Bilateral Hypoplasia of the Internal Carotid Artery with Subarachnoid Hemorrhage and Distal Posterior Cerebral Artery Aneurysm

Bilateral internal carotid artery (ICA) hypoplasia is a rare congenital anomaly. Their actual incidence is higher than what is reported as majority of them remains asymptomatic during lifetime. 1 It is important to differentiate congenital ICA hypoplasia from acquired causes of ICA stenosis like moyamoya disease. The most conclusive differentiating point is the size of the carotid canal that in congenital cases cannot be clearly made out. 2 Further unlike the supraclinoid stenosis of ICA in moyamoya disease, ICA hypoplasia here is much more proximal just distal to its point of origin. 3 Our case was a 27-year-old primigravida, who presented with severe headache. No other relevant positive points were there in the history. Clinical examination revealed neck rigidity. She was conscious, alert, oriented with no de fi cits. Computed tomographic (CT) brain showed extensive intra ventricular hemorrhage involving the lateral and third ventricles, specks of blood in the basal cisterns, and mild hydrocephalus. Bone windows revealed bilateral atretic carotid canals ( ► Fig. 1 ). CT angiography revealed hypoplasia of bilateral ICA that were only 1 to 1.5 mm in diameter and ended in string like structures on both sides. An aneurysm was seen arising from the distal cortical branches of the right P4 segment of posterior cerebral artery (PCA) ( ► Fig