Aneurysms of the sphenoid segment of the middle cerebral artery.

Aneurysms of the M1 segment of the middle cerebral artery are rare. Anatomically they are classified into a "temporal" variety, projecting supero-laterally and a "striate" variety projecting infero-laterally. Between 1960 and 1992, 13 such aneurysms were treated at our Institution. Among them, 11 underwent surgery: 8 (73%) had an excellent or good outcome, 1 (9%) a poor outcome and 2 (18%) died. Two patients treated conservatively carried thrombosed aneurysms: one was a giant unruptured aneurysm with complete occlusion of the parent vessel; the other one was found at autopsy following transsphenoidal surgery and unexplained SAH. All these cases were carefully reviewed with special reference to their clinical and anatomo-surgical features. Exact knowledge of the anatomy of lenticulostriate and temporal branches and awareness of all possible anatomical variants are crucial for correct opening of the Sylvian fissure and successful surgical approach to M1 segment aneurysms.