Diagnostic Neuroradiology

V. N. Kornienko · I. N. Pronin Diagnostic Neuroradiology V. N. Kornienko · I. N. Pronin Diagnostic Neuroradiology Wi...

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V. N. Kornienko · I. N. Pronin Diagnostic Neuroradiology

V. N. Kornienko · I. N. Pronin

Diagnostic Neuroradiology With 1905 Figures and 22 Tables

123

Valery N. Kornienko Igor Nicolaevich Pronin

Burdenko Neurosurgical Institute Dept. of Neuroradiology 4-th Tverskaya-Yamskaya Ulica 16 Moscow, 125047 Russia

ISBN 978-3-540-75652-1

e-ISBN 978-3-540-75653-8

DOI 10.1007/978-3-540-75653-8 Library of Congress Control Number: 2008936632 © 2009 Springer-Verlag Berlin Heidelberg This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: the publishers cannot guarantee the accuracy of any information about dosage and application contained in this book. In every individual case the user must check such information by consulting the relevant literature. Cover design: Frido Steinen-Broo, eStudio Calamar, Spain Production & Typesetting: le-tex publishing services oHG, Leipzig, Germany Printed on acid-free paper 987654321 Springer.com

V.N. Kornienko, M.D., Ph.D., is the head of the Neuroimaging Department of the Burdenko Neurosurgical Institute Russian Academy of Medical Sciences, a professor, an honour scientist of the Russian Federation, and the author of 12 monographs on neuroradiology and more than 500 scientific publications.

I.N. Pronin, M.D., Ph.D., is a professor in the Neuroimaging Department of Burdenko Neurosurgical Institute Russian Academy of Medical Sciences and the author of 2 monographs on neuroradiology as well as 220 scientific publications.

Preface

In the early twentieth century, fledgling radiological technology became the basis for today’s medical visualisation methods. The first neuroradiologists used X-rays to discern anatomical brain disturbances formerly hidden by the skull. In the 1970s, computerized visualisation technology made revolutionary advances in diagnostics, especially in the field of neuroradiology. Direct digital angiography and computed tomography (CT) made it possible to explore in detail the skull cavity, to estimate normal brain anatomy, and to observe pathology. Magnetic resonance imaging (MRI) opened new doors in terms of differentiating between healthy and pathological tissue. Now in the beginning of the twenty-first century, the quality of MR images of the brain can be compared with that of traditional histological slices. Multispiral CT, high-field MRI, and positron emission tomography (PET) make it possible to visualise physiological and biological processes along with their quantitative estimation, and expand the range of diagnostic possibilities concerning brain and spinal cord disease. Noninvasive and minimally invasive methods of diagnostics and treatment including functional CT and MRI are now incorporated into everyday practice. Among them functional MRI, perfusion CT and MRI, methods of cerebral spinal fluid (CSF) flow measurement, diffusion MRI, tractography, and MR spectroscopy aid in making better prognoses regarding the results of treatment, and monitor therapy in vivo. All these methods make it possible to, e.g. carry out CT and MRI navigation during brain surgery, to plan radiotherapy, and to monitor the efficacy of treatment. With such a variety of modern visualisation methods covered in this book, we place emphasis on the physician choosing the method (or sometimes complex of methods) best suited to obtain optimal results. Radiology is the cornerstone of medical diagnostics, and a neuroradiologist may be the first physician to meet the patient in a clinical setting. There are many examples presented in this book of one being the first physician on a case. Even without the history of disease, the neuroradiologist should be able to make the correct diagnosis, guided only by personal clinical experience and the results of neurovisualisation, as proven by the case examples given in the following chapters.

Longstanding experience of neuroradiological investigations and material gained because of the combined work of clinicians, neuroradiologists, MR engineers, and physicists of the Burdenko Neurosurgical Institute of the Russian Academy of Medical Sciences are the basis of this book. The book contains 15 chapters. The first chapter outlines the stages of formation and development of neurovisualisation technology, with a historical background, and gives information necessary for understanding the novel diagnostic methods that help to visualise pathology in the context of anatomical and pathophysiological changes, even on the molecular level. New diagnostic technology makes it possible to obtain quantitative estimation of changes in disease progression, and it plays an important role in making early diagnoses within routine protocols of investigations. The chapter is aimed at readers who are familiar with the basic principles of CT and MR imaging, which is why in it we consider only the main principles and practical aspects of the newest quantitative CT and MRI diagnostic technologies, including diffusion MRI and diffusion tensor imaging, CT perfusion and MR perfusion, functional MRI, proton spectroscopy, and CT angiography and MR angiography. In other chapters, we discuss the diagnostic principles of the main categories of diseases of, and damages to, the CNS. Most of this volume is devoted to the diagnoses of cerebrovascular disease, intracerebral and extracranial tumours and tumour-like processes, inflammatory, demyelinative, and neurodegenerative disease, and traumatic brain and spinal damage. Chapters dedicated to the diagnoses of brain tumours are based on verified clinical cases (more than 30,000) using the complex approach including MRI, MRS, CT and MR perfusions, and diffusion-weighted imaging. Proton MR spectroscopy information is given in single- and multivoxel-regime formats. Each clinical chapter contains the most important information on CNS pathological changes, basic markers for specific diagnose of the diseases, and unique images of rare pathologies. We hope this book will be the source of neuroradiological knowledge for neurosurgeons, neurologists, neuroendocrinologists, neurotraumatologists, and paediatricians with

VIII

clinical experience, as well as for interns, postgraduate students, students, and physicians, who can use it for expanding their neuroradiological skills. We believe that specialists in fields adjacent to neuroradiology, for example, biophysics and medical physics, will be interested in this book as well. Many illustrations are the “visual text” of this helpful reference book and atlas for everyday, practical work. In conclusion, the authors express sincere gratitude for all the officials of our Department of Neuroradiology and our

Preface

Institute, who contributed to the publishing of this book. Our special thanks go to our colleagues Dr. Fadeeva (Chap. 1), Dr. Takush (Chap. 1), Dr. Rodionov (Chap. 1), Dr. Ozerova (Chaps. 2 and 10), Prof. Potapov (Chap. 9), Prof. Kravchuk (Chap. 9), Dr. Zaharova (Chap. 9), Dr. Aroutiunov (Chap. 10), and Dr. Serkov (Chaps. 12, 13, and 14). Moscow, Russia April 2008

V. Kornienko, I. Pronin, and E. Cabanis

Contents

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Neuroradiology: History and New Research Technologies .. . . . . . . . . . . . . . . ... in collaboration with L. Fadeeva, S. Takush, and P. Rodionov Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... History of Russian Neuroradiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... New Functional Methods in Neuroradiology .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Perfusion-Weighted Imaging .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Functional MRI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Proton MR Spectroscopy .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Phosphorus MR Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Neuroradiology and Information Technologies .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Navigation in Neurosurgery .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9

Congenital Malformations of the Brain and Skull . . . . . . . . . . . . . . . . . . . . . . . . .... in collaboration with V. Ozerova Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Organogenesis Impairment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Impairment of Brain Diverticulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Impairment of Gyri and Sulci Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Changes in Brain Size .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Destructive Brain Lesions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Histogenesis Impairment .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Arachnoid Cysts .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Congenital Anterior Cranial Malformations .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

3 3.1 3.2 3.3

Cerebrovascular Diseases and Malformations of the Brain .. . . . . . . . . . . . . .... Stenosis and Thrombosis of the Cerebral Vessels .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Cerebral Ischaemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Lacunar Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

1 1 2 3

11 15 17 22 23 25

29

29 29 41 46 53 53 60 69 80

87 87 101 139

X

Contents

3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20

Chronic Ischaemic Brain Disease . .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stroke in Children ................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Non-Atherosclerotic Stenosis and Occlusion of Cerebral Arteries .. . . . . . . . . . . . . . . . . . Thrombosis of the Venous Sinuses .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Haemorrhagic Infarction ........................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intracerebral Haemorrhages ................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extracerebral Non-traumatic Haemorrhages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intratumoral Haemorrhages ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hypertense Haemorrhages ...................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hypertense Encephalopathy .................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rare Causes of Intracerebral Haemorrhage .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intracranial Arterial Aneurysms ................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intracranial Vascular Malformations . .......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carotid–Cavernous Fistulas . .................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cavernous Angioma . ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Capillary Telangiectasias . ...................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Venous Malformations . ........................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

154

4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Supratentorial Tumours ...................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supratentorial Tumours . ....................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neuroepithelial Tumours . ....................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neuronal and Mixed Neuronal–Glial Tumours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Embryonic Neuroepithelial Tumours . .......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary Lymphoma of the CNS .................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metastatic Tumours .............................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supratentorial Cysts ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Eosinophilic Granuloma . ....................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Myeloma (Kahler’s Disease, Plasmacytoma) . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

333

5 5.1 5.2 5.3 5.4 5.5

Pineal Region Tumours ...................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Germ Cell Tumours .............................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pineal Parenchymal Tumours .................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glial Tumours ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Histological Types of Tumours . .......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

489

6 6.1 6.2

Sellar and Parasellar Tumours .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529 Introduction .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529 Anatomy .. . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529

158 160 172 175 176 188 193 196 197 197 199 247 302 309 316 320

333 333 335 418 425 432 440 464 476 481

489 490 503 510 510

Contents

XI

6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20

Pituitary Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... “Empty” Sella Turcica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Pituitary Adenomas .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Craniopharyngioma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Gliomas of the Optic Nerves, Chiasm, and Hypothalamus .. . . . . . . . . . . . . . . . . . . . . . ... Germinomas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Teratoma, Epidermoid Tumours, and Dermoid Tumours .. . . . . . . . . . . . . . . . . . . . . . . . .... Chordoma .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Hamartomas of the Tuber Cinereum .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Langerhans Cell Histiocytosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Ratke’s Cleft Cysts .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Meningioma .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Neurinoma of the Fifth Cranial Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Metastases ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Paragangliomas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Arachnoid Cyst .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Vascular Disorders: Aneurysm .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Inflammatory Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

531

7 7.1 7.2 7.3 7.4 7.5

Infratentorial Tumours .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Intra-Axial Tumours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Extra-Axial Tumours .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Brainstem Lesions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Меtastases ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

617

8 8.1 8.2

Tumours of the Meninges .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 719 Meningioma .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 719 Non-Meningothelial Tumours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 785

9

Head Trauma .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... in collaboration with A. Potapov, A. Kravchuk, and N. Zaharova Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Primary Brain Injuries .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Secondary Injuries .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

9.1 9.2 9.3 10

531 535 556 573 579 580 585 585 591 592 594 594 598 598 598 605 605

617 617 651 680 705

807 807 808 869

Hydrocephalus .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 919 in collaboration with V. Ozerova and N. Aroutiunov 10.1 Physiology of the Cerebrospinal Fluid System .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 919

XII

Contents

10.2 Techniques for Neuroimaging of CSF Spaces and Quantitative Measurement of CSF Circulation ............................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Quantitative Techniques for Measurement of CSF Flow Velocity by PC MRI .. . . . . . . 10.4 Clinical Studies . ................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Complications . .................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

921

11 11.1 11.2 11.3 11.4 11.5 11.6

945

Intracranial Infections . ...................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bacterial Infection .............................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Granulomatous Infections ...................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fungal Infection (Mycosis) of the CNS .......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Viral Infections . ................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parasitogenic Disorders .......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

921 924 933

945 946 964 969 975 988

12

Toxic and Metabolic Disorders .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003 in collaboration with S. Serkov 12.1 Introduction .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003 12.2 Primary Toxic and Metabolic Encephalopathies .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003 13

Demyelinating Diseases of the Central Nervous System .. . . . . . . . . . . . . . . . . . . in collaboration with S. Serkov 13.1 Introduction .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2 Primary Demyelinating Diseases ............... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3 Disorders with Secondary Demyelination and/or Destruction of White Matter .. . .

1033

14

1075

14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8

Neurodegenerative Disorders of the Central Nervous System . . . . . . . . . . . . . in collaboration with S. Serkov Introduction .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Synucleinopathies .............................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taupathies .. . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cerebral Amyloidoses ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spinocerebellar Degenerations .................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Huntington’s Disease ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hereditary Spastic Paraplegias ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amyotrophic Lateral Sclerosis . ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1033 1034 1063

1075 1076 1078 1080 1084 1084 1085 1086

15 Spine and Spinal Cord Disorders ............ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1093 15.1 Imaging Modality and Normal MRI Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1093 15.2 Specific Features of the Spine and Spinal Cord in Children .. . . . . . . . . . . . . . . . . . . . . . . . 1096

Contents

XIII

15.3 15.4 15.5 15.6 15.7 15.8 15.9

Congenital Spinal Pathology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Spinal Cord Tumours .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Intramedullary Tumours .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... Extramedullary–Intradural Tumours .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Extradural Tumours .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Traumatic Spine and Spinal Cord Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Degenerative Spinal Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

16

Subject Index .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1285

1097 1122 1124 1150 1184 1261 1267

Chapter 1

Neuroradiology: History and New Research Technologies

1

in collaboration with L. Fadeeva, S. Takush, and P. Rodionov

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . History of Russian Neuroradiology .. . . . . . . . . . . . . . . . . . . . . . . . . . . New Functional Methods in Neuroradiology .. . . . . . . . . . . . . . . . . Perfusion-Weighted Imaging .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . Functional MRI .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . Proton MR Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . Phosphorus MR Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . Neuroradiology and Information Technologies .. . . . . . . . . . . . . . Navigation in Neurosurgery .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.1

Introduction

1 2 3 11 15 17 22 23 25

Neuroradiology is a part of general radiology that is dedicated to the diagnostic examination of the brain and spinal cord. The history of neuroradiology, as a whole, reflects the history of radiology development. The birthday of radiology could be considered as 8 November 1895; it was on this day that W. K. Roentgen was experimenting with a cathode tube and discovered a new type of radiation (emission) with high penetrating capacity. Eventually he named this new type of radiation the “X-ray”. Roentgen made the first X-ray image—a skull—in December 1895. In the beginning of January 1896, after 2 months of painstaking research, he published the article “On a New Kind of Rays”, and on 23 January he made a presentation on his discovery to a session of the Würzburg Physics–Medical Society. He showed images of bony skeleton structures, created by X-rays passed through a human body to the surface of the photographic plate. Roentgen’s discovery gave powerful impetus to research in physics, and the world’s scientific community of physicists, mathematicians, biologists and physicians welcomed this breakthrough. For his discovery of X-rays, he received the first Nobel Prize in physics in 1901. X-rays promptly became the new tool in physics research, and in medicine, they provided many opportunities to visualise the internal structures of the human body. Commonly, X-rays were named “Roentgen rays”, the cathode tubes “Roentgen tubes” and the machines

for obtaining the images of the internal structure “Roentgen machines”. The first diagnostic machine was revealed in Germany on 26 January 1896. It could capture the image of bone structures, formed on the photographic layer of specially prepared plate by passing X-rays through the body. For more than a century, medicine has been able to visualise internal organs and bones via X-rays. This method is known as radiography. The successful application of X-rays for visualisation of highcontrast bone structures facilitated the emergence of the new section of medicine: radiology. In Russia, the first roentgenograms (X-ray films) were obtained in the physics laboratories of St. Petersburg (12–13 January 1896) and Moscow (15–16 January 1896). The first Russian X-ray machine for medical diagnostics was designed by A.S. Popov at the end of February 1896, set up in the Krondshtadt Sea Hospital. At the beginning of the twentieth century, X-ray machines were available in many Russian cities: St. Petersburg (St. Petersburg University, the St. Petersburg Military Medical Academy, and the Clinical Institute of St. Petersburg), Moscow (the Moscow University), Kiev (St. Vladimir’s Imperial University) and Kazan, among others. In 1896, in St. Petersburg’s Military Medical Academy and in the Surgical Clinic of the Kiev University, the first operations were performed in the removal of foreign bodies, detected with the help of radiography. The first issue of the radiological magazine, Herald of Radiology, was produced in July 1907 in Odessa, and the first all-Russian Congress of Radiologists took place in Moscow in December 1916; thus, radiology became an independent speciality in Russia. The State Radiological and Cancer Institute was founded in 1918 in St. Petersburg; its first president was the well-known physicist A.F. Ioffe. After a year, the Physics Department of the Institute became an independent institution, the Institute of Radiology and Roentgenology, and M.I. Nemenov was appointed to the position of its director. In front of the Institute, on 29 January 1920, the first-ever monument dedicated to Roentgen was erected. The first radiological clinic was established in the Institute; later, similar clinics emerged in Paris’s Curie Institute and in the Forsell Institute in Stockholm.

2

Chapter 1

In 1919, the Russian Association of Radiologists and Roentgenologists was founded, and in 1920, the journal Herald of Roentgenology and Radiology was issued, which continues to be published today.

1.2

History of Russian Neuroradiology

The history of Russian neuroradiology began with a perspicacious prediction by V.M. Bekhterev, the outstanding Russian neuropathologist. In his presentation on 15 February 1896 in The Clinic of Central Nervous System Diseases, St. Petersburg Military Medical Academy, he told the audience that many diseases of the nerves are caused by changes in the skull and vertebrae and, possibly, X-rays could help to detect these changes. He foresaw visualisation of the paths of intracranial arteries through the skull, with the help of administration of a special substance that absorbs X-rays. He also envisaged the visualisation of a grey matter with X-rays. His predictions have come to fruition today in widely used neuroradiology methods like angiography and computer tomography (CT). V.M. Bekhterev organised the first Russian neuroradiology department in the St. Petersburg Institute, which now bears his name. Russian neuroradiology passed through the same stages as the world’s neuroradiology. Its development was prompted by the general rise of radiological science and practice, and was further stimulated by the organisation of special neurological, neurosurgical and neuropsychiatric institutions, in which the first specialised neuroradiology departments were formed. Such prominent scientists as N.N. Altgauzen, M.D. Galperin, M.B. Kopylov and F.A. Serbinenko (1974), among others, played leading roles in the formation and prospering of Russian neuroradiology. The 1920s was an epoch of pneumoencephalography development. The 1930s were marked by the emergence of brain vessel angiography. The first angiography in Russia was performed in 1930 in the Narkomzdrav Neurosurgery Clinic in Moscow by B.G. Egorov and M.B. Kopylov. They used 25% iodide sodium solution in the procedure. In 1931, with the help of angiography, a traumatic aneurysm of the carotid artery was diagnosed in the same clinic. (Later, the Clinic was reorganised as the Neurosurgery Scientific-Research Institute, which is now the Burdenko Neurosurgical Institute). It was the first clinical case of vessel lesion diagnosis in Russia. In 1965, A.I. Arutiunov and V.N. Kornienko, for the first time in Russia, started to use total angiography of brain vessels with femoral artery catheterisation (Aroutiunov 1971). In 1971, F.A. Serbinenko pioneered the method of radioendovasal occlusion of brain arteries, with the help of detached balloon. This method was subsequently named after him: the Serbinenko method. The history of neuroradiology is, on the one hand, the history of collaboration of radiologists, neurologists and neurosurgeons in the development of clinical methods of central nervous system (CNS) radiological examination. On the other

hand, it is the history of collaboration of physicists, mathematicians, engineers and radiologists in the design and creation of new devices for brain and diagnostics of spinal cord diseases. The 1930s witnessed the arrival of linear tomography methods (tomos is the Greek word meaning “section”) in radiology. Independently from B. Ziedses des Plantes, the Russian scientist V.I. Feoktistov considered the theoretical opportunity of capture of an object’s internal layer on X-ray film in the course of synchronous moving of a tube and a film relative to the motionless isocenter during the objects exposure to the radiation (Feoktistov 1935). From 1935 to 1946, the phenomenon of a nuclear magnetic resonance was discovered. In 1941, E.K. Zavojsky, in Kazakhstan, obtained one of the first nuclear magnetic resonance spectrum of a substance (Zavojsky 1945). The 1950s and 1960s witnessed a quest for practical solutions of tomography problems in neuroradiology, and the subsequent development of electronics and computer techniques. The 1970s and 1980s for Russian neuroradiology were the time of wide introduction of a CT method in the clinical setting, and the appearance of the first magnetic resonance scanners. In the Soviet Union, the first computed tomograph manufactured by EMI (London) was set up in the Scientific Research Institute of Neurology in which, on 21 June 1977, the first CT brain examination in Russia was performed. The first secondgeneration scanner ND8000 (CGR, La Rochelle, France) was set up in 1978 in the Burdenko Moscow Neurosurgical Institute. In 1985, A.N. Konovalov and V.N. Kornienko published the monograph Computed Tomography in the Neurosurgery Clinic, in which they summarised the experience of CT use at the Institute of Neurosurgery. For the period from 1981 to 1985, more than 12,000 patients were examined in the Institute; in the overwhelming majority of them, the initial diagnosis set with the help of CT was later confirmed during the operations. The first Soviet CT scanners of the second generation were made in Kiev. The first MRI scanner produced by Bruker, with the induction of the magnetic field of 0.22 T, was established in the Institute of Cable Industry, Moscow, in 1983. By the end of twentieth century, magnetic resonance imaging (MRI) had been strongly incorporated into a clinical practice, and in some cases (spinal cord examination) became a method of a choice in comparison with the usual CT. The high tissue resolution and a wide variety of types of contrast for MR images are typical for MRI. Currently, MRI employs several physical factors defining the brightness of tissue on the image such as: proton density; Т1, Т2, and Т2* relaxation time of protons in tissue; the movement of protons in the large vessels with a blood–cerebrospinal fluid (CSF) flow and passage of protons through a capillary net; random thermal water molecule motion; anisotropy of the diffusion proton motion and a magnetic susceptibility of tissues; and chemical shift of proton’s resonance frequency in molecular complexes. More importantly, volumetric CT and super-fast MRI open wide diagnostic opportunities of CNS examination not only


on a level of anatomic structures (simulation and support of surgery, endoscopy), but also on a level of molecular and gene biology. Neuroradiology becomes a quantitative method of brain function examination, the method of monitoring, and prediction of the results of therapeutic treatment and surgical intervention of many diseases. Currently, large, specialised neuroradiology departments exist in clinical research centres in Moscow and St. Petersburg. The general radiologists working in radiological departments of hospitals with neurosurgery and neurological or psychiatric departments deal with problems of CNS disease diagnostics. In Russia, the specialty, unfortunately, bears the name “ray diagnostics”, and it includes all the different disciplines (specialities) dealing with various sorts of radiation (emanation): radiology (including CT and MRI), ultrasound diagnostic and radiotherapy (while there is internationally accepted division into radiology) and nuclear medicine, which more precisely reflects the subject (the essence of the matter). In 1990, a society of ray diagnostics was established in Russia. The specialised training on neuroradiology is currently relatively simple: after graduation, a physician attends the special 6-month course on radiology, listens to lectures, and passes the exam on main radiology topics including neuroradiology. Large neurosurgery centres have a specialised 2-year residence on radiology, in which physicians can combine the practical neuroradiological work (from X-ray images description to work on CT and MRI and conducting such diagnostic examination like direct angiography and myelography) with scientific research. Recently, the educational process (from university to the obtainment of neuroradiology qualification) underwent revision in the light of international experience. Russian still lacks a neuroradiological society. In 2001, the Russia Academy of Medical Sciences established neuroradiology as a separate speciality. The Moscow Institute of Neurosurgery (now The Burdenko Neurosurgical Institute) was founded in 1932, based on the Neurosurgery Clinic of the State X-ray (Roentgen) Institute of Russian Ministry of Health. The academician N.N. Burdenko was the Institute organiser and he became its first director. True to his plan, the Institute was created as a complex establishment in which neurologists, radiologists, morphologists, physiologists, ophthalmologists, otolaryngologists, psychologists, and other physicians worked together with neurosurgeons. The Institute’s departments and laboratories promoted the development of such new scientific disciplines as neuroradiology, oto-ophthalmoneurology and paediatric neurosurgery, and helped to develop not only the practice, but also the theory of neurosurgery. In different years, prominent Russian neurosurgeons B.G. Egorov, A.I. Aroutiunov, A.A. Arendt, L.A. Korejsha, V.M. Ugrjumov, S.S. Brjusova, and neuroradiologists M.B. Kopylov, A.N. Kun, Z.N Poljanker and A.S. Plevako, among other scientists and experts, worked in the Institute. Currently, the Institute is the largest neurosurgery centre in Russia and, in fact, the world. There are three Members and Corresponding Members of the Russian Academy of Medical

3

Sciences, more than 40 professors, and more than 100 Ph.D.’s among the more than 2,000 Institute staff. Since 1975, the Institute has been headed by the Member of Russian Academy of Science and Russian Academy of Medical Science Professor, A.N. Konovalov. The Institute is situated in a newly built, specialised surgical complex. In this 14-story building, there are ten various clinical departments and 300 beds. The surgical unit consists of 16 operating rooms. About 5,000 complex surgeries concerning central and peripheral nervous system disorders/diseases are annually performed in the Institute. The Department of Neuroradiology is equipped by six CT scanners (three of them being spiral scanners) and three MRI scanners (with magnetic field inductions of 1,0 and 1.5 T). The department has two analogue–digital angiography (DSA) devices. Standard X-ray machines use digital carriers to record X-ray images. All diagnostic devices and installations are linked by a special informational neuroradiological network that is connected with the general Institute’s network and the Internet. Further development of neuroradiology is closely linked with the increase of processing speed and improvements in computer technologies, increase of the (MRI) magnetic field induction, the development of “open” magnets for biopsy, the intra-operational control, the examination of critically ill patients and patients with complications after an injury, the children, and so forth.

1.3

New Functional Methods in Neuroradiology

The increase of the processing speed of CT and MRI scanners, the invention of new data-registration technologies and the algorithms of data-processing transfer neuroradiology to entire new level. Neuroradiology development the follows the path “from anatomy to brain functions” (Cha 2006). Anatomic scans of standard CT and MRI demonstrate different types of tissue: blood, fat, white and grey matter, bones, and so forth. Modern CT and MRI methods can estimate speed and orientation of diffusive motion of water molecules and “see” the tissues differ in exchange interaction of protons, transport of ions and molecules (K+, Na+), environmental pH and phagocytosis (Hesseltine et al. 2007; Spilt et al. 2006; Cha 2006). With enriched blood flow, MRI can detect areas of the brain having increased neuronal and metabolic activity, find areas of damage in the brain–blood barrier, make a quantitative assessment of microvascular permeability of brain tissue, evaluate the state of receptors on the cell surface as well as hormonal activity, and reveal the presence of certain antigen and protein structures, among other abilities (Chai et al. 2007; Stadlbauer et al. 2007; Hourani et al. 2006; Holshouser et al. 2006; Cha et al. 2006). Thus, CT and MRI perform diagnostics not only on a cellular, but also on a molecular level. As such, diffusion, perfusion, and functional MRI and MR spectroscopy belong to the so-called methods of molecular visualisation.

