A genesis of the Left Internal Carotid Artery Associated with an Aneurysm of the Anterior Communicating Artery

A case of agenesis of the left internal carotid artery associated with an aneurysm of the anterior communicating artery which developed with an acute onset of subarachnoid hemorrhage due to its rupture is presented. The anomaly was demonstrated on angiogram and confirmed at operation for the aneurysm. The absence of the foramen lacerum detected on the axial view of the skull suggested the congenital nature of the anomaly. Fifteen cases (including our own) of total absence of unilateral or bilateral internal carotid arteries associated with intracranial aneurysms were collected from the literature. Nine of these patients (64.3%) had an aneurysm on the anterior communicating artery. The importance of altered hemodynamic forces on the circle of Willis produced by the agenesis of the internal carotid artery as one of the causative effects of the aneurysm in our case is discussed.