Ruptured distal accessory anterior cerebral artery aneurysm--case report.

A 48-year-old man presented with an extremely rare aneurysm arising from an accessory anterior cerebral artery (ACA) manifesting as sudden onset of headache lasting for 5 days. Neurological examination on admission revealed no abnormalities. Computed tomography showed subarachnoid hemorrhage of the interhemispheric fissure and intraparenchymal hematoma of the left cingulate gyrus. Magnetic resonance and cerebral angiography revealed a saccular aneurysm of the distal portion of the accessory ACA classified as the bihemispheric type. Neck clipping of the aneurysm was performed via an interhemispheric approach 17 days after symptom onset. The patient made a good postoperative recovery without neurological deficit. Distal accessory ACA aneurysms tend to arise from the first bifurcation and supply parietal branches. The aneurysms tend to occur on the bihemispheric type of distal accessory ACA. Hemodynamic stress may contribute to formation or development of these aneurysms.