4

1.3.1 Methods of Diffusion Motion Visualisation Diffusion is the basic physical process occurring during the cell’s metabolic reactions. Kinetic energy leads to Brownian motion (random walk) of molecules (thermal motion; the speed is about 10–3 mm2/s). As a whole, the molecular motion of protons in physiological systems is divided into three types: (1) movement with moderate speed in macroscopic vessels (about 10–100 mm/s); (2) slow flow in a capillary net, or perfusion (the speed is about 0.1–10 mm/s); and (3) diffusion motion of molecules (the speed is about 10–3 mm2/s). Blood flow in large vessels is measured as a volume-in-time unit, perfusion flow (a local blood flow) is measured as the volume of blood passing in and out of a given tissue weight (volume) per unit of time and the diffusion factor is estimated by the average square of the distance made by molecules for a time unit. Phenomenologically, the diffusion properties in the isotropic environment is characterised with the help of Fick’s law, which connects the vector of particle flux with the gradient of their concentration. The diffusion factor (coefficient), D, is a factor of proportionality. The higher the value of diffusion factor, the more quickly solution mixing occurs. A. Einstein in 1905 applied the probabilistic approach to the description of diffusive motion. According to such approach, the cumulative motion of all particles is characterised by the probability of displacement of separate molecules from one point of space to another, although the exact trajectory (trace) of each particle is unknown. For a one-dimensional case and the isotropic environment, the displacement dispersion, x2, is connected with the diffusion factor D and diffusion time, t, by Einstein’s formula: x2 = 2 Dt. The higher the value of diffusion factor, the longer an average distance of particle’s displacement (within the same time). The diffusion coefficient unit of measurement is meters squared per second—the square of the circle where the particle would be in 1 s. In the simple experiment (Fig. 1.1), the drop of paint in water always colour produced a coloured circle, and the radius of this circle infinitely grows with a time (Fig. 1.1a). In the case of impenetrable, closed border, the painted area will not grow outside this border (Fig. 1.1b).

Fig. 1.1a–c Schema of the experiment with drops of paint: types

of diffusion motion. a Free diffusion, b uniformly limited diffusion (isotropy), c non-uniformly limited diffusion (anisotropy)

Chapter 1

In the case of presence of obstacles on the water surface, the paint particles bypass them, and the painted area has an elliptic form (Fig. 1.1c). Thus, after awhile since the beginning of the experiment, the painted area is characterised by the size of the spot, its form, and its orientation on the plane. In a three-dimensional case, the law of displacement probability density is set by probability of particle transition in time t from one point, r0, to another point, r. In the simple case of free diffusion in an unlimited, isotropic, and homogeneous environment, this probability has a Gaussian distribution. The volume in which a particle would be contained in time t is sphere with the centre in r0; in the case of the limited isotropic diffusion, the sphere radius would not increase since some moment of time, and in cases of anisotropy or particle speed dependence from the motion direction, the sphere becomes ellipsoid.

1.3.1.1

Diffusion-Weighted MRI

The motion of the water molecule in live tissues occurs within the cell limits (the limited diffusion), as well as in intercellular spaces among structures, which restrict the molecules motion but still leaves them some freedom for manoeuvring between obstacles (the complicated diffusion). The term of measured or apparent diffusion coefficient was introduced to characterise the diffusion proton motion in a complex environment. Generally, this value depends on the structure and microstructure of substance, in which the water molecules are diffusing: D = 2.5 × 10–3 mm2/s in free water at body temperature (Tanner 1970). In the real biological environment, water molecules can encounter natural barriers, such as like cellular membranes and large albumin molecules, which that interfere with free motion of protons. Therefore, in practice, the apparent diffusion coefficient is calculated, and its value is lower than diffusion coefficient for pure water at temperature. The first diffusion-weighted MRI (DWI) was done in 1985 (Le Bihan et al. 1985). DWI was introduced into clinical practice together with third-generation MRI scanners (Le Bihan 1991). Spin echo-echo planar pulse sequences (SE-EPI) with two diffusion gradients (DG) of the same amplitude (G) and duration –δ are used to obtain DWI images. It is possible to apply DG in different directions, for example, in a direction of one of coordinate axes. The degree of weighting signal on diffusion rate is set by the value of the so-called diffusion factor, b, which is a parameter of the pulse sequence timing and depends on DG duration and delay time between them: b = γ2G2δ2(∆ – δ/3). In this formula, γ is the gyromagnetic ratio, G the amplitude, δ is the duration of each diffusion gradient and ∆ is a delay between diffusion gradients. The diffusion factor b is measured in seconds per squared millimetre. The measurements in DWI are performed two times, first with b = 0 s/mm2 and then with b = (500–7,000) s/mm2. DG applied along the direction of each coordinate axes of the scanner are x, y and z in DWI. In diffusion tensor MRI (DTI) measurements are performed (at least) in six DG directions.


5

Fig. 1.2a–d DWI (combined series), obtained with b = 500 s/mm2 (a) and b = 1,000 s/mm2 (b). c,d ADC maps for the same scans

The phase changes caused by the DG, in stationary protons (very low diffusivity) in the structure of macromolecules, are completely compensated by the moment of registration. MR signal from such protons corresponds to T2 of the tissue and is equal to a signal registered in SE-EPI sequence at b = 0 s/mm2. The protons participating in diffusion motion with water molecules get the additional phase, and MR signal from them is lowered. Diffusivity of water in a tissue is visually estimated by the degree of MR signal attenuation on DWI. In our examination, the gradient fields with amplitudes of G = 11 and 22 mT/m were used, which corresponds to diffusion factor values of b = 500 and 1,000 s/mm2, respectively. For each DWI–EPI examination, we obtain five series of scan images: one series is a T2 MRI; three at a supply diffusion gradient on each direction (х: anterior–posterior, y: right–left, and z: superior–inferior); and one, the so-called combined series for average diffusion coefficient (ADC) calculation, without taking into account the anisotropy in a tissue. In Fig. 1.2a,b, the DWI (the combined series) is shown. These images were obtained at b = 500 s/mm2 (Fig. 1.2a) and 1,000 s/mm2 (Fig. 1.2b). The visible (by eye) decrease in MR signal intensity occurs in the case of the phase signal changing in one or two times. It is possible to estimate fast proton diffusion with the ADC of 5 × 10–3 s/mm2 for b = 500 s/mm2. For b = 1,000 s/mm2, the optimum conditions for MR signal decrease visualisation would be for the protons diffusing more slowly, with the ADC on or about the order of 2.5 × 10–3 s/mm2, i.e. almost the same as in free water. With even higher

b values, it is possible to estimate the speed of diffusion motion in cell compartments (Le Bihan 2002). For a quantitative estimation of diffusion water properties in tissue, the parametrical diffusion maps are built on the colour of each pixel as it corresponds to the ADC (Fig. 1.2c,d). On the diffusion map, tissues with high speeds of water diffusion have blue– black colours.

1.3.1.1.1 Diffusion Anisotropy Diffusion anisotropy is a dependence on direction of molecular diffusion ability. The diffusion maps obtained at DG action (effect) on six different directions in the space at b = 1,000 s/ mm2 are shown in Fig. 1.3a–e, and diffusion coefficient maps in a direction of coordinate axes x, y and z are reflected in Fig. 1.3f,h. The anisotropy of diffusion characters of corpus callosum white matter is clearly visible on the images. Water molecules easily diffuse alongside nerve fibres; however, their motion in the transverse direction is limited by the impenetrable myelin membrane. For the description of diffusion properties changing with a direction, mathematical tensors are used. The diffusion tensor is defined as: � Dx x = D � D yx � Dzx −

Dx y Dy y Dz y

D xz � D yz � Dzz �

6

Chapter 1

Fig. 1.3a–i DWI obtained at DG application at six different directions (a–f), and diffusion coefficient maps in a direction of coordinate axes

x (g), y (h), and z (i)


The diffusion tensor is symmetrical, i.e. Dxy = Dyx, for any pair of indexes. This property reflects physical properties of the real environment, namely, diffusion properties would not change from the initial and final points of a diffusing molecule trajectory. Thanks to the diffusion tensor’s symmetry, the six tensor coefficients (three diagonal and three non-diagonal) are sufficient for characterisation of diffusion properties of water molecules. Six coefficients of diffusion tensor define the form of a diffusion ellipsoid, its sizes and its orientation in space (Pierpaoli 1996; Mori and van Zijl 2002). The diffusion isotropy means that diffusion motion of molecules does not depend on the orientation of environment, and during observation, the molecule would not leave the limits of sphere with a radius D, where D = (Dxx + Dyy + Dzz)/3 = ADC. Diffusion anisotropy assumes that, during the observation, due to orientation of environmental elements, the molecule would not leave the borders of the “diffusion ellipsoid” with half-axes λ1 λ2 and λ3; here λ1 λ2 and λ3 are the values of diffusion tensor (eigenvalues). The diffusion anisotropy can be quantitatively estimated with the use of the difference between the diffusion ellipsoid and the sphere with radius Dcp, for instance, with the help of the fractional anisotropy (FA) coefficient, relative anisotropy (RA) coefficient, index of anisotropy (IA) and so forth (Pierpaoli 1996). Diffusion tensor MRI (DTI) is used to visualise the anisotropy of water diffusion in the tissue.

7

In DTI, the line of nerve fibres forming the nerve tracts (paths) may be visualised via the diffusion ellipsoids’ orientation, by connecting the vectors of diffusion tensor (Fig. 1.4). Connection algorithms are relatively complex, and therefore the various methods of calculation like structural modelling (structural modelling involves following the main diffusion directions), connective models (anatomical and functional connectivity), methods of integrated transformations and spherical harmonics (Q-space spherical harmonics), stochastic models (probabilistic models) and so forth are utilised (Mori and van Zijl 2002; Sen and Basser 2005; O’Donnell 2006). These methods enable the tracing of multiple nerve fibres forming a neural tract; therefore, DTI is often called tractography—a demonstration of neural tracts visualisation. In the simple form, partial diffusion anisotropy is coded by colour, and visualisation of the direction of water molecule diffusion motion in tissue is carried out by colouring the pixels a certain colour, depending on orientation of their respective vector (red for the x axis, green for y and dark blue for z) (Fig. 1.5). DTI is a tool of detection of structural communications between brain departments. Establishing such communication is especially important in the case of volumetric processes and the diseases deforming the anatomic structure or destroying white matter, such as tumours, brain injury, arteriovenous malformations, epilepsy and demyelinating diseases.) (Hesseltine et al. 2007; Holshouser 2006).

Fig. 1.4a–e Orientation of diffusion ellipsoids in voxels (a), in the genu (b) and splenium (c) of corpus callosum, and in the brainstem (d). e MR tractography based on the obtained data

8

Chapter 1

Fig. 1.5a–d Colour maps of anisotropy. The white matter conduction tracts (pathways) are marked by colour. a Map of partial anisotropy, b map of relative anisotropy, c map of anisotropy index, d structural map of anisotropy (according to the directions of the diffusion tensor vectors)

1.3.1.1.2 Clinical Application of DWI and DTI Decrease in ADC speed in brain tissue is a sensitive indicator of presence and severity of ischaemic changes (Moseley et al. 1995). Today, DWI is one of the fastest and highly specific methods of early-phase ischaemic stroke diagnostics (within 6 h of onset), during which there is a therapeutic window for restoration of the affected brain tissue. In acute phase of stroke, the affected area on DWI typically has a high MR signal, whereas the surrounding tissues look dark. The ADC maps provide a reverse-in-brightness picture (Fig. 1.6). Diffusion ADC maps are a tool in ischaemia diagnostics and monitoring of stoke and subsequent chronic tissue degeneration caused by ischaemia. Gradually, by the end of second week, the isointense signal from the affected area(s) replaces hyperintense one. Then the signal becomes hypointense, reflecting the focus of encephalomalacia. The high ADC values are observed in areas of chronic and old lacunar strokes. Currently, this method is perhaps unique, capable of detecting the new ischaemic area on the periphery of an old stroke zone (or widening the stroke area) in patients with newly developed focal neurological signs. Generally, the DWI non-invasiveness and swiftness predetermine its leading role in primary diagnostics of ischaemic stroke. All diffusion-weighted examinations are performed without contrast administration. This is important for critically ill and restless patients, and especially for specialised examina-

tions of brain development in children, beginning with the prenatal period. In the last case, DWI enables obtaining both the additional qualitative (visualisation) and quantitative tissue characteristics; it offers new opportunities of microstructure examination in the process of brain development (Konovalov 2001). DWI and ADC maps provide additional diagnostic information for differentiation of neoplasms with similar signs on T1 and T2 MRI (glioma, tumours with ring-shaped contrast accumulation), peritumoral oedema (vasogenic or cytotoxic) and the presence or absence of intratumoral cysts, to name a few (Mulkern et al. 1999). At the same time, as our experience demonstrates, DWI data alone does not allow differentiation between benign astrocytoma and anaplastic tumours, or between anaplastic astrocytoma and glioblastoma (Kornienko et al. 2000). The information concerning the spreading of infiltrating and growing brain neoplasm is more interesting. In many observations, the peripheral part of tumour (as a rule in the case of malignant glioma) is hyperintense on DWI; presumably it is linked with more dense cellular arrangement in the most actively growing tumour area (accordingly, there is a limitation on diffusive proton motion in this area). We used these data for planning the stereotactic biopsy with obligatory tissue sampling from this peripheral part of an intracerebral tumour. DWI provides invaluable information for inflammatory lesion diagnostics of brain and spinal cord (abscesses, empyema) for the immediate time. Purulent abscess content has


9

Fig. 1.6a–c Superacute phase of stroke. a The affected area has a hyperintense MR signal on DWI (b = 1,000), while normal brain tissues

look dark. The regions of ischaemia in left and right hemispheres of cerebellum are violet (b). c T2-weighted image: there are no MR signal alterations Fig. 1.7a,b Purulent complication after

glioblastoma removal. a Wide operational defect MR T2-weighted image. b DWI: the purulent layers (thickening) on the edges of defect are visualised (hyperintense MR signal)

a typical hyperintense MR signal on DWI and can be easily visualised on pretreatment (before draining) and as well on postoperative images. In addition, DWI can be used in the assessment of drainage intervention effectiveness or in the case of verification of the purulent complication in incision wound (Fig. 1.7). The structural organisation properties of some new brain neoplasms—in particular, meningiomas and neurinomas— enable DWI to predict tumour histological type, with high reliability even before intervention. Based on this method data, the epidermoid and arachnoid cysts can be precisely differentiated. Recently, DWI and DTI methods have begun to be applied to visualisation of a neural tract lines—tractography, especially in diagnosing white matter diseases caused by congenital metabolic defects, traumatic (diffusive axonal lesions),

autoimmune, toxic and radiation damage (Lee et al. 2005) (Fig. 1.8). Tractography is a new and promising technique that enables non-invasive viewing of the brain neural tracts (Batchelor et al. 2006). Despite some technical problems, the first results in tractography application to neurosurgery seem promising (Chepuri 2002). It is possible to plan operational access and to estimate the scope of brain hematoma to be removed, taking into account neural tracts and their involvement in the pathological process (dislocation–deformation, invasion, damage), with an aim to maximise the radical tumour resection and to minimise the subsequent complications (Stadlbauer et al. 2007). The results confirm the value of a new diagnostic MR technique that enables increasing MRI specificity in establishing the correct histological diagnosis, and improves the accuracy

10

Fig. 1.8a–f MR tractography. a Axial projection, structural map.

b Coronal projection, structural map. c T2-weighted MRI, axial scan of patient with glioma. d Construction of the corticospinal tract in

of detecting the various components of tumour growth (tumour, infiltration and peritumoral oedema) and the borders of ischaemic lesion(s).

1.3.1.1.3 Perfusion Examinations Methods of perfusion examination are used to consider and make quantitative estimation of the blood movement that supplies each element of organ or tissue volume. It is widely known that, unlike the majority of parenchymatous tissue, brain tissue does not accumulate glucose, and brain cells can produce energy via anaerobic glycolysis only for several minutes. Meanwhile, the brain consumes about 25% of all glucose consumed in the entire body, and for neurons, the uninterrupted and sufficient supply of oxygen and glucose is necessary. There are complex mechanisms of autoregulation that manage brain perfusion to satisfy the demands of the nervous system for energy (released in a course of metabolic processes). There are several modern quantitative methods of brain haemodynamic examination: MRI, CT with contrast enhance-

Chapter 1

coronal plan in zone of tumour location. e T2-weighted MRI of a patient with metastasis in basal ganglia. f Splitting of the nerve fibres around metastasis

ment, CT with Xe, single-photon emission computed tomography (SPECT) imaging and positron emission tomography (PET). The obvious advantages of CT and MRI are minimally invasive, high sensitivity in tissue microcirculation assessment, high resolution, the short examination time (within the framework of standard protocols), and last, but not least, the reproducibility of results (Sorensen and Reimer 2000; TingYim 2002; Cha 2006; Waaijer 2007). The most widespread perfusion examination in neuroradiology is that performed based on intravenous bolus administration (CT and MRI). The dynamic studies of bolus passage demonstrate its distribution in tissue in each given image pixel, depending on time. The following main haemodynamic characteristics are used for quantitative assessment: cerebral blood flow (CBF), the cerebral blood volume (CBV) and mean transit time (MTT). The blood flow characteristics are measured in the ratio to 100 g of brain tissue. Accordingly, the value of CBV is measured in millilitres per 100 g of brain tissue, and CBF is measured in millilitres per 100 g per minute. The local (regional) CBV is defined as percentage of blood volume in a single element of brain tissue volume. MTT is measured in seconds.


Fig. 1.9 Perfusion CT. a Series of dynamic CT scans, b the concentration–time curve in an artery and vein

1.3.1.1.4 Perfusion CT The modern spiral CT scanners present new opportunities in tissue perfusion examination during the first passage of the iodide contrast bolus. This method has high resolution and provides quantitative assessments of tissue perfusion, and currently, it is one of the most perspective methods. Perfusion CT is based on analysing the CT density increase during contrast media passage through brain vascular structures. Contrast bolus (iodine agent with concentration 350–370 mg/ml, speed of administration is 4 ml/s) is administered intravenously. Spiral CT obtains a series of scans with 1-s intervals, within 50–60 s after contrast administration (Fig. 1.9).

1.4

Perfusion-Weighted Imaging

There are MRI methods of haemodynamic perfusion examination, aided by exogenous and endogenous markers: • Contrast media (theory of non-diffusing markers, or central volume theory) • Arterial spin labelling (kinetic theory of diffusing markers) • Obtaining the images that depend on blood oxygenation level (BOLD) The methods of perfusion assessment during contrast bolus passage are called perfusion-weighted MRI, or PWI. These examination methods are currently widely used in MR diagnostics, especially in combination with MR angiography and MR spectroscopy. PWI uses changes of T1 or T2 tissues contrast due to infusion of gadolinium into blood as a contrast agent. Normally, gadolinium does not pass through blood–brain barrier. It can pass into intracellular spaces only in cases of blood–brain barrier disruptions (Cha et al. 2007). The usual MRCM (MR contrast media) concentration in

11

bolus is 0.1 mmol/l—the same as in standard examinations with contrast enhancement. The CM bolus is administrated quickly (about 2–3 s); the speed of administration is 4–5 ml/s, and higher than in the standard infusion. After the bolus, a buffer solution is administrated. Ideally, the bolus envelope curve should have rectangular form. The bolus passage on consecutive (in time) scans corresponds with the sharp decrease of MR signal intensity. In the process of CM bolus passage through the vascular system, multiple registration of the image from the same location occurs (usually it is 10 different levels). The scanning takes place for 1–2 min. The graph of intensity decrease during CM bolus passage provides the curve “signal intensity–time” in each pixel of the scan (Fig. 1.10). The form of this curve for arteries and veins provides arterial and venous function data; with the help of these data, the haemodynamic tissue parameters are calculated. The regional CBV (rCBV) is estimated on the basis of area under curve “concentration–time”; the MTT calculation is performed on the basis of centre of gravity in CM distribution position, regional CBF (rCBF) = rCBV/MTT. The perfusion maps are built in “off-line” mode in the specialised workstations. PWI uses SE or gradient recalled echo (GRE) pulse sequences. The advantages of EPI-SE are the absence of geometrical distortions and good detection of arterial function in large arteries at the base of the skull. The main shortcoming is the echo time (TE) of 40–80 ms, necessary for maintenance of T2 weighting of the MR signal, which limits the time interval between scans. EPI-GRE provides time resolution of 1 s; however, it cannot obviate geometrical distortions. The method of dynamic T1 MRI is used in cases of examination of CM distribution in extracellular spaces. The time range of a dynamic curve in cases of T1 examination is 3–5 min from the moment of CM administration. The CM passage through the vascular net is accompanied by increase of MR signal intensity in areas of CM accumulation. Dependence S (t) is used for construction of the concentration–time curve, Ct. The steepness of the front of the CM accumulation curve (as well as in perfusion CT) characterises a local blood flow, maximum value of MR signal to local blood flow volume; the form of the concentration curve allows estimation of microvascular permeability of blood–brain barrier. The advantage of perfusion examination with the help of the arterial spin labelling (ASL) method is the possibility of perfusion assessment without CM administration (Chai et al. 2007). The method is based on the proximal labelling of water protons with the help of presaturation. The “labelled” spins (they get the additional phase shift) enter (with the blood flow) the vascular brain bloodstream and account for the decrease of MR signal from microvascular structures on dynamic MRI series. The second series is registered in the absence of saturating radiofrequency pulse. The local blood flow is calculated on the difference between the two series (with presaturation and without). Currently, two modifications of ASL are used, continuous (CASL) and pulsed (PASL). The duration of examination is 15 min in the field of about 1.5 T. The MR signal change due to spin labelling is lower than in the case of bolus CM admin-

12

Chapter 1

Fig. 1.10a–e Perfusion MRI. a Series of dynamic MRI and signal intensity–time curves in normal brain tissue. Patient with meningioma.

b The signal intensity–time curve in an artery (1) and vein (2). c–e CBV maps on different levels

istration, and reaches only 15% of the latter (Alsop and Detre 1998). This method could gain recognition in the clinic, probably with the spreading of high-field MRI with the induction of 3 T or higher. Functional MRI (fMRI) utilises the magnetic properties of blood as an exogenous marker in magnetic field 1.5–3 T (discussed below).

1.4.1 Clinical Applications of CT and MRI Perfusion Currently, perfusion examinations are performed to estimate the haemodynamic of brain tumours in cases of differential diagnostics of brain lesions; for tumour-state monitoring after chemo- and radiotherapy; in diagnostics of the tumour recurrence and radiation necrosis; and in cases of brain injury and CNS damage like ischaemia, hypoxia, large-arteries stenoses, blood diseases, vasculitis and moyamoya disease. Epilepsy, migraine, vasospasm various mental diseases (including dementia), autism, and so forth, are prospective in terms of perfusion methods application. CT and MRI perfusion allow building of parametric maps and quantitative characterisation of areas of hyper- and hypoperfusion, which is especially important in tumour and cerebrovascular disease diagnostics. Perfusion maps provide

important additional information about characteristics of normal and pathological tissues (in areas of tumour, oedema, necrosis, and so forth). In neurosurgery, PWI is used in primary differential diagnostics of malignancy levels of brain neoplasms, in particular gliomas. However, it is necessary to remember that perfusion CT and MRI do not allow specifically differentiating tumours according their histology, nor does it enable estimation of the tumour spreading into brain tissue. The hyperperfusion is focussed within the structure of astrocytoma; it can indicate increase of tumour malignancy because the perfusion level of tumour is related to the development of abnormal vascular net (angiogenesis) and thus, with the tumour’s viability. The abnormal vascular net in a tumour can be the evidence of its aggressiveness. In contrast, the decrease of perfusion in a tumour tissue under the influence of chemo- or radiotherapy can be a sign of response to treatment. Use of PWI in target selection for stereotactic intervention is helpful, especially in cases of gliomas that are characterised by full absence of contrast accumulation with the use of standard CT and MRI (Fig. 1.11). PWI potential is higher in assessment of histological type and spreading of extracranial neoplasms than of intracranial ones (Fig. 1.12). PWI successfully visualises meningioma and


13 Fig. 1.11a,b Glioblastoma of right tempo-

ral lobe. a CT with contrast enhancement does not reveal its pathological accumulation. b CBV (based on CT data) map visualises the area of elevated perfusion: the site of biopsy is marked by a circle (region of interest [ROI] 3); CBV in the tumour increased more than three times in comparison with normal white matter (ROI 4)

Fig. 1.12a–d Perfusion maps on the basis

of skull. CT in patient with cranio-orbital meningioma. a CBV, b CBF, c MTT, d TP (time to pike)

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neurinoma of cerebellopontine corners according to the high haemodynamic parameters in meningioangiomatoses. In addition, it was demonstrated that there is a clear correlation between local blood flow (CBF, CBV) and direct angiography data in patients with meningiomas (Fig. 1.13). The tumours with radiopaque shadows in the early capillary phase of angiography have especially high perfusion, and such tumours are characterised by high risk of a intraoperational bleeding in the moment of extraction. CT PWI data are highly specific in demonstrating the blood supply of haemangiomas located in posterior cranial fossa; in this case, early and marked contrasting is combined with high perfusion. PWI is used successfully in differential diagnostics of postoperative continued tumour growth and radionecrosis.

