Introduction: A right aortic arch and agenesis of internal carotid artery (ICA) are both extremely rare vascular devel- opment anomalies. Etiology of the both anomalies might be associated with the abnormal regression of the dorsal aorta. Most cases of ICA are asymptomatic due to sufficient collateral circulation and it is usually an incident finding on head and neck imaging by color Doppler ultrasonography, computed tomography (CT) or magnetic resonance imaging (MRI). ICA agenesis has a significant association - 24-67% - with intracranial aneurysms and their early detection can spare the patient serious complications.
Clinical case: A 28-year-old male had a single episode of hypertension that motivated the realization of several tests. During the investigation he was submitted to a duplex ultrasonography that revealed a diffuse narrowing of the left common carotid artery (CCA), with a markedly decrease in the peak systolic velocity and the absence of the left internal carotid artery (ICA) was suspected. Contrast-enhanced computed tomography (CT) demonstrated no abnormalities, such as cerebral infarc- tion or intracranial vascular malformations, but confirmed a right-sided aortic-arch, with anomalous origin of the left subcla- vian artery with a common origin of both CCAs and the absence of the left ICA. Examination of the head CT in bone window demonstrated an absence of the left internal carotid canal.
Conclusion: This clinical case emphasizes the importance of recognizing this condition due to the associated hemody- namic changes and in order to discover and evaluate other additional vascular malformations (aneurysms, collateral channels) and their life threatening potential risks (subarachnoid hemorrhage or ischemia). Also, it has a special importance in case of planning carotid or trans-sphenoidal hypophyseal surgery. To our knowledge, only 8 cases have been reported right aortic arch associated with agenesis of the left internal carotid artery.