism. Even a cursory review of the top crust of knowledge published each month overwhelms the most voracious data researcher. In an attempt to reach academic consensus, faculty members from many colleges and physicians with specialty interests completed critical reviews of the chapters. We hope that you will find this text clinically valuable and the illustrations skillfully instructive. If we have enlightened the reader and improved his or her clinical expertise, this book has then served our intended purposes. Jerry True David Durrant

Preface “One sees only what one knows.” — Johann Wolfgang von Goethe

The clinician must be able to recognize a condition in order to pursue necessary care. Early recognition requires application of an overview to the outward manifestations of a complex process; localization and diagnosis are required in order to proceed with therapeutic intervention. Of the many texts on clinical neurology, few discuss the potential orthopedic complications associated with nerve injury. This is an important perspective for the developing fields of neurorehabilitation and neuromuscular rehabilitation. The present treatise is meant to serve as a supplement to texts that cover general neurology and orthopedics and to provide an expanded discourse on the pathomechanisms and related presentations of myelopathy, radiculopathy, and peripheral entrapment. With quickly advancing technology in neurology and imaging, interest in, and application of, new methods in the care of spinal disorders have reached an unprecedented level. Great strides have also been made in the early detection and rehabilitation of myelopathy and spinal cord injury. Whether the patient is treated conservatively or surgically, some degree of physical rehabilitation or retraining is often required, and it is therefore imperative that attending clinicians understand patterns of injury and recovery. Additionally, as neurological status may change during the post-traumatic recovery period, follow-up neurological assessment is essential. As life expectancy increases, so will the prevalence of spinal disorders. An increased incidence of myelopathy will be due to degenerative stenosis, vascular disease, and primary and secondary spinal cancer. Intervention will continue to move toward a greater reliance on minimally invasive procedures and rehabilitation, and hence toward a greater emphasis on neurology as it relates to orthopedics (neuro-orthopedics). Early detection and intervention in spinal disorders will become the standard approach, rather than the often-overlooked alternative. The patient with a chronic or complex spinal condition may see a number of independent physicians of various disciplines during the course of care. An integrated approach may be achieved involving a chiropractic physician, pain

specialist, internist, neurosurgeon, and/or orthopedic surgeon. This book is intended to provide “common ground” for physicians who must perform or understand the differential assessment of neurological complications that involve or mimic a spinal condition. It is also intended for the student of clinical neurology and orthopedics, and for the doctor treating neuromusculoskeletal disorders. By reducing the complex field of diagnostic neurology to its common denominators, we hope to introduce the subject in a practical manner and present a concise basis for neurodiagnostic evaluation. The text provides an integrated review of selected anatomy and physiology, clinical localization, classification, and quantification of disorders afflicting the spinal cord, nerve root, and peripheral nerves. It is organized for use as a basic science tool or a quick reference, with abundant tables and graphics included to convey essential and relevant clinical information. Having conducted an indepth review of the literature, we have attempted to reflect current consensus opinion whenever possible. We have also interjected insights and opinions based upon our collective clinical experiences. In addition to recognizing spinal disorders, the clinician must become particularly adept at assessing relatively common patterns of peripheral nerve compromise that may coexist with or mimic spinal presentations. However, this is often not adequately discussed in texts limited to “spinal conditions,” and many general neurology texts are limited in their coverage of both subjects. Combining the topics of spinal and peripheral neurological assessment herein lends itself, for example, to greater understanding of clinical entities such as whole nerve syndrome or double crush syndrome. We have incorporated descriptions of various pathomechanisms in spinal cord and nerve injury and, whenever possible, noted clinically significant timedependent patterns of insult and recovery. There is a vast amount of past and current research data in the fields of neuroanatomy, neurophysiology, and orthopedics that we have not included in this volume. We have carefully chosen what we believe to be relevant information that can be immediately applied to diagnostic and therapeutic approaches to myelopathy and spinal cord injury in clinical practice.

Introduction to Myelopathy and Spinal Cord Injury Myelopathy in its broadest definition includes any pathology involving the spinal cord. Spinal cord injury (SCI) in an empirical sense also includes any condition that causes insult to the cord. However, the term “myelopathy” has customarily been used to describe intrinsic disease processes, whereas SCI has usually referred specifically to a traumatic-onset myelopathy. The most common chronic intrinsic disorders afflicting the cord are the result of degenerative conditions exclusive to the spine — namely, disk derangement, spondylosis, and spinal stenosis. Spinal cord injury from acute trauma involves one or more of the following mechanisms: fracture or dislocation of the spine with impact on the cord; torsional or shear forces on the spine and cord, causing axonal transection; and penetrating injuries that partially or completely sever the cord. The injury may be partial or complete, transient or permanent. There are 7800 new SCIs in the U.S. each year; however, this incidence may be significantly under-reported, because people who instantly die and patients with little residual SCI deficit are not included in the recorded statistics.* Motor vehicle accidents account for the majority of SCI cases, while acts of violence, falls, work injuries, recreational incidents, and athletic injuries constitute the remainder. It is noteworthy that acts of violence have overtaken falls as the second most common source of SCI in the last 4 years; falls overtake motor vehicle accidents as a leading cause of SCI after age 45; and SCI related to acts of violence and sports is less common as age increases.* Other conditions that produce SCI include

infection, immunological disorders, tumor, vascular compromise, herniated intervertebral disk, and degenerative diseases. Monies spent on spinal cord pathology and related conditions will continue to rise, influenced greatly by the large percentage of the population reaching the 65-andabove age group. Of the increasing number of patients with cervical spondylotic myelopathy, many cases will be complicated by cardiovascular disease, impaired glycoregulation, and immunological disorders. Spondylotic myelopathy increases the risk for falls, related injury, and disability, and a higher incidence of cancer in the aged population will also increase the risk for metastatic expansile lesions within the spine. Nevertheless, there is an unprecedented optimism within the scientific community that early diagnosis and intervention in SCI will lead to an improved prognosis and enhanced functional recovery. A vast body of research demonstrates the benefits of exercise and a physical rehabilitative approach to the remodeling characteristics of neurological tissue and the surrounding and supportive tissues of the spine. Advanced imaging techniques allow us to evaluate the anatomic expression of a spinal lesion, its progression, the pattern of recovery, and its relationship to the clinical presentation. Effective management depends upon early identification of the extent and level of neurologic injury, and upon multidisciplinary specialty care of the diverse problems associated with SCI to maximize the potential for tissue recovery and repair.

* National Spinal Cord Injury Association statistics available at http://www.spinalcord.org/resource/Factsheets/factsheet2.html, 2000.

Acknowledgments Any project of this caliber requires delegation, support, negotiation, sacrifice, and donation of considerable time and effort from innumerable sources. The first and most deserving acknowledgment goes to the contributing authors and their support staff. The loved ones, families, and friends of the authors are next on the list of appreciation, because without their understanding, faithful support, and patience during the life-disrupting process of writing a book, the accomplishment and importance of this project would certainly have less merit. We are indebted to Ron Hosek, Ph.D., D.C., M.P.H., for his experience and insight. His scholarly guidance was most valuable. We are also indebted to Ray Conley, D.C., D.A.C.B.R., who deserves credit for his expert review of some of the magnetic resonance (MR) and X-ray images used in this book. Dr. Conley reviewed and qualified over 900 slide images during the initial selection process for the book. Many other individuals have participated and were integral to the completion of this book. These individuals were involved in manuscript preparation, review, editing, photography, computer graphics, and technical advice or troubleshooting. We greatly appreciate the efforts of John Sikes for his energetic assistance. Early in the project John provided a great deal of back-office support and image scanning work to help complete this book. John and Linda Sikes were also invaluable for their help compiling and creating a reference database for the voluminous number of referenced facts. Joleen Riley photographed many of the MRIs that appear in this text and hundreds that were not selected in the final production. Thanks to Lori True for entering text-editing changes and the tedious reference renumbering of many chapters. Thanks to Dan Fortuna for his help compiling research articles and spending many sunny days in the library doing literature searches. Excellent MRI and X-ray case studies were supplied by Richard Leverone, D.C., D.A.C.B.R.; Harold Friedman, M.D.; Ronald Landau, M.D.; James Zelch, M.D.; Brian Mevorah, D.C.; Joseph Kozlowski, M.D., and George Fika, D.C. Bill Atherton D.C., D.A.C.B.R., and Ronald Landau, M.D., generously reviewed MRIs and helped compose figure captions. Thanks to the following: Alex Frost and Kate Herman of BiologyEditors.com, Lisa McCollough and Marce Pollan for reference work and editing; Paul

Ellis, Ph.D., for cadaveric sections and photography; Robert Pearson for anatomical line drawings; Linda Bland, M.D., Greg Page, D.C., D.A.C.N.B., Gloria Y. Niles, D.C., D.A.C.A.N., Marc McRae, M.S., D.C., and Alyson Syrja, D.C., for critical reviews; Phil Serocki and Duwayne Rocus for technical advice that was essential to graphics production; and Gary LaVell, D.C., for general support and computer assistance. We would like to extend thanks to the following colleagues for their supportive words and inspiration: Terry Yochum, D.C., D.A.C.B.R.; Norman Kettner, D.C., D.A.C.B.R.; Arthur Croft, D.C., F.A.C.O.; and Tom Hyde, D.C., D.A.C.B.S.P. An extended apologetic thanks to any and all friends and colleagues whom we forgot to mention. The clinical sciences departments of Canadian Memorial Chiropractic College, Life Chiropractic College West, and New York Chiropractic College; the anatomy department of Logan College of Chiropractic; and the research departments of Life Chiropractic College West, Logan College of Chiropractic, and Cleveland Chiropractic College (KC) all have contributed their support to this book. Thanks to the library departments of National Chiropractic College, New York Chiropractic College, Logan College of Chiropractic, Cleveland Chiropractic College (KC), Life Chiropractic College West, and Palmer Chiropractic College for labored reference searches. A special thanks is extended to Glen Hart for his generosity in hardware troubleshooting and multiple rescues from fatal harddrive crashes who reminds us that “to err is human but to really foul things up requires a computer.” Special appreciation and humble respect goes out to the teachers and mentors who influenced us in the pursuit of lofty goals. First and foremost on this list is Frederick R. Carrick, D.C., Ph.D., D.A.B.C.N., who developed the postgraduate neurology program and the foundation for our neurological training. Great appreciation is extended to our loving wives, Lori True and Christine Durrant, whose devotion and excitement for the completion of this book may exceed our own. Jerome M. True David H. Durrant

Contents Section 1 Myelopathy: Spinal Cord Injury and Selected Clinical Syndromes Chapter 1 Relevant Spinal Cord Anatomy ..........................................................................................................................................3 1.1 Basic Spinal Cord Anatomy ......................................................................................................................................3 1.2 Segmental Spinal Anatomy .......................................................................................................................................5 1.2.1 Regional Neuromere Characteristics.............................................................................................................5 1.2.2 Regional Spinal Canal Characteristics ..........................................................................................................5 1.3 Meninges and Compartments ....................................................................................................................................6 1.3.1 Dura Mater.....................................................................................................................................................6 1.3.2 Arachnoid Mater............................................................................................................................................7 1.3.3 Pia Mater........................................................................................................................................................7 1.3.4 Subarachnoid Space and Cerebrospinal Fluid ..............................................................................................7 1.4 Spinal Vascular Anatomy...........................................................................................................................................8 1.4.1 Extrinsic Spinal Cord Vasculature.................................................................................................................8 1.4.1.1 Radiculomedullary Arteries............................................................................................................8 1.4.1.2 Anterior and Posterior Spinal Arteries ..........................................................................................8 1.4.2 Intraparenchymal Vascular Supply ................................................................................................................9 1.4.3 The Spinal Venous Plexus .............................................................................................................................9 1.5 Cytoarchitectural Organization of Spinal Gray Matter ..........................................................................................10 1.6 Relevant Spinal Cord Pathways ..............................................................................................................................13 1.6.1 Clinically Important Ascending Pathways ..................................................................................................13 1.6.1.1 Posterior Columns ........................................................................................................................13 1.6.1.2 Lateral Spinothalamic Tract .........................................................................................................13 1.6.1.3 Other Ascending Pathways ..........................................................................................................13 1.6.2 Clinically Important Descending Pathways ................................................................................................15 1.6.2.1 Corticospinal Tract .......................................................................................................................15 1.6.2.2 Nonpyramidal Tracts ....................................................................................................................17 1.6.3 Autonomic Pathways ...................................................................................................................................17 1.7 Relevant Spinal Cord Nuclei...................................................................................................................................17 1.8 Anatomy of Spinal-Mediated Myotatic Reflex.......................................................................................................17 References .........................................................................................................................................................................22 Chapter 2 Pathophysiology in Myelopathy and Spinal Cord Injury.................................................................................................23 2.1 Introduction to Pathophysiologic Mechanisms .......................................................................................................23 2.2 Cellular, Ionic, and Biomolecular Mechanisms of Spinal Cord Injury .................................................................23 2.2.1 Free Radical-Mediated Cell Injury..............................................................................................................23 2.2.2 Glutamatergic-Induced Toxicity ..................................................................................................................23 2.2.3 Cation-Mediated Cell Injury .......................................................................................................................24 2.2.4 Programmed Cell Death ..............................................................................................................................24 2.3 Stages of Spinal Cord Injury...................................................................................................................................24 2.4 Spinal Shock ............................................................................................................................................................25 2.5 Spinal Cord Edema..................................................................................................................................................26 2.6 Ischemic Myelopathy...............................................................................................................................................26 2.6.1 Microvascular and Arterial Insufficiency ....................................................................................................27 2.6.1.1 Microvascular Perfusion...............................................................................................................27

2.6.1.2 Tempo of Cord Vascular Insufficiency ........................................................................................27 2.6.1.3 Arterial Insufficiency and Ischemia .............................................................................................27 2.6.2 Spinal Cord Infarction .................................................................................................................................28 2.6.3 Venous Pathology ........................................................................................................................................28 2.7 Myelomalacia...........................................................................................................................................................28 2.8 Cavitation and Gliosis .............................................................................................................................................29 2.9 Spinal Cord Atrophy................................................................................................................................................30 References .........................................................................................................................................................................31 Chapter 3 Physical Mechanisms of Spinal Cord Injury....................................................................................................................35 3.1 Spinal Cord Pathomechanics...................................................................................................................................35 3.2 Types of Spinal Cord Trauma .................................................................................................................................36 3.2.1 Spinal Cord Concussion ..............................................................................................................................37 3.2.2 Spinal Cord Contusion ................................................................................................................................37 3.2.3 Spinal Cord Compression............................................................................................................................37 3.2.4 Penetrating/Transecting Cord Injuries.........................................................................................................38 3.2.5 Tethering and Distraction Injuries...............................................................................................................38 3.3 Vertebral Fracture, Dislocation, and Instability ......................................................................................................38 3.3.1 Causes of Biomechanical Instability...........................................................................................................39 3.3.2 Spinal Fracture and Pathomechanical Intersegmental Motion ...................................................................43 3.3.3 Upper Cervical Fracture Patterns: Fractures of C0–C1–C2 .......................................................................43 3.3.3.1 Posterior Neural Arch Fracture of C1 .........................................................................................43 3.3.3.2 Dens Fracture ...............................................................................................................................43 3.3.3.3 Hangman’s Fracture (Bipedicular Fracture of C2, Traumatic Spondylolisthesis of C2) ...........44 3.3.3.4 Jefferson Fracture of the Atlas (Burst Fracture of C1) ...............................................................44 3.3.4 Cervical Fracture Patterns ...........................................................................................................................44 3.3.4.1 Spinous Process Fracture (Clay Shoveler’s Fracture, Coal Miner’s Fracture) ...........................44 3.3.4.2 Pillar Fracture ...............................................................................................................................44 3.3.4.3 Flexion Teardrop Fracture............................................................................................................45 3.3.4.4 Extension Teardrop Fracture ........................................................................................................45 3.3.5 Fracture Patterns Occurring at any Level of the Spine ..............................................................................46 3.3.5.1 Endplate Burst Fracture ...............................................................................................................46 3.3.5.2 Wedge Fracture (Compression Fracture) .....................................................................................46 3.3.5.3 Chance Fracture............................................................................................................................47 3.3.5.4 Neural Arch Fracture....................................................................................................................48 3.3.6 Spinal Dislocation........................................................................................................................................48 3.3.6.1 Bilateral Cervical Facet Dislocation ............................................................................................48 3.3.6.2 Unilateral Facet Dislocation.........................................................................................................49 3.3.6.3 Spinal Dislocation/Relocation......................................................................................................49 3.4 Spinal Hemorrhage ..................................................................................................................................................49 3.4.1 Subarachnoid Hemorrhage ..........................................................................................................................50 3.4.2 Epidural Hemorrhage ..................................................................................................................................50 3.4.3 Subdural Hemorrhage..................................................................................................................................50 3.4.4 Hematomyelia ..............................................................................................................................................50 3.5 Myelopathy and Disk Herniation ............................................................................................................................50 References .........................................................................................................................................................................53 Chapter 4 Conditions Associated with Myelopathy ..........................................................................................................................55 4.1 Degeneration and Stenosis ......................................................................................................................................55 4.1.1 Spondylotic Myelopathy and Cervical Spondylotic Myelopathy...............................................................55 4.1.1.1 Prevalence.....................................................................................................................................55 4.1.1.2 Pathomechanisms .........................................................................................................................56

4.2

4.3 4.4

4.1.1.3 Clinical Signs and Symptoms and Temporal Pattern of Progression .........................................57 4.1.1.4 Clinical Findings ..........................................................................................................................58 4.1.1.5 Diagnostic Imaging ......................................................................................................................58 4.1.1.6 Differential Considerations ..........................................................................................................59 4.1.2 Ligamentum Flavum Thickening/Buckling.................................................................................................59 4.1.3 Rheumatoid Arthritis and Myelopathy........................................................................................................59 4.1.4 Hypertrophic Spinal Disease .......................................................................................................................60 4.1.4.1 Diffuse Idiopathic Skeletal Hyperostosis.....................................................................................60 4.1.4.2 Ossified Posterior Longitudinal Ligament Syndrome .................................................................61 Expansile Lesions ....................................................................................................................................................62 4.2.1 Syringomyelia ..............................................................................................................................................62 4.2.2 Arachnoid Cyst ............................................................................................................................................64 4.2.3 Epidural Lipomatosis...................................................................................................................................64 4.2.4 Spinal Cord Tumors.....................................................................................................................................64 4.2.4.1 Intramedullary Tumors .................................................................................................................64 4.2.4.1.1 Ependymoma..............................................................................................................64 4.2.4.1.2 Astrocytoma and Oligodendroglioma........................................................................64 4.2.4.1.3 Hemangioblastoma.....................................................................................................66 4.2.4.2 Intradural Extramedullary Tumors...............................................................................................68 4.2.4.2.1 Neural Sheath Tumor .................................................................................................68 4.2.4.2.2 Meningioma ...............................................................................................................68 4.2.4.2.3 Paraganglioma ............................................................................................................69 4.2.4.3 Epidermoid and Dermoid Tumor, and Teratoma ........................................................................70 4.2.4.4 Extradural Tumors........................................................................................................................70 4.2.4.4.1 Lipoma .......................................................................................................................70 4.2.4.4.2 Chordoma ...................................................................................................................70 4.2.4.4.3 Lymphoma..................................................................................................................70 4.2.4.5 Lesions Arising from the Bony Vertebral Column......................................................................70 4.2.4.6 Metastatic Lesions........................................................................................................................70 4.2.5 Epidural Abscess..........................................................................................................................................72 Arteriovenous Malformations..................................................................................................................................72 Noncompressive Myelopathy ..................................................................................................................................76 4.4.1 Postinfectious and Postvaccination Myelitis (Transverse Myelitis) ...........................................................77 4.4.2 Infection .......................................................................................................................................................77 4.4.2.1 Tropical Spastic Paraparesis (Human T-Cell Lymphotrophic Virus I) .......................................77 4.4.2.2 Acquired Immune Deficiency Syndrome ....................................................................................77 4.4.2.3 Lyme Disease ...............................................................................................................................78 4.4.2.4 Tabes Dorsalis (Syphilis) .............................................................................................................78 4.4.3 Spinal Arachnoiditis (Adhesive Arachnoiditis)...........................................................................................78 4.4.4 Toxic Insult ..................................................................................................................................................79 4.4.5 Multiple Sclerosis ........................................................................................................................................79 4.4.6 Radiation Myelopathy .................................................................................................................................79 4.4.7 Decompression Sickness .............................................................................................................................81 4.4.8 Electrical Injury ...........................................................................................................................................81 4.4.9 Metabolic and Nutritional Myelopathies ....................................................................................................81 4.4.9.1 Subacute Combined Degeneration...............................................................................................81 4.4.10 Autoimmune Myelopathy............................................................................................................................81 4.4.11 Paraneoplastic Myelopathy..........................................................................................................................82 4.4.12 Degenerative Neuronal Disorders ...............................................................................................................82 4.4.13 Motor Neuron Disease.................................................................................................................................82 4.4.13.1 Amyotrophic Lateral Sclerosis.....................................................................................................82 4.4.13.2 Spinal Muscular Atrophy .............................................................................................................82 4.4.13.3 Kennedy’s Disease .......................................................................................................................83 4.4.13.4 Familial Spastic Paraplegia ..........................................................................................................83

4.5

Congenital Spinal Anomalies ..................................................................................................................................83 4.5.1 Spina Bifida Aperta: Myelomeningocele ....................................................................................................84 4.5.2 Occult Spinal Dysraphism...........................................................................................................................84 4.5.2.1 Split Cord Malformation..............................................................................................................84 4.5.2.2 Spinal (Dorsal) Dermal Sinus ......................................................................................................85 4.5.2.3 Neuroenteric Cyst.........................................................................................................................86 4.5.3 Caudal Spinal Anomalies ............................................................................................................................87 4.6 Chiari Malformations ..............................................................................................................................................87 4.7 Klippel–Feil Syndrome............................................................................................................................................87 4.8 Scoliosis and Myelopathy .......................................................................................................................................89 References .........................................................................................................................................................................90 Chapter 5 Assessment of Spinal Cord Injury and Myelopathy ........................................................................................................97 5.1 Spasticity, Paresis, Clonus, and Hyperreflexia........................................................................................................97 5.2 Superficial Reflexes and Reflexes of Spinal Automatism ....................................................................................100 5.2.1 Babinski’s Response ..................................................................................................................................102 5.3 Sensory Abnormalities...........................................................................................................................................105 5.3.1 Ataxia.........................................................................................................................................................105 5.4 Spinal Cord Injury Pain.........................................................................................................................................105 5.4.1 Lhermitte’s Sign ........................................................................................................................................105 5.5 Neurogenic Claudication .......................................................................................................................................106 5.6 Sacral Sparing........................................................................................................................................................107 5.7 Autonomic and Other System Considerations......................................................................................................107 5.7.1 Orthostatic Hypotension ............................................................................................................................107 5.7.2 Deep Vein Thrombosis ..............................................................................................................................108 5.7.3 Autonomic Dysreflexia..............................................................................................................................108 5.7.4 Cardiac Complications ..............................................................................................................................109 5.7.5 Respiratory Considerations........................................................................................................................109 5.7.6 Bowel and Bladder Dysfunction ...............................................................................................................109 5.7.7 Sexual Function .........................................................................................................................................110 5.7.8 Skin Complications....................................................................................................................................110 5.7.9 Psychological Considerations....................................................................................................................110 5.7.10 Fever...........................................................................................................................................................111 5.8 Myelopathy and Associated Musculoskeletal Conditions ....................................................................................111 5.8.1 Contractures ...............................................................................................................................................111 5.8.2 Articular Subluxation ................................................................................................................................111 5.8.3 Heterotopic Ossification ............................................................................................................................112 5.8.4 Osteoporosis...............................................................................................................................................112 5.8.5 Neuropathic Arthropathy ...........................................................................................................................112 5.9 Electrodiagnostic Assessment................................................................................................................................112 5.9.1 Somatosensory Evoked Potentials.............................................................................................................113 5.9.2 Motor Evoked Potentials ...........................................................................................................................113 5.9.3 Late Responses ..........................................................................................................................................115 5.9.4 Needle Electromyography .........................................................................................................................115 5.9.5 Sensory Nerve Conduction Studies...........................................................................................................116 5.9.6 Motor Nerve Conduction Studies..............................................................................................................116 5.10 Diagnostic Imaging................................................................................................................................................116 5.10.1 Magnetic Resonance Imaging ...................................................................................................................116 5.10.1.1 Rapid MR Sequencing .............................................................................................................117 5.10.1.2 Turbo Echo MR Sequences .....................................................................................................117 5.10.1.3 Inversion Recovery...................................................................................................................118 5.10.1.4 Contrast Enhancement..............................................................................................................118 5.10.1.5 Kinematic MRI.........................................................................................................................118

5.10.1.6 Functional MRI ........................................................................................................................119 5.10.1.7 Magnetization Transfer ............................................................................................................119 5.10.1.8 Diffusion-Weighted Imaging....................................................................................................119 5.10.1.9 MR Spectroscopy .....................................................................................................................119 5.10.1.10 Three-Dimensional Imaging (Reconstruction) ........................................................................120 5.10.1.11 MR Angiography......................................................................................................................120 5.10.1.12 MR Myelography .....................................................................................................................120 5.10.1.13 Interventional MRI ...................................................................................................................120 5.11 Neurosonography...................................................................................................................................................121 5.11.1 Intraoperative Spinal Sonography .............................................................................................................121 5.12 Computed Tomography .........................................................................................................................................121 5.12.1 CT/Myelography........................................................................................................................................121 5.12.2 Helical CT (Spiral CT)..............................................................................................................................121 5.13 Plain-Film Radiography ........................................................................................................................................121 5.14 Quantitative Considerations in Spinal Cord Imaging ...........................................................................................122 5.14.1 Central Spinal Canal Measurements .........................................................................................................122 5.14.2 Spinal Instability and Vertebral Translation..............................................................................................123 5.14.3 Classifications of Spinal Cord Compression.............................................................................................123 5.14.4 Spinal Cord Cross-Sectional Size and Area .............................................................................................124 5.14.5 Intrinsic Cord Dysmorphism .....................................................................................................................124 5.14.6 Intramedullary Signal Patterns ..................................................................................................................125 5.15 Functional and Laboratory Assessment ................................................................................................................125 5.15.1 Pulmonary Function ..................................................................................................................................125 5.15.2 Cerebrospinal Fluid Evaluation.................................................................................................................126 5.15.3 Amniocentesis............................................................................................................................................126 5.15.4 Blood and Serum Studies ..........................................................................................................................128 5.15.5 Genetic Assessment ...................................................................................................................................128 5.15.6 Bladder Function .......................................................................................................................................129 5.15.6.1 Cystourethrography ....................................................................................................................129 5.15.6.2 Cystometry .................................................................................................................................129 5.15.6.3 Electrodiagnostic Studies of Bladder Function .........................................................................129 5.15.6.4 Uroflowometry............................................................................................................................130 5.15.7 Physical Impairment Assessment ..............................................................................................................130 5.15.7.1 Frankel Classification .................................................................................................................130 5.15.7.2 ASIA/IMSOP Scale....................................................................................................................130 5.15.7.3 Benzel and Larson Scale............................................................................................................130 5.15.7.4 Japanese Orthopedic Association Cervical Myelopathy Score .................................................130 5.15.7.5 Range of Motion (ROM) ...........................................................................................................130 5.15.7.6 Gait .............................................................................................................................................130 5.15.7.7 Muscular Performance ...............................................................................................................132 5.15.7.8 Sensibility ...................................................................................................................................133 5.15.7.9 Balance .......................................................................................................................................133 References .......................................................................................................................................................................133 Chapter 6 Spinal Cord Syndromes and Guide to Neurological Levels ..........................................................................................139 6.1 Vascular Syndromes of the Spinal Cord ...............................................................................................................139 6.1.1 Anterior Spinal Artery Syndrome .............................................................................................................139 6.1.2 Posterior Spinal Artery Syndrome (PSAS) ...............................................................................................139 6.1.3 Radiculomedullary Artery Syndrome (RAS) ............................................................................................139 6.1.4 Central Cord Vascular Syndrome (CCVS)................................................................................................139 6.2 Complete Spinal Cord Transection (Transverse Myelopathy) .............................................................................140 6.3 Central Cord Syndrome.........................................................................................................................................142 6.4 Anterior Cord Syndrome .......................................................................................................................................143

6.5

Posterior Cord Syndrome ......................................................................................................................................143 6.5.1 Posterolateral Cord Syndrome...................................................................................................................144 6.6 Anterior Horn Syndrome (Progressive Muscular Atrophy)..................................................................................145 6.6.1 Polio and Post-Polio Syndrome ................................................................................................................145 6.6.2 Combined Anterior Horn and Pyramidal Tract Disease (Motor Neuron Syndrome) ..............................145 6.7 Multifocal Cord Syndrome....................................................................................................................................146 6.8 Conus Medularis Syndrome ..................................................................................................................................146 6.9 Hemisection Syndrome (Brown–Séquard Syndrome) ..........................................................................................149 6.10 Cervical Medullary Syndrome ..............................................................................................................................149 6.11 Guide to Neurological Levels ...............................................................................................................................151 6.11.1 Cranial-Cervical Lesions (Foramen Magnum Lesions)............................................................................151 6.11.2 Cervical Lesions ........................................................................................................................................152 6.11.2.1 Intact C3 Neurologic Level (C3 Functional Level)...................................................................152 6.11.2.2 Intact C4 Neurologic Level (C4 Functional Level)...................................................................152 6.11.2.3 Intact C5 Neurologic Level (C5 Functional Level)...................................................................152 6.11.2.4 Intact C6 Neurologic Level (C6 Functional Level)...................................................................153 6.11.2.5 Intact C7 Neurologic Level (C7 Functional Level)...................................................................153 6.11.2.6 Intact C8 and T1 Neurologic Levels (C8 and T1 Functional Levels) ......................................153 6.11.3 Thoracic-Intact Lesions (Mid-Thoracic Functional Levels) .....................................................................154 6.11.3.1 Intact T12 Neurologic Level (T12 Functional Level) ...............................................................154 6.11.4 Lumbar Transection Injuries......................................................................................................................154 6.11.4.1 Intact L1 Neurologic Level (L1 Functional Level) ...................................................................154 6.11.4.2 Intact L2 Neurologic Level (L2 Functional Level) ...................................................................154 6.11.4.3 Intact L3 Neurologic Level (L3 Functional Level) ...................................................................154 6.11.4.4 Intact L4 Neurologic Level (L4 Functional Level) ...................................................................154 6.11.4.5 Intact L5 Neurologic Level (L5 Functional Level) ...................................................................155 6.11.5 Sacral Transection Injuries ........................................................................................................................155 6.11.5.1 Intact S1 Neurologic Level (S1 Functional Level) ...................................................................155 6.11.5.2 Intact S2 Neurologic Level and Below......................................................................................155 References .......................................................................................................................................................................157 Section 2 Radiculopathy Chapter 7 Pathomechanisms of Radiculopathy ...............................................................................................................................161 7.1 Spinal Nerve Root Anatomy and Regional Characteristics..................................................................................161 7.1.1 Intervertebral Foramen Anatomy ..............................................................................................................163 7.1.2 Anatomy of the Dural Sleeve and Peripheral Nerve Junction .................................................................165 7.1.3 Blood Supply of the Spinal Nerve Root ...................................................................................................166 7.1.4 The Dorsal Root Ganglia ..........................................................................................................................166 7.1.5 Pathophysiology of Nerve Root Compression..........................................................................................167 7.1.6 Sites of Nerve Root Vulnerability .............................................................................................................168 7.1.7 Pathomechanics Affecting the Nerve Root Complex ...............................................................................169 7.1.8 Nerve Root Double Crush .........................................................................................................................169 7.2 Biochemically Induced Radiculopathy .................................................................................................................170 7.3 Spinal Degeneration and Radiculopathy ...............................................................................................................171 7.3.1 Rostrocaudal Subluxation..........................................................................................................................172 7.4 Fibrosis and Radiculopathy ...................................................................................................................................172 7.4.1 Arachnoiditis and Radiculopathy ..............................................................................................................173 7.5 Acquired Lateral Recess Stenosis and Vascular Stasis.........................................................................................173 7.6 Failed Back Surgery Syndrome.............................................................................................................................175 7.7 Trauma and Radiculopathy....................................................................................................................................176 7.7.1 Nerve Root Avulsion .................................................................................................................................177

7.8

Intervertebral Disk Herniation and Radiculopathy ...............................................................................................177 7.8.1 Experimental Mechanism of Disk Herniation ..........................................................................................177 7.8.2 Conventional Classification of Disk Lesions ............................................................................................178 7.8.2.1 Annular Bulge (Disk Bulge) ......................................................................................................178 7.8.2.2 Disk Protrusion (Herniation)......................................................................................................180 7.8.2.3 Disk Extrusion............................................................................................................................180 7.8.2.4 Free Disk Fragment (Sequestered Disk)....................................................................................182 7.9 Nerve Root Compromise: Expansile Lesions .......................................................................................................183 7.9.1 Schwannoma ..............................................................................................................................................183 7.9.2 Neurofibroma .............................................................................................................................................186 7.9.3 Meningioma ...............................................................................................................................................188 7.9.4 Perineurial Cysts (Tarlov’s Cysts).............................................................................................................189 7.9.5 Synovial Cysts ...........................................................................................................................................189 7.9.6 Metastatic Disease .....................................................................................................................................189 7.10 Vertebral Osteomyelitis and Discitis.....................................................................................................................190 7.11 Spondylolisthesis and Radiculopathy....................................................................................................................190 7.12 Noncompressive Radiculoneuronopathy ...............................................................................................................193 7.12.1 Diabetic Radiculopathy .............................................................................................................................193 7.12.2 Infection .....................................................................................................................................................194 7.12.2.1 Herpes Varicella-Zoster Virus (Shingles)...................................................................................194 7.12.2.2 AIDS-Related Polyradiculopathy...............................................................................................194 7.12.2.3 Lyme Disease .............................................................................................................................194 7.12.3 Coagulopathies...........................................................................................................................................195 References .......................................................................................................................................................................195 Chapter 8 Classic Signs and Symptoms of Radiculopathy.............................................................................................................201 8.1 Sensory Abnormalities...........................................................................................................................................201 8.2 Nerve Root Irritability Signs .................................................................................................................................201 8.3 Reflex Abnormalities .............................................................................................................................................204 8.4 Paresis ....................................................................................................................................................................205 8.5 Muscular Atrophy ..................................................................................................................................................206 8.6 Dysautonomia and Trophic Changes ....................................................................................................................206 8.7 Combined Pain Syndromes: Radicular and Vertebrogenic Pain...........................................................................207 8.7.1 Radiculopathic and Vertebrogenic Symptoms Resembling Visceral Pain................................................209 8.8 Assessment of Radiculopathy ...............................................................................................................................209 8.8.1 Electrodiagnosis and Radiculopathy .........................................................................................................209 8.8.1.1 Needle Electromyographic Evaluation ......................................................................................209 8.8.1.2 Muscles with Segmental Localizing Significance .....................................................................210 8.8.1.3 The Chronology of Electrophysiologic Abnormalities in Radiculopathy.................................210 8.8.1.4 Radiculopathy and Postsurgical EMG Findings........................................................................212 8.8.1.5 Late Reflexes ..............................................................................................................................212 8.8.1.5.1 H-reflex.....................................................................................................................213 8.8.1.5.2 F-wave ......................................................................................................................213 8.8.1.5.3 T-reflex .....................................................................................................................214 8.8.1.6 Nerve Conduction Studies .........................................................................................................215 8.8.1.6.1 Motor Nerve Conduction Studies ............................................................................215 8.8.1.6.2 Sensory Nerve Conduction Studies .........................................................................215 8.8.1.7 Somatosensory and Dermatomal Evoked Potentials .................................................................217 8.8.1.7.1 Mixed Nerve Stimulation.........................................................................................217 8.8.1.7.2 Dermatomal Stimulation ..........................................................................................217 8.8.2 Radiculopathy and Functional Capacity Evaluation.................................................................................218 8.8.3 MRI of Disk, Nerve Root, Venous Plexus, and Muscle...........................................................................220 8.8.3.1 Disk Herniation ..........................................................................................................................220

8.8.3.2 Contrast Enhancement of the Spinal Nerve Root .....................................................................221 8.8.3.3 Enhancement of the Epidural Venous Plexus ............................................................................221 8.8.3.4 MRI of Muscular Atrophy .........................................................................................................222 8.9 Cervical Monoradiculopathy Syndromes ..............................................................................................................223 8.9.1 C1 Radiculopathy ......................................................................................................................................223 8.9.2 C2 Radiculopathy ......................................................................................................................................223 8.9.3 C3 Radiculopathy ......................................................................................................................................224 8.9.4 C4 Radiculopathy ......................................................................................................................................224 8.9.5 C5 Radiculopathy ......................................................................................................................................224 8.9.6 C6 Radiculopathy ......................................................................................................................................229 8.9.7 C7 Radiculopathy ......................................................................................................................................231 8.9.8 C8 Radiculopathy ......................................................................................................................................231 8.10 Thoracic Monoradiculopathy Syndromes .............................................................................................................233 8.10.1 T1 Radiculopathy ......................................................................................................................................233 8.10.2 T2–T12 Radiculopathy ..............................................................................................................................233 8.11 Lumbar and Sacral Monoradiculopathy Syndromes.............................................................................................235 8.11.1 Anatomic Variations of the Lumbosacral Nerve Roots ............................................................................236 8.11.2 L1 Radiculopathy ......................................................................................................................................237 8.11.3 L2 Radiculopathy ......................................................................................................................................238 8.11.4 L3 Radiculopathy ......................................................................................................................................239 8.11.5 L4 Radiculopathy ......................................................................................................................................240 8.11.6 L5 Radiculopathy ......................................................................................................................................242 8.11.7 S1 Radiculopathy.......................................................................................................................................243 8.11.8 S2–S5 Radiculopathy ................................................................................................................................245 8.12 Cauda Equina Syndrome .......................................................................................................................................245 8.12.1 High Lesion within the Cauda Equina......................................................................................................246 References .......................................................................................................................................................................247 Section 3 Peripheral Nerve Entrapment and Compression Neuropathy Chapter 9 Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury ......................................253 9.1 General Organization of Peripheral Nerve Distribution .......................................................................................253 9.1.1 Posterior Primary Divisions ......................................................................................................................253 9.1.2 General Organization of Plexuses .............................................................................................................254 9.2 Cervical Plexus ......................................................................................................................................................254 9.2.1 Cervical Plexus: Sensory Innervation to the Head and Neck ..................................................................254 9.2.2 Cervical Plexus: Sensory Innervation to the Neck and Shoulders...........................................................254 9.2.3 Cervical Plexus in Relationship to Cranial Nerves ..................................................................................254 9.2.4 Motor Fibers within the Cervicobrachial Plexus ......................................................................................255 9.3 Brachial Plexus ......................................................................................................................................................255 9.3.1 Nerves Arising Directly from the Nerve Roots or the Brachial Plexus...................................................256 9.3.2 Nerve Branches Arising from the Upper Trunk .......................................................................................257 9.3.3 Nerves Formed with Contributions from Both the Medial and Lateral Cords ........................................257 9.4 Lumbar Plexus .......................................................................................................................................................257 9.5 Lumbosacral Plexus...............................................................................................................................................259 9.6 Autonomic Nervous System..................................................................................................................................261 9.7 Relevant Anatomy of the Peripheral Nerve ..........................................................................................................261 9.8 Peripheral Nerve Vascularity .................................................................................................................................264 9.9 Biomechanical Characteristics of Peripheral Nerves............................................................................................266 9.10 Classification of Nerve Injuries.............................................................................................................................266 9.10.1 Physiologic Conduction Block ..................................................................................................................266 9.10.2 Neurapraxia................................................................................................................................................266

9.10.3 Axonotmesis ..............................................................................................................................................267 9.10.4 Neurotmesis ...............................................................................................................................................268 9.11 Peripheral Nerve Response to Injury ....................................................................................................................268 9.11.1 Wallerian Degeneration .............................................................................................................................268 9.11.2 Axonal Regeneration .................................................................................................................................269 9.12 Nerve Compression and Related Pathomechanisms.............................................................................................270 9.12.1 Compromised Axonal Transport ...............................................................................................................271 9.12.2 The Double Crush Syndrome or Whole Nerve Syndrome.......................................................................271 9.12.3 Cumulative Trauma Disorder (CTD) ........................................................................................................273 9.13 Myotendinous, Myofascial, and Related Contributions to Entrapment ...............................................................273 9.13.1 Acute Myofascial Injury............................................................................................................................273 9.13.2 Chronic Injuries .........................................................................................................................................273 9.13.2.1 Constant Pressure/Tension Injury ..............................................................................................273 9.13.2.2 Repetitive Injury.........................................................................................................................273 9.13.3 The Cumulative Injury Cycle ....................................................................................................................274 9.13.3.1 Weak and Tight Tissues .............................................................................................................274 9.13.3.2 Friction–Pressure–Tension .........................................................................................................274 9.13.3.3 Decreased Circulation, Edema...................................................................................................274 9.13.4 Inflammation ..............................................................................................................................................275 9.14 Common Predisposing Disorders Associated with Entrapment Neuropathy .......................................................275 9.14.1 General Patterns of Anatomic Distribution...............................................................................................276 9.14.2 Diabetes......................................................................................................................................................277 9.14.3 Uremia........................................................................................................................................................277 9.14.4 Thyroid Disorders......................................................................................................................................277 9.14.5 HIV-1 .........................................................................................................................................................278 9.14.6 Rheumatoid Arthritis .................................................................................................................................278 9.14.7 Respiratory Insufficiency...........................................................................................................................278 References .......................................................................................................................................................................278 Chapter 10 Characteristic Signs and Symptoms of Entrapment.......................................................................................................281 10.1 Assessment of Entrapment Syndromes.................................................................................................................281 10.1.1 History........................................................................................................................................................281 10.1.2 Examination ...............................................................................................................................................281 10.1.3 Nerve Percussion Sign...............................................................................................................................282 10.1.4 Electrodiagnostic Findings ........................................................................................................................283 10.1.5 Entrapment Syndromes Overview.............................................................................................................284 10.2 Proximal Upper Extremity Entrapment ................................................................................................................285 10.2.1 Cervicoaxillary Entrapment Syndromes (Thoracic Outlet Syndrome) ....................................................285 10.2.2 Scalene Entrapment Syndrome .................................................................................................................287 10.2.3 Other Causes of Proximal Plexus Entrapment..........................................................................................288 10.2.3.1 Clinical Signs and Symptoms ....................................................................................................289 10.2.4 Costoclavicular Entrapment Syndrome.....................................................................................................289 10.2.5 Costopectoral Tunnel or Hyperabduction Syndrome................................................................................290 10.2.5.1 Clinical Signs and Symptoms ....................................................................................................290 10.2.6 Axillary Tunnel Entrapment ......................................................................................................................290 10.2.6.1 Electrodiagnostic Evaluation......................................................................................................291 10.2.7 Long Thoracic Nerve Entrapment (Scapular Winging) ............................................................................291 10.2.8 Quadrangular (Quadrilateral) Space Syndrome (Lateral Axillary Hiatus Syndrome) .............................291 10.2.8.1 Clinical Signs and Symptoms ....................................................................................................292 10.2.9 Lateral Antebrachial Symptoms: Lateral Antebrachial Cutaneous Nerve/Musculocutaneous Nerve Entrapment......................................................................................................................................292 10.3 Median Nerve Entrapment Syndromes .................................................................................................................292 10.3.1 Supracondylar Process Syndrome .............................................................................................................292 10.3.1.1 Clinical Signs and Symptoms ....................................................................................................293

10.4

10.5

10.6 10.7

10.3.2 Pronator Teres Muscle Syndrome .............................................................................................................293 10.3.2.1 Clinical Signs and Symptoms ....................................................................................................294 10.3.3 Anterior Interosseous Nerve Syndrome ....................................................................................................295 10.3.3.1 Clinical Signs and Symptoms ....................................................................................................295 10.3.4 Carpal Tunnel Syndrome...........................................................................................................................296 10.3.4.1 Prevalence...................................................................................................................................297 10.3.4.2 Anatomy and Pathomechanics ...................................................................................................297 10.3.4.3 Clinical Signs and Symptoms ....................................................................................................299 10.3.4.4 Electrodiagnostic Evaluation of Carpal Tunnel Syndrome .......................................................301 10.3.4.5 Diagnostic Imaging ....................................................................................................................303 Posterior Upper Extremity Syndromes .................................................................................................................303 10.4.1 Suprascapular Nerve Syndrome ................................................................................................................303 10.4.1.1 Clinical Signs and Symptoms ....................................................................................................304 10.4.2 Lateral Intermuscular Septum/Radial Nerve.............................................................................................305 10.4.3 Brachialis/Brachioradialis/Radial Nerve ...................................................................................................306 10.4.4 Arcade of Frohse/Deep Radial Nerve .......................................................................................................306 10.4.5 Distal Superficial Radial Nerve Entrapment/Cheiralgia Paresthetica.......................................................309 Ulnar Nerve Syndromes ........................................................................................................................................310 10.5.1 Ulnar Nerve Entrapment at the Elbow Cubital Tunnel Syndrome...........................................................310 10.5.1.1 Clinical Signs and Symptoms ....................................................................................................311 10.5.1.2 Electrodiagnostic Evaluation of Ulnar Entrapment at the Elbow .............................................311 10.5.1.3 Diagnostic Imaging ....................................................................................................................311 10.5.2 Guyon’s Canal Syndrome/Ulnar Tunnel Syndrome .................................................................................311 10.5.2.1 Anatomy and Pathomechanics ...................................................................................................311 10.5.2.2 Clinical Signs and Symptoms ....................................................................................................312 Abdominal/Pelvic Entrapment Syndromes ...........................................................................................................314 Lower Extremity Entrapment Syndromes.............................................................................................................317 10.7.1 Psoas Entrapment Syndrome/Iliacus Entrapment Syndrome ...................................................................317 10.7.1.1 Anatomy and Pathomechanics ...................................................................................................317 10.7.1.2 Clinical Signs and Symptoms ....................................................................................................319 10.7.2 Meralgia Paresthetica/Inguinal Tunnel Syndrome (Lateral Femoral Cutaneous Entrapment) ................320 10.7.2.1 Anatomy and Pathomechanics ...................................................................................................320 10.7.2.2 Clinical Signs and Symptoms ....................................................................................................321 10.7.3 Obturator Nerve Entrapment .....................................................................................................................321 10.7.3.1 Anatomy and Pathomechanics ...................................................................................................322 10.7.3.2 Clinical Signs and Symptoms ....................................................................................................322 10.7.4 Iliolumbar–Lumbosacral Ligament Entrapment/Lumbosacral Tunnel Syndrome ...................................322 10.7.4.1 Anatomy and Pathomechanics ...................................................................................................322 10.7.4.2 Clinical Signs and Symptoms ....................................................................................................323 10.7.5 Piriformis Syndrome..................................................................................................................................323 10.7.5.1 Anatomy and Pathomechanics ...................................................................................................323 10.7.5.2 Clinical Signs and Symptoms ....................................................................................................325 10.7.6 Saphenous Nerve Syndrome/Adductor Tunnel Syndrome .......................................................................325 10.7.6.1 Anatomy and Pathomechanics ...................................................................................................325 10.7.6.2 Clinical Signs and Symptoms ....................................................................................................327 10.7.7 Peroneal Tunnel Syndrome/Entrapment at the Knee and Fibular Neck ..................................................327 10.7.7.1 Anatomy and Pathomechanics ...................................................................................................327 10.7.7.2 Clinical Signs and Symptoms ....................................................................................................329 10.7.7.3 Electrodiagnostic Evaluation......................................................................................................329 10.7.8 Anterior Tarsal Tunnel Syndrome/Deep Peroneal Nerve Syndrome........................................................329 10.7.8.1 Anatomy and Pathomechanics ...................................................................................................329 10.7.8.2 Clinical Signs and Symptoms ....................................................................................................330 10.7.9 Medial Tarsal Tunnel Syndrome ...............................................................................................................331 10.7.9.1 Anatomy and Pathomechanics ...................................................................................................331 10.7.9.2 Clinical Signs and Symptoms ....................................................................................................332

10.7.10 Morton’s Neuroma (Metatarsalgia) .........................................................................................................333 10.7.10.1 Anatomy and Pathomechanics ...............................................................................................333 10.7.10.2 Clinical Signs and Symptoms ................................................................................................334 10.8 Summary ................................................................................................................................................................334 References .......................................................................................................................................................................334 Section 4 Appendix ........................................................................................................................................................................341 Index ...............................................................................................................................................................................349

Section 1 Myelopathy: Spinal Cord Injury and Selected Clinical Syndromes

1

Relevant Spinal Cord Anatomy*

The ability to recognize signs and symptoms of acute, subacute, or chronic myelopathy should not be limited to the neurologist or neurosurgeon but should extend to all physicians and physical medicine specialists. The clinician should be familiar with the regional anatomy, risk factors, and early clinical signs. To that end, this chapter reviews relevant regional anatomy, mechanisms of spinovascular insufficiency, infarction, stenotic syndromes, spinal cord injury (SCI), and selected noncompressive myelopathies. Throughout this text, emphasis is placed on assessment. Although the most prevalent spinal syndromes are presented, keep in mind that many incomplete and atypical patterns are seen in clinical practice.

1.1 BASIC SPINAL CORD ANATOMY The spinal cord lies well protected within the spinal canal of the vertebral column. The surrounding vertebrae support the trunk and head and provide a protective covering for the spinal cord throughout intersegmental and global vertebral motion. The column of organized cell bodies and myelinated or unmyelinated axons constituting the spinal cord is somatotopically, longitudinally, and segmentally arranged. In adulthood, the cord averages 42 to 45 cm in length, extending from the medulla oblongata to approximately the L1 vertebral disk level.1 It is generally 25 cm shorter than the 70-cm vertebral column and thus occupies almost two thirds the length of the spinal canal. The adult cord weighs approximately 30 to 35 g and averages 2.5 cm wide. Regions of enlargement occur in the cervical and lumbar areas of the cord, reflecting greater numbers of nerve cell bodies, neurons, and interneurons within the gray matter. These two enlargements correspond to the origin of spinal nerve roots destined for the brachial and lumbar plexuses, which provide innervation to the upper and lower extremities, respectively (see Figure 1.1). The diameter of the cervical enlargement ranges from 9 to 13 mm, and the lumbar enlargement from 8 to 12 mm. By comparison, the normal thoracic cord diameter is approximately 8 to 10 mm.2 The spinal cord terminates in a conical tapering referred to as the conus medularis. At birth, the conus

medularis lies approximately at the level of L3. In adults, the conus normally ends between the T12 and L3 vertebral levels, with the L1–L2 level being the most common site of cord termination. Lumbar and sacral nerve roots originate in the conus, exit, and descend to form the cauda equina. Also extending from the conus is the filum terminale formed from the pia mater, which attaches to the first coccygeal segment. The spinal cord is longitudinally divided by an anterior median fissure and a posterior median sulcus that separate it into right and left symmetric halves. The anterior median fissure is a deep invagination containing the anterior spinal artery; the posterior median sulcus is a shallow midline division of the posterior columns. Nerve roots attach bilaterally to the cord along its dorsal lateral sulcus and ventral lateral sulcus. Each lateral half of the cord is additionally divided into longitudinally organized columns (funiculi) of spinal white matter, consisting of nerve fibers, neuroglia, and blood vessels. This white matter surrounds the central gray portion of the cord. Resembling an “H” on transverse section, the spinal gray matter consists largely of nerve cell bodies in three main categories.3 The first is the internuncial or interneuron: short, small fibers involved in local circuitry between gray matter nerve cells. The second category, motor cells of the cord’s ventral and lateral horns, is in turn subdivided into three subtypes: alpha motor neurons, gamma motor neurons, and preganglionic motor cells of the sympathetic nervous system. The third major category within spinal gray matter is the tract cell; cell bodies of these neurons are involved in relaying sensory information.3 On axial section, the H-shaped gray matter is divided into two symmetric halves representing each side of the body, with a central canal running the entire length of the cord. The anterior portion of the spinal gray matter, or anterior horn, contains nerve cell bodies leading to fibers of the ventral roots. A lateral column, most pronounced in the thoracic region of the cord, contains the preganglionic cells of the autonomic nervous system (ANS). The posterior horn contains the cell bodies of nerves subserving sensory function. Dendritic connections between nerve cell bodies account for the greatest volume of spinal gray matter.4

* This chapter written with John W. Blum.

3

4

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

   


      
      

  



  

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FIGURE 1.1 Dorsal view of the spinal cord and dorsal nerve roots in situ, after removal of the neural arches of the vertebrae. (From DeMeyer, W., Neuroanatomy, Hawal, Philadelphia, PA, 1988, p. 99. With permission.)

The surrounding white matter is organized into three columns: dorsal, ventral, and lateral. The dorsal funiculus consists of the fasciculus gracilis, which carries sensory information from the sacral area and lower extremities, and the fasciculus cuneatus, which carries sensory information from the thoracic and cervical region; these are bounded by the dorsal horns of the spinal gray matter. The ventral and lateral funiculi contain both ascending and descending tracts. Of these, the most important descending pathways are the lateral corticospinal tract, vestibulospinal tract, and reticulospinal fibers; the largest ascending tracts in the ventral and lateral funiculi are the anterolateral spinothalamic fibers and the dorsal and ventral spinocerebellar tracts. Nerve fibers of the spinal white matter can be categorized into five groups: (1) afferent fibers from cells in the dorsal root ganglia, which enter through the dorsal root

and may ascend or descend within the cord before synapsing; (2) long ascending fibers derived from nerve cells in the cord, which conduct afferent impulses to supraspinal levels; (3) long descending fibers from supraspinal sources, which synapse within the spinal gray matter; (4) fibers affecting intrasegmental and intersegmental spinal cord processing; and (5) fibers from motor neurons in the ventral and lateral gray columns, which exit the cord into the ventral spinal nerve root. All of these groups, with the exception of the fifth, constitute longitudinal tracts.4 Myelination is formed from glial cells. Schwann cells, normally found in myelinated peripheral nerves, are not found within the brain and central portion of the spinal cord but are found instead in the transitional zone, within a few millimeters distal to the point at which nerve roots traverse away from the spinal cord.

Relevant Spinal Cord Anatomy

1.2 SEGMENTAL SPINAL ANATOMY The spinal cord can be divided into 31 segments or neuromeres, each contributing to one pair of spinal nerve roots. Each of the 31 paired nerve roots, in turn, represents a segmental level that is further defined as the entire region of the body innervated by that root. For clinical purposes, these segments are often further classified: a dermatome is the cutaneous region(s) subserved by a nerve root; a myotome is the skeletal musculature innervated by the motor contributions from a signal nerve root; and an angiotome comprises those blood vessels innervated by the autonomic fibers within a spinal nerve.5 Not every neuromere contributes to each of these segmental categories, and the distribution of segmental autonomic innervation differs significantly from myotome and dermatome innervation. Autonomic nerves contribute to other functions, such as pseudomotor or pyelomotor modulation; this diffuse autonomic distribution contributes to a more complex clinical presentation in nerve root compromise. Each spinal nerve contains contributions from a primarily sensory dorsal root and a primarily motor ventral root. The spinal nerves are segmentally paired as follows: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1–2 coccygeal.6,7 During fetal and infant development, the vertebral column and dura mater lengthen at a more accelerated rate than the neural tube, leaving the terminal end of the cord highly positioned in relation to the most caudal osseous spinal structures. As a result, spinal nerve roots must descend from their cord segments of origin to their levels of exit from the column through intervertebral foramina.1,3,4

1.2.1 REGIONAL NEUROMERE CHARACTERISTICS The cervical cord spans from C1 to T1 and has an average length of 10 cm. The eight cervical segments closely correspond in position to the adjacent cervical vertebrae. The first seven cervical nerve pairs exit through intervertebral foramina above their corresponding vertebrae; the most caudal cervical nerve pair (C8), however, departs the cord below the most caudal cervical vertebra (C7), which allows for the presence of one more cervical nerve root pair than vertebrae. Many of the roots below the C7 vertebral level do not necessarily exit immediately adjacent to their corresponding vertebrae, due to the variability of cord length among individuals and other variables such as cord segmental lengths and level of cord termination. Two enlargements or widenings are found within the spinal cord, one in the cervical and one in the lumbar region. The cervical enlargement commonly extends from cord segments C3 to T1 and represents the increased number of nerve cell bodies originating from C5–T1 that innervate the upper extremities through the brachial plexus. The lumbar enlargement typically spans cord segments L1 to

5

S3 and is located between the T10 and L1 vertebral bodies; these segments subserve the lower extremities through the lumbosacral plexus. The conus medularis lies approximately at the L1–L2 vertebral level in the adult.8 The cauda equina nerve root bundle emerges from the conus medularis, descending as the lumbar and sacral nerve roots. In cervical cord segments, transverse diameter is characteristically greater than sagittal diameter and varies with each descending cervical segment.2,9 White matter is more prevalent in the cervical cord than in any other spinal segment due to the confluence of ascending and descending tracts in this region. The entire diameter of the thoracic cord is smaller than that of the cervical cord; comparatively, the thoracic cord contains a smaller number of neuronal cell bodies and therefore has a smaller ventral horn as well.9 A lateral gray horn is present and is distinguished among thoracic intermediate gray matter, representing the autonomic cell bodies (and their axial projections) that innervate smooth muscle, cardiac muscle, and glandular tissues. Despite containing relatively less white matter than the cervical cord, lumbar spinal segments display large ventral and dorsal horns. The lumbar ventral horns contain a multitude of neuronal cell bodies with axonal projections innervating skeletal muscles of the lower extremities. Lumbar neural segments have roughly the same sagittal and transverse diameter, giving them the most circular appearance in the entire cord.9 The sacral cord is predominantly composed of gray matter with a relative paucity of white matter. Its superiorto-inferior neuromere length is typically short, averaging only 5 mm; other spinal cord segmental lengths vary from 15 mm in the lumbar to 26 mm in the thoracic and 13 mm in the cervical region.4

1.2.2 REGIONAL SPINAL CANAL CHARACTERISTICS Studies of the adult cervical spinal cord lumen have shown that the mean anterior-to-posterior (A-P) and lateral diameter vary, respectively, from 17 mm and 26 mm at C2 to 14 mm and 25 mm at C5.10 In the normal spine at the C1–C2 vertebral level, the cord is positioned within a spinal canal approximately 2.5 times larger and a dural sac 1.5 times larger than the cord itself. The canal then narrows from C3 to C6,11 decreasing to 1.8 times the cord size by C5–C6, with a dural sac only 1.2 times as large as the cord;12 at the C6 vertebral level, the spinal cord fills approximately 75% of the canal.11 The osseous spinal column surrounding the cervical cord is considered the most distinctive region of the spine and characteristically is the most complicated regional articular system in the body.13 Its 37 separate joints enable the most complex movements of any spinal section and therefore assume the greatest risk for pathomechanical

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Posterior spinal arteries Anterior spinal artery Anterior and posterior rootlets

Pia mater Circumferential arteries Radicular artery Arachnoid

Dentate ligaments

Dura mater Dural sleeve Spinal nerve

FIGURE 1.2 Intradural anatomy. (Copyright J.M. True, D.C.)

sequelae, due to the great degree of flexibility, excursion, and exposure to potential physical trauma. There is less risk of compression from vertebral instability in thoracic segments due to the stabilizing effects of the ribcage. The thoracic spinal canal has the smallest diameter spinal lumen.10 The narrowest region extends approximately from vertebral levels T4–T9, with a mean adult A-P diameter of 14 mm and 15 mm laterally at the T6 vertebra. However, this narrowing predisposes the thoracic cord, a region with a less abundant vascular supply than the other cord segments, to greater risk for vascular compromise. The spinal cord from T4–T9 is also more susceptible to stenotic compromise. Rare thoracic disk herniations (1% of all herniated disks) can impose on the narrow canal, compressing the dura mater, subarachnoid space, and the spinal cord.14 In a review of 280 cases, Arce and Dohrmann14 reported that 75% of thoracic disk protrusions occur between T8 and T12 at the caudal end of the thoracic watershed zone. The lumbar and sacral regions of the canal are spacious by comparison, with progressive lateral expansion accommodating the cauda equina as the canal descends. Lumbar A-P canal diameter averages 15 to 25 mm, and any narrowing to less than 12 to 13 mm is considered diagnostic for lumbar stenosis.15 The cross-sectional area of the lumbar canal is at least 77 ± 13 mm2.16

1.3 MENINGES AND COMPARTMENTS Three membranous layers surrounding the spinal cord provide protection and additional support to the neural tissues within. Collectively known as the meninges, these three structural layers are continuations of the meningeal coverings of the brain; from superficial to deep, they are the dura, arachnoid, and pia mater, respectively (Figure 1.2).

1.3.1 DURA MATER The outermost layer of the spinal cord meninges is the dura mater (pachymeninx), a tough fibrous sheath that provides an imposing barrier rarely penetrable by primary bone tumors, metastasis, bacterial infections, or osteomyelitic tuberculosis. The dura mater is primarily comprised of an outermost loosely arranged fibroelastic layer, a middle layer that is largely fibrous tissue, and an inner layer of flattened fibroblasts called the dural border cell layer.17 There is an abundance of collagenous fibers that lie in longitudinal bundles and have redundant properties, being wavy in configuration when shortened, straight and taut when stretched. A continuation of the dural meningeal layer of the brain, the dura mater extends from the foramen magnum to its termination at the second sacral vertebral body. Dural anchoring also occurs at the rim of the foramen magnum, at the posterior vertebral bodies of C2–C3, and to the posterior longitudinal ligament by Hoffmann’s ligaments.4 The dura extends along each nerve root to form a funnel-shaped sleeve within the intervertebral foramen. Sensory innervation of the anterior aspect of the spinal dura mater is greater than the posterolateral aspect of the dura. Innervation to the dura originates from the sinuvertebral nerve of Von Luschka (recurrent meningeal nerve). Branches that innervate the anterior dura may span several vertebral levels, creating considerable innervation overlap from multiple segments.18 The majority of meningeal nerve fibers terminate as free nerve endings with occasional myelinated fibers supplying encapsulated and lamellated receptors.19 Innervation and free nerve endings in the posterior dura are absent or very minimal. The epidural space surrounding the dura mater contains fatty areolar tissue, loose connective tissue, and an

Relevant Spinal Cord Anatomy

extensive venous plexus network separating the spinal dura from the inner vertebral surface.

1.3.2 ARACHNOID MATER The next meningeal layer, the arachnoid mater, is nearly contiguous with the inner surface of the dura mater. Arachnoid tissue is thin, transparent, loosely arranged, and nonvascular.11 The arachnoid membrane is structurally composed of loose, irregular connective tissue with collagen, elastin, and reticular fibers. The arachnoid is composed of an outermost portion (arachnoid barrier cell layer), presenting tightly packed cells, numerous tight junctions, and no extracellular collagen. In view of its numerous tight junctions, the arachnoid barrier cell layer is considered to represent an effective morphological and physiological meningeal barrier between the cerebrospinal fluid in the subarachnoid space and the blood circulation in the dura.17 The spinal arachnoid layer extends from the intracranial arachnoid layer to the S2 vertebral level. Where the nerve roots pass through the dura and enter the IVF, they carry a prolongation of the arachnoid membrane applied to the inner surface of the dural sleeve. This creates a bilaminar tubular funnel-shaped sleeve composed of dura externally and arachnoid internally. The dura blends with the epineurium of the spinal nerve, and the arachnoid blends with the perineurium of the spinal nerve.20 Cerebrospinal fluid (CSF) fills the subarachnoid space, providing biochemical and immunological support and protection to the central nervous system (CNS). During spinal movement, pressure shifts in the CSF and pulsations of the subarachnoid arteries contribute to rostral and caudal movement of the spinal CSF through subarachnoid spaces. The local venous system of the spinal cord absorbs some of the fluid, providing a potential escape route to systemic circulation for CSF metabolites.4 (See Section 1.3.4 for further discussion of CSF.) Inflammation of the arachnoid membrane is termed arachnoiditis. This condition can result in chronic pain and disability. In the strictest sense, arachnoiditis is inflammation of the piaarachnoid membrane. Chronic arachnoid inflammation will induce localized proliferative fibrosis. Fibrosis associated with arachnoiditis can occur in varying degrees, ranging from mild thickening of the membrane to pronounced adhesions severe enough to block the subarachnoid space.

1.3.3 PIA MATER The pia mater, the innermost meningeal membrane, encases the spinal cord and small blood vessels on the cord surface. This thin double layer of connective tissue can be subdivided into the pia-glia and epi-pia. The avascular pia-glia is the deeper layer and adheres directly to the cord, nerve roots, and rootlets. The pia-glia membrane is similar to the

7

ependymal lining, having discontinuous gap junctions that provide bidirectional exchange of solutes between spinal interstitial fluids and the CSF within the subarachnoid space. The epi-pia encases the vascular elements of the pia mater and joins the pia-glia following the nerve roots to the IVF. Two distinguishing structures of the pia mater help to anchor the spinal cord within its osseous confines. First is the bluish-white filum terminale, a slender, fibrous filament of pia that extends approximately 20 cm from the caudal tip of the conus medullaris to the dorsum of the coccyx. Beginning within the dural sac, the filum terminale eventually pierces the dura and arachnoid membranes at the S2 vertebral level to escape extradurally, but retains its dural and arachnoid coverings. This extradural extension is referred to as the coccygeal ligament. The second specialized supportive component of the pia mater is the dentate ligament, a triangular-shaped, serrated epi-pia extending from its base at the lateral margins of the spinal cord to its apex attaching to the dura mater. There are approximately 22 separate dentate ligaments along each side of the cord in the coronal plane.2,6 The dentate ligament stabilizes the spinal cord by cushioning it from constant movement of the dura mater. The most superior dentate ligament attachment, between the vertebral artery and cranial nerve XII (hypoglossal nerve), provides a landmark where the vertebral artery pierces the dura and enters the posterior fossa at the level of the foramen magnum. The most caudal dentate attachment is usually between the T12 and L1 spinal nerves.7 Surgeons rely on their anatomic knowledge of dentate ligament relationships and attachment points to identify important structures during spinal cord surgery. Intraoperative visualization of the dentate ligament provides identification of the ventral nerve roots and also provides a landmark for localizing the spinothalamic and corticospinal tracts: the ligament typically lies dorsal to the spinothalamic tracts and ventral to the corticospinal tracts.

1.3.4 SUBARACHNOID SPACE CEREBROSPINAL FLUID

AND

The choroid plexus lining the lateral ventricles of the brain secretes CSF and contributes the chemical constituents of the fluid through various cellular transport mechanisms. The unidirectional CSF flow within the ventricles eventually enters the cranial subarachnoid space from the caudal fourth ventricle. Subarachnoid flow of CFS then extends around the brain, spinal cord, and the central canal. Within the cord, pressure gradients enable CSF to flow from the subarachnoid space through arachnoid granulations into the venous sinuses of the cranial dura mater; in addition, the venous system of the spinal cord absorbs

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

some CSF into the local circulation.4 This one-way CSF circulation system is thus a filter for removing metabolites and a means for regulating osmotic pressure gradients in the CNS. The 80- to 150-ml total volume of CFS is replaced four to five times daily, and the pressure ranges from 80 to 180 mm water.6 Normal cellular components of CSF include approximately six lymphocytic cells per mL but no red blood cells (RBCs). The slightly alkaline CSF is transparent and contains chloride, sodium, potassium, and magnesium ions. Protein and glucose are also present but at concentrations much less than in plasma. Pathologic processes can alter CSF volumes, pressures, and constituent characteristics, contributing to or producing life-threatening situations. Any increase in CSF volume must be compensated by a shift in blood or brain tissue volumes. Because the rigid osseous boundaries of the brain and spinal column are unyielding, space-occupying lesions within the CSF circulation can elevate CSF pressure, and potentially cause hydrocephalus. Samples of CSF provide useful diagnostic information in conditions such as infectious meningitis, multiple sclerosis (MS), or subarachnoid hemorrhage. Cellular constituents, fluid color, gamma globulin levels, and glucose and protein concentrations can all be analyzed in an effort to determine the etiologic mechanisms of CNS compromise. Microscopic examination of centrifuged CSF sediment provides diagnostic insight to the presence of extramedullary tumors, leukemia (acute lymphocytic leukemia, ALL), lymphoma, various drop metastases, and germ cell tumors.7 (See additional discussion on CSF in Section 5.15.2.)

1.4 SPINAL VASCULAR ANATOMY Through its blood supply, the spinal cord is exposed to systemic influences that include cardiac insufficiency, infection, metabolic abnormalities, and hematogenous seeding of malignancy. Pathology occurring outside the spine can directly or indirectly influence spinal blood supply, and aortic or vertebral arterial disease can result in cord arterial insufficiency. Vascular-induced injury (infarction) is often irreversible and rapid in onset, whereas the signs of insufficiency may emerge over a longer period of time. Spinal blood vessels themselves are susceptible to physical compression. Many of the patients who develop degenerative stenosis — a risk for compressive myelopathy — fall into the same age group at risk for acquiring cardiac and peripheral vascular disease. Some of these individuals may also have a coagulation disorder from disease or from therapeutic intervention (blood thinners). Clinicians who identify cardiac, vertebral, and/or aortic disease should pay particular attention to the possibility of frank myelopathy or a history suggestive of an undiagnosed intermittent myelopathic presentation.

1.4.1 EXTRINSIC SPINAL CORD VASCULATURE The extrinsic spinal cord vasculature receives the greatest portion of its blood supply rostrally from the vertebral artery and caudally from the artery of Adamkiewicz. The largest vascular supply to the anterior portion of the spinal cord comes from arterial feeders from the cervical and lumbar regions; the thoracic region of the spine makes the least vascular contribution to the cord. Comparatively, the posterior paired arterial system of the spinal cord is less vulnerable to vascular insufficiency due to the greater redundancy of blood vessels supplying it. 1.4.1.1 Radiculomedullary Arteries A group of six to nine medullary arteries arises from spinal arteries supplied by the vertebral, deep cervical, intercostal, descending aorta, and common iliac arteries.21 These collateralizing arteries contribute to the anterior spinal artery (ASA) at various levels along the length of the cord. The posterior spinal arteries (PSAs) are similarly augmented by 10 to 20 small-caliber posterior medullary vessels with which they form a plexus.22 The medullary arteries are variable in size and location, traveling to the spinal cord through the intervertebral foramina along with the segmental spinal nerves.23 Radicular arteries that anastomose directly with the ASA vary in diameter and thus differ significantly in perfusion characteristics. The artery of Adamkiewicz (artery of the lumbar enlargement) is the single largest of these radiculomedullary arteries. This artery variably enters the spinal canal on the left side somewhere between the level of cord segments T9 and L2.21,24,25 It usually accompanies the nerve root of L1 or L2, although it has been found to accompany any nerve root from T7 to L3. As the major source of blood flow to the ASA, the artery of Adamkiewicz provides vascular supply to the lower thoracic cord, lumbar cord, and conus medularis. This contribution is thought to supply approximately 50% of the spinal cord in 50% of individuals. Due to the major vascular contribution of the artery of Adamkiewicz, the clinician should always be aware of those disorders that result in hypotension or compression along its course. A large medullary artery is also present at the C5 or C6 level, providing vascular supply to the cervical enlargement. Other medullary arteries, variable in size and number, may be present higher in the cervical spine and in the thoracic spine. 1.4.1.2 Anterior and Posterior Spinal Arteries The spinal cord is supplied by one (unpaired) anterior and two (paired) posterolateral vessels that travel longitudinally along the length of the cord. The ASA supplies approximately two thirds of the anterior and central spinal cord and the PSAs supply the posterior column region.

Relevant Spinal Cord Anatomy

The outer layer of the cord is perfused by the vasa corona, small circumferential vessels intimate with the pia mater (discussed further in Section 1.4.2 below). The primary arterial supply of the cervical cord is the ASA, which is formed by the Y-shaped union of the paired vertebral arteries.26 The ASA commonly originates from the fourth division or intracranial portion of the vertebral artery above the foramen magnum and usually runs uninterrupted along the spinal cord but may vary slightly in its course along the anterior aspect. There are many discrepancies between anatomical descriptions by anatomists. This may be due in part to different preparation techniques or normal variation in the population. As an example, according to Gillilan,27 the ASA is largest in diameter in the lumbar cord and smallest in the thoracic portion of the spinal cord. Whereas, Turnbull,28 reports that the largest diameter of the ASA is in the thoracic cord. The PSAs arise from the posterior cerebellar arteries, and occasionally the vertebral arteries; they also receive contributions from the posterior radicular arteries. Smaller in diameter than the ASA, the PSAs are paired structures that run along the posterolateral aspect of the spinal cord adjacent to the dorsal roots and appear more plexiform on the dorsal cord25 (Figure 1.3).

1.4.2 INTRAPARENCHYMAL VASCULAR SUPPLY The ASA gives rise to approximately 250 to 300 penetrating sulcal vessels throughout the length of the cord21 which perfuse both the right and left anterior two thirds of the spinal white and gray matter (Figure 1.4). The thoracic region has the smallest quantity of sulcal arteries, and thoracic sulcal arteries have the smallest average diameter (0.14 mm) compared to those of the cervical (0.21 mm) and lumbosacral (0.23 mm) regions.26 This contributes to greater risk for hypoperfusion insult within the thoracic cord. The PSAs send their penetrating branches to the dorsal horn and posterior columns, supplying the dorsal third of the white and gray matter of the cord. The ASA and PSAs anastomose together to form an irregular circumferential plexus of arterial vessels referred to as the vasa corona. This fine vascular network, also called the plial arterial plexus, encircles the cord and anastomoses with larger vessels, penetrating and supplying the outer layers of white matter.21 The cervical and lumbar segments receive the greatest blood supply, corresponding to the spinal cord enlargements and the increased metabolic demands from the greater number of neurons located within the cord enlargements.

