Basilar bifurcation aneurysm associated with bilateral internal carotid occlusion.

A case of subarachnoid hemorrhage from ruptured aneurysm of the basilar bifurcation associated with occlusions of both internal carotid arteries at the neck is presented. Each internal carotid artery mainly received collateral flow at the cavernous portion from the internal maxillary artery through anastomotic artery of the foramen rotundum. Posterior circulation also supplied collateral blood flow via the right posterior communicating artery. This case report suggests that hemodynamic stress may be regarded as an important factor in the formation or development of cerebral aneurysm.