Surgery of basilar aneurysms associated with unexpected rupture of an internal carotid artery aneurysm.

During a surgery of basilar aneurysms via the trans-sylvian approach, we encountered an arterial bleeding caused by rupture of an internal carotid artery aneurysm that had been difficult to diagnose before surgery, as it was a small and brood-neck aneurysm and mimicked arteriosclerosis. In spite of several surgical procedures, the surgical path at the basilar aneurysms became narrow, and we had to abandon the clipping of the aneurysms. Consideration of radiological and intraoperative findings was made for this case, demonstrating a pitfall that neurosurgeons may encounter during surgery.