1.4.3 THE SPINAL VENOUS PLEXUS Venous drainage from the spinal cord is accomplished through a number of medullary veins and an extensive,

9

valveless venous plexus encasing the dural sac (Figure 1.5). The distribution of veins draining the spinal cord is described as intrinsic to the cord, or extrinsic. The intrinsic system has two systems — the central veins and the radial veins. The central veins are prominent, radially oriented vessels that drain blood from the anterior or posterior half of the spinal cord. These vessels exit the cord and join the extrinsic veins on the surface of the cord. The other intrinsic drainage system for the cord is the radial veins or intrinsic veins. These vessels course laterally through the outer edge of the cord, exiting to form the venous vasa corona.21 These spinal intrinsic vessels drain into the anterior and posterior spinal veins. The extrinsic spinal cord venous system consists of an anterior median spinal vein, the posterior spinal vein, posterolateral spinal veins, anterolateral spinal veins, venous vasa corona, medullary veins, and radicular veins. The anterior median spinal vein travels longitudinally from the brainstem to the conus medullaris and may continue as the slender vein of the filum terminale.29 The anterior median spinal vein is always single in the lumbar spine and may be paired in the cervical and thoracic spine. The posterior spinal vein extends the length of the spinal cord, occasionally as high as the medulla. This vessel may be plexiform and quite large over the lumbar and cervical enlargements. The posterolateral and anterolateral veins are longitudinally oriented; however, they are inconsistent and sometimes not apparent. The venous vasa corona collects blood from the outer edge of the cord and channels it to the longitudinal vessels. Medullary veins are numerous and are divided into anterior and posterior groups. The anterior medullary veins drain the anterior half of the cord, and the posterior medullary veins drain the posterior cord. These vessels follow the nerve roots without draining them. Blood from the nerve roots is drained by the radicular veins.29 Medullary veins and radicular veins join within the IVF and exit the dura to converge with the vertebral venous plexus. The largest medullary vein is the great anterior medullary vein, generally located in the left upper lumbar spine, exiting between T11 and L3. The external and internal spinal venous plexus is an extrathecal system that parallels those areas of the cord subserved by the external and internal arteries.25 The internal venous plexus (Batson’s plexus) extends from the coccyx to the foramen magnum and is essentially a continuum of irregular, valveless epidural sinuses. These channels are protected within epidural fat and supported by a network of caliginous fibers, which form a pleomorphic ligament (Hoffmann’s ligament).25 The internal venous plexus lies in the epidural space within the bony vertebral canal. It is also comprised of an anterior and posterior grouping of vessels, which anastomose. The

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

B

A

   

 


 
 

 
 


   

   

        
   

 
  

       FIGURE 1.3 Arterial blood supply of the spinal cord showing spinal and radicular arteries. (A) Anterior view. (B) Posterior view. (From Cramer, G.D. and Darby, S.A., Eds., Basic and Clinical Anatomy of the Spine, Spinal Cord, and ANS, Mosby, St. Louis, MO, 1995, p. 67. With permission.)

internal plexus has a single large posterior median vein, paired anterolateral veins, and paired posterolateral veins. The external venous plexus surrounds the vertebral column and channels blood from the vertebral bodies and paravertebral muscles. This venous system is susceptible to compression from any lesions extending from a vertebral body, such as bone spurs or disk protrusion.

1.5 CYTOARCHITECTURAL ORGANIZATION OF SPINAL GRAY MATTER The gray matter of the cord primarily consists of unmyelinated nerve cell bodies. Characteristic layers or laminae of the spinal gray matter are distinguished by relative size,

Relevant Spinal Cord Anatomy

11

   

    
        


 


     
   


  
    

  

Vertebral artery Ascending cervical artery Spinal branch

Anterior spinal artery

Thyrocervical stem

 


   


Great radicular artery

    

 



   



 

Lumbar artery

A

B

Epidural space Spinal dural mater Posterior spinal artery Subarachnoid space Spinal arachnoid Spinal pia mater Denticulate ligament

Anterior spinal artery

FIGURE 1.4 (A) Arterial feeders of spinal arteries. (B) Axial anatomy of the cervical venous plexus. (C) Axial anatomy of the arterial supply to the cervical spinal cord. (From Duus, P., Topical Diagnosis in Neurology, Thieme Medical, Stuttgart, 1989, p. 64. With permission.)

Spinal branch of thyrocervical artery

C

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Epidural venous plexus

Basivertebral v.

Posterior external venous plexus

Anterior external venous plexus

FIGURE 1.5 The vertebral venous plexus system. (Copyright J.M. True, D.C.)

 
          
  

 
 
    


  







   
   
   

shape, density, and cytological features of the neurons in these regions. This organization, known as the laminae of Rexed, was first described from the observations of Rexed in 1952.30 The layers are consecutively numbered by Roman numerals I through X, beginning with the dorsal horn region and traveling anteriorly to lamina X, which is the remaining gray matter surrounding the central canal (Figure 1.6). Laminae I through IV are the main cutaneous afferent receiving areas and comprise the majority of the posterior horn of the gray matter. Lamina I, II, and V are important for the transmission of pain. Lamina III and IV neurons and interneurons transmit and modulate proprioception and soft touch. Lamina II consists of tightly packed small cells with extensive and highly branched dendrites. This laminar region is named the substantia gelatinosa in reference to the appearance of the cellular layer. This region is believed to be important for receiving and modulating the sensory input that enters the spinal cord. Modulation occurs through the effects of interneuron connections with descending suprasegmental and supraspinal influences. Lamina V receives small-diameter afferents from the skin, muscle, and viscera, and lamina VI receives proprioceptive and some cutaneous afferents.4 Lamina VII, the largest cytoarchitectural region of spinal gray matter, occupies the intermediate zone between the dorsal and ventral horns and much of the space of the ventral horn.3 Lamina VII consists of many cells that function as interneurons, and within the thoracic spine this lamina contains the nucleus thoracicus or Clark’s column. The cell bodies of the sympathetic portion of the autonomic nervous system (ANS) are located within the intermediolateral nucleus from the level of C8 through L3, with their axons exiting the ventral roots from T1 through L3. The preganglion parasympathetic neuronal

 

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FIGURE 1.6 Somatotopic representation in the upper cervical cord. (Copyright J.M. True, D.C.)

cell bodies of the spinal cord lie within the lateral intermediate region of the gray matter at the levels of S2, S3, and S4. The preganglionic axons of the parasympathetic nervous system exit the spine via the ventral nerve roots at the S2, S3, and S4 levels, synapsing within peripheral ganglia located near the pelvic viscera. The anteromedial lateral cell column also occurs in lamina VII. Lamina VIII is in the medial aspect of the ventral horn and receives terminations from some descending fiber tracts, including the vestibulospinal and reticulospinal tract. Lamina IX, within the anterior horn, is divided into groups of cell columns. The sizes and positions of these columns vary along the length of the spinal cord, and they consist of alpha motor and gamma motor neurons. The alpha motor neurons innervate extrafusal muscle fibers, whereas the gamma motor neurons innervate small intrafusal fibers of the muscle spindles, which play an important regulatory role in muscle tone and related function. These columns of alpha and gamma motor neurons

Relevant Spinal Cord Anatomy

are somatotopically arranged, with the more ventrally placed neurons supplying extensor groups and the posterior portion of the ventral horn supplying flexor muscle groups in a lateral to medial arrangement. The lateral groups supply the extremities, and medial-placed neurons supply the trunk.1,3,4

1.6 RELEVANT SPINAL CORD PATHWAYS A comprehensive understanding of neuroanatomical pathways of the spinal cord is critical to rendering a timely and accurate diagnosis. There are dozens of ascending and descending pathways, which are beyond the scope of this chapter. We have discussed the pathways in context of those pathway deficits easily identified on clinical examination. Neurological localization of a spinal cord pathway lesion occurs in two primary planes: the longitudinal plane and the transverse plane. Clinical assessment of critical spinal pathways helps to determine whether findings are due to an isolated lesion, multiple lesions, or a diffuse process. The volume of the spinal cord, size of the tracts, and central gray matter configuration of the spinal cord change in a longitudinal fashion characterized by the anatomy of the cervical, thoracic, and lumbar cord levels (Figure 1.7). A select few of the ascending and descending tracts provide a valuable opportunity to clinically localize a spinal lesion due to the unique functions they subserve and their unique decussating characteristics. These tracts are referred to as long tracts and the positive clinical findings as long tract signs.

1.6.1 CLINICALLY IMPORTANT ASCENDING PATHWAYS 1.6.1.1 Posterior Columns The posterior columns of the spinal cord are comprised of the fasciculus gracilis and more laterally positioned fasciculus cuneatus (Figure 1.8). Axons within the posterior columns are somatotopically arranged: fibers from more caudal regions of the body are located medially within the fasciculus gracilis, and fibers from more rostral regions arise within the fasciculus cuneatus. The gracile fasiculus carries fibers from the lower extremity, whereas the cuneate fasiculus carries fibers from the upper extremity. First-order neuron cell bodies lie within the dorsal root ganglia at all spinal levels. The posterior column axons ascend in an uncrossed fashion within the posterior columns, synapsing with second-order neurons within the gracilis and cuneatus nuclei within the medulla. The axons of the second-order pathway ascend rostrally after decussating within the medial lemniscus to synapse within the ventral posterolateral (VPL) nucleus of the thalamus. Third-order neurons within the VPL ascend to the cortex.

13

Axons within the posterior column–medial lemniscus pathway mediate tactile discrimination, form recognition, vibratory stimuli, and joint and muscle position sense (kinesthesia). These fibers also allow for spatial and temporal discrimination of cutaneous stimuli. Clinical evaluation of the integrity of the posterior columns is generally performed by assessment of vibration, position, and static two-point and moving two-point discrimination. Transection of the dorsal column in the spinal cord leads to ipsilateral loss of sensibility. 1.6.1.2 Lateral Spinothalamic Tract The lateral spinothalamic tract arises in a rostral direction within the anterolateral funiculus. The spinothalamic tract contains nonmyelinated and thinly myelinated axons that transmit pain and temperature sensation arising from free nerve endings. The lateral spinothalamic tract receives input from both fast- and slow-conducting pain fibers. First-order neuron cell bodies are located within the dorsal root ganglia at all spinal levels. First-order axons enter the spinal cord along the dorsolateral tract of Lissauer (lateral root entry zone) at the posterior horn and synapse with second-order neurons. Second-order neurons lie within the deeper layers of the posterior horn and give rise to axons that decussate in the ventral white commissure just anterior to the central spinal canal, converging within the lateral funiculus to form the spinothalamic tract. Secondorder neurons ascend contralaterally within the anterolateral funiculus to synapse within the VPL nucleus of the thalamus and within the posterior interlaminar nuclei of the thalamus. Third-order neurons arise within the VPL of the thalamus and project through the posterior limb of the internal capsule arriving at the primary somatosensory cortex (Brodman’s area 1, 2, and 3). The spinothalamic tracts are also somatotopically arranged, with the sacral dermatomes running more laterally and the cervical dermatomes located medially to the lower extremity (Figure 1.9). Spinal cord transection leads to a contralateral loss of pain and temperature sensation. When a central spinal cord lesion, such as syringomyelia, involves the ventral commissure (where second-order neurons cross the midline of the cord to ascend in the spinothalamic tract), there is a bilateral loss of pain and temperature located one to two dermatomal levels below the cord level of interruption. With slowly expanding lesions, there may be a significant delay from the time of symptom onset to correct diagnosis. 1.6.1.3 Other Ascending Pathways There are numerous ascending pathways in the spinal cord that relay or transmit important sensory information to spinal, brainstem, cerebellar, and subcortical neuronal centers. These tracts are largely involved in transmission

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

    

Axial Section Level: 5th Cervical Segment

          
  
  
    

  


       

  


  
     
      
      
  



 
  
    
    
 
   
   
   
 
    
 
 
   T
   
   

Axial Section Level: 6th Thoracic Segment


 
   
  

 
 


 
   
  

Axial Section Level: 5th Lumbar Segment (T12 Vertebral Level)


   
    

    


  
 
  
 


 





 



   

V    


 
 



V  

 V  



FIGURE 1.7 Anatomical changes over the length of the spine demonstrated in select axial sections. (Copyright J.M. True, D.C.)

of mechanoreceptive kinesthesia for the modulation of fine motor control and posture. Although this sensory information is crucial to normal joint and muscle action, their isolated functions cannot be clinically localized very easily unless the larger tracts are compromised. Ascending

pathways include the dorsal and ventral spinocerebellar, spino-olivary, spinotectal, spinoreticular, spinocervical, and spinovestibular tracts. The spinocerebellar tracts are located in the dorsolateral and ventral cord; they carry afferent information from muscle spindles, Golgi tendon

Relevant Spinal Cord Anatomy

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Lower extremity 3rd order neurons to somesthetic cortex Upper extremity Ventral posterolateral (VPL) nucleus of thalamus

Medial lemniscus

2nd order neurons to thalamus

Nucleus gracilis Nucleus cuneatus Internal arcuate fibers Internal arcuate fiber decussations Dorsal root ganglion

Fasciculus cuneatus Fasciculus gracilis (Dorsal columns)

Spinocerebellar tract

From lower extremity

70 90 45

25

0 Two point discrimination

Proprioception

Pallesthesia

FIGURE 1.8 Dorsal column and medial lemniscal pathway. (Copyright J.M. True, D.C.)

organs, and discriminative touch receptors to the cerebellum. The spinocerebellar tracts have large input from the lower extremities. The spinoreticular tract provides input to the tegmentum of the brainstem and reticular formation, which influences somatic and visceral reflexes.

1.6.2 CLINICALLY IMPORTANT DESCENDING PATHWAYS 1.6.2.1 Corticospinal Tract Clinically relevant descending pathways are divided between the corticospinal tract (often referred to as the pyramidal

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Cortical appreciation of pain

OUCH! Intralaminar nuclei VPL To thalamus

VPM

Periaqueductal gray matter

Trigeminal distribution pain pathway Pons RAS

Sensory nucleus of V

Pons at level of cranial nerve V RAS

V1 V2

Lower medulla

V3 Spinoreticular pathway connections occur throughout all levels of the reticular activating system (RAS) Somatotopic arrangement

RAS

Spinal nucleus ofV cervical level C1-C2 C2 level

Lower limb neurons are located lateral to upperlimb fibers

V3 V2 V1

nd ha unk tr

Spinoreticular tract Spinothalamic tract

le g

Anterolateral fasciculus Nociceptor threshold

Ascends one to two levels before decussating

Anterolateral fasciculus

FIGURE 1.9 Anterolateral nociceptive pathway. (Copyright J.M. True, D.C.)

tract) and nonpyramidal pathways. The cell bodies of the axons comprising the lateral corticospinal tracts lie primarily within layer V of the cerebral cortex. The cell bodies can be found within the premotor cortex (Brodman’s area 6), the primary motor cortex (Brodman’s area 4), and the primary

sensory cortex (Brodman’s areas 3, 1, and 2). The descending fibers of the corticospinal tract strongly influence functions of the distal extremities. The corticospinal tract on each side is comprised of approximately one million fibers, many of them myelinated.31

Relevant Spinal Cord Anatomy

The corticospinal fibers descend within the posterior limb of the internal capsule within the telencephalon. As the descending motor fibers traverse the midbrain they run through the middle portion of the crus cerebri extending through the base of the pons. While descending, approximately 75 to 95% of the corticospinal neurons decussate at the level of the medullary pyramids, converging to form the lateral corticospinal tract located in the dorsal aspect of the lateral funiculus. The distinct pattern of lamination within the corticospinal tract is of great clinical significance (Figure 1.10). Fibers contributing to the lumbar and sacral innervated regions lie within the dorsal lateral aspect of the tract, whereas fibers innervating more caudal and cervical musculature are located more ventromedially, near the central gray matter. Fibers that do not decussate descend ipsilaterally within the anterior corticospinal tract located within the anterior fasciculus. Corticospinal axons descend throughout the length of the spinal cord, synapsing directly on lower motor neurons lying within the anterior gray matter. Noback and colleagues32 propose that approximately 55% of corticospinal fibers project to the cervical region, 20% of the fibers descend to the thoracic region, and the remaining 25% innervate the lumbosacral muscles. Transection of the corticospinal tract causes an ipsilateral spastic paresis, ipsilateral hyperreflexia, and ipsilateral positive Babinski’s sign.

17

The gray rami communicanti contain unmyelinated preganglionic sympathetic fibers and are located at all levels of the spine. White communicanti rami contain myelinated preganglionic fibers and are found at the levels of T1 to L3. The spinal parasympathetic system or sacral outflow arises from the intermediate gray of S2 to S4 levels. These parasympathetic fibers innervate the urinary bladder, anal sphincter, and genitalia (Figures 1.13 and 1.14). The spinal reflex center for micturition is located within the sacral segments and is strongly influenced by descending upper motor neuron (UMN) input. The UMN pathways influencing bowel and bladder function descend within the white matter between the lateral horn and peripheral portion of the spinal cord.34 The bladder is innervated by the sympathetic nervous system arising from the T6 to L3 levels via the hypogastric nerve and plexus. The bladder receives its parasympathetic innervation from the S2 to S4 levels via the pelvic splanchnic nerves. Ascending pathways for bladder and bowel sensation traverse within the peripheral portion of the spinal cord, generally near the location of the sacral fibers within the lateral spinothalamic tract. Vasomotor and sudomotor autonomic UMN pathways descend within the ventrolateral columns of white matter medial to the spinothalamic tract. The efferent pathways synapse at the intermediolateral nuclei prior to emerging to the sympathetic chain ganglia.

1.6.2.2 Nonpyramidal Tracts Nonpyramidal tracts originate within the brainstem and descend to modulate alpha motor neuron function. Large influential nonpyramidal pathways are located within the anterior funiculus of the spinal cord: the reticulospinal tract, vestibulospinal tract, and tectospinal tract. These pathways project to the spinal gray matter, influencing function of axial musculature, muscle tone, reflex activity, posture, and balance.

1.6.3 AUTONOMIC PATHWAYS No anatomically identifiable descending autonomic pathway or tract within the spinal cord exists, although evidence suggests that sympathetic fibers are dispersed within the spinal cord, ultimately projecting to the interomediomedial (IMM) and interomediolateral (IML) neurons of the thoracolumbar cord.33 These descending pathways provide control and regulation of breathing, sweating, urinary bladder control, and blood pressure. The IML and IMM cell columns lie within lamina VII extending from the T1 to L3 cord levels (Figures 1.11 and 1.12). The sympathetic and parasympathetic portions of the ANS are closely integrated by the supraspinal centers forming the central autonomic network (CAN).

1.7 RELEVANT SPINAL CORD NUCLEI A number of motor and sensory nuclei lie within the spinal cord. The ciliospinal center modulates the sympathetic innervation of the eye and is located within the lower end of the cervical enlargement (C8–T2). The nucleus dorsalis of Clarke (C8–L3) is the origin of the dorsal spinocerebellar tract. The interomediolateral cell column (C8–L3) mediates sympathetic functions in the body. The parasympathetic nucleus (S2–S4) is critical to the control of bowel and bladder function. The spinal accessory nucleus (C1–C6) is the origin of the spinal accessory nerve that controls upper trapezius and sternocleidomastoid muscle function. The phrenic nucleus (C3–C6) impacts respiratory efficiency through mediation of diaphragmatic function.

1.8 ANATOMY OF SPINAL-MEDIATED MYOTATIC REFLEX The myotatic reflex is a monosynaptic reflex initiated by muscle and tendinous stretch. The reflex loop is comprised of a sensory or afferent component and a motor or efferent component. Complete interruption of either component of the reflex arc will result in an absent corresponding reflex

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Lower extremity

Motor cortex Trunk Upper extremity

30% of motor fibers originate in the motor cortex (area 4). Another 30% originate in the premotor cortex (area 6). The somatic sensory cortex of parietal lobe contributes the remaining 40% (area 3,1,2).

Internal capsule

Somatotopic arrangement of pyramidal fibers is present from the cortex to cord.

Pyramidal tract

Leg Trunk Arm

Cerebral peduncle

80-85% of pyramidal tract fibers cross in the caudal medulla to become the lateral corticospinal tract. The remaining fibers descend uncrossed as the anterior corticospinal tract.

Pyramidal decussations

Lateral and anterior corticospinal tract

C5 cord Brachial plexus Paraspinals

Uncrossed motor fibers

T6 cord

Sympathetic trunk Intercostal nerves Paraspinals

L5 cord

Lumbosacral plexus Paraspinals

FIGURE 1.10 Corticospinal pathway. (Copyright J.M. True, D.C.)

Relevant Spinal Cord Anatomy

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Gray rami communicantes (GRC) Dorsal root Intermediolateral cell column

White rami communicantes (WRC) Sympathetic component of sinuvertebral nerve

out GRC Ventral root

T1-T12 Levels

Dorsal ramus

Ventral ramus in WRC

Sympathetic chain ganglia To prevertebral ganglia

FIGURE 1.11 Efferent pathway of the sympathetic nervous system. (Copyright J.M. True, D.C.)

Ventral root

Dorsal root Sinuvertebral nerve Dorsal ramus

Sympathetic chain

Ventral ramus

Dural sleeve Aortic nerve plexus Gray ramus White ramus

Splanchnic nerve

FIGURE 1.12 Sympathetic chain ganglia in the mid-thoracic spine. (Copyright J.M. True, D.C.)

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Descending fiber T10-L2 Sympathetic chain

S2-4

Ganglion in inferior hypogastric plexus Inferior hypogastric plexus

Pudendal n.

Ganglion in inferior hypogastric plexus

Prostatic plexus

Seminal vesicle Prostate

Epididymis

FIGURE 1.13 Innervation of the male reproductive organs. (From Cramer, G.D. and Darby, S.A., Eds. Basic and Clinical Anatomy of the Spine, Spinal Cord, and ANS, Mosby, St. Louis, MO, 1995, p. 338. With permission.)

(areflexia). The efferent limb of the reflex arises from the alpha motor neuron pool of the ventral horn. The resting cell potential of the alpha motor neuron population is influenced by interneuron stimuli within the spinal cord and from descending and segmental influences. These influences affect the magnitude of the reflex response to somatic and external stimuli. The detection of muscle stretch begins when the muscle and muscle spindles are stretched. This causes the primary sensory endings (annulospiral endings) of the spindle cell to fire, transmitting a stimulus to the dorsal horn by group 1A fibers. The greater the stretch of the

spindle cells, the higher the frequency of 1A impulses generated by the annulospiral endings. Activation of the spindle cell occurs with the tap of a reflex hammer or rapid tendon stretch. The reflexive muscle contraction in response to the sensory stimuli is referred to as a muscle stretch reflex (MSR). The most commonly performed MSRs are those of the biceps, brachioradialis, triceps, quadriceps (knee), and gastrocnemius (ankle) muscles. MSR evaluation is helpful in the assessment of myelopathy. Compromise of the lateral corticospinal tract is associated with an ipsilateral increase of the MSR response.

Relevant Spinal Cord Anatomy

21

Thoracolumbar level

T12-L2 Sympathetic chain ganglia

Sacral level

Visceral afferents Sympathetic motor

Parasympathetic motor

Inferior mesenteric ganglion

S2 S3 S4 Somatic motor sensory Pelvic nerves

Pudendal nerve

Detrussor muscle (smooth muscle)

Internal sphincter External sphincter (skeletal muscle)

FIGURE 1.14 Innervation of the bladder. (Copyright J.M. True, D.C.)

REFERENCES 1. Chusid, J.G., Correlative Neuroanatomy and Functional Neurology, 18th ed., Los Altos, CA: Lang Medical Publications, 1982. 2. Carpenter, M., Core Text of Neuroanatomy, 4th ed., Baltimore, MD: Williams & Wilkins, 1991. 3. Barr, M.L. and Kiernan, J.A., The Human Nervous System: An Anatomical Viewpoint, 6th ed., Philadelphia, PA: Lippincott, 1993: 67–87. 4. Williams, P.L. and Warwick, R., Gray’s Anatomy, 37th ed., Edinburgh: Churchill–Livingstone, 1989. 5. Byrne, T.N., Benzel, E.C., and Waxman, S.G., Eds., Diseases of the Spine and Spinal Cord, New York: Oxford University Press, 2000. 6. Cramer, G. and Darby, S., General anatomy of the spinal cord, in Cramer, G. and Darby, S., Eds., Basic and Clinical Anatomy of the Spine, Spinal Cord and ANS, St Louis, MO: Mosby, 1995: 52–71.

7. Greenberg, M., Neuroanatomical basics for surgery on the spine, in Allen, M.B. Jr., and Miller, R.H., Eds, Essentials of Neurosurgery: A Guide to Clinical Practice, New York: McGraw–Hill, 1995: 19–35. 8. Fitzgerald, M., Neuroanatomy, Basic and Applied, London: Bailliere Tindal, 1985. 9. Elliot, H., Cross-sectional diameters and areas of the lumbar spinal cord, Anat. Rec., 93: 287–293, 1945. 10. Dommisse, G.F., The Arteries and Veins of the Human Spinal Cord, New York: Churchill–Livingstone, 1975. 11. Cramer, G. and Darby, S., General characteristics of the spine, in Cramer, G. and Darby, S., Eds., Basic and Clinical Anatomy of the Spine, Spinal Cord, and ANS, St. Louis, MO: Mosby, 1995: 17–51. 12. Wackenheim, A., Roentgen Diagnosis of the Craniovertebral Region, Berlin: Springer-Verlag, 1974: 215–251. 13. Bland, J.H., Disorders of the Cervical Spine: Diagnosis and Medical Management, 2nd ed., Philadelphia, PA: Saunders, 1994: 71–91.

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14. Arce, C. and Dohrmann, G., Thoracic disk herniation: improved diagnosis with computed tomographic scanning and a review of the literature, Surg. Neurol., 23(4): 356–361, 1985. 15. Buehler, M.T., Spinal stenosis, J. Manipulative Physiol. Ther., 1(2):103–112, 1978. 16. Schonstrom, N., Lindahl, S., Willen, J. et al., Dynamic changes in the dimensions of the lumbar spinal canal: an experimental study in vitro, J. Orthoped. Res., 7:115–121, 1988. 17. Vandenabeele, F., Creemers, J., and Lambrichts, I. Ultra structure of the human spinal arachnoid mater and dura mater. J. Anat., Oct. 189 (pt. 2):417–30, 1996. 18. Groen, G., Baljet, B., and Drukker, J., The innervation of the spinal dura mater: anatomy and clinical implications, Acta Neurochir., 92(1–4):39–46, 1988. 19. Fricke, B., Andres, K.H., and Von During, M., Nerve fibers innervating the cranial and spinal meninges: morphology of nerve fiber terminals and their structural integration. Microsc. Res. Tech., Apr. 15, 53(2):96–105, 2001. 20. Sunderland, S. Meningeal–neural relations in the intervertebral foramen. J. Neurosurg., 40:756–763, 1974. 21. Moosy, J., Vascular disease of the spinal cord, Chapter 46 in Joynt, R.J., Ed., Clinical Neurology, Vol. 3, Philadelphia, PA: Lippincott, 1991: 1–17. 22. Oliver, J. and Middleditch, A., Blood supply of the spinal cord and vertebral column, in Oliver, J. and Middleditch, A., Eds., Functional Anatomy of the Spine, Oxford: Butterworth–Heinemann, 1991: 141–160. 23. Flanagan, B. et al., MR imaging of the cervical spine, neural vascular anatomy, Am. J. Neuroradiol., 8:27–32, 1987.

24. Adamkiewicz, A., Die Blutgefasse des menschilchen Ruckenmarkes, II: die Gefasser der Ruckenmarksoberflacke, Sitzungsb. Akad. Wissensch. Wein Math-Naturw., 85:101–130, 1882. 25. Parke, W.W., Applied anatomy of the spine, in Rothman, R.H. and Simeone, F.A., Eds, The Spine, Vol. 1, 3rd ed., Philadelphia, PA: Saunders, 1992: 35–87. 26. Hassler, O., Blood supply to human spinal cord: a microangiographic study, Arch. Neurol., 15:302–307, 1966. 27. Gillilan, L.A., The supply of the human spinal cord, J. Comp. Neurol., 110:75–103, 1958. 28. Turnbull, I.M. Blood supply of the spinal cord, in Vinken, P.J. and Bruyn, G.W. (Eds.) Handbook of Clinical Neurology, Vol. XII. Vascular Diseases of the Nervous System. Amsterdam: North Holland, 478–491, 1972. 29. Sliwa, J.A. and Maclean, I.C. Ischemic myelopathy: a review of spinal vasculature and related clinical syndromes. Arch. Phys. Med. Rehabil., Apr. 73:365–372, 1992. 30. Rexed, B., The cytoarchitectonic organization of the spinal cord in the cat, J. Comp. Neurol., 96:415–495, 1952. 31. Byrne, T.N., Disorders of the spinal cord and cauda equina, Curr. Opin. Neurol. Neurosurg., 6(4):545–548, 1993. 32. Noback, C.R., Strominger, N.L., and Demarest, R.J., The Human Nervous System: Structure and Function, Philadelphia, PA: Williams & Wilkins, 1996. 33. Yadollah, H., Anatomy of the spinal and peripheral autonomic nervous system, in Low, P.A., Ed., Clinical Autonomic Disorders: Evaluation and Management, Boston, MA: Little, Brown, 1993: 17–37. 34. DeMeyer, W., Spinal cord, in DeMeyer, W., Ed., Neuroanatomy, Media, PA: Harwal, 1988: 122–123.

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2.1 INTRODUCTION TO PATHOPHYSIOLOGIC MECHANISMS The cascade of biochemical events that follows initial spinal cord trauma may lead to additional neuronal and cellular compromise or death of the patient (Table 2.1). Similar pathophysiologic changes occur in both spinal cord injuries (SCIs) and cervical spondylotic myelopathy.1 Several explanations have emerged to explain the pathophysiology of SCI. The ischemic theory of SCI is a wellresearched mechanism. Compression of the vasculature to the cord is known to produce ischemia and gray matter infarct within minutes.2 The development of intramedullary necrosis follows within the infarcted neuronal tissues.3 Ischemia also develops indirectly following trauma from lipid peroxidation and the release of protaglandins (see more on ischemic mechanisms later in the chapter). In contrast, the neuronal membrane theory proposes that mechanical distortion of the neuronal membrane alters membrane permeability to sodium and thus makes the membrane nonexcitable.4 Direct trauma to long tract pathways may occur with little evidence of cord hemorrhage. Axonal shearing within white matter tracts has been demonstrated in SCI victims without significant injury to the gray matter.5 A free radical theory of neuronal injury proposes activation of reactive oxygen species and lipid peroxidation reactions within regions of tissue damage and ischemia. This process is accelerated following tissue reperfusion. 6 Additional pathophysiologic mechanisms include neuronal apoptosis, neuronal excitotoxic cell death, and cationic-mediated cell injury.7 In practice, many of the mechanisms are interdependent and, in combination, may be responsible for neuronal disruption and degeneration.

2.2 CELLULAR, IONIC, AND BIOMOLECULAR MECHANISMS OF SPINAL CORD INJURY An introduction to the expanding field of cellular, ionic, and biomolecular mechanisms will extend the clinician’s understanding of the mechanisms of tissue injury and recovery. The capacity to prevent, intervene in, and predict the evolution of spinal cord disorders is dependent upon the growing body of knowledge of the most primary elements

of spinal cord function. Novel therapies will incorporate these mechanisms. The hopes for successful pharmaceutical breakthroughs, tissue transplant, and neural regeneration will require further advances in molecular and cellular biology. Responsibilities lie not only with scientists but also with attending clinicians who will direct patients to the therapeutic options available. A lot can be learned about the mechanisms of the central nervous system (CNS) by studying the patterns of tissue recovery.

2.2.1 FREE RADICAL-MEDIATED CELL INJURY Oxygen radicals are highly reactive molecules that are generated during normal metabolism and kept in check by a complex array of cellular defenses. Healthy CNS tissues contain variable concentrations of the antioxidants ascorbic acid, glutathione, ubiquinone, superoxide dismutase, catalase, and alpha-tocopherol.8 The presence of endogenous antioxidants helps to quench excess free radicals, thus reducing the risk for further cell injury. In SCI and tissue injury, whether physical or ischemic, free radical oxygen species are generated in such abundance that normal cellular defense mechanisms are overwhelmed.9 This results in free radical damage and rapid lipid peroxidation of neuronal membranes.9 Membrane phospholipids liberate arachidonic acid, which in turn is metabolized into various groups of vasoactive eicosanoids: thromboxanes, prostaglandins, and leukotrienes. These metabolites play important roles in secondary damage following SCI.10 Arachidonic acid is metabolized by the cyclo-oxygenase pathway to form the prostaglandin or thromboxane groups or through the lipoxygenase pathway to form the leukotriene group of metabolites. The arachidonic acid metabolites leukotriene (LT) C4 and thromboxane B2 elevate in the CSF during the initial phase of SCI to as much as 5 to 9 times normal levels.11 There is little doubt in the scientific community over the production of free radicals and lipid peroxidation following SCI; however, elucidation of the complex interactions and exact biochemicals involved in the process is far from complete.

2.2.2 GLUTAMATERGIC-INDUCED TOXICITY In the CNS, glutamate is an excitatory amino acid that influences the pre- or postsynaptic response through its action on NMDA (N-methyl-D-aspartate) or non-NMDA 23

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TABLE 2.1 Selective Pathophysiologic Mechanisms in SCI • • • • • • • • • •

Free radical-mediated cell injury Cation-mediated cell injury Excitatory amino acids (glutamatergic toxicity) Intracellular-mediated apoptosis Aberrant calcium fluxes Lipid peroxidation Accumulation of arachidonic acid metabolites (eicosanoids) Ischemia/infarction Edema Endogenous opiate receptor activation

receptors. Sources of glutamate include neurons and their supportive glia and terminal portions of descending and ascending spinal cord tracts.12 Cellular insult within the central nervous system injury can lead to increased extracellular levels of glutamate. Impaired intracellular metabolism sensitizes the neuron to potential excitotoxic cell death from the effects of glutamate.13 Glutamate is a secondary mediator of neuronal damage and thus appears to be involved in chronic compressive disorders. Olby and associates14 demonstrated a two- to tenfold increase in glutamate concentration in the lumbar CSF of dogs at intervals of >12 hours after severe, acute thoracolumbar disk herniation injury. Moreover, the severity of the clinical signs was directly related to the glutamate concentration. Dogs with chronic compressive thoracolumbar lesions have a twofold elevation of CSF glutamate concentration, suggesting that excitotoxicity may also be a component of chronic spinal cord compression.

2.2.3 CATION-MEDIATED CELL INJURY Injured tissues and neurons release K+ following injury, which causes voltage-regulated channels to open, allowing an influx of Ca++. With small-tissue injuries, the Ca++ burden is tolerated by the cells because of intrinsic cellular Ca++-binding mechanisms. However, in severely injured cells, Ca++ influx will start an autodestructive cascade that causes the breakdown of membranes and the release of Ca++binding phosphates and phosphatides.8,15 Ca++-activated phospholipase A2 causes the release of arachnidonic acid that is converted to various eicosanoids, some of which are potent vasoconstrictors and edema inducers. The vasoconstriction and tissue swelling help to restrict Ca++ influx to the region; however, the resulting ischemia generates more free radicals that destroy more neuronal membranes.8

2.2.4 PROGRAMMED CELL DEATH Programmed cell death (apoptosis) refers to genetically controlled cellular degeneration that can occur in the absence of acute inflammation. Genes have been identified

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TABLE 2.2 Selective Histopathologic Changes with SCI and Myelopathy • • • • • • • • • •

Demyelination Axonopathy Neuroma Neuronal dropout Gliosis Intramedullary adhesion and tethering Coalescence of microcavitation Cavitation Spinal cord atrophy Surviving neuronal plasticity

that influence CNS apoptosis. Neuronal and glial apoptosis can occur secondary to SCI and spinal cord ischemia.16 Apoptosis serves a number of purposes, which include regulation of the development of cell lines, reduction of cellular redundancy during development, removal of abnormal cells, and regulation of tissue homeostasis.17

2.3 STAGES OF SPINAL CORD INJURY The natural history of SCI can be divided into early, intermediate, and late stages.18 Within the acute phase of SCI, there is disruption of the tissues with subsequent edema, inflammation, and vascular alterations compromising the neurons, myelin, and glial microenvironments. Edema generally occurs within a few minutes and progresses within the ensuing one to two hours after insult. Intraparenchymal edema and swelling of the endothelium results in ischemia, furthering metabolic byproduct accumulation and release and cytokines from injured cells. This initiates a pro-inflammatory cascade contributing to secondary tissue damage. Polymorphonuclear leukocytes and monocytes infiltrate through the vasculature into the damaged parenchyma. The acute lesion is subsequently characterized by traumatic demyelination of the axonal fibers that have not been fully disrupted. Histological changes include axonal irregularities and asymmetric axonal swelling. Magnetic resonance imaging of changes can help qualify the type of tissue changes present. During the intermediate phase of SCI there is a continuation of the inflammatory response. Within 72 hours, macrophages begin to ingest tissue breakdown products. Neuronal degeneration begins to occur distal to the level of axonal injury within descending spinal pathways and also proximally within ascending pathways. The end-stage or late-stage lesion phase follows within six months after injury (Table 2.2). This end stage is characterized by development of multilocular cysts following the removal of debris by white blood cells. The volume of initial intramedullary hemorrhage is relational

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Pathophysiology in Myelopathy and Spinal Cord Injury

to the size and extent of late-injury gliosis. Regeneration of viable neurons in the nerve roots occurs in the late stage. This predominantly occurs at the level of the posterior root ganglia but also occurs at the anterior horn as long as the cell bodies have escaped injury.

2.4 SPINAL SHOCK Central nervous system tissues initially react to trauma in a stereotyped set of responses. In this initial phase, occurring within minutes after injury, neuronal and metabolic activity is rapidly depressed.8 Spinal shock is the term used to describe the initial response that occurs in SCI. Generally, the more severe the SCI and the higher the level of injury within the spinal cord, the greater the severity and duration of the spinal cord shock syndrome. The term “spinal shock” has two primary definitions, the first of which is “hypotension associated with spinal cord injury” and “the transient loss of intrinsic spinal cord reflex activity often lasting several days to several months.”19 Pursuant to the second definition, spinal shock occurs secondary to acute spinal injury or trauma resulting in a pattern of lower motor neuron and autonomic dysfunction occurring days to months after initial onset. This is followed by the development or onset of an upper motor neuron type presentation. Spinal shock is characterized by paralysis of involved skeletal and smooth muscles, areflexia, or flaccid hypotonicity. Generally, there is a complete loss of autonomic function distal to the site of the lesion. This dysautonomia generally results in systemic hypotension, skin hyperemia, and bradycardia due to unopposed vagotonia.20 In cases of mild cord concussion, the somatic motor and sensory components of spinal shock may last an hour or less and have resolved by the time the majority of patients are examined in the trauma center. The reflex autonomic component of spinal shock may last from a few days to a few months depending on the level and severity of SCI. The loss of vasomotor tone contributes to impaired extremity temperature regulation and often edema. Absent sensibility distal to the lesion is also evident. In the majority of SCI with spinal shock, areflexia lasts less than 8 to 9 weeks. A multidisciplinary assessment is necessary in the acute SCI patient because of the associated injuries that occur in 50 to 60% of these cases.21,22 Continual assessment of cardiovascular function, urinary status, blood gases, airway, and ventilation is warranted in the acute spine injury to assure complete stabilization. Poor lung inflation occurs in lower cervical cord injuries from intercostal paralysis, whereas in the high cervical cord injury diaphragmatic paralysis occurs from interruption of the C3–C5 segments and mechanical ventilation is required. Additionally, the polytraumatized patient may have other life-threatening injuries associated with spinal trauma.23 These injuries can endanger ventilation and cardiopulmonary functioning, due to direct trauma

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such as lung and cardiac contusions, ribcage fracture, or aortic injury. Head trauma and abdominal bleeding, as well, are serious associated complications that significantly increase the potential for mortality.24 Foley catheterization is required for bladder atony and loss of sphincter control. Gastrointestinal atony occurs, producing distention of the stomach, small intestine, and large intestine; this may result in complications of ulceration, vomiting, constipation, and fecal impaction. Vascular stasis occurs because of a loss of sympathetic tone and muscular paralysis and almost universally results in deep vein thrombosis, requiring the use of anticoagulants. This decreased or absent vasomotor control results in orthostatic hypotension whenever the patient is moved to the upright position (see discussion of orthostatic hypotension later in the chapter). Neurologic localization of the lesion level and determination of lesion severity are often not possible early after injury. As spinal reflexes return, the patient’s complete clinical picture can be better determined. Sensory, motor, and deep tendon reflexes including pathologic reflex testing of the torso and all extremities are crucial localizing adjuncts. Magnetic resonance imaging (MRI) and computed tomography (CT) are both integral for correlating the level of actual cord trauma. Any patient with SCI should also be assumed to have some degree of postconcussional injury, thus cranial nerves are also assessed along with level of consciousness. During spinal shock the patient demonstrates a hypotensive crisis. In triage, hemorrhagic shock must be differentiated from neurogenic shock. An injury above the T6–T8 level is generally associated with a neurogenictype shock. Bradycardia and hypotension follow spinal cord trauma above the T6 level. This is a result of the interrupted sympathetic outflow to the heart and peripheral vasculature. A quick screen is to increase the return flow to the heart by elevating the legs: lack of response to this maneuver indicates the need for immediate pharmacologic intervention.25-27 Secondary injury to the spinal cord may be minimized with efforts that maintain a normal blood pressure.28 Hypovolemia is not the true problem with the neurogenic shock patient; rather, the acute pathology lies with distribution of the intravascular volume. Therefore, attempting triage with fluids can result in pulmonary edema. The hemorrhagic hypotensive patient needs compressive attention to flowing wounds and special consideration to increasing intravascular volume via intravenous measures. After the period of spinal shock, characteristic upper motor neuron signs such as hyperreflexia are often found to be exaggerated.29,30 For example, the Babinski response, which typically involves dorsiflexion of the great toe and fanning of the remaining toes, may develop into an amplified flexion response involving the hip, knee, and foot upon minimal stimulation of the sole of the foot. This is

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termed the withdrawal reflex or flexion spinal defense reflex. Simple withdrawal responses to plantar stimulation may develop into more complex flexor spasms including abdominal contraction and defecation, referred to as a mass reflex. Stimulation of one leg may cause flexion of that extremity and extension of the other leg: This is the crossed extensor reflex. There may also be heightened muscle stretch reflexes (MSRs) with the onset of some degree of clonus (see the additional discussion of hyperreflexia and clonus in Section 5.2). Some researchers propose that this heightened period of activity following spinal shock may be secondary to interneuronal crossinnervation and other neuroplastic changes involving the spinal cord.31 In the period following spinal shock there may be exaggerated impairment of thermoregulatory sweating below the level of injury paralleling the other heightened responses. This inhibition of the sympathetic nervous system may contribute to the reflexive hypertension seen in autonomic dysreflexia (see additional discussion in Section 5.7). The acutely injured spinal cord patient needs immediate attention in a trauma center specializing in SCI patients. Since progressive secondary injury occurs within minutes to hours following trauma, any measures that prevent additional damage to the spinal cord must be attempted. By inhibiting the cascade of microvascular events occurring post-traumatically, it is assumed that the progressive damage to the cord that occurs during spinal cord shock and reperfusion may be halted or inhibited.

Several processes occur simultaneously, that facilitate progressive efflux of water, sodium, and chloride ions from the capillaries into the extracellular space. Tissue hypoxia or anoxia elicits capillary membrane permeability. The release of histamine, bradykinin, acetylcholine, and other synaptic transmitters contributes to an increase in capillary permeability.34-37 The early edematous process induces increasing water concentrations in the extracellular spaces, which then shift to the intracellular compartments within the initial 48 to 72 hours after injury.34-37 Hemorrhagic insult to the spinal cord gray matter following trauma causes edematous accumulation at the site of injury beginning in the gray matter and spreading centrifugally into the white matter.38-41 Central nervous system edema is associated with increased tissue pressure as well as compression of arterioles, capillaries, and veins, resulting in decreased local blood flow.38 Increased tissue pressure may contribute to the observed sequelae of intravascular sludging, stasis, and resultant ischemia.42 Neural tissue is thus compromised by direct mechanical insult and hemorrhage as well as edematous compression of the swelling spinal cord. As the cord swells, pressure against the constrictive meningeal envelope increases. Unchecked edema in the cord will cause degeneration of the unmyelinated fibers in the white matter. This degeneration is a result of increasing tissue pressure and decreasing local vascular flow. The degree of functional deficit may be associated with the extent of intramedullary microvascular alterations and edema.43

2.5 SPINAL CORD EDEMA

2.6 ISCHEMIC MYELOPATHY

This condition is best described as swelling of the spinal cord due to an influx of hydrophobic metabolites and water into the neural tissue. Significant evidence suggests that inflammatory mediators can cause progressive tissue damage within both central and peripheral nervous system tissues. The increased pressure and pro-inflammatory state within and around the neural tissue contribute to the clinical presentation. The two primary causes of edema in the spinal cord are spinal cord ischemia or anoxia and proinflammatory chemical substances liberated as a result of injury.32 Any direct insult to the neural tissue usually damages the corresponding vasculature, altering microcirculatory dynamics and producing edematous perfusion. Numerous inflammatory mediators accumulate in the acutely injured spinal cord. These mediators include bradykinin, prostaglandins, leukotrienes, platelet-activating factor, substance P, and serotonin. Increased concentrations of prostaglandin E2 have been reported to promote vasodilatation and plasma exudation in parallel with the development of spinal cord edema.33 Substance P is a potent vasodilator, increasing capillary permeability and tissue edema.

Any pathologic process that compromises the limited sources of the arterial supply to the spinal cord may result in infarction or ischemia of the cord. Those patients at greater risk are the elderly patients with known diabetes, atherosclerosis, hypotension, hypertension, and dysautonomia. The elderly patient has additional potential risk secondary to multilevel spondylosis and lateral stenosis. Patients with thoraco-abdominal aortic aneurysm are at risk for spontaneous spinal cord ischemia. Occlusion of an intercostal artery supplying a medullary artery of the thoracic cord is presumably a mechanism of ischemic myelopathy secondary to aortic aneurysm.44 The spinal cord is at risk of arterial infarction from additional causes, including hypotension, angiography, vertebral artery occlusion or dissection, syphilis, sickle cell anemia, polycythemia, leukemia, spinal trauma, decompression sickness, and disk herniation.45 The tempo of neurologic deficit varies with the degree of ischemia and local neuronal metabolic synaptic demands. Ischemic myelopathy may be transient, progressive, and in some cases sudden and debilitating with subsequent organ and/or motor dysfunction. Motor symptoms typically predominate.

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2.6.1 MICROVASCULAR AND ARTERIAL INSUFFICIENCY 2.6.1.1 Microvascular Perfusion The gray matter of the brain and spinal cord requires greater vascular perfusion than the white matter regions. Blood flow to the gray matter is approximately fivefold that of the white matter.46 Comparatively, blood flow to the spinal cord is approximately two thirds to one half that of the brain when equal volumes of respective tissues are examined. Areas of increased synaptic density have the highest oxygen demand and consequently the capillary density in these regions is proportionately increased. Due to its metabolic demands and requirement for perfusion, the gray matter of the spinal cord may be particularly vulnerable to ischemic injury.47 Because of the high density of neuronal cell bodies in the spinal gray matter, compromise can lead to devastating consequences. If the intercostal and lumbar arteries become occluded or compromised as a result of ischemia due to aneurysm, damage to the spinal cord is quite severe.48 Experimentally, the gray matter of the lumbosacral cord undergoes profound histological alterations after thoracic cord ligation.49 The microvasculature of the gray matter of the spinal cord is sensitive to trauma.50 The white matter of the spinal cord is also susceptible to ischemia and axonal shearing; however, the gray matter is more sensitive to hypoxic and ischemic changes.42,48,51,52 Neural damage may occur within minutes to hours after ischemia and cord trauma. Systemic factors that impair the microvascular delivery of oxygen and various nutrients to the spinal cord include segmental arterial hypotension, segmental venous hypertension, increased blood viscosity, erythrocyte aggregation (rouleau and/or sludging), impaired erythrocyte deformability, platelet membrane instability, elevated levels of total fibrinogen, and cardiac insufficiency. Arteriosclerotic lesions of the spinal arteries within the intradural compartment are rare in contrast to arteriosclerotic lesions of the extradural arteries. Moderate fluctuations of systemic blood pressure have a minimal effect on regional and total spinal cord blood flow due to constant autoregulation by intrinsic spinal cord mechanisms.47 Many researchers have demonstrated stenotic lesions in the aorta and extradural vessels. Singh and associates53 described four patients, all of whom had local lesions in the area of the artery of Adamkiewicz and subsequently developed infarcts of the lumbar cord after hypotension was induced. Segmental hypotension and related hypoperfusion along a radicular artery or its branches often results from a thrombotic or atheromatous occlusion at the mouth of these arteries within the aorta. Focal lesions can then give rise to a shower of emboli that migrate and lodge in smaller spinal vessels, contributing to segmental hypotension, intravascular stasis and potential spinal cord infarct.

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To maintain normal function, the cord, spinal nerve root, and peripheral fibers must receive a continuous and adequate supply of nutrients.54 2.6.1.2 Tempo of Cord Vascular Insufficiency Terms utilized to describe the tempo of brain vascular disease are also applicable to the spinal cord. Focal ischemia of the CNS has at least three distinct patterns: (1) transient ischemia attack (TIA) with rapid recovery, (2) stroke in evolution (SIE) progressing slowly, and (3) complete infarction with tissue necrosis. A stroke in evolution may involve varying degrees of hemorrhagic and occlusive etiologies. A wide range of neurological deficits can accompany each of these categories. As previously discussed, the central gray matter of the spinal cord is particularly vulnerable to hypoxic and ischemic compromise. Spinal hypotension secondary to localized dissection of the ascending aorta can result in gray matter necrosis. Gray matter ischemic necrosis can occur in the absence of known structural compromise of the spinal cord vasculature.55 Dohrmann and colleagues42 determined that within 30 to 60 minutes of insult, the blood flow to the gray matter is markedly decreased, with the white matter remaining relatively unaffected in the early stage of compromise. Post-traumatic focal reductions of blood flow occur secondary to constriction and narrowing of the arteries.56 Tissue injury can occur secondary to parenchymal reperfusion, resulting in free-radical generation and subsequent lipid perioxidation, thereby accelerating membrane destruction.6 This reperfusion injury following return of blood flow in CNS ischemia can possibly be reduced or prevented by maintaining adequate serum vitamin E levels prior to the ischemic event.57 High superoxide dismutase levels prior to spinal cord ischemia have also been demonstrated to reduce free-radical damage from reperfusion.6 Ischemic myelopathic infarction results in neuronal atrophy, spongy changes, and cavities or lacunae in the anterior gray matter of the cord. DeJerine’s syndrome of intermittent spinal cord claudication may occur, involving progressive lower extremity motor weakness and pain while walking that promptly disappears with rest. This can occur if blood flow to the spinal cord gray matter is reduced to a level insufficient to meet the CNS metabolic demands. Further vascular occlusion and ischemia then occur as platelets promote thrombus formation, eventually leading to a rapid loss of vascular autoregulation.3,58 2.6.1.3 Arterial Insufficiency and Ischemia Watershed or border regions are areas particularly vulnerable to ischemia due to their location at a distal end of an arterial supply (Table 2.3). In the longitudinal plane, the

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2.6.2 SPINAL CORD INFARCTION TABLE 2.3 Features of Vascular Watershed Zones • A region perfused by tributaries from more than one large artery • A collaterized border zone • Regions highly susceptible to systematic hypotension

irregular augmentation of the anterior and posterior spinal arterial system results in regions of poorly collateralized blood supply in the upper thoracic cord. A border zone of potential ischemia also exists within the cord parenchyma in the transverse plane, at the point where the pial vasa corona meets the distribution of the anterior spinal artery (ASA) and posterior spinal artery (PSA) throughout the spinal cord.59 The watershed regions can be classified into two primary categories. The first category is the anatomic watershed zone. The anatomic region has a reduced number of physical collateral vascular channels or networks. There may be decreased capillation and/or a small number of feeder arteries. Regions of the spinal cord characteristically fall into this category, although there is a significant degree of variability between individuals. The intraspinal anatomic watershed zones occurring between anterior and posterior spinal arteries and the vasa corona territories are extremely vulnerable to systemic hypotension. Common causes of systemic hypotension include dehydration, dysautonomia, hypoalbuminemia, extraspinal arterial atherosclerosis, and cardiac insufficiency with impaired left ventricular output. The second category of watershed zones is acquired. This category encompasses acquired occlusive, compressive, and hemorrhagic vascular syndromes. Occlusive etiologies include embolic obstruction and focal thrombus formation. Compressive vascular mechanisms can occur secondary to space-occupying lesions such as disk herniations or tumors. However, chronic mild impairment of arterial blood supply and ischemia often leads to some compensatory capillary development within the watershed region, thereby evading early clinical detection. Hemorrhagic mechanisms include trauma and stroke. Blunt trauma to the artery of Adamkiewicz or to the anterior spinal artery can result in a clinical entity known as anterior spinal artery syndrome.60 This can also occur secondary to intra-arterial occlusion, hypotension, or extravascular compression. The anatomical spinal cord watershed zones include the T4–T9 segments and the L1 segment. Perfusion of the T4–T9 region of the spinal cord is dependent upon the descending ASA from the cervical region, the ascending ASA supplied from the artery of Adamkiewicz, and the anterior radiculomedullary branches of the intercostal arteries for vascular perfusion. This region typically has insufficient anastomotic connections to prevent cord ischemia in the event of loss of any primary feeder supply (Figure 2.1).

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Spinal cord infarction resulting from impaired delivery of oxygen and nutrients or the impaired removal of metabolic waste products to cord parenchyma produces a localized area of ischemic necrosis (ischemic myelomalacia). Patients on blood anticoagulants may be at greater than normal risk for spontaneous epidural or intradural and/or intraparenchymal hemorrhagic diathesis. Four primary factors predispose tissue to ischemic necrosis: (1) the general status of the blood and cardiovascular system, (2) the anatomical pattern of the vascular supply to the region, (3) the rate of intravascular occlusion, and (4) tissue-specific vulnerability to ischemia. Slowly developing vascular insufficiency is often more innocuous clinically than rapidly induced ischemia secondary to the development of increased collateral circulation. Physical blood vessel compression, torsion, and elongation can cause rapid onset tissue ischemia. The intrinsic spinal cord vessels are exceptionally vulnerable to rapid intermittent compression, torsion, and elongation as a result of changes in posture and pathomechanical dynamics within the degenerative spine.

2.6.3 VENOUS PATHOLOGY Reports of venous spinal cord infarction in the literature are relatively rare. Although venous infarction involves the central elements of the spinal cord, the location of compromise varies. Fibrocartilaginous emboli from disk herniations can occur in the presence of degenerative disk disease. Vascular sepsis can contribute to venous thrombosis and infarction. The limited number of references to spinal cord venous infarction in the literature suggests that it is an uncommon phenomenon. Increased risk for venous infarction has been associated with dural arteriovenous or radiculomeningeal vascular malformations concurrent with hypercoagulable states, sepsis and conditions producing fibrocartilaginous emboli.44,61

2.7 MYELOMALACIA In a study by Fieschi et al.,62 necroscopy was performed on the spinal cord of ten elderly athersclerotic subjects who had died from ischemic brain lesions. In five out of ten subjects, small regions of recent spinal cord softening were evident. The longitudinal extensions of the lesions were greater than their transverse, suggesting the role of gravity on the column of blood. The lesions were often located within the center or at the base of the anterior horns of gray matter usually in the lower cervical and middle dorsal tract.62 In all of these cases, the lesions consisted of rarefaction of tissue with loss of neurons and spongy dissolution. There was nearly always sclerosis of the peri- and intraspinal arterial network.62 Systemic cardiovascular

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RELATIVE A-P CANAL DIAMETER

29

RELATIVE BLOOD SUPPLY

MAXIMAL

T4

THORACIC DISK HERNIATIONS

T4

THE CRITICAL ZONE

MINIMAL

T9

T9

MEDIUM

CONTRECOUP

FIGURE 2.1 Thoracic spine “critical zone.” Considerations of limited canal space, modest blood supply, and disk herniation in thoracic disk disease and clinical instability. (Adapted from White III, A.A., and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 413. With permission.)

disease and the high degree of atherosclerosis contribute to the risk for cord softening. Jellinger and Neumayer63 give an informative correlation of ischemic myelopathic syndromes and pathologic findings. These authors report 21 cases consisting of mixed upper and lower motor neuron paresis syndromes associated with general arteriosclerosis and severe aortic atheroma, all verifiable during necropsy. Mannen64 reported circumscribed ischemic lesions within the gray matter of the spinal cord in 8.3% of unselected elderly subjects; he observed 25 small circumscribed softenings of the gray matter, particularly in the anterior horns, during systematic examination of macroscopic sections of the spinal cords of 300 deceased elderly people. The most frequent location of ischemic damage occurred at the levels of C5 and C6. Most of the specimens came from persons reportedly asymptomatic throughout their lives.64

2.8 CAVITATION AND GLIOSIS Spinal cord injury leads to a complex cascade of events that may result in both cavitation and scarring of spinal cord parenchyma. Post-traumatic spinal cord inflammation is an active process that involves astrocyte morphological changes, mobilization of microglia, excitotoxicity,

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and the release of numerous chemicals. The inflammatory process itself can induce secondary neuronal injury. The loss of intramedullary cellular elements within and around the zone of compromise results in varying patterns of cavitation. Cavitation refers to a void previously occupied by tissue. Spinal trauma and/or infarction can initiate the formation of multifocal regions of microcavitation that may coalesce over time to form a larger region of complex cavitation (Figure 2.2). In vivo experimentation has confirmed that a CNS inflammatory process can initiate secondary tissue damage, progressive cavitation, and glial scarring.65 Hematomyelia is frequently followed by cavitation. Barnett66 suggests that such cavities may result from minor to moderate spine trauma. In vitro experimentation has revealed that the process of cavitation further leads to astrocyte abandonment of neuronal processes, neurite stretching, and secondary injury.65 The cavitating disruption of the neural environment provides a physical and chemical barrier to any potential neuronal regeneration– reinnervation process. Delayed cystic degeneration in the spinal cord may occur adjacent to the region or regions of initial insult and progress over many years.67-69 The formation of excessive gliotic tissue (reactive gliosis) even in the absence of cavitation within the CNS becomes a major obstacle to CNS axonal regeneration.70 Patchy gliosis may

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Enlargement of cystic cavity over months to years

Cystic cavity

Petechial hemorrhage Gliotic tissue

Gradual cystic enlargement

Coalescence of cysts FIGURE 2.2 Enlargement of cystic cavity over months to years. (Copyright J.M. True, D.C.)

occur longitudinally secondary to degeneration of fiber tracts.69 Many studies have demonstrated that in the acutely injured spinal cord growth factors and inflammatory cytokines are released which may potentiate the neuronal repair process. An injured axon may sprout neurites that attempt to cross the injury site. If a microcyst or large single cyst forms it will likely fill with spinal fluid and may progress in size over time. The cystic formation is often lined with ependymal cells and there may be dense packets of astrocytes and glial scar (Figure 2.3).71 This complex barrier can make it nearly impossible for neuronal extensions to cross the injury site. Additionally, the release of chemical substances during the CNS post-injury process may inhibit axonal growth within and around the injury site. The loss of cellular elements within the spinal cord results in spinal cord atrophy, which may be readily evident on MR imaging.65

2.9 SPINAL CORD ATROPHY Numerous histopathologic changes occur with SCI and chronic myelopathy (see Table 2.2). Parenchymal atrophy is a late effect of SCI. Spinal cord atrophy may develop with cervical spondylotic myelopathy and myelopathy associated with ossification of the posterior longitudinal ligament. Following cord trauma, microglial ameboid cells and macrophages release enzymes, phagocytose myelin, and clean up cellular debris. Approximately 30% of the area

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FIGURE 2.3 Large cystic cavity. (Copyright J.M. True, D.C.)

of the injured cord region may be occupied by macrophages a week later, as seen in studies of the cat.72 These cells may persist for many years after an SCI. The experimentally injured cat cord indicates that central cystic cavities may form and be heavily populated with microglial cells and small clumps of macrophage cells.73 These phagocytic cells shrink as the glial scar forms and cord atrophy develops. The oligodendrocyte is associated with remyelination; this cell will proliferate to help remyelinate viable axons. In contrast, if type 1 astrocytes, rather than oligodendrocytes, proliferate in the post-injured cord, remyelination is inhibited. Astrocyte infiltration and mitosis is stimulated by fibroblast growth factor. The astrocyte is the major cell type of the gliotic scar that fills in the extracellular space remaining after nerve fiber degeneration. The change in shape of the atrophic cord following compression or injury may clinically correlate with the neurological presentation. There are very few scientific studies that correlate the diagnostic imaging appearance of the cord with severity of symptoms. Even fewer studies have anatomical correlation of autopsy findings with the patient’s clinical symptoms recorded before death. Gray matter atrophy contributes to the greatest degree of loss in cord axial area when the MRI appearance of the cord is flattened or crescent shaped (Figure 2.4). These patients may have predominant segmental motor loss. When the axial appearance is small and triangular, the damage is more severe and involves the white and gray matter. In these cases, the posterior columns and pyramidal tracts are involved in addition to the anterior horns.74 These patients will have spastic paresis and ataxia.

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Normal cervical cord

Boomerang or crescent appearance on axial MRI: Atrophy of the central gray predominates

Triangular appearance on axial MRI: Atrophy of white and gray matter FIGURE 2.4 The morphological appearance of cord atrophy on axial imaging. Normal cervical cord; boomerang or crescent appearance on axial MRI, with predominant atrophy of the central gray matter; and triangular appearance on axial MRI, with atrophy of white and gray matter. (Copyright J.M. True, D.C.)

REFERENCES 1. Bunge, R.P., Puckett, W.R., Becorra, J.L. et al., Observations on the pathology of human spinal cord injury. A review and classification of 22 new cases with details from a case of chronic cord compression with extensive focal demyelination, Adv. Neurol. 59:75–89, 1993. 2. Dommisse, G.F., The Arteries and Veins of the Human Spinal Cord, New York: Churchill–Livingstone, 1975. 3. Nelson, E. et al., Spinal cord injury: the role of vascular damage in the pathogenesis of central hemorrhagic necrosis, Arch. Neurol., 34:332–333, 1977. 4. Korbine, A.L., The neuronal theory of experimental traumatic spinal cord dysfunction, Surg. Neurol., 3(5):261–264, 1975 5. Quencer, R.M., Bunge, R.P., Egnor, M. et al., Acute traumatic central cord syndrome: MRI-pathological correlations, Neuroradiology, 34(2):85–94, 1992.

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6. Lim, K.H., Connolly, M. et al., Prevention of reperfusion injury of the ischemic spinal cord: use of recombinant superoxide dismutase, Ann. Thorac. Surg., 42:282– 286, 1986. 7. Fehlings, M.G. and Skaf, G., A review of the pathophysiology of cervical spondylotic myelopathy with insights for potential novel mechanisms drawn from traumatic spinal cord injury, Spine, 23(24):2730–2737, 1998. 8. Young, W., Role of calcium in central nervous system injuries, J. Neurotrauma., 9(suppl. 1):9–25, 1992. 9. Braughler, J.M. and Hall, E.D., Involvement of lipid peroxidation in CNS injury, J. Neurotrauma, 9(suppl. 1):105–117, 1992. 10. Mitsuhashi, T., Ikata, T., Morimoto, K., Tonai, T., and Katoh, S., Increased production of eicosanoids, TXA2, PGI2, and LTC4 in experimental spinal cord injuries, Paraplegia, 32(8):524–530, 1994. 11. Nishisho, T., Tonai, T., Tamura, Y., and Ikata, T., Experimental and clinical studies of eicosanoids in cerebrospinal fluid after spinal cord injury, Neurosurgery, 39(5):950–956 (discussion 956–957), 1996. 12. Agrawal, S.K. and Fehlings, M.G., Role of NMDA and non-NMDA ionotropic glutamate receptors in traumatic spinal cord axonal injury, J. Neurosci., 17:1055–1063, 1997. 13. Choi, D.W., Excitotoxic cell death, J. Neurobiol., 23:1261–1276, 1992. 14. Olby, N.J., Sharp. N.J., Munana, K.R., and Papich, M.G., Chronic and acute compressive spinal cord lesions in dogs due to intervertebral disk herniation are associated with elevation in lumbar cerebrospinal fluid glutamate concentration, J. Neurotrauma, 16(12):1215– 1224, 1999. 15. Springer, J.E., Azbill, R.D., Kennedy, S.E. et al., Rapid calpain I activation and cytoskeleton protein degradation following traumatic spinal cord injury: attenuation with riluzole pretreatment, J. Neurochem., 69:1592–1600, 1997. 16. Liu, X.Z., Xu, X.M. et al., Neuronal and glial apoptosis after traumatic spinal cord injury, J. Neurosci., 17:5395– 5406, 1997. 17. Burek, M.J. and Oppenheim, R.W., Programmed cell death in the developing nervous sytem, Brain Pathol., 6:427–446, 1996. 18. Kakulas, B.A., The applied neuropathology of human spinal cord injury, Spinal Cord, 37:79–88, 1999. 19. Byrne, T.N., Benzel, E.C., and Waxman, S.G., Eds., Diseases of the Spine and Spinal Cord, New York: Oxford University Press, 2000: 65. 20. Tator, C.H., Chapter 3, in Tator, C.H., Ed., Early Management of Acute Spinal Cord Injury, New York: Raven Press, 1982: 15–26. 21. Reiss, S., Raque, G.H., Shields, C.B., and Garretson, H.D., Cervical spine fractures with major associated trauma, Neurosurgery, 18(3):327–330, 1986. 22. Stover, S. and Fine, P., Spinal Cord Injury: The Facts and Figures, Birmingham, AL: University of Alabama, 1986. 23. Tscherne, H. and Regel, G., Care of the polytraumatised patient, J. Bone Joint Surg. Br., 78(5):840–852, 1996.

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24. Matsumura, J.S., Prystowsky, J.B., Bresticker, M.A., Meyer, P.R. Jr., Joehl, R.J., and Nahrwold, D.L., Gastrointestinal tract complications after acute spine injury, Arch. Surg., 130(7):751–753, 1995. 25. Green, B., Eismont, F., and O’Heir, J., Pre-hospital management of spinal cord injuries, Paraplegia, 25(3):229– 238, 1987. 26. Meyer, P. and Sullivan, D., Injuries to the spine, Emerg. Med. Clin. North Am., 2:313–329, 1984. 27. Green, B., Callahan, R., Klose, K., and de la Torre, J., Acute spinal cord injury: current concepts, Clin. Orthoped., 154:125–135, 1981. 28. Rawe, S., Lee, W., and Perot, P.L., The histopathology of experimental spinal cord trauma: the effect of systematic blood pressure, J. Neurosurg., 48(6):1002– 1007, 1978. 29. DeJong, R.N. and Haerer, A.F., Case taking and the neurological examination, in Joynt, R.J., Ed., Clinical Neurology, Vol. 1, Philadelphia, PA: Lippincott, 1991: 63–66. 30. Riddoch, G., The reflex functions of the completely divided spinal cord in man, compared with those associated with less severe lesions, Brain, 40:264, 1971. 31. Chambers, W., Liu, C.N., and McCouch, G.P., Anatomical and physiologic correlates of plasticity in the central nervous system, Brain Behav. Evol., 8(1):5–26, 1973. 32. Austin, G. et al., Spinal cord edema, in Austin, G., Ed., The Spinal Cord, 3rd ed., New York: Igaku-Shoin Medical Publishers, 1983. 33. Johnson, M., Carey, F., and McMillan, R.N., Alternative pathways of arachidonate metabolism: prostaglandins, thromboxine and leucotrienes, Essays Biochem., 19:40– 141, 1983. 34. Douglas, W., Histamine and antihistamines, in Goodman, L. and Gilman, A., Eds., The Pharmacologic Basis of Therapeutics, New York: Macmillan, 1970: 621–645. 35. Douglas, W., Hydroxytryptamine and antagonists, in Goodman, L. and Gilman, A., Eds., The Pharmacologic Basis of Therapeutics, New York: Macmillan, 1970: 645–662. 36. Jenker, F., Treating and preventing cerebral edema, Acta Neurol., 4:184, 1958. 37. Rosenbluth, P. and Meirowski, A., Sympathetic blockade: cervical cord syndrome, J. Neurosurg., 1012:107– 112, 1953. 38. Reulen, H., Hadjidemos, A., and Shurman, K., The effect of dexamethasone on water and electrolyte content and on CBF in perifocal brain edema in man, in Reulen, H. and Shurman, K., Eds., Steroids and Brain Edema, New York: Springer-Verlag, 1972: 239–252. 39. Wagner, F., Green, B., and Bucy, P., Spinal cord edema associated with paraplegia, Proc. Spinal Cord Injury Conf., 18:9–10, 1971. 40. Yashon, D., Bingham, W.G., Faddoul, E.M., and Hunt, W.E., Edema of spinal cord following experimental impact trauma, J. Neurosurg., 38:693–697, 1973. 41. Green, B. and Wagner, F., Evolution of edema in the acutely injured spinal cord: a fluorescence microscopic study, Surg. Neurol., 1:98–101, 1973.

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42. Dohrmann, G., Wick, K., and Bucy, P., Spinal cord blood flow patterns in experimental traumatic paraplegia, J. Neurosurg., 38:52–58, 1973. 43. Reed, J., Allen, W.E., and Dohrmann, G.J., Effect of Mannitol on the traumatized spinal cord, microangiography, blood flow patterns and electrophysiology, Spine, 4(5):391–397, 1979. 44. Mawad, M., Rivera, V., Crawford, S. et al., Spinal cord ischemia after resection of thoracoabdominal aortic aneurysm: MR findings in 24 patients, Am. J. Neuroradiol., 11:987–991, 1990. 45. Mikulis, D., Ogilvy, C., McKee, A. et al., Spinal cord infarction and fibrocartilaginous emboli, Am. J. Neuroradiol., 13:155–160, 1992. 46. Ireland, W., Fletcher, T., and Bingham, C., Quantification of microvasculature in the canine spinal cord, Anat. Rec., 200:102–113, 1981. 47. Marcus, M., Heistad, D., Ehrhardt, J., and Abbounb, F., Regulation of total and regional spinal cord blood flow, Circ. Res., 41(1):128–134, 1977. 48. Thompson, G., Dissecting aortic aneurysm with infarction of the spinal cord, Brain, 79:111–118, 1956. 49. Turnball, I., Blood supply of the spinal cord, normal and pathological considerations, Clin. Neurosurg., 20:56– 84, 1973. 50. White, R., Pathology of spinal cord injury in experimental lesions, Clin. Orthoped., 112:16–26, 1975. 51. Collins, W., Piepmeier, J., and Ogle, E., The spinal cord injury problem — a review, Cent. Nerv. Syst. Trauma, 3:317–331, 1986. 52. Gelfan, S. and Tarlov, I., Differential vulnerability of spinal cord structures to anoxia, J. Neurophysiol., 18:170–188, 1955. 53. Singh, U., Silver, J.R., and Welply, N.C., Hypotensive infarction of the spinal cord, Paraplegia., 32(5):314– 322, 1994. 54. Lundborg, G., Nerve Injury and Repair, Edinburgh: Churchill–Livingstone, 1988. 55. Blumbergs, P. and Byrne, E., Hypotensive central infarction of the spinal cord, J. Neurol. Neurosurg. Psychiatry, 43:751–753, 1980. 56. Fried, L. and Goodkin, R., Microangiographic observations of the experimentally traumatized spinal cord, J. Neurosurg., 35:709–714, 1971. 57. Yoshida, M., Shima, K., Taniguchi, Y., Temaki, T., and Tanaka, T., Hypertrophied ligamentum flavum in lumbar spinal canal stenosis. Pathogenesis and morphologic and immunohistochemical observation, Spine, 17(11):1353– 1360, 1992. 58. Senter, H. and Venes, J., Loss of autoregulation and posttraumatic ischemia following experimental spinal cord trauma, J. Neurosurg., 50:198–206, 1979. 59. Moosy, J., Vascular disease of the spinal cord, in Joynt, R.J., Ed., Clinical Neurology, Vol. 3, Philadelphia, PA: J Lippincott, 1991: 1–17. 60. Sliwa, J.A. and Maclean, I.C., Ischemic myelopathy: a review of spinal vasculature and related clinical syndromes, Arch. Phys. Med. Rehabil., 73(4):365–372, 1992.

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61. Naiman, J., Donohue, W., and Prichard, J., Fatal nucleus pulposus embolism of spinal cord after trauma, Neurol. Minneapolis, 11:83–87, 1961. 62. Fieschi, C., Gottlieb, A., and Carolis, V.D., Ischemic lacunae in the spinal cord of arteriosclerotic subjects, J. Neurol. Neurosurg. Psychiatry, 33:138–146, 1970. 63. Jellinger, K. and Neumayer, E., Myelopathy progressive d’origine vascular: contribution anatomoclinique aux syndromes d’une hypovascularisation chronique de la moelle, Acta Neurol. Psychiatry, (62):944–956, 1962. 64. Mannen, T., The vascular lesions in the spinal cord of the aged, Clin. Neurol. Jpn., 3:47–63, 1963. 65. Fitch, M.T., Doller, C., Combs, C.K., Landreth, J.E., and Silver, J., Cellular and molecular mechanisms of glial scarring and progressive cavitation: in vivo and in vitro analysis of inflammation-induced secondary injury after CNS trauma, J. Neurosci., 19(19):8182–8198, 1999. 66. Barnett, H.J.M., Syringomyelia consequent on minor to moderate trauma, in Barnett, H.J.M., Foster, J.B., and Hudgson, P., Eds., Syringomyelia, Philadelphia, PA: Saunders, 1973: 179–243.

