Computed tomography angiography of unilateral agenesis of the internal carotid artery: 2 cases report with focus on embryology, collateral pathways, and imaging.

Congenital absence of internal carotid artery (ICA) is a rare anomaly seen in around 0.01% of the population. High incidence of aneurysms is reported in these patients population. Many patients are asymptomatic as the development of a collateral circulation ensures cerebral perfusion. The embryology, the common collateral pathways, and the imaging findings associated with this anomaly are illustrated with 2 new cases. We reported the cases of 2 totally asymptomatic patients at the time of imaging in which ICA agenesis was proved on computed tomography angiography. On imaging, all the most important findings necessary for ICA agenesis diagnosis have been identified and described. Noninvasive imaging techniques are currently the mainstay of ICA agenesis diagnosis.