Ruptured aneurysm arising from the distal end of a proximal a(1) fenestration : case report and review of the literature.

A 75-year-old female presented with subarachnoid hemorrhage. Angiography revealed a partial duplication (fenestration) in the proximal A(1) segment and a ruptured aneurysm at the distal end of A(1) fenestration. This congenital anomaly accompanying an aneurysm was associated with duplicated ipsilateral middle cerebral artery (MCA). Congenital defect of the arterial wall and hemodynamic factors at the fenestrated A(1) are considered to play a significant role in the development of this aneurysm. The present case is peculiar because not only the ruptured A(1) aneurysm was related with the anterior and middle cerebral artery duplication but also the location of A(1) fenestration and the origin of A(1) aneurysm in a fenestration are quite unusual.