Fenestration of the proximal anterior cerebral artery (A1) with aneurysm manifesting as subarachnoid hemorrhage--case report.

A 50-year-old female presented with rare fenestration of the proximal anterior cerebral artery (A1 segment). This rare congenital anomaly was associated with an aneurysm at the proximal end of A1 fenestration causing subarachnoid hemorrhage, and aplasia of the contralateral A1 segment. Surgical treatment to clip the aneurysm resolved her symptoms. Hemodynamic stress at the arterial fenestration probably caused the aneurysm, possible induced by aplasia of the contralateral A1 segment.