Black process 45.0° 150.0 LPI

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67. Klawans, H.L., Delayed traumatic syringomyelia, Dis. Nerv. Syst., 29(8):525–528, 1968. 68. Nurick, S., Russell, J.A., and Deck, M.D.F., Cystic degeneration of the spinal cord following spinal cord injury, Brain, 93(1):211–222, 1970. 69. Yashon, D., Pathology and pathogenesis, in Yashon, D., Ed., Spinal Injury, New York: Appleton–Century Crofts, 1986: 71–103. 70. Nieto-Sampedro, M., Neurite outgrowth inhibitors in gliotic tissue, Adv. Exp. Med. Biol., 468:207–224, 1999. 71. McDonald, J.W., Repairing the damaged spinal cord, Sci. Am., 281(3):64–73, 1999. 72. Blight, A.R., Delayed myelination macrophage invasion: a candidate for secondary cell damage in spinal cord injury, Cent. Nerv. Sys. Trauma, 2:299–315, 1985. 73. Blight, A.R., Macrophages and inflammatory damage in spinal cord injury, J. Neurotrauma, 9(S1):83–91, 1992. 74. Kameyama, T., Ando, T., Yanagi, T., and Hashizume, Y., Neuroimaging and pathology of the spinal cord in compressive cervical myelopathy, Rinsho Byori, 43(9):886– 90, 1995.

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3

Physical Mechanisms of Spinal Cord Injury*

3.1 SPINAL CORD PATHOMECHANICS The spinal cord moves in relation to the spinal canal, and spinal column movement influences spinal cord dynamics; however, the amplitude of cord translation is restricted by structural anchoring of the cord to the spinal column. The primary anchoring elements of the spinal cord consist of the dentate ligaments and filum terminale. Any condition that places abnormal tension on the spinal cord can potentially lead to neurological insult and related signs and symptoms. Aberrations of posture, particularly within the sagittal plane, can have direct and indirect effects on neuronal pathways and centers within the central nervous system (CNS), specifically the spinal cord.1 In the study of spinal biomechanics, investigations of spinal cord biomechanics are rare. The intrinsic viscoelastic properties of medullary tissue include plasticity and elasticity. Medullary tissue can be mechanically deformed in almost any direction without significant opposing resistance as long as it is not tractioned, but as soon as traction forces are introduced the medullary tissue retracts elastically.2 Breig2 discovered that during cervical canal shortening (as in dorsal extension) the cervical medullary tissue relaxes and takes on plastic characteristics, telescoping into large undulated folds and reducing strain upon CNS structures. During forward head or trunk flexion, lengthening of the spinal canal and medullary tissue produces longitudinal strain along the entire cord and nerve roots. The capacity for elastic deformation allows for changes in length and curvature of the spinal canal during spinal column movement without significant axial cord displacement. The entire spinal cord will change in length from 4.5 to 7.5 cm during changes in maximum positions of lordosis and kyphosis as measured from the dorsal mesencephalon to the conus medullaris.2 Similarly, on lateral flexion, the canal is lengthened on the convex side and shortened on the concave.1 During cervical flexion, the spinal cord translates anteriorly toward the vertebral bodies and, in extension, toward the posterior elements. Research has demonstrated that maximum cord elongation takes place in the lumbar region, some elongation occurs in the thoracic, and minimal elongation occurs within the cervical region.3

Flexion

Extension

Not Analogous

Analogous

FIGURE 3.1 Adjustment of spinal cord and nerve roots to axial deformation during flexion and extension. (Adapted from White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 282. With permission.)

The characteristics of spinal cord elasticity allow the cord to match the length of the spinal canal during movement. As the canal and column reach maximum length during flexion, the physiologic elastic tension of the cord is also at its maximum. Then, near the end of elongation a slight elastic resistance is evident, causing a sudden stiffening and stubborn resistance to further deformation, thus negating the flexible behavior of the cord. The spinal cord tissue also displays plastic deformation characteristics with axial compressive forces by formation into folds having a slight tendency for recovery. This folding during shortening and subsequent unfolding during elongation, similar to that of an accordion, begins with the initial movement of the cord (Figure 3.1). The first phase of cord movement represents the structural properties of the cord, whereas the second phase represents the material properties of the cord.2 Lateral flexion of the spinal column is reported to contribute to ipsilateral relaxation of the pons-cord tract while placing greater tensile stresses upon the contralateral side.4 Maiman and colleagues5 demonstrated a relational coupled motion between the spinal cord and spinal column in an experimental spinal cord injury (SCI) study performed on cats. This coupling ratio of cord motion to spine motion varies with the amount of loading and varies by location

* This chapter written with Edwin P. Patrick.

35

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

A

B

FIGURE 3.2 Postsurgical changes following fusion at C5–C6, C6–C7, and C7–T1. There is evidence of post-traumatic transection of the surgical spinal cord at the (A) C6–C7 and (B) C7–T1 levels. (Spin echo parasagittal T1 and fast spin echo parasagittal C2 midline sagittal sections.) (Courtesy of George W. Fika, D.C.)

within the spine. This ratio of movement is of great significance when traumatic displacement of the spine exceeds the reserve space of the spinal canal or fibroproliferative pathology restricts spinal cord compliance and elasticity. Histologic and microangiographic studies have demonstrated that nerve fibers, blood vessels, and supportive tissues can be injured secondary to tensile or stretch injury across a regional mass effect.2 Research suggests that as little as 20 to 25% compression of the spinal cord will increase axial tension on neural and vascular elements within the spinal cord.6 This can result in disruption and distortion of neural and vascular elements contributing to intramedullary ischemia and infarction with permanent neurological impairment.

3.2 TYPES OF SPINAL CORD TRAUMA Compression of the spinal cord is one of the most prevalent etiologies of neurologic dysfunction associated

with degenerative spine disease and trauma. Spinal cord compression associated with degenerative spondylosis usually results from cord compression by an osteophyte, hypertrophic dorsal lateral facet, hypertrophic or buckled ligamentum flavum, and/or disk herniation. In the case of SCI, the most common cause of cord compression is from vertebral element dislocation and/or fracture. Traumatic cord stretching can also contribute to acute spinal trauma (Figure 3.2).7 The mechanism by which an epidural mass contributes to SCI is complex and multifactorial. Space-occupying lesions within the epidural region often compress the epidural venous plexus, resulting in venous engorgement, and also contribute to arterial insufficiency with diminished arterial pulsation.8 Physical compression of Batson’s plexus results in venous congestion. This results in impaired venous drainage from the spinal cord and increases the risk for cord edema. Mechanical compression of spinal axons may interfere with axonal transport and

Physical Mechanisms of Spinal Cord Injury

subsequently compromise nerve impulse transmission. It has been well established that compression of myelinated fiber tracts results in damage to the myelin.9-11 The larger myelinated fibers within the tracts are more susceptible to physical compromise. Neurological tissue requires oxygen and other nutrients in order to maintain function. Alterations in oxygen levels occur following abnormal pressure or force delivered to the spinal cord, particularly longitudinal tension.12 Yamada et al.13 used both human and animal studies in an attempt to clarify the effect of traction on the filum terminale and lumbosacral cord and its relationship to the pathophysiology of the tethered cord syndrome. The underlying mechanism of this disorder is found to involve derangement of neural tissue metabolism caused by longitudinal tensile-type stress. Mechanical tension applied to the spinal cord reduces its cross-sectional area and places a transverse-type stress across the vessels, possibly reducing their cross-sectional area as well.4 Increased pressure applied to the cord results in reduced afferent and efferent impulse conduction along with increased damage to neural and supporting tissues.14 Pathologic tension applied to the cord may result in increased medullary cord pressures, reduced blood flow, and subsequent reduction of spinal cord perfusion. Additionally, tension applied directly to neural tissue results in impaired oxidative metabolism in the mitochondria.4 Other studies have found that any change in metabolic efficiency of the cellular mitochondria contributes to progressive neuronal dysfunction.15 Vascular hypoperfusion results in altered cellular biosynthesis, impaired neurotransmitter metabolism, ineffective ionic pumps, and inefficient axoplasmic transport. As mentioned previously, in cases of significant spinal cord pathomechanics, there is evidence to suggest that impaired blood flow to both the spinal cord and meningeal complex may occur.16 There are four mechanisms associated with neuroelement distortion-related injury: (1) Extrinsic neurovascular compression, (2) simple distraction, (3) tethering of the neuroelements over extrinsic masses on the sagittal plane (the sagittal bowstring effect), and (4) tethering of the neuroelements of extrinsic masses in the coronal plane (the coronal bowstring effect).17 These pathomechanical mechanisms should be considered in the evaluation of a patient with a distraction injury and spinal cord compromise. An example of coronal tethering occurs when an epidural mass such as a disk herniation or spondylotic bar displaces the cervical cord and deforms the dura. Consequently, this may result in transference of tensile stresses to the spinal cord from the dura via the dentate ligaments, thus increasing the risk of further compromise during neck flexion.18 Spinal cord injury is classified by the type of injury sustained, such as a closed spinal trauma vs. a penetrating type injury, as well as by the segmental cord level of the

37

TABLE 3.1 Criteria for Spinal Cord Concussion 1. Spinal trauma immediately preceding onset of neurological deficits 2. Neurological deficits consistent with spinal cord level of injury 3. Complete neurological recovery within 72 hours of injury Based on data from: Zwimpfer, T.J. and Bernstein, M., Spinal cord concussion, J. Neurosurg., 72(6):894-900, 1990.

injury. The mechanical forces in closed spinal trauma that produce the injury are compression, shear, distraction, and torsion.

3.2.1 SPINAL CORD CONCUSSION The term “spinal cord concussion” is used to describe an immediate transverse lesion of the spinal cord resulting from indirect trauma, such as that secondary to transmission of an impact shockwave to the cord. The trauma usually occurs in the absence of vertebral fracture or dislocation; however, patients commonly have preexisting pathology that causes hypermobility or narrowing of the spinal canal.19 Characteristically, there is immediate impairment of sensory and motor function distal to the lesion. The initial clinical presentation is not easily differentiated from the presentation of spinal shock. The unique feature of spinal concussion is the relatively rapid return of spinal cord functions in a few hours or days, most often within 48 to 72 hours (Table 3.1). By definition, there are no permanent structural abnormalities. There may be reversible spinal cord edema and reversible intracellular and nerve fiber changes.

3.2.2 SPINAL CORD CONTUSION The term “spinal cord contusion” is used to describe trauma of spinal cord tissue secondary to direct insult or hemorrhage. Petechial hemorrhages, predominantly within gray matter, often result in focal spinal dysfunction, and permanent structural pathology may occur. Spinal cord contusion may also be due to vertebral fracture, vertebral dislocation, or intervertebral disk herniation. Diagnostic imaging may not reveal the extent of direct trauma in cases of transient vertebral dislocation or other direct insult with spontaneous reduction. The initial clinical presentation usually involves total paraplegia. The pattern of neurological recovery depends on the degree of tissue injury, and recovery may or may not be complete. A rapid return of sensory function is generally a good prognostic indicator for the recovery of some motor function

3.2.3 SPINAL CORD COMPRESSION The term “spinal cord compression” is used to describe mechanical deformation of the spinal cord by an adjacent

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

TABLE 3.2 Signs and Symptoms Associated with Tethered Cord Syndrome • • • • • • •

Diffuse leg pain Anorectal pain Progressive lower extremity sensorimotor deficits Bowel and bladder dysfunction Back pain Gait disturbance Club foot

structure or tissue. This may be secondary to disk pathology, hypertrophic changes, osteophytosis, vertebral fracture, vertebral dislocation, hematoma, arteriovenous malformation, tumor, or lipomatosis. One of the most common causes of debilitating spinal cord compression is traumatic vertebral fracture–dislocation; the most common degenerative etiology is spondylosis with spinal stenosis. Another common cause of spinal cord compression is intervertebral disk herniation. When disk herniation occurs with spinal stenosis, there is a greater potential for significant cord compression. Spinal cord compression may manifest as partial or complete loss of spinal function but may also occur in the absence of abnormal clinical manifestations.

3.2.4 PENETRATING/TRANSECTING CORD INJURIES Penetrating or transecting cord injuries are usually from a gunshot or knife wound. Axonal shearing in white matter (long tracts) may occur with cord traction injuries from ballistic neck trauma. Bone fragments from comminuted fractures may lacerate the spinal cord, as well. Gunshot injuries to the cord are often more devastating than stab wounds. The degree of tissue damage is greater in missile wounds because of the high kinetic energy of the bullet that is transferred through the spine and cord.20 There is an expanding conical-shaped, fluid-pressure shockwave that follows the projectile; consequently, there is a concussive force injury as well as the penetrating component of the bullet. The patient has a complete loss of function of the severed pathways below the cord laceration.

3.2.5 TETHERING

AND

DISTRACTION INJURIES

Pathologic spinal cord tension is referred to as tethering, and when accompanied by clinical signs and symptoms it is referred to as a tethered cord syndrome (TCS) (Table 3.2). TCS is usually first identified in children and adolescents.21 Initial symptom onset occurs less often in adults.22-24 When it does occur, it is usually the result of predisposing cord tension factors such as spondylotic stenosis or trauma. Signs and symptoms of TCS include progressive lower extremity motor and sensory changes,

TABLE 3.3 Causes of Spinal Cord Tethering • • • • • • • •

Tight filum terminale Diastematomyelia Myelomeningeocele Traction lesions Spinal (bony) dysraphisms Adhesions/fibroproliferation Lumbosacral lipoma Cord herniation through dura

back pain, anorectal pain, gait disturbances, incontinence, leg pain, and scoliosis.21,22,25 Clubfoot may also occur in TCS.21 Conditions that lead to cord tethering may be congenital and/or acquired, with the most common tethering lesions being thickened filum terminale, intradural lipoma, and fibrous adhesions (Figure 3.3).22 Other conditions associated with spinal cord tethering are listed in Table 3.3. The tip of the conus medullaris generally lies within the region of T12–L1. A short filum terminale may draw the conus to levels below the L1 vertebral body. The location of the conus in relationship to the spine is commonly identified on sagittal magnetic resonance imaging (MRI) acquisitions. The absence of a low conus on MRI does not preclude the possibility of TCS, for TCS has been identified in patients who present the conus in a “normal” position.26 Phase-contrast MR may be used to assess longitudinal movement of the spinal cord27 and in some cases can help to ascertain the degree of impaired cord kinetics. Markedly diminished cord motion in children has been associated with a lack of significant postoperative improvement.27 Spinal cord tethering contributes to impairment of oxidative metabolism and electrophysiologic impairment of the lumbosacral cord.3,28 Shortened H-reflex and bulbocavernosus latencies may be recorded when the conus is found lower in the lumbar canal.29 Early diagnosis and intervention are imperative to the successful management of TCS. (See additional information in Section 4.6.)

3.3 VERTEBRAL FRACTURE, DISLOCATION, AND INSTABILITY Blunt trauma to the spine can produce SCI from shear force, compression, or tensile injury to the cord or vasculature. Any rapid reduction in the diameter of the spinal canal and the space available for the cord can result in myelopathy; vertebral fracture, instability, dislocation, and subluxation all have this potential to dynamically alter central canal geometry (Figures 3.4 and 3.5). Spinal cord injury can occur secondary to stretch or concussive forces even in the absence of spinal fracture or obvious dislocation. This is referred to as SCIWORA syndrome (SCI

Physical Mechanisms of Spinal Cord Injury

39

FIGURE 3.3 Cord and root tethering patterns. (Copyright J.M. True, D.C.)

FIGURE 3.4 Burst fracture at C5 with retropulsion of bone fragments into the spinal cord. (Courtesy of E. Shick, M.S. Copyright MedicalVisions.com. With permission.)

without radiographic abnormality) and tends to be more common in children due to greater connective tissue elasticity and spinal column flexibility;30 patients with SCIWORA may not develop obvious neurological complications for days or weeks after the original trauma. The rapid

change in canal diameter causing an SCI may not be apparent in a post-injury imaging study — for example, although a spondylotic bar may contuse the spinal cord during an acceleration/deceleration injury, the post-injury image of the canal at the level of insult may appear to be only mildly narrow. Numerous attempts have been made to classify relationships between bony spinal elements and the spinal cord as a means of fracture assessment.31-33 Meyer et al.34 constructed and described a vertebral fracture classification system including five variables that can result in altered central canal geometry. The first component, a score (1 – 3) of damaged longitudinal columns, describes the loss of vertical support and vertebral stability. The second component is the presence of vertebral listhesis, with lateral or sagittal translation as a subset of this category. The third is the degree of angulation or curvature created by vertebral body collapse in the case of compression fractures. The fourth component is the extent of spinal canal obliteration measured as a percentage of compromise, and the fifth is the percentage of loss of vertebral height from compression. These five variables are scored and assigned a fracture category of type A, B, or C.34 This classification system simplifies the ability to communicate the severity of the fracture by identifying the relationship between canal compromise and neurologic injury.

3.3.1 CAUSES

OF

BIOMECHANICAL INSTABILITY

It is important not only to detect biomechanical instability, but also to understand its etiology, as the course of progression can be more clearly defined if the exact cause has been determined. A three-dimensional coordinate

40

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

FIGURE 3.5 Fracture dislocation of the thoracic spine at T5 on T6. A comminuted fracture of T6 is causing transection of the spinal cord at that level. (Courtesy of E. Shick, M.S. Copyright MedicalVisions.com. With permission.)

+Y Axis Translation +YAxis Rotation

Z

X

+XAxis Translation +X Axis Rotation

+Z Axis Rotation +Z AxisTranslation

Y

FIGURE 3.6 Right-handed Cartesian coordinate system denoting spinal motion segment position, coupled motions, or the direction of forces acting on the motion segment. This figure depicts positive axis rotation and translation. (Copyright David H. Durrant, D.C.)

system has been proposed to reference movement of a spinal motion segment (Figure 3.6). Biomechanical spinal instabilities arise from a variety of causes (see, for instance, Table 3.3). These instabilities can be classified as either primary or secondary instabilities. Primary instabilities are the direct result of damage to the posterior column and are usually associated with trauma. Secondary instabilities, which develop over a period of time as a result of damage or disease, can initiate in any of the columns. Biomechanical instability most commonly occurs secondary to acute trauma, surgical procedures, or cumulative degenerative changes in the spine 35 (Figures 3.7 through 3.9). Acute trauma may produce biomechanical instability by disruption of ligamentous support structures or by fracture with comminution. The degree of biomechanical instability secondary to fracture is not only dependent on the severity of the fracture, but also on the vertebral element and spinal area involved. A three-column model for spine stability has been utilized. The spine is broken into three anatomic configurations along the sagittal plane: the anterior, middle, and posterior columns. If the fracture does not compromise the space available for the cord or the exiting nerve root,

Physical Mechanisms of Spinal Cord Injury

41

FIGURE 3.8 Lateral radiograph of the cervical spine demonstrating prominent anterior listhesis of vertebra C4 with respect to C5. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

FIGURE 3.7 Lateral X-ray of the cervical spine demonstrating anterior listhesis of vertebra C3 with respect to C4. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

there will be little immediate neurological consequence; if the fracture has the potential to heal without deformity, fragmentation, or significant biomechanical alteration, there may be no future consequences of neurological dysfunction. White and Panjabi have proposed a checklist for clinical instability of the cervical, thoracic, and thoracolumbar spine (Tables 3.4 to 3.6).36 Post-traumatic disruption of either all of the anterior or all of the posterior soft tissue elements can lead to obvious and potentially serious pathomechanical intersegmental motion. Incomplete disruption may lead to intermittent episodes of severe catching pain; however, without radiographic evidence of displacement, the clinician’s diagnostic acumen is often challenged. Postsurgical complications due to failed interbody fusion can result in pseudoarthrosis and potential cord compression; failed fusion may require a second fusion procedure to correct excessive intersegmental motion. Successful fusion at one level may create secondary effects from increased compensatory range of motion at adjacent vertebral segments. Biomechanical instability with resulting neurologic compromise has also been associated with many arthritic

TABLE 3.4 Checklist for the Diagnosis of Clinical Instability in the Thoracic and Thoracolumbar Spine Element Anterior elements destroyed or unable to function Posterior elements destroyed or unable to function Disruptions of costovertebral articulations Radiographic criteria Sagittal plane displacement > 2.5 mm (2 pts.) Relative sagittal plane angulation > 5° (2 pts.) Spinal cord or cauda equina damage Dangerous loading anticipated

Point Value 2 2 1 4

2 1

Note: Total of 5 or more = unstable. Source: From White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 335. With permission.

disorders. Quadriplegia or death may result from atlantoaxial subluxation that occurs as a complication of several arthritides.37 Rheumatoid arthritis is the most common causal disorder, but atlantoaxial subluxation may also occur with ankylosing spondylitis and in association with psoriatic arthritis.38 Transverse atlantal ligament laxity and eventual lysis can occur secondary to regional hyperemia. The sero-negative arthropathies can also induce destructive joint changes by hypertrophic bone formations. Joints ankylosed by the sero-negative arthropathies are susceptible

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

TABLE 3.5 Checklist for the Diagnosis of Clinical Instability in the Lumbar Spine

TABLE 3.6 Checklist for the Diagnosis of Clinical Instability in the Middle and Lower Cervical Spine

Element

Element

Anterior elements destroyed or unable to function Posterior elements destroyed or unable to function Radiographic criteria A. Flexion/extension X-rays 1. Sagittal plane translation > 4.5 mm (2 pts.) 2. Sagittal plane rotation >15° at L1–L2, L2–L3, and L3–L4 (2 pts.) >20° at L4–L5 (2 pts.) >25° at L5–S1 (2 pts.) or B. Resting X-rays 1. Sagittal plane translation > 4.5 mm or 15% (2 pts.) 2. Relative sagittal plane angulation > 22° (2 pts.) Cauda equina damage Dangerous loading anticipated

Point Value 2 2 4

3 1

Note: Total of 5 or more = unstable. Source: From White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 352. With permission.

Point Value

Anterior elements destroyed or unable to function Posterior elements destroyed or unable to function Positive stretch test Radiographic criteria A. Flexion/extension X-rays 1. Sagittal plane translation > 3.5 mm or 20% (2 pts.) 2. Sagittal plane rotation > 20° (2 pts.) or B. Resting X-rays 1. Sagittal plane displacement > 3.5 mm or 20% (2 pts.) 2. Relative sagittal plane angulation > 11° (2 pts.) Abnormal disk narrowing Developmentally narrow spinal canal 1. Sagittal diameter < 13 mm or 2. Pavlov’s ratio < 0.8 Spinal cord damage Nerve root damage Dangerous loading anticipated

2 2 2 4

1 1

2 1 1

Note: Total of 5 or more = unstable. Source: From White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 314. With permission.

FIGURE 3.9 Lateral flexion radiograph of the cervical spine demonstrating anterior listhesis of vertebra C6 with respect to C7. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

to fracture or dislocation resulting in significant pathomechanical intersegmental motion, neurological sequelae, and a mortality rate of twice that observed with similar fractures in a normal spine.39 Any sudden development of mobility in a previously immobile spinal segment should raise the clinician’s level of suspicion. The “chin on chest” deformity seen in ankylosing spondylitis40 is caused by a complete dislocation of C1 on C2. Any systemic infection that causes joint destruction, such as tuberculosis, is an obvious precursor to biomechanical instability. Articular and periarticular denervation can lead to neuropathic arthropathy, also referred to as Charcot’s joint. Charcot’s joint changes can occur in the spine. The usual predilection is the lumbar spine. Subluxation and dislocation proceed to destruction and malalignment of articular surfaces and to characteristic disorganization in the neuropathic joint. Lytic destruction from primary or metastatic cancer can also create gross disruption of the spinal segment, altering segmental ranges of motion and thus increasing risk for development of cord compression. Osteoporosis increases the risk for acquiring a compression fracture. This must be differentiated from a pathological fracture due to other causes. MR assessment can help improve the accuracy of the differential workup.

Physical Mechanisms of Spinal Cord Injury

TABLE 3.7 Conditions Associated with Atlantoaxial Instability and Compressive Myelopathy • • • • • • • • •

Down syndrome Rheumatoid arthritis Os odontoidium Odontoid fracture Marfan’s syndrome I-cell disease (mucolipidosis II) Transverse ligament rupture Morquio’s syndrome Atlantodental hypertrophic osteoarthropathy

43

smaller supportive elements of the neck. Upper cervical fractures with SCI are not compatible with life when immediate acute respiratory support is not available. The pattern of fracture seen in subaxial cervical injury is dependent on the complex relationship between the predisposing state (underlying pathology in the region) and the vector and magnitude of force. For example, axial compression may produce a burst fracture; however, adding a flexion component to the vector will produce a flexion tear-drop fracture or a wedge fracture. The individual with underlying osteoporosis will be more susceptible to fractures. 3.3.3.1 Posterior Neural Arch Fracture of C1

“Glacial instability” is a term distinguishing chronic biomechanical instability, describing the gradually developing progressive angulation, translation, or rotational deformity that may manifest secondary to a slow breakdown of supportive elements associated with degenerative processes.41 In contrast to acute biomechanical instability, substantial external forces do not cause immediate movement or progression of the deformity;42 rather, the etiologies of glacial instability include trauma, congenital defect, tumor, spondylosis, and infection (Table 3.7).

3.3.2 SPINAL FRACTURE AND PATHOMECHANICAL INTERSEGMENTAL MOTION It is helpful to understand that different regions of the spine react differently to trauma and disease. Cervical spine fractures have a greater potential for biomechanical instability than thoracic or lumbar spine fractures because the vertebrae are smaller and the bulk of the protective muscles and supportive soft tissues is not as great as in the rest of the spine. This also renders the cervical spinal cord more susceptible to injury — this is particularly evident in the suboccipital spine. Due to the stabilizing capacity of the ribcage, the vast majority of thoracic spine fractures are unaccompanied by the serious neurological consequences of biomechanical instability. However, spinal cord compression may occur with extensive compression, ligament rupture, or vertebral fragmentation43 (as associated with Figure 3.5). Fractures of the lumbar and lumbosacral spine may result in spondylolisthesis and cauda equina compression, in the lower lumbar spine.

3.3.3 UPPER CERVICAL FRACTURE PATTERNS: FRACTURES OF C0–C1–C2 Fractures of the upper cervical spine are common with ballistic trauma involving the head and neck. This fracture pattern occurs because of the flexibility of the cervical spine and relative biomechanical instability created by the large size and weight of the head in relationship to the

This, the most common fracture of the atlas, is an extension injury that involves the posterior arch.44 The mechanism of injury includes compression of the arch between the occiput and the large spinous process of the axis. It is usually a stable fracture, as the arch that has been fractured is usually displaced posteriorly and the fragment does not compromise the space available for the cord; the anterior ring, with the intact transverse atlantal ligament, provides stability for the axis. This fracture is best visualized on the lateral cervical spine radiograph and can be identified by computerized tomography or lateral tomogram (Figure 3.10). 3.3.3.2 Dens Fracture Dens fracture has been classified into three subtypes45 based on the location of the fracture line. Type I fractures involving only the tip of the dens, can be described as avulsion fractures, with a radiographic appearance of an obliquely oriented fracture across the tip. These are considered stable as long as the body of the dens is still restrained by the transverse atlantal ligament. Type II fractures are the most common, occurring at the junction of the body of the axis and the base of the dens; the radiographic representation is a transverse fracture along the base. These are typically unstable, as they can produce a primary biomechanical instability resulting from the architectural bone damage or a secondary biomechanical instability resulting from the ineffectiveness of the transverse atlantal ligament. There is a 36% chance of non-union in cases of type II dens fracture.45 Radiographically, type III fractures show a fracture line extending into the body of the axis; these are usually stable,46 as there is no cord compromise, and they usually heal without incident. The anteroposterior (AP) open mouth radiograph will usually demonstrate a dens fracture. In cases of significant sagittal displacement, the fracture will also be visualized on the lateral cervical spine radiograph. Tomograms or computed tomography will further define the fracture line.

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

likely to be the result of a head-on motor vehicle accident in which sudden hyperextension/deceleration occurs as the chin or head hits the steering wheel or windshield, resulting in upper cervical hyperextension. Such sudden, excessive axial compression in conjunction with hyperextension can result in fracture/dislocation of the neural arch with sudden transection of the spinal cord; this is considered an unstable spinal fracture due to major disruption of the restraint mechanisms. Best visualized on the lateral cervical spine radiograph, it is not a difficult radiographic diagnosis when the displacement is apparent. 3.3.3.4 Jefferson Fracture of the Atlas (Burst Fracture of C1) This fracture is caused by a vertical compression of the lateral masses of the atlas by the occipital condyles. The usual mechanism of injury is a blow to the vertex of the skull. This results in bilateral fractures of the anterior and posterior arches. This forces the lateral masses laterally, usually tearing the transverse atlantal ligament. This is considered an unstable spinal fracture secondary to major bony disruption and compromise of the transverse atlantal ligament. This fracture is best viewed on the AP openmouth view of C1 (Figure 3.11). Greater than 7 mm of total displacement of the lateral masses of C1 on C2 is indicative of biomechanical instability.47

3.3.4 CERVICAL FRACTURE PATTERNS FIGURE 3.10 Lateral X-ray of the cervical spine demonstrating a fracture through the neural arch of the atlas. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

FIGURE 3.11 Open mouth view of the C1–C2 articulation demonstrating lateral instability. Note the left lateral displacement of the C1 vertebral body with respect to the lateral mass of C2. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

3.3.3.3 Hangman’s Fracture (Bipedicular Fracture of C2, Traumatic Spondylolisthesis of C2) Hangman’s fracture refers to a bilateral fracture of the pedicles of the axis caused by sudden hyperextension of the head and neck due to a sudden deceleration from high speed. Despite the derivation of the name from a method of capital punishment, in this country this injury is more

3.3.4.1 Spinous Process Fracture (Clay Shoveler’s Fracture, Coal Miner’s Fracture) The spinous fracture is a flexion injury. The usual mechanism is for a sudden flexion of the cervical spine to avulse the tip of the spinous fracture. A neurological deficit typically does not occur with this fracture; therefore, it is a stable fracture. C7 is most often involved, but it can involve other vertebrae. This fracture is best viewed on the lateral cervical radiograph. The fracture margins are rough and serrated and the fractured tip is usually displaced caudally, which is helpful in differentiating this fracture from a nonunion of a secondary growth center (Figure 3.12).48 3.3.4.2 Pillar Fracture Injury to the cervical pillars typically involves a degree of lateral flexion or rotation. Typically, pillar fractures are unilateral. This is usually a stable fracture; however, a pillar fracture can be unstable depending upon the magnitude of the fracture. Secondary instabilities due to restraint mechanism disruptions can develop. Radiographically, this fracture is best viewed on the cervical pillar view. Bone scintigraphy may be necessary to confirm less obvious pillar fractures. Compression fractures of the pillars also

Physical Mechanisms of Spinal Cord Injury

45

A

FIGURE 3.12 Lateral postmortem view of a cervical spine demonstrating anterior listhesis of vertebra C2 with respect to C3. There is a fracture through the spinous process of C3. (Courtesy of J.P. Ellis, Ph.D.)

occur, altering the articular surface and damaging the subchondral capillary bed. 3.3.4.3 Flexion Teardrop Fracture Flexion teardrop fracture–dislocation is the most severe and unstable injury of the lower cervical spine (Figures 3.13 to 3.15).49 The mechanism of injury is compression and shear force to the anterior border of the cervical vertebra, crushing the vertebral body and fracturing a triangular or teardrop-shaped fragment from its anterior side. A combination of injuries is associated with this fracture: 1. 2. 3. 4. 5.

Posterior subluxation of the vertebral body Fracture of the posterior elements Disruption of the ligamentum flavum Compromise of the spinal cord Rupture or avulsion of the anterior longitudinal ligament

Flexion teardrop fracture is sometimes associated with an acute anterior cord syndrome with complete motor paralysis and loss of pain and temperature sensations (anterior column loss) along with continued ability to perceive position, vibration, and motion (posterior column sparing). Central canal damage is caused by the combination of forward dislocation of the vertebral body,

FIGURE 3.13 Bilateral perched facets of vertebra C4 on C5 and a flexion teardrop fracture of C5 at the anterior inferior vertebral margin. (Courtesy of E. Shick, M.S. Copyright MedicalVisions.com. With permission.)

fracture–dislocation of the posterior elements and complete disruption of supportive soft–tissue structures that contribute to the stability of this segment. This fracture complex is best demonstrated on the lateral cervical spine radiograph (Figure 3.16). 3.3.4.4 Extension Teardrop Fracture The extension teardrop fracture is an avulsion fracture of the anterior–inferior body of the cervical vertebra. This is caused by a forceful extension producing sufficient force on the anterior longitudinal ligament to avulse away a portion of the anterior–inferior vertebral body. The fragment is usually triangular or teardrop shaped. This fracture may be stable or unstable. Stability of an extension teardrop cervical spine fracture is dependent upon the direction of spinal motion. When this fractured spine is flexed, the intact posterior restraint mechanisms prevent excessive segmental mobility. Cervical flexion does not create any potentially dangerous complications in this type of fracture; therefore, in cervical flexion, this fracture is considered to be stable. However, because of the damage to the anterior longitudinal ligament restraints, this injury can produce secondary biomechanical instability during extension, and thus is considered an unstable spinal fracture in extension.

46

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

FIGURE 3.15 C7 flexion teardrop fracture with perivertebral soft-tissue swelling causing airway compromise. Note the anterior listhesis of the C6 vertebral body with respect to C7. (Fast spin echo parasagittal T2-weighted midline sagittal image.) FIGURE 3.14 Lateral radiograph of the cervical spine demonstrating a flexion teardrop fracture involving the anterior–inferior margin of the C3 vertebral body with associated perivertebral soft tissue swelling. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

3.3.5 FRACTURE PATTERNS OCCURRING AT ANY LEVEL OF THE SPINE The pain associated with a fracture may mimic the pain arising from intervertebral disk pathology or from the capsular region. The presence of a spinal fracture may render the region biomechanically unstable, thus increasing the risk for neurologic insult. With a history of trauma or abrupt onset spinal pain, the possibility of fracture should always be considered. 3.3.5.1 Endplate Burst Fracture The endplate burst fracture is a fracture of the vertebral endplates. A vertical compressive force creating an implosion effect of the nucleus pulposus on the vertebral endplates causes this spinal fracture. The nucleus pulposus herniates through the endplates with a sufficient force to cause an actual “bursting” of the cancellous vertebral body. Typically, these fractures compress the anterior and middle columns while sparing the posterior column.33

The integrity of the posterior column, not the middle column, is a better indicator of burst fracture stability.50 A burst fracture is considered stable if there is not any disruption of the posterior restraint elements or displacement of vertebral body fragments into the spinal canal. The clinician must be aware of the possibility of the initial trauma producing a posterior displacement of a free fragment from the vertebral body into the spinal canal. Transient spinal cord compression may occur as a result of posterior fragments and/or the fluid shockwave striking the cord. The fragments may relocate back to their normal vertebral boundaries in a rebound fashion after a crushing blow. Consequently, acute spinal shock may be present without any evidence of fracture displacement. AP and lateral radiographs of the region will usually demonstrate these types of fractures; on the AP view, a vertical fracture line or an increased interpedicular space is a characteristic finding. Computed tomography may be necessary to visualize fragments compressing the thecal sac (see Figure 3.4). 3.3.5.2 Wedge Fracture (Compression Fracture) The wedge or compression fracture is a flexion or lateral flexion injury and is not a difficult diagnostic challenge.

Physical Mechanisms of Spinal Cord Injury

47

B

A

FIGURE 3.16 (A) Lateral neutral radiograph of the cervical spine demonstrating a flexion teardrop fracture of vertebra C7. This injury is unstable due to disruption of the ligaments throughout the posterior elements. (B) Lateral spot view radiograph of the cervical spine through C6–C7. This close-up more clearly delineates the teardrop fracture through the anterosuperior corner of C7 and demonstrates the spinous process widening between C6 and C7. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

The mechanism of injury is an hyperflexion of the superior vertebral segment upon the inferior vertebral segment. There is a measurable decrease in vertical anterior vertebral body height compared to posterior vertebral body height. It is important to determine the degree of vertebral body compression because the greater the percentage of body height lost the greater the probability that there has been disruption of the opposing restraint mechanisms (i.e., ligaments, capsular structures, and muscular attachments). Understanding the amount of flexion required to create the degree of compression can give the clinician an insight into the amount of posterior restraint stress at the moment of injury. In this type of fracture, it is not the vertebral body compression that causes biomechanical instability; it is damage to the posterior vertebral restraint mechanisms that leads to the signs of secondary instability. This is considered a stable fracture unless there is a displaced or separated fracture fragment or there is a significant degree of wedging. The wedge fracture is the most common fracture in the lumbar spine.51 Compression fractures can usually be viewed on the lateral radiograph, although a minimum of

25 to 30% compression is required for conclusive X-ray appreciation and diagnosis (Figure 3.17).52 A computerized tomogram with 3D reconstruction may be needed to appreciate the full extent of the fracture (Figure 3.18). 3.3.5.3 Chance Fracture The Chance fracture results from a shearing flexion mechanism. This has also been called the lap seatbelt fracture or the fulcrum fracture. Chance first described this fracture in 194853 as an obliquely horizontal fracture of the spinous process and the neural arch, extending through the superior portion of the vertebral body. A more complete description includes a horizontal splitting of the spine and the neural arch, ending with an upward curvilinear fracture that usually reaches the upper surface of the body just anterior to the neural foramen.48 This fracture is more common in the upper lumbar spine. The lateral lumbar radiograph ordinarily demonstrates this fracture. Computed tomography may be necessary to fully define the fracture lines.

48

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

C FIGURE 3.16 (C) Sagittal T2-weighted image of the cervical spine. Disruption of the ligaments between C6 and C7 is evident because of the hyperintense signal between the spinous processes. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

3.3.5.4 Neural Arch Fracture Acute fractures of the pars interarticularis are usually the result of extreme hyperextension mechanisms. Best seen on the oblique view, the fracture line is an irregular, vertically oriented radiolucency. Because this fracture is usually unilateral, it does not have the tendency to result in neurological compromise.

3.3.6 SPINAL DISLOCATION Unreduced spinal dislocations in the cervical spine are usually seen by emergency personnel in trauma centers and often significantly compromise the central canal. Dislocations in the thoracic or lumbar spine are not common. The mechanism of spinal dislocations is usually a combination of flexion, extension, rotation, or translation. When dislocation is apparent, there will usually be an accompanying fracture or fractures of the vertebral body or posterior elements. These spinal fractures can be of various magnitudes from a small fleck fracture of a facet to a body or arch fracture of the vertebra. Facet dislocations without fractures have a significantly higher association with cord

FIGURE 3.17 Lateral radiograph of the thoracolumbar spine demonstrating a central compression fracture. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)

syndromes than do rotational facet injuries with fractures.54 Because spinal dislocation is a failure of all three columns,33 these conditions are mechanically unstable. Two types of cervical dislocates are described below. 3.3.6.1 Bilateral Cervical Facet Dislocation In bilateral facet dislocation, the superior facets are dislocated anteriorly to the inferior facets at the intervertebral foramen. The superior facets can displace into the intervertebral foramen and compromise the nerve roots. The central canal is compromised by the posterior arch producing an anterior cord syndrome, unless there is a fracture of the neural arch allowing the posterior elements to be displaced posteriorly. This injury severely disrupts the posterior restraint mechanisms, the anular fibers of the disk, and frequently the anterior longitudinal ligament. This injury is unstable and even X-ray examination should proceed cautiously. A lateral cervical radiograph will demonstrate the characteristic displacement of the superior facets into the neural foramen. A cross-table lateral view allows for the least movement of the patient’s spine and

Physical Mechanisms of Spinal Cord Injury

49

Compression fracture line through posterior aspect of centrum

L4 TP fracture

FIGURE 3.18 Three-dimensional (reconstructed 3-D) CAT scan demonstrating compression fracture of the L5 body and L4 transverse process. (TVP).

is the radiograph of first choice when a bilateral facet dislocate is suspected. 3.3.6.2 Unilateral Facet Dislocation By definition, this is the anterior perching of one of the superior facets in relation to the inferior facet at the intervertebral foramen, and there is certainly compromise of the affected intervertebral foramen on the side of facet dislocate. The central canal is usually not affected because this is a rotational injury. Although there is major disruption of the ligamentous and capsular constraints of the dislocated facet joint, the posterior joint restraints and anular fibers can be spared. The anular fibers are more likely to become involved in dislocates of the lower segments of the cervical spine.55 A unilateral facet dislocate is usually considered a stable injury. The characteristic appearance of the perched facet is best demonstrated on the oblique radiograph. 3.3.6.3 Spinal Dislocation/Relocation In this type of injury, the spinal segment dislocates as a result of a traumatic force, resulting in the disruption of spinal restraint mechanisms; then, either from an opposite force or spontaneously, the spinal dislocation repositions to its normal anatomic position. The disruption of the restraint mechanisms has already been complete, however, which makes this injury unstable even though standard static radiographic studies may appear normal. Clinical findings along with spinal stress radiographs should supply

TABLE 3.8 Conditions Associated with Acute Back Pain and Rapidly Evolving Myelopathy: Spinal Hematoma and Differential Considerations • • • • • •

Acute and subacute transverse myelitis Spinal cord infarction Spinal abscess Acute large disk herniation Neoplasm Spinal fracture or dislocation

the clinician with sufficient evidence to identify the unstable spinal segment.

3.4 SPINAL HEMORRHAGE Spinal hemorrhage can occur within the epidural space, subarachnoid space, or spinal cord parenchyma. Spinal hemorrhage may occur secondary to coagulopathy, anticoagulant therapy, medical intervention, trauma, or vascular malformation. Hemorrhage can lead to neurological compression if the hematoma is confined to a compartmentalized region. Spinal hematomas typically are associated with acute-onset, well-localized spinal pain and a rapidly progressing myelopathy (Table 3.8). Emergency intervention is required to decompress the spinal cord. Recovery from paraplegia secondary to compressive hematoma is dependent on the length of time from onset

50

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

TABLE 3.9 Common Causes of Spontaneous Spinal Subarachnoid Hemorrhage • • • • • • •

Arteriovenous malformations Neoplasm Infectious meningitis Coagulopathy Extreme physical exertion Lumbar puncture Collagen vascular disease

of symptoms to surgical intervention and the extent of spinal cord damage.

3.4.1 SUBARACHNOID HEMORRHAGE Most cases of subarachnoid hemorrhage occur secondary to trauma. A few conditions result in spontaneous subarachnoid hemorrhage, the most common of which is spinal arteriovenous malformations (AVM) (Table 3.9).56 This condition is frequently associated with sudden severe neck or back pain and may be equated with a stabbing knife-type pain. The pain tends to be more severe than pain associated with epidural or subdural hematoma. Evolving subarachnoid hemorrhage may result in radicular, myelopathic, and intracranial symptoms. The cerebrospinal fluid (CSF) study usually reveals blood. Subarachnoid hemorrhage may occur simultaneously with a subdural hematoma, thus increasing the risk for a devastating mass effect upon the adjacent spinal cord.

3.4.2 EPIDURAL HEMORRHAGE Individuals with an underlying coagulopathy or those on anticoagulant therapy are more prone to suffer a bleeding diathesis such as an epidural or subdural hemorrhage with trauma. Epidural hematomas can occur secondary to epidural anesthesia and spinal puncture with the concurrent use of low-molecular-weight heparin.57 The development of a spinal epidural hematoma is characterized by acute spinal pain followed by signs of rapidly progressing myelopathy typically occurring within minutes or hours. Spinal epidural hematomas occur more frequently in the thoracic and thoracolumbar regions. Epidural hematomas commonly develop within the posterior epidural space and may span multiple segments.58 Evaluation of the CSF is variable, sometimes demonstrating blood or an elevated protein level. MRI has become the assessment method of choice for spinal hematoma.59

3.4.3 SUBDURAL HEMORRHAGE Spinal subdural hematomas occur less frequently than epidural hematoma, and they are usually related to trauma.

The epidural predilection may be secondary to greater blood vessel caliber and prevalence within the epidural space.60 The clinical presentation usually involves acuteonset back pain in the absence of radicular symptoms. Like epidural hematomas, the clinical signs and symptoms of myelopathy frequently evolve within minutes or days after the bleeding ensues. A chronic spinal subdural hematoma may result in a less obvious clinical picture and is more apt to mimic the presentation of spondylosis and disk pathology.61 CSF assessment may demonstrate blood if there is an associated subarachnoid hemorrhage. A subdural hematoma may contribute to a spinal fluid block (filling defect), rendering a CSF study more challenging. MRI is the imaging method of choice and should always be considered before myelography.

3.4.4 HEMATOMYELIA “Hematomyelia” is a term used to describe bleeding within the parenchyma of the spinal cord. Hematomyelia often occurs as the result of trauma. The pattern of bleeding usually follows a longitudinal course. The clinical presentation is often abrupt with some progression over the following 1 to 2 days. The most common site of posttraumatic hematomyelia is at the lower cervical cord. The clinical findings are similar to an incomplete hemimyelopathy. The cerebrospinal fluid may be blood stained, although this is not a pathognomonic finding required for diagnosis. Intraspinal microhemorrhages may occur secondary to small ruptures along the walls of the muscular venules.62-65 Spontaneous hematomyelia should alert the attending clinician to the possibility of an arteriovenous malformation or coagulopathy. Hemorrhage secondary to spinal arteriovenous malformations may be microscopic and cumulative, leading to a slow, progressive neurologic decline in clinical presentation.

3.5 MYELOPATHY AND DISK HERNIATION Disk herniation may be classified into one of three general categories based on consistency: (1) soft herniation, (2) mixed soft–calcific herniation (disk-spur complex), and (3) calcified herniation. The soft herniation is more apt to be relatively recent and therefore has the propensity to become larger. It is less rigid than the other categories, allowing for slightly greater physical adaptation within the spinal canal during movement. The calcific disk is rigid and more apt to slowly progress in size with time. Trauma is usually integral to onset of symptoms in any of the three categories. Intervertebral disk herniation, extrusion, or sequestration can contribute to the onset of myelopathy. This may occur secondary to direct mechanical insult to neural elements and/or from an associated interruption of blood supply to the spinal cord (Figure 3.19). Signs and symptoms may be abrupt in onset or may occur gradually,

Physical Mechanisms of Spinal Cord Injury




  
 

51

   



  

      

   
  
  

Disk-spur complex


 
 
   
      

   

       

    
    
   
 
   
    FIGURE 3.19 Anterior spinal cord compression with and without anterior spinal artery (ASA) compression.

paralleling the temporal pattern of spondylotic stenosis. A midline disk herniation exposes the anterior spinal artery (ASA) to compressive forces and is more apt to lead to a pure medullary syndrome. Intervertebral disk hernation may cause altered venous flow and venous stasis with dilatation, which may contribute to a mass effect. Depending on the size and location of disk herniation, it may result in a pure radiculopathy syndrome, pure medullary syndrome, or myeloradiculopathy (Figures 3.20 and 3.21).66 A large cervical disk herniation can cause a Brown– Séquard syndrome.67 With upper cervical disk herniation at C2–C3, radiculopathic symptoms may outweigh cord signs.68 Other signs and symptoms associated with highlevel cervical disk compression of the cord include nonspecific neck and shoulder pain, cervical radiculopathy in a level different than expected, and variable myelopathy characterized by impairment of motor and sensory function more in the upper extremities than lower extremities and mostly starting following trauma. MRI of myelopathy secondary

FIGURE 3.20 Prominent degenerative changes throughout the cervical spine, most pronounced at the C5–C6 and C6–C7 levels where there is intervertebral disk-space narrowing and degenerative endplate change. Mild retrolisthesis at C5–C6 secondary to a degenerative process. Diffuse disk bulges at C3–C4, C5– C6, C6–C7, and C7–T1, with resultant ventral cord compression at C5–C6, C6–C7, and C7–T1. Also demonstrated is facet hypertrophy at the C5–C6, C6–C7, and C7–T1 levels, resulting in dorsal encroachment upon the thecal sac and dorsal cord compression. (Parasagittal fast spin echo T2-weighted image right parasagittal section.)

to disk herniation may be associated with a focal region of high T2-weighted signal intensity not demonstrated on T1 weighting (Figure 3.22). A region of abnormal intramedullary MR signal may lie directly adjacent to, slightly above, or below a disk herniation. The presence of abnormal cord signal at the level of disk pathology without evidence of direct compression of the spinal cord should raise the index of suspicion of a retracted disk herniation, migrated sequestered fragment, or dynamic spinal stenosis with cumulative cord insult. Myelopathy may occur as the result of multisegmental disk herniation contributing to a watershed region of vascular insufficiency.

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Cord compression with deformation

FIGURE 3.21 The same patient as in Figure 3.20. Pronounced focal right paracentral disk herniation with resulting right paracentral cord compression. (Parasagittal fast spin echo T2-weighted image to the right of the midline.)

)

*

FIGURE 3.22 (A) Parasagittal T2-weighted image demonstrating cord compression from C4–C5 HNP. (B) Gradient echo axial image of large right paracentral disk herniation, deforming the ventral cord.

Physical Mechanisms of Spinal Cord Injury

REFERENCES 1. Breig, A., Adverse Mechanical Tension in the Central Nervous System: An Analysis of Cause and Effect, Relief by Functional Neurosurgery, Stockholm: A&W International/John Wiley & Sons, 1978. 2. Breig, A., Skull traction and cervical cord injury, in A New Approach to Improved Rehabilitation, Berlin: Springer-Verlag, 1989. 3. Sarwar, M., Crelin, E.S., Kier, E.L., and Virapongse, C., Experimental cord stretchability and the tethered cord syndrome, Am. J. Neuroradiol., 4(3):641–643, 1983. 4. Harrison, D.E., Cailliet, R., Harrison, D.D., Troyanovich, S.J., and Harrison, S.O., A review of biomechanics of the central nervous system, Part II: spinal cord strains from postural loads, J. Manipulative Physiol. Ther., 22(5):322–332, 1999. 5. Maiman, D.J., Coats, J., and Myklebust, J.B., Cord/spine motion in experimental spinal cord injury, J. Spinal Disord., 2(1):14–19, 1989. 6. Apuzzo, M., Watkins, R., and Dobkin, W., Biomechanics of the neural axis, in Dunsker, S. et al., Eds., The Unstable Spine, Orlando, FL: Grune & Stratton, 1986: 17–23. 7. Silberstein, M. and McLean, K., Non-contiguous spinal injury, clinical and imaging features and postulated mechanisms, Paraplegia, 32(12):817–823, 1994. 8. Elsberg, C.A., Surgical Diseases of the Spinal Cord Membranes and Nerve Root, New York: Hoeher, 1941. 9. Blight, A., Delayed myelination macrophage invasion: a candidate for secondary cell damage in spinal cord injury, Cent. Nerv. Sys. Trauma, 2:299–315, 1985. 10. Noel, P. and Desmedt, J., Cerebral and far-field somatosensory evoked potentials in neurological disorders involving the cervical spinal cord, brainstem, thalamus and cortex, Prog. Clin. Neurophysiol., 7:205–230, 1980. 11. Rudge, P., Ochoa, J., and Gilliatt, R.W., Accute peripheral nerve compression in the baboon, J. Neurol. Sci., 23:403–420, 1974. 12. Baker, P., Ladds, N., and Rubinson, K., Measurement of flow properties of isolated exoplasm in a defined chemical environment, J. Physiol., 269:10–11, 1977. 13. Yamada, S., Zinke, D., and Sanders, D., Pathophysiology of “tethered cord syndrome,” J. Neurosurg., 54: 494–503, 1981. 14. Jarzem, P., Quance, D., Doyle, D., Begin, L., and Kostvik, J., Spinal cord tissue pressure during spinal cord distraction in dogs, Spine, 17:S227–S234, 1992. 15. McCormick, P. and Stein, B., Functional anatomy of the spinal cord related structures, Neurosurg. Clin. North Am., 1:469–489, 1990. 16. Keimh, H.A. and Hilals, S.K., Spinal angiography and scoliosis patients, J. Bone Joint Surg. Am., 53:904–912, 1971. 17. Benzel, E.C., Biomechanics of Spine Stabilization: Principles and Clinical Practice, New York: McGraw–Hill, 1995: 278. 18. Levine, D.N., Pathogenesis of cervical spondylotic myelopathy, J. Neurol. Neurosurg. Psychiatry, 62(4): 334–340, 1997.

53

19. Del Bigio, M.R. and Johnson, G.E., Clinical presentation of spinal cord concussion, Spine, 14(1):37–40, 1989. 20. Byrne, T.N., Spinal cord compression from epidural metastasis, N. Engl. J. Med., 327:614–619, 1992. 21. Giles, L.G., Review of tethered cord syndrome with a radiological and anatomical study: case report, Surg. Radiol. Anat., 13(4):339–343, 1991. 22. Pang, D. and Wilberger, J.E., Jr., Tethered cord syndrome in adults, J. Neurosurg., 57(1):32–47, 1982. 23. Gupta, S.K., Khosla, V.K., Sharma, B.S., Mathuriya, S.N., Pathak, A., and Tewari, M.K., Tethered cord syndrome in adults, Surg. Neurol., 52(4):362–369, 1999. 24. Ratliff, J., Mahoney, P.S., and Kline, D.G., Tethered cord syndrome in adults, South. Med. J., 92(12):1199–1203, 1999. 25. Yamada, S., Zinke, D.E., and Sanders, D., Pathophysiology of “tethered cord syndrome,” J. Neurosurg., 54(4):494–503, 1981. 26. Warder, D.E. and Oakes, W.J., Tethered cord syndrome in the conus in the normal position, Neurosurgery, 33(3):374–378, 1993. 27. Johnson, D.L. and Levy, L.M., Predicting outcome in the tethered cord syndrome: a study of cord motion, Pediatr. Neurosurg., 22(3):115–119, 1995. 28. Yamada, S., Iacono, R.P., Andrade, T., Mandybur, G., and Yamada, P.S., Pathophysiology of tethered cord syndrome, Neurosurg. Clin. North Am., 6(2):311–323, 1995. 29. Hanson, P., Rajaux, P., Gilliard, C., and Biset, E.. Sacral reflex latencies in tethered cord syndrome, Am. J. Phys. Med. Rehabil., 72(1):39–43, 1993. 30. Pang, D. and Wilberger, J.E., Spinal cord injury without radiographic abnormalities in children, J. Neurosurg., 8:360–367, 1951. 31. Roaf, R., International classification of spinal injuries, Paraplegia, 10:78–84, 1972. 32. Allen, B., Jr., Ferguson, R., Lehmann, T. et al. A mechanistic classification of closed, indirect fractures and dislocations of the lower cervical spine, Spine, 7:1–27, 1982. 33. Denis, F., The three column spine and its significance in the classification of acute thoracolumbar spinal injuries, Spine, 8(8):817–831, 1983. 34. Meyer, P., Jr., Apple, D., Jr., Cotler, J., Gupta, P., and Zigler, J., New spine fracture classification system: midwest regional spinal cord injury care system, available at http://www.northwestern.edu/spine/fxclass.htm. Accessed October 2000. 35. Frymoyer, J.W. and Krag, M.H., Spinal stability and instability: definitions, classifications and general principles of management, in Dunsker, S.B. et al., Eds., The Unstable Spine, Orlando, FL: Grune & Stratton, 1986: 1–16. 36. White, A.A., III and Panjabi, M.M., Eds., Clinical Biomechanics of the Spine, 2nd ed., Philadelphia, PA: Lippincott, 1990. 37. Greenfield, G., Radiology of Bone Diseases, 2nd ed., Philadelphia, PA: Lippincott, 1975.

54

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38. Katz, W.A., Rheumatic Diseases: Diagnosis and Management, Philadelphia, PA: Lippincott, 1977. 39. Wade, W., Saltzstein, R., and Maiman, D., Spinal fractures complicating ankylosing spondylitis, Arch. Phys. Med. Rehabil., 70(5):398–401, 1989. 40. Turek, S.L., Orthopedics Principles & Their Application, 4th ed., Philadelphia, PA: Lippincott, 1984. 41. Benzel, E.C., Biomechanics of Spine Stabilization, New York: McGraw–Hill, 1995. 42. Benzel, E.C., Biomechanics of lumbar and lumbosacral spine fracture, in Rea, G.L. and Miller, C.A., Eds., Spinal Trauma, Current Evaluation and Management, Neurosurgical Topics, American Association of Neurological Surgeons (AANS) Publications Committee, Chicago, IL, 1993: 165–195. 43. Gehweiler, J.A., Jr., Daffner, R.H., and Osborne, R.L., Jr., Relevant signs of stable and unstable thoracolumbar vertebral column trauma, Skeletal Radiol., 7:179–183, 1981. 44. Sherk, H.H. and Nicholson, J.T., Fractures of the atlas, J. Bone Joint Surg. Am., 52:1017–1024, 1970. 45. Anderson, D. and D’Alonzo, R.T., Fractures of the odontoid process of the axis, J. Bone Joint Surg. Am., 56:1663–1674, 1974. 46. Felson, B., Fractures, Semin. Roentgenol., 13(1–2), 1978. 47. Rea, G.L. and Miller, C.A., Spinal Trauma, Current Evaluation and Management, Neurosurgical Topics, American Association of Neurological Surgeons (AANS) Publications Committee, Chicago, IL, 1993: 807. 48. Yochum, T.R. and Rowe, L.J., Essentials of Skeletal Radiology, Vol. 1, Baltimore, MD: Williams & Wilkins, 1987. 49. Schneider, R.C. and Kahn, E.A., Chronic neurological sequela of acute trauma to the spine and spinal cord, J. Bone Joint Surg., 38(A):985–997, 1956. 50. James, K.S., Wenger, K.H., Schlegel, J.D., and Dunn, H.K., Biomechanical evaluation of the stability of thoracolumbar burst fractures, Spine, 19(15):1731–1740, 1994. 51. Schinz, H.R. et al., Roentgen Diagnostics, Vol. 2, 2nd ed., New York: Grune & Stratton, 1967. 52. Gehweiler, J.A., Jr., Osborne, R.L., Jr., and Bader, R.F., The Radiology of Vertebral Trauma, Philadelphia, PA: Saunders, 1980. 53. Chance, G.Q., Note on type of flexion fracture of spine, Br. J. Radiol., 21:452–453, 1948.

54. Shanmuganathan, K., Mirvis, S.E., and Levine, A.M., Rotational injury of cervical facets: CT analysis of fracture patterns with implications for management and neurologic outcome, Am. J. Roentgenol., 163(5):1165– 1169, 1994. 55. Braakman, R. and Vinken, P.J., Unilateral facet interlocking in the lower cervical spine, J. Bone Joint Surg. Br., 49:249–257, 1967. 56. Swann, K.W., Ropper, A.H., New, P.J.F., and Poletti, C.E., Spontaneous spinal subarachnoid hemorrhage and subdural hematoma: report of two cases, J. Neurosurg., 61:975–980, 1984. 57. Lumpkin, M., Reports of epidural or spinal hematomas with the concurrent use of low molecular weight heparin and spinal/epidural anesthesia or spinal puncture, FDA Public Advisory, Dec. 15, 1997. 58. Mattle, H., Sieb, J.P., Rohner, M., and Munenthaler, M., Non-traumatic spinal epidural and subdural hematomas, Neurology, 37(8):1351–1356, 1987. 59. Holtas, S., Heiling, M., and Lonntoft, M., Spontaneous spinal epidural hematoma: findings at MR imaging and clinical correlation, Radiology, 199(2):409–413, 1996. 60. Edelson, R.N., Chernik, N.L., and Posner, J.B., Spinal subdural hematomas complicating lumbar puncture. occurrence in thrombocytopenic patients, Arch. Neurol., 31(2):134–137, 1974. 61. Khosla, V.K., Kak, V.K., and Mathuriya, S.N., Chronic spinal subdural hematomas: report of two cases. J. Neurosurg., 63(4):636–639, 1985. 62. Balentine, J., Pathology of experimental spinal cord trauma, I, Lab Invest., 39:236–253, 1978. 63. Balentine, J., Pathology of experimental spinal cord trauma, II, Lab Invest., 39:254–266, 1978. 64. Dohrmann, G. and Bucy, P., The microvasculature in transitory traumatic paraplegia: an electron microscopic study in the monkey, Neurosurgery, 35:263–271, 1971. 65. Dohrmann, G. and Bucy, P., Transitory traumatic paraplegia: electron microscopy of early alterations in myelinated nerve fibers, J. Neurosurg., 36:407–415, 1972. 66. Bucciero, A., Vizioli, L., and Cerillo, A., Soft cervical disk herniation: an analysis of 187 cases, J. Neurosurg. Sci., 42(3):125–130, 1998. 67. Rumana, C.S. and Baskin, D.S., Brown–Séquard syndrome produced by cervical disk herniation: case report and literature review, Surg. Neurol., 45(4):359–361, 1996. 68. Chen, T.Y., The clinical presentation of uppermost cervical disk protrusion, Spine, 25(4):439–442, 2000.

4

Conditions Associated with Myelopathy

4.1 DEGENERATION AND STENOSIS “Spinal stenosis” is a term used to describe narrowing of the neural foramina lateral recess and/or central canal within the vertebral column. Spinal stenosis can be classified into four primary categories. The first of these categories is congenital stenosis, which is developmental and present from birth. The second category refers to an acquired spinal stenosis secondary to injury, disk herniation, spondylosis, or diseases that produce proliferation and remodeling of tissues which compromise the spinal canal (Figure 4.1). The third category is dynamic or functional spinal stenosis. This refers to an alteration of structural relationships within and/or adjacent to the lateral foramina or central spinal canal with positionally induced narrowing during periods of movement. The fourth category is complex stenosis, which refers to a combined presentation with characteristics of two or more of the above categories. Complex spinal stenosis is often associated with the greatest potential for risk to neighboring neural and vascular elements. Degenerative disk disease is one of the most common conditions leading to spinal stenosis.1 The progression of spondylosis can be categorized by radiographic and clinical findings: stage I, cervical disk disease; stage II, spondylosis; stage III, spondylosis with restricted motion; and stage IV, cervical spondylotic myelopathy.2 These stages reflect the temporal pattern of progression. The advancing sequence of pathologic events surrounding spondylosis and the development of spinal stenosis involves morphological changes of the anatomic structures adjacent to the spinal canal. There may be a congenital predisposition to developing clinically significant spinal stenosis. The different variations of spinal canal configuration generally fall into one of the following four categories: (1) oval, (2) triangular, (3) trefoil, or (4) deltoid. An example of congenital lateral stenosis is the short pedicle syndrome. The involved pedicles are typically thick and short in their anteroposterior projection. This developmental anomaly renders the adjacent intervertebral foramen smaller in diameter and area than neighboring foramen. Pedicogenic stenosis also contributes to narrowing of the central spinal canal. Reduced coronal diameter can occur with developmental reduction in interpendicular distance. Common examples of acquired spinal stenosis include facet arthropathy, scoliosis, spondylolithesis, trauma,

intervertebral disk bulge, protrusion, extrusion, and/or free fragment migration. Bony stenosis should be differentiated from other causes. Less commonly, acquired central or lateral canal stenosis can occur secondary to cyst, tumor, or postoperative scar. Early stenosis is often asymptomatic. One study demonstrated lumbar stenosis ranging from 4% to 28% of computed tomography (CT) or magnetic resonance imaging (MRI) scans of asymptomatic subjects.3 Most patients are asymptomatic until the third decade or later and then develop symptoms following a mild vertebral injury. As previously discussed, extreme hyperflexion or hyperextension of the cervical spine exposes the spinal cord to mechanical and microvascular trauma in the normal dimensioned canal. Patients with reduced spinal canal size are at increased risk for spinal cord contusion, compression, and spinal cord injury (SCI) subsequent to trauma.4 One of the most common forms of pathomechanical insult that occurs within the narrowed spinal canal is the pincer effect. The spinal cord is vulnerable to the pincer effect in the presence of disk herniation, spondylosis, vertebral listhesis, thickened or buckled ligaments, and postsurgical hypomobility at adjacent segments (Figure 4.2).

4.1.1 SPONDYLOTIC MYELOPATHY AND CERVICAL SPONDYLOTIC MYELOPATHY 4.1.1.1 Prevalence Spondylotic myelopathy can occur at any level of the spinal cord where the spinal canal is narrowed, although it most commonly afflicts the cervical spine. Significant spondylotic stenosis often occurs with bony canal encroachment superimposed under a congenitally narrowed canal. Cervical spondylotic myelopathy (CSM) was recognized as a distinct clinical entity as early as the 1950s by Brain.5 Clarke and Robinson6 also recognized CSM as a condition distinct from myelopathy due to cervical disk herniation. In the patient population over 50 years old, CSM is the most common cause for spinal cord pathology and spinal cord dysfunction encountered in practice.7 CSM remains the most serious complication of cervical spondylosis. Cervical spondylotic myelopathy may coexist with multisegmental levels of spinal stenosis,8 usually occurring in the patient over age 60, with an average of three lesions per individual.9 Epstein et al.10 estimated that 5% 55

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Right paracentral cord compression

Disk-spur complex

A

B

FIGURE 4.1 (A) Large right paracentral disk-osteophyte complex causing right paracentral spinal cord compression. Diffuse disk bulge at C3–C4 resulting in ventral cord compression. (Parasagittal gradient echo T2-weighted right parasagittal image.) (B) In the same patient, right paracentral spinal cord compression and exiting right nerve root impingement secondary to the disk–osteophyte complex. (Axial gradient echo T2-weighted image through the C3–C4 level.) (Courtesy of Ronald Landau, M.D.)

4.1.1.2 Pathomechanisms

Buckling of ligamentum flavum

Disk herniation

Instability

Spondylosis

Compression at superior edge of vertebra below anterolisthesis

FIGURE 4.2 The “pincher effect” occurs with anterolisthesis, ligamentum flavum hypertrophy, disk herniation, and osteophytic spurs in the spinal canal. (Copyright J.M. True, D.C.)

of patients with cervical stenosis also have lumbar stenosis, which may result in a challenging diagnostic workup. Multilevel spondylotic stenosis can result in a mixed and seemingly contradictory clinical presentation of upper and lower motor neuron dysfunction in the same patient.

Spinal cord compression secondary to spondylosis and central spinal stenosis can also compromise intramedullary blood flow, leading to ischemia and/or infarction (Table 4.1). There are four primary elements which contribute to the development of cervical myelopathy in the presence of advancing cervical spondylosis: (1) circumferential stenotic narrowing of the central spinal canal; (2) development of focal projections into the canal (spondylotic ridges, bars and spurs, or disk herniation); (3) impaired patency or integrity of intrinsic spinal or radicular circulation; and (4) chronic block of CSF flow. The pre-morbid size of the central canal is a major predisposing factor to the development of spondylotic myelopathy. Larger spinal canals have significant reserve space and can therefore tolerate greater degrees of spondylotic intrusion. The posterolateral white matter is vulnerable to the negative effects of spinal cord compression, particularly the corticospinal tract.11 Voskuhl et al.12 proposed the presence of a watershed zone in the region of the funiculus cuneatus, medial spinothalamic, and corticospinal tracts, thus rendering the regions susceptible to ischemic and hypoxic injury.12,13 Autopsies performed on individuals with CSM have commonly revealed relative preservation of the anterior columns, marked gray matter atrophy, degeneration in the lateral and posterior funiculi, and thin myelinated fibers within the white matter suggestive of a demyelinative–remyelinative process.11,14 Degeneration of the medial portion of the posterior columns is usually only noted in cases of severe cord compression.11

Conditions Associated with Myelopathy

57

TABLE 4.1 Cervical Spondylotic Myelopathy (CSM): Potential Causes for Spinal Cord Vascular Insult • • • • • • •

Intermittent or persistent compressive occlusion of the anterior spinal artery (ASA) Anterior spinal cord compression with compromise of sulcul and terminal branches of ASA Intramedulary vascular stasis secondary to tethering of the spinal cord against anterior osteophytes complicated by tension of dentate ligaments Possible reduction of intramedullary collateralization due to multilevel spondylosis and related central canal stenosis Compression of venous channels associated with anterior spinal cord compression Intramedulary capillary venous stasis and edema with absent cord pulsation Cumulative spinal cord ischemia with infarction

4.1.1.3 Clinical Signs and Symptoms and Temporal Pattern of Progression During the early onset of CSM, the presentation may be subtle with the possibility of being overlooked in the presence of more obvious radiculopathic signs and symptoms. Symptom magnification may occur secondary to superimposed injury such as a vehicular injury. CSM usually develops in a gradual and slowly progressive fashion with the duration of symptoms usually ranging from one week to a few years (Table 4.2). In some cases, signs and symptoms of CSM may develop over a few decades. The myelopathic findings may eventually appear to stabilize due to the somewhat self-limiting nature of spondylosis and the reduction of segmental spinal mobility, which occurs with advancing spondylosis (Table 4.3). The most common early complaints of individuals with CSM include insidious-onset, painless paresis characterized by leg stiffness, incoordination, and/or weakness. Paresis may begin in one leg progressing to involve the opposite leg and/or to the ipsilateral arm. The history may be remarkable for falls, frequent episodes of tripping with near falls, and difficulty navigating unlevel ground due to unsteadiness. Leg weakness predominantly involves the small muscles of the foot and distal leg. This often leads to varying degrees of dorsiflexion paresis or foot scuffing. Clearance of the foot during the swing phase of gait becomes even more difficult with lower extremity spasticity. It is not uncommon for these patients to blame their difficulty walking and related symptoms on “old age.” The pattern of gait commonly seen is a broad-based, cautious, dysrhythmic, short stride. The initial sensory complaints predominate in the upper extremities, whereas initial motor compromise usually predominates in the lower extremities. Progressive leg weakness is often followed by the progression of sensory complaints. Early sensory complaints frequently consist of reported patchy numbness, pain, and/or dysesthesia involving the arms or hands with the latter presentation predominating. This characteristically progresses to involve a large diffuse portion of the limb. Upper extremity paresis or clumsiness may be present early in the progression of the disorder although the patients are often unaware of it. Patients over 65 years of age with cervical

TABLE 4.2 Historical Signs and Symptoms Suggestive of Mild to Moderate (Incomplete) Compressive Myelopathy • • • • • • • • • • • • • • • • •

Intermittent extremity shocklike sensations Brief episodes of nonfocal extremity muscle twitching or tightness Intermittent gait “incoordination” or “weakness” Extremity clumsiness with spine pain Multifocal lower extremity temperature dysethesia Intermittent bowel and/or bladder urgency Periodic nonfocal extremity paresthesia with clumsiness Inability to adequately perform complex motor tasks Back pain with radiation during spinal flexion or extension Exertional muscle weakness, tightness, or clumsiness Frequent falls Difficulty ambulating in the dark Progressive avoidance of tasks requiring balance Fear of stairs Wide-based stance Short, cautious steps during ambulation Looking at feet to improve gait

TABLE 4.3 Common Etiology Leading to Spinal Cord Compression in the Elderly • • • •

Spondylosis Falls Fracture Neoplasm

spondylotic myelopathy may present with unilateral or bilateral deltoid paresis or paralysis. 15 Ebara and associates16 characterized a “myelopathy hand” with wasting of the hand muscles similar to that seen in amyotrophy. The numb, clumsy hand is a characteristic feature of upper cervical myelopathy (C1–C5) (Table 4.4). Cervical spondylosis may lead to intermittent or persistent neck discomfort and stiffness. Facet hypertrophy and capsular pain arising from the mid- to lower cervical region can lead to referred pain to the scapular regions. Limited cervical range of motion can place a greater burden

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TABLE 4.4 Relevant Features of Numb Clumsy Hand Syndrome Secondary to High Cervical Myelopathy • Lesion usually between C3–C5 • High cervical compromise of funiculus cuneatus supplying the C6–C8 segments • Finger and hand dysesthesia • Hand stereoanesthesia • Intrinsic hand atrophy • Occipital and/or cervical pain • Late-onset spasticity • Late-onset gait pathology • Mimics lower cervical radiculopathy • Mimics plexopathy • Mimics shoulder pathology

on the lumbar region, thereby contributing to low back pain. Low back pain may also occur from spasticity involving paralumbar and gluteal muscles. Bladder symptoms are rarely severe or the primary presenting complaint.17 Urinary urgency is one of the most common bladder symptoms. Patients with moderate to severe stenotic myelopathy may present with neurogenic or spastic bladder, depending on the level of compression. They may have episodes of urinary and fecal incontinence along with ataxic gait. 4.1.1.4 Clinical Findings Global and segmental cervical active cervical range of motion is typically reduced secondary to soft-tissue changes and disk stiffening associated with spondylosis. The levels adjacent to regions of moderate to severe spondylosis may exhibit compensatory hypermobility on flexion–extension radiographs. Cervical spondylosis may lead to dynamic cord compromise and resultant L’hermittes phenomena during neck movement. This is characterized by a brief, shocklike sensation traversing the spine and extremities. It may occur unilaterally or bilaterally. A position of cervical rotation combined with extension may elicit radicular complaints and L’hermittes phenomena due to central and lateral stenosis (myeloradiculopathy). The toes are often upgoing in response to plantar stimulation, representing a positive Babinski’s response. Multilevel cervical spondylosis with lateral stenosis may present with reduced or absent upper extremity muscle stretch reflexes (MSRs) with preservation or magnification of lower extremity MSRs. In rare cases, the patellar MSR may be the only hyperreflexive MSR due to multilevel cervical radiculopathy and peripheral neuropathy (lower motor neuron lesions) in the elderly patient with CSM. A normal jaw MSR helps rule out more cephalad compromise of the descending corticospinal tract. Abdominal reflexes

FIGURE 4.3 Sagittal T2-weighted image of the cervical spine in a patient with cervical spondylotic myelopathy. Note the marked spinal canal narrowing in the sagittal dimension, especially at C4 and C5. There is also some high signal intensity within the cord, consistent with injury at this level from the narrow canal.

may be diminished with CSM but do not correlate well with degree of lower extremity spasticity.18 Chiles et al.19 retrospectively reviewed the presenting symptoms of his preoperative CSM patients. The most common symptoms were deterioration of hand use (75%), upper extremity sensory complaints (82.9%), and gait difficulties (80.3%). Moderate to severe CSM may be characterized by one of the following presentations: (1) spastic tetraparesis with numbness and extremity hyperreflexia; (2) spastic paraparesis with lesion below C6; (3) spastic tetraparesis, mild or moderate, with deltoid muscle paresis; (4) amyotrophic myelopathic hand with mild long tract signs; or (5) central cord syndrome secondary to cervical spondylosis and trauma.20 4.1.1.5 Diagnostic Imaging Quantitative measurements of the cervical spinal canal on plain X-ray can be helpful indicators of congenital narrowing or acquired stenosis. Plain X-ray does not always accurately reflect osteophytic projection into the central canal that could otherwise be seen on advanced neuroimaging procedures such as CT or MRI. MRI remains the procedure of choice for assessing the effects of spondylosis on the spinal cord. MRI provides the most sensitive means of measuring acute and chronic cord changes secondary to stenosis (Figure 4.3). There is relatively good correlation between clinical severity of CSM and the presence of a region of high T2-weighted MR signal intensity within the cervical cord of symptomatic patients.21-23 Postcontrast imaging should be considered when noncontrast studies are equivocal. Computed tomography and myelography (CTM) have limited use in the evaluation of

Conditions Associated with Myelopathy

CSM. CT can help differentiate bony lesions from soft tissue mass effects such as disk herniation or tumor. CT can also provide an accurate measurement of the spinal cord transverse area, which has been associated with levels of clinical severity (see Section 5.14). 4.1.1.6 Differential Considerations The lower extremity changes characteristic of CSM can occur secondary to myelopathy at other levels. A careful examination should be performed to identify the level of cord involvement. Mid- to lower lumbar spinal stenosis will not typically result in compressive myelopathy, because the conus is rarely located below the level of L1. Conditions that may mimic CSM include thoracic disk herniation, thoracic spondylotic myelopathy, demyelinative disease, primary lateral sclerosis, spinal tumor, and subacute combined degeneration. These conditions can coexist.

