A Case of Right Internal Carotid Agenesis with Associated Transcavernous Anastomosis Revealed by Transient Ischemic Attack.

Agenesis of the internal carotid artery (ICA) is a rare congenital vascular disorder of the cerebral circulation. CT scan of the skull base disclosing complete absence of the bony carotid canal helps to differentiate an agenesis from aplasia or hypoplasia. Although most of the patients remain asymptomatic (thanks to the sufficient collateral circulation provided by the circle of Willis) cerebral infarcts, transient ischemic attacks or intracranial aneurysms have been rarely described in association with agenesis of the ICA. Most often, the vascular territory of the involved ICA is supplied by the contralateral carotid artery and from the vertebrobasilar circulation through the anterior and posterior communicating arteries, respectively. However, collateral supply can also be provided thanks to a transcavernous anastomosis, an aberrant vascular communication between the cavernous portions of the ICAs coursing through the sella turcica. We report here the case of a 55-year-old man with right carotid agenesis and associated transcavernous anastomosis revealed by transient ischemic attack. Embryogenesis, imaging findings, possibilities of collateral circulation and potential complications have also been discussed.