Chapter 1

In both cases, standard CT and MR examinations can show the accumulation of contrast in tissues, and in both cases, blood–brain barrier disruptions are observed. Blood–brain barrier disruptions cause CM extravasation in pathological tissues, with subsequent contrast accumulation. However, the pathophysiological reasons in both cases are different. For tumorous tissues, the perfusion increase or the reaching of normal perfusion level are typical, as in necrotic tissues the blood supply is absent. Blood–brain barrier disruptions in cases of tumours are related to the invasive growth of tumour cells and vascular wall damage. In case of radionecrosis, the disruption of blood– brain barrier is an initial step, and it declares itself (unlike tumours) in the form of perfusion decrease (iso- or hypop-

Fig. 1.13a–c Meningioma of sphenoid wing. a CT scan with contrast enhancement, b CBV map demonstrates the large tumour with high

perfusion indicators, c direct angiography confirms the luxury meningioma blood supply in arterial phase

Fig. 1.14a–c Ischaemic stroke in left MCA territory. a ADC map (the stroke is coloured violet-blue and affects the basal ganglia), b CBF map:

area of deep nucleus damage with very low cerebral blood flow parameters (arrow), c MTT map (the area of penumbra is marked by ROI 1, with light blue)


erfusion). The areas of radionecrosis appear as areas of weak blood filling on CBV maps. The time of CM bolus passage is longer than normal, as in cases of ischaemia. Undoubtedly, ischaemic brain damage occupies first place in the frequency of PWI methods being used. Currently, PWI is an integral part of diagnostics in patients in whom cerebral ischaemia is suspected. The first clinical PWI application in brain lesion diagnostic in humans was performed for stroke diagnosis. At present, perfusion MRI is, perhaps, the sole method of early ischaemia verification, capable of diagnosing the haemodynamic decrease in certain brain areas (as the main mechanism of ischaemic damage), even in the first minutes after appearance of focal neurological signs. The combination of PWI and DWI in patients with brain ischaemia enables detection of the heterogeneity of the ischaemic area(s), to distinguish the nuclear lesion (the area of necrosis) and so-called penumbra (the area of ischaemic half-shadow), with only functional changes (Fig. 1.14). The new approach in PWI use is studying the haemodynamic shifts in brain substance in patients with severe stenosis and occlusion of large extracranial vessels. It turned out, for instance, that there is no clear correlation between stenosis level of internal carotid artery and perfusion decrease on the territory supplied by this artery. One of the main reasons for this is the development of collateral circulation with haemodynamic compensation. Generally, careful analysing of these data in vascular surgery leads to more accurate treatment selection for these patients; in particular it limits the indication for extracranial–intracranial shunting.

15

The use of perfusion CT and MR investigations in children for whom the vessels occlusions are rare (characterised by the small probability of vessels occlusion) is especially important. The hyperintense MR signal in T2 consequence in most cases is caused not due to stroke, but to other reasons (for instance, vasogenic oedema, hypomyelinogenesis). PWI could indeed reveal the ischaemic area in children, for whom the small probability of stroke exists (Konovalov et al. 2001). Another example of PWI use is arteriopathy studies in children. Reasons for this study include idiopathic (primary) and secondary vasculitis, the consequences of moyamoya disease, and sickle cell arteriopathy. For such diseases, perfusion MRI sensitivity is compatible with those of perfusion CT with Xe133, and radionuclide methods. PWI has several advantages in anatomical damage visualisation and in detection of pathological and anomalous blood flow, observed, for instance, in cases of collateral circulation. Revealing the pathological circulation in children is especially significant in situations of patient selection for surgical treatment of arteriopathy. The collateral circulation in children with arteriopathy can be extensive at the time of its primary detection. Dynamic perfusion MRI is used in cinema mode for perfusion-loop, revealing collateral circulation assessment, and time of CM passage to tissue estimation. All this makes this method highly informative in detecting and subsequent observation of patients with moyamoya disease. It is considered that, at an initial stage of this disease, perfusion parametrical imaging demonstrates the increased blood flow in the basal ganglia area, altered peripheral cortical perfusion, deficit, or change of the CM passage time. These signs are typical for this disease.

1.5

Fig. 1.15 Haemodynamic response of brain to the increase of neuronal activity for interchange of stimulus and rest periods

Functional MRI

Brain activity mapping enables revealing of the areas of neuronal activation in response to tests, motor, sensor, and other stimulus. Until recently, similar mapping was performed with the help of radionuclide methods: PET and SPECT imaging. Functional MRI (fMRI) is based on increase of brain haemodynamics in response to cortical neuronal activity due to certain stimulus (Ramsey 2002; Pouratian et al. 2003; Sunaert 2006). BOLD EPI-GRE registers hyperintense MR signal from active areas of the brain cortex. The registration time of one MR image is about 100 ms. fMRI signal intensity, registered by physiological load, is compared with the intensity, registered in the event of its lack. During MRI examination, the stimulation periods (duration of 30 s) alternate with control periods (without stimulation) of the same duration (Fig. 1.15). The total number of scans registered during the examination reaches 20,000. This method of stimulus presenting is called a block paradigm. The areas of statistically significant MR signal increasing during activation, revealed in the course of subsequent mathematical processing of images, correspond to areas of neuronal activity. They are marked with colour—this way the neuronal activity maps are built and these maps are im-

16

Chapter 1

Fig. 1.16a–c fMRI neuronal activity maps of cortical motor centre activation in different patients with intrinsic tumours of the paracentral

area, imposed on a T1 image

Fig. 1.17a–c fMRI maps imposed on 3D brain models. a Patient with a brain tumour of the right frontal lobe, b interrelation of Broca’s area in patient with glioma of the left temporal lobe, c interrelation of motor centres in the case of bilateral stimulation in patient with astrocytoma of the left posterior frontal lobe

posed on T1 MRI sequences (Fig. 1.16). Map construction methods (for instance, brain wave algorithms) subtract images obtained during neuron stimulation from control images obtained in the absence of stimulation. The subtracted image is imposed on a control scan according to its location, and areas of increased neuronal activity are marked with colour. The revealed functionally significant areas could be “imposed” on a T1 MRI sequence of the same section or on a three-dimensional (3D) brain model, and thus it is possible to estimate the ratio between the affected area (tumour) and functionally active brain areas, for example, motor, sensory or visual cortex (Fig. 1.17).

1.5.1 Clinical Application of fMRI Neuronal activity mapping enables planning the surgical approach and studying of the pathophysiological processes in brain. This method is used in neurosurgery in studying cognitive functions. Its perspective is in revealing the epileptic foci. Currently, fMRI is an integral part of MRI protocol in patients with brain tumours located close to the functionally important brain areas. In the majority of cases, the examination results adequately reflect the location of sensomotor, speech and acoustical areas of brain cortex. However, according to


Fig. 1.18 The calculation of the radiation dose to brain tumour depending on location of functionally significant cortical areas

literature and our own study, 8–30% of all observation are not informative due to motion artefacts, lack of precise tests execution by the patients and damage to the above-mentioned cortical centres by tumours. In cases in which fMRI can locate active cortical areas, in 87% of cases there is a correspondence with the results of intraoperational electrophysiological methods, within 1-cm limits, and in 13% of cases, within 2 cm. This is evidence of the high accuracy of the fMRI technique (Nennig et al. 2007). Performing fMRI (currently it is conducted for somatosensory and visual cortices) and tractography with mapping of the functionally active cortical areas, pyramidal or optic tracts. Imposition of these maps over 3D brain images is promising within the framework of one MRI examination for patients with brain tumours. Based on these data, neurosurgeons plan the interventional approach and estimate the volume of neoplasm resection, and radiologists assess the areas of radiation and its distribution in tumour (Fig. 1.18).

1.6

17

detected in vivo in the proton MR spectrum: N-acetylaspartate (NAA), 2 ppm; choline (Cho), 3.2 ppm; creatine (Cr), 3.03 and 3.94 ppm; myo-inositol (mI), 3.56 ppm; glutamate and glutamine (Glx), 2.1–2.5 ppm; lactate (Lac), 1.32 ppm; and a complex of lipids (Lip), 0.8–1.2 ppm. The MR spectrum contains the extensive information about a substance. The peaks’ positions determine a chemical composition, and their width reflects the T2 relaxation time. The area under resonant peak is proportional to proton density and allows calculation of the metabolite concentration. Proton MRS has grown from the high-resolution nuclear MRS. In adjusting of the MR spectrum, the adjusting of MR scanner during examination (prescan) plays a significant role. Currently in proton MRS, two basic methods are used, single voxel (SV) and multivoxel (MV, or chemical shift imaging). MRS is a single-stage detection of spectra from several brain areas. Multinuclear MRS, based on phosphorus, carbon and other element nuclei, are entering clinical practice (Rinck 2003). In the case of SV-MRS, only one brain element (voxel) is chosen for the analysis. The metabolite’s peak distribution on the chemical shift scale (in parts per million) is obtained based on analysis of the structure of frequencies in a signal registered from this voxel (Fig. 1.19). SV-MRS uses pulse sequences point-resolved spectroscopy (PRESS) or stimulated echo acquisition mode (STEAM). STEAM has higher resolution on frequency, but it is very sensitive to the patient’s motions. Resolution of PRESS is a bit lower than is STEAM; however, it is less sensitive to motion. The ratio between metabolites peaks in a spectrum, decrease or increase of the height of separate peaks in a spectrum, are like fingerprints of brain biochemistry: on their basis, it is possible to make a non-invasive assessment of the biochemical process in tissues.

Proton MR Spectroscopy

MR spectroscopy (MRS) is a non-invasive method of brain metabolism assessment. Proton (1Н) МRS is based on a “chemical shift”—the change of proton resonant frequency. This term was developed by N. Ràmsey in 1951, for defining a distinction between frequencies of separate spectral peaks. The chemical shift measured unit is in parts per million (ppm). Following are the main metabolites and corresponding values of the chemical shift; peaks of those metabolites are

Fig. 1.19 Single-voxel proton MRS of brain tissue in a normal volunteer. The peaks of main metabolites are marked on the image

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MV-MRS simultaneously obtains MR spectra for several voxels, and thus it is possible to compare spectra from different elements in an examination area (Fig. 1.20). Processing of the MV-MRS data enables construction of a parametrical map of brain. The concentration of particular metabolites on this map is marked by colour, and thus it is possible to visualise the metabolite distribution in brain, i.e. to obtain an image weighed on the chemical shift. NAA is the most visible peak in the 1Н spectrum (at 2 ppm). In reality, this peak includes different combinations of macromolecules with NAA: N-acetylaspartylglutamate, glycoproteins, and amino acid residues, and thus this peak could be more appropriately termed “N-acetyl groups”. It is considered that in the adult brain, NAA plays at least two roles: (1) as a predecessor of brain lipids, and (2) as a participant in coenzyme A interactions. Some researchers believe that NAA is metabolically inert, and it participates only in maintenance of “deficiency anion” balance in neutral tissues, so it is the indicator of processes with neurotransmitter–neuromodulator participation, and its basic function is to be the form of free storage of aspar-

Chapter 1

tate (Ureniak et al. 1992). In an adult brain, the concentration of NAA in the cortex is higher than in white matter, as the majority of NAA is located in neurons and their branches. Acetyl-CoA-l-aspartate-N-acetyltransferase is a synthetic enzyme used for obtaining NAA in mitochondria. Acetoaspartase is an enzyme that decomposes NAA, and it is mainly located in astrocytes; thus, NAA decomposition occurs mainly in glial cells, and that explains the low NAA concentration in mature glia. Due to the mainly neuronal and axonal NAA location, the NAA peak decreases in cases of neurodegenerative diseases. Animal experiments have confirmed that decreased NAA correlate with neuronal necrosis. Absolute or relative (in relation to creatine) decrease of this peak is considered an indicator of neuronal and axonal damage. However, as NAA is synthesised in mitochondria, theoretically, the exhaustion of energy without permanent neuronal damages could lead to temporal NAA decrease. In children, the NAA concentration in grey and white matter is identical. Rather high concentration of NAA in immature white matter is related with very high activity of lipid synthesis; research of immature brain demonstrated that oligodendroglia predeces-

Fig. 1.20e–f Multivoxel proton MRS in a patient with a brain tumour. a Spectra presentation in each voxel; b enlarged image with measured

points placement; c spectrum of tumour’s tissue, with typical glioma metabolite changes; d–f colour map of different metabolite contents


sors have twice more NAA than do underdeveloped neurons. The choline peak at 3.21 ppm contains the cumulative contribution of trimethylammonium protons (–N(CH3)3+) in choline, betaine and carnitine plus Н5 protons of mI and taurine. The choline contribution is a sum of signals from several choline-containing chemical compounds (phosphoryl choline, glycerophosphoryl choline and free choline), and probably together with choline, which is present in a form of a polar head group in lipid membranes. MRS might not detect the compounds of choline embedded in a membrane; however, in the case of cell membrane destruction caused by the disease, choline is released, accumulated and may be detected. Choline is a structural component of cellular membranes, especially myelin membranes. The choline peak tends to increase in highly malignant tumours and neurodegenerative diseases. Focal inflammation, which leads to considerable local cellularity and often to significant cellular membranes damages, could also result in increasing of choline peak. The creatine peak at 3.03 ppm is caused by protons of methyl (CH3) group of creatine, phosphocreatine, lysine and glutathione. It appears that phosphocreatine is the basic molecule for maintenance of energy-dependent systems in all brain cells. Its concentration is maximal in a cerebellum, followed by grey, and then by white, matter. Usually, it is assumed that the general creatine level is stable in different situations; therefore, the height of creatine peak is often used as reference in comparison with the height of other metabolites peaks. MI that has two peaks at 3.56 and 4.06 ppm, and it is supposed it serves as storage of membranous phosphoinositides, which are the second messengers of the hormonal systems, and which participate in CNS enzyme regulation. It is one of major growth factors, and it is a predecessor of phosphatidylinositol, which in turn is a part of the lipid layers of cellular membranes. It is located primarily in glial cells and therefore could serve as a specific glial marker. Its other possible functions include osmoregulation, cellular nutrition and detoxication. The low combined peak at 3.56 ppm is from glycine and inositol-1-phosphate. Scyllo-inositol is an isomer of mI, which is not exposed to metabolic changes that could inhibit transport and mI (embedding) association with lipids. The singlet peak at 3.35 ppm is believed to originate from the six protons of methane in a molecule of cyclic alcohol of scyllo-inositol, not from taurine as was thought previously. The singlet nature of resonance is caused by a chemical shift, and it is in agreement with biochemical concentration levels of mI compounds, and elimination of the other metabolites of 1Н MRS spectra of mammalian brains in vivo as well as in vitro. The presence of glucose in brain tissues can be detected with MRS, with short TE time by a singlet at 3.43 ppm. The area under this singlet can be used for calculation of brain glucose concentration. It is possible to detect lactate, which is detected by its typical doublet located in 1Н MRS spectra around 1.32 ppm, in trace quantities corresponding to terms of pregnancy. It is believed that lactate, if found in greater quantities, especially in the first hours of life, is an indicator of brain damage. However, lactate presence in 1Н MRS is a normal finding in prematurely born

19

children. The small peak present in the fetus decreases toward 40 weeks’ gestation. Lactate concentration varies as the brain matures—in newborns, it is higher in less- matured areas of the brain, such as parietal, anterior frontal and temporal. In more mature brains, lactate concentration is higher in the basal ganglia and central gyri. In a case when 1Н MRS has a short TE, several small peaks appear in 1Н MR spectra at 2.1 and 2.4 ppm, corresponding to the protons in glutamine and glutamate. Unfortunately, in the case of a magnetic field induction of 1.5 T (usually used in the clinical setting), these peaks overlap, and their separation is difficult on a background of NAA peak. In all probability, with the use of higher magnetic fields, these peaks could become distinguishable, and their analysis could help with detection of metabolic brain damage (which is accompanied by a change of the glutamate peak). Currently, the following areas of proton MRS clinical application are being considered: injury, metabolic and mitochondrial damages, as well as inflammatory and volumetric disorders.

1.6.1 Brain Tumours MRS is now widely used in an estimation of various volumetric brain formations (Meng 2004; Hourani 2006). In spite of the fact that according to MRS data, it is impossible to predict with sufficient confidence the neoplasm histological type, nevertheless, the majority of researchers agree that tumoural processes as a whole are characterised by a low NAA–Cr ratio, increase in Cho–Cr ration, and in some cases, by the lactate peak (Fig. 1.21). In the majority of performed MRS examinations, proton spectroscopy is used in differential diagnostics of astrocytoma, ependymoma and primitive neuroepithelial tumors (PNET). It is noted that typical signs of astrocytoma and ependymoma are the decrease in the NAA–Cho ratio and increase in the ratio of Lac–Cho peaks in relation to those in a healthy hemisphere. In comparison with these tumours, PNET are characterised by an increase in the NAA–Cho ratio and a lower Lac– Cho ratio, which is related to a higher level of Cho in patients with PNET, as with malignant neoplasm. For astrocytoma, in general, the increase of the Cho peak, the change of mI peak (depends on the malignancy level), the significant reduction of the NAA peak and the appearance of a Lac peak are typical. (In some cases, the combination of Lac and Lip peaks is observed, representing single Lac–Lip complex.) For benign astrocytoma, the reduction of NAA peak is typical, and the increase of Cho peak is observed. The height of the mI peak can remain unchanged, or it can rise insignificantly in comparison with contralateral tissues not affected by tumours. The Lac peak is characterised by small elevation, and in rare cases, it cannot be detected at all (Fig. 1.21a). The Cho and Lac peak rise, while the mI peak falls with the increase of malignancy level—in particular, in cases of anaplastic astrocytoma (Fig. 1.21b). The NAA peak is reduced in comparison with its height in the spectrum of benign astro-

20

Chapter 1

Fig. 1.21a–c T2 MRI and proton MR spectra of gliomas with various malignancy levels. a Astrocytoma grade I–II, b anaplastic astrocytoma, c glioblastoma

cytoma. The marked or full reduction of NAA and mI peaks, and the sharp increase of the Lac peak, are observed in spectrum of glioblastoma, which is characterised by the presence of a necrosis area. At the same time, the Lip peak appears and overlaps the Lac peak, and visually, these peaks looks like single complex (Fig. 1.21c). Generally, the height of Cho peak is sharply increased. In clinical practice, it is important to use MRS during postoperational period for diagnostics of the continued neoplasm growth, tumour relapse or radiation necrosis. As a rule, treatment of brain tumours is a combination of surgery with chemo- and radiotherapy. However, current methods and doses of radiotherapy could cause the death of not only tumour cells, but also of healthy cells, especially in cases of lowered sensitivity threshold for radiotherapy. First, endothelium cells of vessels suffer, then brain oedema appears, and as a result, a zone of radiation necrosis could appear. According to statistics, in more than 5% of all patients who undergo radiotherapy because of a neoplasm, brain damage is diagnosed by the end of the first year near the tumour as well as in other areas. The differential diagnosis between the continued growth, tumour relapse and radiation necrosis is extremely complicated, even with functional CT and MRI examinations. The tumour and radiation necrosis both have the similar CT and MRI pictures. CM accumulation in radiation necrosis is almost the same as in an area of tumour growth. In such cases, 1Н MRS is a useful additional method in differential diagnostics. In a radiation necrosis spectrum, the so-called dead peak, a wide Lac–Lip complex in the range of 0.5–1.8 ppm on a background of a full reduction of other metabolites’ peaks, is a typical attribute. In some cases, the Cho peak can be observed, which complicates the differential diagnostics of radiation necrosis and relapse of tumour with necrotic component (glioblastoma, metastasis).

The diagnosis of lymphomas is an important neuroradiology problem. Differential diagnostics of these tumours based on only routine CT and MRI is complicated, and combined chemo- and radiotherapy treatment is more preferable than surgical removal (Kornienko 2004). Therefore, the correct diagnosis influences the tactic choice in treatment and the prognosis of disease. In the majority of cases, it is necessary to differentiate lymphomas with glial tumours and metastasis. The common trend of changes in peaks of Cho, Lac and NAA is observed in lymphoma spectrum as well as in that of astrocytoma. However, these changes are different. With the lymphoma spectrum, the changes of peak heights are not so expressed. The Cho peak increases moderately, and the increased of peak of the Lac–Lip complex is substantial, whereas the decrease in the NAA peak is insignificant.

1.6.2 Ischaemic Stroke Usually, clinical signs and the patient’s medical history provide the physician enough information for establishing the correct diagnosis in an overwhelming majority of the cases. Nevertheless, in an outpatient practice, it is sometimes necessary to differentiate ischaemic lesion from primary brain tumours (low-malignant astrocytoma). CM administration does not provide sufficient information since in an acute stroke phase, there is no brain–blood barrier damage, and CM might not accumulate in the affected area. The same is true of astrocytoma. Proton (1H) MRS use in such cases facilitates considerably differential diagnostics and an establishment of final diagnosis (Podoprigora et al. 2003). In addition, 1H MRS performed permits estimation of the efficiency of conservative treatment and prognosis. In the first hours after an ischaemia onset, anaerobic glycolysis begins in the affected brain area, i.e. Lac appears and its


21

normal values in repeated examinations (dynamic observation) is a favourable prognostic sign. The main metabolites' continued peak reduction combined with the appearance of the Lac peak indicates cell death in the ischaemic area. Another aspect of the use of MRS is differentiation of the primary and secondary lesions revealed in the initial infectious and demyelination processes. Results of infection diagnostics are the most indicative (Pronin et al. 2002). In an abscess spectrum, there is a peak of the Lip–Lac complex as well as peaks specific for abscess content, such as acetate and succinate (the products of anaerobic glycolysis of bacteria), and amino acids valine and leucine (proteolysis products) on a background of absent core metabolite peaks (Fig. 1.22).

1.6.3 Epilepsy Fig. 1.22 Proton spectrum from the central area of abscess (peaks of

metabolites revealed on the spectrum are marked)

level grows quickly, so the Lac peak is revealed in a spectra of acute and subacute ischaemic phases. Hypoxia leads not only to neurons’ dysfunction, but also to their death, which results in the decrease of neuronal mass in affected area. In the spectrum, it is reflected in the form of moderate reduction of the NAA peak. The behaviour of the Cho peak in the case of ischaemia is not so clear. Its decrease is observed in the majority of cases, but this peak increases in others. Possibly, in phases of acute and subacute ischaemia, the Cho peak increase could be related to damage of the integrity of myelin fibre membranes and release of metabolites. At later stages, the Cho concentration decreases, possibly caused by reduction of cell numbers due to their destruction, and accordingly, due to the reduction of total mass of cellular membranes containing Cho. The restoration of the main metabolite peak heights toward

Diagnosis of epilepsy includes numerous methods and examinations, and MRI is only one of them. At the same time, today MRI is the sole method that characterises anatomic changes in a targeted brain area, for example, in the case of medial temporal sclerosis or cortical dysplasia. MRS in such cases is an additional method of brain dysfunction detection since it reveals a decrease in the NAA peak and NAA–Cr ratio in the hippocampus and in an area of dysplastic changes in brain tissue.

1.6.4 Metabolic Disorders MRS is an informative method for estimation of metabolic damages and primitive lesions of white matter in children. Although MRS is not very specific in case of leukodystrophic and metabolic CNS damage, its results nevertheless narrow the pool of possible brain tissue diseases. The majority of the above-mentioned forms of brain damage lead to NAA peak decrease due to neuronal–axonal degeneration and brain tissue loss (Fig. 1.23). In the case of methochromatic leukodystrophy, MRS reveals the significant decrease of the NAA

Fig. 1.23a–c Leukodystrophy in a 6-year-old child. MRI in T2 (a) and T1 (b) reveals areas of pathological hyperintense MR signal of uneven

form behind the posterior horns of the left ventricles. MR spectrum from the pathological area demonstrates the decrease of the NAA peak and the increase of Cho and mI peaks (c)

22

Chapter 1

peak and moderate increase of the Lac peak. A decrease of the Glx peak and an increase of the mI peak are observed. In the case of Canavan’s disease, MRS detects increase of the ratio of NAA–Cho and NAA–Cr peaks. MRS is a useful method of the brain condition estimation in patients with adrenoleukodystrophy. In this case, MRS detects the marked decrease of NAA–Cr and NAA–Cho peak ratios, the increase of Cho–creatine ratio, and the rise of Glx, mI and Lip peaks in an area of maximal changes, revealed with the help of standard MRI. The MR spectral changes in several types of hyperglycaemia including with the increase of glutamine peak (3.55 ррm) are relatively specific.

1.7

Phosphorus MR Spectroscopy

Phosphorus (31Р ) MRS, which utilises resonant frequencies of phosphorus 31Р nucleus in various chemical compounds, is often performed on modern high-field MR scanners. The resonant frequency of 31Р is approximately 0.405 from resonant frequency of a hydrogen atom nucleus in water molecule. The main metabolites of phosphorus spectrum are: phosphomonoesters (PME); inorganic phosphate (Pi); phosphodiesters (PDE); phosphocreatine (PCr); and adenosine triphosphate (ATP), which has three peaks, α, β and γ, as each ATP molecule contains chemically variously three atoms of phosphorus. In Fig. 1.24, the phosphoric brain spectra of an adult with a normal brain (Fig. 1.24a) and patient with astrocytoma (Fig. 1.24b,c) are presented. In the normal brain, the highest central peak in a phosphoric spectrum is phosphocreatine (2.1 ppm). The PDE peak is the second highest, and it reflects the presence of lipid predecessors like phosphoryl Cho, phosphoryl ethanolamine and Lip. This peak is located to the left of the PCr peak, and then the Pi and PME peaks follow. The PME peak includes MR signals from phosphates of sugars: glucose6-phosphate, sucrose-6–phosphate, and hexose-6-phosphate, which partially overlap. To the right of the PCr peak there are three ATP peaks (γ, α and β). PCr and ATP play important

Fig. 1.24a–c Phosphorus MR spectra obtained in the magnetic field of 1.5 T. a 31Р spectrum of a normal adult brain. The main metabolites of the phosphorus spectrum are: phosphomonoesters (PME); inorganic phosphate (Pi) phosphodiesters (PDE); phosphocreatine

roles in brain tissue energy metabolism. Phosphorus spectra are quantitatively estimated according to the ratio of metabolite peak heights to αATP peak height. The homeostasis abnormality accompanied by the decrease of PCr and PDE peaks and increase of ATP peak is typical for tumour tissue (Maintz et al. 2002; Karsmar et al. 1991). Phosphoric spectra in patients with astrocytoma demonstrate visible decrease of PDE–αATP ratio in relation to normal spectra (Fig. 1.24). A meningioma phosphoric spectrum is often characterised by decrease of PCr–αАТР and PDE–αАТР (Maintz et al. 2002). A lymphoma spectrum shows substantial increase of the RME–αАТР ratio (Karsmar et al. 1991). According to some authors, radio- and chemotherapy leads to gradual restoration of the height of phosphoric spectrum peaks (Maintz et al. 2002; Karsmar et al. 1991), but this report requires additional investigations. Chemical shift between Pi and αATP peaks is used for the estimation of intercellular liquid acidity (pH), and the shift between Pi and PCr peaks for pH estimation in tumour tissue (Karsmar et al. 1991). According to Maintz et al. (2002), pH in brain tissue of an adult normally is 7.04 ± 0.01; in tumour tissue pH increases to 7.12 ± 0.02 in glioblastoma and to 7.16 ± 0.03 in meningioma. Changes of metabolite peak heights of the phosphoric spectrum are observed during brain development in children within first the 3 years of life (van der Knaap et al. 1990), in cases of degenerate diseases (van der Knaap et al. 1991), hydrocephaly (Braun et al. 1999), ataxia (Bluml et al. 2003) and creatinine deficiency syndrome (Bianchi et al. 2007). MR scanner adjustment (prescan) is often done manually, and 31Р MRS examination takes a long time. However, current work on the use of echo-planar pulse sequences for fast brain mapping based on 31Р MRS is being done (Ulrich et al. 2007). Fast mapping methods of products of phosphorus metabolism open the opportunities of visualisation of bioenergy changes during brain simulation, for example, the block stimulation in fMRI.