4.1.2 LIGAMENTUM FLAVUM THICKENING/BUCKLING In the adult, the ligamenta flava consist of yellow elastin fibers (80%), type I collagen fibers (20%) interspersed between the elastic fibers, and a few spindle-shaped fibrocytes. Magnetic resonance imaging provides a method for examination of spinal ligaments.10 The higher signal intensity of the ligamentum flavum vs. the posterior longitudinal ligament, on T1-weighted or gradient echo images, occurs due to the high elastin content.24,25 The ligamentum flavum extends far laterally to blend with the fibrous joint capsule along the roof of the lateral recess and intervertebral canal, subsequently, minimal thickening or hypertrophy may cause dorsal compression.26 Thickening of the ligamentum flavum can be identified in both the axial and the sagittal MR planes of acquisition.24 The average thickness of the ligamentum flavum in the lumbar spine is 3 mm.27 Degenerative disk disease results in a loss of vertical disk height (rostrocaudal subluxation) between contiguous spinal motion segments. This decrease in height causes the posterior segment ligaments to infold or buckle.28 Fukuyama et al.29 demonstrated a higher incidence of ligamentum flavum thickening in patients with degenerative spine conditions. Buckling of a thickened or hypertrophied ligament flavum can lead to greater spinal canal compromise.30 Ligamentum hypertrophy occurs as a result of increased mechanical stress in the region. Ligamentous encroachment of the posterolateral aspect of the spinal cord may coexist with degenerative changes occurring within the anterior aspect of the canal, such as tenting of the posterior longitudinal ligament with vertebral disk herniation.

4.1.3 RHEUMATOID ARTHRITIS

AND

MYELOPATHY

Rheumatoid arthritis (RA) is a chronic systemically mediated inflammatory condition associated with progressive

59

damage to synovially lined joints with a loss of cartilage, bony erosion, and ligamentous degeneration. It may involve axial and/or extra-axial joints, although the distal interphalangeal, sacroiliac, and lumbar joints are rarely involved.31 The condition usually afflicts the hand first. Symptoms include articular and periarticular swelling, tenderness, limited range of motion, and morning stiffness. Onset may be slow or rapid. Many other signs and symptoms — such as fatigue, fever, nodules, vasculitis, hematological abnormalities, malaise, and weight loss — may also be associated with RA. Rheumatoid arthritis has been associated with a number of spinal complications which include discitis,32 vertebral body erosion,33 ligamentous erosion,34,35 vertebral instability,34,35 and spinal cord compression.35 Many forms of cervical subluxation can occur. Degenerative and erosive changes associated with RA of the cervical spine usually occur along the subcranial region,36 but this consequence of RA only leads to instability and neurological complications in a small percentage of patients.37 Early in the development of cervical subluxation, symptoms may be limited to neck pain and stiffness. The neurological manifestations include intermittent sensory disturbances, radiculopathy, myelopathy, quadriplegia, and, in rare cases, sudden death. The most common radiographic changes characteristic of RA in the upper cervical spine include atlantoaxial subluxation (AAS), cranial settling (CS), subaxial subluxation (SAS),34,36 periodontoid pannus,34 and atlantoaxial kyphosis.35 RA often results in atlantoaxial instability (AAI) which occurs secondary to weakening, softening, and rupture of cervicocranial junction ligaments.35 AAI is associated with a cumulative inflammatory tissue injury-repair cycle leading to the development of fibrovascular granulation tissue referred to as pannus (Figures 4.4 and 4.5). Erosion of bone occurs where hyperplastic and inflammatory synovium contacts the unprotected interface between joint cartilage and bone. The histologic character and invasive properties of pannus are unique to RA. Pannus can expand and place the cord at risk due to direct physical compression. AAI contributes to the progressive development of AAS often accompanied by an irreducible atlantoaxial kyphosis.35 Cranial settling may then develop accompanied by SAS. Cranial settling is characterized by vertical migration of the odontoid process, which can potentially damage the upper cervical cord and brainstem within the foramen magnum. The combination of pannus formation and excessive vertebral translation associated with instability may contribute to spinal cord compression. Atlantoaxial instability may contribute to the development of pannus. Evidence for this presumption stems from the observation that surgical stabilization of AAI has been associated with rapid reduction of pannus.38 A limited neutral view radiographic study of the cervical spine without flexion and extension views has limited

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TABLE 4.5 Radiographic Measurements in the Assessment of Rheumatoid Arthritis Anterior atlantodens interval Posterior atlantodens interval Atlantoaxial subluxation

FIGURE 4.4 Abnormal soft tissue surrounding the odontoid process of the dens and involving the atlas, representing pannus secondary to rheumatoid arthritis. Note the ventral cord compression with cord deformity. (Midline parasagittal spin echo T1-weighted image through the brain and upper cervical spine.) (Courtesy of Ronald Landau, M.D.)

FIGURE 4.5 Lateral X-ray of the upper cervical spine demonstrating an increased atlantodental interval (ADI), and erosion of the odontoid process of the dens. These abnormalities are secondary to rheumatoid arthritis, causing atlantoaxial instability.

clinical utility in the examination for AAS in the rheumatoid patient. Kauppi and Neva39 reported that radiographic evaluation limited to neutral position views failed to confirm a diagnosis of AAS in 48% of their cases and failed

1/3 A-P cord diameter Compression with abnormal spinal cord signal T1 hypointensity, T2 hyperintensity of cord — moderate T1 hyperintensity, T2 hyperintensity of cord — severe Deformed H-sign • Electrodiagnostic considerations Absolute prolongation of spinal cord conduction time Sensory (SEP) Motor (MEP) Relative prolongation of spinal cord conduction time F-wave amplitude 5% or greater than CMAP amplitude Decreased motor unit recruitment with slow firing rate on EMG • Clinical Findings Grading of spasticity Clonus 2–5 beats >5 beats unsustained Sustained Babinski Extension response of great toe Extension of toes with fanning Atonic or neurogenic bladder MSR hyperreflexia Extremity ataxia Nonsegmental sensory loss

TABLE 5.6 Grading of Muscle Stretch Reflexes: Deep Tendon Reflexes 0 1 2 3 4

Absent Diminished Average (normal) Exaggerated Brisk with clonus

Areflexia Hyporeflexia Average Hyperreflexia Hyperreflexia

The upper cervical cord can be difficult to assess clinically for the localization of myelopathic signs. A variety of clinical procedures can be utilized to evaluate the presence of an upper motor neuron lesion presentation involving

2.) Pyramidal tract

4.) Anterior horn

3.) Lateral and anterior corticospinal tracts

5.) Peripheral nerve or root

6.) Myoneural junction 7.) Myofascial 8.) Myopathic

FIGURE 5.1 Sites where potential compromise will result in muscle weakness. (Copyright J.M. True, D.C.)

the upper extremities (Figure 5.2). The scapulohumeral reflex described by Shimizu et al.2 is a C1–C4 innervated MSR that may be beneficial for localizing high cervical cord lesions. The test is performed by having the patient sitting comfortably, with arms hanging limp at the patient’s side. The examiner taps the spine of the scapula and the acromion process with a large reflex hammer (Babinski hammer) and observes response of the arm and shoulder. If there is elevation of the scapula and/or abduction of the humerus, the reflex is considered hyperactive. Two of the most reproducible pathological signs of the upper extremities are the Hoffmann’s and Tromner’s signs. The Hoffmann maneuver is performed by supporting the patient’s hand with the wrist slightly dorsiflexed and relaxed. The fingers should be slightly flexed. The middle finger should be fully extended with the distal phalanx firmly held between the examiner’s index finger and thumb. The examiner should then nip or snap the nail

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TABLE 5.7 Scale for Grading Motor Strength and Spasticity Grade Description 0 1

1+

2 3 4

No increase in muscle tone Slight increase in muscle tone, manifested by a catch-andrelease or by minimal resistance at the end of the range of motion (ROM) when the affected part(s) is moved in flexion or extension Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the ROM More marked increase in muscle tone through most of the ROM, but affected part(s) easily moved Considerable increase in muscle tone; passive movement difficult Affected part(s) rigid in flexion or extension

Source: Based on Ashworth, B., Preliminary trial of carisoprodol in multiple sclerosis, Practitioner, 192, 540, 1964. With permission.

patient’s relaxed hand. The examiner should grasp the middle phalanx of the third digit. With the middle finger of his or her other hand, the examiner should tap the volar surface of the distal phalanx. The sign is considered positive using the same criteria as the Hoffmann’s sign. A positive Hoffmann’s or Tromner’s sign is suggestive of a corticospinal lesion at or above the fifth or sixth cervical level, but an isolated Hoffmann’s or Tromner’s sign in the absence of other myelopathic signs or symptoms does not confirm a spinal lesion. The examiner should always attempt to correlate with additional long tract signs, diagnostic imaging, and lab work if necessary. Denno and Meadows3 described a Hoffmann’s sign with an additional dynamic component performed by having the patient flex and extend his or her head and neck multiple times to tolerance. These researchers called this test a dynamic Hoffmann’s sign vs. a static Hoffmann’s sign when the neck was not moved. The dynamic Hoffmann’s test may help to elicit upper motor neuron lesion signs in patients with a negative static Hoffmann’s sign and thus increase the sensitivity of the clinical neurological exam.

5.2 SUPERFICIAL REFLEXES AND REFLEXES OF SPINAL AUTOMATISM

Jaw reflex (Brainstem)

Scapulohumeral reflex (Shimizu) (C1-C4 or C5)

BLIND ZONE

Biceps reflex (C5, C6)

FIGURE 5.2 Neurologic lesions high in the cervical cord are difficult to isolate by hyperactive reflex centers, unless the clinician evaluates the scapulohumeral reflex (Shimizu). (Adapted from Shimizu, T., Shimada, H., and Shirakura, K., Scapulohumeral reflex (Shimizu): its clinical significance and testing maneuver, Spine, 18, 2182–2190, 1993. With permission.)

of the patient’s middle finger, inducing brisk forcible flexion of the finger. If this maneuver is followed by flexion of the index finger and adduction of the thumb, the response is referred to as the Hoffmann’s sign. If only one finger responds, this is referred to as an equivocal sign. The Tromner maneuver is an alternative way to evoke a similar response. The examiner should again hold the

Superficial reflexes are those reflexes that respond to stimulation of the skin or mucous membranes. Threshold stimulation can usually be evoked with a cutaneous stimulus such as a stroke with a blunt or sharp object. For this reason, superficial reflexes are often referred to as cutaneomuscular reflexes. Common superficial and pathological reflexes that are easy to evaluate include the abdominal, gluteal, cremasteric, scapulohumoral, and Hoffmann’s responses (Figure 5.3). Unlike the MSR, these responses have an ascending reflex arc extending to the cerebral cortex, a spinal reflex arc, and a descending cortical contribution via the corticospinal tract; thus, a corticospinal tract lesion may interrupt those descending influences to the anterior horn, and a skin stimulus will subsequently result in decreased or absent muscular response caudal to the level of the lesion. If the level of cord compromise is distal to the decussation of the medullary pyramids, loss of the superficial reflex response will be apparent on the ipsilateral side. The dissociation of muscle stretch and superficial reflexes is an important clinical presentation in the workup of the potential myelopathic patient. Distal to the segmental level of corticospinal tract compromise there will be an ipsilateral exaggeration of the MSR and a diminution or absence of the superficial reflexes (Figure 5.3). Occasionally, the abdominal reflexes are preserved in the presence of corticospinal tract disease. This may occur with familial spastic paraparesis and with some transverse spinal cord lesions. Many spinal cord lesions are incomplete; consequently, evocative positioning or combined maneuvers

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Cremasteric reflex. The examiner strokes the medial thigh, the testicle normally elevates on the same side of stimulation.

Abdominal reflex. The examiner strokes the abdomen in all quadrants, the umbilicus normally deviates to the direction of quadrant tested.

Abnormal response: Absence of testicular elevation.

Abnormal response: Absence of umbilical movement in any quadrant.

Examiner touches anus. In the normal patient, the sphincter contracts.

Anal wink reflex

S3 S4 S5

Anal contraction

Abnormal response: Absence of anal contraction FIGURE 5.3A Superficial reflexes: abdominal, anal wink, and cremasteric. (Copyright J.M. True, D.C.)

may be required to elicit the latent abnormal response. Repetition may progressively facilitate the superficial response, providing additional insight as to whether dissociation of the reflexes truly exists.

The superficial reflexes can be exaggerated in a variety of conditions. Hysteria may result in facilitation of the MSR and the superficial response. The superficial reflexes may be exaggerated with parkinsonism and in other

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Scapulohumeral Reflex (Shimizu) Examiner taps spine of scapula or acromion.

Abnormal response: arm abducts or moves, or scapula elevates.

TABLE 5.8 Variations of Toe Response to Plantar Stimulation in the Myelopathic Patient • • • •

Hoffmann's Reflex or Sign Examiner pinches or flicks the patient’s finger tip

Unilateral unresponsive toes Upgoing toes without fanning Isolated extension of big toe Slow tonic upgoing toes with fanning of toes (+ Babinski’s sign)

The crossed extensor reflex is associated with partial or incomplete spinal cord lesions. Stimulation of the leg or foot produces flexion of the same extremity and extension of the contralateral extremity. In severe spinal injury, after the initial episode of spinal shock has subsided, a more exaggerated flexion spinal automatism may occur, called the mass reflex. This spinal reflex occurs following distention of the bladder or from stimulation of the feet or legs. Contraction of the abdomen, sweating, and piloerection below the level of the lesion, along with evacuation of the bowels and bladder and hip flexion, are associated with the mass reflex.

5.2.1 BABINSKI’S RESPONSE

An abnormal response is present if the patient’s index finger and thumb flex. FIGURE 5.3B Pathological superficial reflexes: scapulohumeral (SHR) (Shimizu), and Hoffmann. (Copyright J.M. True, D.C.)

extrapyramidal disorders. The examiner must always investigate other potential signs and symptoms to help confirm or eliminate the possibility of myelopathy. In the SCI patient, a variable degree of spinal automatism is usually present. These spinal-mediated defense reflexes occur as the result of loss of descending inhibitory control of muscle action, following spinal injuries or lesions. The flexion withdraw reflex is the most commonly observed spinal automatism. This reflex process is identical to Babinski’s sign, only more pronounced.4 In complete or near-complete spinal cord lesions, the flexion withdraw reflex can be elicited by stimulating the foot, leg, or toes. The reflex produces varying degrees of hip and knee flexion, dorsiflexion of the ankle, and dorsiflexion of the great toe with fanning of the small toes. The reflex may be reproduced from any type of stimulation, such as pinching, stroking, deep pressure, and, in some patients, by light touch of the extremity.

In the normal individual, stimulation of the plantar surface of the foot by stroking with a blunt pointed object produces a downward twitch of the toes, clinically referred to as downgoing toes. The smaller toes usually respond with a greater degree of flexion than the great toe, and the response is usually brisk. It is important to compare the right and left responses when examining a patient with suspected myelopathy, as a significant side-to-side difference may be an initial sign of an early or subtle lesion (Table 5.8). The plantar reflex is innervated by the fourth lumbar through the second sacral segments via the tibial nerve; thus, lumbosacral polyradiculopathy, lower extremity polyneuropathy, or tibial mononeuropathy will lead to a diminished plantar response on the involved side, but the toes should not be upgoing. Compromise of the corticospinal tract, however, leads to an inversion of the normal downgoing toe response. Stimulation of the sole of the foot will result in dorsiflexion of the great toe and fanning of the toes (Figure 5.4). The extension response of the big toe is typically quite evident. The extension and fanning of the toes is the Babinski’s sign. The extension response may be followed by a flexion response. A variety of extensor or Babinski’s responses may occur. The response is dependent upon a number of variables that include the degree of stimulation and severity of corticospinal tract compromise. Variations include isolated extension of the big toe and extension of the big toe with simultaneous plantar flexion of the small toes. Occasionally, plantar stimulation may be followed by an exaggerated proximal

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Normal response: Examiner strokes sole of foot in the depicted pattern. Toes normally twitch in flexion.

Babinski’s sign present: The patient’s toes fan apart or the great toe extends.

Abnormal response

Ankle clonus response: Examiner pulls up on the patient’s foot brisklydorsiflexing the foot.

Abnormal response: The foot reflexively plantar flexes with multiple down beat contractions.

FIGURE 5.4 Pathological signs of pyramidal tract compromise. Babinski and clonus. (Copyright J.M. True, D.C.)

response with ipsilateral dorsiflexion of the foot and flexion of the knee and hip. With an incomplete corticospinal tract lesion a Babinski’s response may or may not be evident. Having the patient turn his or her head to the side opposite plantar stimulation can occasionally reinforce a Babinski’s sign. This protocol may be helpful in the evaluation of an otherwise latent response. Additionally, pseudo-Babinski’s responses may occur in the absence of corticospinal tract disease. Plantar hyperesthesia can lead to an exaggerated response. In the presence of a true Babinski’s sign there is palpable tonic or clonic contraction of the hamstring muscles. This does

not occur in the presence of a pseudo-Babinski’s sign. The examiner may need to palpate the hamstring muscle groups while performing plantar stimulation. With lesions of the primary motor region of the cortex and the premotor area, there may be a greater extensor response of the toes to plantar stimulation. If the ipsilateral basal ganglia and corticospinal tract are compromised, there may not be a toe extensor response; therefore, an intact basal ganglia appears to be important to the extensor response. Toe extensor responses are normally seen in newborn infants until 18 to 24 months of age. A positive Babinski’s sign is often paralleled by the reduction of

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(A)

(B)

Jaw jerk unchanged

Upper extremity intact Site of cord transection

10

Biceps jerk unchanged Motor and sensory level at T10

-

-

+

+

Most intercostal muscles intact

Superficial abdominal reflexes absent in lower quadrants Sensory loss up to T10 dermatomal level

Lower body paralyzed (paraplegic) Knee jerk 3+ Ankle jerk 3+ Babinski's signs

FIGURE 5.5 Spinal cord, vertebral, and clinical levels. (A) Note the disproportion between the spinal cord and spinal column; below the cervical region, the cord segments are progressively rostral to the vertebral segments. This cord ends at approximately L1–L2 (usually T12–L2). The site of a lesion transecting the spinal cord is shown at cord segment T10. Note that sacral vertebral segments are fused; the roots exit via foramina, not interspaces. (B) A clinical level at T10 with motor, sensory, and reflex markers indicated. After initial spinal shock, deep tendon reflexes in the legs are hyperactive and extensor plantar signs (Babinski’s signs) are present. Superficial abdominal reflexes are present in the two upper quadrants (above T10, marked by the umbilicus) but absent in the two lower quadrants. Descending sympathetic and parasympathetic pathways in the cord (not shown) are also disrupted (but descending sympathetic fibers leaving the cord above T10 to enter the sympathetic chain are preserved). (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, 1993, p. 256. With permission.)

rapid or skilled movements of the foot. A Babinski’s sign can occur in the absence of disease, examples include stages of deep sleep, during deep anesthesia, and in occasional severe states of drug abuse or intoxication. The Babinski’s sign has often been referred to as one of the most important signs in clinical neurology.4 It can be used to indicate the presence of disease along the corticospinal system extending from the cortex through the descending pathways to the anterior horn. Additional maneuvers can be performed to elicit an extensor response in the presence of corticospinal tract disease. Common maneuvers include Chaddock’s sign, which is evoked by stimulating the lateral aspect of the foot; Oppenheim’s sign, elicited upon applying heavy stroking pressure along

the anterior surface of the tibia, and Gordon’s sign, elicited when squeezing the gastrocnemius in the patient with pyramidal disease. The clinician should always evaluate for paresis or paralysis of foot and toe dorsiflexors prior to the evaluation of plantar responses. A loss of the ability to dorsiflex the toes can mask what would be a positive Babinski’s sign. Common causes for a loss of dorsiflexion include an ipsilateral L4 and L5 polyradiculopathy and/or a peroneal mononeuropathy. The examiner should always refer to questionable findings by describing the response characteristics. This becomes extremely important if there is deterioration or improvement in the response of the patient with mild pyramidal tract disease (Figure 5.5).

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5.3 SENSORY ABNORMALITIES In the spinal cord, the sensations of pain and joint position sense are carried in different fiber tracts and are physically separated; therefore, a solitary lesion may only involve one sensory tract. However, complete transverse spinal cord lesion will eradicate all sensory modalities below the level of the lesion. When an SCI is unilateral, the sensory loss is often dissociated. Sensory dissociation refers to the loss of some modalities with sparing of others. For example, sensory dissociation occurs in the presence of a lateralizing spinal cord lesion. The laterally expanding mass produces an ipsilateral loss of vibratory perception and kinesthesia due to posterior column and spinocerebellar tract interruption. Additionally, contralateral loss of pain and temperature sensation occurs one to two dermatomal levels below the actual cord level of the lesion because the spinothalamic tract crosses one to two levels higher than the level of dorsal root entry to the cord. Anterior spinal cord syndromes often result in a bilateral loss or diminishment of pain and temperature perception with the preservation of posterior column modalities such as kinesthesia and vibratory perception. An expansile lesion within the central portion of the spinal cord initially compromises the crossed spinothalamic fibers, resulting in impaired pain and temperature perception, initially preserving the corticospinal tracts and the posterior columns. A central intramedullary lesion may expand to eventually compromise these regions but the initial presentation is instead one of sensory dissociation. Posterior spinal cord compromise will result in initial sparing of pain and temperature with impairment of kinesthesia and vibratory perception. The sensory presentation characteristic of a hemimyelopathy usually includes the preservation of touch, but the loss of proprioception, vibration, pain, and temperature sensation below the level of the lesion.5 An expanding lesion in the cervical spine may result in a rising sensory level deficit, which may initially mimic a polyneuropathy (Figure 5.6).

5.3.1 ATAXIA Injury to sensory pathways of the central nervous system leads to a loss of limb awareness, loss of joint position awareness, and a loss of the ability to efficiently modulate voluntary and involuntary muscular activity. The term “ataxia” refers to the degradation of movement and impaired control of movement secondary to sensory compromise. The patient with a spinal ataxic gait will demonstrate a toe-out, wide-based stance; choppy overcompensated leg movement during ambulation; and a tendency to tap the foot (double tap sign). The patient compensates for the decreased sensibility by greater visual scanning of the environment. The degree of ataxia can be magnified by having mildly ataxic patients close their eyes while

TABLE 5.9 Disorders Associated with Central Nervous System Pain • • • • • • •

Central post-stroke pain Epilepsy Parkinson’s disease Multiple sclerosis Spinal cord injury Syringomyelia Syringobulbia

attempting to walk a straight line or while running the heel down the shin. These patients use visual cues as compensation for the decreased sensory (proprioceptive) input from the skin and musculoskeletal tissues.

5.4 SPINAL CORD INJURY PAIN Pain is exceedingly common following SCI (Table 5.9). Patients with cervical-level SCI frequently have neck pain radiating into the shoulders. These pains are a combination of nociceptive and neuropathic pain production. Pain in the acutely injured patient is primarily nociceptive pain from direct injury to pain afferents. Acute injury pain occurs from damage to the vertebral column, nerve roots, and soft tissues. During rehabilitation, nociceptive pain frequently occurs from poorly fitting orthoses or halo fixators as well as concomitant disk and musculoskeletal injury. One of the consequences of SCI is the development of central pain. This type of pain is neuropathic and does not involve the activation of peripheral nociceptors. Central pain is a common effect of injury to the spinal cord and brain.6 The majority of central pain states seen in clinical practice occur following SCI. The incidence of central pain is highest following cord injury and lowest following stroke. A lesion producing neuropathic pain mechanisms may be located anywhere in the CNS, from the spinal cord dorsal horn to the cerebral afferent processing of the spinothalamic pathways including spinoreticulobulbothalamic and spinomesencephalic projections.

5.4.1 LHERMITTE’S SIGN Lhermitte’s sign is one of many presentations that suggest myelopathy (Table 5.10). The Lhermitte’s sign is the report of an electric shocklike or painful perception into the extremities or along the spine during antiflexion of the cervical spine. The Lhermitte’s sign often occurs in the presence of focal traumatic or demyelinative disorders involving the spinal cord (Table 5.11). Neoplastic disease compromising the spinal cord may also contribute to a Lhermitte’s sign. The mechanical stretching of the irritated spinal cord and thecal membranes facilitates axonal discharge and

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(A) Expanding lesion at C4

4

(B) Rising sensory levels Sensory level at cord level of lesion (C4) T2 levels extend on to arms Next, an obvious sensory level on the trunk (T7)

Area of abnormal sensation rises to L1

Initial dorsal column symptoms and signs simulate polyneuropathy from the frontal aspect

FIGURE 5.6 Rising clinical sensory levels due to an expanding cord lesion. (A) Spinal cord and column showing C4 location of cord lesion. (B) Clinical progression is shown sequentially, from distal to more proximal sensory symptoms and signs. Distal involvement might be mistaken for a polyneuropathy (from the anterior aspect), but note the asymmetry. The medially placed C4 lesion in the posterior columns at first affects only those fibers (fasciculus gracilis) that come from the lowest lumbosacral segments and has yet to involve fibers originating from higher dermatomes. As the lesion expands at the C4 level to involve more and more of the posterior column fibers, the clinical level ascends to L1, to T7, then to T2, and finally to the level of the spinal cord lesion (C4). (In reality, the rising sensory levels usually are not so well demarcated nor so symmetrical, and do not “jump” from one level to another.) Other long tract signs, as well as segmental signs at the level of the lesion, may also be noted in some cases. (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, 1993, p. 312. With permission.)

ephaptic transmission. Cervical flexion combined with a Valsalva maneuver or a supine straight leg raise may help elicit a “slump maneuver” Lhermitte’s sign. Dysesthesia occurring in the legs with cervical flexion is strongly suggestive of cervical myelopathy. Arachnoiditis, multiple sclerosis, and cervical radiculopathy are a few of the more common disorders that can produce a Lhermitte’s sign.

5.5 NEUROGENIC CLAUDICATION Neurogenic claudication of spinal cord origin should be distinguished from claudication secondary to peripheral arterial disease. Neurogenic claudication is characterized by progressive paresis of the lower extremities occurring during exertion. The symptoms are generally relieved by rest. During the early stage of spinal neurogenic claudication, the

lower extremity weakness may be unilateral, progressing to become bilateral. Progressive paresis during exertion is often accompanied by sensory complaints of paresthesia or dysesthesia. Unlike the claudication secondary to cauda equina impairment or arterial insufficiency, neurogenic spinal cord claudication tends to be less painful. As the condition progresses, a lower level of physical exertion is required to induce symptoms. An identifying feature of neurogenic claudication of spinal cord origin is the change in the postexercise from pre-exercise neurologic examination. After a brief period of exercise there may be muscular spasticity and hyperreflexia of the lower extremities, which may not have been noted prior to exercise. This has been referred to by Verbiest as “Afternoon Babinski’s.”7 The lower cervical spine is the most common site of myelopathy resulting in neurogenic claudication. It is not uncommon for the patient

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TABLE 5.10 Correlative Signs of Myelopathy

TABLE 5.12 Autonomic Dysregulation in Myelopathy

• • • • •

• • • • • • • •

• • • • • • •

Inverted radial reflex Finger escape sign Deficient repetitive hand closing Hoffmann’s sign Hoffmann’s sign (dynamic Hoffmann’s sign) during cervical flexion or extension Lhermitte’s response Disassociated MSR (hyporeflexia + hyperreflexia) Ataxic gait Spastic paresis Diminished or absent superficial abdominal reflexes Babinski’s response Impaired fine motor control

TABLE 5.11 Myelopathic Conditions Associated with Lhermitte’s Sign • • • • • • • • •

Multiple sclerosis Cervical spondylosis Cervical disk herniation Spinal metastasis Subacute combined degeneration cis-Platin therapy Cervical radiation therapy Post-traumatic syndrome Herpes zoster

to have corresponding upper extremity radiculopathic signs and symptoms with a history and examination suggestive of neurogenic claudication. When neurogenic claudication arises from the thoracic region, it is usually the lower region.

5.6 SACRAL SPARING In patients with confirmed cord injury, the most reliable indicator of the return of spinal cord function is sacral sparing. Injuries that involve the central aspect of the lower cord in the lumbar enlargement region may not injure axons of the sacral-innervated structures. Sacral sparing suggests a partial lesion and a greater possibility of the return of bladder function, bowel function, and lower extremity muscle strength. In the nontraumatic patient, sacral sparing occurs with intramedullary lower cord tumors. Tests to evaluate sacral sparing include anal and sphincter reflex, flexion strength of the hallux, and perianal sensibility to pinprick. In concordance with Comarr’s findings,8,9 Katoh et al.10 found that in the longterm evaluation of cervical SCI patients, those with preservation of pinprick sensation between the level of the injury and the sacral dermatomes shortly after injury

Urinary sphincter dysfunction Rectal sphincter dysfunction Trophic skin changes Vasomotor instability Sexual dysfunction Anhidrosis Impaired temperature control Autonomic dysreflexia Hypertension Bradycardia Seizures

recovered the most motor function, with 75% of the patients regaining the ability to walk. This pattern of sensory sparing predicted a statistically significant better motor outcome than other patterns of sensory sparing.

5.7 AUTONOMIC AND OTHER SYSTEM CONSIDERATIONS The autonomic nervous system (ANS) plays an intricate role in the control and modulation of the cardiovascular system. Myelopathy can lead to altered autonomic regulation (Table 5.12). Complex neuronal connections from higher CNS centers such as the forebrain, hypothalamus, and brainstem send descending influence to the spinal cord to modulate sympathetic and parasympathetic outflow. These higher CNS centers are influenced by peripheral chemoreceptors and baroreceptors located within the carotid arteries, carotid sinus, aortic arch, renal vasculature, and cardiac chamber walls. Circulatory homeostasis requires a balance between the sympathetic and parasympathetic systems. A loss of the delicate autonomic balance alters peripheral vasotone directly through innervation loss and indirectly from a myriad of neurohormonal shifts. The sympathetic nervous system has a strong influence on peripheral vascular resistance via its extension from the interomediolateral cell column of the thoracic spinal cord. Postganglionic sympathetic fibers can mediate vasoconstriction or vasodilation.

5.7.1 ORTHOSTATIC HYPOTENSION Orthostatic hypotension is a common dysautonomia that occurs following SCI above T5–T6 levels. Reduced cardiac output and peripheral vasoconstrictor tone results in a significant drop in blood pressure when the patient is moved, usually from a recumbent position; this reduced output is consequential to a reduction in cardiac return from poor peripheral vascular resistance. The symptoms of hypotension include dizziness, positional syncope, lightheadedness, nausea, and fatigue. Orthostatic hypotension

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tends to be worse during the initial post-injury period of spinal shock. Neurogenic shock can be differentiated from hypovolemic shock by the presence of compensatory tachycardia in the latter. Severe hypotension within minutes or hours after SCI can contribute to further cord injury as the result of arterial insufficiency and spinal cord parenchymal infarction. During the months following acute SCI, the signs and symptoms associated with orthostatic hypotension may improve secondary to the returning function of some necessary compensatory mechanisms.11

5.7.2 DEEP VEIN THROMBOSIS The patient who has suffered acute SCI is at risk for acquiring deep venous thrombosis (DVT) secondary to the drop in peripheral vascular resistance, impaired sympathetic regulation, diminished venous return, reduced cardiac output, and increased coagulability. DVT occurs with significant prevalence in SCI, warranting consideration of prophylactic intervention12 to prevent pulmonary embolism (PE) and pulmonary impairment or death. The individual with chronic myelopathy and associated physical impairment is also at risk for acquiring DVT. This increased risk is primarily due to decreased physical activity and subsequent venous stasis. It occurs most commonly in the lower extremities. The presence of DVT will cause a delay or modification of rehabilitative intervention and places the individual at risk for pulmonary emboli, which may cause respiratory impairment or death. The risk is greatest in quadriplegia patients who already have impaired respiratory function. The possibility of PE should be assessed with a lung scan and/or ventilation–perfusion study. Close serial clinical evaluation of the patient with myelopathy is required, as the patient may be deafferentated and therefore unable to perceive the pain and tissue changes associated with DVT. DVT usually occurs in the lower extremities; because the paralyzed patient will be unable to easily observe the distal extremities, assistence may be required. The high-level quadriplegic patient may not experience chest pain following pulmonary emboli and therefore may not receive prompt medical attention. Depending upon the level of spinal cord involvement, an individual may experience PE pain in the shoulder region that could be mistaken for pain of primary orthopedic etiology. The clinician should carefully assess for rubor, regional hyperthermia, edema, and circumferential enlargement of the limb; all such findings are suggestive of diminished venous return. A circumferential increase in the extremity of as little as 1 to 2 cm should lead the clinician to suspect DVT. These findings may be accompanied by acute pain in the region of DVT. The presence of venous stasis and sustained dermal pressure increases the risk for a decubitus lesion. If DVT is suspected, prompt assessment should ensue. The diagnostic approach may involve a coagulation profile, ultrasonic venography, magnetic resonance

TABLE 5.13 Autonomic Dysreflexia: Emergency Management Algorithm Check blood pressure: Taken every 3 minutes in both arms during autonomic dysreflexia attack and for 2 hours after the attack is resolved. Remove noxious stimuli: Investigate below level of injury. Check bladder: Look for distention and catheterize bladder (anesthetize using 2% Lidocaine jelly). Look for obstructions and clear or replace catheter line. Look for UA infection or other genitourinary disorder. Check bowel: Anesthetize rectum using 2% Lidocaine jelly. Examine for impaction and remove. Check skin: Look for insect bites, tight clothing, pressure ulcers, etc. Assess environment: Check bed and wheelchair cushion for comfort. Avoid rapid changes in temperature. Check for upset gastrointestinal tract: Look for poor food combining, gas, dysbiosis, gastritis, enteritis. Avoid rapid tube feeding and food that is too hot or too cold. Female-specific: Evaluate for menstrual cramping, vaginitis, uterine contractions. Male-specific: Evaluate for reflexogenic erection or genital constriction. Look for catheter problems or constriction. Admit patient for hospitalization: Take this step if blood pressure is uncontrolled or the source of irritation is not found. Source: Based on Stover, S. UAB Model Spinal Cord Injury Care System, Spain Rehabilitation Center, Birmingham, AL, 1999. NIDRR, Office of Special Education and Rehabilitative Services, U.S. Dept. of Education, Washington, D.C.

angiography, impedance plethysmography, or radionuclide scanning.

5.7.3 AUTONOMIC DYSREFLEXIA Spinal cord injuries occurring above the T6 level can result in a serious complication referred to as autonomic dysreflexia (AD), a potentially devastating reaction that, if left untreated, can lead to stroke or death (Table 5.13). The presenting symptoms of autonomic dysreflexia are generally diverse and constitutional. They include a pounding headache, cutis anserina, paresthesia, shivering, flushing and sweating above the level of injury, nasal congestion, desire to void, anxiety, malaise, and nausea.13 Hypertension, bradycardia, bronchospasm, and seizures are lifethreatening signs in AD associated with death or serious morbidity. The main objective sign to monitor in AD is blood pressure. A large increase in blood pressure above 170 systolic requires hospitalization if the source of irritation or exacerbation is not found. Seemingly innocuous stimuli as well as noxious stimuli may produce the overactive sympathetic response, causing a rapid rise in blood pressure with other autonomic signs and symptoms. One of the primary goals should be to find and quickly eliminate or reduce the promoting stimuli. Whenever a patient with SCI above the level of T8 presents with a resting

Assessment of Spinal Cord Injury and Myelopathy

diastolic or systolic pressure 20 mmHg greater than baseline, autonomic hyperreflexia should be considered.14 AD results from impaired modulation of sympathetic activity and/or a loss of descending regulatory influences from the cardiovascular regulatory centers within the medulla. The afferent stimuli leading to a segmentally facilitated response at the spinal cord level usually arise from the viscera. The most common etiologies are defecation, distention of the bowel or bladder, gall bladder disease, and urinary tract infection. Cutaneous sores or lesions creating noxious stimuli may stimulate the syndrome. In the female patient, this may be mediated by fibroid uterine disease.

5.7.4 CARDIAC COMPLICATIONS The patient with acute SCI may require tracheal intervention; this can lead to vagal stimulation mediated by tracheal stimulation and physiological suppression of function, which may cause an autonomically mediated slowing of the heart rate. Bradycardia below 60 BPM will result in decreased pulmonary perfusion, increasing the risk for systemic hypoxia. Extreme bradycardia may lead to cardiac arrest. Electrocardiographic monitoring, pulse volume recording, and pulse oximetry help to identify this potentially life-threatening condition. The individual with paralysis, like the sedentary individual without SCI, is prone to deconditioning and developing hyperlipidemia, elevated low-density lipoprotein (LDL), and a drop in the level of protective high-density lipoprotein (HDL) due to limited physical activity. This change in the blood lipid patterns increases the risk for acquiring coronary artery disease (CAD). The loss of skeletal muscle mass may contribute to impaired glycoregulation and hyperglycemia, thus increasing the risk for tissue glycosylation and related vascular pathology. Cardiac irregularity may occur secondary to the dysautonomic state. Diminished sympathetic influence can lead to a relative state of hyperparasympatheticonia. This may lead to supraventricular or ventricular arrhythmias. Ambulatory electrocardiography may reveal abnormal heart rate variation (R-R intervals) and arrhythmia.15

5.7.5 RESPIRATORY CONSIDERATIONS Cervical or upper thoracic spinal cord SCI influences respiratory control and efficiency; transverse or complete SCI at these levels results in paralysis of respiratory muscles. Many muscles contribute to inspiration, whereas expiration is primarily a passive process that occurs when the intercostal and diaphragmatic muscles relax, returning the diaphragm to its dome shape rising within the chest cavity (Table 5.14). Normal abdominal muscle tone helps to contain the viscera and maintain abdominal and subdiaphragmatic pressures that assist the expiratory excursion of the diaphragm.

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TABLE 5.14 Respiratory Muscles: Innervation Levels Muscle

Cord Level

Action

Diaphragm Sternocleidomastoid Trapezius Scalene Serratus anterior Pectoralis major Erector spinae Intercostal

C2–C4 Acc. N. and C2 Acc. N. and C3–C4 C2–C7 C5–C7 C5–T1 Segmentally dependent T1–T12

Diaphragm excursion Elevates sternum Stabilizes scapula Raises ribs Raises ribs Raises ribs Extends spinal column Segmentally dependent

The greatest degree of respiratory impairment occurs secondary to diaphragmatic paralysis, for it contributes to approximately three quarters of the tidal volume when supine and two thirds of the tidal volume when sitting.16 The most important accessory muscles of respiration are the sternocleidomastoid muscles (SCM), which elevate the sternum, allowing for greater ribcage expansion. After spinal cord compromise, an aggressive rehabilitative approach should be applied to all respiratory muscles that have a corresponding functional spinal cord level. Respiratory impairment will result in increased risk for atelectasis, respiratory infection, and systemic hypoxia. The primary cause of death in acute SCI is respiratory insufficiency.17

5.7.6 BOWEL

AND

BLADDER DYSFUNCTION

Abnormal patterns of micturition and bowel function are common features of moderate to severe spinal cord disease or injury. Disturbances of the bowel and bladder occur in myelopathy due to the loss of suprasegmental facilitatory and inhibitory influences from the pontomesencephalic tegmentum via the reticulospinal tract. Corticospinal pathways also contribute inhibitory influences. Acute spinal cord lesions often result in a state of shock that may be associated with inhibition of the bladder wall, resulting in urinary retention and overflow incontinence. The bladder should not be allowed to retain more than 400 to 500 mL of urine in order to reduce the risk for infection, renal compromise, and autonomic hyperreflexia. As the state of spinal shock resolves and lower extremity muscular spasticity develops, the bladder often becomes spastic, resulting in automaticity and incontinence. This is referred to as the neurogenic bladder or spinal bladder. The patient with myelopathy will not appreciate the degree of bladder fullness, and a rise in intravesical pressure often induces a rapid, reflexively driven emptying of the bladder. The patient can often stimulate the exaggerated bladder response by tapping the abdomen or stroking the inner thigh. This stimulates reflexive detrussor contraction and sphincter relaxation with subsequent emptying of the bladder.

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It is important to note that voluntary micturition is not lost with unilateral spinal cord lesions.18 This is why some patients with spondylotic myelopathy and incomplete cord syndromes do not present with a neurogenic bladder. If the spinal cord is compromised in the region of the conus medularis, a lower motor neuron bladder condition may result. A lower motor neuron lesion results in a flaccid bladder that will distend to the point of overflow incontinence. Sustained urinary retention may result in a medical emergency. A similar pathologic mechanism and presentation in SCI occurs relative to the bowel, producing atony and impaction. The anatomical pathways subserving the bowel are similar to that of the bladder. Parasympathetic innervation occurs at S3–S5. Spinal shock often results in paralytic ileus, and in some cases the colon may progressively dilate to become a neurogenic megacolon. The dilated colon contributes to the risk for fecal impaction and diverticuli. The clinical assessment of the patient with suspected ileus should include careful auscultation of the abdomen, for the patient may not experience any visceral sensation. The anal reflex generally remains intact unless there is a complete transverse cord lesion. Sphincter control of the bowel is lost with SCI. A lower motor neuron lesion (LMNL) occurs when the anterior horn cells of S3–S5 within the conus medullaris or the S3–S5 nerve roots are injured. This LMNL presents with impaired peristalsis, atony, and a flaccid anal sphincter. The loss of anal sphincter tone and control leads to fecal incontinence. Significant bowel or bladder disease may develop without any sensation of pain. The SCI patient should be evaluated for GI or pelvic disease on a frequent basis because of the absence of early subjective indicators of visceral disease.

few of these individuals were able to experience ejaculation or orgasm. In contrast, Comarr8,9 noted that in 150 males with SCI 82% were able to obtain erections; only 1% could ejaculate and have an orgasm. Preservation of pinprick sensation in the sacral dermatomes is a more significant prognostic indicator for the SCI male to recover function of erection and ejaculation than preservation of light touch, perception, or retained volitional motor function of the pelvic muscles. The clinical presence of a bulbocavernosus reflex and/or anal sphincter tone suggests that the individual has retained upper motor neuron sexual function. An individual with an incomplete spinal cord lesion may have normal sexual function. Atrophy of the testicles is relatively common following spinal trauma and can be noted as early as 3 to 4 months after an injury; male SCI patients are often sterile, which in part may be secondary to abnormal temperature regulation. Spinal cord injury above L1 in women generally results in a limited ability to achieve orgasm but fertility is not affected. Female paraplegics who are still menstruating are able to conceive and give natural birth to children. Ohry et al.20 reported that women who suffered an SCI had no significant change in their sex hormone levels when compared to non-spinal-injured women. This aspect of female sexual function typically remains unchanged after an SCI. In complete cord transectional lesions, there is loss of vaginal sensation; however, there may be some emotional satisfaction from intercourse. Women with SCI may attain a state of heightened arousal secondary to tactile stimuli above the sensory level of injury. Few paraplegic women are able to experience orgasms.

5.7.7 SEXUAL FUNCTION

The individual with SCI will lose some sensation below the level of the segmental compromise. This will lead to a reduction or loss of the ability to perceive injury to the skin, thus increasing the likelihood of progressive skin damage. Muscular paresis or paralysis accompanying spinal insult leads to sustained postures and risk for pressure necrosis of cutaneous and subcutaneous tissues. This breakdown of the skin is referred to as a decubitus ulcer. A weight-shifting program must be initiated in order to reduce the risk for complicated skin lesions. The goal of intervention is to prevent skin breakdown, increase tissue tolerance for pressure, and improve skin hygiene.

An ablative injury to the spinal cord above the level of L1 impairs the capacity for voluntary erections in the male subject. There are two primary categories of erection: psychogenic and reflex. A psychogenic erection occurs as the result of descending messages from the brain initiated by voluntary, visual, or auditory arousal. Reflex erection occurs secondary to direct physical contact to the penis or other erogenous areas. The nerves that control the erection arise from the S2–S4 segments of the spinal cord within the conus. Spinal cord insult above these segments impairs the ability to have a psychogenically induced erection, although some of these patients may obtain an erection with physical stimulation. The ejaculatory capacity varies greatly between SCI patients. The ejaculatory process is mediated by multiple spinal segments, and it is usually impaired to some degree with myelopathy. Jochheim and Wahle19 reported that 30 to 75% of SCI male patients with spastic paralysis were unable to obtain an erection. Very

5.7.8 SKIN COMPLICATIONS

5.7.9 PSYCHOLOGICAL CONSIDERATIONS The individual who suffers a SCI experiences a foreverlife-changing experience. He or she will have to learn to adapt to physical and nonphysical limitations. This is often a long and arduous road to travel. Immediately after the injury there is often a period of grief and denial relative

Assessment of Spinal Cord Injury and Myelopathy

to both the severity and chronicity of their presentation. The individual’s hopes and short-term goals may not be realistic. Many have a difficult time conceptualizing the potential permanency of their limitations. As they progress through physical rehabilitation, the physical limitations are realized and greater attention is focused on the ramifications of the spinal injury. In some cases, the degree of disability may be magnified. Realization of the permanency and degree of limitations often precedes moderate to severe depression. The individual may begin to manifest negative behavior towards their therapist, doctors, friends, and family members. The period of initial depression may extend from a few weeks to more than a year. During this time, psychological support is necessary. The support may be limited to a social worker, psychologist, or in some cases psychiatric attention. A team approach may be required to improve the coping skills and enhance the motivation level of the patient with SCI. Underlying psychiatric illness may become manifest or magnified by the onset of myelopathy. Individuals must be motivated to capitalize on the functions they have and must be shown that they can improve their status.

5.7.10 FEVER Spinal cord injury may result in elevated body temperature secondary to numerous etiologies, which include infection and impaired physiologic temperature regulation due to the SCI. The injured patient may be unable to experience symptoms associated with an infection due to the level of SCI placing a greater demand on the expertise of the attending health care team. An undetected infection in an SCI patient can lead to significant complications or death. Respiratory infections are more common during the immediate post-injury period and can contribute to a febrile state. Two to four weeks after SCI, urinary tract infections become a more common cause for temperature elevation. An infected decubitus lesion is not an uncommon cause for a febrile state. Some individuals with spinal cord injury may experience persistent elevation of their body temperature secondary to impairment of physiologic temperature-regulating capacity. The development of a persistent or spiking fever in a patient with SCI should prompt a diligent search for an infectious or otherwise treatable etiology. The workup for infection should include CBC with differential, urinalysis, blood culture, and chest X-ray if necessary. The SCI patient may develop spinal osteomyelitis associated with post-traumatic spinal surgery, requiring appropriate work-up. Radioisotope tagging may be required to identify a potential region of infection within the chest or abdomen. If a fever of unknown origin persists 4 to 6 weeks after the initial workup, the assessment should be repeated prior to assuming the fever is secondary to

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TABLE 5.15 Factors Limiting Joint Range of Motion in Patients with Myelopathy • • • • • • • • • • •

Joint subluxation Adhesive capsulitis Contractures Muscle hypertonicity Spasticity Pain Joint deformity Heterotrophic ossification Neuropathic arthropathy Degenerative joint disease Paralysis/paresis

impaired thermoregulatory mechanisms in the absence of other pathology. The fever associated with SCI-related disruption of temperature regulation mechanisms often improves over time.

5.8 MYELOPATHY AND ASSOCIATED MUSCULOSKELETAL CONDITIONS The workup of the individual with myelopathy is ongoing, due to potential complications and musculoskeletal consequences. It is important that the rehabilitative approach be tailored to the individual’s unique musculoskeletal presentation. No two myelopathic presentations will be exactly the same due to varying degrees of SCI and predisposing peripheral musculoskeletal states. Unidentified progressive musculoskeletal complications will impact the individual’s capacity to participate in physical rehabilitation, subsequently reducing the potential for recovery (Table 5.15).

5.8.1 CONTRACTURES Chronic limb or joint immobilization can lead to physiologic shortening of supportive and contractile tissues, resulting in contractures. Additional causes of contractures include chronic spasticity, unopposed pull of agonist muscle, paralysis, and bodily positioning. The presence of contracture contributes to disability by greatly impairing the ability to perform activities of daily living (ADLs). Risk for contractures can be significantly reduced by implementing periodic assisted range of motion (ROM) exercises, applying various forms of traction, and utilizing specialized beds.

5.8.2 ARTICULAR SUBLUXATION The shoulder is vulnerable to subluxation due to its anatomic configuration and dependence upon surrounding

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

muscles for stability. Individuals with high SCI (above C5) lose the shoulder-stabilizing functions of the deltoid and rotator cuff muscles. Paralysis of periscapular muscles further contributes to shoulder pathomechanics and alteration of the angle of the glenoid fossa. The glenoid fossa tends to take on a lateral and downward angle.14 Paralysis of the supraspinatus muscle contributes to translation and subsequently subluxation of the humeral head. An intact C5 level offers some stabilization to the shoulder, reducing the risk for subluxation.

5.8.3 HETEROTOPIC OSSIFICATION Heterotopic ossification (HO) refers to the formation of bone in abnormal areas, usually within connective tissue between muscle and tendon planes. A relatively common complication of SCI, HO may involve axial and extraaxial joints and tends to occur more frequently around the hip, followed by the knees, shoulders, and elbows. Usually appearing within 1 to 4 months after injury, HO can sometimes take several years to develop.21 Heterotopic bone formation occurring a year or more after SCI may result from tissue injury secondary to infection. During the early stages of HO, the condition may be clinically silent. Progressive HO is often associated with an inflammatory response, edema, focal hyperthermia, and pain affecting the involved joint. The hips are the most frequently involved joint often afflicted within the flexor or adductor areas. The differential considerations are many and include thrombophlebitis, deep venous thrombosis, cellulitis, joint sepsis, osteomyelitis, and fracture. The workup often requires venography and a bone scan. A bone scan can demonstrate HO 7 to 10 days earlier than a plain X-ray. The three-phase bone scan provides the earliest detection. A classification system has been developed differentiating between myositis ossificans and HO.21

5.8.4 OSTEOPOROSIS A common complication of SCI is osteoporosis. This often occurs as the result of immobilization secondary to paresis or paralysis. Osteoporosis results from the rate of bone resorption exceeding that of bone deposition due to inadequent physical loads. The bone loss tends to progress more rapidly during the first year after SCI. The presence of osteoporosis increases the risk for trabecular failure and fracture. Bone injury may occur due to strong involuntary muscle contractions.

5.8.5 NEUROPATHIC ARTHROPATHY Any condition that compromises sensory and neuroregulatory feedback from articular and periarticular structures may contribute to the development of the neuropathic joint. Myelopathic conditions that have been associated with neurosensory deficits and neurogenic arthropathy

include spinal trauma with paraplegia,22-24 tabes dorsalis,25 and syringomyelia.26-28 Syringomyelia may contribute to the development of neuropathic arthropathy (NA) due to compromise of decussating fibers of the spinothalamic tract. Cervical syringomyelia in rare instances may lead to the triad of syringomyelia tardia, paraplegia, and neuropathic arthrosis of the shoulder.29 The shoulder may be susceptible to NA due to the propensity for glenohumeral instability and related cumulative trauma with deafferentation. The sequence of pathological features that characterize NA include deafferentation, distention of the involved joint space due to effusion, ligamentous laxity, biomechanical instability, cumulative destruction of articular cartilage, and hypertrophic and atrophic remodeling of the bony architecture. Severe deafferentation of an articular complex results in impairment of autonomic regulation, poorly mediated periarticular muscle tone, and a loss of reflexive muscular protection, rendering the joint susceptible to cumulative microtrauma. There are three primary radiographic patterns: (1) atrophic, (2) hypertrophic, and (3) a mixed appearance.30

5.9 ELECTRODIAGNOSTIC ASSESSMENT Electrodiagnostic studies such as electromyography, nerve conduction studies, and somatosensory evoked-potential studies are an extension of the clinical examination and should be correlated with information gathered in the history, physical examination, and imaging work-up. Electrodiagnostic testing can be used to evaluate physiologic function of the nerves of the central and peripheral nervous system. A normal electrophysiologic study does not always exclude the possibility that minimal to mild nerve damage has occurred. The primary reasons for performing electrodiagnostic testing include confirming or excluding neurological compromise, localizing neurologic compromise, and determining the extent of neurologic injury. Electrodiagnostic tests often utilized to provide quantitative information after SCI include the compound motor unit action potential (CMAP, or M-response), sensory nerve action potential (SNAP), segmental responses (Hreflex or F-wave), needle electromyography (NEMG), somatosensory evoked potential (SEP), motor evoked potential (MEP), and NEMG in conjunction with bladder function studies. A discussion of bladder studies is found in Section 5.15.3.3. Timing of electrodiagnostic evaluation must be considered in order to avoid false-negative results. Acute injury of spinal cord axons can result in immediate compromise of SEP and MEP latencies and amplitudes. Consequently, these two procedures are good for acute and subacute monitoring of SCI. Muscle membrane instability secondary to denervation may not manifest for 2 to 6 weeks although the needle EMG may reveal reduced motor-unit firing rates and reduced motor-unit recruitment density immediately. The CMAP or M-response may not

Assessment of Spinal Cord Injury and Myelopathy

SSEP tests integrity of the posterior column

From upper extremity

MEP tests integrity of the corticospinal pathway

From lower extremity

To segmental muscles

FIGURE 5.7 Motor evoked potentials test the corticospinal pathway, from cortex to peripheral muscle end organ. (Copyright J.M. True, D.C.)

reflect axonal loss for 5 to 10 days after the onset of myosynaptic degradation and muscle degeneration. After an acute spinal injury, T-reflexes may be absent for many weeks to months.

5.9.1 SOMATOSENSORY EVOKED POTENTIALS Somatosensory evoked potentials test the largest myelinated fibers of the medial lemniscal system, the group 1A muscle afferent fibers and the group II afferent fibers. The SEP response is generated via electrical stimulation of the peripheral mixed nerve and recorded from various locations along the course of the nerve from periphery, spinal cord, and cerebral cortex. Thus, SEPs have the potential to detect CNS pathology involving the posterior columns (Figure 5.7). They have excellent correlation for vibration and joint position sense loss; however, the SEP study is poor for exact localization and it does not specify the nature of the pathology producing the neurophysiologic deficit. SEP studies are commonly used in the intensive care unit or operating room for diagnosis, monitoring, and establishing a prognosis in SCI and cervical spondylotic myelopathy (CSM).31,32 Within general neurological practice, they are also used for the correlation and diagnosis of CSM or posterior column disease.33-39 The most important information recorded from evoked potential studies is the latency, which refers to the time of stimulus to the onset of the recorded waveform. This value varies according to the nerve studied. Latencies vary considerably between upper and lower extremity stimulation, because of the length-dependent variable of nerve conduction: the longer the nerve length, the longer the latency of the response. Both animal and human studies suggest that the SEP components are dependent upon the integrity of posterior column medial-lemniscal pathways.

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Somatosensory evoked potential evaluation can be helpful for the assessment of suspected myelopathy in the patient with impaired vibration or joint position sense. SEP evaluation may help localize a spinal lesion, but the findings will not reveal the type of compromise present. Noel and Desmedt35 reported that sural nerve SEPs were often abnormal in patients with compressive cervical myelopathy. They also report that lower extremity sural testing was more sensitive than upper extremity SEP evaluation. Some researchers report a higher detection rate of CSM using tibial SEPs.34,36,39 It has been suggested that lower extremity SEP procedures may uncover silent myelopathy even in the absence of gross myelopathic clinical findings.34,35 Yu and Jones39 found that SEP studies were occasionally more sensitive than their clinical examination. Snowden et al.37 found dermatomal evoked potentials (DEP) to be a more sensitive indicator of spinal stenosis than needle electromyography (Figure 5.8). Focal compromise of the spinal cord will usually be associated with slowing between two spine recording sites. Diffuse myelopathy or multiple sclerosis often leads to an absent scalp potential. Upper extremity SEP studies can be helpful in the localization of cervical myelopathy. A poor cervical response can be expected with a cord lesion at C6 or C7 to median stimulation. Ulnar stimulation with high cervical recording can provide a good screen of peripheral to central conduction across the cervical cord.40 High cervical lesions, which spare the recording of cervical potentials from a lower level, are often associated with attenuation of scalp responses. Somatosensory evoked potential abnormalities may be present in patients with a number of spinal disorders, including intrinsic expansile cord lesions such as syringomyelia. Abnormal SEPs have been reported in patients with multiple sclerosis, hereditary spinocerebellar degeneration, subacute combined degeneration, and hereditary spastic paraplegia. The SEP study should be considered a valuable part of the myelopathic risk profile.

5.9.2 MOTOR EVOKED POTENTIALS Motor evoked potentials can be obtained by stimulating the neural pathways over the cortex or over the spine. The former is often referred to as transcortical magnetic stimulation. MEP assessment can be used to evoke the central and peripheral motor pathway allowing for measurement of the motor conduction time from the cerebral cortex to the muscle or from the spine to designated muscles. Motor evoked potentials are usually recorded at extremity muscles. MEP assessment can lead to the measurement of central motor conduction time (CMCT). Chokroverty et al.41 and Jarrat42 reported that some patients with cervical myelopathy demonstrated abnormal central conduction characteristics after transcortical stimulation. Other conditions associated with prolonged

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

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FIGURE 5.8 Somatosensory evoked potentials test the posterior columns by stimulating the peripheral nervous system or extremity mixed nerves and recording the impulse at various locations as it ascends to the cortex. (Copyright J.M. True, D.C.)

CMCT include myelopathy associated with rheumatoid arthritis, cervical stenosis, post-traumatic syringomyelia, and complete and incomplete thoracic cord injuries.

MEP abnormalities often do not improve after surgical intervention for CSM and are more likely to improve after shunting for syringomyelia.43

Assessment of Spinal Cord Injury and Myelopathy

115

3. Stimulation of alpha motoneurons producing an efferent volley F-wave

2. Antidromic conduction

4. Orthodromic conduction

1. Stimulation at the wrist

5. Recording from the distal innervated muscle

FIGURE 5.9 The F-wave is valuable for evaluation of cord injury because the central component of the test depends on activation of intact alpha motor neurons. (Copyright J.M. True, D.C.)

Transcortical stimulation (TCS) and F-waves have been used to serially study the postsurgical neurological improvement of myelopathy from disk herniation. This study44 demonstrated that functional motor improvement was accompanied by an increase in spinal cord motor conduction velocity in patients with mild neurological impairment after surgery, whereas no definite change was seen in patients with moderate or severe neurological impairment. TCS has been evaluated in incomplete SCI; however, one study found no correlation between the TCS data and clinical assessment beyond the initial recovery period.45

5.9.3 LATE RESPONSES The three general types of late reflexes beneficial for evaluation of central neuronal integrity are the F-wave, Hreflex, and the T-reflex. Obtaining baseline segmental responses can be used to help monitor myelopathic changes. Useful measurements include minimal H-reflex and F-wave latencies, F-wave chronodispersion, F-wave persistence, and H/M and F/M amplitude ratios.46 The Fwave response is a late response that occurs following the compound motor action potential. It is a recurrent discharge of antidromically activated alpha motor neurons (Figure 5.9). The F-wave can be used to assess the effects of supraspinal and segmental influences on the central state of the alpha motor neuron population within the spinal cord. F-waves are often absent in patients with spinal shock, reduced in persistence in patients with acute SCI without spinal shock, and normal in persistence in patients with chronic SCI.47 During spinal shock, the loss of tendon tap reflexes and flaccid muscle tone were associated with a low persistence of F-waves and loss of flexor reflexes, whereas H-reflexes were readily elicitable. During the transition to spasticity, the reappearance of tendon tap reflexes and muscle tone and the occurrence of spasms were associated with the recovery of F-waves and flexor reflex excitability.48,49 The F-wave amplitude may be increased in patients with chronic myelopathy due to compromised descending

inhibitory influences. A reproducible, abnormally large amplitude F-wave may occur ipsilateral to the side of myelopathy. The F-waves are typically larger in amplitude than the uninvolved side coinciding with the side of muscular spasticity.50,51 Serial F-wave studies may occasionally be helpful in the assessment of therapeutic efficacy in the myelopathic patient. H-reflexes are often absent or markedly suppressed in patients with spinal shock within 24 hours of injury; however, the response will usually recover to normal amplitudes within several days post-injury. This recovery will occur despite the fact that the F-wave response will be absent for several weeks post-injury. The H-reflex can be used to monitor the development of hyperactive muscle stretch reflexes after the onset of myelopathy and associated upper motor neuron (UMN) weakness. Deep tendon reflexes (T-reflexes) are also proportionally more depressed in spinal shock than H-reflexes. The H-reflex will be elicitable for days or weeks before the development of clinical reflexes.47 The maximum H-reflex amplitude can be placed over the M-wave amplitude (H/M ratio) in order to calculate the magnitude of the spinal motoneuronal response that responds through reflexive stimuli. H/M ratio increases parallel to the development of muscular spasticity.52 Similar findings have been reported using a F/M ratio.51 The T-reflex is another valuable late reflex study to record from a patient with suspected or confirmed myelopathy. In a study by Karandreas et al.,53 pathological Treflexes were found in 73.1% of the patients, while EMG — which was the next more effective method — was positive in 38.5% of the cases. Eight pathologically delayed T-waves were recorded from muscles with clinically normal or even exaggerated reflexes.

5.9.4 NEEDLE ELECTROMYOGRAPHY A pure upper motor neuron lesion characteristically presents with normal insertional activity, an absence of fibrillation potentials, and normal-appearing motor unit action potential morphology. Insertional activity in the muscle

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

may be decreased if there is profound motor loss. At the level of the segmental lesion there may be compromise of the alpha motor neuron pool, thus creating a lower motor neuron lesion. This may result in muscle denervation changes. Acute and subacute EMG changes are characterized by insertional instability and spontaneous discharges such as sharp waves and fibrillations. Chronic muscle denervation changes are characterized by large or prolonged-duration polyphasic motor unit action potentials and reduced recruitment density. Electromyogram changes corresponding to spinal segments below the level of compromised gray matter will present with a pattern of corticospinal loss. Myelopathic compromise of the corticospinal tract results in diminished descending input to the alpha motor neuron pool. This loss of UMN drive subsequently contributes to a slight delay in motor unit response, a reduction of motor unit recruitment (firing) density, and slowed motor unit firing rate. Excited motor units fire slower than expected for the degree of contraction and voluntary effort. This stands in contrast to the characteristic rapid motor-unit-firing pattern of lower motor neuron involvement such as radiculopathy. Fasciculation potentials without evidence of other LMNL electromyographic characteristics may appear in the lower extremities with cervical myelopathy. Lower extremity fasciculations have been abated with cervical surgical decompression procedures.54,55 Fasciculations are likely to occur secondary to the loss of suprasegmental inhibitory influences. Mild passive muscle stretch performed during needle recording may increase the occurrence of spontaneous fasciculations or a cramp discharge in the presence of mild spasticity.

5.9.5 SENSORY NERVE CONDUCTION STUDIES Sensory nerve conduction evaluation can help determine whether there is a preganglionic or postganglionic sensory lesion. Postganglionic injury resulting in sensory axonopathy will lead to a reduction of the sensory nerve action potential amplitude and area under the waveform. In contrast, a lesion proximal to the dorsal root ganglia (DRG) will spare the distal axons, therefore preserving the distal SNAP.

5.9.6 MOTOR NERVE CONDUCTION STUDIES Evaluation of the compound motor unit action potential can provide insight relative to the degree of lower motor neuron (LMN) compromise with the anterior horn after SCI or chronic compressive myelopathy. Reduced CMAP amplitude and decreased area suggest a loss of motor axons, although muscle atrophy can also result in similar CMAP appearances. Needle electromyography can help differentiate the presence of disuse vs. denervation atrophy of a muscle. Collateral motor axon sprouting from spared axons and related muscle fiber reinnervation can contribute to some recovery of CMAP amplitude. It has

TABLE 5.16 Possible Magnetic Resonance Findings in Acute Spinal Cord Injury • • • • • • • • • • • • • • • •

Vertebral subluxation Vertebral dislocation Vertebral lithesis Ligamentous avulsion Vertebral fracture Bone edema Disk herniation, extrusion, and sequestration Extradural hematoma Intradural hematoma Intramuscular hematoma Intramedullary hemorrhage Intramedullary edema Intramedullary cavitation Cord enlargement Cord compression Cord transection

been estimated that a motor axon can reinnervate neighboring denervated muscle fibers, increasing the size of the motor unit as much as two- to fourfold.56

5.10 DIAGNOSTIC IMAGING The goal of imaging is to evaluate anatomy and tissue function without utilizing invasive and potentially harmful techniques whenever possible. There are three primary goals in imaging of the spinal lesion: (1) localization, (2) characterization, and (3) assessment of secondary compromise and potential compromise. Effective imaging requires magnification of the inherent differences between tissues by using methods that provide contrasting information. This information may be anatomic, biomechanical, or biochemical in nature. Numerous imaging modalities, protocols, and techniques are now available, each providing a unique window into the body (Table 5.16). Rapidly advancing technology brings us closer to the physiology, biochemistry, and assessment of the dynamic properties of tissue at the microstructural level. Several of the existing and potential applications of imaging in the assessment of SCI, myelitis, and chronic myelopathy are described below; this discussion is meant to provide a brief introduction, and the reader is referred to neuroradiology texts for a more detailed treatment of the methods available.

5.10.1 MAGNETIC RESONANCE IMAGING Magnetic resonance imaging (MRI) is a noninvasive and relatively safe technology. The signal used in MRI arises primarily from protons within the body’s water, although other constituents are involved as well. Energy given off

Assessment of Spinal Cord Injury and Myelopathy

Canal to Body Ratio = 1:1

117

A

B

AP Canal Diameter 13 - 22 mm

D

C A A- 1 mm Epidural Space B- 1 mm Dura/Arachnoid C- At Least 1 mm Subarachnoid Space D- 8-9 mm AP Cord Width

FIGURE 5.10 MRI measurements for the determination of available cord space within the spinal canal. Measurements A, B, and C should be assessed circumferentially around the cord. (Copyright J.M. True, D.C.)

TABLE 5.17 Conditions Associated with Spinal Cord Enlargement

TABLE 5.18 Contraindications in Magnetic Resonance Imaging

• • • • • • • •

• Relative Claustrophobia Surgical staples • Absolute Pacemaker or other implanted device Confirmed orbital ferromagnetic fragments Ferromagnetic vascular clips Intracranial vascular clips

Intramedullary tumor Spinal cord infarction Syringomyelia Viral and bacterial infections Multiple sclerosis Intramedullary hemorrhage Intramedullary edema Radiation myelopathy

by the changing spin cycles of tissue protons is influenced by the application of radiofrequencies and pulsed magnetic fields. Each tissue has a unique signal pattern dependent upon the type, quantity, and density of molecular elements. During the MR study, the signals are recorded and encoded to create a multiplanar or dimensional rendering of tissue relationships. Tissues can be identified based on a three-dimensional function of density in addition to their T1 and T2 MR-specific relaxation properties. The major differences between MR and computed tomography (CT) imaging are that in MRI (1) images have complex values of amplitude and phase for each pixel, (2) tissue signals are noninstantaneous and can be constructed over time, (3) image contrast reflects three mechanisms (T1, T2, and density), and (4) Fourier transform data are directly acquired. Magnetic resonance imaging is also the initial test of choice for evaluating the spinal cord because it provides excellent soft-tissue resolution and characterization of tissue properties. MRI can be used to assess the size and volume of the spinal cord (Figure 5.10, Table 5.17). MRI is more sensitive than either myelography or CT in the assessment of intrinsic spinal cord lesions57 and extramedullary pathology. MRI and CT should be considered complementary studies due to the moderate degree of concordance in the differentiation of

disk and osseous pathology.58 Many specialized protocols can be applied in MR imaging, some of which are listed below. MRI is contraindicated in patients with the conditions shown in Table 5.18. 5.10.1.1 Rapid MR Sequencing Echo planar imaging (EPI) has many applications for CNS evaluation, particularly in the brain. EPI protocol allows for more rapid information to generate an image than other common forms of imaging. EPI can literally acquire T2-weighted images within 2 to 3 seconds. Ultra-fast EPI is so quick that it can effectively be used to evaluate physiology; subsequently, it is used to perform functionalactivation MR studies. 5.10.1.2 Turbo Echo MR Sequences Turbospin echo (TSE) sequences are a type of T2-weighted imaging useful for the evaluation of spondylosis and degenerative spinal conditions, because this technique reduces involuntary motion artifact and requires a relatively short acquisition time. Contrast resolution is generally higher with TSE than SE when evaluating intrinsic spinal cord lesions, therefore, TSE protocol should be considered when evaluating for intrinsic spinal cord conditions.59 Its

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TABLE 5.19 Properties of Magnetic Resonance Contrast Agent Gd-DTPA

TABLE 5.20 Indications for Use of Magnetic Resonance Contrast Agents

• • • • • • •

• • • • • • • • • •

Helps differentiate disk from scar Helps classify tumors Serial evaluation of reparative process Detects vertebral endplate leaks Reveals altered blood/cord barrier Demonstrates region of aggressive tumor activity Improves detection of vascularized granulation tissue

detailed delineation of spinal anatomy allows for grading of spinal stenosis and evaluation of myelopathy.60 5.10.1.3 Inversion Recovery The use of inversion recovery sequences with a short T1-time suppresses signals arising from fat. This provides good contrast for bone edema after spinal injury that may otherwise be difficult to see. The presence of acute or subacute bone edema suggests the possibility of spinal fracture, risk for vertebral instability, and risk for SCI and raises the possibility of post-traumatic vertebral dislocation with spontaneous reduction. 5.10.1.4 Contrast Enhancement Gadolinium (gadolinium diethylenetriamine pentaacetic acid, Gd-DTPA) is the most widely utilized contrast agent for neuroimaging (Table 5.19). Gd-DTPA is administered by intravenous injection and is primarily a T1-shortening agent that enhances the properties of various tissues and their vascular states (Table 5.20). It has become an invaluable tool in imaging the central nervous system due to its ability to pass through a breakdown in the blood-brain and blood-spine barrier. The properties of Gd-DTPA allow for the enhancement of highly vascularized tissue, helping to differentiate epidural scar from disk, vascularized tumor from normal surrounding tissue, and regions of acute inflammation. It is particularly helpful in the assessment of the postoperative back. Pre- and postcontrast image comparisons are required. 5.10.1.5 Kinematic MRI Kinematic MRI or cine MRI provides useful information about the relationship of pathology to the spine in various positions. This protocol should only be considered an adjunctive part of a routine MRI study of the region in question. This study simulates some of the normal daily movements and therefore may help explain intermittent neurological presentations. It may be particularly helpful in the evaluation of dynamic stenosis, vertebral instability, subluxation, and the work-up for ligamentous injury.

