Congenital aplasia of the internal carotid artery

Introduction: Agenesis, aplasia, and hypoplasia of the internal carotid artery (ICA) are very rare congenital anomalies, occuring in less than 0.01% of the population. We report a case of congenital absence of ICA incidentally diagnosed by extracranial Duplex sonography (ECD) and confirmed by magnetic resonance imaging (MRI) and MRI-angiography.

Case report: A 57-year-old healthy man presented with a bruit over the right internal and external carotid arteries. ECD demonstrated a hypoplastic right common carotid artery (CCA) and a relatively large external carotid artery (ECA). The ICA could not be seen on imaging nor on flow measurement. MRI-angiography confirmed our results. MRI-scan of the base of the skull showed absence of the right carotid channel and aplasia of the ICA which led us to the diagnosis of a congenital absence of the ICA.

Discussion: Absence of the ICA is a very rare anomaly. It can be completely asymptomatic as in our patient. If clinical symptoms occur they are usually related to cerebrovascular ischemia, compression by enlarged intracranial vessels, and associated cerebral aneurysms.

Our case represents type A of the six pathways of collateral circulation in association with the absence of the ICA described by Lie (1): According to the MRI-angiography a collateral circulation to the ipsilateral anterior cerebral artery (ACA) through a patent anterior communicating artery (ACOM) and to the ipsilateral middle cerebral artery (ACM) from the posterior communicating artery was seen.

Conclusion: Diagnosis of absent ICA and the underlying cerebral vascular pattern is important regarding the clinical and surgical problems related to this condition. Because of the documented increased prevalance of intracranial aneurysm formation these patients should be followed carefully.

(1) Lie TA. Congenital Anomalies of the Carotid Arteries. Amsterdam: Excerpta Medica; 1968: 35–51