Multiple sclerosis (MS) is the most common acquired white matter neurodegenerative disorder. Although the precise etiology of MS is unknown, autoimmune-mediated demylenation is the favored cause. MS primarily affects young adults of northern European descent with a higher incidence in temperate climates. The peak age of symptom onset is 20 to 40 years. A female preponderance exist at a ratio of 1.7 to 2:1 in adults (5 to 10:1 in children and adolescents). The clinical course of MS is variable but most often involves relapsing-remitting disease which often becomes chronic and progressive. Acute-fulminent MS (Marburg type) is rare but carries high morbidity and mortality.

The principle imaging modality for evaluating MS is magnetic resonance (MR) imaging. The sensitivity if MR imaging for detecting MS is up to 85% and far exceeds other test. Imaging findings vary with the activity of disease and correlation of specific imaging with clinical findings is poor. The presence of three or more discrete lesions of 5mm or greater in size in characteristic locations and a compatible clinical history almost assures the diagnosis.

The typical appearance of MS on MR is of multiple punctuate white matter lesions which are hyperintense on T2-weighted and iso- to hypointense on T1-weighted images. The majority of lesions are less than 1 cm, although lesions may measure up to several centimeters. The shape of larger lesions is usually round or ovoid with a beveled appearance on T1- and proton density weighted images. Perivenular extensions into deep white matter are very common and termed "Dawson's fingers". The periventricular white matter is a favorite site for MS plaques particularly along the lateral aspects of the atria and occipital horns. Inversion recovery imagingallows for better detection of these lesions due the heavily T2-weighted appearance of the brain parenchyma without bright CSF signal. MS plaques are also commonly seen in the corpus callosum, corona radiata, internal capsule, visual pathways, and centrum semiovale Any structures that contain myelin can harbor MS plaques, including the brain stem, spinal cord, and even within the gray matter of the cerebral cortex and basal ganglia. A distinctive site in the brain stem is the ventrolateral aspect of the pons at the fifth nerve root entry zone. Brain stem and cerebellar plaques are more prevalent in the adolescent age group.

Acute MS plaques are associated with transient breakdown of the blood-brain barrier and may enhance after the administration of Gadolinium. Enhancement can be used to follow the progression of disease and to assess the response to therapy.

Diffusion weighted images may also be very helpful in the evaluation of multiple sclerosis. Specifically, acute plaques may manifest as foci abnormal increased signal intensity. It is theorized that this change is secondary to an increase in the size of the extra cellular space due to acute demyelination and axonal loss, superimposed on chronic gliosis. Alternatively, there may be restricted diffusion in active MS. This may be caused from intracellular inflammatory cellular infiltration without extracellular edema.

DWI for MS - Click for HyperLink
New Insights - Click for HyperLink