Tumor Infection Infarction Suspected fibrosis Differentiating scar vs. disk Arteriovenous malformation Postsurgical status Post-traumatic lesions Suspected metastatic disease Demyelinative disease

Kinematic MRI may help identify whether a region of high signal intensity within the spinal cord might be related to repeated microtrauma secondary to dynamic stenosis. The procedure can occasionally document an unstable disk protrusion that changes in size during spinal translation. Kinematic MRI has been used to demonstrate abnormal fluid flow and spinal cord compression by a spinal arachnoid cyst.61 Dynamic MRI has been helpful in the assessment of rheumatoid arthritis with upper cervical instability.62 Flexion/extension MRI of the cervical spine is useful for evaluating the patient at risk for spinal cord compression secondary to vertebral instability and to help determine candidacy for decompression and arthrodesis.63 Kinematic MRI studies of the cervical spine have demonstrated significant changes in spine and cord length during flexion and extension.64 When comparing flexion to extension, the cervical spinal canal and spinal cord have been shown to lengthen as much as 12 mm (cord) and 28 mm (canal).64 Flexion/extension MRI of the cervical spine is useful for evaluating the patient at risk for spinal cord compression secondary to vertebral instability to help determine candidacy for decompression and arthrodesis.62 Dynamic MRI of the cervical spinal cord has demonstrated linear elongation of 6 to 10% of its normal resting length along the anterior and posterior surfaces with average displacement of 1 to 3 mm.65 The greatest translation during cervical cord flexion occurs along the posterior surface of the cord. The information obtained with kinematic cervical MRI may change therapeutic management60 and is important in planning stabilizing operations for the cervical spine.62 For the purpose of assessing the potential of kinematic MRI, four classifications of pathology have been proposed: stage I, cervical disk disease; stage II, spondylosis; stage III, spondylosis and restricted motion; and stage IV, cervical spondylotic myelopathy.60 In one study, the use of kinematic MRI changed the course of surgical management in stages III and IV.60 With significant spinal cord compression, movement (translation) of the cord is

Assessment of Spinal Cord Injury and Myelopathy

diminished. Follow up on post-operative cases has demonstrated good recovery of spinal cord and CSF motion.66 5.10.1.6 Functional MRI Functional magnetic resonance imaging (fMRI), primarily utilized for brain assessment, identifies focal regions of increased neuronal-cellular activity activated by the performance of isolated physical or cognitive tasks. The technique applies blood-oxygen-level-dependent (BOLD) imaging to detect changes in MR contrast associated with changes in tissue oxygen concentration. BOLD imaging is effective because of the magnetic properties of hemoglobin. When oxygen binds to iron (oxyhemoglobin), the magnetic properties of iron are suppressed. When oxygen is not bound to iron (deoxyhemoglobin), the magnetic properties of hemoglobin are enhanced. Oxyhemoglobin is diamagnetic and deoxyhemoglobin paramagnetic. This acquired difference in magnetic characteristics of hemoglobin while passing through the tissue allows for differentiating regions of greater deoxygenated vs. oxygenated hemoglobin. This results in the ability to generate an image delineating regions of increased cellular metabolism and increased oxygen uptake. High-field fMRI therefore provides a noninvasive method for identifying regions of activated tissue. This technique holds great promise for the evaluation of the spinal cord. In fact, fMRI has recently been used to demonstrate spinal cord motor activation associated with unilateral handclosing tasks.67,68 5.10.1.7 Magnetization Transfer Magnetization transfer (MT) in MR imaging refers to the relaxation properties between two interactive populations of protons: free mobile water protons and protons with restricted mobility in semisolid macromolecular pools.69 This property combined with new technology has proved a unique contrast mechanism in tissue imaging different from other commonly used protocols. This protocol was applied to MRI in order to improve contrast between stationary and moving fluids. MT improved the contrast between background neural tissue and the circulating blood. The MT protocol has been applied to spinal imaging, allowing for improved cord-to-CSF contrast and creating a myelogram-like effect. Disk material creates moderate MT suppression, creating improved contrast between disk material and CSF.70 MT provides a new basis for contrasting between different tissues within the brain and spine. It provides a window into the behavior of tissue that will help to study the stages, degree, and evolution of tissue injury, remodeling, and repair. Emerging quantitative MT imaging has been used to characterize pathologic tissue and to quantify the biochemical attributes and quantity of myelin comprising white matter.71,72

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5.10.1.8 Diffusion-Weighted Imaging New MR techniques and protocols are being developed in an attempt to further distinguish unique structural characteristics of tissues and their function in health and disease. Water within tissues diffuses across different planes in a translational motion. MR imaging of this mechanism provides a new method for characterizing tissues at the microscopic level. Values are assigned to water-diffusion properties and lead to the generation of an MR image. When diffusion occurs equally in all directions, it is referred to as isotropic. When it occurs in a specific direction or an asymmetric pattern, it is referred to as anisotropic. Isotropic diffusion is more likely to take place in tissues that lack an ordered microarchitecture. An ordered microarchitecture is more apt to influence water diffusion, leading to greater anisotropy. Factors that influence diffusion properties include connective tissue density, cell packing density, membrane fluidity, intracellular organelle arrangement, nerve fiber density, degree of myelination, viscosity, temperature, and blood flow to the region. MR diffusion imaging techniques actually measure apparent diffusion coefficients because the vast array of tissue variables renders pure assessment impossible. Biochemical and tissue micoarchitectural changes with tissue injury or disease will alter the pattern of water diffusion. This pattern can be demonstrated by using this specialized MR technique. Diffusion imaging of the brain has been used to help classify the potential for neurological recovery vs. irreversible tissue damage after ischemia or infarction.73 Advancing knowledge about water-diffusion characteristics within the human spinal cord will provide valuable insight about the nature of spinal cord pathology. The requirement for higher resolution and the effects of motion have made the prospect of diffusion-weighted imaging challenging in the assessment of the spinal cord.74,75 Diffusion imaging is helpful in the assessment of white matter damage76 and will continue to impact the evaluation of stroke, multiple sclerosis, amyotrophic lateral sclerosis, head injury, and SCI.77 Diffusion-weighted echo planar imaging (DW-EPI) improves delineation between gray and white matter.78 The application of DW-EPI provides greater insight about the evolution of ischemic, compressive, and demyelinating disorders. It may also provide delineation of specific spinal tract compromise in the future. 5.10.1.9 MR Spectroscopy Magnetic resonance spectroscopy (MRS) of the CNS has been primarily restricted to the brain and brainstem due to technical limitations. The MR spectroscopy protocol can be added to routine MR assessment of the brain and brainstem with MR spectra can be obtained in a relatively short period of time. Numerous metabolites have been

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identified based on their spectral signature. MRS may be utilized to visualize tumor metabolite signatures within the vicinity of the spine. MR spectroscopy provides the ability to obtain additional information about tissue characterization and chemical shift patterns. Advances in MR technology with improved filtering techniques and spatial and temporal resolution hold great promise for the use of MRI spectroscopy in the assessment of SCI and disease. Brain MRS has become a form of noninvasive biopsy able to detect changes in the chemical environment within and around lesions. It helps to delineate the true biochemical zone of pathology that may lie outside the confines of structural pathology. Phosphorus-31 MR spectroscopy is of value in assessing malignant changes of the vertebral column through marked elevation of the tumor marker phosphomonoester (PME).79 Animal studies have demonstrated the potential role of phosphorus-31 nuclear magnetic resonance spectroscopy in the evaluation of changes in spinal cord myelin80 and cellular bioenergetics secondary to trauma and ischemia.81 5.10.1.10

Three-Dimensional Imaging (Reconstruction)

Advanced imaging procedures with good spatial resolution such as MRI, CT, and high-resolution ultrasonography acquire datasets that can be manipulated to provide three-dimensional renditions of the surface and intrinsic anatomy of the spinal column, spinal cord, and nerve roots. Sectional anatomy can be viewed, allowing for teaching, improved clinical correlation, procedural planning, postoperative follow-up, and for use for near-realtime computer-assisted intervention. Clinical application of three-dimensional imaging has helped bridge the gap of communication between the radiologist and attending clinician. It has also broadened the field of interventional radiology. The application of three-dimensional imaging is rapidly advancing the potential of CT, MRI, and ultrasonography and creating a form of virtual endoscopy that allows for “fly throughs and fly bys” using tissue datasets. Computed tomography reconstruction has been used for more than a decade to aid the assessment of spinal disorders.82 Three-dimensional surface reconstruction with CT can provide accurate reconstruction of complex spinal column fractures and the relationship to the spinal cord.83 The datasets can also be manipulated to drive technology capable of fabricating physical models of the anatomy in question. MR three-dimensional imaging can provide for volumetric evaluation of tumor size and configuration. Volume-rendered imaging provides the capacity for creating dimensional projection that goes beyond the computer screen and may involve holography and other forms of stereoscopic displays.

5.10.1.11

MR Angiography

Magnetic resonance imaging is the primary method for noninvasive assessment of patients suspected to have a spinal cord lesion. Pathological conditions of the spinal vasculature often results in morphological and hemodynamic changes which include: (1) increased size of vessels, (2) increased vessel tortuousity, (3) vascular occlusion, and (4) altered intravascular flow dynamics. These gross deviations of normal vascular characteristics provide an opportunity to apply available MR methods to quantify and characterize vascular pathology. Postcontrast MR angiography (MRA) complements the routine MRI evaluation by improving the detection and display of normal and abnormal intradural vessels84 although there are limitations relative to the delineation of spinal veins vs. arteries. Spinal intradural vessels as small as 1-mm diameter have been detected on postcontrast MRA images.84 The use of MRA improves the detection and dynamic assessment of vascular malformations and vascularized tumors and the detection of arterial and venous occlusive disease. MRA can also be used to screen for dural arteriovenous fistulas. The addition of three-dimensional acquisitions and phase display helps differentiate feeder arteries of spinal vascular lesions.85 Fast three-dimensional contrast-enhanced MRA will visualize arterial branches that correlate well with digital subtraction angiography.86 In the future, gadolinium-enhanced three-dimensional MRA may achieve enough spatial and temporal resolution to differentiate spinal arteries from spinal veins, helping to clarify the nature of vascular lesions.84 The combined use of MRA and diffusion imaging in the future will allow for improved characterization of intramedullary arterial insufficiency and infarction. 5.10.1.12

MR Myelography

Magnetic resonance imaging of cerebrospinal fluid dynamics and cord motion can help differentiate pathomechanisms associated with different lesions. It is particularly helpful in assessing the dynamics of CSF spaces, cystic lesions, and the biomechanics of a tethered cord.66 Spinal cord velocity curves can be evaluated with phasecontrast MRI, providing valuable insight into the evaluation of tethering and spinal dysraphism.87 5.10.1.13

Interventional MRI

Advancing MR technology is leading this imaging modality into the interventional setting. MRI is capable of providing rapid multiplanar acquisitions during operative procedures. The development of specialized open magnets provides a greater opportunity for easy access to the patient by multiple people. Special technological modifications are required for the use of MRI in this setting, some of which have already been applied. MR imaging

Assessment of Spinal Cord Injury and Myelopathy

can provide a real-time window of anatomy during interventional procedures. There is also the added benefit of performing image-guided stereotaxic procedures, which reduces reliance on pre-operative films. The potential applications of interventional MRI include interventional disk procedures as well as image-guided biopsies, surgical spinal procedures, and positioning for arthrodesis placement.

5.11 NEUROSONOGRAPHY Many methods can be utilized to image the spine and spinal cord. Ultrasound is portable, noninvasive, and relatively inexpensive. New-generation equipment provides superior spatial and contrast resolution without known biological side effects and offers the option of full-thickness tissue imaging. There is no associated ionizing radiation, and image acquisitions can be obtained in multiple planes. Ultrasonography has emerged as a valuable option for assessing infants, particularly those with occult dysraphic lesions, and for performing intraoperative imaging. The creation of a surgical window provides an opportunity for the induction of a sonographic beam to investigate the integrity of underlying and surrounding tissues. Intraoperative spinal sonography (IOSS) can help direct the surgeon to the shortest route to a spinal lesion, subsequently limiting the degree of tissue compromise.

5.11.1 INTRAOPERATIVE SPINAL SONOGRAPHY Ultrasonography provides a method for intraoperative evaluation of spinal cord pathology,88 specifically in the localization of intrinsic tumors, abscesses, vascular malformations, hematomas, and syrinx formations. Ultrasound imaging can be performed at low cost and without ionizing radiation. Intrinsic spinal cord pathology can be localized and characterized without cord manipulation or incision. Intrinsic lesions of the spinal cord can be identified by the following criteria: (1) expansion of the spinal cord, (2) obliteration of the central echo complex, (3) abnormal cord echogenicity, and (4) abnormal spinal cord pulsation.89 The technique is used to direct the neurosurgeon to the spinal lesion using the shortest and potentially safest route which helps to limit tissue damage. The procedure is usually performed with the patient prone with entry through a laminectomy or laminotomy site. It is often performed throughout the procedure to identify operative progress.

5.12 COMPUTED TOMOGRAPHY 5.12.1 CT/MYELOGRAPHY If a patient is unable to undergo a spinal MRI, computed tomography (CT) with myelography provides a viable alternative. CT/myelography should be considered in those patients with contraindications to MRI. Myelography

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TABLE 5.21 Spinal Mass Effects: Myelographic Features • • • • •

Non-filling of nerve root sleeve Extradural filling defect Flattening of the spinal cord Multiple indentations Obstruction of contrast flow

has some associated risk; therefore, its use should be limited. CT and myelography should generally be performed together to improve the sensitivity and specificity of the test. Post-myelographic CT scan provides a higher yield of information than isolated CT evaluation.90 CT/myelography should be considered when MRI findings are disconcordant with the clinical presentation and a spinal lesion is still suspected. Computed tomography/myelography provides an accurate method for assessing the relationship of the spinal nerve root to adjacent bone and surrounding cerebrospinal fluid (Table 5.21). When a physical mass is large enough to block the flow of CSF, a cutoff or column-filling defect becomes apparent on myelography. A dynamic (variable position) myelogram can help identify significant positional central or lateral stenosis with CSF cutoff. However, it is difficult to determine the extent of an intradural lesion such as syringomyelia and distal pathology if a complete myelographic block is present.90

5.12.2 HELICAL CT (SPIRAL CT) Computed tomography remains a superior method of imaging for bone and soft-tissue pathology associated with calcific changes. Thin-slice CT is a valuable method of assessment for failed spinal fusion. The development of helical techniques has revolutionized the science and application of CT. This protocol provides quicker and sharper axial images and utilizes an overlapping imaging sequence91 to reduce radiation exposure as compared to conventional CT, while increasing the field of view. Faster scan times also decrease patient discomfort, anxiety, and movement artifact, therefore rendering a more detailed image. Greater coverage of a region can be performed in a short period of time, so helical CT is an important addition to a trauma center. The procedure is so efficient that rapid whole-body helical CT scanning can be performed on patients who have sustained multifocal trauma, often within minutes.

5.13 PLAIN-FILM RADIOGRAPHY Plain-film radiography is valuable as a cost-effective method of initially evaluating the structural and biomechanical

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TABLE 5.22 Classification of Intersegmental Motion Patterns Parmobility • Normal Type I: Intersegmental motion within the average (mean) for population studied • Abnormal Type II: Normal intersegmental motion associated with pain at the same segmental level or within biomechanically connected structures Hypomobility • Normal Type I: Reduced intersegmental motion within normal ranges without evidence of pain or spondylosis • Pathomechanical Type II: Abnormally reduced intersegmental motion; associated with pain, reactive myospasm, and/or spondylosis Type III: Immobilization; complete loss of intersegmental motion; may or may not be associated with pain or neurological findings Hypermobility • Normal Type I: Excessive intersegmental motion without evidence of pain or spondylosis • Pathomechanical Type II: Excessive intersegmental motion in the tissue-damaging range with 2–3.5 mm, 1–2.5 mm (thoracic), or 3–4.5 mm (lumbar) of translation in the sagittal plane (one direction) and/or angular displacement 11°; often associated with pain or neurological findings Parakinetic mobility • Normal Type I: Intersegmental motion occurring in a direction or pattern other than that expected, without evidence of pain or spondylosis • Pathomechanical Type II: Abnormal intersegmental-coupled motion or excursion pattern in the tissue-deforming or -damaging range that occurs in an unexpected direction or pattern; may or may not be associated with pain, reactive myospasm, and other symptoms Type III: Biomechanical instability; excessive intersegmental motion in an unexpected direction or pattern in the sagittal plane, with translation of 3.5 mm or greater (cervical), 2.5 or greater (thoracic), or 4.5 or greater (lumbar) and/or angular displacement >11°; often associated with pain or neurological findings Note: This table defines the types of motion that are seen at the intersegmental level. The type II and III pathomechanical motions may further be qualified by temporal characteristics using the terms acute, glacial (slowly progressive), and chronic. Type II and III measurement criteria are based on mid- and lower cervical spine flexion and extension positional radiographs taken at 72-inch source-image distance. Rotary and lateral motions can also be considered in type II and III pathomechanical mobility patterns, although these ranges are not reported. Source: True, Durrant.

integrity of the osseous elements of the spine. It is a valuable front-line method for the evaluation of fractures, dislocations, congenital bony malformations, segmental function, and postural considerations. The plain-film study can also help determine the risk for positional or dynamic central and/or lateral spinal stenosis in a weight-bearing position. Visualization of the spine by plain film should include lateral, anteroposterior, and open-mouth views including the C1 through the T1 vertebra. Oblique views are beneficial for dislocation and fracture visualization. Also unique to the radiographic work-up is the ability to evaluate segmental biomechanics. Segmental movement may fall into one of the following categories: (1) normal (par mobility); (2) hypomobility, including immobilization; (3) hypermobility, including instability; and (4) parakinetic mobility (Table 5.22). This portion of the assessment can be performed using flexion and extension views. On rare occasions, lateral-bending views may also be taken. If a fracture is suspected, the X-ray work-up should be supplemented with conventional or helical CT. If SCI is suspected, the study should be correlated with MR imaging.

5.14 QUANTITATIVE CONSIDERATIONS IN SPINAL CORD IMAGING It is important to evaluate the size, configuration, and signal characteristics of the spinal canal and spinal cord when reviewing advanced neuroimaging studies. Special attention should be given to the region of the spinal cord adjacent to areas of acquired stenosis. There is variation in spinal column size between individual cords;92 therefore, it can be helpful to compare morphometric information from the suspected segmental level of involvement to an uninvolved segmental level.

5.14.1 CENTRAL SPINAL CANAL MEASUREMENTS Reserve space around the spinal cord is necessary to ensure adequate blood supply and biomechanics. The transverse area of the spinal canal is generally smaller in patients with myelopathy when compared to normal individuals.93 The spinal cord becomes particularly vulnerable to compression secondary to disk herniation or other mass effect within a developmentally narrowed central spinal canal.94 A narrow cervical canal is an unfavorable finding in patients who have suffered flexionextension injury.95 The sagittal diameter of the cervical, thoracic, and lumbar spinal canal can be quantitatively measured on MRI or CT as well as plain-film radiography (Figure 5.11). There is generally good correlation between the sagittal diameter of the spondylotic cervical spinal canal and the development of myelopathic sign and symptoms. A sagittal measurement of the cervical spinal canal can be made on a plain-film radiograph measuring from the posterior surface

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Average Diameter of the Spinal Canal at Four Different Levels

C5

Mean Lumen Diameters

T7

AP-14 mm Lat.-25 mm

AP -14 mm Lat -15 mm

T11

AP -16.5 mm Lat -19.3 mm

L5

AP -12 mm Lat -24 mm

FIGURE 5.11 The narrow zone of the spinal canal extends from approximately T4 to T9 vertebral levels. The narrowest region of the spinal canal is at the T6 level. The wide lateral diameter of the lumbosacral canal easily accommodates the cauda equina. (Copyright J.M. True, D.C.)

of the vertebral body to the closest surface of the spinolaminar junction at the same vertebral level; however, this method may be somewhat inaccurate due to radiographic magnification. Cervical mid-sagittal diameter between 10 and 13 mm is a premyelopathic condition due to the limited tolerance for hypertrophic bony changes projecting more than 2 mm.96 A cervical sagittal canal measurement of 12 or less is considered a critical factor in the development of cervical spondylotic myelopathy on plain films.97,98 The normal cervical canal diameter ranges from 17 to 18 mm at C3– C7. An alternative method of measurement is the application of the ratio between the sagittal measurement of the canal and the vertebral body referred to as the canal/body ratio or Torg–Pavlov ratio.99 A spinal canal/body ratio of less than 0.80 on a lateral cervical spine roentgenogram is indicative of cervical spinal canal stenosis.100

5.14.2 SPINAL INSTABILITY AND VERTEBRAL TRANSLATION Segmental vertebral hypermobility in conjunction with central stenosis increases the risk for cord and supportive vascular microcontusion during movement. The degree of vertebral translation or instability can be determined on positional radiographic views or kinematic MRI. Injury to the ascending and descending tracts of the spinal cord generally is more devastating than focal injury to the cellular elements of the gray horn. Injury to the white matter may compromise ascending or descending pathways that control function below the level of compromise, thus the clinical deficit has the potential to be more complex and incapacitating than the segmental effects of anterior horn insult.101

5.14.3 CLASSIFICATIONS OF SPINAL CORD COMPRESSION Nagata et al.102 described four classifications of spinal cord compression assessed with T1-weighted sagittal MRI acquisitions of the cervical spine. In Class 0, there is no

FIGURE 5.12 Classifications of spinal cord compression visualized on T2-weighted MRI, sagittal acquisition. (Copyright J.M. True, D.C.)

compression. In Class 1, the cord is slightly compressed. In Class 2, the cord width is compressed by less than one third, and in Class 3 the cord width is decreased by one third or more (Figure 5.12). These researchers found that the greater the degree of cord compression, the greater the severity of myelopathy and clinical sequelae. The spinal cord may be displaced within the spinal canal without obvious compression, which may lead to abnormal tension patterns within the cord (Table 5.23).

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TABLE 5.23 Magnetic Resonance Imaging Appearance with Increasing Levels of Mechanical Spinal Cord Compression

Cervical Cord

Cord Square 2 Area (mm)

2

>75 mm 1. Cord deviation without deformation 2. Cord deviation with deformation 3. Cord deviation without cord deformation with adjacent focal cord MR signal abnormality 4. Cord deviation with deformation and adjacent abnormal MR signal 5. Cord deformation, abnormal signal and focal enlargement

Normal

2

50 mm

Moderate Compression

2

40 mm Severe Compression

A–B=11.9

FIGURE 5.14 A reduced square area of the spinal cord correlates with severity of myelopathic symptoms. (Copyright J.M. True, D.C.)

C–D-7.2

E–F=12.0

G–H=13.6

FIGURE 5.13 Quantitative measurements of the cervical spinal canal at various levels. Central canal stenosis at C5–C6 is due to prominent disk bulging. (Parasagittal fast spin echo T2weighted midline sagittal image.)

cord area by greater than 30% as compared to adjacent regions or a transverse cord area of less than 60 mm2 depicted by CT has been associated with increased prevalence of myelopathic symptoms.104 Nagata et al.102 correlated MRI cord appearance with myelopathic presentation. These researchers suggest that a cross-sectional cervical cord area less than 50 mm2 carries a high risk of myelopathic symptoms and loss of functional capacity (Figure 5.14). A transverse cord area less than 40 mm2 is a poor prognostic finding, and surgery in these patients is often indicated;105 unfortunately, cord area of less than 30 mm2 has been associated with a poor response to surgery.106

5.14.4 SPINAL CORD CROSS-SECTIONAL SIZE AND AREA

5.14.5 INTRINSIC CORD DYSMORPHISM

The spinal cord cross-section and sagittal images can be evaluated on MR (Figure 5.13). The normal cervical spinal cord measures approximately 8.5 to 11.5 mm in diameter. Small cord diameter (atrophy) may occur secondary to neuronal and support element dropout due to injury. An enlarged cord may occur secondary to a focal or diffuse expanding intramedullary lesion. Ono and associates103 devised the anteroposterior (AP) compression ratio (the ratio of the AP canal diameter to the lateral cord diameter) and effectively correlated it with the severity of spinal cord compromise. A reduction of the cross-sectional spinal

The ability to evaluate and provide calculations in digitized images also offers additional advantages as part of a positional spinal MRI study. High-field, 1.5-Tesla MRI can readily demonstrate the central “H” configuration of the normal spinal gray matter on axial specialized T2 gradient echo pulse sequences; thus, distortions of the central gray can be quantified to correlate with myelopathic symptoms.107 Distortion of the “H” configuration suggests greater likelihood for microvascular and neural compromise as well as gray matter atrophy of the spinal cord (Figures 5.15 and 5.16).

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FIGURE 5.15 The distorted H-sign. (Copyright J.M. True, D.C.)

Cord compression with deformation

FIGURE 5.17 Posterior bony spur at C5–C6 with corresponding ventral cord compression. The associated abnormal signal changes within the cervical spinal cord at this level are compatible with myelomalacia. (Parasagittal fast spin echo T2-weighted midline sagittal image.) FIGURE 5.16 Spinal cord compression with a distorted H-sign. (Axial fast spin echo T2-weighted image through the C2–C3 level.) (Same patient as in Figures 3.21 and 3.22.)

and low-intensity signal on T1WI with a poor prognosis for clinical recovery. This may indicate more severe cord pathology such as severe necrotic, spongiform, or myelomalacic changes.111

5.14.6 INTRAMEDULLARY SIGNAL PATTERNS Spinal cord injury may be associated with abnormal signal changes within the spinal cord. The relationship between increased intramedullary signal intensity and histologic findings has been reported by many researchers.101,108 Takahashi108 was one of the first researchers to report a focal region of abnormal high-intensity signal within a chronically compressed region of the spinal cord. Linear high-intensity signal regions on T2-weighted images (T2WI) have been associated with clinical evidence of extensive anterior horn cell compromise and radiographic evidence of cavitation.101 It has been postulated that focal high T2-weighted signals within the spinal cord represent inflammation, edema, vascular ischemia, myelomalacia, and/or gliosis (Figure 5.17). Some of these signal aberrancies resolve after decompressive surgical intervention;109 however, Kulkanari et al.110 reported good correlation between regions of high-intensity signal on T2WI

5.15 FUNCTIONAL AND LABORATORY ASSESSMENT The majority of back complaints are mechanical in nature. Laboratory evaluation can be used to help identify the cause of nonmechanical back pain and conditions that render the spinal cord vulnerable to compression or other forms of neurological compromise. Functional assessment forms the basis of diagnosis and is critical to evaluation of the progression or rehabilitation of impairment.

5.15.1 PULMONARY FUNCTION Cervical or thoracic SCI results in varying degrees of respiratory impairment. Pulmonary function tests provide quantifiable discrimination between degrees of impairment.112 Additionally, these tests are practical and cost effective, providing valuable data to follow the patient with

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acute, subacute, or chronic myelopathy. More advanced methods of measurement are available. The five primary reasons for performing a pulmonary function profile are (1) to assess the need for acute intervention, (2) to determine the degree of neurologic and related pulmonary impairment, (3) to help identify the type of respiratory or physical therapy required, (4) to assess the ability to move secretions, and (5) to serve as a baseline for outcome assessment. The normal respiratory rate (RR) at rest falls between 12 and 14 breaths per minute. The RR in patients with myelopathy or SCI with respiratory impairment will increase in an attempt to compensate for their reduced lung expansion and vital capacity. The ability to inflate the lungs is also impaired, thus chest wall excursion is reduced. Vital capacity is defined as the maximum amount of air that can be forcibly exhaled after maximum inhalation. A greater vital capacity increases the patient’s ability to clear and expel airway secretions. A greater vital capacity also improves the ability to inflate the alveoli, reducing the risk for atelectasis. Reduced vital capacity will cause a reduction of the SaO2 unless there is an adequate compensatory increase in the RR. The vital capacity can be quantified by utilizing a hand-held spirometer. The average normal vital capacity is approximately 4500 mL.113 A vital capacity of 800 mL is enough to maintain respiration without mechanical support.14 A vital capacity of approximately 1500 mL is required to have an effective functional cough to clear lung secretions.114 Peak expiratory flow (PEF) tests the patient’s ability to properly ventilate and expel pulmonary secretions. PEF represents the greatest flow that can be achieved during forceful exhalation. The amount of arterial oxygen saturation in the body can be measured by pulse oximetry. The oximeter sensor is usually a finger cuff or clip placed over the distal end of a digit. The normal arterial oxygen saturation (SaO2) is 97% or greater. Increasing SaO2 values is consistent with improved functional respiratory capacity.112

5.15.2 CEREBROSPINAL FLUID EVALUATION The CSF surrounding the brain and spinal cord performs four major functions: (1) physical support and protection, (2) method of excretion, (3) provision of controlled chemical environment, and (4) intra- and extracerebral transport.115 Cerebrospinal fluid assessment should only be considered when a biochemical, serology, or cytology assay of the spinal fluid might provide clinically relevant insight that would change the course of care. The laboratory investigation of CSF is indicated for suspicions of CNS infection, immunological disorders, subarachnoid bleeding, meningeal carcinoma, and MS. Cytology may be helpful in assessment for neoplastic cells (Table 5.24). Normal CSF from a patient without infection has low protein, no phagocytic cells or inflammatory by-products.

In patients with bacterial meningitis, the classic CSF findings are leukocytic pleocytosis, increased protein, decreased glucose, and increased intrathecal pressure. The most common organisms producing bacterial meningitis in neonates are Group B streptococci and Gram-negative enteric bacilli. In children and adults, Streptococcus pneumoniae or Neisseria meningitides are the organisms most frequently responsible for bacterial meningitis. Viral meningitis may be caused from any one of dozens of DNA or RNA viruses. Some of the more common etiologic viruses are herpes simplex virus, influenza type A or B, HIV, Epstein–Barr virus, and St. Louis encephalitis virus. A spinal fluid tap is strongly contraindicated in the presence of known or suspected increased intracranial pressure. Relative contraindications include headache, unconsciousness, local sepsis, suspected spinal cord compression, and neck stiffness. Neuroimaging should be performed prior to most CSF studies. A lumbar puncture, usually at the interspace of the L3 to L4 vertebrae or below, is performed to obtain CSF fluid that is then usually apportioned for (1) chemistry and serology, (2) bacteriology, and (3) microscopy. Practical biochemical tests of interest are glucose, total protein, and specific protein assays. The CSF glucose concentration is usually about two thirds the level of the plasma. A decrease in CSF glucose levels may occur secondary to (1) a disorder in carriermediated transport of glucose into CSF, (2) active metabolism of glucose by cells or organisms, and (3) increased metabolism by the CNS.115 A low CSF glucose level may occur with meningeal metastasis or primary carcinoma. A decreased level of CSF protein may occur due to (1) decreased dialysis from plasma, (2) leakage of CSF, or (3) increased protein removal.115 An increased level of total protein is one of the most useful nonspecific indicators of a pathologic state. An increase in protein may occur due to the one of the following reasons: (1) lysis of blood from a traumatic tap, 2) increased permeability of the epithelial membranes, (3) increased production by CNS tissue, (4) obstruction, or (5) decreased rate of removal.115 Electrophoretic separation of protein subtypes can be helpful in the evaluation of immune-mediated spinal cord disease and in cases of CSF total protein elevation. Electrophoretic separation may demonstrate banding of the IgG proteins, referred to as oligoclonal banding, and often occurs in the presence of inflammatory disorders such as multiple sclerosis, HTLV-1, HIV, or Lyme disease. These types of gamma globulins may stimulate immunocompetent cell lines.

5.15.3 AMNIOCENTESIS Amniocentesis refers to sampling of the amniotic fluid during pregnancy. Many congenital anomalies with neurological consequences can be prenatally detected. Biochemical assessment of amniotic fluid may be performed

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TABLE 5.24 Cerebrospinal Fluid Abnormalities. CSF Abnormalities in Various Conditions Affecting the Spinal Cord CSF Appearance

Pressure (mm hg)

Protein (mg/dl)

Glucose (mg/dl)

Normal Acute bacterial meningitis

Clear Cloudy

100–200 Decreased

20–45 Increased

50–80 Decreased

< 6 Lymphocytes Increased (PMN or mono)

Amyotrophic lateral sclerosis Aseptic (viral) meningitis

Clear

Mild increase

Normal

Increased

Clear or cloudy

Normal or increased Normal or increased

Increased

Normal

Culture, virus specific antibodies, polymerase chain reaction (PCR)

Diabetes

Clear

Increased

Increased

Fungal meningitis

Clear or cloudy

Increased

Increased (50–400) Increased

Increased (mononuclear), lymphocytic pleocytosis Normal

Decreased

Culture, antigen detection and serology

Guillain–Barre Syndrome

Clear or cloudy

Normal

Increased

Normal

Hepatic disease

Clear or xanthochromic Bloody or xanthochromic Clear or cloudy

Normal or increased Increased

Increased

Normal

Increased (monocytes), leukocytic pleocytosis Normal or increased (lymphocytes) Normal

Increased

Increased

Increased

Normal or decreased Normal

Normal to increased Normal to mildy increased Increased

Increased (24–1200) Increased

Normal

Normal or increased

Normal or decreased

Condition

Hemorrhage HTLV-1

Meningeal carcinomatosis Multiple sclerosis

Clear or cloudy Clear or cloudy

Decreased

Neoplasm

Clear or xanthochromic

Subarachnoid hemorrhage Tuberculous meningitis

Bloody or xanthochromic Cloudy

Increased

Increased

Increased

Increased

Normal or decreased Decreased

Neuroborreliosis

Clear or cloudy

Increased

Increased (100)

Normal or decreased

Neurosyphilis

Clear or cloudy

Normal or increased

Increased

Normal

Increased (50–200) Increased

Mild decrease (30–40) Normal

Neurosarcoidosis Paraneoplastic

Clear or cloudy

Normal or increased

Cytology

Increased (RBC) Increased (WBC or mononuclear) Increased (PMN) Increased (WBC)

Additional CSF Tests

Culture, Gram’s stain, polymerase chain reaction (PCR) Neurofilament

Rule-out active infection

Glutamine

Increased IgG specific antibodies, oligoclonal bands Beta-Glucuronidase

Oligoclonal bands, increased IgG index, myelin basic protein Normal or increased Neuron specific enolase (lymphocytes/ (NSE), carcinembryonic mononuclear) antigen (CEA) Increased (RBC and WBC) Increased Culture, PCR (PMN-early) (lymphs-late) Increased Lyme antibodies, (monocytes) oligoclonal bands, fibronectin Increased VDRL (monocytes) Increased Angiotension converting (monocytes) enzyme (ACE) Increased Antibodies (many others) (WBC’s 8–20) AniYo Anti-Hu

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in high-risk patients to test for chromosomal abnormalities, neural tube defects, gestational development, fetal pulmonary development, and presence of hemolytic disease. The confirmation or suspicion of congenital maldevelopment on fetal ultrasound indicates the need for amniocentesis. Amniotic fluid specimens are usually taken between the gestation period of 14 to 21 weeks. The sample is assessed for fetal cells, which can then be used for chromosomal and intracellular enzyme evaluation. Tests used to screen for neural tube defects include alphafetoprotein (AFP) and CNS-specific acetylcholinesterase (ACE). When both ACE and AFP are elevated, there is a higher probability that neural tube defect is present. AFP assessment does not provide an absolute marker for neural tube defects but has been associated with increased prevalence. The sensitivity of AFP is improved when performed along with other serum tests. The maternal triple screen is a common profile consisting of AFP, estriol, and human chorion gonadotropin (HCG) levels.

5.15.4 BLOOD

AND

SERUM STUDIES

Blood and serum studies can be useful in the workup of a patient with suspected acute myelopathy, particularly transverse myelitis or meningitis. An elevated white blood cell count (WBC) is indicative of an acute inflammatory state or the response to a local or systemic infection. The white blood cell types and quantities provide further insight relative to the degree and stage of the infection. An elevated erythrocyte mean cell volume (macrocytosis) can be one of the earliest indicators of B12 and/or folate deficiency, increasing the risk for subacute combined degeneration The fluidity of the blood is dependent on normal quantities of platelets, normal ratio and interaction of proteins of the fibrinolytic system. When there is risk for hemorrhagic stroke, hematomyelia, or impaired clotting due to coumadin, clotting factors should be monitored. Spinal subdural hematoma may occur following lumbar puncture in patients on blood thinners or with platelet counts below 40,000 mm3. Prothrombin time, activated partial thromboplastin time, plasma fibrinogen, and tests for defective platelet function are usually performed in the evaluation of the hemorrhagic patient. Serum assessment of triglycerides, cholesterol, and their subtype lipids can help ascertain risk for peripheral vascular disease. Chronic elevation of LDL, especially when accompanied by a concomitant reduction of the HDL fraction of cholesterol, increases the risk for acquiring obstructive arterial disease. Obstructive disease within the thoracic and abdominal aorta increases the susceptibility of the spine to hypotension secondary to compromise of arterial feeders from the aorta, such as the large artery of Adamkiewicz. Elevated cholesterol accompanied by other cardiovascular risk factors should warrant further

cardiac and peripheral arterial assessment, particularly in the patient who may be undergoing major abdominal or chest surgery. A drop in systemic blood pressure in a patient with aortic disease may result in spinal cord injury. A serum metabolic profile helps to provide an indication of overall health. Disease states such as hepatitis, diabetes, and uremia, although unrelated to SCI, can hamper the healing and rehabilitation process. The metabolic profile can also be used to assess the risk for or presence of infectious complications after SCI, particularly involving the pulmonary system and urinary tract. A blood culture and Gram’s stain should be performed to rule out septicemia in the patient with suspected infectious myelitis. In cases of suspected or known transverse myelitis or meningitis, both blood and CSF cultures should be performed. With aseptic meningitis, in addition to direct culture of the virus, enzyme linked immunosorbent assay (ELISA), Western blot, or polymerase chain reaction (PCR), and virus specific antibody testing are methods used to identify different viruses that may also be present in the serum as well as CSF. Systemic inflammatory markers such as C-reactive protein (CRP) are helpful in the initial assessment and follow-up of the patients with infectious or postinfectious myelopathy. Plasma pH, CO2, and serum acid–base relationships should be evaluated in the SCI patient with known or suspected respiratory impairment. Acidosis due to hypoventilation should be monitored in patients with respiratory insufficiency due to SCI. Respiratory acidosis occurs secondary to pulmonary CO2 retention, which results in an excess of H2CO3. This causes a drop in the plasma pH, hence the term respiratory acidosis. Undiagnosed post-traumatic urinary infection with pyelonephritis may cause renal acidosis, complicating the acidosis due to hypoventilation. If metastasis or paraneoplastic syndrome is suspected, serum tumor markers may be useful. They can be used to screen the patient with possible disease, used for adjunctive disease staging, and used to detect disease recurrence. Most serum tumor markers cannot be used to confirm the diagnosis of cancer but they will raise the probability of its presence. Common serum tumor markers are carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), and human chorionic gonadotropin (beta-HCG).

5.15.5 GENETIC ASSESSMENT Some inherited disorders escape detection by more conventional laboratory measures such as serum and CSF biochemical assays. Recent advances in molecular genetics make it possible to determine the precise location of genes which cause or contribute to neurological disease states. The mapped gene location provides for accurate hereditary diagnosis.

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TABLE 5.25 Cystourethrographic Presentations Lesion Site

Electromyogram

Cystogram

Clinical

Complete supraconus myelopathy Incomplete supraconus myelopathy

Detrusor sphincter dyssynergy Normal sphincter

Detrusor hyperreflexia Detrusor hyperreflexia

Lesion of the conus medullaris

Decreased activity

Detrusor areflexia

Spontaneous voiding; incomplete voiding Increased urinary frequency; painful urge; urge incontinence Urinary retention

Each human cell contains 46 chromosomes arranged into 23 pairs, 22 autosomes plus the sex chromosomes X and Y. This chromosomal arrangement is referred to as the human genome. The primary infrastructure of the chromosome is a continuous DNA double strand consisting of approximately 50 to 200 million base pairs in length, dependent upon the size of the chromosome. The gene is comprised of a series of base pairs. The chromosome represents a discrete unit of the genome containing a complex array of genes composed up to an average length of a few thousand base pairs. The gene further represents the basic unit of inheritance, comprised of a nucleic acid arrangement capable of encoding proteins for the synthesis and modulation of other structures. An abnormal gene, gene sequence, or gene interaction may be inherited or acquired through a mutation, which represents an alteration of its nucleic acid sequence. Many common conditions are known to arise from the complex interaction between environmental and genetic mechanisms. Linkage mapping, linkage analysis, gene isolation, and positional cloning represent some of the techniques for identifying and isolating gene locations. Through these and other methods, genetic testing has identified the chromosomal location and mutant gene characteristics for a number of neurological disorders. In some cases, a genetic diagnosis is possible, whereas in other cases, it remains suggestive. Some of the diseases identified by genetic testing are Friedreich’s ataxia; spinal muscular atrophy, types 1, 2, and 3; familial amyotrophic lateral sclerosis; and neurofibromatosis type I and II. An extensive discussion of genetic markers extends beyond the scope of this chapter and book.

5.15.6 BLADDER FUNCTION 5.15.6.1 Cystourethrography Spinal cord injury and disease can cause urinary bladder dysfunction. Functional evaluation of the urinary bladder and related peripheral mechanisms can help differentiate whether the urinary presentation is directly related to spinal cord compromise or secondary to coexistent cauda equina syndrome, peripheral neuropathy, autonomic neuropathy, or intrinsic bladder pathology (Table 5.25).

5.15.6.2 Cystometry Cystometry refers to the testing of bladder function. Carefully performed cystometry can provide valuable insight about detrusor muscle function. In the patient with SCI or myelopathy due to other causes, cystometry can help to evaluate (1) bladder wall sensation, (2) motility of the bladder, (3) sphincter integrity, (4) response to filling pressures, and (5) neurological response. Cystometry can be performed with sterile water insufflation. Sterile water is instilled into the empty bladder at a rate of 1 mL/sec. In the normal bladder, the first desire to void occurs after about 175 to 250 mL of water has been introduced.116 Normally, at this filling pressure, there are no signs of detrusor contraction. An intravesicle pressure elevation in excess of 15 cm H2O is considered to represent a detrusor contraction.117 The following observations and recordings are critical to cystometric assessment: (1) perception of temperature, (2) perception of filling pressure, (3) pressure at the time of experiencing the urge to void, (4) pressure at the time of painful distention, (5) pressure at the time of voiding, and (6) quality and character of the urinary stream. Ambulatory cystometry can be performed. It is more commonly used to assess stress incontinence in women but could be used to assess urge incontinence in the patient with suspected spinal cord dysfunction. 5.15.6.3 Electrodiagnostic Studies of Bladder Function Electromyography of the pelvic basin muscles or monitoring the activity of the internal and external sphincters is often done in conjunction with cystourethrography. Electromyographic measurement of the function of the urogenital diaphragm and levator ani muscle during cystometry can provide further quantifiable information about neurological and muscular integrity. Interruption of spinal or supraspinal pathways to the bladder results in detrusor overactivity. Electromyographic assessment of the detrusor sphincter can help determine whether there is sphincter dyssynergy. This is characterized during cystometry by inability to voluntarily suppress the detrusor reflex contraction and early involuntary voiding with low intravesicle pressure. This will help to ascertain the severity of

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the neurogenic bladder condition and to assess risk for intravesicle urinary retention. Increased urinary retention or incomplete voiding increases the risk for acquiring a urinary tract infection, which could stimulate a state of autonomic hyperreflexia and lead to infectious complications. Cortical evoked potentials are reported to be of value for (1) differentiating between intraspinal and extraspinal lesions of the afferent pathways of the detrusor if the etiology is unknown, (2) differentiating between neurogenic and myogenic damage to the urinary bladder, and (3) selecting patients not suitable for intravesical electrotherapy for bladder rehabilitation. The findings of a cortical evoked potential study should be correlated with pudendal somatosensory evoked potentials and clinical symptomatology.118 5.15.6.4 Uroflowometry Urethral function can also be assessed by uroflowometry, a procedure requiring the patient to void into a flowmeter unit providing for the calculation of average flow rate, maximum flow rate, time to peak flow, and urinary volume voided.117 This test can be used to evaluate detrusordyssynergy and pathology along the course of the urethra.

5.15.7 PHYSICAL IMPAIRMENT ASSESSMENT Spinal cord compromise, whether acute or chronic, results in varying degrees of functional impairment. The pattern of impairment is dependent upon the (1) duration of compromise, (2) cause of injury, (3) location of insult, (4) degree of tissue damage, and (5) capacity for recovery. It is important to evaluate baseline neurological and related orthopedic impairment in order to efficiently plan and effectively initiate a therapeutic and rehabilitative approach. Periodic quantitative follow-up assessments should be used whenever possible in order to better evaluate therapeutic outcome and to become aware of progressive impairment early. The use of quantitative measurements of function can also be extremely motivating for myelopathic patients if there is even small incremental improvement in any aspect of their physical performance. Impairment scales can also be used to assess the status of the patient. Some of these scales are presented below. 5.15.7.1 Frankel Classification The first goal in the assessment of the patient with myelopathy is to localize the level of neurologic injury and baseline simple clinical findings below the intact level. This should include emphasis on sensory and motor assessment. It is important to use a method of assessment that has significant inter-observer reliability and can be easily used for reevaluation. The Frankel scale was one of the first such methods for classifying clinical neurological deficits.119

5.15.7.2 ASIA/IMSOP Scale The Frankel scale, however, lacks some specificity with reference to the extent of neurological deficit and dysfunction. The American Spinal Injury Association (ASIA) and the International Medical Society of Paraplegia (IMSOP) have published a modified scale referred to as the International Standards for Neurologic and Functional Classification of Spinal Cord Injury.120 This classification method provides a measure of assessment of the segmental level of injury on either side of the body, which is important in the evaluation of an incomplete SCI (Figure 5.18). 5.15.7.3 Benzel and Larson Scale The more incomplete the myelopathy, the better the prognosis. Benzel and Larson121 proposed a neurological grading scale for SCI that expands the Frankel scale, allowing more precise quantification of the patient with an incomplete myelopathy. This scale was initially applied to patients with thoracic and lumbar spine injuries. 5.15.7.4 Japanese Orthopedic Association Cervical Myelopathy Score This scale is based on a regression score where patients with the worst myelopathic symptoms have the lowest numerical score. This scale is based on functional capacity assessment of hand dexterity and ambulation along with the extent of sensory deficits and sphincter dysfunction. Patients with larger degrees of cord compression tend to have lower Japanese Orthopedic Association (JOA) scores (Table 5.26).102 5.15.7.5 Range of Motion (ROM) Range of motion (ROM) is easy to evaluate and an important measure of physical capacity. Dual inclinometry is the best way to measure ROM because it provides digital quantification and allows determination of the range based upon movement at two points, which is more accurate, especially in the spinal cord patient with spasticity. ROM measurements can be used as a baseline for joint movement to assess functional range (1) with contracture, (2) with muscle hypertonicity, (3) with reactive spasticity or clonus, or (4) with pain limitation, as well as for orthopedic-joint assessment with normal musculotendinous status. ROM can be evaluated passively with the assistance of the examiner or actively with voluntary effort on behalf of the patient. 5.15.7.6 Gait Ambulation in SCI is not possible without stabilization of the trunk, hip, and knee. SCI above the L3 cord level is not conducive to functional independent ambulation. Even

FIGURE 5.18 (From American Spinal Injury Association. Copyright 2000. Used with permission.)

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TABLE 5.26 Japanese Orthopaedic Association Criteria for Assessment of Cervical Myelopathy • Motor dysfunction of the upper extremity Score 0 = Unable to feed oneself 1 = Unable to handle chopsticks, able to eat with a spoon 2 = Handle chopsticks with slight difficulty 3 = None • Motor dysfunction of the lower extremity Score 0 = Unable to walk 1 = Walk on flat floor with walking aid 2 = Up and/or down stairs with hand rail 3 = None • Sensory deficit A. Upper extremity Score 0 = Severe sensory loss or pain 1 = Mild sensory loss 2 = None B. Lower extremity; same as A C. Trunk; same as A • Sphincter dysfunction Score 0 = Unable to void 1 = Marked difficulty in micturition (retention, strangury) 2 = Difficulty in micturition (dysuria, hesitation) 3 = None Source: From Nagata, K. et al., Clinical value of magnetic resonance imaging for cervical myelopathy, Spine, 15, 1089, 1990. With permission.

gait patterns in L3–L4 lumbar cord injuries may involve considerable abnormality of gait. The ataxia and spasticity in the lower extremities of lumbosacral level hemiplegics make ambulation challenging. Gait requires integrated supraspinal neurological control of the muscles of locomotion with maintenance of postural tone. The pattern of gait and the method of assistance required depend upon the level and degree of SCI. This is discussed in more detail in Section 6.11.3. In patients with incomplete lower cord injuries, there will be diminished kinesthetic perception and spasticity. This gait pattern is termed spastic ataxia. Patients with spondylotic myelopathy or with posterior column compromise may only demonstrate ataxia and slow speed in gait. CSM patients usually demonstrate reduced gait velocity and step length, prolonged double support, increased step width, and reduced ankle joint extension during treadmill walking.122 Knee and hip motion is generally unaffected. In mild or subtle cases of myelopathy, the degree of ataxia can be magnified with gait evaluation on a treadmill. Changes in cervical position may induce a functional stenosis producing changes in gait patterns

and stability. Too often gait evaluation is limited to walking a short distance in a small examination room often not exceeding 10 to 12 feet in length at a slow pace. Subtle myelopathic symptoms may be amplified by having the patient maintain some degree of cervical flexion or extension. Patients with ataxia are very unstable and require vigilant supervision during evocative maneuvers. It is recommended that spotters be present at the patient’s side or use of a safety harness to ensure safety during treadmill gait evaluation. Additionally, the demonstration or facilitation of pathologic reflexes and/or subjective neurologic perceptions in the asymptomatic patient during sustained cervical positions would be highly suggestive of functional stenosis.3 5.15.7.7 Muscular Performance The evaluation of muscular performance is important in the patient with some preservation of muscle function at the level of SCI or below. A number of physical parameters can be measured, the most important being strength, power, endurance, muscle activation patterns, and torque. The most practical parameters to measure are strength, endurance, and muscle activation patterns. Strength is defined as the ability of a muscle or group of muscles to exert force.123 Force exertion is an essential component of functional capacity. Strength testing falls into one of two categories, either static or dynamic. Static testing is a method in which force is measured without limb (joint) movement. Dynamic testing requires movement of the joint and muscle(s) against resistance. Dynamic testing can further be subcategorized into isotonic and isokinetic testing. Isotonic testing allows for dynamic assessment with fixed resistance and variable velocity. Isokinetic testing is a dynamic assessment of an individual’s ability to apply force at constant rate of speed. Isotonic testing comes closer to simulating normal activities, although isokinetic testing provides a more accurate method of measuring change. The assessment of muscular strength can be placed into three primary categories: (1) isolated, (2) regional, and (3) kinetic chain. Assessment of isolated muscular evaluation is important for testing segmental (nerve root) neuromuscular integrity and to allow for more accurate reevaluation. Isolated muscle testing also allows a complex movement to be broken down into its muscular subcomponents. One or more paretic muscles may render a joint mechanically unstable during complex tasks where the agonist is otherwise strong. Regional strength assessment refers to the evaluation of muscles required to perform a task placing primary demand on one joint. An example would be shoulder assessment. This is important for testing the capacity to perform isolated “normal tasks.” Kinetic chain evaluation

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TABLE 5.27 Methods of Quantifying Sensibility Method

Primary Cord Pathway Device

Moving 2-pt. discrimination Static 2-pt. discrimination Pressure Digit/joint kinesthesia Barognosis Vibration Temperature Pain

Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Anterolateral pathway Anterolateral pathway

requires observation and testing of many muscles and joints to complete a task, such as the muscle groups required for transfers from a wheelchair to bed. 5.15.7.8 Sensibility The approach to measuring sensibility can be twofold. The goal of the first approach should be to localize the spinal level of involvement and the specific tracts compromised. The latter approach is to test specific sensory modalities. This method of assessment can be followed by more quantifiable protocol to help determine changes in sensibility (Table 5.27). 5.15.7.9 Balance Balance is maintained through three primary mechanisms: (1) sensory input, (2) motor output, and (3) CNS integration. Sensory input is comprised of information obtained from visual input and vestibular, skin, joint, and muscle receptors. The neuromuscular apparatus responds in order to maintain equilibrium. The CNS integrates the input and modulates the musculoskeletal response. The patient with myelopathy will have some degree of compromise of all three components. This may contribute to imbalance while standing, walking, sitting, or lying. Balance can be measured in a given position or while performing a task. Balance may be qualitatively assessed or measured quantitatively through many available devices.

REFERENCES 1. Nieuwenhuys, R., Voogd, J., and van Huijzen, C., The Human Central Nervous System: A Synopsis and Atlas, 3rd ed., New York: Springer-Verlag, 1988. 2. Shimizu, T., Shimada, H., and Shirakira, K., Scapulohumeral reflex (Shimizu): its clinical significance and testing maneuver, Spine, 18(15):2182–2190, 1993. 3. Denno, J.J. and Meadows, G.R., Early diagnosis of cervical spondylotic myelopathy: a useful clinical sign, Spine, 16(12):1353–1355, 1991.

Dellon wheel Dellon wheel Semmes monofilaments Goniometry Weighted containers Vibrometer Test tube Pin (sharp-dull test); algometer

4. DeJong, R.N. and Haerer, A.F., Case taking and the neurological examination, in Joynt, R.J., Ed., Clinical Neurology, Vol. 1, Philadelphia, PA: Lippincott, 1991: 63–66. 5. Clark, C., Cervical spondylotic myelopathy: history and physical findings, Spine, 13:847–849, 1988. 6. Bowsher, D., Central pain following spinal and supraspinal lesions, Spinal Cord, 37:235–238, 1999. 7. Verbiest, H., Neurogenic intermittent claudication — lesions of the spinal canal and cauda equina, stenosis of the vertebral canal, narrowing of the intervertebral foramen, entrapment of peripheral nerve, in Vinken, P.J. and Bruyn, G.W., Eds., Handbook of Clinical Neurology, Vol. 20, Amsterdam: North-Holland, 1976: 611–804. 8. Comarr, A.E., Sexuality and fertility among spinal cord and/or cauda equina injuries, J. Am. Paraplegia Soc., 8(4):67–75, 1985. 9. Comarr, A.E., Neurology of spinal-cord-injured patients, Semin. Urol., 10(2):74–82, 1992. 10. Katoh, S. and el Masry, W.S., Motor recovery of patients presenting with motor paralysis and sensory sparing following cervical spinal cord injuries, Paraplegia, 33(9):506–509, 1995. 11. Tator, C.H., Maintaining cardiovascular function body temperature control, in Tator C.H., Ed., Early Management of Acute Spinal Cord Injury, New York: Raven Press, 1982: 276. 12. Merli, G.J., Herbison, G.J., Ditunno, J.F. et al., Deep vein thrombosis, prophylaxis in acute spinal cord injured patients, Arch. Phys. Med. Rehabil., 69(9):661–664, 1988. 13. Karlsson, A.K., Autonomic dysreflexia, Spinal Cord, 37:383–391, 1999. 14. Lazarski, M. and Sinnott, M., Role of the physical therapist in the management of patients with acute spinal cord injury, in Hochschuler, S.H., Cotler, H.B., and Guyer, R.D., Eds., Rehabilitation of the Spine: Science and Practice, St. Louis, MO: Mosby, 1993: 347–367. 15. Schwartz, P.J. and Vanoli, E., Cardiac arrhythmias solicited by interaction between acute myocardial ischemia and sympathetic hyperactivity: a new experimental model for the study of anti-arrhythmic drugs, J. Cardiovasc Pharmacol., 3:1251–1259, 1981.

134

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

16. Frownfelter, D.L., Chest Physical Therapy and Pulmonary Rehabilitation: An Interdisciplinary Approach, St. Louis, MO: Mosby-Yearbook, 1978: 12–15. 17. Fishburn, M.J., Marino, R.J., and Ditunno, J.F., Jr., Atelectasis and pneumonia in acute spinal cord injury, Arch. Phys. Med. Rehabil., 71(3):197–200, 1990. 18. Nathan, P. and Smith, M., The centrifugal pathways for micturition within the spinal cord, J. Neurol. Neurosurg. Psychiatry, 21:177, 1958. 19. Jochheim, K.A. and Wahle, H., A study on sexual function in 56 male patients with complete irreversible lesions of the spinal cord and cauda equina, Paraplegia, 8(3):166–172, 1970. 20. Ohry, A., Peleg, D., Goldman, J., David, A., and Rozin, R., Sexual function, pregnancy and delivery in spinal cord injured women, Gynecol. Obstet. Invest., 9(6);281– 291, 1978. 21. Stover, S.L., Niewmann, K.M.W., and Miller, J.M., III, Disodium etidronate in the prevention of postoperative recurrence of heterotopic ossification in spinal-cord injury patients, J. Bone Joint Surg. Am., 58(5):683–688, 1976. 22. Crim, J.R., Bassett, L.W., Gold, R.H., Mirra, J.M. et al., Spinal neuroarthropathy after traumatic paraplegia, Am. J. Neuroradiol., 9(2):359–362, 1988. 23. Kalen, V., Isono, S.S., Cho, C.S., and Perkash, I., Charcot arthropathy of the spine in long-standing paraplegia, Spine, 12(1):42–47, 1987. 24. Schwartz, H.S., Traumatic Charcot spine, J. Spinal Disord., 3(3):269–275, 1990. 25. Spuziak, M.I., X-ray diagnosis of neurogenic osteoarthropathies [in Russian], Vestn. Rentgenol. Radiol., 6:12–16, 1989. 26. Blanco, J. and Kesselring, J., Neuroarthropathy, kyphoscoliosis and progressive tetraparesis in cervical syringomyelia [in German], Schweiz Arch. Neurol. Psychiatr., 141(5):407–417, 1990. 27. Nigrisoli, M., Moscato, M., and Padovani, G., Syringomyelic arthropathy: a description of two cases and a review of the literature, Chir. Organi. Mov., 76(3):237– 244, 1991. 28. Ruiz Ezquerro, J.J., Perez Arellano, J.L., Lopez Alburquerque, J.T. et al., Syringomyelic arthropathy [in Spanish], Ann. Med. Int., 7(7):337–339, 1990. 29. Tully, J.G. and Latteri, A., Paraplegia, syringomyelia tarda and neuropathic arthrosis of the shoulder: a triad, Clin. Orthoped., 134:244–248, 1978. 30. Norman, A., Robbins, H., and Milgram, J.E., The acute neuropathic arthropathy — a rapid, severely disorganizing form of arthritis, Radiology, 90(6):1159–1164, 1968. 31. Dennis, G.C., Dehkordi, O., Millis, R.M., Said, B., and Baganz, M.D., Somatosensory evoked potentials, neurological examination and magnetic resonance imaging for assessment of cervical spinal cord decompression, Life Sci., 66(5):389–397, 2000. 32. Tani, T., Ishida, K., Ushida, T., and Yamamato, H., Intraoperative electroneurography in the assessment of the level of operation for cervical spondylotic myelopathy in the elderly, J. Bone Joint Surg. Br., 82(2):269–274, 2000.

33. Chang, M., Liao, K.K., Cheung, S.C., Kong, K.W., and Chang, S.P., “Numb, clumsy hands” and tactile agnosia secondary to high cervical spondylolytic myelopathy: a clinical and electrophysiological correlation, Acta Neurol. Scand., 86:622–625, 1992. 34. Dvorak, J., Epidemiology, physical examination, and neurodiagnostics, Spine, 23(24):2663–2673, 1998. 35. Noel, P. and Desmedt, J., Cerebral and far-field somatosensory evoked potentials in neurological disorders involving the cervical spinal cord, brainstem, thalamus and cortex, Prog. Clin. Neurophysiol., 7:205–230, 1980. 36. Perlik, S. and Fisher, M., Somatosensory evoked response evaluation of cervical spondylolytic myelopathy, Muscle Nerve, 10:481–489, 1987. 37. Snowden, M.L., Haselkorn, J. et al., Dermatomal somatosensory evoked potentials in the diagnosis of spinal stenosis: comparison with imaging studies, Muscle Nerve, 15:1036–1044, 1992. 38. Yiannikas, C., Shahani, B., and Young, R., Short-latency somatosensory-evoked potentials from radial, median, ulnar, and peroneal nerve stimulation in the assessment of cervical spondylosis. Comparison with conventional electromyography, Arch. Neurol., 43:1264–1271, 1986. 39. Yu, Y. and Jones, S., Somatosensory evoked potentials in cervical spondylosis: correlation of median, ulnar and posterior tibial nerve responses with clinical and radiological findings, Brain, 108:273–300, 1985. 40. Veilleux, M. and Daube, J., The value of ulnar somatosensory evoked potentials (SEPs) in cervical myelopathy, Electroencephalogr. Clin. Neurophysiol., 68:415– 423, 1987. 41. Chokroverty, S., Sachdeo, R., and Duvoisin, R., Magnetic stimulation of the human cervical vertebral column, Neurology, 39(1):394, 1989. 42. Jarratt, J.A., Barker, A.T., Freeston, I.L. Jalinous, R., et al., Magnetic stimulation of the human nervous system: clinical applications. In Chokroverty, S., Ed., Magnetic Stimulation in Clinical Neurophysiology, Stoneham, MA. Butterworth Publishers, 1990:185–203. 43. Little, J.W., Robinson, P., Umlauf, R., and Britell, C., Lower extremity manifestations of spasticity in chronic spinal cord injury, Am. J. Phys. Med. Rehabil., 68:32– 36, 1989. 44. Chang, C.W. and Lin, S.M., Predictability of surgical results of herniated disk-induced cervical myelopathy based on spinal cord motor conduction study, Neurosurg. Rev., 22(2–3):107–111, 1999. 45. Smith, H.C., Savic, G., Frankel, H.L. et al., Corticospinal function studied over time following incomplete spinal cord injury, Spinal Cord, 38(5):292–300, 2000. 46. Little, J.W. and Stiens, S.A., Electrodiagnosis in spinal cord injury, in Robinson, L.R., Ed., New Developments in Electrodiagnostic Medicine, Phys. Med. Rehab. Clin. North Am., Aug. 5(3):571–593, 1994. 47. Leis, A.A., Kronenberg, M.F., Stetkarova, I., Paske, W.C., and Stokic, D.S., Spinal motoneuron excitability after acute spinal cord injury in humans, Neurology, 47(1):231–237, 1996.

Assessment of Spinal Cord Injury and Myelopathy

48. Hiersemenzel, L.P., Curt, A., and Dietz, V., From spinal shock to spasticity: neuronal adaptations to a spinal cord injury, Neurology, 54(8):1574–1582, 2000. 49. Curt, A., Keck, M.E., and Dietz, V., Clinical value of Fwave recordings in traumatic cervical spinal cord injury, Electroencephalogr. Clin. Neurophysiol., 105(3):189– 193, 1997. 50. Epstein, N.E., Epstein, J., Carras, R., Murthy, V., and Hyman, R., Coexisting cervical and lumbar spinal stenosis: diagnosis and management, Neurosurgery, 15(4):489–496, 1984. 51. Eisen, A. and Odusote, K., Amplitude of the F wave: a potential means of documenting spasticity, Neurology, 29:1306–1309, 1979. 52. Little, J.W. and Halar, E.M., H-reflex changes following spinal cord injury, Arch. Phys. Med. Rehabil., 66:19–22, 1985. 53. Karandreas, N., Piperos, P., Dimitriou, D., Kokotis, P., and Zambelis, T., Electrophysiological recording of tendon reflexes in cervical myelopathy, Electromyogr. Clin. Neurophysiol., 40(2):83–88, 2000. 54. Kadson, D., Cervical spondylotic myelopathy with reversible fasciculations in the lower extremities, Arch. Neurol., 34:774–776, 1977. 55. King, R. and Stoops, W., Cervical myelopathy with fasciculations in the lower extremities, J. Neurosurg., 20:948–952, 1963. 56. Yang, J.F., Stein, R.B., Jhamandas, J., and Gordon, T., Motor unit numbers and contractile properties after spinal cord injury, Ann. Neurol., 28:496–502, 1990. 57. Low, V. and Khangure, M.S., MRI Spectrum of intrinsic spinal cord lesions, Australas Radiol., 35(3):212–219, 1991. 58. Shafaie, F.F., Wippold, F.J., II, Gado, M., Pilgram, T.K., and Riew, K.D., Comparison of computed tomography, myelography and magnetic resonance imaging in the evaluation of cervical spondylotic myelopathy and radiculopathy, Spine, 24(17):1781–1785, 1999. 59. Aprile, I., Biasizzo, E., Petralia, B. et al., 1996. Comparative assessment of conventional spin echo sequences and turbo spin echo in the study with magnetic resonance of the lesions of the spinal cord [in Italian; English abstract], Radiol. Med. Torino., 92(4):377–380, 1996. 60. Muhle, C., Metzner, J., Brinkmann, G. et al., Comparison of T2-weighted turbo spin-echo and ultrafast HASTE sequence in the diagnosis of cervical myelopathies and spinal stenosis in static and kinematic MRT of the spine [in German], Rofo Fortschr. Geb. Rontgenstr. Neuen Bildgeb. Verfahr., 167(5):467–473, 1997. 61. Shimizu, H., Tominaga, T., Takahashi, A., and Yoshimoto, T., Cinemagnetic resonance imaging of spinal intradural arachnoid cysts, Neurosurgery, 41(1):95–100, 1997. 62. Allmann, K.H., Uhl, M., Uhrmeister, P., Neumann, K., Von Kempis, J., and Langer, M., Functional MR imaging of the cervical spine in patients with rheumatoid arthritis, Acta Radiol., 39(5):543–546, 1998. 63. Weng, M.S. and Haynes, R.J., Flexion and extension cervical MRI in a pediatric population, J. Pediatr. Orthoped., 16(3):359–363, 1996.

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64. Koschorek, F., Jensen, H.P., and Terwey, B., Dynamic studies of cervical spinal canal and spinal cord by magnetic resonance imaging, Acta Radiol. Suppl., 369:727– 729, 1986. 65. Yuan, Q., Dougherty, L., and Margulies, S.S., In vivo human cervical spinal cord deformation and displacement in flexion, Spine, 23(15):1677–1683, 1998. 66. Levy, L.M., MR imaging of cerebrospinal fluid flow and spinal cord motion in neurologic disorders of the spine [review], Magn. Reson. Imaging Clin. North Am., 7(3):573–87, 1999. 67. Yoshizawa, T., Nose, T., Moore, G.J., and Sillerud, L.O., Functional magnetic resonance imaging of motor activation in the human cervical spinal cord, Neuroimage, 4(3, pt 1):174–182, 1996. 68. Stroman, P.W., Nance, P.W., and Ryner, L.M., BOLD MRI of the human cervical spinal cord at 3 tesla, Magn. Reson. Med., 42(3):571–576, 1999. 69. Finelli, D.A., Magnetization transfer in neuroimaging, Magn. Reson. Imaging Clin. North Am., 6(1):31–52, 1998. 70. Finelli, D.A., Hurst, G.C., Karaman, B.A., Simon, J.E., Duerk, J.L., and Bellon, E.M., Use of magnetization transfer for improved contrast on gradient-echo MR images of the cervical spine, Radiology, 193(1):165– 171, 1994. 71. Henkelmann, R.M., Huang, X., Siang, Q.S., Stanisz, G.J., Swanson, S.D., and Bronskill, M.J., Quantitative interpretation of magnetization transfer, Magn. Reson. Med., 29(6):759–766, 1993. 72. Li, J.G., Graham, S.J., and Henkelman, R.M., A flexible magnetization transfer line shape derived from tissue experimental data, Magn. Reson. Med., 37:866–871, 1997. 73. Westbrook, C. and Kaut, C., Advanced imaging techniques, in Westbrook, C. and Kaut, C., Eds., MRI in Practice, 2nd ed., Malden, MA: Blackwell Science, 1998: 276–300. 74. Clark, C.A., Barker, G.J., and Tofts, P.S., Magnetic resonance diffusion imaging of the human cervical spinal cord in vivo, Magn. Reson. Med., 41(6):1269–1273, 1999. 75. Bammer, R., Fazekas, F., Augustin, M. et al., Diffusionweighted MR imaging of the spinal cord, Am. J. Neuroradiol., 21(3):587–591, 2000. 76. Clark, C.A., Werring, D.J., and Miller, D.H., Diffusion imaging of the spinal cord in vivo, estimation of the principal diffusivities and application to multiple sclerosis, Magn. Reson. Med., 43(1):133–138, 2000. 77. Makris, N., Worth, A.J., Sorensen, A.G. et al., Morphometry of in vivo human white matter association pathways with diffusion-weighted magnetic resonance imaging, Ann. Neurol., 42(6):951–962, 1997. 78. Nagayoshi, K., Ito, Y., Monzen, Y., Kimura, S., and Yamheuchi, J., Delineation of the white and gray matter of the normal human cervical spinal cord using diffusion-weighted echo planar imaging [in Japanese; English abstract], Nippon Igaku Hoshasen Gakkai Zasshi, 58(11):578–580, 1998.

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79. Sijens, P.E., van den Bent, M.J., and Oudkerk, M., Phosphorus-31 chemical shift imaging of metastatic tumors located in the spine region, Invest. Radiol., 32(6):344– 350, 1997. 80. O’Donnel, J.M., Akino, M., Zhu, H., and Stokes, B.T., Phosphorus-31 nuclear magnetic resonance spectroscopy of the spinal cord in the pig, rat, and rabbit, Invest. Radiol., 31(3):121–125, 1996. 81. Akino, M., O’Donnel, J.M., Robitaille, P.M., and Stokes, B.T., Phosphorus-31 magnetic resonance spectroscopy studies of pig spinal cord injury: myelin changes, intracellular pH, and bioenergetics, Invest. Radiol., 32(7):382–388, 1997. 82. Zinreich, S.J., Rosenbaum, A.E., Wang, H. et al., Clinical role of 3-D CT reconstructions for defining spinal disease, Acta Radiol. Suppl., 369:699–702, 1986. 83. Kosling, S., Dietrich, K., Steinecke, R., Kloppel, R., and Schulz, H.G., Diagnostic value of 3-D CT surface reconstruction in spinal fractures, Eur. Radiol., 7(1):61–64, 1997. 84. Bowen, B.C. and Pattany, P.M., MR angiography of the spine, Magn. Reson. Imaging Clin. North Am., 6(1):165– 178, 1998. 85. Mascalchi, M., Quilici, N., Ferrito, G. et al., Identification of the feeding arteries of spinal vascular lesions via phase-contrast MR angiography with three-dimensional acquisition and phase display, Am. J. Neuroradiol., 18(2):351–358, 1997. 86. Binkert, C.A., Kollias, S.S., and Valavanis, A., Spinal cord vascular disease, characterization with fast threedimensional contrast-enhanced MR angiography, Am. J. Neuroradiol., 20(10):1785–1793, 1999. 87. Morikawa, K., Phase-contrast magnetic resonance imaging study on cord motion in patients with spinal dysraphism, comparison with healthy subjects, Osaka City Med. J., 45(1):89–107, 1999. 88. Baleriaux, D., The spinal cord [review], Curr Opin Neurol. Neurosurg., 4(6):852–857, 1991. 89. Wiest, P.W. and Sullivan, L.M., Neonatal, spinal, and intraoperative neural sonography, in Orrison W.W., Ed., Neuroimaging, Philadelphia, PA: Saunders, 2000: 396– 407. 90. An, H.S., Cervical disk disease, in An, H.S., Ed., Synopsis of Spine Surgery, Baltimore, MD: Williams & Wilkins, 1998: 204–206. 91. Levy, R.A., Three-dimensional craniocervical helical CT: is isotropic imaging possible?, Radiology, 197(3):645–648, 1995. 92. Kameyama, T., Hashizume, Y., Ando, T., and Takahashi, A., Morphometry of the normal cadaveric cervical spinal cord, Spine, 19(18):2077–2081, 1994. 93. Suzuki, M. and Shimamura, T., Morphological study of the axial view of the cervical spinal cord by MR images, Nippon Seikeigeka Gakkai Zasshi, 68(1):1–13, 1994. 94. Parke, W., Correlative anatomy of cervical spondylotic myelopathy, Spine, 13:831–837, 1988. 95. Pettersson, K., Karrholm, J., Tooanen, G., and Hildingsson, C., Decreased width of the spinal canal in patients with chronic symptoms after whiplash injury, Spine, 20(15):1664–1667, 1995.

96. Edwards, W.C. and LaRocca, H., The developmental segmental diameter of the cervical spinal canal in patients with cervical spondylosis, Spine, 8:20–27, 1983. 97. Arnold, J.G.J., The clinical manifestations of spondylchondrosis (spondylosis) of the cervical spine, Ann. Surg., 141:872–889, 1955. 98. Inoue, H., Ohmori, K., Takatsu, T., Teramoto, T., Ishida, Y., and Suzuki, K., Morphological analysis of the cervical spinal canal, dural tube and spinal cord in normal individuals using CT myelography, Neuroradiology, 38(2):148–151, 1996. 99. Pavlov, H., Torg, J.S., Robie, B., and Jahre, C., Cervical spinal stenosis, determination with vertebral body ratio method, Radiology, 164(3):771–775, 1987. 100. Torg, J., Pavlov, H., Genuario, S. et al., Neurapraxia of the cervical spinal cord with transient quadriplegia, J. Bone Joint Surg. Am., 68:1354–1370, 1986. 101. Wada, E., Ohmura, M., and Yonenobu, K., Intramedullary changes of the spinal cord and cervical spondylotic myelopathy, Spine, 20:2226–2232, 1995. 102. Nagata, K., Kiyonaga, K., Ohashi, P., Sigara, M., Miyazaki, S., and Inoue, A., Clinical value of magnetic resonance imaging for cervical myelopathy, Spine, 15(11):1088–1096, 1990. 103. Ono, K., Ota, H., Tada, K., and Yamamoto, T., Cervical myelopathy secondary to multiple spondylotic protrusions: a clinicopathologic study, Spine, 2:109–125, 1977. 104. Penning, I., Wilmink, J.T., van Woerden, H.H., and Knol, E., CT myelographic findings in degenerative disorders of the cervical spine: clinical significance, Am. J. Roentgenol., 146:793–801, 1986. 105. Law, M.D., Jr., Bernhardt, M., and White, A.A. III, Cervical spondylotic myelopathy: a review of surgical indications and decision making, Yale J. Biol. Med., 66(3):165–77, 1993. 106. Fujiwara, K., Yonenobu, K., Ebara, S. et al., The prognosis of surgery for cervical compression myelopathy: an analysis of factors involved, J. Bone Joint Surg. Br., 71:393–398, 1989. 107. Ahmad, I., Rosenbaum, A.E., Yu, F.S., Collins, G.H., Collins, C.S., and Poe, L.B. Intrinsic cervical spinal cord deformation on MRI, “the distorted ‘H’ sign,” J. Spinal Disord., 9(6):494–499, 1996. 108. Takahashi, M., Sakamoto, Y., Miyawaki, M., and Bussaic, H., Increased MR signal intensity secondary to chronic cervical cord compression, Neuroradiology, 29:550–556, 1987. 109. Mehalic, T., Pezzuti, R., and Applebaum, B., Magnetic resonance imaging and cervical spondylolytic myelopathy, Neurosurgery, 26:216–226, 1990. 110. Kulkanari, M.V., Mcardle, C.B., Kopanicky, D. et al., Acute spinal cord injury: MR imaging at 1.5T, Radiology, 164:837–843, 1987. 111. Ohshio, I., Hatayama, A., Kaneda, K., Takahara, M. and Nagashim, K., Correlation between histopathologic features and magnetic resonance images of spinal cord lesions, Spine, 18(9):1140–1149, 1993.

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112. Demeter, S.L., Corsaco, E.M., and Wolfe, T., Pulmonary function testing, in Demeter, S.L,, Andersson, G.B.J., Smith, P.M., Eds., Disability Evaluation, St. Louis, MO: Mosby, 1996: 304–317. 113. Wetzel, J., Respiratory evaluation and treatment, in Adkins, H.V., Ed., Spinal Cord Injury, New York: Churchill-Livingstone, 1985: 78–81. 114. Jacobs, S.R. and Roberts, J.D., Respiratory system management, in Ruskin, A.P., Ed., Current Therapy in Physiatry, Philadelphia, PA: Saunders, 1984: 368. 115. Sedor, F.A., Body fluid analysis, in Bishop, M.L., Duben-Von Laufen, J.L., and Fody, E.P., Eds., Clinical Chemistry Principles, Procedures, Correlations, Philadelphia, PA: Lippincott, 1985: 488–490. 116. DeJong, R.N., (rev. by Haerer, A.F.), Examination of the autonomic nervous system, in Dejong, R.N., Ed., (rev. by Haerer, A.F.), The Neurological Examination, Philadelphia, PA: Lippincott, 1992: 519–520. 117. Bradley, W.E., The diagnosis and treatment of patients with neurological dysfunction of the urinary bladder, in Lowe, P.A., Ed., Clinical Autonomic Disorders, Boston, MA: Little, Brown, 1993: 574–580.

