Infraoptic course of the anterior cerebral artery originating from the extradural internal carotid artery associated with contralateral internal carotid artery agenesis and multiple intracerebral aneurysms

A 63-year-old woman presented with infraoptic course of the anterior cerebral artery (ACA) originating from the extradural internal carotid artery (ICA) associated with contralateral ICA agenesis and multiple intracerebral aneurysms. The extradural origin of the infraoptic course of ACA was identified with constructive interference in steady state magnetic resonance (MR) imaging, and confirmed at surgery. The aneurysms were successfully clipped and embolized with coils. The anomalous artery of this rare anomaly almost always arises from the intradural ICA. MR imaging is useful for evaluating the anatomical details of this anomaly.