(PCr); and adenosine triphosphate (ATP), which has three peaks, α, β and γ. b T2-weighted image of a tumour. c 31Р spectrum of a patient with anaplastic astrocytoma, demonstrating the decrease of PDE–αATP peaks ratio


1.8

Neuroradiology and Information Technologies

As the volume of diagnostic information grows, network support and the use of specialised workstations for the expanded digital processing of examination data is becoming increasingly more necessary. Workstations and digital diagnostic devices use the same user interfaces, browser program for examination results, programs of СT and MRI data processing, and they are equipped with the programs for recording images on CD and other magnetic carriers which assures that the multimodal operations function well. The use of digital technologies in modern radiology is the standard for all developed countries, and it is taking root in Russia. The old film technologies of data presentation and storage of films are gradually become obsolete. The need for additional computer processing for obtaining more detailed information on the pathology in question is arising more often (Rodionov et al. 2002).

Fig. 1.25a–i 3D modelling based on CT and MRI for planning of neurosurgical intervention. a 3D superposition of 3D models of bones, brain vascular structures and tumour, with the use of CT (meningioma of posterior cranial fossa), b dural arteriovenous fistula of parietal region (CT angiography), c superposition of cortical surface and convex vein (based on MRI), d 3D superposition of bones, brain vascular structures and tumour (CТ angiography, volume ren-

23

Modern superfast spiral CT scanners and high-field MR scanners are constructed with the use of the newest technical achievements, modern hardware and the software. In diagnostically complex cases, after CT and MRI imaging, the neuroradiologist can continue to study the obtained data for making a diagnostic conclusion without the patient present. For this purpose, the diagnostic images can be digitally stored and transferred to a graphic computer station for the subsequent processing and analysis by a local network or by the Internet. Modern diagnostics requires additional postprocessing on special graphic computer stations equipped with powerful software packages with mathematical analysis and modelling, which can be performed, again, in the absence of the patient. Use of remote graphic stations for postprocessing is prompted by the necessity of 3D image construction, including the combined models of soft tissues of a head, skull, brain and its vascular system for neurosurgery intervention modelling (Fig. 1.25).

dering, petroclival meningioma), e 3D superposition of 3D models of the skin surface and tumour (falx meningioma), f 3D model of cervical part of vertebra (view from the internal surface of vertebral canal to the intervertebral foramens in the case of a removed section of vertebra in patient with spondylosis and intervertebral foramen compression at the C3–C4 level), g–i see next page

24

Chapter 1

Fig. 1.25a–i (continued) 3D modelling based on CT and MRI for planning of neurosurgical intervention. g 3D processing of volumerendered data of CT angiography of cervical vessels, h 3D process-

ing of CT data in patient with a fracture of a thoracic vertebra with dislocation, i 3D model of ventricular system in child with open hydrocephalus

The analysis of DTI (calculation of average and anisotropic diffusion speed, construction of parametrical maps of fibre tracing, and so forth), perfusion examinations (calculation of blood flow parameters, parametrical maps construction), and other such parameters, requires mathematical processing. As a rule, subsequent viewing of the obtained results, for example, in clinical conferences or directly in operation room of a surgical hospital, is also carried out on the graphic stations. The special unified data format Digital Imaging and Communications in Medicine (DICOM 3.0) developed by the American College of Radiology (ARC) and National Electrical Manufacturers Association (NEMA) is used for storage and transfer of medical images in modern radiology. In modern medical clinics, imaging results are often stored on

a short-term basis in the operative memory of the diagnostic device (CT, MRI, angiosystem) or in the operative memory of a graphic station. However, operative memory is limited and is not intended for the long-term data storage necessary in scientific work. As a rule, the archiving of examination results is necessary for long-term storage on any replaceable data carriers (for example, magneto-optical discs). Another variant is the use of Picture Archiving and Communication System (PACS), which requires the creation of special remote archives on servers in which rather large files can be stored for a long time in a “hot” state, and in this case, the interesting information is quickly accessible via network for search and viewing, and if necessary, for new data processing. The digital storage of medical data is more preferably in comparison with film archives. Films could be stored for about 10 years in cases of strict compliance with all storage rules, while digital archives could exist indefinitely. Images are accessible for repeated calculations and analysis, which is especially important in neuroradiology, due to frequent necessity of dynamic observation for the patient during long periods. Taking into account the high cost of film and significant expenses for service of photographic developing apparatus, it is no surprise that digital technologies of storage, transfer and representation of the medical information are increasingly coming into practice all over the world. The Neuroradiology Department of the Burdenko Neurosurgical Institute of Russian Academy of Medical Science developed a system to organise the information radiological system for obtaining, storage, transfer and postprocessing of diagnostic medical images. This system covers all diagnostic devices in the Neuroradiology Department. Moreover, it includes several graphic stations for viewing and postprocessing of medical images. The rooms equipped with digital diagnostic devices, and working and viewing graphic stations, have special connections to the network printers for image printing to film. Personal computers of scientific employees—engineers

Fig. 1.26 Schema of the computer radiological network for obtaining, storage, transmission and postprocessing of medical images in the Neuroradiology Department of Burdenko Institute of Neurosurgery


Fig. 1.27 Operating room with a navigational system for surgery

and researchers—located in the rooms of the Neuroradiology Department are connected to the network and equipped with the special software capable of working with DICOM images (Fig. 1.26). It is necessary to note that, for the past 10 years, the quantity amount of diagnostic examinations performed with use of digital methods has grown significantly, and image processing has become more complicated.

1.9

Navigation in Neurosurgery

Development of digital medical technologies, appearance of fast portable computers and successes in neuroradiology due to the advent of CTI and MRI paved the way for celebrated technological breakthroughs in stereotactic neurosurgery. This has led to development of modern navigating systems that enable surgeons to navigate quickly and precisely in the 3D space of a surgical incision during operation, with a 1- to 2-mm precision. Such systems allow surgeons to perform intervention with minimal injury to the surrounding tissues. Such systems use so-called frameless technology, unlike classical stereotaxis, which uses a frame-based navigating method. Navigation is based on “binding” of space coordinates to certain reference points that have static positions in geonavigating systems, e.g. stars or geodetic towers. Classical medical stereotactic devices use for these purposes a special frame fastened tightly to a patient’s skull before the operation. All further calculations are based on the mutual relation between intracranial structures and the reference points of a frame and its geometrical centre. Navigation of the surgical tool is made with the help of relatively large facilities such as various arches and guides fastened to a frame. Such technical decisions in classical stereotaxis limits the neurosurgeon’s actions in an incision and allows the carrying out of only simple manipulations (biopsy, implantation of electrode, catheter, cyst lancing).

25

The essence of frameless navigation is the following: Based on MRI and CT data, obtained before operation (as a rule, for 1–2 days), 3D images of the patient’s head are built with graphic station software. The surgeon, according to the 3D image, chooses accessible reference points (for example, a tip of a nose, teeth, curves of an auricle) on a surface of the patient’s head. Before the operation and after introduction of narcosis, the special small navigating frame [with a light-emitting diode (LED)], which, unlike classical stereotaxis, can be fixed practically any place on the head and in any way suitable for the given operation, is firmly fastened to the patient’s head at some distance from that area of interest. This frame, in the form of a partial arch, does not close the operational field and does not limit the surgeon in his or her actions. With the use of a special LED pointer, a preliminary “registration” is performed, i.e. the computer system “fuses” a 3D image of the patient’s head from its memory with real head position. All systems consist of the aerial receiver, LED pointer, reference arch and computer algorithm of work with the 3D image. This allows the neurosurgeon at any moment of operation to determine the position of his or her tool, with 1- to 2-mm precision, to plan an access trajectory, and to move toward the chosen target with the optimal and least invasive way (Fig. 1.27). Today, the optimal application for frameless navigation is the surgery of basal and small convex located tumours (Fig. 1.28) and for removal of foreign bodies from the skull cavity. Methods of combining CT, MRI and angiographic data into 3D models of the head (fusion algorithm) is especially advantageous in radiosurgery, allowing minimisation of pathological areas, with a 0.1-mm precision during the targeting of radiation to brain tissues (Fig. 1.29).

Fig. 1.28 Monitor of a workstation during preparation of removal of a brain tumour

26

Chapter 1

Fig. 1.29a,b Radiosurgical equipment. a Gamma knife device in the Burdenko Institute of Neurosurgery, b schema of target calculation (in

the planning stage) according to CT and MRI data

Refere n c e s 1. Alsop D, Detre J (1996) Reduced transit time sensitivity in noninvasive magnetic resonance imaging of human cerebral blood flow. J Cereb Blood Metab 16:1236–1249

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2. Aroutiunov A, Kornienko V (1971) Total cerebral angiography. Medicine Publishers, Moscow, p 167 (in Russian)

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3. Batchelor P et al (2006) Quantification of the shape of fibre tracts. Magn Reson Med 55:896–903

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4. Bianchi M et al (2007) Treatment monitoring of brain creatine deficiency syndromes: a 1H- and 31P MR spectroscopy study. AJNR Am J Neuroradiol 28:548–554 5. Bluml S et al (2003) Membrane phospholipids and high-energy metabolites in childhood ataxia with CNS hypomyelination. Neurology 61:648–654 6. Braun K et al (1999) Cerebral metabolism in experimental hydrocephalus: an in vivo 1H and 31P magnetic resonance spectroscopy study. J Neurosurg 91:660668

17. Knaap M van der et al (1992) 1H and 31P magnetic resonance spectroscopy of the brain in degenerative cerebral disorders. Ann Neurol 31:202–211 18. Konovalov A, Kornienko V (1985) Computed tomography in neurosurgical clinic. Moscow Medicine Publishers, Moscow, p 290 (in Russian) 19. Konovalov A, Kornienko V, Ozerova V, Pronin I (2001) Neuroimaging in paediatrics. Antidor, Moscow. p 435 (in Russian)

7. Cha S (2006) Update on brain tumour imaging: from anatomy to physiology. AJNR Am J Neuroradiol 27:475–487

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9. Chai J-W et al (2007) Characterisation of focal brain lesions by gradient-echo arterial spine-tagging perfusion imaging. Neuroradiol J 20:149–158 10. Chepuri N, Yen Yi-Fen, Burdette J (2002) Diffusion anisotropy in the corpus callosum. AJNR Am J Neuroradiol 3:803–808 11. Feoktistov V (1938) The theory of tomography. Vestn Roentgenol Radiol 21:143–152 (in Russian) 12. Hesseltine S et al (2007) Application of diffusion tensor imaging and fibre tractography. Appl Radiol 1:8–23 13. Holshouser B et al (2006) Prospective longitudinal proton magnetic resonance spectroscopic imaging in adult traumatic brain injury. J Magn Reson Imaging 24:33–40

22. Kornienko V, Pronin I, Golanov A et al (2004) Neuroimaging of primary lymphomas of brain. J Med. Visualis 1:6–15 (in Russian) 23. Kornienko V, Pronin I, Pyanykh O et al (2007) Study of brain perfusion, using CT. J Med. Visualis 2:70–81. 24. Le Bihan D, Breton E (1985) Imagerie de diffusion invivo par resonance magnetique nucleaire. CR Acad Sc II Paris 301:1109–1112 25. Le Bihan D, Turner R (1991) Intravoxel incoherent motion imaging using spin echoes. Magn Reson Med 19:221–227 26. Le Bihan D, P van Zijl (2002) From the diffusion coefficient to the diffusion tensor. NMR Biomed 15:431–434 27. Lee S-K et al (2005) Diffusion-tensor MR imaging and fibre tractography: a new method of describing aberrant fibre connection in developmental CNS anomalies. Radiographics 25:53–68


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33. Mulkern R, Gudbjartsson H, Westin C еt al (1999) Multicomponent apparent diffusion coefficients in human brain. NMR Biomed 12:51–62

46. Stadlbauer A et al (2007) Changes in fibre integrity, diffusivity, and metabolism of the pyramidal tract adjacent to gliomas: a quantitative diffusion tensor fibre tracking and MR spectroscopic imaging study. AJNR Am J Neuroradiol 28:462–469

34. Nennig E et al (2007) Functional magnetic resonance imaging for cranial neuronavigation: methods for automated and standardised data processing and management. Neuroradiol J 20:159–158 35. O’Donnell L-J et al (2006) A method for clustering white matter fiber tracts. Neuroradiol J 27:1032–1036 36. Pierpaoli C, Jezzard P, Basser PJ et al (1996) Diffusion tensor MR imaging of the human brain. Radiology 201:637–648 37. Podoprigora A, Pronin I, Fadeeva L et al (2003) Proton MR spectroscopy in ischaemic brain disease. ZH Neurol Psikhiatr SS Korsakova 9(Suppl.):162 (in Russian) 38. Pouratian N, Sheth S, Bookheimer S et al (2003) Applications and limitations of perfusion-dependent functional brain mapping for neurosurgical guidance. Neurosurg Focus 15:1 39. Pronin I, Kornienko V, Podoprigora A et al (2002) Complex MR imaging of brain abscesses. J Vopr Neurochir 1:7–11 (in Russian) 40. Ramsey N, Hoogduin H, Jansma J (2002) Functional MRI experiments: acquisition, analysis, and interpretation of data. Eur Neuropsychopharmacol 12:517–526

47. Sunaert S (2006) Presurgical planning for tumour resectioning. J Magn Reson Imaging 23:887–905 48. Tanner J (1970) Use of stimulated echo in NMR diffusion studies. J Chem Phys 52:2523–2526 49. Ting-Yim L (2002) Functional CT: physiological models. Trends Biotechnol 20:1–8 50. Ulrich M et al (2007) 31P-1H echo planar spectroscopic imaging of human brain in vivo. Magn Reson Med 57:784–790 51. Ureniak J et al (1992) Specific expression of N-acetylaspartate in neurons, oligodendrocyte type-2 astrocyte progenitors, and immature oligodendrocytes in vitro. J Neurochem 59:55–61 52. Waaijer A et al (2007) Reproducibility of quantitative CNS brain perfusion measurements in patients with symptomatic unilateral carotid artery stenosis. AJNR Am J Neuroradiol 28:927–932 53. Zavoisky EK (1945) Spin-magnetic resonance in paramagnetics. J Phys Acad Sci USSR 9:211–245 (in Russian)

Chapter 2

2

Congenital Malformations of the Brain and Skull

in collaboration with V. Ozerova

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9

Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . Organogenesis Impairment .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impairment of Brain Diverticulation .. . . . . . . . . . . . . . . . . . . . . . . . . Impairment of Gyri and Sulci Formation .. . . . . . . . . . . . . . . . . . . . . Changes in Brain Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Destructive Brain Lesions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Histogenesis Impairment .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Arachnoid Cysts .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Congenital Anterior Cranial Malformations . . . . . . . . . . . . . .. . . .

2.1

Introduction

29 29 41 46 53 53 60 69 80

Congenital brain malformations occur as a result of embryogenesis impairment and present as an anatomic defect or destructive brain lesion (Arendt 1968; Barkovich 2000; DeMyer 1971; Glenn and Barkovich 2006; Harwood-Nash et al. 1976; Polianker et al 1965; van der Knaap et al. 2006). It is very difficult to make a diagnosis of congenital brain malformation, based on clinical findings, and use of CT and MRI is essential in these cases. A child may have numerous brain malformations, frequently accompanied by congenital abnormalities of other organs and systems due to chromosomal balance impairment or noxious exposures during embryogenesis. Exogenous factors as well as hypoxia cause developmental defects of neural tissue, and focal and diffuse brain damage. CT and MRI allow distinguishing of changes that have occurred due to chromosomal abnormalities and due to noxious exogenous factors. There are several classifications of congenital brain malformations (DeMyer 1971; van der Knapp et al. 1988; Kornienko et al. 1993); however, there is a lack of united classification based on aetiology, pathogenesis and clinical findings at present. According to the Burdenko Institute of Neurosurgery of Russian Academy of Medical Sciences data, 22.6% children with hydrocephalus have brain malformations (nearly one in every fifth child), and 11.8% have numerous malformations.

2.2

Organogenesis Impairment

2.2.1 Impairment of Neural Tube Closure 2.2.1.1

Chiari Malformation Type I

Chiari malformation (Chiari type I) is caudal displacement of the cerebellar tonsils via the foramen magnum into the vertebral channel. In healthy children aged 5–15 years, the cerebellar tonsil are located a bit lower than in children aged 5 years and younger (and in adults). Hence, cerebellar tonsil displacement up to 5 mm below the foramen magnum in children aged 5–15 years should not be regarded abnormal (Altman et al. 1992; Barkovich 2000; Harwood-Nash et al. 1976; Kornienko et al. 1993). This malformation is more frequently isolated, but concomitants hydrocephalus and hydromyelia, craniocervical dysgenesia, platibasia, basilar impression, occipitalisation of the atlas and Klippel-Feil malformation are not infrequent in these patients (Barkovich 2000). Patients have the following clinical features: occipital headaches, cranial nerve palsies, and dissociated anaesthesia in limbs (due to hydromyelia). Precise diagnosis of Chiari type I malformation is possible only with MRI, which detects low positioning of cerebellar tonsils in relation to the foramen magnum (Fig. 2.1). Vertebral angiography reveals an indirect sign of this pathology: lowering of the caudal loop of the posterior inferior cerebellar artery into the vertebral channel, sometimes up to the С4 level. One should be more astute in suspicion of Chiari type I malformation if a patient has several of the above-listed signs. Such patients should undergo cervical spine MRI to exclude syringomyelia (present in 20–25% of cases).

2.2.1.2

Chiari Malformation Type II

Chiari malformation type II (Chiari type II) is a complex of malformations of the hindbrain, vertebral column and supratentorial structures. Almost all patients with Chiari type II have congenital myelomeningocele. According to

30

Chapter 2 Fig. 2.1a,b Chiari I malformation in a

5-year-old child. а MRI: the cerebellar tonsils are lowered down to С2, b Vertebral angiography: the caudal loop of the posterior inferior cerebellar artery is down to the vertebral canal below С2

Fig. 2.2a–f Chiari II malformation. Case 1: a 9-year-old child. CT (а,b) after a shunting operation. Transverse banding of cerebellar structures is visualised in the enlarged aperture of incisura tentorii; the tectum is elongated, and the massa intermedia is enlarged. Case 2: a 4-month-old child. MRI (с,d): The posterior surface pyramids of the os temporal is concave, cerebellar hemispheres extend anteriorly

and laterally to the pons, the fourth ventricle is small and the third and lateral ventricles are enlarged. There is breaking of the tectum on the image, the fourth ventricle is narrow and extends down into the foramen magnum and there is a cervicomedullary kink at the C2 level (e). PSIF (f): there is no CSF flow into the spinal canal


our data, Chiari type II is found in 0.1% of children with hydrocephalus. X-ray diagnosis of Chiari type II malformation is based on a group of different diagnostic procedures. Cranial X-ray reveals several manifestations of this malformation: holes on the most apical points of cranial vault bones, low placement of the inion, the more inferior attachment of tentorium cerebelli and very shallow posterior fossa, signs of hydrocephalus, enlargement of the foramen magnum, lumbar meningocele and spina bifida. Changes in the location of skull-base brain cisterns, ventricles and the aqueduct were detected before the CT era by ventriculography and myelography, using air or Xray-positive contrast media. These changes include changes in the location of tonsils and medulla in relation to the foramen magnum, elongations and/or ectopy of the fourth ventricle, Sylvian aqueduct narrowing or deformity, enlargement of the third and the lateral ventricles, and thickening of massa intermedia. Cerebral angiography is less informative. It only detects the extent of hydrocephalus, lower location of posterior inferior cerebral artery, and the confluens sinuum. CT and MRI can detail the intrusion of posterior fossa structures into the enlarged tentorium cerebelli foramen, displacement, deformity of the brainstem. Incorrect location of posterior fossa structures may be revealed on CT in children after a shunting operation for hydrocephalus, because enlarged ventricles mask impaired development of the tentorium cerebelli and pathological displacement of brain structures. After surgery due to regression of hydrocephalus, the enlarged foramen of the tentorium cerebelli is much better distinguished, as well as a beak-shaped tectum and lifted cerebellar vermis with transverse folds. The most complete picture of Chiari type II syndrome is obtained on МRI: enlargement of foramen magnum, and low placement of the tentorium cerebelli and brainstem. (The pons is usually narrowed in anteroposterior direction, and the medulla is elongated and sunk into the vertebral canal; Altman et al. 1992; Harwood-Nash et al. 1976; Kornienko et al. 1993; Naidich et al. 1983.) If the medulla is sunk below the dentate ligament, then the spinal cord is also lowered and forms a characteristic “knee” (Fig. 2.2). The fourth ventricle is narrowed, lowered and sometimes enlarged. The inferior and posterior elongated lamina tecti has a beak-like shape. In 80–90% of cases, dysgenesia of corpus callosum is revealed (hypoplasia or splenium agenesia, rostrum agenesia) along with extension of the massa intermedia.

2.2.1.3

Chiari Malformation Type III

Chiari Malformation type III is a very rare abnormality. The posterior fossa contains herniations (of the cerebellum and sometimes the brainstem) through a posterior spina bifida at the С1–С2 level (Barkovich 2000).

31

2.2.2 Cephaloceles (Craniocephalic Herniations) These abnormalities in impairment of neural tube closure present by way of developmental defect of the cranial bones and dura mater, with extracranial extension of brain structures (Delvert et al. 1982; Naidich et al. 1992; Polianker et al. 1965; Yokota et al. 1986). Based on the contents of a herniation, several types of craniocephalic herniations are distinguished: • Meningocele: isolated herniation of dura mater and CSF • Meningoencephalocele: herniation of dura mater, CSF and brain structures • Encephalon cystocele; meningoencephalocele contains a portion of the ventricular system • Atretic cephalocele: a tethered herniation containing dura mater, fibrous tissue and degeneratively changed brain structures • Gliocele: a glial cyst containing CSF Herniations are usually distinguished according to the location of the cranial bones through which they prolapse (Polianker et al. 1965; Naidich et al. 1992; Barkovich 2000): • Occipital • Of the cranial vault –– Interfrontal –– Of the anterior fonticulus –– Interparietal –– Of the posterior fonticulus –– Temporal • Frontobasilar –– Frontonasal –– Fronto-ethmoid (sincipital) –– Nasofrontal –– Naso-ethmoidal –– Naso-orbital • Basilar –– Trans-ethmoidal –– Spheno-ethmoidal –– Trans-sphenoidal –– Frontosphenoidal –– Spheno-orbital • Cranioschisis –– Cranial: superior facial fissure –– Basilar: inferior facial fissure –– Cervico-occipital fissure In occipital and cranial vault herniations, cranial bone junctions and fonticuli are the gates for herniation (Figs. 2.3, 2.4, 2.5). Frontobasilar herniations protrude through embryologically weak cranial regions. Frontonasal herniations protrude through the nasofrontal fonticulus, upper tip of nasal bones membrane, frontal bone and cartilage capsule (Fig. 2.6). Naso-ethmoid herniations protrude through the foramen cecum of the frontal bone (where the frontal and ethmoidal bones meet) into the nasal cavity (Fig. 2.7).

32

Chapter 2

Fig. 2.3a–c Occipital herniation. Case 1 (a): X-ray craniogram of an 8-day-old child. A finger-shaped defect in the squamous part of occipital bone confluent with the foramen magnum is seen along with

a soft tissue mass. Case 2 (b,c): 7-day-old child. The CT image shows a defect in the squamous part of occipital bone. Brain parenchyma, meninges and CSF cysts are present in the herniation

Fig. 2.4a–f Occipital herniation (meningoencephalocystocele) of an 18-day-old child. CT with 3D reconstruction: general appearance of head with occipital herniation (a). Axial FLAIR image MRI: defect in the squamous part of occipital bone, brain parenchyma with cystic cavities, and meninges are present the herniation (b). Sagittal Т2-weighted image (c) and fluid-attenuated inversion-recovery (FLAIR) image (d): posterior dislocation and traction of midbrain

and posterior fossa structures into a herniation, brainstem deformity with lowering downwards into foramen magnum, dilation of the interpeduncular cistern, ectopy of the fourth ventricle, and the third and the lateral ventricles are dilated with hydrocephalus. CTVG (e,f): contrast medium filling of the dilated third and the lateral ventricles, elongated Sylvian aqueduct, the fourth ventricle with ectopy


33

Fig. 2.5a–h Interparietal herniation (meningocele) in 5-month-old child. T1-weighted image (a–d), MR-venography (e,f) and CT with 3D reconstruction (g,h). There is a herniation of dura mater along with medially positioned bone defect in the posterior parietal region. The superior sagittal sinus is duplicated at the site of herniation

34

Chapter 2 Fig. 2.6a,b Frontonasal meningocele in a

3.5-year-old child. CT images (а,b)

Fig. 2.7a–c Naso-ethmoid herniation in an 8-month-old child. CT in sagittal and coronal planes (a,b) and CT with 3D reconstruction (c): internal surface of skull base

Fig. 2.8a–c Trans-ethmoid meningocele in a 1.5-year-old child. CT images (а–c)


35 Fig. 2.9a,b Trans-sphenoidal meningocele

in a 9-month-old child. a CT shows round defect in the body of the sphenoid bone. b Coronal CT shows soft-tissue herniation adjacent to the body of sphenoid bone, seen on a background of air in nasopharynx

Fig. 2.10a–c Leftward spheno-orbital herniation in a 2-month-old child. CT (а,b) and X-ray craniogram (c)

Naso-orbital herniations protrude through frontal, ethmoidal and lacrimal bones, and appear on the anterior and internal portions of orbits near the internal angle of the eye fissure. Basilar herniations protrude through the ethmoid or sphenoid bones. Trans-ethmoidal herniations perforate sieve-like lamina and prolapse into the anterior portion of the nasal cavity (Fig. 2.8). Spheno-ethmoidal herniations penetrate via the junction of the ethmoid and sphenoid bones and appear in the posterior portion of nasal cavity and nasopharynx. In trans-sphenoidal herniations, the cranial defect is located at the bottom of sella turcica or within the body of sphenoid bone. Herniation masses may be preserved in the sphenoid sinus or protrude into the nasopharynx (Fig. 2.9). Spheno-orbital herniations (of posterior orbital location) may have different gates. Herniation masses may protrude through the superior orbital (sphenoidal) fissure, optic nerve channel, or congenital abnormal fissure of the sphenoid bone, or through the sphenoid and frontal bones. Herniation mass-

es located near the apical part of the orbit cause unilateral exophthalmus (Figs. 2.10, 2.11). If CT or MRI are not available, then X-ray or linear cranial tomography may be used to detect herniation gates. However, 3D MRI or CT reconstruction allow detection of internal as well as external rings of herniation and intracerebral relationships of tissues including the arteriovenous system. Additionally performed CT or MR ventriculography aids in ascertaining how the contents of herniation communicate with the CSF space.

