This case demonstrates a hypoplastic right internal carotid artery. The narrow right carotid canal, fetal right PCA with prominent right P1 artery add further evidence towards this.

Agenesis, aplasia, and hypoplasia of the internal carotid artery (ICA) are rare congenital anomalies, occurring in less than 0.01% of the population.

As in this case the most common type of collateral flow is through the circle of Willis.

Although this case is an incidental finding, recognition is important as it is associated with cerebral aneurysms and has an implication during carotid endarterectomy and transsphenoidal hypophyseal surgery.