Unruptured Saccular Aneurysm Arising from the Fenestrated A1 Segment of the Anterior Cerebral Artery: Report of 2 Cases.

Some cases of aneurysms originating from the fenestrated A1 segment of the anterior cerebral artery (ACA) have been reported, but the pitfalls of the surgical procedure have not been well determined. We herein report 2 cases of a saccular aneurysm arising from the fenestrated A1 segment. Case 1 was a 72-year-old man incidentally diagnosed with an unruptured left ACA aneurysm on magnetic resonance imaging (MRI). Cerebral angiography revealed a saccular aneurysm arising from the proximal end of the left A1 segment. He underwent surgical clipping via the left pterional approach. The aneurysm originated from the proximal bifurcation of the fenestrated left A1 segment. A fenestrated ring clip was applied to obliterate the aneurysmal neck and one small fenestrated trunk, preserving the other fenestrated trunk and perforators around the fenestration. Case 2 was a 73-year-old man incidentally diagnosed with an unruptured ACA aneurysm on MRI. Cerebral angiography revealed a saccular aneurysm arising from the proximal end of the fenestrated left A1 segment. He underwent surgical clipping via the interhemispheric approach. The aneurysm originated from the proximal bifurcation of the fenestrated left A1 segment. A fenestrated ring clip was applied to obliterate the aneurysmal neck and one hypoplastic fenestrated trunk, preserving the other fenestrated trunk and perforators around the aneurysm. Detailed intraoperative evaluations of the anatomical structure and hemodynamics around the fenestration are important. The intentional obliteration of a fenestrated trunk and application of fenestrated clips need to be considered in difficult cases in order to expose the aneurysmal neck.