DEMYELINATING DISEASES OF THE BRAIN

John R. Hesselink, MD, FACR

MR imaging is exquisitely sensitive for detecting brain abnormalities. Particularly in the evaluation of white matter diseases, MR far outperforms any other imaging technique. Lesions that may be quite subtle or even invisible on CT are often clearly seen on the MR scan. The MR signal characteristics of white matter lesions are similar and relatively nonspecific, but other distinguishing features are often present to assist in diagnosis, such as the pattern of the abnormality, location, and enhancement features.

The white matter is affected by many disease processes. The primary demyelinating disease is multiple sclerosis, but many other metabolic and inflammatory disorders result in deficient or abnormal myelination. Histologically, myelin abnormalities are either demyelin-ating or dysmyelinating. Demyelination implies destruction of myelin. Dysmyelination refers to defective formation or maintenance of myelin resulting from dysfunction of the oligodendrocytes. Most of the dysmyelinating disorders are caused by metabolic defects that present in infancy. White matter diseases in older children and adults are generally demyelinating or a combination of the two processes.