Internal carotid artery agenesis: diagnosis, clinical spectrum, associated conditions and its importance in the era of stroke interventions

Background: Internal carotid artery (ICA) agenesis has been usually reported as an asymptomatic condition in association with other congenital anomalies. However, it is less well described in the context of clinical neurological syndromes. Method: Five cases of ICA agenesis are reviewed. The diagnosis of ICA agenesis was based on the absence of bony carotid canal on computed tomography. Brain CT and magnetic resonance image (MRI) scans were done in all the patients and four vessels digital angiograms were obtained in two. Clinical presentation, coexistent radiological findings and associated abnormalities are reviewed. Findings: The initial presentations were pulsatile tinnitus, ischemic stroke, migraine, Horner's syndrome, and subarachnoid hemorrhage. Collateral circulation was supplied via the posterior communicating artery and the anterior communicating artery. Ophthalmic artery was supplied by meningeal arteries. On CT, all cases demonstrated agenesis of the bony carotid canal. Smaller cavernous sinus were detected in all cases, enlargement of the foramen spinosum was found in three patients and hyper-pneumatization of the petrous apex was detected in two cases. In one patient a cerebral aneurysms was detected and treated with an endovascular approach. Other associated vascular abnormalities were aortic origin of the vertebral artery in two patients, ICA coiling in two cases and fenestration of basilar artery in one case. Conclusion: ICA agenesis is usually asymptomatic but occasionally may be associated with ischemic stroke. Collateral supply is usually effective in preventing stroke but may become inefficient leading to ischemia. Associated anomalies such as cerebral aneurysms are commonly depicted on the same side as the ICA agenesis and may represent a potential life-threatening condition.