Anomalous communication of external carotid and vertebral arteries with associated intracranial parenchymal arteriovenous malformation: magnetic resonance angiography and angiographic findings.

A case of anomalous communication of the external carotid and vertebral arteries via a pro-atlantal intersegmental artery (PIA) with an associated intracranial parenchymal arteriovenous malformation (AVM) is presented. The course of the PIA is displayed by both conventional catheter angiography and by MR angiography (MRA). To our knowledge, neither an associated intracranial parenchymal AVM nor depiction of this congenital anomaly on MRA has been previously described. We also briefly review the embryology and anatomy of this anomaly.