[A rare anomaly of the circle of Willis : infra-optic course of both anterior cerebral arteries: associated aneurysm of the basilar bifurcation (author's transl)].

A rare anomaly of the A1 portion of both ACA associated with a saccular aneurysm of the basilar bifudcation is presented. Based upon this case and eigth other cases in the literature, the anatomical and radiological features of the anomaly are precised : the anomalous artery comes from the internal carotid artery right over the cavernous sinus, very close to the origin of the ophtalmic artery; it rums medailly below the inferior aspect of the optic nerve, thus being projected under the plane of the optic canal on oblique angiograms; finally, it crosses the anterior edge of the optic chiasm up to the interhemispheric fissure. By itself the anomaly is asymptomatic but it should not be considered as a mere curiosity since it has most often been found associated with a variety of cerebral vasculature anomalies and in particular with encor more saccular aneurysms of the circle of Willis.