Aneurysm in the horizontal segment of the anterior cerebral artery confirmed by cerebral vasospasm--case report.

A rare aneurysm in the horizontal segment (A1) of the right anterior cerebral artery was found in a 58-year-old male presenting with subarachnoid hemorrhage. No obvious bleeding source was observed on the day of onset, but 7 days later, a definite diagnosis was made based on the discovery of cerebral vasospasm by a repeat angiogram. The aneurysm was clipped via the right frontotemporal approach 15 days after onset. He suddenly developed neurological symptoms such as consciousness disturbance, right hemiplegia, and aphasia on the 4th postoperative day, when remission of the cerebral vasospasm was confirmed by transcranial Doppler ultrasound examinations and cerebral angiography. The ischemic symptoms were probably due to cerebral embolus caused by intraluminal thrombi, which had formed during the maximum phase of vasospasm and became detached during the remission phase.