Congenital Agenesis of Right Internal Carotid Artery: A Report of Two Cases

Abstract

Congenital unilateral agenesis of the internal carotid artery (ICA) is a rare anomaly. Due to proper sufficient collateral circulation via the circle of Willis most cases are asymptomatic, but patients can also present with ischemic or hemorrhagic cerebrovascular insults. The absence of the bony carotid canal is essential to differentiate this anomaly from chronic ICA occlusion. Awareness of this situation by clinicians and radiologists is essential because these patients have an increased incidence of various intracranial pathologies. We report two cases of this rare developmental congenital abnormality occurring in two young patients and describe the presentation, diagnosis, determined developmental causes, imaging findings, and complications.

Unilateral agenesis of internal carotid artery associated with superior cerebellar artery aneurysm and anomalous origin of ophthalmic artery arising from the ipsilateral posterior communicating artery

“…ICA genesis is a rare congenital anomaly [3] . The congenital absence of ICA may be unilateral or bilateral, with a higher proportion of cases being unilateral, and there is a left-sided predominance of ICA agenesis with a ratio of 3:1 [2] .…”

“…As agenesis of the ICA usually leads to sufficient collateral circulation to the affected side of the brain parenchyma, most cases are asymptomatic and are therefore frequently identified incidentally [1 , 4] . However, some patients can also present with subarachnoid hemorrhage from aneurysm rupture or symptoms related to associated vascular insufficiency due to changes in the collateral flow [3 , 5] .…”

“…Embryologically, the primitive ICA originates from the fetal third aortic arches and cranial extensions of the embryonic dorsal aorta around the 3-mm fetal stage [3 , 6] . ICA development is completed at 6 gestational weeks [1] .…”

“…If the embryonic ICA does not develop or fails to develop before the fifth embryonic week, the ICA and carotid canal cannot develop [5] . Therefore, the absence of the bony carotid canal is essential to differentiate congenital agenesis from the acquired type of ICA occlusion, such as atherosclerotic occlusion or dissection [3] . The present case showed no bony carotid canal on the left side.…”

“…Agenesis, aplasia, or hypoplasia of the internal carotid artery (ICA) are rare congenital vascular anomalies, seen in less than 0.01% of the population [1 , 2] . Most cases of ICA agenesis are clinically silent due to well-developed sufficient collateral circulations; therefore, it is usually detected incidentally on head and neck imaging [3] . The most common type of collateral flow is through the circle of Willis and less commonly provided via persistent embryologic vessels or transcranial collaterals through the external carotid artery system [2] .…”