Intracranial carotid anastomosis and partial aplasia of an internal carotid artery.

A rare arterial anastomosis between the right and left internal carotid arteries at the base at the skull, with aplasia of the cervical part of the left internal carotid artery is reported. The case is unusual because, in addition to the vascular anomaly of the carotid artery, there is an aneurysm of the anterior communicating artery and bilateral renal cysts. The condition is a complex malformation syndrome caused by defective regression of the third branchial artery. Because of the characteristic angiographic aspects such a case should be called transverse carotid anastomosis.