The infra-optic course of the anterior cerebral arteries: an anatomic case report.

Although variations of the anterior part of the cerebral arterial circle of Willis are quite well known, though some anomalies are exceedingly rare. In a 61-year-old female individual, on both sides the precommunicating parts of the anterior cerebral artery were found to course inferiorly to the ipsilateral optic nerves. This anomaly was associated with an agenesis of a left posterior communicating artery. The anatomic features, the possible high prevalence of associated aneurysms of the anterior communicating artery complex as well as implications for surgical planning or endovascular treatment are outlined and embryologic considerations and discussed.