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118. Kiss, G., Madersbacher, H., and Poewe, W., Cortical evoked potentials of the vesicourethral junction — a predictor for the outcome of intravesical electrostimulation in patients with sensory and motor detrusor dysfunction, World J. Urol., 16(5):308–312, 1998. 119. Frankel, H., Hancock, D., Hyslop, G. et al., The value of postural reduction in the initial management of closed injuries of the spine with paraplegia and tetraplegia. I, Paraplegia, 7(3):179–192, 1969. 120. American Spinal Injury Association (ASIA) and International Medical Society of Paraplegia (IMSOP), International Standards for Neurological and Functional Classifications of Spinal Cord Injury, rev. ed., Chicago, IL: ASIA/IMSOP, 2000. 121. Benzel, E.C. and Larson, S.J., Recovery of nerve root function after complete quadriplegia from cervical spine fractures, Neurosurgery, 19(5):809–812, 1986. 122. Kuhtz-Buschbeck, J.P., Johnk, K., Mader, S., Stolze, H., and Mehdorn, M., Analysis of gait in cervical myelopathy, Gait Posture, 9(3):184–189, 1999. 123. Anderson, G.B.J., Evaluation of Muscle Function in the Adult Spine: Principles and Practice, New York: Raven Press, 1991: 241–274.

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The degree of spinal cord injury (SCI) can be determined based on the clinical evaluation of function below the level of injury. If no sensory or motor function below the level of injury is detectable, the SCI would be classified as “complete.” However, many patients with SCI or myelopathy have incomplete patterns of neurological compromise. Because of the consistent arrangement and location of ascending and descending spinal cord pathways and segmental-level neuronal cell bodies, predictable neurologic syndromes occur with injury to a given region.

6.1 VASCULAR SYNDROMES OF THE SPINAL CORD Vascular syndromes are potential emergencies requiring astute recognition. We have simplified the presentations so that they might be recognized.

6.1.1 ANTERIOR SPINAL ARTERY SYNDROME Anterior spinal artery syndrome (ASAS) refers to the signs and symptoms associated with SCI that occur secondary to anterior spinal artery occlusion or hypotension. ASAS is a severe ischemic event in the distribution of the anterior spinal artery (Table 6.1). This region of vascular supply includes the anterior funiculi, anterior horns, base of the dorsal horns, anteromedial aspect of the lateral funiculi, and the periependymal regions (Figure 6.1). Occlusion of the anterior spinal artery results in an abruptonset, complex presentation (Table 6.2). The patient may describe lancing pain in a girdle-like distribution, rapid onset paralysis, impaired bowel and bladder control, sexual dysfunction, and a dissociated loss of pain and temperature sensation below the level of the lesion. Thermoanesthesia and analgesia often occur secondary to ischemic or infarctive changes within the spinothalamic tracts. A segmental loss of muscle function may develop within minutes or hours corresponding to the level of the lesion. There is a sparing of vibratory perception, position sense, and light touch because the posterior columns have a separate blood supply from the posterior spinal arteries (Figure 6.2).

6.1.2 POSTERIOR SPINAL ARTERY SYNDROME (PSAS) Posterior spinal artery syndrome (PSAS) is less common than ASA syndrome. The paired posterior spinal arteries allow for more extensive collateral flow, reducing the risk

for spinal cord arterial insufficiency. The area of the spinal cord perfused by the posterior vascular network is smaller than the area subserved by the ASA and its branches. This syndrome presentation is less complex than ASAS (Table 6.3). The PSAS results from ischemic insult to the fasiculus cuneatus, fasiculus gracilus, and posterior spinocerebellar tract. Vibratory perception and position sense are usually the first modalities lost. There is often a reduction or loss of associated segmental muscle stretch reflexes. Gait in these patients is ataxic and cautious. A positive Romberg sign is present with poor coordination.

6.1.3 RADICULOMEDULLARY ARTERY SYNDROME (RAS) Compromise of the radiculomedullary artery at the intervertebral foramen may contribute to spinal cord arterial insufficiency. Spondylosis and osteophytic narrowing of the intervertebral foramen (IVF) can result in encroachment of the arterial supply. The radiculomedullary arteries are not found at every vertebral level. Multilevel radiculomedullary compromise within the IVF may result in a pathologic watershed zone within the spinal cord. The signs of RAS are variable depending on the pattern of intramedullary insufficiency.

6.1.4 CENTRAL CORD VASCULAR SYNDROME (CCVS) The central cord vascular syndrome (CCVS) is one of the most common cervical cord syndromes, more common in male patients of middle and older age groups who have preexisting cervical spondylosis and stenosis. A CCVS is characterized by flaccid motor deficits of the distal upper extremities often accompanied by dysesthesia. Usually sensation from the sacral region is spared because the outer periphery of the cord is unaffected. A central cord syndrome may occur secondary to aortic disease and hypotension. Herrick and Mills1 report two cases of central spinal cord infarction that primarily involved the gray matter. A CCVS may be difficult to differentiate from an ASAS. Systemic hypotension may lead to severe impairment of perfusion through a watershed zone occurring between the territory perfused by AS and PS arteries.2 The CCVS presents very similar to ASAS due to compromise of the anterior horn and anterior commissure. 139

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Posterior spinal artery

Anterior sulcal (sulcocommissural) artery

The anterior spinal artery supplies the anterior 2/3 of the cord. This includes the central gray matter and lateral columns of the spinal cord. The posterior spinal and circumferential arteries supply the remaining 1/3 of the cord. A compressive lesion or thrombosis within the anterior artery produces paresthesias, pain, spastic paresis, flaccid paralysis and bowel and bladder dysfunction. The posterior columns are usually spared, leaving proprioception and vibration intact.

Posterior spinal distribution Circumferential branches

Anterior spinal artery located within sulcus

Anterior sulcal distribution

Circumferential distribution

Posterior spinal artery

FIGURE 6.1 Intramedullary arterial supply to the spinal cord. (Copyright J.M. True, D.C.)

TABLE 6.1 Selective Causes of Ischemia and Infarction within the Distribution of the Anterior Spinal Arterya • • • • • • • • • • • a

Intervertebral disk herniation Complications of discectomy Ballistic trauma to the spine Angiography Surgical complications of aortoiliac disease Complications of surgery Polyarteritis Sickle cell anemia Giant cell arteritis Syphilis Arteriosclerosis Not listed in order of prevalence.

6.2 COMPLETE SPINAL CORD TRANSECTION (TRANSVERSE MYELOPATHY) Transverse myelopathy results in complete interruption of all ascending and descending tracts at the level of the lesion. This results in a loss of motor, sensory, autonomic, and reflex functions.

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TABLE 6.2 Anterior Spinal Artery Syndrome • • • • • • •

Radicular and ascending leg pain Sensory level for pain and temperature Sudden progressive paraplegia Flaccidity (acute), spasticity (late) Areflexia (acute), hyperreflexia with Babinski’s sign (late) Sparing of touch, vibration, and temperature Urinary and fecal incontinence (uncommon)

TABLE 6.3 Posterior Spinal Artery Syndrome • • • •

Suspended global anesthesia Regional tendon and cutaneous reflex loss Dorsal column sensory level Sparing of anterior cord functions

Radicular pain, radicular paresthesia, and/or focal pain over the spine may have localizing significance. Focal pain may be elicited through spinal percussion and/or palpatory techniques. Hypoalgesia or anesthesia below the

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Spinal cord (T7) Posterior spinal arteries Territory of the posterior spinal artery

Posterior columns

Lateral corticospinal tract

Territory of the anteriorspinal artery

Lateral spinothalamic tract Anterior spinothalamic tract Anterior spinal artery

Motor loss below T7 (paraplegic) T7 level Segmental sensory loss

Loss of pain-temperature sensation

Several segments of cord infarction

FIGURE 6.2 Anterior spinal artery territory and syndrome. The anterior spinal artery (with its collateral supply) irrigates the anterior two thirds of the cord (diagonal hatching). All segmental functions are affected in the infarcted cord levels. Deficits in pain–temperature sensation occur below the sensory level, due to interruption of all ascending information in the spinothalamic tracts bilaterally. The posterior columns (and posterolateral columns), serving vibration and some aspects of fine touch and joint position sense, are preserved. The lateral corticospinal tract involvement causes paraplegia. (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, Oxford, 1993, p. 307. With permission.)

level of the lesion often provides important localizing significance. With a complete transverse lesion, all sensory modalities below the level of compromise will be absent. Paraplegia or tetraplegia occurs below the level of a complete transverse lesion. All unattended lesions above the level of C3 are fatal due to respiratory failure secondary to paralysis of diaphragmatic and accessory respiratory muscles. Acute SCI with transverse myelopathy results in a period of spinal shock. After recovery from spinal shock, hypertonicity and spasticity develop below the level of the lesion. The toes are upgoing (Babinski’s response) to plantar stimulation, and there is a loss of superficial reflexes

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and the cremasteric response. At the level of the transverse lesion lower motor neuron findings include flaccid paresis, hyporeflexia, fasciculations, and atrophy. The specific location of a transverse myelopathy in the thoracic region can sometimes be difficult to assess solely by clinical examination. Transverse myelopathy may result in urinary and rectal dysfunction with incontinence. Initially atonic, and later hyperreflexive, rectal and bladder sphincteric dysfunction occurs. Stimulation of the perineum often produces a reflex contraction of the spastic bladder with subsequent involuntary partial voiding. Constipation with risk for fecal impaction occurs as a result of the atonic bowel presentation. Voluntary control of the bladder is not possible

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TABLE 6.4 Central Cord Syndrome: Clinical Characteristics • • • •

Bandlike thermoanesthesia or thermodysesthesia Bandlike analgesia or hypoalgesia Preservation of light touch Dissociated sensory loss

with a complete transverse myelopathy because of the loss of descending influences. Anhidrosis and trophic skin changes may be seen below the level of the transverse lesion. There is sexual dysfunction with impotence.

6.3 CENTRAL CORD SYNDROME The acute central cord syndrome is characterized by a disproportionate loss of motor power in the upper extremities vs. the lower extremities with varying degrees of sensory involvement. Patients with a central cord syndrome may be capable of substantial recovery unless there is persistent spinal cord compression. A chronic central cord syndrome can occur secondary to lesions that compromise the central portion of the spinal cord, such as syringomyelia, hydromyelia, and intramedullary spinal cord tumors. A central cord syndrome within the cervical region is usually associated with severe hand paresis, which is disproportionate to pyramidal long tract signs in the lower extremities. The hands are often the last region to recover. Post-traumatic central cord compromise can occur in the absence of spinal fracture or dislocation with severe hyperextension. An acute central spinal cord syndrome can occur secondary to ballistic cervical injuries. Weakness in the arms is usually the predominant motor finding. There may be a patchy hypoesthesia of the extremities involving the segmental level below the lesion. The signs and symptoms are often temporary and may be secondary to high-velocity stretch injury to neurons within the central gray matter and corticospinal tracts within the cervical enlargement. A post-traumatic cervical syrinx may be noted incidentally upon cervical MRI evaluation. One of the earliest manifestations of a central cord syndrome results from insult to the spinothalamic fibers crossing in the midline (Table 6.4; Figure 6.3). These fibers convey pain and temperature sensibility. Injury to decussating spinothalamic fibers in this region results in a disassociated sensory clinical presentation due to preservation of the posterior column fibers. Damage to the crossing fibers will produce a loss of pain and temperature perception in a suspended vestlike pattern. With a true midline lesion there will be a relatively symmetric crossover

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spinothalamic deficit. With small paramedian lesions, sensory dissociation will be present, but the degree of thermohypoesthesia and hypoalgesia may be asymmetric. The clinical presentation and region of sensory loss will expand consistent with the expansile evolution of the lesion. In a small study, Quencer and colleagues3 evaluated the magnetic resonance imaging (MRI) appearance of spinal cords from patients with acute traumatic central cord syndrome. All patients exhibited hyperintense signal within the parenchyma of the cervical spinal cord on gradient echo MRI, representing cord edema. None showed MRI features characteristic of hemorrhage on T1-weighted spin echo or T2-weighted gradient echo studies. Gross and histological examination of the necropsy specimens showed no evidence of blood or blood products within the cord parenchyma: the primary finding was diffuse disruption of axons, especially within the lateral columns of the cervical cord in the region occupied by the corticospinal tracts. An interesting observation in this study was that the central gray matter was found to be intact.3 These researchers noted that patients with preexisting cervical stenosis or spondylosis were more likely to have a predominant white matter injury with little evidence for intraparenchymal hemorrhage following acute cervical trauma. With enlargement and dorsal migration of a central cord lesion, the posterior columns may be involved, resulting in superimposition of diminished vibratory and kinesthetic loss. Extreme anterolateral migration of a central lesion may compromise the spinothalamic tract. This results in impairment of pain and temperature perception below the level of the lesion. If anterolateral lesion migration is predominantly ipsilateral, the degree of clinical pain and temperature loss will be greater contralateral to the side of the lesion. Medial to lateral progression of a central cord lesion will initially spare sacral pain and temperature sensibility. Pure anterior horn lesions are characterized by segmental flaccid paresis, atrophy, and hyporeflexia. Extensive lateral involvement with a central cord syndrome can include compromise of the corticospinal tracts resulting in spastic paresis or paralysis below the segmental level of the lesion. Clinical characteristics of upper motor neuron lesion (UMNL) include hyperreflexia, spasticity, and pathologic reflex responses such as upgoing toes to plantar stimulation in adults. Sparing of autonomic functions occurs in the presence of small central spinal cord lesions. Extreme lateral extension of a central cord lesion may result in compromise of the intermediolateral cell column. If this occurs at the C8–T2 neurologic levels, it can result in an ipsilateral Horner’s syndrome (miosis, lid ptosis, and ipsilateral facial anhidrosis). Lateral mass expansion with extensive damage to the lateral horns will contribute to extremity trophic changes.

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(A) Cervical cord Lesion (cavity)

143 Posterior columns (vibration, aspects of fine touch, and joint position sense) Corticospinal tract

Segmental gray matter damage

2nd order pain-temperature fiber (B)

Spinothalamic tract Anterior white (pain-temperature) commissure (crossing spinothalamic tract fibers) Loss of pain-temperature sensation (damage to crossing fibers); also multisegmental motor deficits

FIGURE 6.3 Syringomyelia. (A) In a representative section of the cervical cord, the lesion (a central cavity) involves the anterior white commissure (just ventral to the central canal) through which the second-order fibers of the pain–temperature pathway cross. (B) Pain–temperature sensation is lost only at (or slightly below) each segment of damage from the syringomyelic cavity, but is not lost from lower parts of the body since the spinothalamic tracts themselves are unaffected. Lower motor neuron deficits are also variably present in each affected segment because of damage to the anterior horns of the spinal cord. Compare with the anterior spinal artery syndrome. (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, Oxford, 1993, p. 308. With permission.)

6.4 ANTERIOR CORD SYNDROME The second most common cervical syndrome is the anterior cord syndrome (ACS). Schneider4 originally described the anterior cord syndrome following acute cervical trauma. ACS is often associated with cervical flexion and extension injury that may be accompanied by vertebral fracture, dislocation, or disk herniation. ACS occurs when the anterior portion of the spinal cord is compromised through direct trauma or ischemia. By definition, there is sparing of the posterior columns with preservation of proprioception, light touch, and position sense (Table 6.5). Mild cases of ACS may be associated with retention of some motor function

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due to sparing of descending fibers within the lateral corticospinal tracts. The prognosis for anterior cord syndrome is usually not as good as with the central cord syndrome.

6.5 POSTERIOR CORD SYNDROME A pure posterior cord syndrome (PCS) is rare, characterized by selective compromise of the posterior columns (Figure 6.4). This typically occurs secondary to neurosyphilis or an expansile extradural lesion lying within the posterior cervical canal. An expansile lesion may initially present as a PCS, eventually developing into a posterolateral

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A

B

FIGURE 6.4 (A) Posterior cord (column) syndrome. (B) Axial T2 weighted cervical spine image demonstrating bilateral posterior column high-intensity signal. This patient has confirmed pernicious anemia.

TABLE 6.5 Anterior Cord Syndrome: Clinical Characteristics • • • •

Preservation of proprioception Preservation of vibratory perception Diminished or loss of pain and temperature sensation below lesion Complete or incomplete motor loss

TABLE 6.6 Posterior Cord (Column) Syndrome: Clinical Characteristics • • • • • • •

Impaired vibration sense Abnormal position sense Loss of deep pressure perception Diminished tactile localization Sensory gait ataxia Tactile and postural hallucinations Spared pain and temperature perception

cord syndrome. The primary differential evaluation of posterior column presentation should include tabes dorsalis, central spinal canal stenosis, and demyelinative disease such as multiple sclerosis. The characteristic sensory presentation of PCS includes a loss of proprioception and discriminative sensation distal to the lesion (Table 6.6). There is often a positive Romberg sign and sensory ataxia; during the Romberg maneuver, the loss of balance increases dramatically with closing of the eyes. Patients with sensory ataxia will attempt to observe their feet during ambulation, using visual cues to help correct for loss of kinesthesia. The clinician may occasionally observe a double tap sign during gait, reflecting the individual’s attempt to increase afferentation.

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TABLE 6.7 Syndrome of Posterolateral Columns (Subacute Combined Degeneration): Clinical Characteristics • Distal extremity paresthesia • Sensory ataxia • Hyperreflexia (superimposed peripheral neuropathy may cause hyporeflexia) • Muscular spasticity • Bilateral toe extensor signs (Babinski’s) • Impaired proprioception and vibratory sense • Sparing of pain and temperature sensibility

Posterior column compromise may lead to truncal ataxia, secondary to impaired proprioception and postural perception. Some degree of truncal and extremity disuse muscle atrophy and paresis usually occurs secondary to involuntary and voluntary limitation of physical activity. Patients with moderate to severe posterior column compromise often present with diminished or absent patellar and Achilles muscle stretch reflexes (MSRs). Individuals may also complain of urinary incontinence.

6.5.1 POSTEROLATERAL CORD SYNDROME The posterior spinocerebellar tract, fasciculus cuneatus, and fasciculus gracilis may be compromised in a number of conditions. Contributing conditions include vitamin B12 deficiency with subacute combined degeneration, vacuolar myelopathy secondary to autoimmune deficiency syndrome (AIDS), and cervical spondylosis with ligamentum flava buckling and hypertrophy. Many patients with posterior column lesions initially complain of distal extremity paresthesia, sensory ataxia, and loss of proprioceptive functions (Table 6.7; Figure 6.5). The patient may report diminished distal extremity vibratory perception during examination in the early stages of compromise. As the condition progresses,

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FIGURE 6.5 Posterolateral cord syndrome.

loss of vibratory perception intensifies and impaired joint position sense becomes more apparent, but, with early detection, most conditions will not progress to this level of severity. If posterolateral cord syndrome is suspected, the clinician should always evaluate for subtle or progressive sensory disturbances. Subacute combined degeneration spares the spinothalamic tract, preserving pain and temperature sensation. In the absence of obvious long tract signs, peripheral neuropathy should also be considered in the differential diagnosis of lower extremity sensory loss. Autonomic centers or pathways are not typically involved with posterolateral compromise.

6.6 ANTERIOR HORN SYNDROME (PROGRESSIVE MUSCULAR ATROPHY) Several diseases selectively compromise the motor cells of the anterior horn (Figure 6.6). Diseases that selectively afflict the anterior horn lead to progressive muscular atrophy. Prior to development of the polio vaccine, the most common cause for acute anterior horn syndrome was poliomyelitis. Less common is an acute syndrome secondary to other enteroviruses. Lymphoma, on rare occasions, has been associated with subacute motor neuronopathy involving the anterior horn. A few forms of inherited spinal muscular atrophy may present as an isolated anterior horn syndrome. In a pure anterior horn syndrome, sensation is normal, due to sparing of the sensory tracts and fibers. A lower motor neuron presentation occurs at the segmental level of insult. The clinical findings include flaccid paresis/paralysis, atrophy, hypotonus, and hyporeflexia within affected segmental levels. Additional findings may include axial and extra-axial fasciculations. With selective anterior horn compromise there is sparing of the autonomic tract or fibers (Table 6.8).

6.6.1 POLIO

AND

POST-POLIO SYNDROME

Poliomyelitis is an extremely rare viral disease caused by a picornavirus that is transmitted initially through the gastrointestinal system. Spinal cord infection results in aggressive degeneration of the anterior horn and alpha motor neurons. Involvement is not limited to the spinal cord, as areas of the brain and brainstem may also be

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FIGURE 6.6 Anterior horn cord syndrome.

TABLE 6.8 Anterior Horn Syndrome: Clinical Characteristics • • • • •

Diffuse weakness (LMNL) Muscular atrophy Reduced muscle tone Muscle fasciculations Hyporeflexia or areflexia

afflicted. Some infected individuals only experience minor illness with a sore throat, vomiting, malaise, abdominal pain, and mild headache. Others go on to suffer devastating motor neuron loss with associated lower motor neuron features. After the initial illness, some neurological recovery might occur during the ensuing 4 to 8 years, likely due to partial anterior horn cell recovery and collateral sprouting.5 As many as 25 to 60% of patients afflicted with polio may acquire additional signs and symptoms 25 to 50 years after the initial infection.6 The post-polio syndrome (PPS) is characterized by predominant musculoskeletal symptoms and post-polio progressive muscular atrophy. There may be new onset of joint pain, muscle pain, and acquired pathomechanical lesions such as scoliosis. There may be progressive impairment of bulbar and spinal involvement including muscles not previously affected. The specific etiology of post-polio syndrome has not been determined but it has been proposed that surviving motor neurons with extensive collateral sprouts may become compromised secondary to metabolic and/or age-related changes leading to critical axonal dropout and muscular impairment.5 The diagnosis of PPS can be made assuming the following criteria are met: (1) history of poliomyelitis with 15 years of functional stability; (2) residual asymmetric muscular atrophy, hypotonia, paresis, and areflexia; (3) new onset of neuromuscular symptoms to include paresis and atrophy; and (4) exclusion of other possible etiologies.7

6.6.2 COMBINED ANTERIOR HORN AND PYRAMIDAL TRACT DISEASE (MOTOR NEURON SYNDROME) Combined anterior horn and pyramidal tract disease syndrome is often referred to as amyotrophic lateral sclerosis

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Irregular intramedullary lesions

FIGURE 6.7 Combined anterior horn and pyramidal tract cord syndrome.

TABLE 6.9 Spinal Motor Neuron Disease: Clinical Characteristicsa • Upper motor neuron lesion (UMNL) Spastic paresis Extensor plantar responses Hyperreflexia • Lower motor neuron lesion (LMNL) Muscular atrophy Flaccid paresis Fasciculations a

Combined upper and lower motor neuron signs.

(ALS) (Figure 6.7). ALS is a terminal progressive disease with features similar to spastic paraplegia and the spinal muscular atrophies. Damage to the anterior horns will result in flaccid paresis, whereas coexistent compromise of the pyramidal tracts produces spastic paresis. In ALS, spinal presentations usually predominate in the early stages, eventually progressing to bulbar paralysis. The disorder is most predominant in males.8 Early clinical signs are often unilateral and limited to the distal extremities. ALS can progress to compromise any striated muscle and occasionally spares the pelvic floor sphincters and external ocular muscles. Sensory perception is characteristically spared. ALS develops into a complex presentation of combined upper and lower motor neuron disease (Table 6.9). This presentation often coexists within the same extremity. The individual may present with hand atrophy and evidence of spasticity after passive extension of the fingers. MSR hyporeflexia secondary to anterior horn insult may appear normal with coexistence of upper motor neuron mechanisms from impaired pyramidal fibers. Upper motor neuron presentations include spasticity, hyperreflexia, and spastic paresis, whereas the lower motor neuron presentations include flaccid paresis, hyporeflexia, hypotonus, and fasciculations. Lower extremity muscle stretch reflexes are usually hyperreflexive during most of this disease process. Bulbar deficits, when present, may cause a rapid decline in the condition. These deficits may manifest as explosive dysarthria, difficulty swallowing,

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FIGURE 6.8 Multifocal cord syndrome.

glossal spasticity, and loss of vital capacity. ALS causes death by respiratory paralysis, cardiac failure, or suffocation from aspiration of food or liquids due to loss of swallowing control.

6.7 MULTIFOCAL CORD SYNDROME The multifocal cord syndrome does not follow any of the classic presentations of the other syndromes described in this chapter. The more common etiologies for multifocal cord syndrome include multilevel stenosis and/or multifocal demylinative disease. There may be increased vulnerability secondary to metabolic influences such as diabetes. Demyelinative lesions do not characteristically occur within watershed regions; therefore, the presentation is not characteristic of vascular syndromes. Demyelinative changes can occur anywhere throughout the spinal cord (Figure 6.8). Multifocal stenosis can lead to multisegmental lower motor neuron paresis with superimposed upper motor neuron and other long tract signs (myeloradiculopathy).

6.8 CONUS MEDULARIS SYNDROME The distal end of the spinal cord tapers to a conical shaped tip referred to as the conus medullaris. The conus contains the segments (neuromeres) for the lumbar and sacral regions and generally lies posterior to the L1 vertebral body or at the L1–L2 disk interspace. Most of the lumbar cord neuromeres lie within the conus adjacent to the T12 vertebral body, and most of the sacral cord segments lie opposite the L1 vertebral body.

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A

B

C

FIGURE 6.9 (A) Distal spinal cord neoplasm visualized in the axial plane, demonstrating marked cord expansion encompassing the entire spinal canal. (Axial spin echo T1-weighted image through the conus medullaris following gadolinium enhancement.) (B, C) Round enhancing mass contained within the conus medullaris, confirmed as a myxopapillary adenoma. Note expansion of the distal spinal cord. There is also a central nonenhancing area representing focal cystic degeneration. (Parasagittal spin echo T1-weighted image following gadolinium enhancement; parasagittal spin echo T2-weighted image.) These two images are to the right of the midline. (Courtesy Dr. Mary Ann Hordesky–Storr, D.C.)

TABLE 6.10 Epiconus Syndrome: Clinical Characteristics • • • • •

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Loss of bladder control Loss of perianal muscle control Absent bulbocavernosis reflex Absent anal wink reflex Flaccid paresis of lower extremity

A conus syndrome may arise from intraparenchymal or extraparenchymal pathology (Figure 6.9). The conus is susceptible to injury at the T11–12 and T12–L1 levels due to greater segmental movement as compared to the more immobile thoracic region. Injury to the upper portion of the conus medullaris may result in a combined upper and lower motor neuron presentation often preceded by initial flaccid paralysis of the legs, bladder, and anal sphincter (Figure 6.10; Table 6.10). This is often followed by muscular atrophy, muscle spasticity, positive Babinski’s response, and

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A. Lower cord A Lower cord lesion

Distal ipsilateral lower extremity spastic hemiparesis

(hemisection)

Contralateral loss of pain and temperature below level of lesion

B

High radicular and lateral conus lesion

Ipsilateral loss of light touch and kinesthesia below level of lesion Ipsilateral lower extremity hyperreflexia below level of lesion Ipsilateral positive Babinbski

C D B. Lateral conus

Midline distal conus/epiconus lesion

Ipsilateral lower extremity muscle hypertonicity below level of lesion Ipsilateral segmental sensory and paresis

Midline cauda equina lesion

C. Distal conus

D. Cauda equina Prominent radicular pain

Ipsilateral segmental flaccid muscle paresis/paralysis

Motor findings are usually not severe

Ipsilateral segmental sensory loss

Rarely severe pain

No dissociated sensory loss

Bilateral perineal pain

Bowel/bladder function

Infrasegmental ipsilateral hyperreflexia Infrasegmental ipsilateral spastic hemiparesis/paralysis Ipsilateral positive Babinski May have reflex neurogenic bladder with large lesion

Epiconus: absent achilles MSR Conus: Intact patellar and achilles MSRs. May be hyperreflexive Saddle anesthesia is a late sign Early and marked urinary and fecal incontinence

Patellar and achilles MSRs may be absent Late onset sphincter disturbance Saddle distribution of sensory loss

May develop a motor paralytic bladder Bilateral lower extremity flaccid paresis/paralysis

May develop an autonomous bladder in severe cases

FIGURE 6.10 Localizing patterns in lesions of the lower cord, conus medullaris, and cauda equina. (Copyright J.M. True, D.C.)

hyperreflexia. The sensory presentation is variable, and sensory sparing may be limited to perianal sensation. In more severe cases of conus medullaris insult, bowel and bladder deficits may be profound. Compromise limited to the distal tip of the conus may spare the greater portion of descending pyramidal fibers, thus raising the possibility that long tract signs may be minimally present or nonexistent. An extraparenchymal lesion arising from the region of the distal conus may result in a unilateral or bilateral lower motor neuron presentation due to polyradiculopathy, bladder impairment, and perineal and perianal sensory disturbances.

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Injury to the conus or epiconus may also injure the cauda equina. Neurological compromise within the conus generally has the same prognosis as spinal cord compromise at more rostral levels. A high lumbar disk herniation may result in compression of the conus medullaris (Figure 6.11). Compromise of the cauda equina has a much better prognosis than SCI due to the greater capacity for neurologic recovery of the descending nerve roots. Urodynamic assessment is an important part of the differential workup of any patient with a neurologically significant lesion at the thoracolumbar vertebral level.9

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FIGURE 6.11 A high lumbar disk herniation is rare; however, it may produce cord or conus medullaris compression as well as spinal nerve root compression. (Copyright J.M. True, D.C.)

TABLE 6.11 Hemisection Cord Syndrome (Brown–Séquard): Clinical Characteristics • Ipsilateral loss of vibratory perception • Segmental lower motor neuron signs at the level of the lesion • Ipsilateral loss of proprioception (position sense) (below level of lesion) • Contralateral loss of pain and temperature sensibility (one or two segments below level of lesions) • Ipsilateral motor loss with spastic paresis • Inability to walk • Loss of normal bowel and bladder function

6.9 HEMISECTION SYNDROME (BROWN–SÉQUARD SYNDROME) A Brown–Séquard syndrome refers to injury to the lateral half (hemisection) of the spinal cord. This syndrome is characterized by ipsilateral motor deficits, ipsilateral proprioceptive loss, diminished ipsilateral vibratory perception, and contralateral loss of pain and temperature sensation. In mild cases there may be sparing of sphincter function (Table 6.11). A number of different mechanisms have been found to contribute to the hemisection syndrome. The most common cause is observed with hyperextension injuries and facet and compression fractures, including those studied by Braakman and Penning.10 The Brown–Séquard syndrome occurs most often after cervical injuries and less frequently after thoracic cord injuries. Large or expansile extramedullary lesions can compress the spinal cord, resulting in a Brown–Séquard syndrome. Spinal cord hemisection may be incomplete with some sparing of descending and ascending nerve fibers.

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Hemimyelopathy occurs more commonly from posttraumatic concussions or contusions as well as due to an expansile lesion. Initially, the presentation may be subtle. Patients taking anticoagulants may suffer post-traumatic or spontaneous hemimyelopathy secondary to hematomyelia and/or epidural hematoma. Additional causes of Brown–Séquard syndrome include vertebral fracture-dislocations, severe spondylosis with projective exostosis, migration of disk or bone fragments, hematoma, or metastasis. Interruption of the crossed ipsilateral spinothalamic tract and spinothalamic projections results in contralateral loss of pain and temperature (Figure 6.12). The contralateral sensory loss occurs one to two segments below the level of cord compromise due to the descent of the spinothalamic fibers as they decussate. This anatomic arrangement results in preservation of ipsilateral spinothalamic sensibility (pain and temperature) below the level of the lesion. Contralateral pain and temperature loss with contralateral preservation of posterior column sensation creates a disassociated sensory loss distal to the SCI. There is ipsilateral loss of deep sensibility that includes joint position sense, two-point discrimination, and vibratory loss secondary to ipsilateral compromise of the posterior columns. Ipsilateral interruption of the dorsal spinocerebellar tract contributes to positional disorientation and abnormal kinesthesia. Compromise of the ipsilateral descending corticospinal tracts will lead to spastic paresis or paralysis below the segmental level of the lesion. Motor functions contralateral to the lesion are spared. An acute hemicord syndrome may initially present with ipsilateral hypotonicity and hyporeflexia below the segmental level secondary to spinal shock. After recovery from spinal shock, ipsilateral MSR hyperreflexia, ipsilateral muscle spasticity, and Babinski’s responses develop below the involved segmental level. Ipsilateral compromise of the vasomotor fibers of the lateral columns contributes to dysautonomia presenting cutaneous hyperemia and absent or impaired sweat secretion. The lesion that causes the Brown–Séquard syndrome may also injure the anterior horn cells and associated nerve root or roots. This will result in segmental flaccid paresis or paralysis, muscle atrophy, and hyporeflexia. Segmental anesthesia and analgesia may be present if sensory portions of the nerve root are injured.

6.10 CERVICAL MEDULLARY SYNDROME Injury to the upper cervical cord may involve the medulla. Cervical medullary syndrome describes those syndromes involving injury to the upper cervical cord and lower brainstem. Lesions in the region of the foramen magnum are usually associated with a complex sensory and motor presentation. Compromise of cranial nerves IX–XII may occur. There is often suboccipital pain in the distribution of the C2 nerve root. Cerviocogenic headaches may accompany neck stiffness and reactive paracervical myospasm.

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FIGURE 6.12 Brown–Séquard syndrome. Principal deficits resulting from a right hemitransectional lesion of the spinal cord, shown here at T4 cord level. (A) Dissociated sensory loss, with deficit (shaded) or “dorsal column” modalities (vibration, some aspects of fine touch, and joint position sense) ipsilaterally below the lesion and spinothalamic (pain–temperature) deficit (shown by hatching) contralateral and almost up to the level of the lesion. Corticospinal motor deficits occur ipsilaterally below the lesion. All segmental functions are affected ipsilaterally at the level of the lesion. (B) In this highly simplified schema, “dorsal column” modalities are conveyed by first order neuronal fibers that enter the right side of the cord at each segment and would ascend in the right (ipsilateral) dorsal column without synapse until the medulla, if not blocked by the T4 lesion represented in (D). (C) The second order neuronal pain–temperature fibers cross just above their segmental level of origin to form the right lateral spinothalamic tract. (D) The position of the three main ascending and descending tracts are seen in the cross-section of the cord at T4 (lesion shaded). (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, Oxford, 1993, p. 271. With permission.)

Lesions extending into the region of the foramen magnum may be associated with a downbeat nystagmus, cerebellar ataxia, and cerebrospinal fluid (CSF) block with increased intracranial pressure. Clinical features of the cervical medullary syndrome include respiratory insufficiency or arrest, systemic hypotension, varying degrees of quadriparesis or quadriplegia, long tract sensory findings, bladder dysfunction, and lower cranial nerve involvement (Table 6.12). Hypoesthesia may extend from from C1–C4. There may be hemifacial sensory loss. It is critical to evaluate cranial nerve function in all potential cases of cervical medullary syndrome. The assessment of facial sensibility will help determine whether there is involvement of the trigeminal

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TABLE 6.12 Cervicomedullary Syndrome: Clinical Characteristics • • • • •

Respiratory insufficiency or arrest Arterial hypotension Varying degrees of tetraparesis Facial sensory loss Greater arm than leg weakness

nerve or the nucleus of the spinal tract of V, which extends as caudal as the C3 segment. The patient may complain of a perioral distribution of sensory disturbance or loss,

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suggesting injury to the lower medulla or upper cervical cord. Cervical medullary compromise can mimic a central cord syndrome due to the greater weakness of the arm than the leg. Compromise of the C1–C4 segments of the spinal cord may include insult to the spinal accessory nerve, cranial nerve XI. This nerve innervates the sternocleidomastoid (SCM) muscle and the upper portion of the trapezius muscle. Nerve damage will result in abnormal head position, trapezius, and SCM muscle atrophy and paresis. This will result in difficulty or inability to elevate the ipsilateral shoulder and difficulty rotating the head and neck towards the side opposite the lesion.

6.11 GUIDE TO NEUROLOGICAL LEVELS Classification of SCI using the “intact functional level” is one of the most clinically relevant systems for predicting outcome and physical rehabilitation requirements. The intact functional level classification scheme is based on the features observed with complete transection injury at a particular level, although incomplete patterns are more commonly seen in clinical practice. Polytraumatized patients often have complex neurological injuries including head trauma as well as cord and root findings. Patients with noncompressive myelopathy may exhibit a multifocal cord presentation or a combination of myelopathy and polyradiculopathy. A review of neurological levels provides a basis for diagnosis, therapeutic planning, and taking steps to improve the patient’s capacity to perform activities of daily living.

6.11.1 CRANIAL-CERVICAL LESIONS (FORAMEN MAGNUM LESIONS) Etiologies of foramen magnum lesions include tumors, multiple sclerosis (MS), Arnold–Chiari malformation, atlantoaxial dislocation, syringomyelia, and other congenital anomalies of the cervical cranial junction. This region can be a diagnostic challenge for the attending clinician as the symptoms are often vague and intermittent. Patients with Arnold–Chiari malformation type I without meningocele may present with progressive cerebellar dysfunction due to compromise of the cerebellar tonsils within the foramen magnum. This type I presentation may be characterized by increased intracranial pressure, myelopathy, upper cervical syringomyelia, and lower cranial nerve dysfunction. Many foramen magnum lesions are treatable; therefore, early diagnosis and intervention are important. Congenital anomalies of the cranial cervical junction are often asymptomatic. A lesion within the foramen magnum may contribute to suboccipital or upper neck pain that is often increased with cervical movement in various positions. Pain may radiate into the shoulders or

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proximal arm on the involved side. The pattern of pain is not unlike that of spondylosis. In many cases, spondylosis of mid- and lower cervical regions may coexist with the foramen magnum level lesion. Tumors at the foramen magnum constitute approximately 1% of all intracranial and intraspinal tumors.11 The cranial nerve signs and symptoms may include hemifacial dysesthesia, dysarthria, dysphonia, and dysphasia. Motor involvement generally presents as an upper motor neuron lesion with spastic weakness. Corticospinal tracts may be compromised by extramedullary intradural neurofibromas or meningiomas. Spastic paresis generally begins in the ipsilateral arm followed in order by weakness of the ipsilateral and contralateral leg. Foramen magnum tumors may occasionally cause signs of lower motor neuron weakness, atrophy, and reduced MSRs within the upper extremities and hands.12 Paresthesia associated with lesion at the foramen magnum often occurs along the ulnar aspect of the forearm and hand, but the mechanism whereby the upper motor neuron weakness and sensory loss occur in the same upper extremity has not been fully explained. The sensory abnormalities tend to be disassociated; therefore, patients suffering from hypoalgesia have preserved tactile sensation. When L’hermitte’s sign is frequently positive, the patient may exhibit some degree of vibratory abnormality over the clavicle or region of the acromion process.12 A relatively common cause of cervical-cranial abnormality resulting in myelopathy is that of atlantoaxial dislocation. This may occur secondary to hypoplasia of the odontoid process or incompetence of the transverse ligament. Some of the disorders associated with atlantoaxial instability and subsequent dislocation include congenital anomalies of the region, basilar impression, congenital scoliosis, neurofibromatosis, and rheumatoid arthritis. Metastatic cancer may be rarely seen at the dens. Atlantoaxial subluxation may result in physical spinal cord compression. This generally occurs when the sagittal diameter of the spinal canal is less than 14 mm, but physical compression of the spinal cord has been reported to occur occasionally at 15 to 17 mm.13 These upper cervical spine canal measurements where spinal cord compression occurs are larger than lower cervical spine measurements reported to occur between 10 and 13 mm.14 The mechanism of neural injury in many cases of atlantoaxial subluxation is compression of the medullary cervical junction by the odontoid process. (See Section 3.3.2.) The symptoms of atlantoaxial instability often are intermittent and involve weakness of an upper motor neuron type and some degree of wasting of the muscles of the upper extremities. Ataxia, dizziness, and lower cranial nerve symptoms are not uncommon. The presentation may mimic demyelinative disease.

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6.11.2 CERVICAL LESIONS Neoplasms involving the upper cervical spine have signs and symptoms that mimic lesions of the cranial-cervical region arising at the foramen magnum. The first cervical root does not have a sensory dermatomal distribution, but the second cervical root does innervate the posterior aspect of the scalp, explaining the pattern of radicular pain. In the presence of neoplasms involving the cervical spine, simple neck movements may result in pain radiating along the back of the head accompanied by dysesthesia. The descending tract of the trigeminal nerve may also be compromised, producing paresthesia or numbness in the face or loss of the corneal reflex.15 Fatality associated with high cervical transectional lesions, if not instantaneous, usually ensues within a matter of hours or days. Respiration becomes the critical factor when the motor neurons become disconnected from the respiratory center, inducing respiratory paralysis. Even incomplete transection creates problems, as respiration becomes depressed and insufficient due to spinal shock. Mortality increases after the initial injury because of the high risk of complications secondary to pneumonia. Autonomic functions are lost below the lesion. Bladder tonus and bowel function are lost as is sweating and piloerection. The lower extremities become edematous in response to impaired vasomotor tone and temperature regulation. With high spinal cord transection, determining which neurologic level is intact and functional is paramount. For the sake of the following discussion, a neurologic level is considered intact if its corresponding nerve root is intact and functional; thus, a neurologically intact C2 level will have a functional C2 nerve root while all segments caudally are completely dysfunctional. The presentations listed below may be incomplete. 6.11.2.1 Intact C3 Neurologic Level (C3 Functional Level) The presentation of the intact C3 neurologic level after cervical transection injury includes complete absence of upper extremity sensibility and loss of sensation caudal to approximately 3 inches above the nipple line along the anterior chest wall. The patient is completely tetraplegic. Deep tendon reflexes may be initially absent due to spinal shock but become brisk to exaggerated, with pathologic reflexes when the spinal shock dissipates. The patient is devoid of independent respiratory function due to disruption of diaphragmatic innervation and will require artificial respiratory assistance for the duration of life. Tracheostomy is necessary along with respiratory physiotherapy to clear lung secretions. Voluntary bowel and bladder function is nonexistent, requiring complete assistance. The mortality rate is very high due to respiratory complications.

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6.11.2.2 Intact C4 Neurologic Level (C4 Functional Level) A functional C4 neurologic level varies slightly from the C3 presentation. Hyperreflexia of deep tendon reflexes are deficits in the upper extremities beginning several inches lower on the mid-portion of the anterior chest wall. Motor findings include upper extremity spastic paralysis, but shoulder shrug function remains intact. The patient has respiratory insufficiency. The respiratory impairment is not complete, as the C4 neurologic level provides primary innervation to the diaphragm, but respiratory function remains depressed due to denervation of intercostal and abdominal muscles. C4 is the highest cervical functional level compatible with independent respiration. However, respiratory complications are common, and regular cough assistance is necessary to prevent pneumonia. Patients with functional C4 level generally have good head and neck control and can subsequently use a mouth stick. They are also capable of utilizing chin switches, breath control, eyebrow motion, and tongue switching for wheelchair or computer control. All activities of daily living require assistance. A mechanical lift for bed and toilet transfers is required. The patient is catheterized and the rectum must be manually cleared with assistance. 6.11.2.3 Intact C5 Neurologic Level (C5 Functional Level) The intact C5 neurologic level has a significantly different presentation than C4 with some upper extremity function preserved. Sensibility is intact along the lateral aspect of the arm from the shoulder to the elbow crease and along the upper anterior chest region. The biceps MSR is intact but may be absent during spinal shock, becoming brisk as spinal shock resolves. This first cord level subservient to the brachial plexus allows a functional but paretic deltoid muscle with mild biceps participation. Intact shoulder movement includes flexion, extension, and abduction with mild sparing of elbow flexion. The respiratory reserve remains depressed. As with all cord lesions above T10, the patient is unable to elicit a strong cough and will need assistance. A patient with a C5 functional level has a lesion just caudal to the C5 myotomal segment. The individual generally has full innervation of the trapezius, sternocleidomastoid, and upper cervical paraspinal musculature. The patient has intact rhomboids, deltoids, and major muscles of the rotator cuff, although these may be mildly paretic due to the contribution from the level of C6. These innervated muscles of the shoulder provide for scapular retraction and weak protraction, glenohumeral abduction, internal and external shoulder rotation. Elbow flexion is possible but is often mildly paretic due to the loss of C6

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nerve contribution. There is generally little to no elbow and wrist extension or hand function. Sensation is typically intact over the deltoid region and radial aspect of the thumb. This individual needs assistance in order to perform a prehensive pinch, often requiring electric hand splints with head, shoulder, and chin controls. The individual with a C5 functional level may require mobile arm supports. This individual generally has difficulty changing positions. Endurance is generally low because of reduced respiratory reserve. Bowel and bladder function requires assistance. These patients are not capable of independent transfers without a sliding board and subsequently are confined to a motorized wheelchair or bed. 6.11.2.4 Intact C6 Neurologic Level (C6 Functional Level) The C6 functional level represents one of the most common levels of quadriplegia. Over 50% of spinal cord injuries occur at the C6 level or slightly lower. The C6 neurologic level contributes to the brachial plexus and as a result the clinical picture begins to change significantly as some hand movement returns. Sensation of the lateral upper extremity extending distal to the thumb, index finger, and a portion of the middle finger is preserved. The biceps and brachioradialis muscle functions are intact; therefore, elbow flexion and supination are possible. With an intact C6 level, the supraspinatus and rotator cuff complex is fully innervated and strong. There is generally good stability and biomechanics at the glenohumeral joint. The serratus anterior, latissimus dorsi, and pectoralis major muscles receive partial innervation and are subsequently mildly paretic. The wrist extensor group receives partial innervation but remains paretic as the extensor carpi radialis muscle receives C7 innervation. The C6 intact individual will retain some function of pronation; however, forearm pronation and wrist extension remain paretic. Muscles distal to the proximal arm and shoulder are spastic, paretic, or paralyzed. Respiration is mildly depressed. There is a complete absence of voluntary finger extension or flexor power. This individual typically requires hand devices in order to enable prehension. Preservation of elbow flexors gives the individual the power to sit up independently or to assist with of this maneuver. There is greater capability of rolling over in bed. A strong individual with a functional C6 level may be able to independently transfer to a wheelchair. This individual is capable of feeding himself with hand-assistant devices and may contribute to toilet and dressing activities. This individual is capable of using elbow flexors and shoulder abductors and flexors to help guide a wheelchair. With extension of the wrist, typically the thumb and fingers approximate each other in a grasping motion. As the wrist is dropped in a flexion position, tightness of the finger extension

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muscles provides passive release. Hand splints can help enhance this mechanism. 6.11.2.5 Intact C7 Neurologic Level (C7 Functional Level) Impaired paretic grasp function allows additional motor tasks in the patient with an intact C7 neurologic level. Sensory sparing is not precise at this level but will contribute sensation to the middle digit. Triceps, biceps, and brachioradialis muscle stretch reflexes are normal. Clinical motor representation from C7 includes elbow extension, wrist flexion, and long finger extension. The intact C7 level patient gains three important motor functions: forearm extension using the triceps, finger extension, and finger flexion. Occasionally, these functions may be absent due to individual variations in anatomy between the C7 and C8 levels. A patient can generally lift his body, as he can stabilize his arm at the triceps and has a greater capability of shoulder girdle depression. Subacromial degeneration is common from continually lifting themselves during transfers. The patient has the advantage of grasp and release afforded by activated finger extensors and flexors. Fine motor dexterity of the hands is impaired, as the intrinsic muscles of the hand are innervated from C8–T1 levels. The C7 quadriplegic typically is confined to a wheelchair and transfers well between bed, wheelchair, car, and toilet following successful rehabilitation. Occasionally, C6-spared and C7-spared quadriplegics can drive a car with the proper enabling devices. 6.11.2.6 Intact C8 and T1 Neurologic Levels (C8 and T1 Functional Levels) The quadriplegic with intact C8 level muscles is able to grasp objects, thus making it possible for these patients to manage many activities of daily living. Proximal upper extremity sensibility sensation is normal to the upper extremity except along the proximal medial arm several inches below the elbow to the axillary region. Upper extremity reflexes are intact. Patients with intact C8 neurologic functions have preservation of finger flexion as well as extension but lack interossei function. They are able to voluntarily grasp and release but develop a clawhand-type deformity. Fine control grasp is difficult. Finger abduction is impaired, and adduction is present with a lost ability to perform pinch maneuvers. With sparing of T1 and C8 levels, there is full innervation of the upper extremity musculature, including the intrinsic muscles of the hand. This individual has normal strength, fine motor capacity, and dexterity of grasp and release as well as normal proximal muscular potential. This individual has not regained trunk stability. The T1 patient may be independent in bed activities and is able to transfer to and from a wheelchair or car without assistance.

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This individual can drive an automobile given appropriate hand controls. The individual with C8 and T1 functional levels can often be independent in most household activities with wheelchair access. Work is also possible with minimal assistance if the work area is set up for wheelchair access.

6.11.3 THORACIC-INTACT LESIONS (MID-THORACIC FUNCTIONAL LEVELS) The patient with neurologic levels intact above T2 has complete upper extremity strength and an intact brachial plexus. This patient’s motor loss is a paraplegic pattern. Sensation rostral to the mid-chest region is intact along with upper extremity sensibility. Upper extremity MSRs are normal. Trunk stability remains problematic, and there is total or partial lower extremity paralysis depending on the degree of cord damage. Sensibility assessment is the most accurate method to determine the level of neurologic involvement; sensory dermatomal landmarks contribute to localization of the lesion level. Motor function should be attempted. The intercostal, paraspinal, and abdominal muscles are segmentally innervated. Beevor’s sign during performance of a half sit-up is also a sign of abdominal muscle denervation. When the cord lesion is below T6, the patient retains significant trunk control compared to the patient with a high thoracic lesion. The T6 level individual has functional innervation of long muscles of the upper and mid-back and may use the intercostals for respiration. Respiratory reserve and endurance are therefore improved. This individual is typically independent in most phases of self-care. Full leg bracing becomes possible and the individual may be able to stabilize the upper extremities adequately to apply braces while recumbent. The individual with a functional mid-thoracic level typically can transfer independently to and from a wheelchair because of strong (innervated) upper extremities. Assistance is often not required. In conjunction with long leg braces and lower trunk stabilization, this individual is able to stand erect for a long period of time. Ambulation requires help and is not functional. The lower thoracic intact patient has increased wheelchair control and can negotiate the street environment or participate in wheelchair sports. 6.11.3.1 Intact T12 Neurologic Level (T12 Functional Level) The individual with sparing of T12 function has use of the rectus abdominus and oblique muscles of the abdomen and all muscles of the thorax which provides good trunk stabilization and respiratory ability. The low back and hip musculature are not innervated. This individual may utilize bilateral long leg braces with spine stabilization for household ambulation.

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6.11.4 LUMBAR TRANSECTION INJURIES 6.11.4.1 Intact L1 Neurologic Level (L1 Functional Level) A complete lumbar transection injury results in spastic paralysis of the lower extremities after spinal shock. Voluntary control of the bowel and bladder function is nonexistent in upper lumbar lesions. Although the bladder may be less hyperreflexic and store more urine, patients must be routinely catheterized if the reflexive sphincter tone cannot be overcome by manual maneuvers. There is increased anal sphincter tone with hyperreflexia, and defecation requires anal dilation, hard Valsalva straining, and frequent manual extraction. Lumbar transection with an intact L1 neurologic level is characterized by absent sensation below the L1 dermatomal sensory band. Paralysis or paresis is present in all the muscles of the lower extremity. There may be some slight hip flexion ability. The cremasteric reflex is diminished or absent. Achilles, hamstring, and patellar reflexes are exaggerated. 6.11.4.2 Intact L2 Neurologic Level (L2 Functional Level) An intact L2 neurologic level is associated with strong hip flexion and paretic leg adduction. The quadriceps are paretic, resulting in severe lower extremity disability even with partial innervation. The unopposed iliopsoas and adductor action results in a lower extremity deformation with a predominant flexion and adducted presentation. Sensation is absent below the L2 dermatome. The patellar and Achilles MSRs become hyperreflexive after resolution of spinal shock. Ambulation is possible for some motivated patients, although most patients find ambulation tedious with leg braces and prefer a wheelchair. 6.11.4.3 Intact L3 Neurologic Level (L3 Functional Level) The intact L3 neurologic level patient has increased quadriceps power as compared to an L2 level patient. However, knee stabilization requires a knee–ankle foot orthoses. The iliopsoas and the adductor muscles are fully functional. Paretic knee extension is possible and the hip may become flexed, adducted, and externally rotated. Sensation is intact including and above the L3 dermatome. The bladder is hyperreflexive. 6.11.4.4 Intact L4 Neurologic Level (L4 Functional Level) In the intact L4 level paraplegic, strong quadriceps muscle function allows stabilization of the knee. Foot–ankle dorsiflexion and inversion are preserved. Sensation along the

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medial aspect of the lower leg and foot is preserved. The patellar reflex is normal. As spinal shock dissipates the Achilles MSRs become hyperresponsive. The patient with an intact L4 level retains significant functional muscle action of the quadratus musculature, lower erector spinae, quadriceps, and hip flexors. The major stabilizers of the hips remain absent and the ankles are unstable. Long leg bracing is not necessary because of the stabilization of the knee. Frail ankles typically need to be supported by an ankle-stabilizing orthotic, (ankle–foot orthoses, A.F.O.). These patients occasionally require bilateral canes or crutches due to destabilization of the hip from the lack of hip extension. Canes with support above the wrists will provide greater assistance.

6.11.5 SACRAL TRANSECTION INJURIES

6.11.4.5 Intact L5 Neurologic Level (L5 Functional Level) The neurologically intact L5 level leaves only the lateral side and plantar surfaces of the foot and sometimes the back of the leg void of sensation in the lower extremities. The Achilles tendon reflex becomes hyperreflexive after spinal shock resolves. The gluteus medius muscle receives partial innervation but the paretic gluteus maximus muscle results in hip flexion deformity. The neurologically intact medial hamstring muscle allows paretic knee flexion but the lateral hamstrings remain paralyzed. A dorsiflexion deformity of the foot may occur, characterized by dorsiflexion and inversion of the foot with unopposed plantar flexion and eversion. Incontinence is common because of poor sphincter tone. Manual extraction of feces is necessary if the patient is unable to evacuate by straining. In male patients, erection is not possible without a prosthetic implant.

Bowel and bladder incontinence is the major functional concern of the S2-level patient. Sexual function in upper sacral levels is impaired with impotence common in complete cord lesions at this level. The extent of bulbocavernosus and superficial anal reflex loss is dependent upon the degree of compromise below S2. Complete anesthesia or diminished sensation in the anal–scrotal–perineal regions is typical. The individual will be unable to contract the bladder (autonomous bladder) with a rise in urinary retention and elevated intravesical pressure which results in overflow incontinence. Intermittent catheterization may be required to reduce the risk of lower urinary tract infection if the patient is unable to successfully void using manual assistance. Any maneuvers that increase intraabdominal pressure may contribute to urinary and fecal incontinence requiring the use of incontinence pads or underwear. Ambulation and lower extremity muscle stretch reflexes are preserved (Figure 6.13).

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6.11.5.1 Intact S1 Neurologic Level (S1 Functional Level) In the intact S1 level, there is loss of bowel and bladder function. Poor sphincter control is common, and episodes of incontinence may occur. The perianal region is anesthetic and is the only analgesic region of the lower body. The Achilles reflex will be normal or depressed based upon small S2 representation. The gluteus maximus will display mild paresis, as do the soleus and gastrocnemius muscles. Toe clawing may occur due to intrinsic foot muscle paresis. These patients are fully ambulatory, and only a few patients need ankle bracing or a cane. 6.11.5.2 Intact S2 Neurologic Level and Below

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FIGURE 6.13 Summary diagram of spinal cord injury functional classification, vertebral level, cord level function, and functional capacity. (Copyright J.M. True, D.C.)

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REFERENCES 1. Herrick, M. and Mills, P., Infarction of the spinal cord: two cases of selective gray matter involvement secondary to asymptomatic aortic disease, Arch. Neurol., 24(3):228–241, 1971. 2. Hogan, E. and Romanul, F., Spinal cord infarction occurring during insertion of aortic graft, Neurology, 16(1):67–74, 1966. 3. Quencer, R.M., Bunge, R.P., Egnor, M. et al., Acute traumatic central cord syndrome: MRI-pathological correlations, Neuroradiology, 34(2):85–94, 1992. 4. Schneider, R.D., A syndrome in acute cervical injuries for which early operation is indicated, J. Neurosurg., 8:360–367, 1951. 5. Dimitru, D., Central nervous system disorders, in Dimitru, D., Ed., Electrodiagnostic Medicine, St. Louis, MO: Mosby, 1995: 481–482. 6. Chetwynd, J., Botting, C., and Hogan, D., Post-polio syndrome in New Zealand: a survey of 700 polio survivors, N.Z. Med. J., 106:406–408, 1993. 7. Dalakas, M.C. and Hallet, M., The post-polio syndrome, in Flum, F., Ed., Advances in Contemporary Neurology, Philadelphia, PA: F.A. Davis, 1988: 51–94. 8. Mumenthaler, M., Degenerative and heredodegenerative diseases principally involving the spinal cord, in Neurology, Stuttgart: Georg Thieme Verlag, 1983: 254–261.

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9. Pesce, F., Castellano, V., Finazzi Argo, E., Giannantoni, A., Tamburro, F., and Vespasiani, G.. Voiding dysfunction in patients with spinal cord lesions at the thoracolumbar vertebral junction, Spinal Cord, 35(1):37–39, 1997. 10. Braakman, R. and Penning, L., Injuries of the cervical spine, in Vinknpg, A. and Bruyng, W., Eds., Handbook of Clinical Neurology, New York: Elsevier, 1976: 25, 227–380. 11. Adams, R.D. and Victor, M., Pain in the back, neck and extremities, in Adams, R.D. and Victor, M., Eds., Principles of Neurology, New York: McGraw–Hill, 1985: 149–172. 12. McCray, D.L., The significance of abnormalities of the cervical spine, Am. J. Radiol., 84:3–25, 1960. 13. Greenberg, A.D., Atlanto-axial dislocations, Brain, 91:655–684, 1968. 14. Wolfe, B.S., Kilnony, M., and Malice, L., The sagittal diameter of the bony cervical spinal canal and significant cervical spondylosis, J. Mt. Sinai Hosp., 23:283–292, 1965. 15. DeMayer, W., Anatomy and neurology of the spinal cord, in Joynt, R.J., Ed., Clinical Neurology, Vol. 3, Philadelphia, PA: Lippincott, 1991: 16.

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Section 2 Radiculopathy

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Pathomechanisms of Radiculopathy

Radiculopathy is a peripheral neurologic syndrome resulting from mechanical injury and chemical irritation of the spinal nerve roots. Mechanical injury to the nerve root occurs with compression, traction, or frictional forces. Chemical irritation occurs as a response to nerve root ischemia, vascular stasis, or nerve root exposure to inflammatory components released during tissue injury. The classic signs associated with radiculopathy include neck or back pain with spasm, mild to moderate peripheral numbness, shooting pain, or extremity weakness in the distribution of a nerve root. Radiculopathy is often seen in the post-trauma patient with intervertebral disk herniation. Direct compression of the nerve root is not necessary to produce radiculopathic symptoms. A radicular pattern of pain or deficit will frequently occur with any condition that produces inflammation in the nerve root area. Osteophytic projections, degenerative disk disease, and lateral recess stenosis are common etiologies of radiculopathy in the degenerative spine. Localization of the neurologic deficit requires an understanding of the segmental innervation patterns in the body and extremities. There is considerable overlap of innervation from contiguous spinal levels to the skin, muscles, and skeleton, so that deficit localization is sometimes difficult. Occasionally, multiple nerve roots are involved, further complicating the localization process. Confirmation of subtle or multilevel radiculopathy is based on the anatomic and functional correlatives between diagnostic imaging and examination findings. Common correlative procedures include positive orthopedic tension or compression signs, neurologic indicators (reflex changes, motor fatigue, sensory deficits, or pain patterns), electrodiagnostic findings, and diagnostic imaging findings, including magnetic resonance (MR), computed tomography (CT), and plain films. This chapter covers the relevant anatomy of the nerve root, the pathological processes, and the most common differential conditions seen with radiculopathy.

7.1 SPINAL NERVE ROOT ANATOMY AND REGIONAL CHARACTERISTICS Spinal nerve roots represent the anatomic and functional link between the peripheral and central nervous systems. Thirty-one pairs of nerve roots exit the spinal column. The first pair of cervical nerve roots exits the spine between the atlas and occiput, and the last sacral and coccygeal pairs of nerve roots pass through the sacral hiatus. The

remaining 28 pairs of nerve roots traverse the intervertebral foramen (IVF) formed by the pedicle arches of the superior and inferior contiguous vertebrae, the zygapophyseal structures to the posterior, and the intervertebral disk to the anterior. Early in embryonic development, the spinal cord and spinal column are of similar lengths. As development proceeds, however, the longitudinal growth of the vertebral column exceeds that of the spinal cord, and consequently the spinal cord usually terminates at the level of T12–L1. This tapered termination of the cord is referred to as the conus medullaris. The cervical nerve roots descend the equivalent of one neuromere (segmental cord level) before horizontally traversing their respective neural foramina. Thus, the C5–C6 disk will compress the C6 nerve root. This arrangement of nerve roots exiting above the respective numbered vertebrae changes at the thoracic level as a result of the anatomic configuration of the eight cervical nerve roots and seven cervical vertebrae (Figure 7.1). The thoracic and lumbar spinal roots exit below their respective vertebrae. Accordingly, the L4–L5 lateral disk will compress the L4 nerve root. Because the spinal cord ends at the T12–L1 level, the lumbar and sacral nerve roots must travel a longer vertical path before exiting their respective neural foramina. The descending nerve roots travel a long course within the spinal canal and are therefore susceptible to central stenotic syndromes. The length of the nerve roots from the spinal cord to the foramina in the human lumbosacral spine varies from about 60 mm at the L1 level to about 170 mm at the S1 level.1 Nerve cell bodies of the motor axons exist within the spinal cord gray matter of the anterior horn. These populations of motor neuron cell bodies in the anterior gray matter of the cord are classified as alpha and gamma groups. Motor rootlets converge from clusters of motoneuron axons and exit the ventrolateral surface of the spinal cord. Ventral rootlets and their projections comprise primarily efferent motor axons and a small percentage of afferent axons. These rootlets join to form the ventral root and travel in an anterolateral direction to converge with the dorsal root within the lateral recess (Figure 7.2). Sensory input from peripheral and axial receptors enters the dorsal aspect of the cord through a configuration of nerve fibers called the dorsal rootlets. The cell bodies of sensory axons are not found within the gray matter of the dorsal horn of the spinal cord; rather, they are located within the dorsal root ganglia (DRG) distal to the spinal cord within the IVF.2 161

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Vertebral Level

Root Level C1

C1

C2 C3

C2 Cervical Spine

C3

C4

C4 C5

C5

Cervical enlargement

C6

C6

C7

C7 T1

C8

T2 T1

T3 T2

T4

The spinal cord has 31 pairs of spinal nerves segmentally innervating the body. The first cervical nerve exits the spinal canal above the first cervical vertebra. There are eight cervical nerves with seven cervical vertebra. The first thoracic nerve exits below the first thoracic segment. The thoracic and lumbar spine have the same corresponding number of spinal nerves as number of vertebrae.

T3 T5 Thoracic Spine

T4 T5

T6

T6 T7

T7

T8

T8

T9

T9

T10

T10 T11

T11

T12

Lumbar enlargement T12

L1 Cord termination L1-L2 level Lumbar Spine

L2

L1

Conus medularis

L3 L2 L4 L3 L5

L4

Sacral Spine

S1

L5

S2 S3 S4 S5 Coccygeal nerves

FIGURE 7.1 Anatomical relationships of the spine and nerve roots. (Copyright J.M. True, D.C.)

The anterior and posterior rootlets merge just distal to the DRG to form the spinal nerve. Dorsal root fibers comprise the largest volume of the spinal nerve (Figure 7.3). At the point where the convergence occurs,

the sensory and motor nerve components are no longer separate. The commingled rootlets interweave in a fascicular pattern to form the mixed spinal nerve. The spinal nerve is usually only a few millimeters long and then

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Recurrent meningeal n.

Spinal nerve

Dural sleeve

Ventral root CSF

Dorsal root Epidural venous plexus

FIGURE 7.2 Anatomy of the lateral recess in the cervical spine. (Copyright J.M. True, D.C.)

The cross-sectional appearance of the nerve roots just proximal to the formation of a mixed spinal nerve. Dorsal root (sensory portion)

Ventral root (motor portion)

Motor axons Sensory axons

TABLE 7.2 Structures Innervated by the Medial Branch of the Dorsal Rami • Zygapophyseal joints at level of exit and segment below • Deep back muscles that arise from the spinous process and lamina (level specific) • Spinal ligaments: ligamentum flavum, supraspinatus, and intertransverse ligament • Interspinous ligament (root level specific) • Periosteum of vertebral arch

Spinal nerve

FIGURE 7.3 Within the spinal nerve, sensory and motor fibers become interweaved in a fascicular pattern. (Copyright J.M. True, D.C.)

TABLE 7.1 Structures Innervated by the Lateral Branch of the Dorsal Rami • • • •

Erector spinae Skin overlying the spine Skin of the upper buttock and top of hip Splenis capitus and cervicis muscles (cervical region)

divides into the ventral and dorsal rami. In the cervical and lumbosacral spine, the ventral rami course anterior to the spine and intermingle to form the plexes and major nerves of the extremitites. In the thoracic spine, the ventral rami form the intercostal nerves. The dorsal rami are much smaller than the ventral rami. The dorsal rami branch into two or three branches that supply innervation to the muscles, ligaments, zygapophyseal joints, and skin overlying the spine (Tables 7.1 to 7.4; Figures 7.4 and 7.5).

TABLE 7.3 Structures Innervated by the Recurrent Meningeal Nerve • • • • • •

Posterior annular fibers Posterior longitudinal ligament Periosteum of vertebral bodies Epidural and basivertebral veins Epidural adipose tissue Anterior dura mater

7.1.1 INTERVERTEBRAL FORAMEN ANATOMY The primary contents of the IVF include the spinal nerve, the DRG, connective tissue, fat, the radicular artery, the radicular vein, and two to four recurrent meningeal nerves (Figure 7.6). This group of structures is referred to as the nerve root complex (Table 7.5).3 The nerve root typically occupies approximately one quarter to one third of the volume of the IVF. This can be readily observed on sagittal MR images. The nerve-to-IVF

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1.

4. 6.

5.

7.

2.

8.

9.

10. 3. 1. Branches to anterior vertebral body and anterior longitudinal ligament

12. 11.

2. Sinuvertebral nerve

7. Ventral ramus 8. Dorsal ramus

3. Branch to ligamentum flavum and apophyseal joint

9. Lateral branch of dorsal ramus

4. Paraspinal sympathetic ganglion

10. Medial branch of dorsal ramus

5. Branch to posterior longitudinal ligament and vertebral body

11. Ascending articular branch

6. Gray and white rami communicans

12. Descending articular branch

FIGURE 7.4 Axial view of peripheral nerve anatomy of the spine. (Copyright J.M. True, D.C.)

TABLE 7.4 Structures Innervated by Nerves Associated with the Sympathetic Trunk and Gray Rami Communicans • • • •

Posterolateral intervertebral disk Anterior disk Anterior longitudinal ligament Periosteum of the anterior and lateral vertebral bodies

ratio will vary in the presence of pathologic osseous and soft-tissue foraminal stenosis. Nerve root distension or enlargement will contribute to an abnormal nerve-to-IVF ratio. The most common causes of an abnormal ratio include spondylosis and lateral disk herniation. In the lumbar spine, IVF area decreases in volume from levels L1 to L5, whereas the circumference of the traversing lumbar nerve roots increases.4 The L5 IVF is smaller in diameter than the lumbar levels above it, yet the diameter of the L5 nerve root is the largest of the lumbar roots. This change in nerve-to-IVF ratio predisposes the L5–S1 region to lateral stenotic syndromes and radiculopathy.5 The nerve-to-IVF ratio may also be reduced by the presence of transforaminal ligaments. Bogduk and Twomey5 refer to transforaminal ligaments as false ligaments that probably represent thickenings of the ventral

TABLE 7.5 Contents of the IVF • • • • •

Mixed spinal nerve root Dural sleeve Branches of radiculomedullary artery Two to four recurrent meningeal nerve branches Veins that communicate between the internal and external venous plexuses • Dorsal root ganglia (when laterally located)

portion of the intertransverse ligament. These narrow bands of collagen fibers are found attaching to the lateral IVF margins but are not always present. The nerve root may be compromised by ossification of this ligament or when the ligament reduces the available space for a normal nerve-to-IVF ratio. The extent to which compartmentalization of the IVF by a transforaminal ligament contributes to the development of radiculopathy is unknown. A small study of cervical IVF anatomy demonstrated that nerve root compression occurred at the entrance zone of the intervertebral foramina. In the anterior aspect of the IVF, compression of the nerve roots was caused by protruding discs and osteophytes of the uncovertebral region, whereas the superior articular process, the ligamentum flavum, and the periradicular fibrous tissues affected the nerve posteriorly.6

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9

Spinal nerve

11

3 4

8

1.- Branch to anterior longitudinal ligament 2.- Branches to lateral aspect of IVD 3.- Branches to IVD from gray rami 4.- Branches to IVD from ventral rami 5.- Medial branch of dorsal rami 6.- Lateral branch of dorsal rami 7.- Descending articular branch 8.- Ascending articular branch 9.- Sympathetic trunk 10.- White rami communicantes 11.- Gray rami communicantes 12.- Lumbar splanchnic nerves 13.- Ventral ramus 14.- Dorsal ramus 15.- Extradural root anastomoses (variable)

Anterior longitudinal ligament

10

9 1

15

5

10

2

7

11

12

14

8 6

Innervation to disc

2 13

5 14

4

2

1

6 5

12

13

12

6

FIGURE 7.5 Lateral view of peripheral nerve anatomy of the spine. (Copyright J.M. True, D.C.)

Spinal nerve Ligamentum flavum Posterior longitudinal ligament

Radicular artery Transforaminal ligament (variable) Superior facet

Sinuvertebral nerve

Intraforaminal venous plexus

Intervertebral disk

Intraforaminal adipose tissue FIGURE 7.6 Intervertebral foramen anatomy. (Copyright J.M. True, D.C.)

7.1.2 ANATOMY OF THE DURAL SLEEVE PERIPHERAL NERVE JUNCTION

AND

The nerve roots exit the thecal sac through dural openings surrounded by thick, membranous, funnel-shaped dural extensions referred to as nerve root sleeves or epiradicular

sheathes.7 The dural sleeve is an extension of the arachnoid mater and dura mater; it encloses the nerve root and cerebrospinal fluid (CSF), tapering to merge with the epineurium of the spinal nerve.5 The greatest portion of the spinal nerve root is intradural. The subarachnoid space and CSF extend along the length of the dural sleeve. The

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Arachnoid Dura mater Pia mater Dorsal root ganglion Rami communicans

Dorsal root Ventral root Subarachnoid space

Ventral ramus

Cauda equina

Dorsal ramus

Sinuvertebral nerve

FIGURE 7.7 Lumbar spinal nerve and surrounding anatomy. (Copyright J.M. True, D.C.)

dura and dural sleeve are both pain sensitive and chemosensitive.8 This may have clinical relevance for those patients who develop radicular-like symptoms after dural sleeve encroachment without actual nerve root compression (Figure 7.7). Like the peripheral nerves, the nerve root is encapsulated by endoneurium. The structures within the endoneurium include sensory and motor axons, collagen fibers, blood vessels, and a population of fibroblasts. In peripheral nerves, the perineurium acts as a diffusion barrier to macromolecules.9 The perineurium separates into two layers, and only part of it continues in the nerve root sheath. The nerve root lacks both the epineurium and the perineurium of the peripheral nerve.10 This creates an increased permeability within the endoneurial vasculature of nerve roots and the DRG to plasma proteins compared with the endoneurial vessels of peripheral nerves.11 Consequently, the nerve root is more vulnerable to inflammatory chemicals than the peripheral nerve. The monocollagen content of the nerve root is approximately one fifth that found within the peripheral nerves.12 Because the nerve root has a lower collagen content than the peripheral nerve, the nerve root is less capable of resisting deformation stressors. Also, the proximal spinal nerve root has extraneural supportive cells resembling those in the central nervous system. These supportive cells are not found in peripheral nerves. The proximal portions of the nerve root contain microglial cells, oligodendrocytes, and astrocytes. A few millimeters distal to the proximal nerve root is an area

referred to as the dome-shaped junction. Schwann cells distal to this junction are consistent with the microanatomy of the peripheral nervous system.

7.1.3 BLOOD SUPPLY

OF THE

SPINAL NERVE ROOT

The two primary nutrient pathways to the spinal nerve root occur through vascular supply and diffusion from the CSF.13,14 The blood supply to the vertebrae and the nerve roots arise from the segmental artery. The segmental artery gives off a dorsal branch, which further branches to supply the vertebral arch, with an additional branch supplying the posterior vertebral body, and a smaller longitudinally oriented arterial branch that supplies the nerve root. The artery that supplies the posterior intervertebral body perforates the posterior longitudinal ligament. The longitudinal radicular artery provides several collateral radicular arteries, which may lie anterior and posterior to the nerve root, branching to provide perforating interfascicular arteries. The interfascicular arteries are redundant, often coiled in appearance, allowing for nerve root translation and stretch, without compromising blood flow to the nerve root. The interfascicular arteries supply precapillary arterioles, which in turn supply intraneuronal capillaries. Nerve roots receive their blood supply from both ends. The nerve root has adequate vasculature to prevent a watershed zone in most cases of slow onset compression;15 however, a large intradural or extradural lesion may reduce the blood supply to the nerve root and inhibit CSF flow to the nerve root sleeve, thus reducing nutrient delivery.

