A 44-year-old man with a 22-year history of headaches presented with a generalized tonic-clonic seizure. In his early 20s, he had undergone cerebral biopsy of lesions thought to be responsible for a month-long headache. The biopsy was nondiagnostic and he was treated with corticosteroids for 6 months. His headache abated, but he reported difficulty managing his finances during the ensuing 20 years. Physical examination demonstrated a Kokmen Short Test of Mental Status score of 23 of 38 (a score <29 implies impaired cognition), a left homonymous hemianopsia, and apraxia of the left hand. Laboratory findings showed an elevated C-reactive protein level of 21 mg/L (to convert to nanomoles per liter, multiply by 9.524), and cerebrospinal fluid analysis showed an opening pressure of 248 mm H2O and a protein level of 0.059 g/dL (to convert to grams per liter, multiply by 10.0). Imaging findings are shown in the Figure and were interpreted to be unchanged from magnetic resonance imaging conducted 13 months previously. Frameless stereotactic biopsy was undertaken. Pathology was consistent with small vessel vasculitis characterized by nongranulomatous fibrinoid degeneration and perivascular hemorrhage. He was treated with corticosteroids and levetiracetam. At 6-month follow-up, the patient was seizure free with a left homonymous hemianopsia and had undergone neuropsychometric testing, which indicated a moderate to severe cognitive disorder.