ACR Codes: 1.2
Multiple sclerosis (MS) is the most common demyelinating disease. The prevalence is highest in people of Northern European descent and incidence increases as the population moves farther from the equator. It tends to affect women more than men and usually has a clinical onset between the ages of 20 and 50 with a waxing and waning course. The distribution of demyelination is somewhat random in the white matter, but has a predilection for the periventricular white matter, corpus callosum, visual system from optic nerve to occipital lobe, and spinal cord. Spinal cord involvement is often symptomatic while brain lesions can frequently be asymptomatic. The exact cause is unknown but the most common theory is an immune-mediated phenomenon in genetically susceptible individuals.
MRI has recently proven to be the most sensitive imaging test available in the evaluation of multiple sclerosis. The sensitivity of MRI in detecting MS is approximately 85%. Interestingly, the distribution and number of plaques seen on MRI do not necessarily correlate with the severity of the clinical disease state. MRI findings are considered suggestive of MS when 3 or more lesions are found in a periventricular location and they are at least 5mm in size. Oblong lesions at the calloseptal interface and perivenular extensions in the deep white matter (known as Dawson's Fingers) are also characteristic. Involvement of the corpus callosum on the sagittal Flair or T2 images is often striking and highly suggestive of multiple sclerosis.
MS plaques are most often ovoid or round in shape and can have a lesion-within-a-lesion or bulls-eye appearance. Most demyelinating plaques are hyperintense on T2, PD, and Flair images. The corresponding lesions are hypointense or isointense on T1 images prior to contrast medium administration. The contrast enhancement represents disruption of the normal blood-brain-barrier. The amount of gadolinium enhancement has been correlated to the activity level of the demyelinating process.
Using MRS (MR Spectroscopy) loss of total brain NAA has been reported. Total brain NAA measurements may be more accurate than lesion spectroscopy - that is subject to volume averaging, misplacement/mismatching of voxels, and patient motion.
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Disease Topic 1143 
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