Diagnosis

Cystic multiple sclerosis

Findings

A magnetic resonance imaging (MRI) study of the brain was performed (figures 1 and 2). There were ring lesions in the posterior right frontal lobe associated with moderated edema (figure 2). The lesions did not enhance after injection of gadolinium. The periphery was hyperintense on T2-weighted images and the central portion of the lesion was isointense on T1-weighted images and hyperintense on T2-weighted sequences. A few hyperintense T2 signal abnormalities were present in the centrum semiovale bilaterally. The differ-ential diagnosis at this point favored abscess(es), metastatic disease, and less likely an atypical demyelinating disease.

Given the patient's history of aggressive nevi, a stereotactic biopsy was performed. The hospital course was uneventful. The patient was started on steroid therapy.

Discussion

Multiple sclerosis (MS) is a clinical diagnosis that should never be made based on imaging results alone. It is best characterized by episodes of focal neurologic deficits of the brain, spinal cord, and optic nerves with relapses and remissions. The progression of the disease is unpredictable with almost certain disability. Autoimmune-mediated demyelination is favored as a cause for the disease. There is no cure. Approximately 95% of patients present between 18 and 50 years of age. MRI with contrast has the advantage of detecting lesions both in space (location) and time (acute versus chronic). Lesions appear hypo- to isointense on T1- weighted and hyperintense on T2-weighted sequences. Occasionally, a thin peripheral hyperintense T1 signal may be seen attributed to protein and lipid-laden macrophages and free radicals. Classic locations for lesions to occur are in the calloseptal interface, periventricular white matter, corpus callosum, and brachium pontis. Lesions may also occur in the floor of the fourth ventricle and periaquaductal gray matter. Some authorities require at least three lesions of 5 mm or more in size and in the classic locations to establish the imaging diagnosis.

Histopathologically, there is infiltration of lymphocytes and plasma cells in a venous perivascular distribution. This produces the classic periventricular ovoid appearance. There is myelin loss with relative sparing of axons, nerve cells, and blood vessels. The cellular inflammatory reaction causes damage to the blood brain barrier, which allows influx of water and protein, correlating with contrast enhancement. In the acute setting, this may last for 4 to 8 weeks.

Lesions with a similar appearance to MS with regard to imaging and clinical presentation exist. These are acute disseminating encephalomyelitis (ADEM), vasculitides, and Lyme disease. ADEM is distinguished from MS by its single episode of acute onset of fever and headaches. It rarely relapses. If all lesions enhance, the likelihood of ADEM increases over MS. Vasculitic lesions tend to be more peripheral than MS lesions and show infarction in vascular territories. Lyme disease must be differentiated from MS since the former is treatable. The clinical presentation of Lyme disease may also have a waxing and waning course and present with optic neuritis.

1. Chakrabortty S, et al: Intracerebral ring-enhancing lesions in a patient with multiple sclerosis: A case report. Surg Neurol 43:591-594, 1995.

Prepared by Michael S. Goldman, MD and R. Anthony Lloyd II, MD, Department of Radiology, Division of Neuroradiology at the University of Maryland Medical School, Baltimore, MD.