Multiple sclerosis presenting as a single mass lesion.

A 6-year-old male presented with a subacute onset of hemiplegia and a mass lesion on computed tomography scan. Pathology from a surgical biopsy revealed demyelination only. Ten months later, he had a recurrence on the opposite side. A magnetic resonance imaging scan revealed a corresponding mass lesion in the other cerebral hemisphere, allowing the diagnosis of multiple sclerosis. Consideration should be given to diagnoses other than a tumor when the clinical picture and radiologic features are atypical.