Ruptured proximal anterior cerebral artery (A1) aneurysm located at an anomalous branching of the fronto-orbital artery--a case report.

Cerebral aneurysms are occasionally associated with anomalies of cerebral arteries, that should be recognized pre- and intra-operatively. Most of the previous reports on the anomalies of the anterior cerebral artery have been concerned with hypoplasia, fenestration, and infra-optic course of the A1, variant A1 perforators or Heubner's artery, multi-channeled anterior communicating artery, and azygos anterior cerebral artery. The author experienced a patient with a ruptured proximal anterior cerebral artery (A1) aneurysm located at an anomalous origin of the fronto-orbital artery from the A1. The fronto-orbital artery normally branches off the anterior cerebral artery just distal to the anterior communicating artery (proximal A2). An anomalous branching of the fronto-orbital artery off the A1 seems very rare. This anomalous artery could be mistaken for an unusually large medial lenticulostriate artery, aberrant frontopolar artery, or the third A2. The author reviewed the literature on anomalies of the A1 and the fronto-orbital artery.