Congenital Internal Carotid Artery Hypoplasia with a Contralateral Extracranial ICA Aneurysm: Case Report

Introduction: Congenital internal carotid artery hypoplasia (CICAH) is a developmental anomaly where the internal carotid artery (ICA) is underdeveloped, averaging a diameter of 1.6-1.7mm. It’s usually unilateral, with an estimated incidence of 0.01%, though bilateral cases have been reported. It’s typically asymptomatic but can manifest clinically through ischemic events, such as transient ischemic attack (TIA) or stroke. CICAH is associated with a 10-fold increased risk of aneurysm formation, possibly due to higher hemodynamic stress secondary to compensatory blood flow in collateral circulation.

Methods: A 48-year-old male presented with left-sided headache and right-sided hemiparesis, numbness, and paresthesias. The patient’s medical history included obesity, hypertension, migraines with aura, and a 32-year smoking history. After a few minutes, hemiparesis subsided. Therefore, the patient was diagnosed with a TIA. CT and US imaging were ordered to rule out an ischemic attack and carotid atherosclerosis.

Results: Doppler ultrasound reported unremarkable atherosclerotic plaque on the right carotid bulb. CTA found a hypoplastic right ICA that, 15mm after its origin, abruptly reduces its 8mm caliber to approximately 1.2mm; a small right carotid foramen; and an incidental left extracranial ICA saccular aneurysm measuring 4x3mm. Cardiovascular risk factors were treated pharmacologically, CICAH was managed expectantly, and two days later, the aneurysm was treated with pure coiling. The patient was stable in his last follow-up.

Conclusion : CICAH is a known risk factor for aneurysm formation and ischemic events. Thus, close follow-up and management of cardiovascular risk factors are crucial to offset these increased risks. Physicians must recognize CICAH and differentiate it from acquired stenosis of the ICA; a small carotid foramen supports the former’s diagnosis. As far as we are aware, this is the only reported case of a CICAH presenting with a contralateral extracranial ICA aneurysm. CICAH is underdiagnosed; further studies are needed to understand its true clinical implications.