Congenital absence of internal carotid artery with intercavernous anastomosis: Case report and systematic review of the literature.

The absence of an internal carotid artery is a rare congenital anomaly. In the absence of the internal carotid artery, collateral circulations develop through the circle of Willis, persistent embryonic arteries or transcranial collaterals of the external carotid artery. Six pathways of collateral circulation have been described. Intercavernous anastomosis is between cavernous segments of the bilateral internal carotid arteries and is rarely seen. Patients with an absence of the internal carotid artery can be completely asymptomatic. However, these patients can present with subarachnoid hemorrhage or stroke accompanying cerebral aneurysm or abnormal collateral. We combined our case with 33 previous publications to form a retrospective series including 35 cases of unilateral internal carotid artery agenesis with intercavernous anastomosis.