A rare embryologic variation: carotid-anterior cerebral artery anastomosis or infraoptic course of the anterior cerebral artery.

Carotid-anterior cerebral artery anastomosis constitutes an anomaly of the anterior part of the arterial circle of the brain. The anterior cerebral a. arises a few millimeters above the emergence of the internal carotid from the cavernous sinus, at the usual level of origin of the ophthalmic a. It travels medially, beneath the optic n., and then describes a curve with a superolateral concavity to arrive at the anterior part of the optic chiasma, where it anastomoses with the anterior communicating a. This asymptomatic variant of course is often associated with other cerebral vascular anomalies, especially arterial aneurysms. On the basis of 2 new cases discovered by chance, together with a review of the literature, various hypotheses capable of explaining the embryologic origin of these anomalies are discussed.