Bilateral Internal Carotid Artery Segmental Agenesis: Embryology, Common Collateral Pathways, Clinical Presentation, and Clinical Importance of a Rare Condition

Background Bilateral segmental agenesis of the internal carotid artery is a rare congenital anomaly. We present a case of bilateral internal carotid artery segmental agenesis in an asymptomatic 18-year-old man. Embryology, common collateral pathways, clinical presentation, and clinical importance of this condition are discussed. According to our review of the literature, this report is the first to describe bilateral internal carotid artery segmental agenesis in a patient studied with magnetic resonance imaging, computed tomography, Doppler ultrasonography, and digital subtraction angiography. Case Description An 18-year-old man presented to our hospital complaining of occasional mild headaches. Neurologic examination was unremarkable. Imaging findings consisted of bilateral segmental agenesis of the internal carotid arteries. Conclusion Bilateral segmental agenesis of internal carotid artery may be completely asymptomatic and harmless, but associated conditions, such as cerebral aneurysms or abnormal collateral circulation, should alert clinicians to the possibilities of subarachnoid hemorrhage or cerebral ischemia.