2.2.3 Agenesia of the Corpus Callosum Formation of corpus callosum, septum pellucidum and fornix begins at the 11th and terminates at the 16th week of intrauterine life, and so the extent of corpus callosum defects depends on the stage of fetal development at which corpus callosum development terminates. Primary agenesia occurs in the 12th week of fetal life as a consequence of vascular or inflammatory damage of commissural lamina and may be isolated

36

Chapter 2

Fig. 2.11a–c Leftward spheno-orbital herniation (meningocele) in a 14-month-old child. CT (а,b) and МRI (c)

or concomitant with other malformations, such as agenesia of septum pellucidum or holoprocencephaly. Secondary dysgenesia—complete or partial destruction of corpus callosum—is a result of encephalomalacia and occurs after completion of corpus callosum development in traumatic and toxic lesions, and anoxia in the anterior cerebral artery territory. Agenesia of corpus callosum prevalence, according to our data, is encountered in 2.9% of children with hydrocephalus, but only in 0.8% of them is it “pure”, and in the rest of cases, other brain malformations accompany it. Agenesia of corpus callosum has no characteristic clinical picture, and neurological signs are frequently caused by concomitant cerebral diseases (Arendt 1968; Castillo et al. 2000; Harwood-Nash et al. 1976; Kornienko et al. 1993). There are no X-ray craniography signs of this pathology. If

it coincides with other developmental abnormalities of brain and skull, then signs of the latter may predominate. CT semiotics of agenesia of corpus callosum presents as follows: widely expanded anterior horns of the lateral ventricles, and upward position of the third ventricle between them, medial walls of the lateral ventricles become oriented in parallel to each other, and the posterior horns are usually dilated (Fig. 2.12). MRI performed in three planes gives the most complete information about the extent of corpus callosum developmental defects: partial (hypogenesia), complete (agenesia), or partial developmental defect (dysgenesia) (Figs. 2.13, 2.14). Median sagittal slices are the most informative, as they allow distinguishing of the formation of all regions of corpus callosum— rostrum, genu, body, and splenium. Agenesia (hypogenesia)

Fig. 2.12a–c Agenesia of corpus callosum in a 1-year-old child. CT (а–c) images: the third ventricle is located upwards, between the sepa-

rated and moderately dilated lateral ventricles, and corpus callosum is not visualised


37

Fig. 2.13a–d Agenesia of the corpus callosum in a 1-year-old child. Т1- and Т2-weighted images in three planes (а–d). The corpus callosum is not visualised, and the lateral ventricles are asymmetrical and widely separated

Fig. 2.14a–c Marked hypogenesia of corpus callosum in a 3.5-year-old child. MRI in three planes (а–c): a part of genu of corpus callosum is

seen, the lateral ventricles are separated and their posterior portions are dilated

38

Chapter 2

Fig. 2.15a–c Lipoma of the genu of corpus callosum in a 4-year-old child. CT (а–c): round hypodense mass (–110 HU) with peripheral

calcinations Fig. 2.16a,b Pericallosal lipoma in a

6-year-old child. T1-weighted image in sagittal (а) and coronal (b) planes: a nutshelllike lipoma with a typical hyperintense signal is located above the body of corpus callosum, clear-cutting its splenium

Fig. 2.17a,b Pericallosal lipoma in a 6-year-old child. Т1-weighted image in sagittal (а) and T2-weighted image in axial (b) planes. At the site of hypogenesia of corpus callosum, there is a horseshoe-like mass with hyperintense signal typical for lipoma


39

Fig. 2.18a–b Lipoma of the quadrigeminal cistern. T1-weighted image in three planes (а–c): irregular-shaped mass with hyperintense signal located between the lamina tecti and the upper portion of the vermis

of the corpus callosum frequently accompanies the absence or hypoplasia of hippocampus, amygdala, heterotopia of grey matter or other brain malformations (Castillo et al. 2000; Glenn and Barkovich 2006). Lipoma of the corpus callosum always accompanies hypo, dys- or agenesia of the corpus callosum, although it is an intrahemispheric formation located near corpus callosum. X-ray craniograms may be useful in cases of giant interhemispheric lipomas with peripheral petrificates. On CT, lipoma is detected as a clear-cut hypodense lesion. Lipoma has even and clear borders, is calcinated in some places, and its CT density is significantly lower than that of CSF [–80 to -110 Hounsfield units (HU)] (Fig. 2.15). On MRI, lipoma appears as a structure of different shape and size, markedly hyperintense on Т1-weighted images. It may be located in any part of corpus callosum—above or below, or near the splenium, body or genu (Figs. 2.16–2.18). Giant lipomas are characterised by chemical shift artefacts due to differences in magnetisation characteristics of water protons and fat tissue.

2.2.4 Dandy-Walker Malformation This malformation is a cystic dilatation of the fourth ventricle, combined with agenesia of cerebellar vermis, upward location of tentorium cerebelli and hydrocephalus (Altman et al. 1992; Fitz 1983; Harwood-Nash et al. 1976; Irger 1981).

2.2.4.1

Dandy-Walker Malformation Type I

Dandy-Walker malformation type I (a true Dandy-Walker cyst) is a cystic dilatation of the fourth ventricle, with absence of Magendie and Luschka foramens, partial or complete agenesia of cerebellar vermis and upward location of tentorium cerebelli and hydrocephalus. Connection between the fourth ventricle and perimedullary space is absent. This malforma-

tion results from the abnormality of rhombencephalic vesicle cover and adjacent meningeal structures, which develop between the 7th and the 10th weeks of embryonic life. From the embryological point of view, the fourth ventricle cyst in true Dandy-Walker malformation is locked or half-locked. External foramina of the fourth ventricle are usually absent, but one of them may be preserved, as well as the connection with the third ventricle.

2.2.4.2

Dandy-Walker Malformation Type II

Dandy-Walker malformation type II is a partial agenesia of cerebellar vermis due to posterior dilatation of the tela chorioidea backwards and above the vermal rudiment. The connection between the fourth ventricle, perimedullary and subarachnoid space is retained. According to McLaurin (in 1985), in 65% of cases, DandyWalker malformation may be combined with other developmental CNS abnormalities: polymicrogyria, cerebral and cerebellar hemispheres heterotopia, incorrect brainstem position as well as developmental abnormalities in other organs and systems (polydactyly, syndactyly, congenital cardiac defects, cleft palate, and so forth). To our knowledge, classic Dandy-Walker cysts are found in 6.4% of children with occlusion hydrocephalus. Clinical signs of this malformation are presented in general with signs of hypertensive hydrocephalus and symptoms of posterior fossa involvement: gait and static disturbances, nystagmus and others. Progressive course of hydrocephalus is usually observed at birth or soon thereafter. Craniographic features are scanty. Predominantly, they are the signs of hypertensive hydrocephalus. Enlargement of posterior fossa is revealed by upward location of the transverse sinus. Sometimes posterior protrusion of occipital bone within the lambdoid suture is found, which is easily palpated during examination of a child.

40

Chapter 2

Fig. 2.19a–c Dandy-Walker malformation in a 4-month-old child. CT (а–c): the fourth ventricle is widely connected with a CSF cyst that almost totally occupies the enlarged posterior fossa, the vermis of cerebellum is absent, cerebellar hemispheres are hypoplastic, and the third and the lateral ventricles are markedly dilated

Fig. 2.20a–c Dandy-Walker malformation in a 3-month-old child. MRI (а–c) brainstem, vermis and cerebellar hemispheres hypoplasia. A

CSF cyst occupies the enlarged posterior fossa, the tentorium cerebelli is located upwards, and the third and the lateral ventricles are markedly dilated

CT and MRI reveal a characteristic picture: cystic dilatation of the fourth ventricle, which fills all the posterior fossa; the vermis is not seen or has marked hypoplasia; the cerebellar hemispheres have slid apart and decreased in volume, tentorium cerebelli is located upwards, and the third and lateral ventricles are hydrocephalically dilated (Figs. 2.19, 2.20). Communication of the subarachnoid space with the cystic dilated fourth ventricle may be detected by CT cisternography. In the absence of connection, contrast medium fills posterior fossa cisterns and chiasmal cisterns, but not the fourth ventricle. To detect connection between the fourth and the third ventricles, CT ventriculography is indicated. It may reveal intrusion of some contrast medium into the cystic dilata-

tion of the fourth ventricle (Fig. 2.21). MRI PSIF [a reversed form of fast imaging with steady state precession (FISP)] may also detect the CSF flow into the fourth and the third ventricles and further into cisterna magna, if the signal of CSF flow is absent.

2.2.5 Variant of Dandy-Walker Syndrome This malformation—according to our data—presents in 3.5% of cases among all children with hydrocephalus and 6.2% of children with open hydrocephalus. Clinical features of hydrocephalus are usually the manifesting signs. CT and MRI


41

Fig. 2.21a–c Dandy-Walker malformation in an 18-month-old child. а CT, b,c CTVG. A contrast medium introduced into the lateral ven-

tricle filled both lateral and the third ventricles, partially reaching the cyst-like dilated fourth ventricle (its density was increased to compare with native CT scans)

Fig. 2.22a–c Variety of Dandy-Walker malformation in an 8-monthold child. Т2-weighted image (а) and Т1-weighted image (b): hypoplasia of vermis, cerebellar hemispheres and brainstem; the fourth ventricle is widely connected with the CSF cyst in posterior fossa.

PSIF (c): the effect of flow void from excessive CSF movement in the Sylvian aqueduct, within the enlarged cisterna magna and craniovertebral junction

reveal wide communication between the fourth ventricle and cisterna magna. The cistern magna is enlarged in size; vermis and cerebellar hemispheres are hypoplastic to various extents (Fig. 2.22). The lateral and the third ventricles are hydrocephalic, and the extent of their dilation varies from mild to severe with periventricular oedema. To judge whether a connection between this CSF cyst and the ventricular system exists, and to distinguish it from a retrocerebellar arachnoid cyst, CT ventriculography, CT cisternography or MRI PSIF are indicated. This detects communication between the ventricular system and subarachnoid space of the spinal cord (Fig. 2.23).

2.3

Impairment of Brain Diverticulation

2.3.1 Holoprosencephaly The term holoprosencephaly was coined by W. Demyer and W. Zeman in 1960 to define a group of malformations in which the prosencephalon tends to remain as a whole, combined with facial malformations. Holoprosencephaly is a defect of separation of the primary brain vesicle, not completely transformed to di- and telencephalon by the fifth week of embryonic life. The etiological factors of holoprosencephaly are radiation exposure in the first half of pregnancy and chromosomal abnormalities (trisomies of chromosomes 16

42

Fig. 2.23a–f Variety of Dandy-Walker malformation and progressive

Chapter 2

open internal hydrocephalus in a 2-year-old child. CТ (а–c), CTVG (d–f): 10 min after CM injection into the right lateral ventricle, all

portions of ventricular system were enhanced to identical extents, as well as the CSF cyst in posterior fossa. Contrast failed to reach the area of periventricular oedema

and 18, Down’s syndrome, and so forth). This malformation is frequently combined with developmental defects of medial facial bones, and absence of olfactory bulbs, corpus callosum and falx cerebri. Holoprosencephaly may be alobar, semilobar or lobar (Fitz 1983; Harwood-Nash et al. 1976; Manelfe and Sevely 1982; Polianker et al. 1965; Smirniotopoulos et al. 1992) Alobar and semilobar are the most severe forms. According to our data, holoprosencephaly presents in 0.9% of cases among children with hydrocephalus. Clinical signs of hydrocephalus depend on the extent of brain damage. The alobar form has poor prognosis and cannot be treated surgically or pharmacologically. The brain is markedly reduced in size and contains a single large cavity with a dorsal sack instead of the third and the lateral ventricles, thalami are

united, and olfactory bulbs and tracts, corpus callosum and falx cerebri are absent (Fig. 2.24). Facial malformations are the obligatory component. They may appear as cyclopia, etmo- or cebocephalia and/or median or paired cleft palate. In all these facial malformations, hypo- or aplasia of medial facial bones (nasal bones, vomer) and skull (crista galli, sphenoid bone) are present. In semilobar holoprosencephaly, the brain is also small, with rudiments of occipital lobes, sole ventricular cavity and maldeveloped falx cerebri. Interhemispheric fissures are present in the anterior or posterior portions, the corpus callosum may be completely or partially absent, the thalami and basal ganglia are united, and olfactory bulbs and tracts are usually absent. Facial malformations are infrequent. Usually, they ap-


43

Fig. 2.24a–c Alobar holoprosencephaly. CT [according to Manelfe and Sevely (1992)]: а Posterior fossa structures are not changed. b,c The supratentorial space is occupied by the giant cavity, represented by a single ventricle and a dorsal sack. Basal ganglia and thalami are confluent, and the interhemispheric fissure is absent

Fig. 2.25a–c Semilobar holoprosencephaly in a 7-year-old child. CТ: the third and the lateral ventricles form a single cavity; large falx cerebri is visualised only in the anterior and posterior portions of the interhemispheric fissure

pear as cleft palate and orbital hypotelorism; true hypertelorism is rarely seen. CT and MRI reveal the sole cavity (but it is smaller than in the alobar form) and part of the falx cerebri (Figs. 2.25, 2.26). As corpus callosum is completely or partially absent, the dorsal sack rises upwards and forms the interhemispheric cyst. This cyst was termed diencephalic by G. Brocklechurst in 1973; later in 1979, F. Probst called it a primary interhemispheric cyst, distinguishing it from the secondary interhemispheric cyst found in agenesia of the corpus callosum, in which falx cerebri produces invagination in the third ventricle cover. The interhemispheric cyst may pass beyond the cranial vault borders, forming a herniation. To confirm a diencephalic cyst, CT ventriculography is indicated (Fig. 2.27).

The mildest form of holoprosencephaly is lobar. According to our data, lobar holoprosencephaly is found in children with open hydrocephalus, the signs of which were detected on X-ray craniograms. On CT, brain hemispheres are separated except for the anterior portions, the lateral ventricles are united, the septum pellucidum is absent, the inferior and posterior horns are well presented and the corpus callosum is absent (Fig. 2.28). Lobar holoprosencephaly is hard to distinguish from congenital agenesia of septum pellucidum or its rupture in severe hydrocephalus. The Y-shaped appearance of the third ventricle and marked flattening of the cover of anterior horns of the lateral ventricles are distinguishing features of holoprosencephaly.

44

Chapter 2

Fig. 2.26a–h Semilobar holoprosencephaly in a 4-year-old child. a,b CТ series of slices. c–h МRI in three planes: in the anterior and medial portions, hemispheres are not separated; the longitudinal fissure is visible only in the posterior portion. Only the splenium of corpus callosum is present


Fig. 2.27a–f Semilobar holoprosencephaly in an 11-month-old child. CТ (а,b) and МRI (c): a single ventricular cavity is located medially; the dorsal sack goes upward into the interhemispheric fissure, form-

45

ing a cyst, and then goes beyond the borders of skull via a bony defect having a herniation appearance. CTVG (d–f): CM infused into a herniation sack reached the ventricular system via the dorsal sack

46

Chapter 2

Fig. 2.28a,b Lobar holoprosencephaly in a 5-year-old child. CТ images (a,b): posterior fossa structures are not changed. The ventricular cavity is divided into the third and the lateral ventricles, septum pel-

lucidum is absent, there is hypoplasia of corpus callosum (only its posterior portion is seen) and the posterior third of the interhemispheric fissure is not visible

2.3.2 Septo-Optic Dysplasia

and, therefore, are more marked in children with complete lissencephaly. Microcephaly and muscle hypotonia are typical for complete lissencephaly. Infantile spasms are frequent. Refractory epilepsy develops in the early age. The majority of patients have regions of agyria and pachygyria—the former are frequently found in parieto-occipital regions, the latter in frontal and temporal regions. CT and MRI reveal these changes: the brain surface is weakly striated, has a smoothened picture of grey and white matter, and vertically oriented Sylvian fissures, which gives the whole brain a figure-8 appearance. The thin external layer of cortex is separated from the thicker deep cortical layer by a zone of white mater (the “zone of disseminated cells”), which seems normally myelinated. It is suggested that the internal layer is represented by young neurons, the migration of which was delayed. This appearance resembles a brain in the 23rd to 24th weeks of development, when sulci start to form (Barkovich 2000). Cases of severe agyria may be combined with hypogenesia of corpus callosum, dilatation of posterior horns of the lateral ventricles and brainstem hypoplasia (Figs. 2.31, 2.32). Pachygyria regions are also represented by thickened cortex, but wide sulci and small gyri are present. In focal pachygyria, the changes may be detected in any area of the brain, and in diffuse pachygyria, which is frequently combined with agyria. Predominating changes are found in the parieto-occipital regions.

Septo-optic dysplasia is a hypoplasia of optic nerves, combined with hypoplasia or absence of the septum pellucidum. It is thought that septo-optic dysplasia is a result of different genetic abnormalities and intrauterine ischaemic events during the first two trimesters of pregnancy. Clinical features of this syndrome are variable and depend on the degree of vision impairment and presence of pituitary–hypothalamic dysfunction, which are seen in two thirds of cases. Diagnosis is confirmed by optic discs hypoplasia, absence of the septum pellucidum and optic nerves atrophy detection on CT and MRI (Fig. 2.29).

2.4

Impairment of Gyri and Sulci Formation

2.4.1 Lissencephaly Lissencephaly (from the Greek words liss and enkephal, meaning literally “smooth brain”) is related to impaired development of gyri and sulci (Byrd 1988, 1989). Agyria is absence of gyri on the brain surface; it is synonymous with complete lissencephaly, whereas pachygyria means presence of wide and flat gyri and is synonymous with incomplete lissencephaly (Barkovich 2000; Byrd et al. 1988, 1989) (Fig. 2.30). Clinical features depend on the extent of retarded brain development


Fig. 2.29a–e Septo-optic dysplasia, dysgenesia of corpus callosum and interhemispheric arachnoid cyst in the left occipital region in a 2-year-old child with blindness and epilepsy. MRI in two planes (а–c) and study of optic nerves in a T2 fat-saturated sequence (d,e).

47

The cystic cavity is seen in the left occipital region, the septum pellucidum is absent, there is dysplastic corpus callosum and excessive accumulation of CSF in the chiasmatic region, and chiasma and optic nerves are thinned

Fig. 2.30a,b Lissencephaly in a 2-year-old

child with psychomotor impairment and infantile spasms. МRI, Т1-weighted (а) and Т2-weighted (b) images: wide and flat gyri and small sulci in frontal and temporal regions, almost complete absence of gyri and sulci in posterior parieto-occipital regions of cerebral hemispheres, cerebral white matter is underdeveloped and the lateral ventricles are dilated

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Chapter 2

Fig. 2.31a–f Lissencephaly in a 2-year-old child. MRI in axial (а–c) and sagittal (d) planes and in 3D reconstruction (e,f): weakly outlined sulci and gyri in all brain regions, weak differentiation of white and grey matter, and CSF spaces are dilated

Fig. 2.32a–c Agyria and agenesia of corpus callosum in a 4-month-old child. MRI: Т2-weighted images in three planes. Gyri and sulci are

hardly outlined, the cortex is wide, white matter is underdeveloped, the corpus callosum is not differentiated, the lateral ventricles are separated and the Sylvian fissures are widened


49

2.4.2 Schizencephaly Schizencephaly (agenetic porencephaly) is a congenital (unior bilateral) cleft that usually passes along the primary brain fissures (lateral, central) up to the lateral ventricle. Yakovlev and Wadsworth (1946) distinguished schizencephaly with detached (open) and closed (stuck) borders. In type I, the borders of fissure are slid widely apart, and the space between them is filled with CSF. In type II, the borders of fissure are locked, tightly adjacent to each other, separated only by deep and narrow sulcus and lined with ependyma and arachnoid membrane. Destruction of cortex in schizencephaly is accompanied by heterotopia of grey matter on the fissure borders. Diagnosis of schizencephaly with open borders by CT and MRI is simple: fissures in brain parenchyma of various sizes are revealed, which go towards the external wall of the lateral ventricle and join it (Fig. 2.33). CSF in fissures possesses the same features on MRI and CT as does ventricular CSF. Schizencephaly with closed borders is difficult to detect by CT, whereas MRI gives a complete picture about connections between fissures and the lateral ventricle and the structure of its walls (Fig. 2.34). Some-

Fig. 2.33 Schizencephaly with opened borders in a 4.5-year-old

child. CT: the fissure borders are separated and filled with CSF

Fig. 2.34a–f Schizencephaly with closed (locked) borders in a 2-year-old child. CT (а,b) and МRI (c–f): narrow fissure in parietal region leftwards goes up to the lateral ventricle; its borders are covered by grey matter

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times, a papillary with a porencephalic channel may be found on the internal side of the lateral ventricle.

2.4.3 Heterotopy

Chapter 2

There is no area of perifocal oedema in heterotopy, in contrast to brain tumours (Fig. 2.35). Subependymal nodules have smooth surfaces and narrow the lumen of lateral ventricles (Fig. 2.36). Subcortical nodules sometimes contain vessels or CSF resembling a tumour. Diffuse (ribbon-like) heterotopy looks like striae of grey matter located deeply and separated from cortex by a layer of white matter (Fig. 2.37). Sometimes several types are combined, i.e. mixed heterotopy (Fig. 2.38).

Heterotopy is a cluster of grey matter cells in atypical places, due to retardation of radial neuronal migration (Barkovich et al. 1992; Byrd et al. 1989). Grey matter heterotopy may be combined with other structural abnormalities. Almost all patients with grey matter heterotopy have epilepsy and may have motor or mental deficits. Subependymal, focal (nodular) and diffuse (ribbon-like) heterotopy are distinguished. MRI is more sensitive than CT is in diagnosis of this abnormality. Heterotopy appears as nodules or wider areas isodense and isointense in grey matter without contrast enhancement in the subependymal, periventricular spaces or subcortically.

Polymicrogyria (cortical dysplasia) is a migration abnormality in which neurons reach the cortex, but formation of the latter is impaired, and this causes the development of many small gyri. Most or least part of the hemisphere is affected. The Sylvian fissure is a predominant area of location; how-

Fig. 2.35a–f Nodular heterotopy of grey matter in a 12-year-old child with focal epilepsy. CT (а,b): focal accumulation of grey matter in the right parietal lobe, appearing as a clear-cut nodule on a border

of the sulcus. Т2- and Т1-weighted images (c–f): the signal of foci is isointense to those of grey matter CSF in the right parietal lobe. The lateral ventricles are of usual size

2.4.4 Polymicrogyria (Cortical Dysplasia)


Fig. 2.36a–c Subependymal heterotopy of grey matter. Case 1. CT

(a): external walls of the lateral ventricles are scalloped, they are isodense with cerebral grey matter and the ventricular lumen is un-

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evenly narrowed. Case 2, MRI (b,c): a 12-year-old child with multiple subependymal nodular masses of grey matter lining lateral ventricles

Fig. 2.37a–c Ribbon-like heterotopy (double cortex) in a 2-year-old child with epilepsy. Т1- and Т2-weighted images: the second grey matter layer is located between cortex and main part of white matter, which duplicates the shape of gyri, being separated from cortex by a thin striae of white matter

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Chapter 2

Fig. 2.38a–f Mixed diffuse-nodular and subendymal heterotopy of grey matter in a 7-year-old child with epilepsy. Т2-weighted images (а,b), proton-density images (c,d), and Т1-weighted images (e,f). Extensive area of signal change in the right temporo-occipito-pari-

etal region isointense with grey matter is seen. The adjacent portion of the lateral ventricle is narrowed, and there are subependymal nodules on its external wall

Fig. 2.39a–c Polymicrogyria in a 6-month-old child with epilepsy, mental retardation and motor deficits. CТ (а–c): uneven and incorrectly formed brain surface with many small gyri, the anterior por-

tion of the interhemispheric fissure and the lateral cerebral fissures are markedly increased in size, the latter are located vertically and the third and the lateral ventricles are dilated


ever, frontal lobes may be affected, sometimes bilaterally (Fig. 2.39). Severity of clinical symptoms (epilepsy, failure to thrive and motor deficits) depend upon the length of lesion. CT and MRI appearance of cortical dysplasia vary: uneven, incorrectly formed surface or, vice versa, exceptionally smooth due to adhesion of the external cortical (molecular) layer on micro-fissures. It may appear as pachygyria with uneven wide gyri or normal. The polymicrogyria cortex is isodense on CT and isointense on MRI in comparison with normal cortex; however, sometimes part of it may be calcinated.

2.4.5 Rhombencephalosynapsis Rhombencephalosynapsis (RS) is the absence of separation of the cerebellum in the vermis and hemispheres. It is a rare malformation, and the diagnosis cannot be made without MRI. The incidence of RS is 0.13% (Barkovich 2000; Toelle et al. 2002; van der Knapp et al. 1988). The age of incidence varies greatly—from fetuses to 39-year-olds. The aetiology is unknown, as there are no specific symptoms of this malformation. Rhombencephalosynapsis is frequently combined with other brain malformations: Chiari type II, corpus callosum dysgenesia (up to agenesia), developmental defects of gyri and sulci, hydrocephalus and absence of septum pellucidum. Other abnormalities can include cardiovascular, renal and limb (hypoplasia of phalanxes, syndactyly) (van der Knapp et al. 1988). MRI in T1- and T2-weighted sequences reveals the absence of demarcation between hemispheres and the vermis, and the downward location of tentorium cerebelli (Figs. 2.40, 2.41).

2.4.6 Lhermitte-Duclos Disease (Dysplastic Cerebellar Gangliocytoma) Lhermitte-Duclos disease (dysplastic cerebellar gangliocytoma) is characterised by a separated area of cerebellar cortex enlargement, which sometimes extends into the vermis and contralateral hemisphere. Microscopy reveals thickening of abnormal ganglionic cells in the granular cortical layer, thickening of excessively myelinated marginal layer and thinned layer of Purkinje cells. Clinically, this pathology may manifest itself with cerebellar signs in any age, or may be asymptomatic and revealed only in autopsy. On CT, an area of moderate volume enlargement with deformity of adjacent tissues is seen without changes in density. On MRI, a clear-cut area of changed signal intensity on T1- and T2-weighted images is seen, which cause fourth ventricle deformity. Some contrast enhancement may be seen in the pathological area on CT and MRI (Fig. 2.42).

