Aneurysms arising from the proximal (A1) segment of the anterior cerebral artery. A study of 38 cases.

This study reviews aneurysms of the proximal segment (A1) of the anterior cerebral artery in 38 patients (23 men and 15 women) and their surgical, angiographic, and clinical management. Thirty-seven aneurysms were saccular and one was fusiform. The incidence of A1 aneurysms among a total of 4295 aneurysm cases treated was 0.88%. Multiple aneurysms occurred in 17 patients (44.7%) of the 38 cases; in 10 (58.8%), there was bleeding from the A1 aneurysm. The aneurysms were classified into five categories according to the mode of origin of the aneurysm in relation to the A1 segment: in 21 cases, aneurysms originated from the junction of the A1 segment and a perforating artery; in eight, from the A1 segment directly; in six, from the proximal end of the A1 fenestration; and in two, from the junction of the A1 segment and the cortical branch. One patient had a fusiform aneurysm. Computerized tomography (CT) of these aneurysms revealed bleeding extending to the septum pellucidum similar to that of anterior communicating artery aneurysms. When performing radical surgery it is very important to recognize the characteristics of A1 aneurysms, including multiplicity, a high incidence of vascular anomalies (especially A1 fenestration), and their similarity to anterior communicating artery aneurysms on CT.