7.1.4 THE DORSAL ROOT GANGLIA The subarachnoid space ends in the region of the DRG, so the shock-absorbing property of CSF around the spinal nerve is not substantial. The surrounding membranes of the DRG comprise the distal leptomeninges, which become the perineurium and epineurium of the peripheral nervous system. Dense connective tissue encapsulation of the DRG increases the risk of pathologic compartmentalization. Increased compartmental pressure within a CSF will contribute to peripheral dysesthesias and spinal radicular pain syndromes. Furthermore, the DRG is sensitive to mechanical pressure, and neural discharge will occur after minimal traction or external compression. The neurons of the DRG often become spontaneously active as a result of a direct lesion to their peripheral processes.16 The dorsal nerve root does not produce a sustained neural discharge after acute mechanical injury unless preexisting chronic nerve compromise is present, but when the DRG is involved, sustained neural discharge is easily elicited.17 The blood supply of the DRG differs from that of other portions of the nerve root in that the DRG has a rich microvascular supply.11 For this reason, the capillary bed

Pathomechanisms of Radiculopathy

167

Dura mater

Arachnoid

Pia mater

Dorsal root ganglion

Internal or subarticular

Sublaminar or intraforaminal

Lateral or extraforaminal

FIGURE 7.8 Variable positions of the dorsal root ganglion within the IVF. (Copyright J.M. True, D.C.)

TABLE 7.6 Factors Increasing Nerve Root Injury to Compression Forces

Sublaminar space

Intraspinal Extraforaminal

DRG

Intraforaminal space

FIGURE 7.9 The dorsal root ganglia is exposed to greater risk of compression when it is located in more medial positions within the intervertebral foramen and spinal canal. (Copyright J.M. True, D.C.)

may expose the DRG neurons to sensitizing chemicals from systemic or metabolic influences and exudative edema. Sensory fibers from the periphery enter the DRG in a dermatomal laminar pattern with organization of the fibers by the diameter size of the nerve fiber. In the peripheral nerve, fibers of different diameters are arranged in a random fascicular fashion. At the DRG, large fiber afferents begin to migrate posteromedially, and small unmyelinated fibers distribute themselves anterolaterally. The DRG is usually found within the IVF, but it can be located within the spinal canal, lateral to the neural foramina or in the medial subarticular aspect of the IVF (Figure 7.8).18

• • • • • • • •

Absence of perineurium in the subarachnoid space Conditions causing poor vascular perfusion to root and spinal nerve Narrowed intervertebral foramen from stenosis or osteophytosis Rapid-onset compression Sustained compression Perineural fibrosis Metabolic disease Presence of proinflammatory biochemicals

The DRG is vulnerable to physical insult within the medial third of the IVF particularly from posterolateral disk herniation and osteophytic spurs (Figure 7.9).

7.1.5 PATHOPHYSIOLOGY OF NERVE ROOT COMPRESSION A nerve fiber begins physically deforming when the external pressure exceeds the intraneuronal hydrostatic pressure. Electrophysiologic conduction block occurs at different degrees of external pressure, depending on the axon diameter. A complete compression block of the peripheral nerve occurs at the nerve trunk when approximately 150-mmHg pressure is applied.19 Spinal nerve roots have demonstrated conduction block at only 30 mmHg of pressure.19 When compression of the nerve root complex occurs, direct mechanical effects include conduction block, interruption of axonal flow, and vascular sequelae that include hypoxia and metabolic byproduct accumulation, which compromise impulse propagation (Table 7.6). Nerve root compression contributes to a loss of impulse propagation via impairment of axonal transport.20

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Anoxia and hypoxia may compromise fast and slow anterograde axonal transport as well as retrograde axonal transport.21,22 Axonal transport is required for the replenishment of neurotransmitter complexes. Axonal transport may be impaired in various pathologic conditions such as ischemia, compression, infection, immunologic cascades, and axonal degeneration and regeneration.23 Moderate to severe compression of a nerve root complex may induce direct pathomechanical effects on the nerve fibers, such as deformation of the nodes of Ranvier and invagination of the paranodal myelin sheaths.24 Neurologic function is highly dependent on the availability of oxygen. A classic study of the frog nerve by Grundfest22 showed that a nerve can function under high external loads as long as there is a high concentration of available oxygen. Even at normal extraneural pressure levels, if the intraneural oxygen level decreases, the nerve will become more susceptible to compressive loads. Conversely, even with an adequate systemic circulatory capacity to make oxygen available to the nerve root complex, focal vascular insufficiency within the complex will render it hypoxic. The combination of vascular insufficiency and diminished arterial oxygen saturation will result in greater susceptibility to intraneural hypoxia. Nerve root compression often results in impairment of intraneural blood flow.25 The endoneurial vessels of nerve roots, in particular the DRG, are more permeable to plasma proteins than the endoneurial vessels of peripheral nerves.5,11,26 Physical deformation of the nerve root increases the permeability of the microvasculature, leading to the formation of edema within the intraneuronal environment.27,28 Large-diameter nerve fibers within the nerve roots are more susceptible to compression and deformation than small-diameter fibers.29 Mild mechanical compromise of the nerve root complex can result in selective sensory and motor presentations limited to the large-diameter fibers. Focal demyelination of large myelinated fibers without axonopathy results in neural impulses firing in a dysynchronous volley. Olmarker et al.30 have shown that compression of the nerve root complex, even at low pressures (e.g., 5 to 10 mmHg), may induce short-term changes within the intraneural microcirculation. Initially, the intraneural venous blood flow is compromised. The intravenous pressures result in retrograde stasis within the intraneural capillary beds and a breakdown of the capillary junctions. This contributes to exudation and extravascular intraneural edema formation. Rapid spinal nerve root compression influences the degree of clinical deficit and recovery characteristics. Rapid-onset compression (between 0.05 and 0.10 sec) causes a more pronounced effect than slow-onset compression (over a 20-sec interval) with similar level pressures.31 Rapid-onset as well as sustained compressive

TABLE 7.7 Effects of Chronic Nerve Root Compression • • • • • • • •

Altered intraneural blood flow Increased intraneural permeability to macromolecules Impaired axonal transport Intraneural edema Fibroblast invasion Intraneural fibrosis and compartmentalization Impaired nutrient delivery Perineural fibrosis with recurrent microstretch injuries

insult results in pronounced intraneural edema, impaired vascular flow, conductive changes, and reduced capacity for nerve conduction recovery.13,31 This is an important consideration relative to intermittent and slow-onset compression syndromes compared with rapid-onset disk herniation and spine injuries after motor vehicle collisions. The magnitude of compression is also important in the development of symptoms. Changes in spinal nerve root conduction occur at pressures between 15 and 75 mmHg. Motor conduction velocity recovers more rapidly than sensory conduction when nerve root compression pressures reach 100 to 200 mmHg.32 Spinal nerve root compression can be present without overt symptoms.33 In such cases, however, there is invariably an absence of trauma, but the presence of a longstanding condition, such as osteophytosis or lateral recess stenosis, producing a slow-onset of compression (Table 7.7).

7.1.6 SITES

OF

NERVE ROOT VULNERABILITY

The spine contains many osteoligamentous spaces that accommodate and protect delicate neurovascular structures. These spaces include the central vertebral canal, the IVF, and the foramen transversarium. The morphologic relationships of these osteoligamentous spaces differ in various intravertebral and intervertebral locations (Table 7.8). The spatial relationship of the nervous tissue to osseous and nonosseous elements of the spinal canal and the IVF is an important consideration in the development of radicular compression.7 The dynamic properties of these spaces are strongly dependent on the anatomic characteristics and relationships of the tissues making up their margins. The dynamics of the intervertebral motion segment affect the relative instantaneous size and volume of the intrinsic osteoligamentous canals and foramina. The volume of the IVF increases slightly during flexion and decreases during extension. These changes are more pronounced in the cervical spine. Yoo and colleagues34 found that, in the neutral position and at extremes of flexion and extension in the cervical spine, 20º of axial rotation produced a decrease in the mean size of the foramen on the ipsilateral side and an increase on the contralateral side. Compared with the measurement at

Pathomechanisms of Radiculopathy

TABLE 7.8 Causes of Neurovascular Compression within the Intervertebral Foramen • • • • • • • • • • • • • •

Osteoligamentous hypertrophic stenosis Transforaminal ligament compartmentalization Combined stenosis (disk, facet, ligament, etc.) Intervertebral pathomechanics and dynamic stenosis Degenerative disk disease and rostrocaudal subluxation Venous dilation Intraforaminal and intraneural fibrosis Pedicogenic stenosis Vertebral expansion or collapse Isolated foraminal soft-tissue mass Intraspinal soft-tissue mass involving one or more foramina Paraspinal soft-tissue mass involving one or more foramina Intraforaminal foreign body or enlarged nerve root Intervertebral disk bulge or protrusion

neutral position, 30º of extension caused a 13.2% decrease in the cervical foraminal dimensions, and 30º of flexion caused a 10.6% increase.34 This IVF narrowing explains one of the mechanisms involved in reproducing radicular pain with Spurling’s clinical maneuver. This orthopedic test is performed by turning the patient’s head to the side of complaint and extending it backward with gradual downward pressure. A controlled downward blow to the vertex of the head can also be used to reproduce symptoms. During forward flexion in the lumbar spine, the spinal cord and nerve roots of the cauda equina move anteriorly. These same structures move posteriorly when the patient assumes a supine position and during lumbar extension. Lateral lumbar translation results in lateral deviation of these structures. The lumbar and sacral nerve roots are exposed to compressive insult at multiple locations prior to exiting the spine. These nerve roots are vulnerable as they descend through the central spinal canal (central zone) and traverse the lateral zone. The lateral zone is comprised of three primary divisions, which are the subarticular, foraminal, and extraforaminal divisions. Physical compression of a nerve root may occur in the central zone and within any one of the divisions of the lateral zone. The nerve root is more vulnerable to compression within the lateral zone than the central zone (central canal) secondary to less reserve space and due to the greater propensity for space-occupying pathology in the lateral zone. More common causes of nerve root compression in the lateral zone include paracentral or far lateral intervertebral disk pathology, subarticular stenosis, facet cyst, nerve root entrapment with lytic spondylolisthesis, capsular hypertrophy, and rostrocaudal subluxation associated with degenerative disk disease.

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7.1.7 PATHOMECHANICS AFFECTING ROOT COMPLEX

THE

NERVE

Breig35 demonstrated that when the spine moves there is no significant axial displacement of the spinal nerve root relative to the canal. During extension, however, the nerve root increases in cross-sectional diameter, and consequently there is a slackening and widening of the nerve root sleeve. During forward flexion, the dural sleeves and nerve roots were found to straighten gradually. This adaptability of the nerve roots greatly reduces friction between the nerve roots and their adjacent sheaths during movement. Severe fibrotic adherence of the nerve roots and their perineural structures results in excessive traction at the nerve root attachment to the spinal cord. Some of the signs and symptoms of radiculopathy develop from irritation created by immobilization of the nerve root and dural sleeve. Because the dura mater is mechanosensitive, traction of the dura over a space-occupying lesion, such as a herniated disk or osteophyte, may result in pain originating from the dura.36 The nerve root near a disk herniation is sensitive to mechanical deformation, as observed in patients under epidural anesthesia during laminectomy and disk excision.37 For patients with paresthesia secondary to neuroforaminal compression, extension-induced narrowing may magnify symptoms. Concomitant adduction of the painful arm and contralateral lateral flexion may cause stretching of the nerve root within the narrowed foramen, thereby worsening symptoms. Conversely, shoulder abduction and cervical flexion may lessen symptoms. Nerve root tension signs are common in cervical and lumbosacral radiculopathy. Cervical motions that reduce foramen size also tend to elicit symptoms associated with neuropathology at the IVF.34 In lumbosacral radiculopathies, a positive straight leg raise test is highly correlative to nerve root compression. See Section 8.2 for an expanded discussion of nerve root irritability.

7.1.8 NERVE ROOT DOUBLE CRUSH The term double crush refers to compressive insult of a single nerve root in two distinct locations. The term double crush may also be used to describe compression of two adjacent nerve roots by a single source, although this should more correctly be referred to as polyradiculopathy describing the site of compressive etiology so as not to be confused with the pathophysiology associated with multifocal compromise along the same axon. Multifocal compression may render the nerve root more vulnerable to axonpathy secondary to greater impairment of axonal transport, retrograde axonal transport, and the general synthesis and trafficking of neuronal proteins. When a nerve root is compromised at two or more locations, it is possible that

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the resulting radiculopathy will be more refractory to treatment. If lumbosacral roots are compressed at multiple locations, a greater amount of tethering will occur, increasing the possibility of greater root injury following trauma. One of the most common causes of double crush insult to the nerve root occurs when the descending lumbar nerve root is compressed within the central canal (central zone) by the disk above the level of root exit, combined with compression from subarticular stenosis in the lateral zone of the IVF. The second example occurs when the nerve root is compressed both in the lateral zone by subarticular stenosis and by a far lateral (extraforaminal) disk protrusion or osteophytic projection. A third example of double crush occurs in the lower lumbar spine when two levels of disk herniation compress the same descending root. When considering moderate or severe lumbar stenosis, there are many possibilities for double crush of the cauda equina and exiting nerve roots. MR imaging and MR myelography are extremely helpful for the assessment of nerve root double crush, using appropriate scan techniques. Conventional myelography is not as sensitive as MRI for identifying nerve root double crush. For example, conventional myelography may reveal a subarticular nerve root cutoff (CSF block), and the CSF block thereby masks coexistent extraforaminal nerve root compression.

7.2 BIOCHEMICALLY INDUCED RADICULOPATHY Inflammatory substances arising from a degenerative or herniated nucleus pulposus may spread and contact the nerve root, inducing a chemical radiculitis. This inflammatory process promotes edema and membrane damage to axons in the nerve root.38-43 A study by Kayama and colleagues in dogs demonstrated significant loss of conduction velocity across the nerve root area 7 days after incision of the annulus without herniation.38 This incision caused leakage of nucleus pulposus material into the epidural space. Nerve conduction in the incision group was 13 ± 14 m/sec compared with 73 ± 5 m/sec in the control group. Similar reductions in nerve root conduction times were seen when preparations of nucleus pulposus cells were applied to the cauda equina of pigs.44 Another study in dogs demonstrated that nerve root injury occurring with exposure to nucleus pulposus material reverses in approximately 2 months.45 A loss of blood flow to the nerve root preceded and was related to the observed changes in motor nerve conduction velocity during the 2-month recovery.46 These experiments suggest that a biochemical or membrane-bound substance causes the radiculopathy without physical nerve root compression. In our experience, many patients present with signs and symptoms of radiculopathy in the absence of direct nerve root compression.

2. Distention of Mass Disk

1. Mass of HNP

3. Inflammatory interface

Nerve root

FIGURE 7.10 Three factors that may contribute to the production of leg pain (sciatica) with lumbar disk herniation are (1) the mass of the ruptured discal material, (2) intradiscal distention secondary to water–proteoglycan content within the mass, and (3) the inflammatory interface between the disk fragment and nerve root. (From McCulloch, J.A. Essentials of Spinal Microsurgery, Lippincott-Raven, Philadelphia, PA, 1998. With permission.)

Biochemically induced degradation of the nerve root is a plausible mechanism for the production of radiculopathic signs in acute cases. Some researchers report that involvement of inflammatory mediators in radiculopathy only explains a part of the pathophysiologic mechanism of acute radiculopathic symptoms, and these mediators are not found in chronic disk lesions (Figures 7.10 and 7.11).47 One substance thought to be responsible for the production of symptoms is the enzyme phospholipase A2, which has been shown to be a significant inflammatory substance found in markedly high levels in herniated disk material.38,42,48-50 Other biochemicals directly or indirectly associated with nerve root inflammation include phospholipase A2; prostaglandin E2; leukotrienes; nitric oxide; immunoglobulins; proinflammatory cytokines, such as interleukin (IL)-1a, IL-1b, and IL-6; tumor necrosis factor alpha (TNF-a) and autoimmune reaction (macrophages expressing IL-1b, intercellular adhesion molecules); and metallo-proteinases.47,51 Phospholipase A2 is the enzyme responsible for the rate-limiting step in the liberation of arachidonic acid from cell membranes at the site of inflammation. Arachidonic acid leads to the production of chemical mediators of inflammation and nociceptive activation, such as prostaglandins and leukotrienes. Variable concentrations of phospholipase A2 in the region of disk injury may account for the lack of correlation between the extent of intervertebral disk herniation or degeneration seen on MR imaging and the level of pain reported by the patient. The most probable mechanism responsible for this connection between phospholipase A2 and radiculitis is the direct enzymatic effects of phospholipase A2 on the phospholipids of the neural components, effects on the microcirculation, and chemical sensitization of nociceptors within the annulus or surrounding tissues by secondary phospholipase A2-mediated inflammatory byproducts.48,50 The algesic

Pathomechanisms of Radiculopathy

Nerve root

171

Dorsal root ganglion Disk herniation Apophyseal trauma

Pathomechanical dysfunction

7.3 SPINAL DEGENERATION AND RADICULOPATHY

Venous congestion Inflammatogenic metabolites

Inflammatory response

Fibrous infiltration disrupted axoplasmic flow

Trophic nerve and cell changes

Electrophysiological changes

by the immune system, resulting in an autoimmune inflammatory response.48,52 Antigen–antibody complexes have been found in the pericellular capsule of herniated disk material but not in healthy disks or residual disk material.53 One study has indicated that the predominant inflammatory cells surrounding herniated nucleus pulposus material in both acute and chronic radiculopathies are macrophages.54 Macrophages are the only inflammatory cells that have clinical relevance in disk tissue inflammation.

Metabolic changes

Sympathetic influence

Synaptic sensitization of dorsal horn

Mechanosensitization of peripheral nerve fibers

Radicular Pain! FIGURE 7.11 Proposed mechanism of radicular pain pathogenesis. (Modified from Hasue, M., Pain in the nerve root, Spine, 18(14), 1056, 1993. With permission.)

and sensitizing potential of phospholipase A2 on A-delta and C fibers directly activates the nociceptors to fire or lowers the threshold of these nociceptors to firing via mechanical stimulation. As previously discussed, this sensitization of the nerve root and DRG is in part responsible for the production of radicular pain. In the absence of degeneration or injury, the nucleus pulposus is contained by the annulus and thus is sheltered from the immune system. Consequently, with disk herniation or annular tear, the nuclear material is not recognized

Spondylosis and posterolateral exostosis are common causes of IVF stenosis, lateral recess stenosis, or central spinal canal stenosis. Routine radiographs or CT scans often demonstrate disk-spur complexes or isolated osteophytosis. Osteophytic changes are more prevalent within particular segmental levels of the spine. The levels of the cervical spine most frequently affected are C5–C6 and C6–C7. In the thoracic spine, the T8 level is most vulnerable. In the lumbar spine, the L4–L5 and L5–S1 levels are the regions most often involved.55 The larger the osteophytic bar or projection, the greater the potential for a mass effect on neural structures and their blood supply. The osteoarthritic spine is particularly vulnerable to trauma.55 The four general classifications of compression syndromes associated with spondylosis are lateral or radicular syndrome, medial or spinal syndrome, combined medial– lateral syndrome or myeloradiculopathy, and vascular syndromes.56 Lateral recess stenosis has four subcategories: (1) lateral stenosis from hypertrophic enlargement of the superior facet, (2) subarticular stenosis, (3) dynamic stenosis that occurs from increased intersegmental motion or clinical instability, and (4) fixed stenosis that occurs when degeneration and stenosis are severe.57 Osteophytosis is more prevalent where Sharpey’s fibers attach to the vertebral body.58 This transitional region of bone and periosteum is usually several millimeters from the discovertebral junction. In this region, osteophytes generally begin as clawlike, horizontal, calcific projections off the vertebral body. As the spur develops, it begins to project in a vertical or inferior direction, forming an osseous bar as both vertebral margins fuse. Progressive osteophytosis results in an expansile mass effect on neighboring neurovascular tissues. Posterior or posterolateral projections are often visualized on MR images as tenting of the posterior longitudinal ligament (PLL). Ligamentous tenting may be a significant source of chronic pain because of the irritation to the free nerve endings in the PLL.59 Spondylotic myelopathy and radiculopathy can occur when osteophytic projections progress to the point of compressing both vascular and neural elements within the IVF, the lateral recess, and the central spinal canal (Figure 7.12).

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

A

B

FIGURE 7.12 (A) Midline sagittal fast spin-echo T2-weighted image and (B) axial fast spin echo T2-weighted image through L4– L5. There is pronounced posterior element hypertrophy at the L3–L4 and L4–L5 levels. Posterior element hypertrophy, ligamentum flavum hypertrophy, and disk protrusion contribute to a near complete obliteration of the spinal canal at L4–L5.

7.3.1 ROSTROCAUDAL SUBLUXATION The intervertebral disk probably reflects aging more than any other musculoskeletal tissue. Degenerative changes within the fibrocartilaginous matrix of the intervertebral disk lead to concentric and radial tears of the annulus along with loss of disk hydration. A loss of intervertebral disk volume and associated reduction of vertical height of the disk leads to IVF narrowing and increased physical loading upon the facet joints. The loss of intervertebral disk height and approximation of adjacent vertebral bodies represents one of the most common structural abnormalities of the spine. This is referred to as rostrocaudal subluxation (RCS). Reduced dimensions of the intervertebral foramen will in more severe cases result in physical and vascular compromise of the nerve root complex. This loss of intervertebral disk height is often associated with a degenerative cycle leading to facet arthropathy, ligamentous hypertrophy, spinal motion segment pathomechanics, spondylosis, and subsequent central and/or lateral stenosis. RCS most often occurs in the lower lumbar spine, predominantly at the L4-5 and L5-S1 levels and in the cervical spine at C5-6 and C6-7. Rostrocaudal subluxation may be asymptomatic in some individuals and become symptomatic following trivial trauma. RCS resulting in IVF narrowing predisposes the nerve root complex to greater injury in vehicular trauma. The combination of degenerative disk changes and loss of vertical disk height often results in some degree of laxity of the ligamentum flavum. This laxity produces a buckling (sometimes referred to as hypertrophy) of the ligamentum flavum into the foramen or the posterolateral aspect of the spinal canal. Osteophytic projections and

ligamentum flavum hypertrophy contribute to a complex acquired stenosis and higher risk for radicular compromise. See more on ligamentum flavum hypertrophy in Section 4.1.2. RSC is easily identified on lateral view X-rays by the approximation of adjacent vertebral bodies caused by a loss of intervertebral disk height. RSC is identified on MRI by loss of intervertebral disk volume and height, varying degrees of intervertebral disk bulging, loss of IVF dimension, and decreased intradiscal signal on T2-weighted imaging. There is diminished delineation between the inner annular–nuclear complex and the annular outer fibers on T-2 weighted acquisitions due to dehydration and desiccation of the disk.

7.4 FIBROSIS AND RADICULOPATHY During spinal movement, the nerve roots slide within their dural sleeves. Compressive lesions that deform the nerve root, its adjacent sleeve, or the surrounding vasculature induce edema formation, which in turn may lead to fibroblast invasion and fibrosis in the nerve root and IVF. Fibrotic adhesions between the nerve root and dural sleeve inhibit this sliding motion and compromise the elasticity of the nerve root and dural sleeve. In this situation, the nerve root and dural sleeve are subjected to abnormal tensions that induce the cyclic development of inflammation. Inflamed nerve roots are in turn sensitized to compression or traction 60 and cause pain syndromes (Figure 7.13).17 When fibrotic tissue compartmentalizes the peridural space in the region of the descending or exiting nerve root, the nerve root is immobilized and susceptible to compression from acute or recurrent disk

Pathomechanisms of Radiculopathy

Nerve

Mass effect

Blockage or Reduction

Ischemia Nerve endings activated or sensitized

Bradykinin Potassium Histamine

Inflammation Entrapment Adhesion

Fibroproliferation FIGURE 7.13 Common pathomechanisms of radicular pain. (Copyright J.M. True, D.C.)

pathology. If a nerve root cannot move out of the path of a mass effect, it is rendered more susceptible to compression and is also at risk for traction-type injuries because of loss of elasticity. The elastic limit of a normal nerve root is approximately 15% of its resting length, and any stress beyond 21% of its resting length may bring about complete failure.61 Mild compressive lesions may only slightly decrease the extent of movement between the nerve root sleeve and nerve root. A chronic compressive lesion may induce fibrotic adherence and mechanical approximation that severely impairs nerve root movement.62,63 This results in nerve root traction microinjuries against the pedicles, vertebral arches, and/or posterior vertebral body projections. Fibrosis of the nerve root sleeve results in cumulative microinjury and a vicious cycle of scar-tissue formation. Painless extremity movement is dependent on normal biomechanics within the IVF and nerve root elasticity. A loss of neural elasticity can lead to traction-induced nociception and microavulsion of scar tissue, stimulating an inflammatory cascade.

7.4.1 ARACHNOIDITIS

AND

RADICULOPATHY

The CSF flow through the subarachnoid space is critical to the health of the nerve root. Blood vessels physically course through the subarachnoid space to the nerve root complex, and CSF extends into the subarachnoid space within the dural sleeve. Any inflammatory or physical

173

obstruction of vascular or CSF circulation within the subarachnoid space will compromise the nerve root. Inflammatory changes can occur at the pia-arachnoid complex in the absence of an epidural mass effect. The inflammatory cascade may be initiated or perpetuated by septic or aseptic stimuli. This may involve exposure to an infectious, biochemically or iatrogenic chemically induced antigenic response. (See Section 7.2, Biochemically Induced Radiculopathy.) Arachnoiditis refers to an inflammatory process afflicting the arachnoid lining of the spinal cord, thecal sac, or nerve roots. It may be associated with discomfort, severe incapacitating pain, and neurological disability. The arachnoid membrane is an avascular membrane; it is highly fenestrated and lies along the inner aspect of the dura mater. There are varying degrees of arachnoiditis that will contribute to radiculopathy. These are arachnoiditis, adhesive arachnoiditis and calcific arachnoiditis. During the early stage of radiculitis there is inflammation of the pia-arachnoid membranes associated with hyperemia and nerve root swelling. In response, there is fibrinous exudation and deposition of collagenous fibrils or strands between the nerve root and the pia-arachnoid membranes. This may lead to minor subarachnoidal adhesions, which may be resorbed or physically broken loose with normal activities. With progressive arachnoiditis, there will be profound fibroproliferation with thicker fibrotic bridging adhering the nerve roots to the pia-arachnoid complex. This process represents the progression to adhesive arachnoiditis. This cascade of events can result in progressive severe scarring, axonopathy, nerve root atrophy, and adhesive attachment of the nerve root and to the surrounding leptomeninges. Dense scar tissue can result in an intrathecal mass effect with constriction and subsequent compression of the nerve root as well as obstruction of CSF flow. This associated CSF block will not likely be evident upon routine MR imaging but may be revealed with MR myelography or selective root myelography. Severe chronic progression of arachnoiditis may lead to calcification of dense scar tissue with further progression of radiculopathy.

7.5 ACQUIRED LATERAL RECESS STENOSIS AND VASCULAR STASIS A reduction in the central spinal canal or IVF diameter often produces vascular stasis. A study by Cooper and colleagues63 demonstrated clear evidence of vascular congestion and fibrosis within the microvasculature, intraneural and perineural tissues in patients undergoing decompressive disk surgery; there was an absence of similar findings in control cadaver spines. Degenerative disk disease with osteophytic proliferation and disk herniation can lead to compression of the dural veins and dilation of

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Anterior and posterior recurrent meningeal nerve Radiculomedullary artery and vein

Posterior (P)

Anterior (A)

A A

Connective tissue and fat

Spinal nerve

Normal IVF

A

P

Zygapophyseal arthrosis

A

P

P

P

Moderate/severe

Posterolateral disk herniation

Uncinate arthrosis

A

P

A

Retrolisthesis

Loss of disk height

A

P

Severe

P

A

P

Extreme

Progressive spondylitic obliteration of the IVF FIGURE 7.14 Pathological IVF variations of the cervical spine. (Copyright J.M. True, D.C.)

adjacent noncompressed veins. The risk of intra-arachnoid and intradural exudation substantially increases in this situation. Chronic intraneural ischemia will result in intraneural fibrosis.64 Pain, paresthesia, sensory deficits, and motor weakness are clinical manifestations of neural ischemia with or without mechanical deformation of the nerve root. The veins in the IVF are extremely vulnerable to mechanical compression. The IVF is dynamic and constantly changing in dimension secondary to coupled movement of the vertebral motion segment. During foraminal dynamics, the mean cervical foraminal measurement at 30º of flexion increases approximately 24.7% compared with the measurement at 30º of extension.34 The veins are positionally compromised during extremes of extension but typically not long enough to induce a progressive ischemic or inflammatory cascade. Many pathologic considerations contribute to IVF stenosis and lateral recess stenosis, as illustrated in Figure 7.14. The normal IVF is approximately two thirds larger than the nerve root complex. An adequate nerve-

to-IVF ratio allows for normal movement without nerve root compromise. Certain congenital configurations of the IVF can predispose an individual to an acquired stenosis and radicular compromise. A study of 160 cadaver lumbar foramina by Hoyland and colleagues62 demonstrated that, concurrent with IVF compromise, there is often distortion of the large venous plexus within the foramen. In eight of the cadaver specimens with distortion of the venous plexus, there was an absence of direct nerve compression. The investigators further described the pathologic changes within and around the nerve root complex of the IVF as including intraneural fibrosis, edema of the nerve roots, and focal demyelination (Figure 7.15). They reported that the most severe neural changes secondary to compression resulted from dilation of foraminal veins. Basement membrane thickening was also reported, suggesting endothelial cell compromise secondary to vascular changes within the thickened fibrous sheath. It therefore appears that venous obstruction is an important pathogenic mechanism in the development of perineural and intraneural fibrosis.63

Pathomechanisms of Radiculopathy

175


   
   
 

   
   

    

  
    
 

FIGURE 7.15 A lateral disk protrusion may compress the venous plexus within the lower portion of the neural foramen, producing venous stasis, dilatation, and local tissue ischemia. A chronic process may lead to perineural fibrosis and nerve fiber atrophy. (Copyright J.M. True, D.C.)

7.6 FAILED BACK SURGERY SYNDROME

Conservative

Surgical

Spine pain

Extremity pain

Palsy

Increasing severity FIGURE 7.16 Generalized linear relationship between radicular signs and symptoms and treatment options. (From Tsuji, H., Comprehensive Atlas of Lumbar Spine Surgery, Saunders, Philadelphia, PA, 1991. With permission.)

Other researchers also have reported the effects of venous stasis after IVF stenosis. Watanabe and Parke65 concluded that the venous side of the radiculomedullary circulation is the most vulnerable component to compression. Yoshizawa and colleagues66 recently concluded from their experimental studies that there is a vascular “watershed area” near the base of the dural sleeve. Sunderland67 concluded that venous congestion and retrograde stasis in intraneural capillaries represent an important pathophysiologic mechanism in nerve compression syndromes. Moderate to severe venous congestion could theoretically reduce the space available for the nerve root in the IVF.68

There is a general linear relationship between the need for surgery and the severity of symptoms (Figure 7.16). However, postsurgical complications and undesirable outcomes are at greater risk of occurring with poor patient selection. Postsurgical stenosis and fibrosis in the central spinal canal and IVF are of great concern. Some medications and contrast agents are inflammogenic. Proinflammatory chemicals include therapeutic and diagnostic pharmaceutical agents and some contrast media, especially legacy myelographic agents. Additionally, epidural fibrosis will occur secondary to infection, ischemia, bleeding, thrombosis, and immunologic reaction to surgical sponges and glove powder. Severe iatrogenic fibrosis can result in acquired stenosis and contribute to progressive pathomechanics between central and peripheral neural elements. Pretherapeutic considerations should include evaluation of systemic risk for abnormal fibrinolytic activity and habitual patterns, such as smoking, that may increase the risk for epidural fibrosis and altered collagen cross-linking. Common factors contributing to failed back surgery syndrome (FBSS) include recurrent disk herniation (12–16%), lateral (58%) or central (7–14%) spinal stenosis, arachnoiditis (6–16%), and epidural fibrosis (6–8%).69 FBSS has also been reported to result from poor surgical selection or technique and peridural fibrosis.70 A nerve root entrapped by fibrosis is rendered more susceptible to recurrent or residual disk herniation. Surgical disruption of granulation tissue may lead to increased postsurgical fibrosis. The clinical signs and symptoms secondary to intervertebral disk herniation, extrusion, or sequestration may respond to surgical decompression, but the prognosis

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

for postsurgical recovery from fibrotic debridement is poor. A large percentage of failed back surgery patients with continued pain may also be the result of chemically mediated pain mechanisms. According to Saal,42 “Management of chemically mediated pain by surgical removal of the disk is analogous to excision of a painful sensory nerve. Not only is this ineffective, but it frequently intensifies the pain, by creating a neuropathic pain pattern.”

Stenosis of Iateral recess and IVF

Fibrotic adhesion of nerve root preventing normal nerve root glide DRG

7.7 TRAUMA AND RADICULOPATHY IVF

Spinal trauma may lead to nerve root injury secondary to avulsion, contusion, stretch, and/or compressive injury. Nerve root contusion and stretch injuries represent transient physical pathomechanisms. Compressive insult may be transient or may persist after the original trauma. Signs of root compression may occur as a result of neural injury anywhere from the rootlets on the spinal cord to the spinal nerve in the distal portion of the IVF. Common causes of persistent post-traumatic nerve root compression include hematoma, disk herniation, displaced vertebral fracture, or vertebral dislocation. Any condition that distorts and narrows the dimensions of the IVF may result in nerve root compromise. Unilateral facet dislocation, vertebral body fracture, and ligamentous disruption with a shift of bony elements may produce transient, partial, or complete occlusion of the IVF or cause a traction injury of the nerve root. Preexisting spondylosis with spurring or spinal stenosis due to other causes may infringe on the reserve space surrounding the neural elements, increasing the risk for concussive and stretch injury of the nerve root (Figure 7.17). Perineural fibrosis and postsurgical scarring may adhere the nerve root sleeve to the surrounding tissues, predisposing the nerve root to tensile strain injury from reduced gliding capacity of the nerve during vertebral motion. Patients with chronic radiculopathy may have significant fibroproliferation within the lateral recess and IVF which lowers the threshold for subsequent nerve root injury and aggravated symptoms. Individuals with ankylosing spondylitis are prone to fractures.71,72 This may be due to greater focal stress placed upon select bony regions due to the general spinal rigidity created by the ankylosis. The greater risk for fracture in ankylosing spondylitis is associated with an increased risk for associated nerve root injury. Diminished bone strength increases the risk for acquiring reduced IVF dimensions secondary to fracture. The World Health Organization (WHO) has classified bone density characteristics into the following four primary categories: (1) normal, (2) osteopenic, (3) osteoporotic without fractures, and (4) severely osteoporotic.73 Low bone mineral density and reduced trabecular density are associated with increased risk for acquiring a fracture due to loss of subcortical bony support.74 During the aging process, trabecular bone loss

Osteophytic spur

Pedicle Nerve root

Osteophytic projections into the nerve root

Traction of neural elements

Spondylolisthesis

FIGURE 7.17 Degenerative factors that increase the risk for nerve root injury and tethering. (Copyright J.M. True, D.C.)

is similar between men and women although women commonly acquire greater loss of trabecular connectivity.75 Whiplash injury is a common pseudomechanistic term that describes a constellation of symptoms following injury sustained in a motor vehicle accident (MVA). Considerable debate can be found in the scientific literature regarding the very definition of whiplash, including its mechanism of onset, prevalence, extent of related injuries, and how to name this complex trauma disorder.76-78 Injuries to the body result from rapid acceleration or deceleration forces transmitted through the head, neck, and body within a few hundred milliseconds after vehicle impact.80 Rear-end collisions are responsible for approximately 85% of reported whiplash injuries.76 MVAs are one of the most frequent causes of radiculopathy. Although more than one third of patients acutely complain of paresthesias following an MVA, neurogenic thoracic outlet syndrome is more commonly the cause than cervical radiculopathy.81 Symptoms associated with whiplash can be classified in a loose time frame of acute and late whiplash syndromes. Patients with cervical spondylosis are more likely to present with late-onset abnormal clinical findings after whiplash injury.82 Osteophytosis and bony hypertrophic changes which narrow the IVF may contribute to contusion and/or avulsive injury to the nerve root. After vertebral trauma, plain radiographic studies should be performed in

Pathomechanisms of Radiculopathy

any patient with reduced range of motion (ROM) or lateralizing pain symptoms. Oblique projections and flexion– extension plain films are essential for evaluating the posttraumatic patient with mild radicular symptoms. The diagnostic yield, however, may be low in cases with transient IVF occlusion or nerve root traction injuries. Flexion–extension X-rays should not be performed on acutely injured patients if fracture or biomechanical instability is suspected. Spiral (helical) CT or magnetic resonance imaging (MRI) is suggested for the patient with moderate to severe acute injury, with peripheral neurological symptoms. CT scanning is indicated in more severe spine trauma because of its greater capacity to detect occult fractures. However, injury to the spinal cord, nerve root, or smaller nerves intrinsic to the spinal column may occur in the absence of bony changes, thus may be underestimated on radiographic studies. The magnitude of soft-tissue trauma is therefore best assessed with MRI, which is superior for the evaluation of spinal cord and nerve root trauma.83 MRI is also superior to conventional plain-film radiography for the acute assessment of prevertebral or paravertebral hemorrhage or edema, spinal cord edema, ligamentous injury, acute disk pathology, and spinal cord compression.84

7.7.1 NERVE ROOT AVULSION Significant neural element injury can occur with spinal trauma with or without associated bony injury. Traction insult applied to the shoulder and/or neck may result in cervical nerve root avulsion and avulsion of elements of the brachial plexus. The two injuries may occur in the same instance. A penetrating injury from a foreign object may also lead to nerve root avulsion. If nerve root avulsion occurs in the region of the neuroforamen and the dural sleeve is stretched but intact, it often results in the formation of a pseudomeningocele. This CSF-filled lesion can be detected by myelography, CT, or MRI. The ventral nerve root is more vulnerable to traction-induced avulsion than the posterior nerve root because it is significantly thinner and traverses a slightly greater vertical course.61 The posterior root is more resistant to stretch due to the thick dural sheath and convergence of the posterior roots into the dorsal root ganglia, which provides additional stability.61,85 Complete structural separation of the nerve root results in an intravertebral and preganglionic lesion associated with profound segmental weakness, impaired dermatomal sensibility, and severe diffuse radiating pain. Because of the magnitude of trauma sustained in nerve root avulsion, the clinical presentation may be complex due to coexistent diffuse plexopathy, cervical injury, and limb fractures. Isolated ventral root avulsion will lead to considerable sparing of dermatomal sensibility. Incomplete sensory and motor root avulsion will contribute to a less distinct presentation. Severe traumatic plexopathies are often associated with nerve root avulsion.86 The C8 and T1 levels are

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TABLE 7.9 Predisposing Factors to Disk Derangement • • • • • • • • • • • •

Excessive loading pressure Increased intradiscal expansion pressure Intradiscal degeneration Endplate microfractures and sclerosis leading to closure Impaired nutrient delivery to the disk Subchondral trabecular failure Coalescence of annular tears Excessive shearing forces Cumulative microtrauma Macrotrauma Facet tropism Segmental dysfunction

the most common levels of root avulsion due to limited connective tissue anchoring to the transverse processes.85 Careful assessment of intrinsic hand function should always be performed in suspected cases of nerve root avulsion. Magnetic resonance imaging is a valuable method for assessing the post-traumatic nerve root status, although the clinician should be aware that volume averaging and 4–5 mm slice thickness may occasionally result in falsepositive or false-negative MR interpretations. The sensitivity of MRI can be improved with the use of gadolinium enhancement, which provides a method of investigating the spinal cord surface at the root entry zone (injury site) and the integrity of intradural nerve root stump (injury site).87 The area of post-traumatic neural avulsion is likely to enhance. CT myelography offers the benefit of thinslice acquisitions of 1 to 3 mm, providing a sensitive preoperative indicator of complete or partial nerve root avulsion in post-traumatic injuries.88

7.8 INTERVERTEBRAL DISK HERNIATION AND RADICULOPATHY Disk herniation is well documented as one of the most common etiologies of radiculopathy.36,89-93 For example, in a study by Modic and colleagues,91 72% of patients with acute radiculopathy had a herniated nucleus pulposus. Direct correlation among the size of the disk lesion, clinical presentation, and treatment outcome is not always clear.91 Many patients older than 60 years may have one or more relatively asymptomatic herniations. It should be noted, however, that intermittent pain and loss of functional capacity accompany virtually all relatively asymptomatic herniations (Table 7.9).

7.8.1 EXPERIMENTAL MECHANISM OF DISK HERNIATION A normal intervertebral disk has a high capacity for accepting axial loads. Many studies have been performed

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In combination

Anterolateral flexion

Axial compressive blow

Annular failure Nuclear extrusion

FIGURE 7.18 Physical mechanisms contributing to annular disruption. (Copyright J.M. True, D.C.)

on the behavior of the disk under variable stressors. One of these showed that the normal intervertebral disk loses about 0.6 mm of vertical height and bulges approximately 0.34 mm in a radialward direction under a compressive axial load of 1700 N.94 This study determined that the disk withstands a maximum compressive force of 7000 N before failure; by comparison, the maximum force needed to produce failure of the endplate was 2500 N.94 These findings indicate that compression alone does not produce disk prolapse in the experimentally prepared spine. Adams and Hutton90 were able to experimentally produce disk herniation in a two-vertebrae specimen by applying sudden compression to the specimen with simultaneous lateral and full forward flexion. The disk prolapse occurred on the open disk wedge side opposite the side of lateral flexion. Clinically, disk herniation is often seen after a lifting injury or motor vehicle accident in which lateral flexion and forward flexion positions of the spine occur at the time of traumatic compression or shear (Figure 7.18).

7.8.2 CONVENTIONAL CLASSIFICATION LESIONS

OF

DISK

The classification of disk herniations is often confusing and imprecise. The term disk herniation implies that a rupture or tear of annular fibers occurs allowing the migration of nuclear material beyond the vertebral margin. The nuclear material may protrude out and cause a distention of the outer annulus fibrosis or rupture through the annulus and extrude behind the posterior longitudinal ligament. Additionally, in cases with a greater degree of extrusion, the nuclear material may become separated from the disk of origin and migrate into the epidural space or lateral recess as a free fragment. The confusion in describing the previously mentioned lesions stems from the limited resolution of diagnostic imaging technology and the poor

standardization of terminology. This resolution inadequacy is most problematic in confirming small-to-moderate sized subannular herniations and confirming whether an extrusion has separated from the disk as a free fragment. The second problem is the plethora of terms used to describe a disk herniation. Some of the terms encountered are disk herniation, protrusion, extrusion, nuclear extrusion, prolapse, bulging disk, slipped disk, ruptured disk, and sequestered disk. We have classified disk lesions into four main groups based on their appearance on MR imaging. They are annular bulge; protrusion (herniation); extrusion; and free disk fragment (sequestration). These categories can be applied to the description of disk lesions throughout the spine. The next consideration in describing a disk lesion is whether the herniation is contained by the annulus or uncontained and in a subligamentous position under the posterior longitudinal ligament (PLL). When disk material has migrated around or through the PLL, it is called transligamentous extrusion. The sizes of disk herniations are categorized as small, moderate, and large. The location of the disk herniation in relation to midline spinal anatomy should be described. The majority of disk lesions involve herniation in a central posterior or posterolateral direction. Herniations that occur in a lateral direction or through the anterior portion of the intervertebral disk are not as common. The pathoanatomical relationship of the herniation to the adjacent neural and spinal elements should be evaluated and described. Compression of the nerve root or spinal cord is described as mild, moderate, and severe. Effacement of the thecal sac, nerve root, or cord is also clinically significant because of compression of the surrounding vasculature and contact with the inflammatory interface of discal material. 7.8.2.1 Annular Bulge (Disk Bulge) The term annular bulge should be reserved for describing symmetric annular extension beyond the posterior margin of the vertebral body without evidence of internal concentric annular fiber disruption (Figure 7.19a). An annular bulge does not often directly contact the nerve root. The disk bulge may be accompanied by a loss of intradiscal proteoglycans and water content with a resultant loss of vertical disk height and laxity of annular fibers. There will often be some loss of cross-sectional IVF area. Two important criteria for identifying an annular bulge are broadbased annular extension and a symmetrically enlarged margin. Large disk bulges are often secondary to radial tears of the annulus.95 A short-based focal disk extension is more typical of internal annular derangement and nuclear migration. This type of bulge often represents a small disk herniation and may easily progress to a larger degree of nuclear protrusion because of a loss of the containing annular fibers. Degeneration will predispose annular

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179

Axial

Sagittal

Contained

Diffuse annular bulge

Intradiscal mass displacement Focal disk bulge or focal protrusion with annular fiber disruption

Subtotal annular disruption Disk herniation or protrusion (Intra-annular protrusion)

Uncontained

Disk extrusion (subligamentous)

Transligamentous disk extrusion

Disk extrusion with sequestration

FIGURE 7.19A Classifications of disk injury. Although degenerative disk disease is sometimes included as a classification of disk lesion, its role in disk injury is more of a predisposing factor to disk herniation resulting from internal derangement. (Copyright J.M. True, D.C.)

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Radial tear to outer annular edge

Concentric annular tears

FIGURE 7.19B Predisposing intradiscal factors that increase the risk for complete annular failure during trauma. (Copyright J.M. True, D.C.)

fibers to failure following trauma (Figure 7.19b). The abnormality of the bulging annulus has been well documented by Yu and colleagues,96 who saw radial tears in 84% of disks bulging more than 2.5 mm (Figure 7.20). Discontinuity of the annulus, such as a radial tear, results in a nonuniform stress pattern that increases the risk of structural failure at the boundary.97

2.5 mm FIGURE 7.20 Radial tears of the annulus fibrosis are usually present when a disk bulge or protrusion extends more than 2.5 mm beyond the outer vertebral margin. (After Yu et al.95)

Sinuvertebral nerve Disk herniation

PLL

Spinal nerve

Dura mater

Anterior root

IVF

Posterior root

FIGURE 7.21 The sinuvertebral nerve is vulnerable to disk herniation due to its anterior position within the spinal canal. Sinuvertebral nerve compromise may result in discogenic pain without spinal nerve root effacement. (Copyright J.M. True, D.C.)

7.8.2.2 Disk Protrusion (Herniation) A disk herniation represents a rupture of nuclear material through a defect in the annulus, producing a focal extension of the disk or asymmetric, broad-based extension of the disk margin.98 The term disk protrusion is synonymous with the term subannular contained nuclear herniation. A portion of nuclear material may eccentrically migrate through compromised internal annular fibers without extruding beyond the outer annular fibers. This produces an abrupt, asymmetric extension beyond the vertebral margin without the degree of gradual tapering typically observed with an annular bulge. The protruding subannular disk material often migrates in a caudal direction. Intervertebral disk herniations result in some degree of central canal or foraminal occlusion. Therefore, when thecal sac effacement is present, compression of the epidural venous plexus and sinuvertebral nerve is possible (Figures 7.21 and 7.22). Lateral disk herniations may compress the intraforaminal venous plexus or segmental artery (Figure 7.23). These symptom-producing pathomechanisms should always be a consideration in rapid-onset disk herniation, with or without nerve root compression. 7.8.2.3 Disk Extrusion The classification of an extruded disk is applied when portions of the nucleus pulposus fibrocartilage and endplate cartilage have migrated through compromised outer

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181

L4-5 disk herniation

Thecal sac

L5

A

B FIGURE 7.22 (A) Cadaveric depiction of an L4–L5 disk herniation effacing the thecal sac. (Courtesy of J. Paul Ellis, Ph.D.) (B) Photomicrotome of a lumbar intervertebral disk. The arrow demarks a midline posterior disk herniation. The abbreviation RL denotes a rim lesion. (Courtesy of Shiwei Yu, M.D.)

Venous plexus congestion may occur with thecal sac effacement. Chronic compression produces engorgement and dilation of local venous tributaries, which can contribute to the development of inflammation and fibrous infiltration secondary to venous stasis.

Internal vertebral venous plexus congestion

Reduced venous drainage through IVF FIGURE 7.23 Intervertebral disk herniation compromising the epidural venous plexus.

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FIGURE 7.24 Intervertebral disk herniation with tenting of the posterior longitudinal ligament. (Parasagittal T1- and T2-weighted images).

larger subligamentous extrusion will cause a tenting of the PLL (Figure 7.24). Extruded nuclear material can migrate superiorward or inferiorward as a result of the high-pressure containment of the PLL (Figure 7.25). Disk extrusion material, when moderate to large in size, may migrate around or through the PLL or follow the dural sleeve into the IVF. This is characteristic of an uncontained disk herniation. Depending on location, a moderate- to large-sized extrusion may also compress the root, cord, or both and cause a myeloradiculopathy. Disk extrusion increases the risk of the release of inflammogenic compounds into the nerve root environment, as previously described. Subligamentous tenting or deformation of the PLL may contribute to a chronic low back pain syndrome. This is based on the fact that the PLL contains an extensive webwork of free nerve endings supplied from the sinuvertebral nerves (Figure 7.26).59 7.8.2.4 Free Disk Fragment (Sequestered Disk)

FIGURE 7.25 Parasagittal T1-weighted image through the cervical spine demonstrating a subligamentous C5–C6 intervertebral disk herniation.

annular fibers. Disk extrusions are also qualified by their size, being described as small, moderate, and large. This type of herniation may be subligamentous or transligamentous depending on whether the extrusion is under the PLL or extends around or through the PLL. A moderate-sized or

The term free disk fragment refers to the extra-annular separation and migration of a piece of nuclear material, which is no longer contiguous with the parent nucleus.98 This is often referred to as a sequestered disk herniation (Figure 7.27). Occasionally, a free fragment migrates behind the midportion of the body of the adjacent vertebra, making it difficult to determine the disk of origin without scrutiny. A free disk fragment may be subligamentous between the vertebral body and PLL or migrate to a transligamentous position in the epidural space. A migrated free fragment may compromise the ipsilateral lateral recess or IVF above or below the level of injury, causing

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183

The distribution of the left lumbar sinuvertebral nerve (SVN) is represented by this figure. The pedicle has been transected and the neural arch and dural sac removed to reveal the nerve in the floor of the vertebral canal.

A

PLL

SVN D IVD A Pedicle Gray rami Ventral ramus

a

SVN D DRG

FIGURE 7.26 Innervation of the posterior longitudinal ligament. (From Bogduk, N., The innervation of the lumbar spine, Spine, 8(3):287, 1983. With permission.)

significant nerve root compression. Disk fragments migrate in a superior (42%) or inferior (40%) direction from the donor disk, with the displaced disk components most frequently (94%) becoming lodged into the right or left half of the anterior epidural space, rarely straddling the midline.99 An intradural disk extrusion can occur, although it is not common. Cauda equina syndromes are common with intradural migration of an extruded lumbar disk fragment Table 7.10.100 MR imaging is very sensitive to free fragment when the scan slice is optimal. In these cases, MR imaging is not always able to determine if a free fragment is present.101

7.9 NERVE ROOT COMPROMISE: EXPANSILE LESIONS Benign cysts and tumors may perfectly simulate radiculopathy from a herniated disk. The patient’s symptoms will be reproduced with neuro-orthopedic maneuvers that compress the tumor against the nerve root or traction the nerve root across the mass. The presence of radiographic abnormality such as IVF erosion is a hallmark

indicator of a schwannoma, neurofibroma, or other expansile lesion. MRI is the best procedure for noninvasive diagnosis of tumors and cysts. Patients with benign spinal tumors may be treated conservatively for years before symptoms accentuate to a red-flag level of obvious neurological compression. In one study, the duration of symptoms prior to diagnosis of a sacral area tumor ranged from 1 month to 9 years (Table 7.11).102

7.9.1 SCHWANNOMA Schwannomas are benign nerve sheath tumors that commonly occur singularly in otherwise normal individuals. Schwannomas are one of the most common benign tumors to afflict the nerve root and occur with greatest prevalence in the thoracic spine, although they can occur along any spinal nerve.103 They are encapsulated tumors that arise in an eccentric fashion from Schwann cells of the peripheral nerve. In the spine, they usually occur as intradural extramedullary lesions and on rare occasions may acquire an extradural extension, most commonly arising from the sensory portion of the nerve root. Schwannomas usually present as intraforamenal masses, which expand in size

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

FIGURE 7.27 (A) Axial spin echo T1-weighted image following gadolinium enhancement through the L4–L5 interspace. The image demonstrates a free disk fragment within the right lateral recess. There is an enhancing rim of granulation tissue surrounding the free disk fragment. The patient has undergone partial microdiscectomy and hemilaminectomy at this level. (B) Parasagittal spin echo T1-weighted image of the same patient, demonstrating fragmented free-floating disk material within the right lateral portion of the spinal canal.

TABLE 7.11 Nerve Sheath Tumors

TABLE 7.10 Common Findings Associated with Intervertebral Disk Pathology • • • • • • • • • • • •

Annular tears Rim lesions Nuclear migration Disk desiccation or annular fiber degradation with rostrocaudal subluxation Discogenic inflammation or infection Osteophytosis at the annular rim Sharpey’s fiber disruption Release of proinflammatory phospholipase A2 and metallo-proteins following disk injury Endplate herniation (Schmorl’s node) Facet imbrication and segmental dysfunction Facet arthrosis and hypertrophy Foraminal encroachment

• Most commonly occurs as an intradural/extramedullary mass. • Types: Schwannoma, neurofibroma Ganglioneuroma, neurofibrosarcoma (rare) • Primarily seen in middle-aged adults. • Variable location: Intradural/extramedullary (70% to 75%) “Dumbbell” (15%) Extradural (15%) Intramedullary (90% hyperintense on T2-weighted image (“target” appearance common) Virtually 100% enhance Source: Osbourne, A. Diagnostic Neuroradiology: An Atlas/Text, St. Louis, MO: Mosby, 1993, p. 897. With permission.

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185

The tumor’s growth is contained by the foramen causing the characteristic dumbbell shape.

FIGURE 7.28 The dumbbell or hourglass tumor characteristically describes the morphological appearance of a schwannoma, neurofibroma, or meningioma as it expands intraspinally and extraspinally through the IVF. (Copyright J.M. True, D.C.)

A

B

FIGURE 7.29 (A) Axial T1-weighted image through the thoracic spine demonstrating a large soft-tissue mass surrounding the left nerve root which widens the neural foramen. (B) Axial T2-weighted image of the thoracic spine of the patient shown in Figure 7.30a. This postcontrast image reveals the hypertintensity characteristic of a tumor such as a neurofibroma or schwannoma.

and eventually displace and compress the adjacent nerve root. They do not characteristically invade the originating spinal nerve root.104 A large schwannoma may extend into the spinal canal and displace and compress the spinal cord, although they rarely occur as isolated intramedullary tumors. Expansion from the IVF leads to the development of a dumbbell or hourglass configuration as the tumor conforms to the lower resistance outside the rigid boundaries of the IVF (Figure 7.28). Appearance of a dumbbell-shaped mass in the thoracic spine is highly suggestive of neurofibroma, schwannoma, or meningioma (Figure 7.29). Schwannomas usually occur as isolated lesions with the exception of approximately 5% of cases, which occur in neurofibromatosis, type 2 (NF-2).105,106 The term

“schwannomatosis” has recently been applied to classify the occurrence of multifocal schwannomas not otherwise associated with NF-2.107 Isolated schwannomas tend to be more prevalent in older individuals, usually occurring in the fifth and sixth decades, and are extremely rare in children with the exception of those occurring in association with NF-2.108 Malignant transformation of schwannomas is rare. Schwannomas are generally slow-developing expansile lesions, which characteristically grow to a relatively large size prior to being associated with radiculopathy. Radiculopathy occurs secondary to crowding of the IVF. The clinical presentation often mimics radiculopathy due to more common causes such as far lateral disk herniation, uncovertebral

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A

B

FIGURE 7.30 (A) Oblique radiograph of the cervical spine demonstrates marked bony erosion with expansion of the right neural foramen at the C2–C3 level. Erosion of the pedicle and scalloping of the posterior bony elements are apparent. (B) Coronal spin echo T1-weighted image of the cervical spine following the administration of gadolinium. This image demonstrates a large lobulated enhancing mass, which extends along the nerve root and expands the right neural foramen. There is a mass effect upon the right lateral aspect of the spinal cord with subsequent spinal cord deformity. There is intense homogenous enhancement of the extra-spinal lesion following the administration of gadolinium, consistent with a schwannoma.

hypertrophy in the cervical spine, spondylolisthesis, and degenerative spondylosis. Schwannomas have been reported to cause thoracic outlet-type symptoms following extension from the C7 root.109 Schwannomas of the cauda equina can mimic the common complaints of low back pain. Because of the mobility of the nerve roots and the relatively wide lumbar canal, tumors arising in the region of the conus medullaris can become larger than most other spinal tumors. General differentiating features of neurological compromise secondary to a cauda equina schwannoma vs. disk pathology include increased back pain while lying recumbent, polyradiculopathy, and a refractory response to conservative intervention.110 The first sign of a schwannoma as a cause for back and extremity pain can be bony erosion and resorption within the IVF due to the expansile lesion. Bony erosion of the IVF in the cervical spine may be evident on oblique views (Figure 7.30a). Lateral radiographic views in the lumbar spine will often reveal the associated bony changes. This finding may be seen during the incidental work-up for trauma or neck symptoms due to other causes. Hyperostosis and bony sclerosis are rare. The schwannomas generally appear hypointense– isointense on T1-weighted MR images and hyperintense on T2-weighted images. 111 Schwannomas typically

enhance on MRI following contrast administration, whereas disk herniations do not enhance (Figure 7.30b). They tend to be slightly more vascular than other forms of neuromas. Microcystic changes may be evident and tend to be more prevalent in spinal tumors than in intracranial lesions.112 Macrocystic changes are less common.113 Focal regions of low T2-weighted signal intensity may represent intratumoral hemorrhage, a dense cellular region, or collagen deposition.112 Cystic changes help to differentiate the tumor from neurofibromas and meningiomas, which are less apt to demonstrate intratumoral cysts.106 This is more likely to occur with a more chronic lesion. Tumor extension can be classified as intradural intra-arachnoid, intraforaminal extra-arachnoid, and extraforaminal.114 CT myelography may demonstrate nerve root cutoff, the extent of bony enlargement of the IVF, and thinning of the adjacent pedicles. The CT study will help determine the risk for acquired intersegmental instability secondary to bony changes.

7.9.2 NEUROFIBROMA Neurofibromas are a form of nerve sheath tumor. Like schwannomas, they are neurogenic tumors that arise from the sensory portion of the nerve root and present

Pathomechanisms of Radiculopathy

187

A

B

C

FIGURE 7.31 (A) Axial CT soft-tissue window slice through the L3 level. A large soft-tissue density has eroded the right pedicle and enlarged the right neural foramen. This is characteristic of a neurofibroma. (Courtesy of George W. Fika, D.C.) (B) Axial T1weighted image through the L3 level of the same patient. The large mass is again seen markedly enlarging the right neural foramen and displacing the thecal sac. (Courtesy of George W. Fika, D.C.) (C) Sagittal T1-weighted MRI through the lumbar spine of the same patient. The tumor is again seen markedly eroding the posterior vertebral bodies and enlarging the neural foramen. (Courtesy of George W. Fika, D.C.)

as an intraforaminal, intradural, extramedullary lesion. Intraspinal neurofibromas are rare and usually are associated with neurofibromatosis, type 1 (NF-1) (von Recklinghausen’s disease).103,106 NF-1 is a genetic disease with a wide range of neurological manifestations; it has more profound complications when the disorder manifests during childhood. These complications include symptomatic optic pathway tumors, cerebral gliomas, symptomatic aqueductal stenosis, and spinal cord compression. The predominant neurological features in adults with NF-1 are chronic pain and malignant peripheral nerve sheath tumors.115 Thus, neurofibromas associated with NF-1 represent a more aggressive lesion than schwannomas. Neoplastic schwann cells infiltrate the adjacent nerve root and may become life-threatening. The radiculopathic signs and symptoms may occur

abruptly due to the more aggressive nature of this nerve sheath tumor. Schwannomas and neurofibromas generally have a similar radiographic appearance. IVF erosion and expansion are usually present. Arising from the spinal nerve, the tumor commonly produces a dumbbell or hourglass shape because of the bony constrictions of the IVF (Figure 7.31). The neurofibroma is a solid tumor and therefore has a slightly more homogenous MR appearance. It generally appears hypointense–isointense on T1-weighted imaging and hyperintense on T2-weighted imaging. Unlike schwannomas, neurofibromas do not characteristically present with cystic changes and may present with a “target appearance” with a central nonenhancing region that is hypointense on T2-weighted imaging (Figure 7.32).116,117

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B

A

C

FIGURE 7.32 (A) Oblique X-ray of the lumbar spine demonstrating marked bony expansion of the right neural foramen secondary to a neurofibroma. (B) Axial spin echo T1-weighted image through the L5–S1 level revealing a large, round mass markedly expanding the right neural foramen. There is a mass effect upon the right lateral recess at this level. This presentation represents a neurofibroma. (C) Right parasagittal spin echo T1-weighted image at L5–S1 demonstrating a large, round mass, which follows the course of the exiting right nerve root, compatible with neurofibroma.

7.9.3 MENINGIOMA Meningiomas are relatively common spinal neoplasms accounting for as much as one fourth to one third of intraspinal expansile lesions.104,118 Spinal meningiomas

are slow growing and almost always benign. Meningiomas may occur within the spinal canal as an intradural extramedullary tumor or epidural location, although they may occur adjacent to nerve roots and occasionally

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189

The most common location of the cyst occurs on the extradural components of sacral or coccygeal nerve roots. They may occasionally be found on nerve roots in other areas of the spine (Figure 7.33). Although most are asymptomatic, they occasionally cause low back pain, sciatic radicular pain, and sacrococcygeal pain. Sensory and motor deficits in the lower extremities imitate lumbar or lumbosacral disk herniation. Urinary dysfunction may occur with large lesions in the sacral canal. Symptoms occur because the expanding cyst impinges upon adjacent nerve roots. The cysts are described as thin walled and CSF filled. They are formed in a space between the endoneurium and the perineurium. Microscopically, the cyst walls consist of peripheral nerve fibers or ganglionic cells covered with meningeal epithelium.123 Erosion of the surrounding bone or IVF may occur because of the pulsatile action of CSF flow. The MR appearance of a perineurial cystic lesion is that of an intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images comparable with CSF.120 FIGURE 7.33 Right lumbar parasagittal (A) spin echo T1weighted and (B) fast spin echo T2-weighted images demonstrating a round, cystic lesion expanding the right neural foramen at the T11–T12 level compatible with a perineural cyst.

extend through the IVF, producing a classic dumbbell lesion. Meningiomas occur more commonly in the thoracic spine, followed by their occurrence in the cervical spine.111 Radicular pain may occur early on the side of the tumor. This may be accompanied by years of focal back pain before MRI confirms the diagnosis. As the lesion expands, signs of cord compression will become obvious. The appearance of meningiomas on MRI is very similar to schwannomas. They are usually isointense to the spinal cord on T1-weighted imaging and are also of low signal intensity as compared to CSF on T2-weighted imaging. The low signal changes are readily apparent when compared to the surrounding hyperintense CSF signal. Because they develop slowly, calcification may occur and will contribute to low T2-weighted signal changes.

7.9.4 PERINEURIAL CYSTS (TARLOV’S CYSTS) Perineurial cysts are reported in the literature to occur in a wide range of prevalence. Paulsen et al.119 reported that lumbosacral perineurial cysts were common lesions, occurring with a prevalence of 4.6% The researchers reviewed 500 sequential lumbosacral spine MRIs and found 23 patients with perineurial cysts; however, only five patients (1%) were symptomatic from the cysts.119 Most researchers report the prevalence to be rare, although the majority of published studies are single case reports.120-122 All case reports and reviews agree that perineurial cysts are usually asymptomatic.

7.9.5 SYNOVIAL CYSTS Facet cysts can cause direct compression of the nerve root or posterolateral aspect of the spinal cord, depending on their size and location. Synovial cysts are rare and occur most frequently at the L4–L5 and L5–S1 levels.124,125 Tissue studies have demonstrated that facet synovial cysts contain various components, including loose fibrous connective tissue, dense fibrous connective tissue, a hyperplastic synovial membrane, and fine calcifications.126 Facet cysts may contain serous fluid and, occasionally, blood. Facet cysts are sometimes mistaken for a tumor within the neural foramen. Facet joint arthrography can be helpful in both diagnosis and treatment of synovial cysts,127 although arthrography is not often required given the availability of MRI. Additional diagnostic considerations having MR appearance similar to synovial cysts include a large or migrated free disk fragment or a cystic nerve root tumor.

7.9.6 METASTATIC DISEASE Spinal metastasis rarely causes radicular symptoms without also causing cord compression. Symptoms associated with metastatic tumor spread usually begin when the nerve root or neurovascular structures within the IVF and cord are compressed or infiltrated by cancer. Hematogenous spread to the nerve root is less common than direct compression by an expanding tumor mass from the vertebral body or lamina.128 Early symptoms may be indistinguishable from radiculopathy or severe far lateral IVF stenosis. Symptoms may result from bony destruction or vertebral collapse, compression of the nerve root by tumor expansion, or from direct metastatic invasion of the nerve

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root. With solitary metastasis, depending on the level and spinal structure invaded, cervical spinal tumors produce neck pain, with diffuse radiation into the shoulder and arm. Lumbar tumors produce diffuse back pain with weakness in the distribution of the lumbar root. Metastatic bony destruction almost universally causes significant pain except in spinal cord injury and patients with congenital insensitivity to pain. Vertebral collapse is a late effect of metastasis. Patients with leptomeningeal metastasis usually have multifocal complex neurological presentations because the CNS is affected at multiple locations (Figure 7.34). Patients with leptomeningeal metastasis often have complex neurological symptoms involving the brain, cranial nerves, and spinal roots, with occasional signs of meningeal irritation.103,128 Leptomeningeal metastases frequently result in a multifocal neurologic presentation. The patient may present with headaches and ataxia with involvement of the brain, or cranial nerve deficits such as diplopia or dysphagia. Back pain, weakness, and absent reflexes are a few of the signs of leptomeningeal metastasis to the roots and the spine. Metastasis may also cause brachial or lumbosacral plexopathy or, in rare cases, isolated peripheral nerve involvement. The most common brachial plexus metastasis occurs from an apical lung tumor (Pancoast tumor) or lymph node metastasis from breast cancer.128 Lower brachial plexus invasion produces C8–T1 deficits; paresthesia, numbness, and weakness in the distal ulnar innervated structures; occasional Horner’s syndrome; and ipsilateral miosis, ptosis, hypohydrosis, paralysis of orbital muscle, and vasodilatation in the ipsilateral half of the face.129

7.10 VERTEBRAL OSTEOMYELITIS AND DISCITIS Infectious organisms can reside and proliferate within tissues of the spinal column. Pyogenic infections of the spinal column usually afflict the vertebral body and/or the intervertebral disk. Coexistent infection of both regions is referred to as spondylodiscitis (Figure 7.35). The source of infection may be secondary to hematogenous seeding or direct inoculation from a foreign body or surgical intervention. Children are more prone to develop discitis, whereas adults are more likely to develop osteomyelitis.130 Juvenile discitis occurs more frequently in girls under 2 years of age, with staphylococcus being the most common infectious etiology. Osteomyelitis occurs more often in men over 50 years old. Pyogenic infection is characterized by infiltration of polymorphonuclear leukocytes, vasodilatation, edema, and fibrin deposition. During the acute inflammatory process, the local release of lytic enzymes can degrade supportive connective tissue. The loss of supportive tissue integrity promotes further spread of the infectious organism and

weakening of involved structures. Under axial loads, the weakened supportive tissues may give way, resulting in an expansile lesion comprised of abscess and degraded disk or osseous matrix. Progressive osteomyelitis and/or discitis can result in an expansile lesion, which may compromise the adjacent nerve root and/or spinal cord. Disk protrusion and fragmentation can occur in combination with disk space infections, resulting in migration of discal material as a consequence of the infectious process.131 This can lead to infection, inflammation, and compressive insult to the adjacent nerve root. Magnetic resonance imaging is the most sensitive imaging technique for the detection of discitis, although the MRI findings typically lag behind acute tissue destruction in the acute phase and tissue repair during the recovery phase. Due to this imaging lag, historical, clinical, and laboratory correlation is critical. Sequential MRI studies are often required to gauge the therapeutic response. Comparison of pre- and post-contrast spin echo T1-weighted imaging increases the sensitivity of detecting infectious changes.132 Gadolinium enhancement can increase or persist after symptom resolution.133 Acute MRI changes are characterized by increased signal intensity on T2-weighted images and decreased signal intensity on T1-weighted images. The healing phase is characterized on MRI by reduced intervertebral disk height (rostrocaudal subluxation), decreased intradiscal and endplate subchondral T2-weighted signal intensity, and resultant fibrous or bony fusion of vertebral bodies. Laboratory methods of diagnosis include C-reactive protein, serum sedimentation rate, and a complete blood count with differential. It is usually important to culture the organism following needle biopsy and to test for antibiotic sensitivity. If the patient with infectious spondylodiscitis demonstrates signs of spinal cord and/or nerve root involvement, surgical decompression and debridement may become a neurosurgical emergency.

