[Twenty-six cases regarding the proximal anterior cerebral artery]

The authors report twenty-six aneurysms of the proximal anterior cerebral artery (A1 segment). Fourteen cases were male and twelve cases were female. Saccular aneurysms were twenty-four and fusiform aneurysms were two. The incidence of the A1 aneurysms was 0.76%. Clinicopathologically, multiplicity of this aneurysm was distinctive, and eleven cases had multiplicity (42.3%). In the seven cases among them, the A1 aneurysms bled (63.6%). These 26 aneurysms were classified into five types according to the mode of the origin of the aneurysm from the A1 segment: (a) fifteen aneurysms originating from the junction of the A1 segment and the small perforating artery, (b) five from the A1 directly, (c) three from the proximal end of the fenestration of the A1, (d) two were fusiform aneurysms, (e) one from the junction of the A1 and the cortical branch. In CT scan of these aneurysms, bleeding extending to the septum pellucidum is very similar to that of the anterior communicating artery aneurysms.