Dorsally projected internal carotid aneurysms (aneurysms projecting upward on the lateral view of the carotid angiogram) are rare. We have encountered 5 such cases (3%) in our series of 150 intracranial internal carotid aneurysms in the past five years. These aneurysms were located in the portion of the internal carotid artery between the origin of the posterior communicating artery and the distal carotid bifurcation. They characteristically had a wide-based neck with thin wall. Although clipping of this type of aneurysms should be the choice of treatment, it carries a high risk of intraoperative rupture, most likely at the neck. Two of the 5 cases ruptured intraoperatively; another ruptured one month after the operation from a part of the semi-spherical aneurysm which had not been included in the clip. Two patients died because of rupture. Three representative cases are described and various technical problems including selection of an appropriate clip for this type of aneurysm and measures to be taken in case of intraoperative rupture are discussed.