7.11 SPONDYLOLISTHESIS AND RADICULOPATHY Radiculopathy and spondylolisthesis are relatively uncommon, as compared to nerve root compression from disk herniation in the lumbar spine. However, in cases of spondylotic spondylolisthesis, radiculopathy occurs in 60 to 70% of patients.134 Spondylolisthesis refers to the anterior displacement or listhesis of a vertebral body in relationship to the vertebral body immediately below. The term listhesis refers to slippage or displacement without reference to direction. Spondylolisthesis may occur without a defect in the neural arch or secondary to a defect in the neural arch. If there is a defect in the neural arch, the term spondylotic spondylolisthesis should be applied. With an intact neural arch, the term non-spondylotic spondylolisthesis should be

Pathomechanisms of Radiculopathy

191

A

B

C

FIGURE 7.34 (A) Sagittal T1-weighted image of the lumbar spine. Notice the absence of the normal high signal intensity of the vertebral body at L2 and the “check mark” fracture of the superior endplate. There is also an area of marrow replacement at the posterior aspect of T11. These findings are most consistent with metastatic disease. (B) Sagittal spin echo T1-weighted image with contrast of the lumbar spine. This image is the same as that in (A) with the addition of contrast media. Notice how the metastasis enhances and becomes isointense to the normal vertebral bodies. Also, there is protrusion of the mass into the spinal canal. (C) Axial spin echo T1-weighted image with contrast at the level of L2. This image is of the same patient seen in the previous two views. The mass obliterates the posterolateral third of L2 and extends through the pedicle into the posterior elements, narrowing both the intervertebral foramen and spinal canal.

used. Spondylolisthesis is relatively common and usually involves the 4th or 5th lumbar vertebrae. Consequently, the radiculopathic symptoms may reflect L4, L5, or S1

nerve root involvement. The most common root involved is the L5 root. Cervical spondylolisthesis is rare, but when present, it is often found at the C6 level. Cervical

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C

A

B FIGURE 7.35 (A) Lateral radiograph of the lumbosacral junction demonstrating destruction of the inferior endplate of L5 and the superior endplate of S1 secondary to osteomyelitis and discitis. (B) Sagittal fat-suppressed T1-weighted image of the lumbosacral junction demonstrating diffuse high signal intensity of L5 and S1 secondary to an inflammatory process. (C) Sagittal T2-weighted image of the lumbosacral junction of the same patient. The infection is associated with hypertintensity on T2-weighted images and is seen extending into the spinal canal. (Courtesy of Shiwei Yu, M.D.)

spondylolisthesis is commonly associated with spina bifida occulta, suggesting a congenital predisposition. There are many opinions relative to the etiology, clinical significance,

therapeutic options, and prognosis with spondylolisthesis. The cause of spondylolisthesis remains controversial. The most commonly reported symptoms associated with

Pathomechanisms of Radiculopathy

degenerative spondylolisthesis and lateral stenosis are neurogenic claudication and radiculopathy.135 There are five pathoetiologic classifications of spondylolisthesis as follows:135a Type I: Dysplastic. The dysplastic type refers to spondylolisthesis with a congenital abnormality involving the neural arch inclusive of hypoplasia. Type II: Isthmic. Refers to physical compromise of the pars interarticularis. (a) Stress or fatigue fracture, or (b) elongated intact pars, or (c) an acute fracture of the pars. Type III: Degenerative (pseudo-spondylolisthesis): This form of spondylolisthesis occurs secondary to chronic degenerative arthrosis at the facet joints and diskovertebral articulations in the absence of a pars separation. Degenerative changes of the facet joint complex can cause laxity and subsequent anterolothesis of the vertebral complex. Type IV: Traumatic type refers to spondylolisthesis secondary to fracture of a portion of the neural arch other than the pars interarticularis. Type V: Pathologic. This category is characterized by the presence of generalized or localized bone disease such as metastatic bone destruction, severe osteoporosis, and Paget’s disease. The diagnosis of radiculopathy and spondylolisthesis often presents a challenge to the attending clinician. Spondylolisthesis can be found in asymptomatic individuals as well as symptomatic patients with concurrent radiculopathy produced from other mechanisms. Paradoxically, patients with severe spondylolisthesis may not report back pain, and patients with relatively less severe spondylolisthesis may have severe back-related complaints. One of the most common complaints associated with spondylolisthesis is a deep dull, aching discomfort or pain focal to the region of spondylolysis. Neurologic evaluation of the lower extremities may be unremarkable unless neurogenic claudication or radiculopathy is present (see Figure 8.19). Loss of Achilles reflexes and weakness in anterior tibial muscles are common in degenerative non-spondylotic spondylolisthesis.136 The pain associated with spondylolisthesis may be a combination of sclerotomal and radicular etiology. Radiculopathic symptoms in spondylotic spondylolisthesis result from a combination of the tethering effect on the nerve roots, compression of the roots from a ligamentum flavum process, impingement of the nerve roots within the foramen, or symptom production from an associated disk herniation and inflammation. In degenerative spondylolisthesis where the neural arch is intact, compression of the cauda equina occurs from a pincer effect caused by dislocation of the intervertebral body and intrusion of the neural arch into the spinal canal. This may produce a

193

complete or partial CSF block on conventional myelography or MR myelography in addition to nerve root compromise.136 In cases of spondylotic spondylolisthesis, root compression in the IVF has been demonstrated to occur from a ligamentum flavum process. The ligament flavum process is a bony fixed process that lies on the internal inferior aspect of the laminar arch, associated with the ligamentum flavum and area of lysis. This bony process protrudes into the IVF and was found to be the cause of root compression in the majority of spondylotic spondylolisthesis patients studied.134 Distortion and swelling of the posterior disk margin (pseudo-disk) occur in spondylolisthesis, which also may be a source of radiculopathic symptom production. Anterolisthesis of the vertebral segment causes a pseudo-disk herniation appearance on MR sagittal or axial images, due to deformation of the posterior annular fibers causing a bulging of the intervertebral disk into the anterior portion of the adjacent spinal canal and neuroforamen. A complete lumbar radiographic study should be performed to rule out spondylolysis of the posterior arch. If a recent fracture of the posterior (neural) arch is suspected, but not seen on routine x-rays, a bone scan is indicated. Single positron emission computed tomography (SPECT) imaging with multiplanar acquisitions can be utilized to evaluate for bone remodeling (increased bone activity secondary to varying levels of trabecular failure or fracture). MRI assessment may demonstrate interruption of the cortical margins of the pars interarticularis, confirming spondylolysis. T-2 weighted images and inversion recovery (fat suppression) technique may reveal regions of high signal in the pars or an area of defect, suggesting bone marrow inflammation/edema compatible with a traumatic separation. Sagittal MR images are critical in the evaluation of the volume and contents of intervertebral foramen. The lumbar nerve root can often be visualized on sagittal views. The intervertebral foramen should be compared to supra-adjacent and infra-adjacent levels. The nerve/IVF ratio should be conceptualized. The MRI may reveal an abnormal nerve root appearance, such as flattening, edematous enlargement, or focal high signal within the nerve root at the level of the spondylolisthesis. In patients with spondylotic spondylolisthesis, evidence of neuroforaminal impingement of the nerve root is often correlative to the segmental level of radiculopathy.137

7.12 NONCOMPRESSIVE RADICULONEURONOPATHY 7.12.1 DIABETIC RADICULOPATHY Diabetic radiculopathy or diabetic polyradiculopathy is a rare complication of diabetes that occurs in middle-aged diabetic patients. This condition is also referred to as

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diabetic proximal neuropathy, diabetic femoral neuropathy, diabetic myelopathy, diabetic plexopathy, diabetic myopathy, Bruns–Garland syndrome, and diabetic amyotrophy.138 This severe, debilitating neuropathy begins with symptoms located unilaterally and focally in the leg, thigh, or buttock and spreads to involve other regions of the same extremity.139 Anterior thigh pain is the most common initial symptom. Pain may be severe and is usually unrelieved by overthe-counter medication. Proximal leg, thigh, or hip weakness develops over a period of weeks to months. The condition often expands to involve the opposite side because of multifocal involvement of lumbosacral roots, plexus, and peripheral nerves (i.e., diabetic lumbosacral radiculoplexus neuropathy). Although motor, sensory, and autonomic fibers are all involved, motor weakness predominates and sensory loss is usually mild. Hyporeflexia or areflexia of the quadriceps muscle stretch reflex is commonly seen. Bowel and bladder involvement is rare. The clinical picture can resemble that of high lumbar disk herniation.140 Another rare complication of uncontrolled type 2 diabetes is thoracic polyradiculopathy. A patient presenting with abdominal pain and paraspinal denervation may have thoracic polyradiculopathy caused by an underlying type 2 diabetes.141 These patients will present with radicular symptoms in the flank or diffuse abdominal pain that is often worse at night and aggravated by light pressure. Thoracic segments T6–T12 are most commonly affected.142 Pain may be unilateral or bilateral and is often accompanied by weight loss. Cutaneous sensory abnormalities are common, and localized abdominal wall paresis with protrusion may occur.142,143

7.12.2 INFECTION 7.12.2.1 Herpes Varicella-Zoster Virus (Shingles) Herpes zoster is a dorsal root-specific disease most commonly affecting the thoracic roots. The trigeminal nerves are the next most frequently affected. With thoracic involvement, symptoms begin as a deep burning pain in the flank or ribs and precede the classic appearance of cutaneous vesicular eruption. The disease tends to be confused initially with radiculopathy or other conditions. Within 3 weeks of the initial symptoms, there is a cutaneous eruption of small clusters of vesicles that follow a dermatomal distribution.144 Motor loss is rare because the disease has a predilection for the dorsal root ganglia. Herpes zoster has also been reported to mimic radiculopathy of the distal extremities. Segmental zoster paresis (SZP) is the focal, asymmetrical, neurogenic weakness that may occur in a limb affected by cutaneous herpes zoster. The appearance of paresis occurs in conjunction with the appearance of vesicular eruption. These patients are generally over 60 years of age. With cervical or lumbar involvement, C5,6,7 or L2,3,4 innervated mus-

cles are the most common segments affected. In addition to this radiculopathic-type involvement, peripheral nerves may also occasionally become involved and manifest as mononeuropathies of the median, ulnar, long thoracic, recurrent laryngeal, and phrenic nerves.145 Severe herpes zoster infection may produce neurogenic bladder, diaphragmatic paralysis, or an ascending paralysis similar to Guillain–Barré syndrome.144 7.12.2.2 AIDS-Related Polyradiculopathy Cytomegalovirus (CMV) has been implicated in the production of polyradicular signs and symptoms in AIDS patients,146,147 and herpes zoster may also be involved in production of AIDS-related polyneuropathy. This rare complication of AIDS should be considered in HIV patients with myeloradicular-type symptoms. AIDS polyradiculopathy is predominantly a motor axonal neuropathy most commonly affecting the lumbosacral roots and cord.148 A retrospective study suggested that in as many as 13% of the cases reviewed, CMV polyradiculopathy was the first manifestation of AIDS.146 MRI may demonstrate enhancement of the pial lining of the conus medullaris, cauda equina, and lumbar nerve roots following contrast enhancement.6 7.12.2.3 Lyme Disease Lyme disease is found throughout the world almost anywhere ticks are present. The disease is caused by the spirochete Borrelia burgdorferi and transmitted by the tick genus Ixodes. In most of North America, the most common vector tick is Ixodes dammini.149 The initial disease begins a few days to a few weeks after a bite from a disease-carrying tick. The disease progresses in three stages.149,150 The first stage follows an acute bite, which develops into a clinically characteristic red macule or papule that slowly expands over 3 to 4 weeks and tends to clear centrally. This identifiable lesion is called erythema migrans. The second stage follows, with systemic infection spreading to the muscles, joints, heart, and nervous system. Signs of a constitutional viral infection progress: fever, fatigue, headache, neck stiffness, and swollen glands. Neurological symptoms develop in stage 2 of the disease. The patient often develops meningitis-type symptoms that fluctuate between moderate/severe and mild/nonexistent over a period of several weeks. Approximately 50% patients with stage 2 disease will develop peripheral nerve involvement resembling radiculitis. These symptoms include severe radicular pain, spine pain, paresthesias, motor weakness, and depressed tendon responses. Stage 3 is the late phase of infection. Serious neurological signs predominate such as ataxia, seizures, paraparesis, quadriparesis, and other signs of encephalomyelitis. Without a history of tick bite or the suggestive triad

Pathomechanisms of Radiculopathy

of (1) meningitis, (2) radiculoneuritis, and (3) facial palsies, the diagnosis is often difficult because of the pleiomorphism of neurological manifestations. These can be localized or diffuse, with central involvement, meningitis, or peripheral manifestations.150 Lyme disease should be in the differential diagnosis when atypical radicular symptoms occur in conjunction with mild meningitis and arthalgic pain. A history of tick bite or erythema migrans with insidious onset polyradiculoneuritis are clear indications of the disease.149

7.12.3 COAGULOPATHIES Bleeding disorders may result in nerve root or cord hemorrhage. Hemophilia is the most common. Excessive Coumadin® medication should be considered as a risk and a possible etiology for hemorrhage following musculoskeletal trauma.

REFERENCES 1. Sunderland, S., Avulsion of nerve roots, in Vinken, P.J., Ed., Handbook of Clinical Neurology, New York: Elsevier, 1976: 393–435. 2. Cohen, M.S., Wall, E.J., Brown, R.A., Rydevik, B., and Garfin, S.R., AcroMed. Award in basic science: cauda equina anatomy. Part II. Extrathecal nerve roots and dorsal root ganglia, Spine, 15:1248–1251, 1990. 3. Rauschning, W., Normal and pathologic anatomy of the lumbar root canals, Spine, 12:1008–1019, 1987. 4. Hasue, M., Kikuchi, S., Sakuyama, Y., and Ito, T., Anatomic study of the interrelationship between lumbosacral nerve roots and their surrounding tissues, Spine, 8:50–58, 1983. 5. Bogduk, N. and Twomey, L.T., Clinical Anatomy of the Lumbar Spine and Sacrum, New York: J.A. Majors, 1997. 6. Talpos, D., Tien, R.D., and Hesselink, J.R., Magnetic resonance imaging of AIDS-related polyradiculopathy, Neurology, 41:1995–1997, 1991. 7. Kikuchi, S., Hasue, M., Nishiyama, K., and Ito, T., Anatomic and clinical studies of radicular symptoms, Spine, 9:23–30, 1984. 8. Mahdi, M.E., Latif, F., and Janko, M., The spinal nerve root innervation, and a new concept of the clinicopathological interrelations in back pain and sciatica, Neurochirurgia, 24:137–141, 1981. 9. Olsson, Y. and Kristensson, K., The perineurium as a diffusion barrier to protein tracers following trauma to nerves, Acta Neuropathol., 23:105–111, 1973. 10. Haller, F.R. and Low, F.N., The fine structure of the peripheral nerve root sheath in the subarachnoid space in the rat and other laboratory animals, Am. J. Anat., 131:1–20, 1971.

195

11. Arvidsson, B., Distribution of intravenously injected protein tracers in peripheral ganglia of adult mice, Exp. Neurol., 63:388–410, 1979. 12. Stodieck, L., Beel, J., and Luttges, M., Structural properties of spinal nerve roots: protein composition, Exp. Neurol., 91:41–51, 1986. 13. Garfin, S., Rydevik, B., Lind, B., and Massie, J., Spinal nerve root compression, Spine, 20:1810–1820, 1995. 14. Rydevik, B., Holm, S., Brown, M., and Lundborg, G., Diffusion from the cerebrospinal fluid as a nutritional pathway for spinal nerve roots, Acta Physiol. Scand., 138:247–248, 1990. 15. Kobayashi, S., Yoshizawa, H., and Nakai, S., Experimental study on the dynamics of lumbosacral nerve root circulation, Spine, 25:298–305, 2000. 16. Burchiel, K., Effects of electrical and mechanical stimulation on two foci of spontaneous activity which develop in primary afferent neurons after peripheral axotomy, Pain, 18:249–265, 1984. 17. Howe, J., Loeser, J., and Calvin, W., Mechanosensitivity of dorsal root ganglia in chronically injured axons: a physiological basis for the radicular pain of nerve root compression, Pain, 3:25–41, 1977. 18. Hasue, M., Kunogi, J., Konno, S., and Kikuchi, S., Classification by position of the dorsal root ganglia in lumbosacral region, Spine, 14:1261–1264, 1989. 19. Sharpless, S., Susceptibility of spinal roots to compression block: the research status of spinal manipulative therapy, NINDC Mongr., 15:155–161, 1975. 20. Dahlin, L. and McLean, W.G., Effects of graded experimental compression on slow and fast axonal transport in rabbit vagus nerve, J. Neurol. Sci., 72:19–30, 1986. 21. Dahlin, L., Rydevik, B., McLean, W.G., and Sjostrand, J., Changes in fast axonal transport during experimental nerve compression at low pressures, Exp. Neurol., 84:29–36, 1984. 22. Grundfest, H., Effects of hydrostatic pressures upon the excitability, the recovery, and the potential sequences of frog nerve, Cold Spring Harbor Symp. Quant. Biol., 4:179–187, 1936. 23. Danielsen, N., Lundborg, G., and Frizell, M., Nerve repair and axonal transport: distribution of axonally transported proteins during maturation period in regenerating rabbit hypoglossal nerve, J. Neurol. Sci., 73:269–277, 1986. 24. Edwards, D. and Cattell, M., Further observations on decrement in nerve conduction, Am. J. Physiol., 87:359– 367, 1928. 25. Yoshizawa, H., Kobayashi, S., and Kubota, K., Effects of compression on intraradicular blood flow in dog, Spine, 14:1220–1225, 1989. 26. Jacobs, J., Macfarlande, R., and Cavanagh, J., Vascular leakage in the dorsal root ganglia of the rat studied with horseradish peroxidase, J. Neurol. Sci., 29:95–107, 1976. 27. Kobayashi, S., Yoshizawa, H., Hachiya, Y., Ukai, T., and Morita, T., Vasogenic edema induced by compression injury to the spinal nerve root, Spine, 18:1410–1424, 1993.

196

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

28. Olmarker, K., Rydevik, B., and Holm, S., Edema formation in spinal nerve roots induced by experimental, graded compression: an experimental study of the pig cauda equina with special reference to differences in effects between rapid and slow onset of compression, Spine, 14:569–573, 1989. 29. Dahlin, L., Shyu, B.C., Danielsen, N., and Anderson, S.A., Effects of nerve compression or ischemia on conduction properties of myelinated and non-myelinated nerve fibers: an experimental study in rabbit common peroneal nerve, Acta Physiol. Scand., 136:97–105, 1989. 30. Olmarker, K., Rydevik, B., Holm, S., and Bagge, U., Effects of experimental, graded compression on blood flow in spinal nerve roots: a vital microscopic study on the porcine cauda equina, J. Orthoped. Res., 7:817–823, 1989. 31. Olmarker, K., Holm, S., and Rydevik, B., Importance of compression onset rate for the degree of impairment of impulse propagation in experimental compression injury of the porcine cauda equina, Spine, 15:416–419, 1990. 32. Pedowitz, R., Garfin, S.R., Massie, J.B., and Hargens, A.R., Effects of magnitude and duration of compression on spinal nerve root conduction, Spine, 17:194–199, 1992. 33. Hitselberger, W. and Witten, R., Abnormal myelograms in asymptomatic patients, J. Neurosurg., 28:204–206, 1968. 34. Yoo, J., Zou, D., Edwards, W., Bayley, J., and Yuan, H., Effects of cervical spine motion on the neuroforamenal dimensions of human cervical spine, Spine, 17:1131– 1135, 1992. 35. Breig, A., Biomechanics of the Central Nervous System, Stockholm: Almqvist & Wiskell, 1960. 36. Smyth, M. and Wright, V., Sciatica and the intervertebral disk: an experimental study, J. Bone Joint Surg. Am., 40:1401–1418, 1958. 37. Brown, M.D., Gepstein, R., and Pallares, V., Somatosensory Evoked Potentials During Epidural Anesthesia, presented at the 32nd Annual Meeting of the Orthopaedic Research Society, New Orleans, LA. 1986. 38. Kayama, S., Konno, S., Olmarker, K., Yabuki, S., and Kikuchi, S., Incision of the annulus fibrosus induces nerve root morphologic, vascular and functional changes: an experimental study, Spine, 21:2539–2543, 1996. 39. Marshall, L.L. and Trethewie, E.R., Chemical irritation of nerve-root in disk prolapse, Lancet, 2(7824):320, 1973. 40. Nachemson, A., Intradiscal measurements of pH in patients with lumbar rhizopathies, Acta Orthoped. Scand., 40:23–42, 1969. 41. Olmarker, K., Blomquist, J., Stromberg, J., Nannmark, U., Thomsen, P., and Rydevik, B., Inflammatogenic properties of nucleus pulposus, Spine, 20:665–669, 1995. 42. Saal, J., The role of inflammation in lumbar pain, Spine, 20:1821–1827, 1995. 43. Cavanaugh, J., Neural mechanisms of lumbar pain, Spine, 20:1804–1809, 1995.

44. Kayama, S., Olmarker, K., Larsson, K., Sjogren-Jansson, E., Lindahl, A., and Rydevik, B., Cultured, autologous nucleus pulposus cells induce functional changes in spinal nerve roots, Spine, 23:2155–2158, 1998. 45. Otani, K., Arai, I., Mao, G.P., Konno, S., Olmarker, K., and Kikuchi, S., Experimental disk herniation: evaluation of the natural course, Spine, 22:2894–2899, 1997. 46. Otani, K., Arai, I., Mao, G.P., Konno, S., Olmarker, K., and Kikuchi, S., Nucleus pulposus-induced nerve root injury: relationship between blood flow and motor nerve conduction velocity, Neurosurgery, 45:614–619, 1999. 47. Goupille, P., Jayson, M.I., Valat, J.P., and Freemont, A.J., The role of inflammation in disk herniation-associated radiculopathy, Semin. Arthritis Rheum., 28:60–71, 1998. 48. Hasue, M., Pain and the nerve root: an interdisciplinary approach, Spine, 18:2053–2058, 1993. 49. Saal, J.S., Franson, R., Dobrow, R., Saal, J.A., White, A., and Goldthwaite, N., High levels of inflammatory phospholipase A activity in lumbar disk herniations, Spine, 15:674–678, 1990. 50. Wehling, P., Evans, C., and Schulitz, K., The interaction between synovial cytokines and peripheral nerve function: a potential element in the development of radicular syndrome, Z. Orthoped., 128:442–446, 1990. 51. Kawakami, M., Tamaki, T., Hayashi, N., Hashizume, H., and Nishi, H., Possible mechanism of painful radiculopathy in lumbar disk herniation, Clin. Orthoped., 351:241–251, 1998. 52. Doita, M., Kanatani, T., Harada, T., and Mizuni, K., Immunohistologic study of the ruptured intervertebral disk of the lumbar spine, Spine, 21:235–241, 1996. 53. Satoh, K., Konno, S., Nishiyama, K., Olmarker, K., and Kikuchi, S., Presence and distribution of antigen–antibody complexes in the herniated nucleus pulposus, Spine, 24:1980–1984, 1999. 54. Habtemariam, A., Gronblad, M., Virri, J., Seitsalo, S., and Karaharju, E., A comparative immunohistochemical study of inflammatory cells in acute-stage and chronicstage disk herniations, Spine, 23:2159–2165, 1998. 55. Bland, J.H., Disorders of the Cervical Spine: Diagnosis and Medical Management, 2nd ed., Philadelphia, PA: Saunders, 1994. 56. Ferguson, R.J. and Caplan, L.R., Cervical spondylitic myelopathy, Neurol. Clin., 3:373–382, 1985. 57. Yochum, T.R. and Rowe, L.J., Esssentials of Skeletal Radiology, 2nd ed., Baltimore, MD: Lippincott, 1996. 58. Resnick, D., Degenerative disease of the vertebral column, Radiology, 156:3–14, 1985. 59. Jinkins, J.R., Whittemore, A.R., and Bradley, W.G., The anatomic basis of vertebrogenic pain and the autonomic syndrome associated with lumbar disk extrusion, Am. J. Neuroradiol., 10:219–231, 1989. 60. Kuslich, S., Ulstrom, C., and Michael, C., The tissue origin of low back pain and sciatica: a report of pain response to tissue stimulation during operations on the lumbar spine using local anesthesia, Orthoped. Clin. North Am., 22:181–187, 1991. 61. Sunderland, S. and Bradley, K., Stress-strain phenomena in human spinal nerve roots, Brain, 84:120–125, 1961.

Pathomechanisms of Radiculopathy

62. Hoyland, J., Freemont, A.J., and Jayson, M.I., Intervertebral foramen venous obstruction: a cause of periradicular fibrosis, Spine, 14:558–568, 1989. 63. Cooper, R.G., Freemont, A.J., Hoyland, J.A., Jenkins, J.P., West, C.G., Illingworth, K.J., and Jayson, M.I., Herniated intervertebral disk-associated periradicular fibrosis and vascular abnormalities occur without inflammatory cell infiltration, Spine, 20(5):591–8, 1995. 64. Eames, R. and Long, I., Clinical and pathological study of ischemic neuropathy, J. Neurol. Neurosurg. Psychiatry, 30:215–221, 1967. 65. Watanabe, R. and Parke, W., Structure of lumbosacral spinal nerve roots: anatomy and pathology in spinal stenosis, J. Clin. Orthoped. Surg. Jpn., 22:529–539, 1987. 66. Yoshizawa, H., Kobayashi, S., and Hachiya, Y., Blood supply of nerve roots and dorsal root ganglia, Orthoped. Clin. North Am., 22:195–211, 1991. 67. Sunderland, S., The nerve lesion in the carpal tunnel syndrome, J. Neurol. Neurosurg. Psychiatry, 39:615– 626, 1976. 68. Sunderland, S., Anatomical perivertebral influences in the intervertebral foramen: the research status of manipulative therapy, NINDC Monogr., 15:129–140, 1975. 69. Burton, C., Kirkaldy-Willis, W., and Yong-Hign, K., Causes of failure of surgery on the lumbar spine, Clin. Orthoped., 157:191–199, 1981. 70. Robertson, J.T., Role of peridural fibrosis in the failed back: a review, Eur. Spine J., 5(suppl. 1):S2–S6, 1996. 71. Ozgocmen, S. and Ardicoglu, O., Odontoid fracture complicating ankylosing spondylitis, Spinal Cord, 38:117–119, 2000. 72. Hanson, J.A. and Miria, S., Predisposition for spinal fracture in ankylosing spondylitis, Am. J. Roentgenol., 174:150, 2000. 73. Andresen, R., Haidekker, M.A., Radmer, S., and Banzer, D., CT determination of bone mineral density and structural investigations on the axial skeleton for estimating the osteoporosis-related fracture risk by means of a risk score, Br. J. Radiol., 72:569–578, 1999. 74. Legrand, E., Chappard, D., Pascaretti, C., Duquenne, M., Krebs, S., Rohmer, V., Basle, M.F., and Audran, M., Trabecular bone microarchitecture, bone mineral density, and vertebral fractures in male osteoporosis, J. Bone Mineral Res., 15:13–19, 2000. 75. Seeman, E., The structural basis of bone fragility in men, Bone, 25:143–147, 1999. 76. Evans, R.W., Whiplash injuries, in Evans, R.W., Ed., Neurology and Trauma, Philadelphia, PA: Saunders, 1996: 439–457. 77. Croft, A.C., A proposed classification of cervical acceleration–deceleration (CAD) injuries with review of prognostic research, Palmer J. Res., 1:10–21, 1994. 78. Tarola, G.A., Whiplash: contemporary considerations in assessment, management, treatment, and prognosis, J. Neuromusculoskeletal Syst., 1(4):156–166, 1993. 79. Barnsley, L., Lord, S., and Bogduk, N., Whiplash injury, Pain, 58:283–307, 1994.

197

80. Croft, A.C., Biomechanics, in Foreman, S.M. and Croft, A.C., Eds., Whiplash Injuries: The Cervical Acceleration/Deceleration Syndrome, Baltimore, MD: Williams & Wilkins, 1995. 81. Evans, R.W., Some observations on whiplash injuries, Neurol. Clin., 10:975–997, 1992. 82. Bonuccelli, U., Pavese, N., Lucetti, C., Renna, M.R., Gambaccini, G., Bernardini, S., Canapicchi, R., Carrozzi, L., and Murri, L., Late whiplash syndrome: a clinical and magnetic resonance imaging study, Funct. Neurol., 14:219–225, 1999. 83. Wilmink, J.T., MR imaging of the spine: trauma and degerative disease, Eur. Radiol., 9:1259–1266, 1999. 84. Katzberg, R.W., Benedetti, P.F., Drake, C.M., Ivanovic, M., Levine, R.A., Beatty, C.S., Nemzek, W.R., McFall, R.A., Ontell, F.K., Bishop, D.M., Poirier, V.C., and Chong, B.W., Acute cervical spine injuries: prospective MR imaging assessment at a level 1 trauma center, Radiology, 213:203–12, 1999. 85. Dumitru, D. and Dreyfuss, P., Dermatomal/segmental somatosensory evoked potential evaluation of L5–S1 unilateral/unilevel radiculopathies, Muscle Nerve, 19:442–449, 1996. 86. Yeoman, P.M., Brachial plexus injuries, J. Bone Joint Surg. Br., 47:187, 1965. 87. Hayashi, N., Yamamoto, S., Okubo, T. et al., Avulsion injury of cervical nerve roots: enhanced intradural nerve roots at MR imaging, Radiology, 206:817–822, 1998. 88. Carvalho, G.A., Nikkhah, G., Msatthies, C., Penkert, G., and Samii, M., Diagnosis of root avulsion in traumatic brachial plexus injuries: value of computerized tomography myelography and magnetic resonance imaging, J. Neurosurg., 86:69–76, 1997. 89. Abdullah, A.F., Ditto, E.W., III, Byrd, E.B., and Williams, R., Extreme lateral lumbar disk herniations, J. Neurosurg., 41:229–234, 1974. 90. Adams, M.A. and Hutton, W.C., Prolapsed intervertebral disk: a hyperflexion injury, Spine, 7:184–191, 1982. 91. Modic, M., Ross, J.S., Obuchowski, N., Browning, K., Cianflocco, A., and Mazanec, D., Contrast-enhanced MR imaging in acute lumbar radiculopathy: a pilot study of the natural history, Radiology, 195:429–435, 1995. 92. Spangfort, E., The lumbar disk herniation: a computeraided analysis of 2504 operations, Acta Orthoped. Scand., 142(suppl.):1–95, 1972. 93. Toyone, T., Takahashi, K., Kitahara, H., Yamagata, M., Murakami, M., and Moriya, H., Visualisation of symptomatic nerve roots: prospective study of contrastenhanced MRI in patients with lumbar disk herniation, J. Bone Joint Surg. Br., 75:529–533, 1993. 94. Brinckmann, P. and Horst, M., The influences of vertebral body fracture, intradiscal injection, and partial discectomy on the radial bulge and height of human lumbar discs, Spine, 10:138–145, 1985. 95. Yu, S., Haughton, V., Sether, L., and Wagner, M., Annulus fibrosus in bulging intervertebral disks, Radiology, 169:761–763, 1988.

198

Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

96. Yu, S., Sether, L., Ho, P., Wagner, M., and Haughton, V., Tears of the annulus fibrosus: correlation between MR and pathologic findings in cadavers, Am. J. Neuroradiol., 9:367–370, 1988. 97. Brinckmann, P., Injury of the annulus fibrosus and disk protrusions: an in vitro investigation on human lumbar discs, Spine, 11:149–153, 1986. 98. Modic, M., Degenerative disorders of the spine, in Patterson, A., Ed., Magnetic Resonance Imaging of the Spine, St Louis, MO: Mosby, 1994: 94–130. 99. Schellinger, D., Manz, H.J., Vidic, B. et al., Disk fragment migration, Radiology, 175:831–836, 1990. 100. Peyser, E. and Harari, A., Intradural rupture of lumbar intervertebral disk: report of two cases with review of the literature, Surg. Neurol., 8:95–98, 1977. 101. Masaryk, T.J., Ross, J.S., Modic, M.T., Boumphrey, F., Bohlman, H., and Wilber, G., High-resolution MR imaging of sequestered lumbar intervertebral disks, Am. J. Roentgenol., 150:1155–1162, 1988. 102. Feldenzer, J.A., McGauley, J.L., and McGillicuddy, J.E., Sacral and presacral tumors: problems in diagnosis and management, Neurosurgery, 25:884–891, 1989. 103. Mulder, D.W. and Dale, A.J.D., Spinal cord tumors and disks, in Joynt, R., Ed., Clinical Neurology, Philadelphia, PA: Lippincott, 15–17, 1991. 104. Burger, P.C., Scheithauer, B.W., and Vogel, F.S., Spinal meninges, spinal nerve roots, and spinal cord, in Surgical Pathology of the Nervous System and Its Coverings, 3rd ed., New York: Churchill-Livingstone, 605–660, 1991. 105. Gentry, L.R., Mehta, R.C., Appen, R.E., and Weinstein, J.M., MR imaging of primary trochlear nerve neoplasms, Am. J. Neuroradiol., 12:707–713, 1991. 106. Lee, R.R. and Melhem, A., Spinal neoplasms, in Orrison, W.W., Ed., Neuroimaging, Philadelphia, PA: Saunders, 2000: 1353–1354. 107. MacCollin, M., Woodfin, W., Kronn, D., and Short, M.P., Schwannomatosis: a clinical and pathologic study, Neurology, 46:1072–1079, 1996. 108. Osborn, A.G., Tumors, cysts and tumor-like lesions of the spine and spinal cord, in Osbourn, A.G., Ed., Diagnostic Neuroradiology, St Louis, MO: Mosby, 1993: 876–918. 109. Atasoy, E., Thoracic outlet compression syndrome caused by a schwannoma of the C7 nerve root, J. Hand Surg. Br., 22:662–663, 1997. 110. Caputo, L.A. and Cusimano, M.D., Schwannoma of the cauda equina, J. Manip Physiol. Ther., 20:124–129, 1997. 111. Sevick, R.J., Cervical spine tumors, in Ross, J.S., Ed., Neuroimaging Clinics of North America, Philadelphia, PA: Saunders, 385–400, 1995. 112. Demachi, H., Takashima, T., Kadoya, M., Suzuki, M., Konishi, H., Tomita, K., Yonezawa, K., and Ubukata, A., MR imaging of spinal neurinomas with pathological correlation. J. Comput. Assist. Tomogr., 14(2):250–254, 1990. 113. Miyawaki, T., Nakamura, A., Hayashi, H., and Kurihara, K., Macrocystic schwannoma in the seventh cervical nerve, Plast. Reconstr Surg., 104:789–792, 1999.

114. Kato, T., George, B., Mourier, K.L., Lot, G., Gelbert, F., and Mikol, J., Intraforaminal neurinoma in the lumbosacral region, Neurol. Med. Chir. Tokyo, 33:86–91, 1993. 115. Creange, A., Zeller, J., Rostaing-Rigattieri, S., Brugieres, P., Degos, J.D., Revuz, J., and Wolkenstein, P., Neurological complications of neurofibromatosis type 1 in adulthood, Brain, 122(Pt 3):473–481, 1999. 116. Burk, D.L., Jr., Brumberg, J.A., Kanal, E. et al., Spinal and paraspinal neurofibromatosis: surface coil imaging at 1.5T, Radiology, 162:797–801, 1987. 117. Varma, D.G., Moulopoulos, A., Sara, A.S., Leeds, N., Kumar, R., Kim, E.E., and Wallace, S., MR imaging of extracranial nerve sheath tumors, J. Comput. Assist. Tomogr., 16(3):448–453, 1992. 118. Roux, F.X., Natal, F., Pinaudeau, M., Borne, G., Devaux, B., and Meder, J.F., Intraspinal meningiomas: review of 54 cases with discussion of poor prognosis factors and modern therapeutic management, Surg. Neurol., 46:458–463, 1996. 119. Paulsen, R.D., Call, G.A., and Murtagh, F.R., Prevalence and percutaneous drainage of cysts of the sacral nerve root sheath (Tarlov cysts), Am. J. Neuroradiol., 15:293– 297, 1994. 120. Araki, Y., Tsukaguchi, I., Ishida, T. et al., MRI of symptomatic sacral perineural cyst, Radiat. Med., 10:250– 252, 1992. 121. Su, C.C., Shirane, R., Okubo, T., Kayama, T., and Yoshimoto, T., Surgical treatment of a sacral nerve root cyst with intermittent claudication in an 85-year-old patient: case report, Surg. Neurol., 45:283–286, 1996. 122. Arun Kumar, M.J., Selvapandian, S., and Chandy, M.J., Sacral nerve root cysts: a review on pathophysiology, Neurol. India, 47:61–64, 1999. 123. Kato, T., Takamura, H., Goto, S., Sasaki, H., Makino, K., Ozaki, N., and Hodozuka, A., Sacral perineural cyst: report of a case [abstract], No Shinkei Geka., 16:893– 897, 1988. 124. Liu, S.S., Williams, K.D., Drayer, B.P., Spetzler, R.F., and Sonntag, V.K., Synovial cysts of the lumbosacral spine: diagnosis by MR imaging, Am. J. Roentgenol., 154(1):163–166, 1990. 125. Silbergleit, R., Gebarski, S.S., Brunberg, J.A., McGillicuddy, J., and Blaivas, M., Lumbar synovial cysts: correlation of myelographic CT, MR and pathologic findings, Am. J. Neuroradiol., 11:777–779, 1990. 126. Liu, S., Williams, K.D., Drayer, B., Spetzler, R.F., and Sonntag, V.K., Synovial cysts of the lumbosacral spine: diagnosis by MR imaging, Am. J. Roentgenol., 154:163– 166, 1990. 127. Casselman, E., Radiologic recognition of symptomatic spinal synovial cysts, Am. J. Neuroradiol., 6:971–973, 1985. 128. Posner, J.B., Neurologic Complications of Cancer, Philadelphia, PA: F.A. Davis, 1995. 129. Duus, P., Topical Diagnosis in Neurology. Anatomy, Physiology, Signs, Symptoms, 2nd ed., New York: Thieme Medical, 1989.

Pathomechanisms of Radiculopathy

130. Mark, A.S., Infectious and inflammatory diseases of the spine, in Orrision, W.W., Ed., Neuroimaging, Philadelphia, PA: Saunders, 1377–1379, 2000. 131. Jinkins, J.R., Bazan, C., III, and Xiong, L., MR of disk protrusion engendered by infectious spondylitis, J. Comput. Assist. Tomogr., 20:715–718, 1996. 132. Rivero, M.G., Salvatore, A.J., and de Wouters, L., Spontaneous infection spondylodiscitis in adults, Medicina B Ser., 59:143–150, 1999. 133. Gillams, A.R., Chaddha, B., and Carter, A.P., MR appearance of the temporal evolution and resolution of infectious spondylitis, Am. J. Roentgenol., 166:903– 907, 1996. 134. Stears, J.C., Radiculopathy in spondylosis/spondylolisthesis. The laminar/ligamentum flavum process. Acta. Radiol., Suppl. 369:723-6, 1986. 135. Bolesta, M.J. and Bohlmann, H.H., Degenerative spondylolisthesis. Instr. Course Lect., 38:157–65, 1989. 135a. Wiltse, L.L., Newman, P.H., MacNab, I., Classification of spondylolysis and spondylolisthesis. Clin. Orthop., 117:23, 1976. 136. Epstein, J.A., Epstein, B.S., Lavine, L.S., Carras, R., and Rosenthal, A.D., Degenerative lumbar spondylolisthesis with an intact neural arch (pseudospondylolisthesis). J. Neurosurg., Feb, 44(2):139-47, 1976. 137. Jinkins, J.R. and Rauch, A., Magnetic resonance imaging of entrapment of lumbar nerve roots in spondylotic spondylolisthesis. J. Bone Joint Surg., (Am). Nov, 76(11):1643-8, 1994. 138. Donaghy, M., Lumbosacral plexus lesions, in Dyck, P.J. and Thomas, P.K., Eds., Peripheral Neuropathy, 3rd ed., Philadelphia, PA: Saunders, 1993: 953. 139. Dyck, P.J., Norell, J.E., and Dyck, P.J., Microvasculitis and ischemia in diabetic lumbosacral radiculoplexus neuropathy, Neurology, 53:2113–2121, 1999. 140. Naftulin, S., Fast, A., and Thomas, M., Diabetic lumbar radiculopathy: sciatica without disk herniation, Spine, 18:2419–2422, 1993.

199

141. Hayes, F.J., Redmond, J.M., and McKenna, M.J., Thoracic polyradiculopathy: abdominal wall swelling and sensory symptoms in diabetes mellitus, Ir. Med. J., 87:150–151, 1994. 142. Chaudhuri, K.R., Wren, D.R., Werring, D., and Watkins, P.J., Unilateral abdominal muscle herniation with pain: a distinctive variant of diabetic radiculopathy, Diabet. Med., 14:803–807, 1997. 143. Longstreth, G.F., Diabetic thoracic polyradiculopathy: ten patients with abdominal pain, Am. J. Gastroenterol., 92:502–505, 1997. 144. Baringer, R.J. and Townsend, J.J., Herpesvirus infection of the peripheral nervous system, in Dyck, P.J. and Thomas, P.K., Eds., Peripheral Neuropathy, 3rd ed., Philadelphia, PA: Saunders, 1993: 1333–1342. 145. Merchut, M.P. and Gruener, G., Segmental zoster paresis of limbs, Electromyogr. Clin. Neurophysiol., 36:369– 375, 1996. 146. Anders, H.J. and Goebel, F.D., Cytomegalovirus polyradiculopathy in patients with AIDS, Clin. Infect. Dis., 27:345–352, 1998. 147. Wolf, D.G. and Spector, S.A., Diagnosis of human cytomegalovirus central nervous system disease in AIDS patients by DNA amplification from cerebrospinal fluid, J. Infect. Dis., 166:1412–1415, 1992. 148. Corral, I., Quereda, C., Casado, J.L., Cobo, J., Navas, E., Perez-Elias, M.J., Pintado, V., Fortun, J., and Guerrero, A., Acute polyradiculopathies in HIV-infected patients, J. Neurol., 1244(8):499–504, 1997. 149. Reik, L., Peripheral neuropathy in Lyme disease, in Dyck, P.J. and Thomas, P.K., Eds., Peripheral Neuropathy, 3rd ed., Philadelphia, PA: Saunders, 1993: 1401–1411. 150. Lecomte, F., Mihout, B., and Humbert, G., Neurological manifestations of Lyme disease and treatments, Biomed. Pharmacother., 43:409–413, 1989.

8

Classic Signs and Symptoms of Radiculopathy

Many clinical signs such as foot drop or sciatic pain with antalgia point to the diagnosis of radiculopathy. However, confirmation of the cause of radiculopathy may be perplexing except when magnetic resonance imaging (MRI) demonstrates a moderate- to large-sized disk herniation compressing the same level nerve root as clinically expected. Diagnostically, complex conditions involving multiroot symptoms, intermittent root compression, or biochemically induced radiculopathies are often difficult to confirm without additional diagnostic investigation. The most commonly reported symptoms of radiculopathy are pain, tingling, numbness, and weakness. Although patients most often complain of sensory symptoms, these symptoms are not as clinically significant as motor loss. When paresis is present, it is highly probable that electrodiagnostic studies will be abnormal (Figure 8.1).1 This chapter discusses the common signs and symptoms of radiculopathy and the concomitant pain patterns that occur with or mimic radiculopathy. The pathogenesis and clinical significance of these signs are individually reviewed. Section 8.8, Assessment of Radiculopathy, reviews the clinical importance and utility of tests such as electromyography, nerve conduction studies, somatosensory evoked potentials, and MRI, which is an important tool for anatomical localization of root level compression. A brief review of important MRI characteristics of the disk and nerve root is presented. The remainder of the chapter is devoted to localization of monoradicular syndromes. This clinically valuable section discusses each spinal nerve root level and the signs and symptoms associated with each radiculopathic presentation.

8.1 SENSORY ABNORMALITIES Patients with radiculopathy commonly describe sensory symptoms such as pain, paresthesia (tingling), or numbness in a segmental distribution corresponding to the level of involvement. These segmental levels of sensory innervation are called dermatomes (Figure 8.2). The sensory evaluation should include comparative pin prick, twopoint discrimination, pallesthetic (vibratory) perception, and joint position sense (Table 8.1). Sensory symptoms associated with radiculopathy result from a combination of neurapraxic and axonotmestic damage to the nerve root. The decreased dermatomal sensation associated with radiculopathy is a result of

conduction block or loss of axon continuity in the sensory nerves of the nerve root. When the patient describes a region of numbness, there is usually a decreased perception of pin prick or vibratory sensation; however, severe numbness is usually associated with a peripheral nerve lesion or neuropathy (Figure 8.3). The region of hypesthesia will usually follow a dermatomal pattern, whereas the paresthesia and perceived pain may appear diffuse or nondermatomal. This type of pain, sclerotomal pain, occurs when there is root level involvement of afferent fibers originating from segmental muscles and deep tissue structures. The mechanism of pain production is not clearly understood. Compression of the intraneural microcirculation is thought to be part of the pathophysiologic process. It should be noted that the epineural circulation provides 50% of the blood flow to the local nerve fiber.2 Ischemia to the nerve root may occur in disk lesions without direct nerve root compromise, producing a painful dysesthesia. This occurs with compression of the radicular artery in the lateral recess. The shooting pain associated with radiculopathy may be a result of hypersensitivity and spontaneous activity of the regenerating axons in the root and spinal nerve. When nerve root compression results in axonotmesis, the proximal axon sends out sprouts in an attempt to reinnervate the distal end organ. Axonal sprouts that fail to regenerate may form mechanosensitive and chemosensitive neuromas in the area of axonal damage. The presence of neuromas, changes in vascular permeability, increased sensitivity to neuropeptides, and other trophic effects of nerve root compression result in spontaneous nerve root firing,3 which causes the characteristic pain of radiculopathy described by patients as a shooting pain or “electric pain” into the extremities (Figure 8.4). These spontaneous, ectopically generated sensory symptoms are a type of neuropathic pain.

8.2 NERVE ROOT IRRITABILITY SIGNS Neuro-orthopedic tests that compress or stretch an irritated nerve root are a routine part of the clinical examination. These maneuvers are designed to reproduce the patient’s radiculopathic symptoms. In mild to moderate cases of radiculopathy, nerve root sensitivity to mechanical stimulation may be one of the earliest signs of radiculopathy. Nerve root irritability signs can often be elicited before the clinical appearance of sensory deficits, reflex changes, 201

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Perineural fibrosis Disk herniation

Uncinate process/vertebral exostosis

Zone of inflammation Perineural edema

Intraneural edema

Hypertrophy of the ligamentum flavum Synovial cyst

Facet arthrosis exostosis

Spinal infection, tumor or metastasis are ominous conditions that may result in a rapid neurological decline.

FIGURE 8.1 Pathologies contributing to compressive root and spinal nerve syndromes. (Copyright J.M. True, D.C.)

TABLE 8.1 Dermatomal Landmarks Thumb Middle finger Little finger Breast nipple Umbilicus Medial knee Medial ankle Web space great toe Little toe/lat. foot

C6 C7 C8 T4 T10 L3 L4 L5 S1

or muscular paresis in mild to moderate radiculopathy. In cases of chronic symptomatic radiculopathy associated with spondylosis, nerve root tension signs are consistently present, with varying degrees of sensory, motor, or reflex abnormalities. The nerve root and nerve root sleeve slides within the intervertebral foramen during movement of the spine and extremities. For example, the straight leg raise maneuver translates the lumbar nerve roots approximately 2 to 5 mm at the level of the intervertebral foramen (IVF).4 This movement is constrained by direct compression of the nerve root and by the secondary reflexive spasm of muscles that guard against further stretch of an irritated nerve membrane. In a review of 2000 patients with surgically demonstrated disk herniations, Spangfort5 found that the straight leg raise tension sign was positive in 90% of cases (Figure 8.5).

In the upper extremity the most common neuro-orthopedic tests for nerve irritability are variations of the foraminal compression test, shoulder depressor test, Bikele’s sign, and Bakody’s sign. In the lower extremity, variations of the straight leg raise, Kemp’s test, and femoral stretch are important (Table 8.2). The application of additional tension to a traditional clinical maneuver may magnify a subclinical presentation. This can be accomplished in the upper extremity by extending the arm, extending the wrist, and laterally flexing the neck to the opposite side. In the lower extremity, a straight leg raise and passive foot dorsiflexion, also called Braggard’s maneuver, can be performed. To stretch and challenge the middle to lower cervical nerve root levels, Adson’s maneuver should be performed with the arm in less than 40º of abduction. Conversely, a patient’s radiculopathic presentation may be alleviated by putting the extremity in a position that decreases tension on the nerve root. For example, elbow flexion reduces tension on the midcervical nerve roots and arm abduction also relieves root tension. It is common with middle to lower cervical radiculopathies for the patient to hold the arm against the body or elevated with shoulder abduction and elbow flexion to reduce pain into the extremity; this is known as Bakody’s sign. A differential diagnosis of plexopathy must also be considered when other indicators of radiculopathy are not present. Evocative maneuvers such as cervical extension with ipsilateral rotation can magnify radiculopathic clinical presentations by reducing available foraminal space,

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203

C2 C2 C3

C4 C3

C5

T2

T2

T3 T4 T5 T6 T7 T8 T9 T10 T11 T12

T1 C6

C5

C4

T1 C6 C8 Palm

C8 Palm

S3

L1 L1

C7

L2

C8

Dorsum

C7

L2

L3

L3

C6 L4

L2

C8

Dorsum

C6

C7

S4-5

C7

S2

L4

L5

L3

S2

L5 L4

Key Sensory Points S1

L5

S1

L5 S1

S1

FIGURE 8.2 Dermatomes: segmental innervation of the skin. (From American Spinal Injury Association. Copyright 2000. Used with permission.)

Skin C1 C1 C2 C3 C4 C5 C6 C7

C2 C3 C4 C5

C6 C7

C6

C7

C8

Peripheral nerve

C8 FIGURE 8.3 Simplified schematic of plurisegmental sensory innervation to the upper extremity. Multilevel cutaneous innervation renders it more difficult to isolate a sensory deficit when a single nerve root is involved. (Copyright J.M. True, D.C.)

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Motion of the neck or extremity may produce the lancinating pain sensation associated with radiculopathy

TABLE 8.2 Nerve Root Irritability Signs • Upper Extremity Bikele’s sign Bakody’s sign Foraminal compression Shoulder depression Soto hall Valsalva’s maneuver Déjérine’s sign • Lower extremity Straight leg raise and variations Braggard’s sign Lindner’s sign Turyn’s sign

FIGURE 8.4 Motion of the neck or upper extremity may produce lancinating pain secondary to radiculopathy. (Copyright J.M. True, D.C.)

90 60 Axial MRI L

R I S K

FL EX I

Nerve root compression from lower lumbar HNP should be suspected when straight leg raising below 50 produces radiation of pain in to the posterior thigh or leg.

Y LIT BI

R

L O W

30

Absence of a radicular component on SLR does not exclude the possibility of disc herniation.

Hip and Sacroiliac syndromes in absence of radicular pain 0

FIGURE 8.5 The supine straight leg raise. (Copyright J.M. True, D.C.)

which leads to pain, nerve root compression, and subsequent neural injury.6 Thus, changes in cervical spine position can produce microstretch injury of the nerve root in the foramen as well as direct compression of the nerve root.

8.3 REFLEX ABNORMALITIES Muscle stretch reflexes (MSRs), also referred to as deep tendon reflexes (DTRs) and monosynaptic reflexes, have significant clinical relevance in the evaluation of radiculopathy. The MSR is an involuntary response elicited by stimulation of the tendon (usually a brisk tap of the tendon using a reflex hammer). Because the MSR is an involuntary and readily reproducible response, it is one of the most objective indicators of neurological involvement.

The MSR is generated from the stimulation of specialized receptors called muscle spindle cells that are very sensitive to stretch. These small encapsulated receptors are located throughout skeletal muscles. The muscle spindle cell in conjunction with another receptor, the Golgi tendon organ, acts as a transducer that provides mechanoreceptive (proprioceptive) feedback information to the central nervous system concerning dynamic and passive muscle length and tension. The spindle cell receptors fire in response to rapid stretching from the tendon hammer tap, and this produces an initial afferent volley that in turn synapses with motor neurons of the anterior horn to reproduce the reflexive muscle contraction (Figure 8.6). The normal MSR is dependent on (1) an intact afferent limb (carried by group Ia sensory nerves), (2) a functional synapse in the spinal cord, (3) an

Classic Signs and Symptoms of Radiculopathy

205

To thalamus, basal ganglia and cerebellum

Renshaw neuron

1

CJM T19 9

Tendon and muscle are stretched by reflex hammer

5

Muscle spindle cell fires 1A afferent fiber

The 1A afferent fiber synapses directly to an alpha-motoneuron inducing it to fire. The 1A afferent fiber also connects polysynaptically with antagonist musculature and inhibitory Renshaw neurons.

2

Agonist muscle reflexively contracts in response to stretch Antagonist muscle contracts to break the acceleration of agonist muscle.

FIGURE 8.6 The monosynaptic muscle stretch reflex. (Copyright J.M. True, D.C.)

TABLE 8.3 Grading of Muscle Stretch Reflexes, (Deep Tendon Reflexes) 0 1 2 3 4

Absent Diminished Average (normal) Exaggerated Brisk with clonus

intact alpha motor neuron, (4) an intact motor nerve, (5) a functional synapse at the myoneural junction, and (6) an adequately healthy muscle. The MSR is graded by the intensity of observed response on a scale of zero to four (Table 8.3). The most common deep tendon reflexes and methods of elicitation are listed in Table 8.4. The afferent limb of the reflex arc is more susceptible than the efferent limb with respect to sensitivity of the MSR to detect a disorder within any of the components of the reflex. Polyneuropathies cause significant suppression of the MSR. Reflexes are usually suppressed in moderate cases of

radiculopathy and are only absent in chronic or severe root compromise. The reflex response may still be elicited in severe monoradiculopathy because of the multisegmental innervation to most muscles. Accentuated reflexes occur with upper motor neuron lesions such as cord compression or other pyramidal tract disease.

8.4 PARESIS Motor weakness may occur with radiculopathy because the ventral nerve root is first to be compressed due to its vulnerable position in the lateral recess. The distal muscles supplied from the ventral root of one vertebral level are collectively called a myotome. Paresis of extremity muscles innervated by a given myotome helps to diagnostically localize the vertebral level of radiculopathy. In cases of moderate to severe radiculopathy, significant myotomal weakness is usually present. Functional capacity or performance muscle testing may be the most accurate noninvasive tests for quantifying a nerve root deficit. Needle electromyography (EMG), however, is the gold standard for quantifying and localizing radiculopathy,

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TABLE 8.4 Deep Tendon Reflexes Upper Extremity

Stimulation Site

Scapulohumeral C5–C6 Pectoral C5–T1 Biceps C5–C6 Brachioradialis C5–C6 Triceps C7–C8 Finger flexor C8–T1

Tendon tap on the medial border of the scapula Tendon tap on the proximal tendon insertion Tendon tap on the distal biceps tendon Tendon tap on the brachioradialis tendon Tendon tap on the distal triceps tendon Tendon tap on the examiner’s fingers resting on the palmer surface of the patient’s flexed fingers

Lower Extremity

Stimulation Site

Patellar L3–L4 Tendon tap on the infrapatellar quadriceps tendon Hamstring (biceps femoris) L4–S1 Tendon tap on the biceps femoris tendon proximal to fibular head insertion Achilles S1–S2 Tendon tap on the Achilles tendon just above the calcaneal insertion

especially in subacute presentations after 3 to 6 weeks post-onset. When evaluating muscular performance, the clinician must always attempt to fatigue those muscles that are innervated by a suspected level of radicular involvement. The smallest muscle groups innervated by a radicular level should be used as an initial screen for pathology. The viable motor units of the partially denervated larger muscles are more capable of compensation; consequently, these muscles may appear normal in strength during routine physical assessment. Paresis can be evaluated by resisted muscle contraction in the primary planes of joint movement. Paresis secondary to lumbar monoradiculopathy will often be subtle as a result of multisegmental innervation from adjacent radicular levels. For this reason, paresis occurs rather than paralysis. Paresis is typically first identified by the patient’s inability to complete a full arc of joint movement against resistance before complete fatigue and failure.

8.5 MUSCULAR ATROPHY Denervation due to nerve root compression secondary to disk herniation is reflected by atrophic changes of muscle fibers.7 Segmental denervation results in a loss of motor axons, producing a dispersed atrophic pattern in those muscles innervated by the spinal root level. The majority of skeletal muscles are innervated by more than one radicular level; therefore, isolated compromise of a single nerve root will not lead to extensive atrophy. Monoradiculopathies, themselves, are often incomplete, making it difficult to assess muscular wasting using circumferential limb measurements during the physical examination because the side-to-side difference may be relatively small (Figure 8.7). Muscular performance studies will contribute more to the objective assessment of a

Normal

Atrophic

FIGURE 8.7 Gastrocnemius muscle denervation atrophy associated with an S1 radiculopathy. (Copyright J.M. True, D.C.)

mild to moderate monoradicular syndrome and influence treatment decisions more than any other test. MR imaging of muscular atrophy due to denervation is currently only performed on an academic basis, but as protocols improve its use may become more common. Radicular compromise results in a loss of motor fibers from the dorsal primary rami, resulting in corresponding atrophy of the intrinsic paraspinal musculature. Sparing of the paraspinal intrinsic musculature is a differential consideration in the diagnosis of a peripheral nerve lesion. This pattern becomes important during needle EMG evaluation.

8.6 DYSAUTONOMIA AND TROPHIC CHANGES No sympathetic branches exit the spinal cord above the T2 and below the L2 radicular levels.8,9 The most common sites of monoradiculopathy are between C5–C8 and

Classic Signs and Symptoms of Radiculopathy

207

    


  
     


    


  
 
   
 
    

 



      
  
   


     

   
     
  


FIGURE 8.8 Sources of spinal pain producing radicular and pseudoradicular symptoms. Additional differential considerations include arachnoiditis, tumors, cysts, osteomyelitis, cancer, and osteoporosis. (Copyright J.M. True, D.C.)

L4–S1 and do not result in overt sympathetic compromise; therefore, the absence of sympathetic signs and symptoms, such as impaired perspiration or microvascular changes, constitutes an important differential consideration in the evaluation of plexus and peripheral nerve lesions. Moderate to severe nerve root presentations are often multiphasic and may contribute to complex regional pain syndromes. These sequelae include autonomic dysfunction, trophic changes, cutaneous and myalgic hyperalgesia, and a decrease in muscle tone. Peripheral nerve lesions result in a greater ablation of sympathetic function than radiculopathy. Palpation and observation of the skin may reveal the peau d’orange effect, pilomotor erection, sweating, trophic changes, tenderness, and hyperesthesia indicative of denervation supersensitivity (autonomic nervous system dysfunction). These signs may involve the dermatome, myotome, or sclerotome with disk derangement.8,10 A pilomotor effect secondary to a radiculopathy may become evident with exposure of the skin to cool air. This has been referred to as cutis anserina (“gooseflesh”) in the dermatomes of affected segmental levels secondary to cervical spondylosis and disk herniation.11

8.7 COMBINED PAIN SYNDROMES: RADICULAR AND VERTEBROGENIC PAIN The source of pain in nerve root syndromes is often complex. The patient’s pain may come from localized injury

to tissues surrounding the nerve root, such as the facet joint or the outer disk. Injury to intrinsic skeletal structures (periosteum, facet joints, ligaments, and spinal intrinsic muscles) produces a deep referral of diffuse pain, distal to the area of injury. This poorly localized pain is called vertebrogenic pain or sclerotomal pain. The referral of pain distal to the skeletal injury site is thought to occur from convergence of pain fibers on the same second-order neurons in the dorsal horn that project pain from both the injury location and the distal referral site. Nociceptive and sclerotogenous pain may coexist with a radicular pattern of pain to create a combined pain syndrome. Pain arising from intrinsic spinal motion segment structures often has a referral pattern that is diffuse and only generally localized to a segmental level. Intervertebral joint pain or a facet syndrome can produce a pseudoradicular syndrome, resulting in sclerotogenous or vertebrogenic referred pain. Examples of various spinal pathology capable of producing somatic referred pain are illustrated in Figure 8.8. Conventional localizing signs for nerve root involvement are late to appear and often absent in patients with vertebrogenic pain. Incomplete radicular nerve compression often leads to nonclassic findings on physical examination.12 Also, radicular pain is sometimes difficult to differentiate from sclerotogenous pain when multiple roots or different pain-producing structures are involved. For example, in a study of subjects with documented cervical spine disorders, Frykholm13 found that stimulation of the cervical dorsal root produced pain within a dermatomal distribution but that stimulation of the ventral

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Myotomal

Dermatomal

Sclerotomal

FIGURE 8.9 Monoradiculopathy may result in variable patterns of pain, dysesthesia, paresis, and autonomic disturbances due to the wide distribution of segmental innervation in the upper extremity. This example demonstrates segmental distribution of the C6 nerve root. (Copyright J.M. True, D.C.)

B

A

L1-2 C2-3

L2-3

C3-4

L3-4

C4-5 C5 -6 C8-T1

C6-7

L4-5 L5-S1

FIGURE 8.10 The sclerotomal or vertebrogenic referral pain pattern generated from irritation or injury to capsular and pericapsular tissues does not follow a dermatomal pattern. This diffuse pattern is variable between patients and may occur with or without radiculopathy. (A) Posterior cervical sclerotomal pattern. (B) Posterior lumbar sclerotomal pattern. (Copyright J.M. True, D.C.)

root produced a more diffuse pain in the neck, shoulder, and upper arm (Figure 8.9). Sensory involvement may produce a range of symptoms from mild paresthesia, to severe pain, or near complete dermatomal anesthesia. Studies by Smyth and Wright14 indicated that the length of the “pain band” is proportional to the size of the herniation imposed on the nerve root. An example of this is a small lumbar disk herniation that results in radiating pain to the thigh. A larger disk herniation with a greater degree of nerve root compression may result in radicular pain extending farther down the leg to the foot. Consideration should also be given to the likelihood that larger amounts of disk material produce larger inflammatory responses and thus contribute to greater symptom production. Vertebrogenic pain referring to the lower extremities from irritation to lumbar skeletal structures is

highly variable. Because of this variability, interpretation of the source of pain from the pattern of referral is very difficult. Vertebrogenic pain may refer to the inguinal region when the upper lumbar spine is the source of pain. In the lower lumbar spine, pain will extend into the buttock, over the greater trochanter, down the back of the thigh to the knee, and sometimes down the posterior or outer calf to the ankle. Rarely does sclerotogenous or referred pain reach the foot or toes.15 In the cervical spine, sclerotogenous pain may refer to pain in the back of the skull, the top of the shoulder, between the shoulder blades, and in the upper arm (Figure 8.10).16 Additionally, patients with diffuse chronic back pain may have associated intraspinal adhesions that contribute to pain production. As suggested by Parke and Watanabe,17 mechanical disruption of adhesions and the associated

Classic Signs and Symptoms of Radiculopathy

perivascular nociceptive fibers may be another source of discogenic pain. In that study, adhesions between the ventral dura and the posterior longitudinal ligament PLL were found in 16% of the specimens at the L3–L4 level, 40% were found at the L4–L5 level, and 36% were found at the L5–S1 level.17 Microscopic evaluation of the adhesions demonstrated disruption of neurovascular bundles containing branches of the sinuvertebral nerve where they coursed between the adherent dura and the posterior longitudinal ligament (PLL). The investigators assumed that forced separation of these adhesions during disk herniation and elevation of the PLL probably would amplify the degree and extent of nociceptor activation and contribute to low back pain.17 Additionally, dural connections between dorsal nerve roots and the intradural membrane have been documented.18 This may create abnormal tethering patterns in nerve roots exposed to compression and result in atypical radicular deficits or pain patterns.

8.7.1 RADICULOPATHIC AND VERTEBROGENIC SYMPTOMS RESEMBLING VISCERAL PAIN Cervicogenic angina or pseudoangina is a clinical entity that mimics angina pectoris associated with heart disease. Noncardiac angina results from irritation of the lower cervical roots (C6 and C7), which produces pectoralis pain. Several important factors differentiate pseudoangina from angina of cardiac origin. In pseudoangina, shock, fever, elevated sedimentation rate, and isoenzyme changes are not present, and the electrocardiogram is normal. Pseudoangina may be aggravated by neck movement,11 whereas cardiogenic angina is increased with exertion. Intercostal radicular pain will also produce pain in the anterior chest.19 Spinal pathology may mimic gallbladder disease, gastrointestinal disease, renal disease, and disturbances in bowel, bladder, gynecologic, or sexual function.20 Visceral disease typically does not produce segmental paresis or cause loss of deep tendon reflexes. Visceral referred pain is usually deep and diffuse, whereas primary somatic pain can be localized by mechanical provocation. The only exceptions are chronic visceral pain that has resulted in the production of trigger points or spasm and organic disease that directly compresses or infiltrates the nervous system. As a general rule of thumb, referred pain is not worsened by palpation.21

8.8 ASSESSMENT OF RADICULOPATHY The diagnosis of radiculopathy requires correlation of findings from different components of the evaluation process. These examination components may include the patient’s history, the clinical examination, blood testing, cerebrospinal fluid (CSF) assessment, electrodiagnostics, functional testing, and diagnostic imaging. Each of these components of the evaluation provides unique information

209

that helps confirm or reject diagnostic suspicions. The electrodiagnostic evaluation provides an objective physiologic measure of neurological integrity and function, whereas advanced imaging such as MRI provides excellent anatomic detail with reasonably high sensitivity but low specificity to nerve function and clinical symptoms. Functional assessment can evaluate segmental muscular performance more specifically as well as physical attributes such as power, endurance, fatigability, and closed kinetic chain strength. Functional assessment may also include quantitative testing such as functional capacity, coordination, and gait analysis. Utilization of the methods available can provide an invaluable, cost-effective measure of therapeutic outcome and prognostic insight for neurologic and related orthopedic recovery.

8.8.1 ELECTRODIAGNOSIS

AND

RADICULOPATHY

Physical compromise of the nerve root may result in structural nerve damage, impairment of intraneural blood flow, disrupted axonal transport, and the development of intraneural edema. These changes lead to neurophysiologic features, many of which can be quantified by electrodiagnostic testing. Some electrodiagnostic changes characteristically occur during the early phase of nerve injury, during the late or chronic phase, or may be limited to the recovery process. Pathology occurring at the same segmental level in different individuals can lead to diverse clinical and electrodiagnostic presentations due to anatomical variations within the nerve root and regional anatomy. Sensory presentations occur more frequently than sensorimotor or pure motor root involvement, thus accounting for some of the false-negative needle EMG studies in symptomatic patients. Most radiculopathies are relatively mild or incomplete, resulting in a small percentage of motor units being denervated. This limits the diagnostic utility of needle electromyography. 8.8.1.1 Needle Electromyographic Evaluation Electromyography is a classic and important electrodiagnostic method for assessing patients with suspected radiculopathy. The diagnosis of radiculopathy requires that abnormal EMG patterns be present in two or more extremity muscles innervated by two different peripheral nerves supplied by the same segmental level. Abnormal paraspinal potentials will help confirm the segmental level of radiculopathy (Table 8.5). Moderate to severe nerve root insult often results in some degree of motor axonopathy. Radiculopathy involving only the dorsal root is not detectable on needle EMG. Acute or subacute nerve injury is characterized during the EMG evaluation by the presence of muscle denervation supersensitivity.22 Denervation supersensitivity develops in part from the hypersensitization of muscle fibers to

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TABLE 8.5 EMG Indicators of Nerve Root Pathology • Abnormal EMG activity in two separate muscles with same segmental level innervation • Abnormal EMG activity in paraspinal muscles • Spontaneous activity: sharp waves, fibrillations, fasciculations • Prolonged insertional activity • Altered morphology of motor unit action potential Complex/dispersed, increased amplitude, irregular/prolonged • Poor recruitment • Rapid firing rate

acetylcholine and circulating neuropeptides. This produces spontaneous activation of motor units, which can be observed on needle EMG evaluation. Muscle denervation supersensitivity also leads to prolonged or increased needle insertional activity. Spontaneous activity, if reproducible in at least two muscles supplied by different nerves with the same segmental origin, indicates a high probability of radiculopathy or other lower motor neuron disease. These changes may not be detected in all patients with radiculopathy and also may not be evident until 2 to 6 weeks following acute nerve (motor axon) injury. Spontaneous potentials may manifest as fibrillations, positive sharp waves, fasciculations, and other discharge patterns. Fibrillation potentials are small-amplitude discharges with a characteristic diphasic or triphasic waveform. They fire in a regular temporal pattern originating from a single motor unit. Positive sharp waves are an abnormal discharge with a characteristic downward spike and slow return to baseline negativity (positivity is displayed as a downward deflection on EMG). Fasciculations refer to fine, irregular twitchings of muscle fiber groups that may be visible or palpable. During the clinical examination, fasciculations may be observed in a muscle at rest or may be evoked on muscle percussion. It should be noted that fibrillations, positive sharp waves, and fasciculations also occur in conditions other than radiculopathy. Chronic muscle denervation with incomplete reinnervation is characterized by reduced motor unit recruitment density, fast motor unit firing rate, and large motor units. This is represented by large, often polyphasic motor unit action potentials on EMG examination. Nerve root injury may be limited to disruption of the myelin and sparing of the axons, resulting in a normal EMG study with clinical evidence of intermittent dysesthesia and/or episodic muscle weakness. Injuries resulting in nerve demyelination will cause desychronization of nerve impulse propagation with diminishment of the corresponding muscle stretch reflexes. Paraspinal muscles should be evaluated with needle EMG in cases of suspected radiculopathy. The presence of abnormal paraspinal and extremity findings signifies radiculopathy, although the absence of paraspinal abnormalities

does not exclude radiculopathy. This absence may occur secondarily to the sparing of fibers of the primary dorsal rami or due to the earlier reinnervation of paraspinal muscles. Paraspinal abnormalities may also occur in the absence of abnormal extremity changes if nerve compromise is limited to the muscular territory innervated by the dorsal primary rami. The multifidus muscle is monosegmentally innervated; however, it lies beneath other muscle layers and therefore can be a challenge to isolate during EMG evaluation (Figure 8.11). The more accessible superficial paraspinal muscles are plurisegmentally innervated, making them less suitable for localizing nerve root involvement. Denervation results in a decreased number of motor units capable of contraction. In an effort to maintain muscular function, the central nervous system responds by causing the remaining motor units to fire at a faster rate. This may help improve muscle performance in the presence of denervation. However, the fast firing rates results in early fatigue of the intact motor unit, which becomes evident during muscle endurance (functional capacity) testing. 8.8.1.2 Muscles with Segmental Localizing Significance In the upper extremity, the rhomboid muscle groups only receive innervation from the C5 radicular level. The anterior deltoid is predominately innervated by C5. Motor innervation from the C7 level does not extend to the intrinsic hand muscles. The hand muscles are innervated by C8 and predominately T1 levels. Significant L5 contribution below the ankle is found in the extensor digitorum brevis (EDB) muscle. The EDB will often be atrophic with an ipsilateral chronic L5 radiculopathy. The gastrocnemius and soleus are important S1 muscles. There is no S2 representation within the paraspinal muscle groups. Therefore, S2-level EMG sampling must be performed in the gluteus maximus, the soleus muscle, and the intrinsic muscles of the foot (Table 8.6). 8.8.1.3 The Chronology of Electrophysiologic Abnormalities in Radiculopathy Spontaneous potentials in the form of fibrillations, sharp waves, and fasciculations may become evident within 2 to 6 weeks after radicular motor axonopathy. A number of electrophysiologic findings may be present from the onset of radicular insult. If needle EMG sampling is warranted during the initial 2- to 6-week window, the examiner should carefully evaluate the motor recruitment interval and look for early polyphasic motor unit action potentials (MUAPs). These are large MUAPs with multiple peaks that cross the baseline, changing phase or polarity five or more times. A reduced number of recruited

Classic Signs and Symptoms of Radiculopathy

211

Psoas major

Iliocostalis lumborum

Quadratus lumborum

Multifidus

Latissimus dorsi

Semispinalis lumborum

1.5-2cm

Longissimus thoracis

FIGURE 8.11 General location of needle electrode placement in the multifidus muscle of the lumbar spine. (Copyright J.M. True, D.C.)

TABLE 8.6 Minimal Screen Needle Electromyographic Examination Upper Extremity

Lower Extremity

Muscle

Root Level

Muscle

Root Level

Cervical paraspinal muscles Deltoid Biceps brachii Triceps Extensor carpi radialis Flexor carpi radialis Pronator teres Thenar muscles Dorsal interossei Hypothenar muscles

C4–T2 C5, C6 C5, C6 C6, C7, C8 C6, C7, C8 C6, C7, C8 C6, C7 C8, T1 C8, T1 C8, T1

Lumbosacral paraspinal muscles Quadriceps femoris Gluteus medius Tibialis anterior Peroneus longus Medial gastrocnemius Lateral gastrocnemius Extensor hallucis longus

L1–S1 L2, L3, L4 L4, L5, S1 L4, L5, S1 L5, S1 S1, S2 L5, S1, S2 L5, S1

Note: Additional muscles should be investigated should the diagnosis be unclear. In the paraspinal regions, the root level designations refer to the bony level that should be examined (i.e., the multifidi muscle layer). Source: Dumitru, D., Electrodiagnostic Medicine, Hanley & Belfus, Philadelphia, PA, 1995. With permission.

motor units secondary to axonopathy results in muscle weakness (paresis). In an attempt to improve functional strength, a good voluntary effort on the part of the patient will result in an increased firing frequency (rate) of intact motor units. This can be noted on needle EMG sampling, represented by an increased firing rate and reduced recruitment density. The early presence of polyphasic muscle unit potentials in the

absence of denervation supersensitivity may be due to ephaptic transmission from adjacent motor axons. Approximately 1 week after the onset of radicular injury, needle EMG sampling may reveal occasional positive (sharp) waves in the paraspinal muscles. Within 12 to 14 days, sharp waves may become evident in proximal limb muscles, and fibrillation potentials often begin to appear in the involved paraspinal muscle groups. A mild

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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes

Distal peripheral muscles reinnervate last due to length of nerve segment

Paraspinals reinnervate first Temporal electromyographic signs of reinnervation

Normal MUAP

Polyphasic MUAP

Large dispersed Large MUAP MUAP following collateral reinnervation

FIGURE 8.12 Electrodiagnostic signs of muscle reinnervation. (Copyright J.M. True, D.C.)

radiculopathy may be missed on routine EMG sampling during this period. In ongoing radiculopathy, a complex electrophysiologic presentation develops over a time span of 18 to 21 weeks. During this period, electrophysiologic confirmation of radiculopathy is usually obvious. Denervation supersensitivity may be present with an associated increase in insertional activity and spontaneous potential frequency. Motor recruitment is reduced, and there is an increase in the firing pattern. Reinnervation patterns may become evident 4 to 6 weeks after radicular compromise. Reinnervation changes are dependent on axonal repair and collateral innervation at the level of the radiculopathy. EMG characteristics of reinnervation include large polyphasic MUAPs or MUAPs with multiple turns or serration. If incomplete reinnervation takes place, the total number of viable motor units within the muscle will be reduced, but the size of each viable motor unit will be larger. Consequently, the EMG will demonstrate large motor units with increased area, prolonged duration, and larger amplitude. Reinnervation contributes to reorganization of the compound motor unit action potential (CMAP). If recovery is nearly full with reinnervation, the CMAP will return to its pretraumatic normal morphologic appearance. Complete motor unit reorganization can take many months or even years (Figure 8.12).

8.8.1.4 Radiculopathy and Postsurgical EMG Findings Ascribing significance to postlaminectomy paraspinal EMG findings can be difficult. Spontaneous potentials in the form of fibrillations and sharp waves may be present on needle sampling of the paraspinal muscles in the region of the postsurgical scar. EMG findings at least 3 cm lateral to the scar may be diagnostic. Investigation of the levels innervated by the primary anterior rami is more important in the postsurgical assessment for reinnervation. A poor reinnervation pattern may be indicative of residual or recurrent radicular pathology. 8.8.1.5 Late Reflexes Late reflexes are electrical conduction responses that involve a central spinal cord-mediated component in production of the response. The most common are the Hreflex, F-wave, and the tendon reflex, or T-reflex. They have significant value in the investigation of radiculopathy because these tests are some of the few electrophysiologic tests that assess the proximal portion of the nerve root. Late reflexes are not able to specifically localize a proximal pathology because general demyelination plexopathy and peripheral entrapment may produce abnormal responses. The information derived from the late reflex is

Classic Signs and Symptoms of Radiculopathy

213

IVF

L4

The H-reflex is normal with an isolated lesion involving L4 or L5 roots, because the response is elicited predominately from S1 fibers in the posterior tibial nerve to the gastroc/soleus muscle. A delayed H-reflex would be expected when a lesion occurs in the S1 nerve root, sacral plexus or lower spinal cord.

L5

Lesion

Either lesion will produce a delayed H-reflex

S1 Lesion

Other differentials to consider with a delayed response are the presence of polyneuropathy, cauda equina involvement and root anomalies. H-reflex

FIGURE 8.13 The H-reflex as a diagnostic indicator of an S1-level lesion. (Copyright J.M. True, D.C.)

an indicator of pathology and is used in conjunction with other tests and clinical findings to help localize the source of the patient’s pathology. 8.8.1.5.1 H-reflex An H-reflex can be recorded from many muscles in the body; however, in only two muscles is the H-reflex reliably reproduced. These clinically relevant reflexes involve recording at the gastrocnemius–soleus muscles (S1), following stimulation of the posterior tibial nerve at the knee and recording at the flexor carpi radialis muscle (C6 and C7), following stimulation of the median nerve at the wrist. The depolarization response travels both up and down the nerve. The H-reflex is believed to represent a monosynaptic response to firing of large peripheral myelinated sensory axons.23 The tibial H-reflex is the electrophysiologic measurement of the Achilles muscle stretch reflex (MSR). When the wave of depolarization reaches the dorsal root, it enters the dorsal horn and makes an excitatory connection to alpha motor neurons, causing the motor neurons to fire. The response travels back down the nerve and stimulates the gastrocnemius-soleus muscle. This in turn is recorded with instrumentation. The amplitude of the H-reflex by itself is not a reliable indicator of pathology. The H-reflex latency is assessed by measuring from the onset of the stimulus to the initial waveform deviation from the baseline in any direction. The latency value of the H-reflex is the most reliable and reproducible indicator of pathology derived from this test (Figure 8.13). The normal H-reflex value is length dependent, thus taller patients have longer latencies. Generally, the top end latency value is below 32 ms. An H-reflex nomogram should be used in order to predict the normal latency taking into account leg length. An absolute unilateral latency delay of the H-reflex suggests compromise somewhere along its anatomic course and does not always indicate S1 radiculopathy. The finding must always be

correlated with the clinical presentation and the remaining electrodiagnostic findings. Side-to-side latency delays of greater than 1.0 to 1.5 msec (