[Neuroradiological aspects of encephalitis disseminata]

Magnetic resonance imaging (MRI) has developed without doubt to the most important investigation method in multiple sclerosis. MRI is very sensitive to detect MS lesions but unfortunately of limited specificity. The purpose of this review is 1. to work up the MRI characteristics of MS lesions, 2. to derive recommendations for MRT-protocolls for daily radiological work and 3. to discuss new MR developments. MS lesions in the acute inflammatory stage show first an enhancement of GD-DTPA due to break down of the blood brain barrier and develop a T2-hyperintensity due to an edema. The following disease course is categorized in a phase of reparation and remyelinisation respectively, of gliosis and a defect stage. MS-plaques in the remyelinisation and gliotic phase appear as hyperintens lesions on T2-weighted scans. Chronic MS lesions with a defect are also T2-hyperintens and demonstrate additionally due to severe axonal loss a hypointensity on short TR SE scans. MS lesions exhibit a characteristic distribution. They are found typically periventricular, in the corpus callosum and at the calloso-septal interface, cortico-subcortical and infratentorial. The most important MR criteria to predict conversion from suspected (CSMS) to clinical definite MS (CDMS) are GD-DTPA enhancement and juxtacortical lesion localisation followed by the parameter periventricular and infratentorial localisation. Based on guidelines for the use of MRI in drug studies and on equivalent recommendations for the routine diagnostic we suggest rational and economic MRT protocols for cerebral, spinal, and N. opticus investigations. Such standardised protocols shall help to make MRI investigations more efficient and better comparable. New MR developments include measurement of magnetisation transfer and T2-relaxation, diffusion weighted imaging, proton MR spectroscopy, and quantification of lesion load. These methods can analyse more specifically tissue changes in MS plaques and yet can reveal changes in normal appearing white matter.