Congenital Absence of the Internal Carotid Artery With Intercavernous Anastomosis.

Absence of the internal carotid artery (ICA) is a rare congenital anomaly. Six pathways of alternative collateral circulation have been described. We present a case depicting absence of the left ICA and a Lie type D pattern of collateral circulation, with an intercavernous branch from the right cavernous ICA passing along the floor of the sella to the contralateral side, supplying the left middle cerebral artery. Association with cerebral aneurysms has been found, as seen in this case. Recognition of this vascular anatomic variant is important to understand thromboembolic disease in these patients and the increased risks of surgery, such as transsphenoidal pituitary surgery. Also, it highlights the importance of imaging these patients to detect and monitor associated cerebral aneurysms.