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2.5

Changes in Brain Size

2.5.1 Unilateral Megalencephaly Unilateral megalencephaly is a hamartoma-like—local or total enlargement of a cerebral hemisphere with defects of neuronal migration. Clinically, it presents with refractory epilepsy, hemiplegia and failure of development mental and physical. On CT and MRI, enlargement of a part or the whole hemisphere is seen, cortex is dysplastic and thickened, with uneven gyri and small fissures, and some gyri may be normal or smooth. The lateral ventricle is dilated on the affected side; its anterior horn is elongated and straightened. Sometimes the corresponding part of brain (or hemisphere) has a peculiar hamartoma-like appearance (Figs. 2.43, 2.44).

2.5.2 Microcephaly The term microcephaly is related to different sporadic and genetic disorders. In children, head circumference lags behind the age-adjusted normal value, and marked failure to thrive is seen without focal neurological signs. The brain usually has a thin cortex and smoothened sulci. On X-ray craniogram, the skull is small in size, cranial vault bones are thickened, no fingerprint seen and cranial sutures are closed and thickened. CT and MRI usually reveal small brain with smoothened gyri and sulci (Fig. 2.45).

2.6

Destructive Brain Lesions

2.6.1 Porencephaly Porencephaly is a CSF-filled cavity within the brain tissue (Barkovich 2000; Harwood-Nash et al. 1976; Kornienko et al. 1993). Aetiological factors of porencephaly are anoxia, massive haemorrhage and traumatic or inflammatory process to which developing brain was exposed in the intrauterine or early postnatal period. In closed porencephaly, the cavity is connected neither with ventricles nor with subarachnoid space. Yakovlev and Wadsworth (1946) distinguished agenetic porencephaly, developed before 6 months of intrauterine life, and encephaloclastic porencephaly, formed within the last trimester of pregnancy or after birth. Histology of the internal walls is a distinguishing feature of these variants. Agenetic porencephaly is infrequently accompanied by agenesia of the corpus callosum. According to our data, porencephaly is seen in 4.5% of cases in children with hydrocephalus. Porencephaly is caused by other developmental brain abnormalities in almost half of the cases. The clinical picture depends on location and size of the cavity.

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Fig. 2.40a–c Rhombencephalosynapsis in a 1.5-month-old child

with Chiari II malformation, obstructive hydrocephalus and lumbosacral meningomyeloradiculocele. MRI in sagittal and coronal planes (а,b): downward location of tentorium cerebelli, the pons is

Fig. 2.41a–c Multiple malformations in a 5-year-old child: Chiari II, rhombencephalosynapsis, dysgenesia of corpus callosum and cortical dysgenesia. MRI Т1- and Т2-weighted images: the cerebellum is not divided into vermis and hemispheres, medulla and cerebellar tonsils are sunk into foramen magnum, the fourth ventricle is not

Chapter 2

situated at the level of low margin of clivus and the cerebellum is not divided into vermis and hemispheres. MRI (c) of lumbosacral spine reveals the meningomyeloradiculocele

differentiated, tectum is elongated and beak-shaped, corpus callosum is underdeveloped (only splenium and a part of body are differentiated), the lateral ventricles are separated and asymmetrical, and the gyri of medial surfaces of cerebral hemispheres has a peculiar appearance (elongation–stenogyria)


Fig. 2.42a–f Lhermitte-Duclos syndrome in a 1-year-old child. CT

(a) reveals a mildly hyperdense area in the right cerebellar hemisphere, and (b) after contrast medium enhancement accumulated to a mild extent in the pathological area. The Т2-weighted image (c)

Fig. 2.43a–c Leftward megalencephaly in a 12-month-old child with

severe psychomotor retardation, epilepsy, severe rightward hemiparesis. CT (а–c): the left cerebral hemisphere is enlarged, sulci and gyri are smoothened and the left lateral ventricle is greater than the

55

reveals an area of unevenly increased signal intensity in the right cerebellar hemisphere and vermis. The fourth ventricle is deformed. MRI with contrast enhancement (d–f): slight hyperintensity in the pathological area is seen

right one—its anterior horn is elongated in the anterior direction. A markedly hypodense focus in the interhemispheric fissure (–25 HU) indicates possible lipoma

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Fig. 2.44a–f Rightward megalencephaly in a 9-month-old child with epilepsy and severe leftward hemiparesis. CT (а,b), Т1-weighted images (c,d), and Т2-weighted images (e,f): enlargement of the right hemi-

Chapter 2

sphere is seen, the right lateral ventricle is greater than the left one, its anterior horn is narrowed and elongated in the anterior direction, and gyri and sulci in the parietal and occipital regions are smoothened

Fig. 2.45a–c Microcephaly in a 18-month-old child with psychomotor retardation (skull circumference is 42 cm). MRI (а–c): the skull is small, signal from brain parenchyma is unchanged, there is dysplasia of corpus callosum and ventricular system is not dilated


Porencephaly has no typical picture on X-ray craniogram. Signs of hydrocephalus may be seen, and rarely, thinning and protrusion of cranial vault bones on the affected side. On CT, a hypodense (CSF isodense) area is seen, with clear-cut borders and connection with the lateral ventricle and/or subarachnoid space (Fig. 2.46). Intravenous contrast enhancement does not increase density of the cavity walls, which allows differentiation from cystic brain tumours and abscesses. CT ventriculography reveals simultaneous filling of ventricular system and the porencephalic cyst, with contrast medium. On MRI, the porencephalic cavity appears as a clearly delineated area of changed signal, isointense with CSF in all sequences (Fig. 2.47). It is easy to define the quality of these cavities margins (grey or white matter), which allows estimation of the time when the cavity was formed.

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Porencephaly is always defined as a developmental defect of amiculum cerebri. Raybaud (1983) distinguished porencephaly of posterior fossa as a histogenetic defect of the cerebellum, infrequently combined with defects of supratentorial structures. CT and MRI reveal wide CSF cavity connected with the fourth ventricle (Fig. 2.48).

2.6.2 Hydranencephaly Hydranencephaly is an anencephalic hydrocephalus. Yakovlev and Wadsworth (1946) suggest that hydranencephaly is a brain infarction developed during the embryonic period, due to occlusion of internal carotid arteries. Massive brain destruction has been described after neonatal viral infection

Fig. 2.46a–c Closed porencephaly in a 10-month-old child. MRI (a,b): sharply delineated cavities that are isointense to CSF in frontal lobes. PSIF (c): thin septa are present between cavity and ventricle

Fig. 2.47a–c Porencephaly of the left lateral ventricle in a 5-year-old child with epilepsy and rightward hemiparesis. МRI (а) in axial (Т2)

and (b,c) sagittal (Т1) planes: the CSF cyst is widely connected with the left lateral ventricle

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Chapter 2

Fig. 2.48a–e Posterior fossa porencephaly in a 4-month-old child. Т2- weighted images (а–c) and Т1-weighted images (d,e): the CSF cyst in the left half of posterior fossa is connected with the fourth ventricle and subarachnoid space of the cervical portion of vertebral column. The third and lateral ventricles are dilated

and toxoplasmosis. Children may have micro-, normo- or megalencephaly. They markedly fail to thrive in both physical and mental development. Cerebral angiography in hydranencephaly often reveals thrombosis of supraclinoid portions of internal carotid arteries. According to our own institute's data, hydranencephaly is seen in 1.34% of cases among children with hydrocephalus. In most cases, CT and MRI pictures of hydranencephaly is typical: posterior fossa structures are correctly formed, thalami and basal ganglia are hypoplastic and the cerebral hemispheres consist of thin-walled vesicles filled with CSF. Sometimes islands of brain tissue are detected, which are located in different hemispheric regions. The falx cerebri, albeit incorrectly formed, is always seen on CT and MRI (Figs. 2.49, 2.50), which is what distinguishes it from alobar holoprosencephaly.

2.6.3 Multicystic Encephalomalacia Multicystic encephalomalacia is a result of a diffuse stroke that occurred during the intrauterine period, con- or postnatally. It appears as numerous cysts of various sizes and shapes, separated from each other by glial septi. Location of the lesions

depends on the stroke’s origin. After thrombosis or embolism, brain regions are affected by the vascular territories involved. Asphyxia damages cortex and peripheral white matter; in severe cases, only periventricular white matter remains intact. If the cause of encephalomalacia is infection, then location of lesions is not specific and depend on location of the inflammatory process. On CT, cystic hypodense lesions of various sizes and shapes, and separated by septi, are seen. These lesions are located in different affected brain regions, sometimes with calcification. On MRI, areas of encephalomalacia correspond to CSF signal on T1 and T2 sequences. Sometimes, the MR signal is heterogeneous due to glial septi and CSF components. The ventricular system may be variably dilated, depending on the severity of lesions (Fig. 2.51).

2.6.4 Hypoxic (Hypoxic–Ischaemic) Brain Lesions Hypoxic (hypoxic–ischaemic) brain lesions manifest themselves by different changes, depending on timing and location of lesions. Clinical signs in neonates include seizures, hypotonia in extremities and lethargy. Neonatal asphyxia decreases blood oxygen content (hypoxia), increases content of carbon


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Fig. 2.49a–c Hydranencephaly in a 11-month-old child with severe psychomotor retardation. CT (а–c): posterior fossa structures are correctly formed, and the cerebral hemispheres appear as thin-walled vesicles filled with CSF. A large falx cerebri is partially present with islands of brain tissue alongside it

Fig. 2.50a,b Hydranencephaly in a

11-month-old child with severe psychomotor retardation. Т1-weighted (а) and Т2-weighted (b) images: cerebral hemispheres appear as thin-walled vesicles filled with CSF. Brain tissue appears as thin striae between CSF and cranial vault bones

Fig. 2.51a–c Multicystic encephalomalacia in a 3-year-old child. Т1-weighted (а,b) and Т2-weighted (c) images in axial and sagittal planes: cerebral hemispheres possess many cystic cavities filled with CSF that are separated by thin septi, and the ventricular system is dilated

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Chapter 2

Fig. 2.52a–c Periventricular leukomalacia in a 1-year-old child with psychomotor retardation (placental detachment in his mother during labour). Т1-weighted (а) and Т2-weighted (b,c) images: white matter is underdeveloped, chains of hyperintensity in T2 images of various sizes within superior portions of the lateral ventricles bodies

dioxide, and causes systemic hypotension. Increased carbon dioxide and decreased oxygen content cause loss of autoregulation of brain vessels. Systemic hypotension combined with loss of vascular autoregulation causes brain hypoperfusion. On CT, hypodensity of white matter in periventricular areas, basal ganglia and thalami is seen. On MRI, foci of changed signal identical to CSF signal (periventricular leukomalacia) are revealed (Fig. 2.52).

2.7

Histogenesis Impairment

2.7.1 Neurocutaneous Disorders (Phakomatoses) Neurocutaneous disorders (phakomatoses) are congenital neurocutaneous disorders affecting numerous structures of neuroectodermal origin: nervous system, vessels, skin, retina, eyeball and sometimes viscera (Barkovich 2000; Gomez 1988; Hart et al. 2000; Kornienko et al. 1993; Smirniotopoulos et al. 1992). “Classic” syndromes include the following: neurofibromatosis types 1 and 2 (von Recklinghausen’s disease) Bourneville-Pringle disease, von Hippel-Lindau disease, Sturge-Weber syndrome (encephalotrigeminal angiomatosis) and neurocutaneous melanosis.

2.7.1.1

Neurofibromatosis (von Recklinghausen’s disease)

2.7.1.1.1 Neurofibromatosis Type I Neurofibromatosis type I (NF I) is one of the most frequent autosomal-dominant disorders of CNS, the locus for which is on chromosome q17 (Barkovich 2000; Bilaniuk et al. 1997;

Smirniotopoulos et al. 1992). Its incidence is 1 case per 3,000– 5,000 in the general population. Criteria of neurofibromatosis type 1 are as follows: over five café-au-lait spots on skin over 5 min in diameter in children and over 15 min in diameter in postpubertal period; two or more neurofibromas of any type or a single plexiform one; freckles in subaxillary and inguinal regions; optic nerve, chiasm and optic tract glioma (uni- or bilateral); two or more pigmented hamartomas of the iris (Lisch nodes); sphenoid crest dysplasia; thinning of cortical layer of long tubular bones; and NF type I in consanguine relatives. Clinical features of NF type I are café-au-lait spots on skin appearing during the first year of life, two or more neurofibromas, optic pathways glioma (and other intracranial astrocytomas), kyphoscoliosis, sphenoid crest dysplasia, vascular dysplasia, peripheral myelin sheath tumours, epilepsy and mental disorders. Optic pathway glioma is the most frequent sign of NF type I. One or both optic nerves chiasm and optic tracts may be affected, which is easily revealed on CT with contrast enhancement and MRI (Fig. 2.53). Fat-saturation sequences in MRI are useful for examination of the orbits. Astrocytomas may be located sub- as well as supratentorially. In NF type I, hydrocephalus is usually caused by Sylvian aqueduct stenosis, midbrain tegmentum or tectum glioma. The tumour is not detected by CT but always found on MRI. Vascular dysplasia may be presented by stenosis or occlusion of internal carotid artery or its major branches (due to proliferation of intima), or arterial aneurysm. Dysplasia of the sphenoid crest is the most frequently observed bony abnormality, which may cause intraorbital protrusion of temporal lobe and, hence, exophthalmus.


Fig. 2.53a–f NF I in a 5-year-old child with complete blindness and

café-au-lait spots on the skin. Т2-weighted (а–c) and Т1-weighted (d–f) images: glioma of the optic chiasm with a cystic component in the third ventricle cavity. The tumour expands alongside optic tracts.

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Glioma of the right optic nerve, as well as multiple foci of hyperintensity in thalami, brainstem, and cerebellar hemispheres are seen, along with obstructive hydrocephalus at the foramina of Monroe level

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Chapter 2

Fig. 2.54a–c NF II in an 8-year-old child. МRI with contrast enhancement: multiple tumours in sub- and supratentorial spaces, and nodular

tumours under the skin of the scalp

2.7.1.1.2 Neurofibromatosis Type II Neurofibromatosis type II (NF II) is also an autosomal-dominant disorder, the locus for which is on chromosome 22. The incidence is about 1 case per 5,000 in the general population (Castillo et al. 2000). Diagnostic criteria of NF type II are as follows: bilateral eighth cranial nerve neurinomas (confirmed on CT on MRI) or NF II in consanguine relatives; unilateral eighth cranial nerve neurinoma; or one of two signs of brain neurofibroma, meningioma, glioma or schwannoma; or two signs unilateral eighth cranial nerve neurinoma, multiple brain neurofibroma, meningioma, glioma, schwannoma or calcifications into the brain. Clinical features are caused by eighth cranial nerve tumours or neurofibroma, meningioma, glioma or schwannoma; the latter may be numerous. If NF II is suspected, then CT or MRI should be performed with contrast enhancement to define multifocal character of lesions (Figs. 2.54–2.56).

2.7.1.2

Sturge-Weber Syndrome (Encephalotrigeminal Angiomatosis)

Sturge-Weber syndrome (encephalotrigeminal angiomatosis) is a congenital sporadic disorder, but familial cases have been described. The type of inheritance is unknown (Barkovich 2000; Wasenko et al. 1990). Diagnostic criteria of Sturge-Weber syndrome are facial angioma, retinal angioma, meningial angiomatosis with atrophy of adjacent brain tissue, calcifications in affected brain regions, secondary glaucoma and generalised seizures. As usual, on craniograms peculiar calcifications alongside cerebral gyri are visualised. Frequently they are located in parieto-occipito-temporal regions (Fig. 2.57). On CT, calcifi-

cations of various sizes are found in cortical parts of hemispheres, sometimes markedly extended (Fig. 2.58). MRI may reveal hypointense periventricular veins. After intravenous contrast enhancement, meningeal angiomas accumulate contrast medium, repeating the picture of sulci and gyri. An enlarged choroid plexus of the ipsilateral lateral ventricle and periventricular veins are well contrasted. On MRI, small calcifications may be less discernible. The affected hemisphere is atrophic due to ischaemic change.

2.7.1.3 Bourneville-Pringle Disease (Tuberous Sclerosis) Bourneville-Pringle disease (tuberous sclerosis) is an autosomal-dominant disorder. Two genes are responsible for this disorder, TSC1 (located on chromosome 9q34), and TSC2 (located on chromosome 16p13/3). The incidence is 1 case per 100,000 in the general population (Gomez et al. 1988; Kinglsey et al. 1986). Barkovich (2000) outlined the following diagnostic criteria of Bourneville-Pringle disease. First-line histologically confirmed signs: facial angiofibroma, multiple fibromas, cortical tuberculi, subependymal nodules or giant-cell astrocytoma, multiple retinal astrocytomas and multiple calcified subependymal nodules protruding into ventricular lumen (confirmed by CT and MRI). Second-line signs: the disorder in consanguine relatives, cardiac rhabdomyoma, retinal hamartoma or achromatic proliferations, cerebral tubercles (by CT and/or MRI), noncalcinated subependymal nodules (in CT or MRI), Sjögren’s patches, plaques on the forehead, lymphangiomyomatosis of lungs, angiomyolipoma of the kidney and kidney cysts. Third-line evidence: depigmented spots, multiple white nevus, pink and red papules (“confetti-like” skin lesions), kidney cysts, chaotic distribution of enamel on primary or permanent teeth, hamartoma-like rectal polyps, cysts of bones, liver


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Fig. 2.55a–h NF II in a 13-year-old child. CT (а–e) and МRI (f–h) before and after contrast enhancement: bilateral neurinomas of both eighth cranial nerves are seen. On CT in the “bony window”, dilation of the internal acoustic meatus bilaterally is clearly seen. On MRI with contrast enhancement (h), homogeneous accumulation of contrast medium within the tumour tissue is seen

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Chapter 2

Fig. 2.56a–f NF II in a 15-year-old child. Т1-weighted image before (а,b) and after contrast enhancement (c–f): giant neurinoma of the right eighth cranial nerve and multiple neurinomas in the vertebral canal

Fig. 2.57a,b Sturge-Weber syndrome in an

8-year-old child. X-ray craniograms: typical calcifications in the left occipital region


65

Fig. 2.58a–c Sturge-Weber disease in a 4-year-old child. CT (а): multiple calcifications lining fissures and gyri of right temporo-occipital regions. The right lateral ventricle is enlarged. MRI (b,c) shows foci of hypointensity (calcifications) in the right hemisphere, which is smaller than the left one

and kidney hamartomas, lymphangiomyomatosis of lungs, heterotopy and infantile spasms. Tuberous sclerosis may be diagnosed in a patient having a single first-line sign or two second-line signs, or a single second-line and two third-line signs. Tuberous sclerosis is probable if a patient has one secondline and one third-line sign, or three three-line signs. Tuberous sclerosis is suspected if a patient has one secondline and two third-line signs. The most frequent manifestations of tuberous sclerosis are myoclonic seizures since early childhood, psychiatric symptoms, adenomas of sebaceous glands and retinal hamartoma. Multiple calcifications are revealed within the walls of lateral ventricles and in brain parenchyma on X-ray craniograms. The walls of the third and the lateral ventricles sometimes contain subependymal nodules isodense with brain parenchyma (subependymal hamartomas that calcinate with disease progression), as well as calcinated foci, and are seen on CT (Fig. 2.59). On MRI, subependymal hamartomas are distinguished as nodules isointense with white matter that protrude into the lumen of the ventricle, and cortical nodules are hyperintense on Т2-weighted images. Infrequently (in about 15% of tuberous sclerosis cases) subependymal giant-cell astrocytomas are found within interventricular foramina. On CT and MRI, they are usually isointense and isodense, with good contrast enhancement (Fig. 2.60).

2.7.1.4

von Hippel-Lindau Disease

von Hippel-Lindau disease (angiomatosis of the central nervous system) is an autosomal-dominant disorder, the gene being located on chromosome 3p25–p26 (Barkovich 2000; Hart

et al. 2000). Its diagnostic criteria are its permanent signs, such as retinal angioma; cerebellar hemangioblastoma; spinal hemangioblastoma; and inconstant signs such as kidney carcinoma; pheochromocytoma; liver angioma; and kidney, liver and pancreatic cysts. Clinical features depend on the extent of cerebellar involvement, spinal cord and retina. CT reveals a cystic tumour, with contrast enhancement in the nodular part, which is less pronounced in the cyst walls. MRI reveals a cystic clear-cut tumour: MR signal from a tumour nodule markedly increases after intravenous contrast enhancement (Fig. 2.61).

2.7.1.5

Neurocutaneous Melanosis

Neurocutaneous melanosis is a very rare disease of this group, which was described for the first time by J. Rokitansky in 1861. The type of inheritance is not known. Diagnostic criteria are a large single or multiple small and moderate pigment nevi on skin, brain melanoma and/or meningeal melanosis. The disorder manifests by multiple congenital pigment nevi on the skin (more frequently on the posterior sides of trunk and extremities, brown or black in colour), which are often confluent into large fields, without signs of malignancy, and by intracranial brain and meningeal melanomas. Histology reveals accumulation of melanocytes on the ventral surface of the brainstem, in nuclei and cerebellar white matter, in cervical and lumbar vertebral regions, in the anterior portions of temporal lobes and in the amygdale, thalami and basal portions of dura and pia mater. The clinical picture is characterised by cerebral involvement and manifests as headaches, vomiting, dizziness and so forth. The characteristic MRI fea-

66

Fig. 2.59a–i Tuberous sclerosis in a 1-year-old child with epilepsy, manifested at 5 months of age. CT (а–c) reveals multiple calcinated foci of various sizes in the lateral ventricles walls, foci of heterogeneous density in the left frontal region and hypodense focus in the right temporal focus. Т2-weighted images (d–f) reveal hyperintense foci in the white matter of cerebral hemispheres and in subcortical

Chapter 2

brain regions bilaterally. MRI using Т1-weighted images (g–i) reveals hyperintense foci in the lateral ventricles walls and in white matters of both cerebral hemispheres. A large lesion in the left frontal region of cortical and subcortical location has a heterogeneous signal on both sequences


Fig. 2.60a–f Subependymal giant-cell astrocytoma in a 15-year-old

child with tuberous sclerosis. CT with contrast enhancement (a,b): a tumour with heterogeneously increased density with few peripheral calcifications within anterior horn of the right lateral ventricle. Various sizes of calcifications subependymally and in the white matter and hydrocephalus are seen. Т2-weighted (c,d) and Т1-weighted (e,f)

67

images: the tumour is isointense with cerebral grey matter. Small cysts (hyperintense lesions) appear in its stroma. There is hydrocephalus present. Hypointense calcification is seen in the right lateral ventricle wall. Calcifications in the white matter are weakly differentiated (to as compared with CT)

Fig. 2.61a–c Craniospinal hemangioblastoma in a 15-year-old child. Т2-weighted (а), Т1- weighted (b,c) images after contrast enhancement:

a small tumour nodule is seen within the cystic cavity, which intensely accumulates contrast medium

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Fig. 2.62a–i Neurocutaneous melanosis in a 9-year-old child. MRI

before (a–d) and after contrast enhancement (e–i). The right occipital region melanoma on the Т1-weighted image (without contrast enhancement) is isointense; in the central part of the T2-weighted image. A small hyperintense lesion is located in the central part of the T2-weighted image, suggestive of melanin. Melanin deposits are

Chapter 2

found in amygdale nucleuses bilaterally. On the Т2-weighted image (d) in the sagittal plane, there is a hyperintense lesion (melanin deposits with hamartoma-like changes of brain stem tissue); after contrast enhancement, contrast medium accumulation is seen in pathological lesions and meninges


ture is hyperintensity of the amygdale and other affected regions of brain and spinal cord and their meninges (Fig. 2.62).

2.8

Arachnoid Cysts

An arachnoid cyst is a congenital extracerebral mass that contains CSF encircled by walls composed of arachnoid membrane. Internal and external walls of the cyst consist of thin layers of arachnoid cells and join unchanged arachnoid membrane at the margins. True (congenital) arachnoid cysts contain specific membranes and enzymes possessing secretory activity (Barkovich 2000; Galassi et al. 1982; Kornienko et al. 1993; Muhametjanov et al. 1995). According to the data of the Burdenko Institute of Neurosurgery, arachnoid cysts make up about 10% all masses of brain in children, 7.4% of cases are found in children with hydrocephalus, 4% of cases in children with open hydrocephalus and in 11.5% of cases in children with obstructive hydrocephalus. Clinical features of arachnoid cysts depend on their location, volume and relation to CSF spaces (Fig. 2.63). They may not cause neurological deficits for a long period. These cysts may develop in late childhood or adulthood. Cysts located close to CSF pathways manifest themselves by showing early signs of progressive hydrocephalus. This is explained by mechanical compression of CSF pathways as well as with impairment of venous flow due to CSF stasis in the basal cisterns. As a result, the asymptomatic period becomes shorter, and neurological signs are more severe due

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to proximity of arachnoid cysts to brainstem, diencephalic structures, Sylvian aqueduct and the third and the fourth ventricles. The common feature is a predominance of progressive hydrocephalus signs that mask focal neurological signs—due to the significant ability of children to compensate for the neurological signs. Only in the stage of decompensation do signs of increased exposure of adjoining structures to mass of arachnoid cysts appear: In retrocerebellar cysts, there are cerebellar and brainstem signs. In cysts of the incisura tentorii and cerebellopontine angle, there are pyramidal signs due to brainstem compression. In suprasellar cysts, there is involvement of cerebral and oral portions of the brainstem, and chiasm and optic nerves, as well as presentation of hyperkinesis, endocrine and diencephalic signs. CT and MRI are the main diagnostic tools for arachnoid cysts. They reveal straightforward homogeneous masses isodense and isointense with CSF in all sequences, unevenly separated from walls of adjacent lateral ventricles. In contrast to tumours, arachnoid cysts do not show contrast enhancement and perifocal oedema. If a sub- or supratentorial suprasellar arachnoid cyst, or a cyst located in the cerebellopontine angle or incisura tentorii, is suspected, then it is necessary to perform CT ventriculography (CTVG) to distinguish a cyst from dilated ventricular system. CTVG reveals a defect of contrast accumulation where a cyst is present. Arachnoid cysts—irrespective of their location—may be completely or partially connected with the subarachnoid space or isolated. Connection between arachnoid cysts with the subarachnoid space (or its absence) may be revealed by CT cisternography

Fig. 2.63a,b Illustration of intracranial arachnoid cyst location (а lateral, b medial brain surface). 1 cyst of the lateral cerebral fissure, 2 cyst of convex brain surface, 3 parasagittal cyst, 4 suprasellar cyst, 5 intrasellar cyst, 6 tentorium cerebelli cyst, 7 superior retrocerebellar cyst, 8 inferior retrocerebellar cyst, 9 cerebellopontine angle cyst

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Fig. 2.64a–c Retrocerebellar arachnoid cyst in a 14-year-old child. The cyst is situated near the internal occipital eminence, and compresses and produces deformity of the fourth ventricle (isodense to

Chapter 2

CSF). The third and the lateral ventricles are dilated. Periventricular oedema near anterior and posterior horns of the lateral ventricles is noted

Fig. 2.65a–d Retrocerebellar arachnoid

cyst in a 1-year-old child. МRI in axial (а,b) and sagittal (c) planes reveals a cyst occupying the most part of posterior fossa. Compressed posterior fossa structures are displaced in the anterior direction. PSIF (d) reveals CSF flow from the cyst into the subarachnoid space of the spinal cord


Fig. 2.66a–c Giant superior retrocerebellar arachnoid cyst in an

8-month-old child with progressive hydrocephalus. MRI in axial and sagittal planes: T2-weighted (а) and Т1-weighted (b) images. MR signal of the cyst is isointense to CSF. The cyst is located above and

(CTCG), MRI PSIF, or MRI and CT with intrathecal injection of contrast media mixture (Galassi et al. 1982).

