Fenestration of the middle cerebral artery with an associated ruptured aneurysm.

Intracranial arterial fenestrations are uncommon developmental anomalies that may alter local hemodynamic stress patterns and may be associated with intracranial aneurysms. A 75-year-old woman presented with a mild subarachnoid hemorrhage. Cerebral angiography demonstrated a 5 mm aneurysm arising from the middle cerebral artery (MCA) associated with a dramatic fenestration of the proximal M1 segment of the MCA. The patient underwent craniotomy with microsurgical aneurysm clipping. The aneurysm arose immediately distal to the fenestration. Several fine perforating arteries were dissected away from the neck of the aneurysm to allow for safe clip placement. Postoperatively, the patient awoke without deficit and was discharged to home on the fifth postoperative day in good condition. Anomalies of the intracranial vasculature are common and we describe a rare proximal MCA fenestration with an associated ruptured aneurysm at the site of the fenestration. Neurosurgeons should be thoroughly familiar with such potential "normal variants" to avoid operative complications that may result from the anomalous circulation in such cases.