Magnetic resonance findings in leucodystrophies and MS.

White matter diseases are a frequent diagnosis problem in adult patients. They are divided into leucodystrophy, defined by abnormal white matter from the beginning, and leucoencephalopathy, with an initial normal white matter. In addition, two different natures have to be considered: vascular and non-vascular. Vascular diseases are mainly acquired and related to atherosclerosis. Genetic vascular disorders are mostly secondary to Notch3 mutations, defined as cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL). Occurrence of leucoaraiosis and lacunae on T2 sequences, and microbleeds on Gradient Echo sequences, strongly suggest this diagnosis. Some magnetic resonance (MR) patterns can help to identify genetic leucodystrophies, such as childhood ataxia with central nervous system hypomyelination/leucoencephalopathy with vanishing white matter disease (progressive rarefaction and cystic degeneration of the affected white matter, replaced by water); Alexander disease (hypointense signals on T2 sequences involving grey matter, brainstem and cervical cord, with marked atrophy); megalencephalic leucoencephalopathy with subcortical cysts (diffuse, symmetrical white matter lesions, with constant frontoparietal and anterotemporal subcortical cysts); leucoencephalopathy with brainstem and spinal cord involvement and high lactates syndrome (extensive demyelination, involvement of the brainstem, i.e. cerebellar peduncles, intraparenchymal and mesencephalic trigeminal nerves and spinal cord, mainly in the lateral corticospinal tracts and dorsal columns). Half of the genetic adult leucodystrophies remain without any precise diagnosis. This review describes MR in the adult leucoencephalopathies and in multiple sclerosis (MS). The first part will focus on MR patterns of vascular and nonvascular adult leucoencephalopathies, the second part on MR findings in MS and MS-related diseases. Specific MR patterns in both diseases will be summarized and compared.