2.8.1 Arachnoid Cysts of the Posterior Fossa Arachnoid cysts of the posterior fossa may originate from the cisterna magna, in which case they are called inferior retrocerebellar cysts. The area of hypodensity and MR signal changes in these cases is located in the posterior inferior portions of posterior fossa and expands into both cerebellar hemispheres (symmetrically or asymmetrically). The fourth ventricle is displaced upwards along with cerebellar hemispheres. Superior retrocerebellar cysts are located in the superior portions of cerebellum and expand into both cerebellar hemispheres. These cysts are regarded as an abnormality of lateral pontine cistern. Giant retrocerebellar cysts, taking up the major part of posterior fossa, cause obstructive hydrocephalus (Fig. 2.64). Retrocerebellar cysts, pervading posterior fossa structures, cause compression of CSF pathways and markedly dilate the ventricular system (Figs. 2.65–2.67). There are difficulties in distinguishing posterior fossa cysts from tumoral cysts and Dandy-Walker malformation. If contents of a mass are denser than CSF is, then tumour is more likely. Cerebellopontine angle arachnoid cysts, originating from the lateral pontine cistern, may be located only in the posterior fossa, sub- and supratentorial in middle cerebral fossa, which leads to suspicion of a dilated inferior horn of the lat-

71

behind cerebellum, more rightwards; it intrudes into the supratentorial space, compressing the third ventricle. The Sylvian aqueduct is visualised but narrowed; the fourth ventricle is compressed. PSIF images a turbulent CSF flow via foramina of Monroe

eral ventricle. A large amount of the supratentorial portion of an arachnoid cyst may cause compression of the lateral wall of the lateral ventricle. Local signs of this fraction of a cyst are thinning and protrusion of the cranial bones that form middle cerebral fossa, due to long-term exposure of still-notfirm cranial bones to compression by a mass. A subtentorial cyst (or a part of a cyst that is located sub- and supratentorial) displaces and compresses the fourth ventricle (Fig. 2.68). Arachnoid cysts of incisura tentorii originate from this group of cisterns and have sub- and supratentorial components of different or identical volume. They usually compress the brainstem markedly, as well as the Sylvian aqueduct, which causes marked dilatation of the third and the lateral ventricles. Quadrigeminal and circumferential cisterns are usually involved. The degree of their participation in cyst origin is variable. Cysts originating from lamina tecti cistern are positioned medially; they compress brainstem and cause deformity of the posterior portion of the third ventricle. Large and giant cysts expanding into the interhemispheric fissure dislocate and cause deformity of medial walls of the lateral ventricles. On the side of predominant cyst location, the lateral ventricle changes its shape, and the contralateral ventricle becomes dilated to a lesser extent, being exposed to milder compression (Fig. 2.69). CTVG reveals a defect of accumulation where the cyst is located; the lateral ventricles are well contrasted. Sagittal and coronal MRI allow judgement about the relationship of a cyst to adjacent structures of the middle cerebral fossa, midbrain and cerebral hemispheres.

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Fig. 2.67a–f Giant retrocerebellar arachnoid cyst. CT (а,b) reveals a

large CSF cyst that occupies the major part of posterior fossa. Cerebellum and brainstem are deformed and pushed into the anterior direction. Т2-weighted (c,d) and Т1-weighted (e) images demonstrate

Chapter 2

that the cyst expands into oral and caudal directions. PSIF (f) reveals turbulent CSF flow in a cystic cavity. There is no CSF flow from the cyst into the subarachnoid space of the spinal cord


Fig. 2.68a–f Case 1. An arachnoid cyst in the cerebellopontine angle

in a 2-year-old child, sub- and supratentorial location. CТ (а–c): the cyst is isodense to CSF, and the third and the lateral ventricles are markedly dilated due to occlusion of the aqueduct of Sylvius. Case 2,

73

MRI (d–f): posterior fossa arachnoid cyst in left cerebellopontine angle. The fourth ventricle is compressed. The third and the lateral ventricles are very large

74

Fig. 2.69a–f Arachnoid cyst of tentorium cerebelli in a 2-year-old

child. CT (а,b): a cyst containing CSF is located in sub- and supratentorial spaces. Т1- and Т2- (c–e) weighted images in axial and sagittal planes: a cyst compresses and produces deformity of brainstem, and

2.8.2 Suprasellar Arachnoid Cysts Suprasellar arachnoid cysts are the most difficult in terms of diagnosis, as they may imitate dilated chiasmal cisterns and the third ventricle (Fig. 2.70). In most cases, the cavity of the third ventricle invaginated, causing its marked dilatation and occlusion of the Monroe foramina (Fig. 2.71). Sometimes they protrude through enlarged foramina of Monroe (uni- or bi-

Chapter 2

posterior portion of the third and the fourth ventricles—obstructive hydrocephalus. Series of CTVG (f): an accumulation defect within the arachnoid cyst is seen on the background of the contrasted part of the lateral and the third ventricle

laterally) into the lumen of the lateral ventricles. Suprasellar arachnoid cyst volume enlarges quite slowly, and hydrocephalus is well compensated in the initial stage. The main CT sign of a suprasellar arachnoid cyst expanding into the third ventricle is a balloon-shaped dilation of the latter and marked dilation of the lateral ventricle, which is sometimes asymmetrical. A follow-up CT after lateral ventricles shunting erases doubt of the presence of this arachnoid


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Fig. 2.70a–c Suprasellar arachnoid cyst in a 9-year-old child. Т2-weighted (а) and Т1-weighted (b) images: a small arachnoid cyst located in the suprasellar area; its posterior border is in the interpeduncular cistern. The bottom of the third ventricle is lifted. The optic chiasm is pushed forward. PSIF in the sagittal plane (c) demonstrates a turbulent CSF flow via foramina of Monroe, the third and the fourth ventricles, and the Sylvian aqueduct. MR signal of the cyst is isointense to CSF

Fig. 2.71a–c Suprasellar arachnoid cyst expanding into the cavity of

the third ventricle in a 2.5-year-old child. CT (а): balloon-shaped dilation of the third ventricle; the lateral ventricles are dilated. MRI in

sagittal plane, Т1-weighted image (b) and PSIF (c): marked dilatation of the third ventricle; the lumen of the aqueduct of Sylvius is intact

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Chapter 2

Fig. 2.72a–f Suprasellar arachnoid cyst expanding into the cavity of the third ventricle and via foramina of Monroe into the lateral ventricles in a 2-year-old child. CT (а–d): the third ventricle is balloonshaped and dilatated; the lateral ventricles are markedly enlarged.

The cyst borders are not visualised. CTVG (e,f): defects of its accumulation are clearly seen in the site of the cyst in the third ventricle cavity and adjacent portions of the lateral ventricles (near foramina of Monroe)

Fig. 2.73a–c MR cisternography in three planes of a 10-year-old

cyst within the third ventricle cavity, which goes via interventricular foramen into the left lateral ventricle. MR cisternography confirms the connection between arachnoid cyst and skull-base cisterns–communicating cyst

child with suprasellar arachnoid cyst, expanding into the cavity of the third ventricle and the left lateral ventricle. Contrast medium injected intrathecally filled the skull-base cisterns and suprasellar


cyst, as the dilated third ventricle does not dwindle in volume, retaining its balloon-like shape. Additionally, the diagnosis of a suprasellar arachnoid cyst may be confirmed by CTVG and CTCG. CTVG reveals defect of accumulation in the third ventricle, and if the cyst penetrates into the lateral ventricle(s), then the additional defect is seen within the Monroe foramina (Fig. 2.72). In cardiac-gated phase-contrast MRI (CG pcMRI), it is possible to detect connection between the arachnoid cyst and basal brain cisterns (Fig. 2.73). MRI PSIF is a reliable technique used to diagnose the connection between a suprasellar arachnoid cyst and basal brain cisterns. Pulsatile flow, not detected before surgery, becomes clear after a third

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ventriculostomy, when signal from CSF flow from the third ventricle to the interpeduncular cistern is lost (Fig. 2.74).

2.8.3 Arachnoid Cysts of Lateral Cerebral Fissures Arachnoid cysts of lateral cerebral fissures are most frequently seen among supratentorial cysts. They may be uni- or bilateral, remain asymptomatic for a long time and infrequently are an occasional finding in CT or MRI. Clinical manifestation begins when a cyst reaches a large volume and causes displacement and deformity of ventricular system (Figs. 2.75–2.77).

Fig. 2.74a–d MRI in a 2-year-old child after the third ventricle’s ventriculostomy for

suprasellar arachnoid cyst expanding into the cavity of the third ventricle. Т1-weighted image (а): a cyst with polycyclic borders is located in the suprasellar area and the third ventricle. b PSIF: loss of signal from CSF flow in the interpeduncular, prepontine and premedullary cisterns. c,d Т2-weighted image: a focus of signal loss from CSF flow in the bottom of the third ventricle and the prepontine cistern

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Chapter 2

Fig. 2.75a–c Lateral cerebral fissure arachnoid cyst leftwards in a 5-year-old child with epilepsy. CT: a mass with even, clear-cut borders,

isodense to CSF in the lateral cerebral fissure leftwards; the left lateral ventricle is compressed, and the ventricular system is displaced rightwards

Fig. 2.76a–c Lateral cerebral fissure arachnoid cyst leftwards in a 10-year-old child with epilepsy. Т2-weighted (а) and Т1-weighted (b,c) images: c see next page


79 Fig. 2.76a–c (continued) there is a large left lateral cerebral fissure arachnoid cyst isointense to CSF in the lateral ventricles. Adjacent brain structures are compressed, and the ventricular system is slightly displaced rightwards

Fig. 2.77a–c Lateral cerebral fissure arachnoid cyst rightwards in a 7-year-old child. CT without contrast enhancement (a): there is a mass isodense to CSF in the right temporal region. CTVG (b,c): a

contrast medium filled the skull-base cisterns and partially reached the cyst cavity and ventricular system (partially communicating arachnoid cyst)

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Chapter 2

Fig. 2.78a–c Giant interhemispheric cyst of the left parietal region and agenesia of corpus callosum in a 6-year-old child. МRI: in axial and sagittal (а,b Т1-weighted) and coronal (c Т2-weighted image) planes. The cyst occupies the major part of the parietal lobe,

its medial border is adjacent to falx cerebri, and the corpus callosum is not visualised. MR signal of the cyst is identical to CSF on both sequences

2.8.4 Interhemispheric and Parasagittal Arachnoid Cysts

Forms of craniosynostosis derive their names from the prematurely fused suture(s) involved: coronal, sagittal, lambdoid and mixed. Craniosynostosis may also be accompanied by intracranial hypertension. Diagnosis is based on clinical signs, changes in skull shape and X-ray craniography findings; the latter reveal marked “fingerprints” in skull bones, absence of a single or many sutures and changes of cerebral fossa shapes. 3D CT may depict completely changes in the skull shape, its bones, density of brain tissue and size of the ventricular system (sometimes enlarged). If craniosynostosis is combined with facial bony abnormalities, then the case is classified as a craniofacial syndrome or craniofacial dysraphism. Crouzon syndrome (of autosomal-dominant inheritance) is a combination of coronal craniosynostosis with orbital hypertelorism, exophtalmus, a beak-shaped nose and micrognathism. Apert syndrome (of autosomal-dominant inheritance) is a combination of coronal craniosynostosis with orbital hypertelorism, hypoplasia of median facial structures (flat face), obliquity of eye fissures and syndactyly. Cloverleaf syndrome (of autosomal-recessive inheritance) presents with a trefoil-like head shape, low positioning of ear helices and facial deformity (Fig. 2.81). Platybasia is a flattening of skull base with dwindling of the basal angle (a junction of line from nasion to the tubercle of sella turcica or its centre, with the line going from this point to the anterior margin of foramen magnum). Normally, the angle is 125–140° (Fig. 2.82). Basilar impression is a protrusion of foramen magnum and superior cervical vertebrae into the cranial cavity, combined infrequently with developmental defects of superior cervical vertebrae. Changes in relationship between bony structures,

Interhemispheric and parasagittal arachnoid cysts are located in the interhemispheric fissure and are adjacent to the falx cerebri (Fig. 2.78). Usually, CT and MRI reveal a combination of these cysts with agenesia of corpus callosum, and infrequently with porencephaly. CTVG and MRI confirm the diagnosis of interhemispheric arachnoid cysts, as these procedures allow ascertainment of the relationship between ventricles and a cyst, the walls of which are poorly visualised on axial CT scans.

2.9

Congenital Anterior Cranial Malformations

2.9.1 Craniosynostosis Craniosynostosis is a premature fusion of one or more cranial sutures. In congenital craniosynostosis, clinical manifestations are more severe, as in almost all of these cases all sutures are fused. Due to premature closure of a single or many sutures, the growth of skull becomes limited. Compensatory skull growth causes changing in the skull’s shape. There are several types of skull deformities: • Scaphocephaly (sagittal suture synostosis) • Brachycephaly (bicoronal synostosis) • Oxycephaly (turricephaly and high-head syndrome) • Acrocephaly or “tower-like skull” (synostosis of all sutures; Fig. 2.79) • Trigonocephaly (premature fusion of the frontal metopic suture; Fig. 2.80) • Plagiocephaly or “askew skull” (unilateral coronal synostosis; frontal and occipital displacement due to premature fusion of the half of coronal and lambdoid sutures)


Fig. 2.79a–i Complete craniostenosis in an 11-year-old child. 3D CT

(а–c), appearance of cranial bones from inside (d,e): fingerprints in the cranial vault bones are markedly enhanced, sutures are not differentiated and the skull-base fossae are shortened. CT in three planes

81

(f–i): orbits are widely separated, density of brain parenchyma is not changed and the ventricular system is correctly located and not dilated

82

Chapter 2 Fig. 2.80a,b Trigonocephaly in a 9-month-

old child. MRI (a,b): The shape of posterior fosse is normal; there is pointed frontal region. There are no signal intensity alterations of brain tissue at sub- and supratentorial locations

Fig. 2.81a–c Cloverleaf syndrome with Chiari II in a 9-month-old child. CT (a–c): the head has an asymmetrical trefoil shape (cloverleaf);

herniation of cerebellar contents into the cervical canal to the C2 level is seen, and the tentorium is placed low. Marked hydrocephalus is present Fig. 2.82a,b Platybasia in a 10-year-old

child. МRI: Т1-weighted (a) and Т2weighted (b) images: flattening of skull base is seen, the basal angle is increased and the brainstem is deformed


83 Fig. 2.83a,b MRI in a 2.5-year-old child

with basilar impression and Chiari II malformation. On Т1-weighted (a) and Т2weighted (b) images, the pons and medulla are elongated with deformity, the lower pole of cerebellar tonsils is narrowed at the С3 level, the fourth ventricle is elongated and narrowed and the tentorium cerebelli is situated downwards. The cervical spine protrudes into the posterior fossa

posterior fossa structures and basal cisterns cause hydrocephalus (Fig. 2.83). Amniotic deformities (unequal conjoined twins) draw surgeons’ attention, as it is possible to separate them (Konovalov et al. 1991). Craniopagus parasiticus is an instance of twins, one of whom is a parasitic twin head (with an undeveloped or underdeveloped body) conjoined to the head of the developed twin. We observed three cases of craniopagus parasiticus. In all cases, selective cerebral angiography was performed to ascertain cerebral blood supply. Partial blood supply of

each child’s brain with vessels of the other child was found on angiography, and according to contemporary classification, these cases were related to the fourth group of craniopagus parasiticus. In the third case, CT and MRI were performed in addition to angiography, and no pathological changes of density or MR signal were revealed. Only a deformity due to enlargement and rotation of one child’s head against the other’s head was found. The first two twins were not separated, and the third pair of twins was successfully separated; since then, children developed relatively normally (Fig. 2.84).

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Chapter 2


9 Fig. 2.84a–f Craniopagus parasiticus twins. Angiograms (а,b carotid, c vertebral) reveal crossed cerebral blood supply. Photo (d) and X-ray craniogram (e) of twins before surgery and photos (f) of children after surgery. g,h MRI of one of the girls 9 years after surgery: Structures of posterior fossa are not changed and correctly located. In the right parietal region, there is a clearly delineated area of high signal intensity, possibly due to ischaemia after surgery. The right lat-

85

eral ventricle is wider than the left one, and the subarachnoid spaces of a convex brain surface are dilated rightwards. i MRI of the second twin: a large area of changed signal isointense to CSF in a T1-weighted image in the right temporal hemisphere (porencephalic cavity). j MR angiogram (MRA): asymmetrical location of arteries of the right and the left cerebral hemispheres and branches of basilar artery

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Chapter 2

Refere n c e s Altman N et al (1992) Posterior fossa malformations. AJNR Am J Neuroradiol 13:691–724 Arendt A (1968) [Fundamentals of paediatric neurosurgery.] Medicina, Moscow (in Russian) Barkovich A (2000) Pediatric neuroimaging, 3rd edn. Lippincott Williams & Wilkins, Philadelphia Barkovich A et al (1992) Gray matter heterotopias: MR characteristics and correlation with developmental and neurologic manifestations. Radiology 182:493–499

Kingsley D et al (1986) Tuberous sclerosis: a clinicoradiological evaluation of 110 cases with particular reference to atypical presentation. Neuroradiology 28:38–46 Knaap M van der et al (1988) Classification of congenital abnormalities of the CNS. AJNR Am J Neuroradiol 9:315–326 Knaap M van der et al (2006) Cerebral white matter abnormalities in 6p25 deletion syndrome. AJNR Am J Neuroradiol 27:586–588 Konovalov A et al (1991) [The successful separation of a craniopagus.] Zh Vopr Neirokhir Im N N Burdenko 2:3–10 (in Russian)

Bilaniuk L et al (1997) Neurofibromatosis type 1: brain stem tumours. Neuroradiology 39:642–653

Kornienko V, Ozerova V (1993) [Paediatric neuroradiology.] Medicina, Moscow (in Russian)

Byrd S et al (1988) The CT and MR evaluation of lissencephaly. AJNR Am J Neuroradiol 9:923–927

Manelfe C, Sevely A (1982) Neuroradiological study of holoprosencephalies. J Neuroradiol 9:15–45

Byrd S et al (1989) The CT and MR evaluation of migrational disorders of the brain. Part I. Lissencephaly and pachygyria. Pediatr Radiol 19:151–156

McLaurin RL (1985) Dandy-Walker syndrom. In: Neurosurgery Ed.Wilkins M, Rengahary S. MCGraw-Hill Book Company 215156

Castillo M et al (2000) Imaging of congenital abnormalities of the brain. In: Orrison W (ed) Neuroimaging. Saunders, Philadelphia, pp 1516–1536

Muhametjanov H et al (1995) [Congenital intracranial arachnoid cysts in children.] Almaty, Tylyn (in Russian)

Delvert J (1982) Anterior dysraphism. J Neuroradiol 1:71–89

Naidich T et al (1983) Chiari II malformation: part IV. The hindbrain deformity. Neuroradiology 25:179–197

DeMyer W (1971) Classification of cerebral malformations. Birth Defects 7:78–9

Naidich T et al (1992) Cephaloceles and related malformations. AJNR Am J Neuroradiol 13:655–690

Fitz CR (1983) Holoprosencephaly and related entities. Neuroradiology 25:225–238

Raybaud C (1983) Destructive lesions of the brain. Neuroradiology 25(4):265-91

Galassi E et al (1982) CT scan and metrizamide CT cisternography in arachnoid cysts of the middle cranial fossa: classification and pathophysiological aspects. Surg Neurol 17:363–369

Polianker Z et al (1965) [A combination of congenital craniocerebral hernia with other craniocerebral maldevelopment.] Vopr Okhr Materin Det 12:39–42 (in Russian)

Glenn O, Barkovich A (2006) MRI of the fetal brain and spine: an increasingly important tool in prenatal diagnosis: part 1. AJNR Am J Neuroradiol 27:1604–1611

Probst F (1979) The prosencephalies. Springer, Berlin Heidelberg New York

Glenn O, Barkovich A (2006) MRI of the fetal brain and spine: an increasingly important tool in prenatal diagnosis: part 2. AJNR Am J Neuroradiol 27:1807–1814 Gomez M (1988) Tuberous sclerosis, 2nd edn. Raven, New York Hart B et al (2000) Neurocutaneous syndromes. In: Orrison W (ed) Neuroimaging. Saunders, Philadelphia, 1717–1759

Smirniotopoulos J et al (1992) The phakomatoses. AJNR Am J Neuroradiol 13:725–746 Toelle S et al (2002) Rhombencephalosynapsis: clinical findings and neuroimaging in 9 children. Neuropediatrics 33:209–214 Wasenko J et al (1990) Sturge-Weber syndrome: comparison of MR and CT characteristics. AJNR Am J Neuroradiol 11:215–220

Harwood-Nash D et al (1976) Neuroradiology in infants and children. Mosby, St. Louis

Yakovlev P, Wadsworth R (1946) Schizencephalies: A study of the congenital clefts in the cerebral mantle, J.Neuropathol ExpNeurol 5:116-130

Irger I (1981) [Dandy-Walker syndrome.] Vopr Neirokhir 2:51–59 (in Russian)

Yokota A et al (1986) Anterior basal encephalocele of the neonatal and infantile period. Neurosurgery 19:468–478

Chapter 3

3

Cerebrovascular Diseases and Malformations of the Brain

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20

Stenosis and Thrombosis of the Cerebral Vessels . . . . . . . . .. . Cerebral Ischaemia .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lacunar Infarction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . Chronic Ischaemic Brain Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stroke in Children .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Non-Atherosclerotic Stenosis and Occlusion of Cerebral Arteries . . . . . . . . . . . . . . . . . . . . . . . . . . Thrombosis of the Venous Sinuses .. . . . . . . . . . . . . . . . . . . . . . . . . Haemorrhagic Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intracerebral Haemorrhages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extracerebral Non-traumatic Haemorrhages .. . . . . . . . . . . . . . Intratumoral Haemorrhages .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hypertense Haemorrhages .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hypertense Encephalopathy .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rare Causes of Intracerebral Haemorrhage . . . . . . . . . . . . . .. . Intracranial Arterial Aneurysms .. . . . . . . . . . . . . . . . . . . . . . . . . .. . Intracranial Vascular Malformations .. . . . . . . . . . . . . . . . . . . . .. . Carotid–Cavernous Fistulas .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cavernous Angioma .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Capillary Telangiectasias .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Venous Malformations .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.1

Stenosis and Thrombosis of the Cerebral Vessels

87 101 139 154 158 160 172 175 176 188 193 196 197 197 199 247 302 309 316 320

Atherosclerotic lesions of the vessels, leading to stenosis and occlusion of the epiaortic and cerebral arteries, are one of the main causes of brain infarction in adults (Seeger 1995). Atherosclerosis accounts for 90% of brain thromboembolisms in the developed countries.

3.1.1 Atherosclerosis of the Cervical and Cerebral Vessels The pathogenesis of atherosclerotic transformation of blood vessel wall is in fact a multifaceted process. The main reasons are alteration (or the response to the alteration of vessel’s wall) and abnormalities of cell proliferation, somewhat resembling that in a malignant transformation. The above-mentioned factors may work alone or in combination in atherosclerotic lesion development.

The first stage of plaque organization is likely to be linked to local changes of the vessel endothelium or minimal alteration of intima. Platelet aggregation starts at the site of such alteration. The damaged endothelium becomes permeable for large molecules such as lipoproteins. Phagocytes and smooth muscle cells migrate to the site of alteration, and they begin to proliferate and accumulate fat esters that slip through damaged wall. Their subsequent death leads to release of the cell’s detritus that in turn serves a main substratum for the cholesterol plaque. Further development of this process results in creation of a fibrous covering (which covers fat-containing cells that continue to accumulate detritus and cholesterol crystals). Secondary inflammatory changes are accompanied by growth of granulation tissue and neovascularisation. Atherosclerotic plaques often contain small haemorrhages and necrotic areas. The plaque damage leads to the disruption of the relatively smooth surface of internal artery wall, and ulcerations in the degenerated plaque are the sites where thrombi form—these are the main sources of the subsequent distal thromboembolism.

3.1.2 Classification of Artery Stenosis As a rule, the atherosclerotic process leading to stenosis is located in the bifurcations and ostia of big arteries. Atherosclerosis affects carotid arteries more frequently (the difference is 20%) than it does arteries of posterior circulation territory. Lesions of the extracranial parts of carotid arteries are found fourfold more frequently than are lesions of the intracranial parts of carotids. The degree of cervical artery stenosis is estimated as a ratio between the square of the functioning part of artery at the site of stenosis and square of the same artery in the site not affected by stenosis (Ferguson et al. 1999). The absence of blood-flow imaging means complete artery occlusion. The crucial point in treatment selection (conservative therapy or surgical–endovasal intervention) is the level of stenosis. In this regard, all stenoses are divided into two categories: (1) stenoses less than 50%—in these cases, surgical inter-

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Fig 3.1a,b CTA of cervical arteries. MIP reconstruction in frontal (a) and axial projections (b). Atherosclerotic plaque with heterogeneous structure is visualised within the ostium of the right internal carotid artery

vention should not be performed; and (2) stenosis more than 70–75%—in these cases, surgical intervention is preferable. It is important to assess the consistency (using CT) and echo characteristics (using ultrasound) of the atherosclerotic plaque, which narrows the artery, in order to define the strategy of surgical intervention. The following plaque classification is based on the CT data: • Homogeneous (low density in comparison with the artery itself) • Heterogeneous (includes areas of low and high density) (Fig. 3.1) • Partly or totally calcified (contains calcium in the plaque structure) In terms of atherosclerotic lesion spreading (on the artery wall), all plaques are divided into local (length less than 1.5 cm) and prolonged (length exceeds 1.5 cm). In terms of location, there are local plaques (occupy part of the artery wall), semi-concentric plaques (occupy half of the artery wall perimeter) and concentric plaques (occupy more than half of the artery wall perimeter). In assessing plaques by the type of surface, one can detect plaques with a smooth surface and plaques with uneven surface, which contain ulcerations and haemorrhages.

