Magnetic resonance imaging (MRI) is now considered 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 tis sue contrast in MRI which allows gray matter, unmyelinated, and myelinated white matter to be distinguished and their respective disorders identified. The pre sent book is devoted to the disorders of myelin and myelination. A growing amount of detailed in vivo information about myelin, myelination, and myelin dis orders has been derived both from MRI and from MR spectroscopy (MRS). This prompted us to review the clinical, laboratory, biochemical, and pathological data on this subject in order to integrate all available information and to provide im proved 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. After a brief historical review about the increasing knowledge on myelin and my elin 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 me tabolism are concerned. This classification serves as a guide throughout the book. All items of the classification will be discussed and, whenever relevant and possi ble, be illustrated by MR images.
