Multiple sclerosis simulating a mass lesion

Thr eases of two young women with a homonymous hemianopia ore described. Both women had a progressively enlarging mass lesion that was seen with neuroimaging studies. One patient had neurologic deterioration despite intravenous corticosteroid treatment. In each ease, results of a stereotactic biopsy showed demyelination that was consistent with multiple sclerosis. Multiple sclerosis infrequently presents as a mass lesion. The atypical clinical and radiographic features of large demyelinating plaques may lead to an erroneous diagnosis of a brain tumor, infection, or demyelination from other causes.