UNUSUAL ANEURYSMS OF THE DISTAL INTERNAL CAROTID-ARTERY

Background: Supraclinoid carotid aneurysms have traditionally been cla ssified according to their relation to the major carotid branches, but considerable variation exists with respect to site of origin, project ion, and relationship to the skull base. Distal internal carotid aneur ysms with a superior or medial projection are uncommon vascular lesion s, with an unusually high incidence of operative complications. Method s: Surgical experience with five patients suffering from subarachnoid hemorrhage due to ruptured aneurysms of the dorsomedial wall of the di stal internal carotid artery is presented, with emphasis on their angi ographic appearance, anatomical features, and operative management. Re sults: All five patients underwent surgical clipping. Intra-operative rupture occurred in two cases, with avulsion of the aneurysm from the internal carotid artery in both. A third patient experienced recurrent subarachnoid hemorrhage three days after uneventful surgery, due to t he clip shearing off of the parent vessel. Conclusions: Distal interna l carotid aneurysms do not conform to the usual principles of aneurysm formation and are unique in their dorsomedial location unrelated to a n arterial bifurcation. Although their anatomy is straightforward and exposure is not restricted by bone or dural structures of the skull ba se, they possess extremely fragile necks which make surgical managemen t particularly hazardous.