T1 post-gad T2 T2 6 weeks later

Diagnosis: Multiple sclerosis

Multiple sclerosis is thought to be an autoimmune mediated demyelinating process. It is the most common demyelinating disease , after small vessel ischemia of aging. Women are affected about twice as often as men. The onset is usually between 20 and 40 years age. On imaging, MS typically appears as oval shaped periventricular lesions which are perpendicular to the lateral ventricles. The second most common site of involvement is the corpus callosum. In adults, posterior fossa MS involvement makes up 10% of all cases. This is in contrast to adolescents where the posterior fossa is the most common site of MS involvement. On CT, MS appears as an iso or hypodense lesion which may show enhancement. On MR, the MS plaques are hypointense on T1 and hyperintense on T2 with variable enhancement. Ovoid periventricular lesions are characteristic. This appearance of MS is more compatible with the Marburg variety of MS where the disease presents with mass-like enhancing lesions. Another atypical appearance of MS is called Belo concentric sclerosis in which the MS lesion is tumefactive with a significant amount of enhancement but with multiple concentric layers resembling onion skin in the central aspect.

When this patient initially presented with multiple enhancing white matter lesions after an acute viral syndrome, the diagnosis of ADEM was considered. ADEM (acute disseminated encephalomyelitis) is an immune mediated process which occurs secondary to prior vaccination or viral syndrome. ADEM tends to occur in children and young adults with an abrupt onset and follows a monophasic course. Patients may present one to three weeks after their vaccination or viral syndrome with headache, fever, or drowsiness. Patients may then rapidly progress with seizures, focal neurologic deficit, and eventually even death. On imaging it may be impossible to differentiate ADEM from multiple sclerosis. The best way to tell them apart is with follow-up MRI. If new lesions occur, multiple sclerosis is more likely due to the biphasic nature of ADEM. The presence of the new enhancing lesion on the follow-up MRI in this patient makes multiple sclerosis more likely. Related Cases

Caldemeyer KS, Harris TM, Smith RR, Edwards MK. Gadolinium enhancement in acute disseminated encephalomyelitis. J Comput Assist Tomogr, Jul-Aug 1991; 15(4):p673-5.

Kesselring J, Miller DH, Robb SA, Kendall BE, Moseley IF, Kingsley D, du Boulay EP, McDonald WI. Acute disseminated encephalomyelitis. MRI findings and the distinction from multiple sclerosis. Brain, Apr 1990; 113 (pt 2): p291-302.

Multiple sclerosis PML Gliomatosis