Bilateral absence of the internal carotid artery and basilar aneurysm.

Bilateral agenesis or hypoplasia of the internal carotid artery (ICA) is a rare anomaly of embryogenesis and the simultaneous occurrence of aneurysms is higher than in the general population. We report a 74-year-old patient presenting a spontaneous subarachnoid haemorrhage whose CT-angiography showed a basilar aneurysm and bilateral absence of the internal carotid arteries. Also bilateral hypoplastic carotid canal in the skull base was identified. Digital subtraction angiography after surgical clipping of the aneurysm confirmed the absence of the internal carotid arteries; anterior circulation was totally supplied by enlarged posterior communicating arteries.