Magnetic resonance imaging (MRI) is now considered to be the imaging modality of choice for the majority of disorders affecting the central nervous system. This is particularly true for gray and white matter disorders, thanks to the superb soft tissue contrast in MRI which allows gray matter, unmyelinated, and myelinated white matter to be distinguished and their respective disorders identified. The present book is devoted to the disorders of myelin and myelination. A growing amount of detailed in vivo information about myelin, myelination, and myelin disorders has been derived both from MRI and from MR spectroscopy (MRS). This prompted us to review the clin-ical,laboratory,biochemical, and pathological data on this subject in order to integrate all available information and to provide improved insights into normal and disordered myelin and myelination. We will show how the synthesis of all available information contributes to the interpretation of MR images.
Following a brief historical review of the increasing knowledge on myelin and myelin disorders, we propose a new classification of myelin disorders based on the subcellular localization of the enzymatic defects as far as the inborn errors of metabolism are concerned. This classification serves as a guide throughout the book. All items of the classification will be discussed and, whenever relevant and possible, illustrated by MR images.
We are aware of the fact that in a number of myelin disorders MRI is not a part of the usual diagnostic work up because a definite diagnosis is reached by other means, such as biochemical investigations of blood and urine, enzyme assessment or detection of specific antibodies. However, in many disorders MRI may facilitate a rapid diagnosis and early instigation of treatment, thus preventing structural cerebral damage. In other cases the role of MRI is to visualize the extent of brain damage and give an indication of the prognosis. In disorders which present in a nonspecific way, for instance with behavioral problems or learning difficulties, MRI can be one of the first-line investigations. It is important to be acquainted with the various MRI patterns of the myelin disorders, as an early diagnosis may be of major importance in young families with a view to the provision of adequate genetic counseling.
MRS has been of limited clinical importance until now, and its application in patients only has a short history. We do, however, expect it to be a promising technique in the field of myelin and myelin disorders in clinical as well as in basic, experimental research and have, therefore, devoted a separate chapter to this subject.
This volume was written by a neuroradiologist and a neurologist/child neurologist. It is the product of close cooperation, animated discussions, strong arguments, restructuring, rewriting, and editing, in which they had an equal share. If the reader finds value in this monograph, it is because of this dual effort.
Amsterdam and Utrecht, March 1989
M.S. van der Knaap
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