Congenital absence of the internal carotid artery (ICA) is a rare anomaly that occurs in less than 0.01% of the population. It encompasses agenesis, aplasia, and hypoplasia.

The diameter of the right carotid canal is smaller than the contralateral side which supports the diagnosis.

Collateral flow through the circle of Willis mainly from the right posterior communicating artery, as in this case, is the most common type.

A left fetal communicating posterior cerebral artery is noted (normal variant).