We report a 29-year-old man with a unique presentation of vasculitis as acute unilateral subdural effusion and meningoencephalitis. Magnetic resonance imaging showed a brainstem lesion that spread to the thalamus over time. There were no systemic features of vasculitis other than a positive pathergy test. Histopathological examination from the pathergy site showed neutrophilic infiltrate and leucocytoclastic vasculitis. The condition was steroid responsive and he remained in remission at two years′ follow-up. The anatomy of the brainstem lesion, absence of other inflammatory and infective conditions on evaluation suggests a vasculitic pathology either as primary central nervous system angiitis or as neurological presentation of systemic vasculitis like Behηet′s disease although the international diagnostic criteria for Behηet′s were not fulfilled.