3.1.3 Pathological Deformities and Abnormalities of the Epiaortic Arteries Among all cases of cerebral vascular insufficiency, not the least role is played by pathological deformations and congenital abnormalities of the epiaortic arteries. They account for about 12% of all ischaemic stroke cases. In 40% of all cases, the pathological deformation of the carotids coincides with

atherosclerotic lesions of the same artery, which significantly increases the risk of stroke in the area of that artery. The following types of pathological deformation are defined: • C- and S-shaped coiling (Figs. 3.2–3.5) • Artery twisted at a sharp angle (kinking) (Fig. 3.6) • Formation of pathological loops and spirals (coiling) (Fig. 3.7) • Combination of various types of deformations (Fig. 3.8) The main criteria for surgical treatment of pathological deformations in extracranial segments of cerebral arteries are the presence of clinical signs of brain disorder due to circulation dysfunction and the haemodynamic significance of deformation (maximum systolic velocity = 200 cm/s or more). Currently, numerous methods are being used in diagnosing of atherosclerotic changes in cervical and brain vessels. Important among the methods is digital cerebral angiography, which identifies of the degree and spread of vessel narrowing and revealing collateral blood flow (Wolpert 1992; Osborn 1999). It is necessary to mention the increased role of various noninvasive methods such as ultrasound Doppler, duplex scanning, and spiral and multispiral CT and MRA (Furst 1996; Shier et al. 1997; Callida 1999; Shakhnovich 2002). Ultrasound method. Transcranial Doppler reveals linear speed asymmetry of blood flow between intracranial magistral arteries in the case of stenosis, and it assesses collateral circulation reserves and their compensatory ability, and transcranial Doppler helps to detect microemboli in the area of intracranial arteries. Colour duplex scanning of the extracranial segments of carotid and vertebral arteries reveals of the presence of artery stenoses, estimating their degree and haemodynamic significance (Geroulakos 1996; Calliada 1999).


89

Fig. 3.2a–c MRA of cervical arteries. Marked coiling with a twist of the right vertebral artery and hypoplasia of the left vertebral artery are

seen. 2D TOF regimen

Fig.3.3a–c Coiling of extracranial segment of the internal carotid artery. CT angiography [(CTA) a,b] and MRA (c)

with contrast enhancement (different patients)

90

Fig. 3.4a–i Coiling of vertebral arteries in the V1 segment. MRA (a)

with contrast enhancement, MIP reconstruction (b,c), MRA in 2D TOF regimen (d), and 3D reconstruction with application of “Navi-

Chapter 3

gator” algorithm (e,f). S-shaped coiling of initial segments of both vertebral arteries is seen. CTA (g–i) of another patient’s cervical arteries coiling combined with a twist of left vertebral artery ostium


91

Fig. 3.5 Coiling of the right and the left common carotid arteries on DSI

Fig. 3.6a–c MRA with contrast enhancement of cervical arteries. MIP reconstruction (a–c). A marked twist is visualised within the ostium of the left vertebral artery

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Fig. 3.7a–c 2D TOF MRA of cerebral arteries. MIP reconstruction (a) and 3D reconstruction with application of “Navigator” algorithm (b,c)

of loop of the right internal carotid artery

Fig. 3.8a–c Combination of coiling and twist of the V1 segment of the left vertebral artery. MRA with contrast enhancement: MIP

reconstruction (a,b) and 3D (c) reconstruction (a view from behind) Fig. 3.9 Ultrasound duplex scanning at the level of bifurcation of the common carotid

artery. Stenosis of carotid artery lumen is seen


93

Fig. 3.10a–c Thrombosis of cerebral arteries in different patients. Digital angiogram: thrombosis of internal carotid artery ostium (a,b) and

stenosis of supraclinoid segment of internal carotid artery (c)

Duplex scanning also assesses the plaque’s morphological structure (Fig. 3.9). Digital subtraction angiography. Direct infusion of the contrast into the artery is still considered the gold standard by many researchers in terms of diagnostics of different disorders of brain circulation system (Fig. 3.10). It is noteworthy that in the diagnosis of stenosis, cerebral angiography pursues three main goals: (1) to define the degree of stenosis, (2) to identify concomitant changes in blood vessels, and (3) to estimate current and (more importantly) the potential collateral circulation. The main indication for vascular surgery is a severe stenosis of more than 70% of initial vessel diameter. Taking that into consideration, the exact measurement of stenosis degree is an extremely important task. At least two projections are necessary for adequate estimation of stenosis degree. The percent of stenosis is calculated on a basis of comparison between vessel diameter at the site of stenosis and vessel diameter at the site located distally to the site of stenosis, with subsequent multiplication by 100. It is very important to distinguish the full occlusion from the so-called pseudoocclusion, as patients with the stenoses (even with very severe cases) remain candidates for thromboendarterectomy, unlike patients with full occlusion. In these cases, the modified procedure with prolonged imaging of a vessel and with slow contrast infusion is appropriate. CT and CT angiography. Unlike direct angiography, which adequately identifies only an internal part of the vessel, CT has bigger potential as an assessment of atherosclerotic lesions on the vessel wall. CT with contrast enhancement allows us not only to estimate the blood flow in the vessel, but, and what is especially important, also to visualise degenerative (atheromatous) changes of the vessel wall, and it distinguishes between calci-

fied plaques and non-calcified (“soft”) plaques. CT is highly sensitive, even to the minimal calcifications (Fig. 3.11). Spiral CT angiography has even greater potential. Use of thin slices (1 mm and less) in the examination of a large anatomic volume and single-stage bolus contrast infusion yields high-quality images of the main vessels after subsequent megaframe initialisation packet (MIP) processing (Link 1996). Thus, depending on the type of used program, it is possible to obtain the image of arteries only, or the simultaneous image of arteries and veins. The subsequent mathematical processing on a workstation raises the quality of vessel images, especially with use of 3D colour reconstruction of the vessel (Goddard 2001; Marcus et al. 1999). It also performs quantitative analysis of the site of stenosis (Figs. 3.12–3.14). One of the big advantages of CT angiography is the ability to examine a large anatomic volume, as the subsequent processing and 2D and 3D reconstruction of vessels provides a unique opportunity to reconstruct a vessel’s trajectory in the background of cervical vertebra or skull bones (Fig. 3.15). MRT. The estimation of vessel patency with the use of standard MR scanning modes can involve certain complexities, due to various factors. In standard Т1 and Т2 modes, normal vessels have a low MR signal that is caused by a so-called flow–void phenomenon. Presence of an iso- or hyperintense signal from an arterial vessel in these modes is suspicious with regard to thrombosis, stenosis or occlusion (Fig. 3.16). However, the slow blood flow in certain vessels’ segments (in the sites of widening or coiling) and the effect of “saturation” on extreme scans of T1-weighted imaging can lead to increase of the signal from vessels and hence can resemble vessel stenosis and partial thrombosis. Moreover, presence of typical effect of signal loss from a vessel on Т1- and Т2weighted imaging is still not the confirmation of the stenosis absence. Therefore, the appropriate MRI estimation of intra-

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Fig. 3.11a–c CTA of cervical arteries in patients with atherosclerosis of cerebral arteries. MIP reconstruction in axial (a), frontal (b), and sagittal (c) projections reveals small calcinated plaques in ostium of the left internal carotid artery and right vertebral artery (near bifurcation). Different patients

Fig. 3.12a–f CTA in patients with atherosclerosis of cerebral arteries. CTA of cervical arteries: MIP reconstruction (a,b), 3D reconstruction (c,d), and virtual endoscopy (e,f). In the ostium of the left

internal carotid artery, atherosclerotic plaque with heterogeneous structure with soft-tissue and calcinated components is visualised. The plaque causes marked stenosis of carotid arteries bilaterally


95

Fig. 3.13a–c CTA in patient with atherosclerosis of cervical arteries: MIP reformation in coronal plane (a) and 3D reconstruction (b) and virtual endoscopy (c). Calcinated plaques are visualised in ostium of the internal carotid arteries

Fig. 3.14a–f Techniques for quantitative assessment of stenosis of an artery: MIP reconstruction in coronal projection (a) and calculation

of lumen square at the level of stenosis and above a plaque (b,c). Another example: calculation of maximal size and of lumen square at the level of stenosis (d–f)

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Chapter 3 Fig. 3.15a,b CTA of cervical arteries. MIP (a) and 3D (b) re-

construction of vertebral artery trajectory at the level of cervical vertebrae

Fig. 3.16a–f Thrombosis of the left internal carotid artery: MRI in T2-weighted images (a–c) and FLAIR (d). Hyperintensity is seen within the internal carotid artery at the level of pyramid of temporal bone and sinus cavernosus. A small infarction is seen in the left basal ganglia on Т2- (e) and Т1- (f) weighted images


97 Fig. 3.17a–c Thrombosis of the right internal carotid artery. Т2-weighted imaging (a) and 3D TOF MRA (b,c) demonstrate that (a typical image) the right internal carotid artery is absent. Blood supply of the right middle cerebral artery must proceed via the anterior communicating artery of the left internal carotid artery area

Fig. 3.18a–c Thrombosis of the left internal carotid artery. Т2-weighted imaging (a) and 3D TOF MRA, MIP reconstruction in axial (b) and

coronal (c) projections. A typical image—the left internal carotid artery is absent

and extracranial vessels should be performed with the use of special MRA software. MRA. Currently, several methods with the application of time-of-flight (TOF) and phase-contrast (PC) techniques are being used in MRA of cranial and cervical arteries. The use of the PC technique is limited by the required length of the examination and relatively smaller resolution in comparison with TOF. It is necessary to emphasise the use of different approaches and MR techniques in the imaging of cranial and cervical arteries. In order to maximise the visualisation of extracranial segment of carotid and vertebral arteries, it is preferable to scan in coronal and sagittal planes, because they have an advantage over the axial plane in maximising the visualisation of artery length. On the other hand, it is always necessary to remember that axial orientation of scans receives a higher signal from an artery and therefore achieves greater difference in signals between stationary tissue and moving blood. Considering the fact that the duration of vessel examination remains relatively long, it is preferable to maximise the visible

length of arteries, clarifying the image quality. In the imaging of cranial arteries, we prefer an axial orientation of scans, thus obtaining high-quality images of vessels, with enough capture of anatomical space. The different sets of techniques are used in an examination of cranial and extracranial arteries. In our institute, 3D TOF angiography is used mainly in examination of cranial segments of the carotid arteries (within the boundaries of a skull). The combination of magnetization transfer pulse sequences and saturation of MR signal from vein produces high-quality images of cerebral arteries in both hemispheres. A stenosis is visible in the form of local loss of signal from the vessel, with the restoration of an artery image distal to the site of stenosis. Occlusion leads to full disappearance of high MR signal from the vessel, then the absence of respective artery distally, and finally the site of occlusion (Figs. 3.17–3.19). As a rule, various ischaemic changes of the brain tissue— depending on the stage of ischaemia—are visualised in the area of occluded artery supply. In our opinion, the potential of the 3D TOF technique is limited by the low sensitivity of this

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Fig. 3.19a–c Thrombosis of the left vertebral artery. Т2-weighted imaging (a,b) and 3D TOF MRA (c) do not depict the left vertebral artery

in cervical region (arrow), and post-ischaemic changes are seen in the left cerebellar hemisphere. MRA demonstrates a small fragment of the left vertebral artery (arrow)

Fig. 3.20a–c Stenosis of ostium of the right internal carotid artery. 2D TOF MRA (a) and virtual endoscopy (b,c) reveal stenosis of the affected artery (arrows)

Fig. 3.21a–c MRA of cervical arteries, with contrast enhancement. MIP reconstruction (a): coronal projection. 3D reconstruction (b): cervical arteries branching from the arch of aorta (common branching of brachiocephalic trunk and the left internal carotid artery),

and their characteristics at cervical level (stenosis of distal segment of the left common carotid artery). Virtual endoscopy at the level of stenosis (c)


99

Fig. 3.22a–f MRA of cervical arteries, with contrast enhancement (3D reconstruction). Forward (a) and backward (b) view and in different

angles (c–f). Coiling of the V1 segment of the left and hypoplasia of the right vertebral arteries

method to the visualisation of streams with low-velocity flow, for instance, at the site of stenosis. This can be the reason of overestimation of stenosis length and degree. 2D TOF angiography is used mainly for examination of extracranial segments of carotid and vertebral arteries from the arch of the aorta up to the point of their entry into the cranium. The capture of anatomical space with the use of this technique is greater than with the use of 3D TOF, which visualises the large segment of an artery in a short time (about 10–12 min). An obligatory condition is simultaneous use of saturation volumes for the suppression of the MR signal from the veins (Fig. 3.20). Although 2D TOF technique better visualises the lowvelocity blood flow than does the 3D TOF method, it nevertheless has many disadvantages that decrease the quality of blood flow estimation. In the case of severe stenosis due to out-phasing of spins, observed when the blood flow through the narrowed artery at the site of stenosis becomes turbulent and complex, this technique can overestimate the length of artery affected by stenosis. At the same time, our vast experience in MR diagnostics of epiaortic vessels stenoses revealed a high degree of correlation between data obtained from the

usage of 2D TOF method and from selective angiography. 3D MRA with the bolus infusion of contrast medium is a relatively new, minimally invasive method of cerebral vessel visualisation (Borisch et al. 2003; Roberge 2003; Alvarez-Linera et al. 2003; Lombardy and Bartolozzi 2004). It is still less used for cranial vessels examination, due to lower resolution than that of usual 3D TOF. The method uses high-speed impulse sequence based on the gradient-echo technique. With a large anatomical capture, the quick examination time of 30–60 s occurs during breath holding, thus preventing occurrence of artefacts from breathing and swallowing. MR contrast medium is administered intravenously at a rate of 4–5 ml/s. The usage of new, highly concentrated contrast medium (like Gadovist, with a concentration 1 mmol/ ml) decreases the quantity of infused solution for MRA of cervical vessels from 20 to 10 ml. The subsequent mathematical 2D or 3D postprocessing yields images in any projection and under any visual angle (Figs. 3.21–3.24). The main limitation of this program is insufficient visualisation of arteries with a low-velocity flow, for example, in

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Chapter 3

Fig. 3.23a–d MRA without contrast enhancement of ostium of the internal carotid artery (a–c different patients) reveals stenosis of the initial artery segment. Thrombosis of the internal carotid artery: the small “stump” of the carotid artery with thrombosis is visualised (d)

Fig. 3.24a–f Thrombosis of ostium of the internal carotid artery. The first observation (a,b): occlusion of ostium of the right internal carotid artery (arrow); virtual endoscopy (c) confirms the complete

occlusion of the artery. Another case: thrombosis of ostium of the left internal carotid artery. 3D reconstruction (d,e) and virtual endoscopy (f)


prolonged hypoplasia of the vertebral artery. It is possible to compensate this disadvantage by performing beforehand 2D TOF MR examination (Fig. 3.25). Comparison of the data obtained at complex examination obviates diagnostic mistakes (Lell 2007). As a whole, according to the opinion of the majority of researchers this method of MRA, especially in combination with CT angiography, can replace direct angiography of cervical vessels in case of suspicion of atherosclerotic narrowing of an artery.

3.2

Cerebral Ischaemia

The term stroke is widely used; however, it is not a precise term for a definition of the sudden beginning of neurological deficiency. Clinically, this condition is often called cerebrovascular accident. Stroke, or cerebrovascular accident, is a blood supply disturbance of the brain. A set of pathological conditions, including atherosclerosis, thrombosis, embolism, hypoperfusion, vasculitis and venous

Fig. 3.25a–f 2D TOF: MIP reconstruction (a) and bolus contrast enhancement MRA (b,c) illustrate stenosis of ostium of the left vertebral artery. 2D TOF regimen reveals that the length of stenosis is greater than was seen in a study with contrast enhancement. Another

101

stasis, can affect brain vessels and lead to a stroke. Neuroimaging methods always played the important role in stroke diagnosis; nevertheless, their main role was in excluding other brain pathology or in estimation of surgically accessible lesions. In clinical and diagnostic medicine development, stroke treatment has undergone certain changes, and now the main studies in this area are focused on early diagnostics of brain changes occurring just after blood circulation disruption and treatment strategies of the patient’s category based on obtained data. Wider use of the latest CT and MRI protocols, such as DWI/PWI in clinical practice, vastly expanded treatment options for already-occurred ischaemic changes. What is particularly important is that it became possible to prevent further development of brain damage resulting from the pathological chain of reaction, which starts after a critical decrease of brain perfusion. Frequently, cerebrovascular disease results from decrease or termination of blood supply, glucose and other metabolites

patient: 2D TOF (d) and bolus contrast enhancement MRA and 3D reconstruction (e,f). 2D TOF regimen visualises hypoplasia of the right vertebral artery better

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Chapter 3

Fig. 3.26a–i Global cerebral ischaemia. Т2-weighted imaging (a–c), FLAIR (d–f), and Т1-weighted imaging (g–i) reveal areas of signal change

in periventricular regions in occipital and parietal lobes, and basal ganglia. Ventriculomegaly and foci of haemorrhagic transformation in basal ganglia are seen bilaterally (Т1-weighted image)


103

Fig. 3.27a–f Global cerebral ischaemia. FLAIR (a–c), T1 (d) WI and MRAG (e,f). Post-ischemic changes in occipito-parietal regions and basal ganglia bilaterally along with astrophy and ventriculomegaly are seen

as well as from insufficient excretion of biological products. As an outcome, neural tissue cannot function properly under conditions of decreased blood flow. Another term synonymous with stroke is brain ischaemia. As a whole, brain ischaemia is divided into two main categories: global brain ischaemia, or ischaemia in which different regions of the brain are involved, can result in severe cardiac dysfunction, systemic arterial hypotension, or cardiac arrest (Figs. 3.26,–3.28); and local brain ischaemia, which results from limited disruption of brain circulation in the area of one artery (Fig. 3.29). The latter type of brain ischaemia occurs more often, and this chapter is dedicated to it. Three main aetiological reasons lay at the foundation of stroke symptoms: brain infarction, cerebral haemorrhage and subarachnoid haemorrhage. In clinical practice, the most common is an ischaemic infarction developing due to inadequate blood flow in certain vascular area. It is necessary to note that a good deal of literature is dedicated to the problem of stroke both in Russia and abroad. The process of understanding of pathophysiological changes

occurring during the stroke underwent substantial modifications. During the past several years, much new data concerning stroke diagnostic as well as treatment have been obtained. Nevertheless, the foundations of the stroke theory were outlined at the end of past century by the work of Russian scientists such as N.K. Bogolepov (1971), I.V. Gannushkina (1973, 1975), E.V. Shmidt (1976), E.I. Gusev (1979) and N.V. Vereshchagin (1986).

3.2.1 Pathophysiology of Cerebral Ischaemia A clear understanding of pathophysiological reactions developing in the background of critical cerebral blood flow reduction is an important point of any diagnostics of ischaemic cerebral insult, correct interpretation of the obtained data and correct assessment of diagnostic changes on CT and MR images of the affected brain in the course of the ischaemic process.

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Chapter 3

Fig. 3.28a–f Global cerebral ischaemia. Т2-weighted (a), FLAIR (b,c), Т1-weighted (d) images and DWI (e). Post-ischaemic changes in frontoparietal-temporal regions with haemorrhagic transformation in basal ganglia bilaterally. МR spectroscopy reveals marked decrease of the NAA peak, and a two-humped lipid–lactate peak appeared (f)

Fig. 3.29a–c Ischaemia in the right middle cerebral artery area. Т2-weighted (a), Т1-weighted (b) images and DWI (c) clearly demonstrate the area of signal change in the right temporal region


The consequences of acute focal ischaemia and degree of its damaging influence crucially depend on the severity and duration of such blood flow decrease. Experiments with biological models demonstrated that neuronal electrical activity loss happens within seconds after arterial occlusion (Garcia 1983). In general, loss of function of the affected site of a brain develops when the brain blood flow decreases to a level of 15–20 ml/100 g/min (Mies 1991; Hossmann 1994). A brief picture of the experimentally established cascade of the metabolic reactions occurring in brain tissue as a result of blood flow decrease is presented in the Table 3.1. Blood flow decrease to 70–80% of normal levels (below 50 ml/100 g per minute) is accompanied by the reaction of albumin synthesis inhibition (Hossmann 1994). This level is considered the first critical level of a cerebral ischaemia. Further blood flow decrease to 50% of normal levels (approximately 35 ml/100 g/min) leads to anaerobic glycolysis activation and increased lactate concentration, development of lactic acidosis and cytotoxic oedema. Progressive brain ischaemia and further blood flow decrease (to 20 ml/100 g/ min) is accompanied by decrease of ATP synthesis, development of energy insufficiency, destabilization of cellular membranes, the release of amino acidergic transmitters, and by the function impairment of the active ion transport canals. Blood flow decrease below the critical level of 10 ml/100 g/min leads to cell membrane depolarization, currently considered the main criterion of irreversible cell damage (Hossmann 1994). In addition, it is necessary to note that blood flow decrease in an ischaemic area has heterogeneous character. The heterogeneity has been clearly proved in experimental as well as in clinical studies. The central ischaemic core has the lowest perfusion, which leads to prompt (within several minutes) cell death. The peripheral ischaemic area retains higher perfusion level, and irreversible cell changes develop for a period more prolonged. This peripheral ischaemic but alive area is called the area of penumbra (Astrup et al. 1981; Fisher and Garcia 1996). This area retains energy metabolism, and it has only functional changes. Further development of ischaemia leads to exhausting of local perfusion reserve (for instance, in the case of inadequate treatment or orthostatic hypotension), and neurons become highly sensitive to any further blood flow de-

105

Fig. 3.30 Schematic representation of temporal lobe infarction components after thrombosis of the middle cerebral artery. Arrows show areas of irreversible changes (core of infarction) and area of ischaemic penumbra

crease; the core can undergo irreversible structural changes because of this. The ischaemic core expands at the expense of the penumbra’s continuing necrosis. The penumbra, however, can be salvaged by blood flow restoration and use of neuroprotective agents. The penumbra is a main target for early diagnostics with the use of modern neuroradiological methods and early treatment (Fig. 3.30).

Table 3.1 Brain tissue reactions to blood flow decrease

a

Local blood flow (ml/100 g/min)

Brain tissue reactions

55–80a

Normal state

Below 50–55 (the first critical level)

Albumin synthesis inhibition Selective genes expression

Down to 35 (50% decrease; the second critical level)

Anaerobic glycolysis activation. Increase lactate, cytotoxic oedema

Down to 20 (the third critical level)

Energy deficiency (decrease ATP synthesis)

10–15

Anoxic membrane depolarization, cell death

Normal blood flow limits vary, depending on examination time and location of sites where measurement is taking place (in the same person) from 45 to 110 ml/100 g/min. (Astrup et al. 1981; Obrenovitch 1995; Ueda et al. 1999)

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3.2.1.1

Chapter 3

Pathology

Macroscopic brain examination in the acute phase of ischaemia might not reveal any pathological changes. However, microscopic examination can detect neuronal changes like mitochondrial swelling and disorganization (neurons are more sensitive to ischaemia than are astrocytes and oligodendroglia) that are visible 20 min after ischaemia onset. Such changes can be the sole mark of ischaemia during the first 6 h. Then, microscopic examination reveals neuronal corrugation cytoplasmic eosinophilia, ribosomal aggregation and synaptic “encrustation”. Macroscopic changes become visible after 6 h from ischaemia onset. The time of maximum expression of focal brain oedema, which represents cytotoxic oedema, is the interval between 24 and 48 h; this leads to brain gyri thickening and to the blurring of boundaries between grey and white matter. The duration of acute ischaemia is the first 2 days. Then, subacute infarction phase starts. During this phase, the processes of further brain thickening and softening unfold. This period lasts 7–10 days (after stroke onset). Brain oedema in the ischaemic area is maximally expressed at 3–5 days after stroke onset. At this stage, vasogenic and cytotoxic brain oedema take place. At this time, the reparation processes are active. Microglia cells, neutrophiles and macrophages begin to phagocytise necrotic tissue. This process leads to cystic cavity formation. Reparation processes are more actively unfolding at the peripheral infarction area. The chronic phase can extend to several weeks or even months. In this period, damaged necrotic tissue is resorbed with the formation of the areas of encephalomalacia, surrounded by gliosis of adjacent brain tissue. The wrinkled gyri and the dilatation of adjacent parts of ventricular system can be found in cases of relatively large infarction areas. The above-mentioned pathological changes appear in almost any type of infarction; however, the specific condition of the damaged tissue site varies, depending on the location, size and cause of the ischaemia.

3.2.1.2

Epidemiology

During the past decade, statistical observations revealed the considerable growth of the morbidity of cardiovascular diseases, which in turn translated into the increased number of stroke cases and cases of chronic brain circulation disorders. Annually, about 6 million people worldwide suffer from stroke, and about 450,000 suffer from stroke in Russia. This means that every 1.5 min, someone in Russia develops stroke symptoms for first time (Gusev and Skvortsova 2001; Gusev et al. 2003). The same data on frequency of new stroke cases are reported for the United States population, and it was mentioned that 80% of all these cases are ischaemic stroke as opposed to haemorrhagic stroke (which accounts for the remaining 20%). According to data of the joint studies that were conducted in the United States and Europe, ischaemic stroke morbidity is

about 130–200 cases in a year per 100,000; however, it reaches 550 cases per 100,000 in seniors (64–75 years old). It is necessary to note that according to the international epidemiological studies, 4.7 million people die annually from stroke. In the majority of countries, including the United States and Europe, stroke is the second or third leading cause of death. In Russia, this disease occupies second place, after cardiovascular disease. Stroke mortality at 30 days is close to 35%, and in the course of a year, 50% of stroke patients die— every second one (Gusev and Skvortsova 2001). Stroke is the main cause of disability, and the increase of stroke morbidity is observed in persons of working age (

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