Carotid-anterior cerebral artery anastomosis with aneurysm: case report and review of the literature.

A ruptured aneurysm at the origin of the bilateral pericallosal arteries with an anomalous anterior cerebral artery was found in a 56-year-old man. The abnormal solitary anterior cerebral artery arose from the intracranial proximal internal carotid artery, passed underneath the ipsilateral optic nerve, and turned upward at the midline as a common trunk of the bilateral pericallosal arteries. Subarachnoid hemorrhage recurred 15 days postoperatively, and the patient did poorly. The 20 published cases of this rare anomaly (an infraoptic course of the anterior cerebral artery with a low bifurcation of the internal carotid artery) are reviewed. This anomaly should be referred to by the descriptive term "carotid-anterior cerebral artery anastomosis." It is frequently associated with aneurysms.