Bilateral internal carotid artery agenesis: a case study and review of the literature.

Bilateral internal carotid artery agenesis is a rare lesion, with only 18 cases previously reported. Blood supply to the anterior cerebral circulation is most commonly through enlarged basilar and posterior communicating arteries. Occasionally collateral flow is through abnormal transsellar anastomoses or anastomoses between the external carotid and intracranial systems. Associated intracranial aneurysms occur in 25% of patients, accounting for a significant incidence of intracranial hemorrhage as the initial symptom. Diagnosis is best made by cerebral arteriography with computed tomography to verify the congenital nature of the abnormality by demonstrating the absence of carotid canals. This is the second case to begin with transient ischemic attacks suggestive of carotid territory ischemia but originating from the vertebral system. Angiographic findings included absent internal carotid arteries, small common carotid arteries, and bilateral high-grade stenoses at the origins of large vertebral arteries. This is the first such case to be treated with reimplantation of the vertebral artery with resolution of symptoms.