[Basilar bifurcation aneurysm associated with internal carotid artery occlusion. Report of two cases].

Two cases of subarachnoid hemorrhage caused by rupture of a basilar bifurcation aneurysm associated with occlusion of the internal carotid artery (ICA) at the neck are presented. Case 1, a 71-year-old female, was hospitalized in a coma. Angiography demonstrated occlusion of the bilateral ICA, collateral blood supply through the branches of the foramen rotundum or vidian artery from the maxillary arteries and right posterior communicating artery, and a saccular aneurysm at the basilar bifurcation. The patient died 1 month later following rerupture of the aneurysm. Case 2, a 64-year-old male, was hospitalized for drowsiness. Angiography showed occlusion of the right ICA, collateral blood supply through a tortuous artery (a vidian artery), and a large aneurysm at the basilar bifurcation. Posterior circulation supplied anteriorly through the right posterior communicating artery. The patient died 1 month later because of rerupture of the aneurysm. Laminar thrombosis of the right ICA and an anastomotic vessel, seemingly a branch of the foramen rotundum or a vidian artery, were demonstrated by autopsy. The combination of cerebral aneurysm and collateral circulation is extremely rare in cases of occlusion of the ICA. The two cases described here suggest that hemodynamic stress is an important factor in the formation of cerebral aneurysms.