Rare congenital variations of the internal carotid artery identified incidentally: findings from CT angiography.

Background: Congenital anomalies of the internal carotid artery (ICA) are rare and often asymptomatic, posing diagnostic and clinical challenges during surgical or endovascular procedures. This study aimed to assess the incidence and features of ICA agenesis, hypoplasia, and fenestration in patients undergoing carotid CT angiography (CTA).

Materials and methods: Following ethics approval, a retrospective review of 1950 carotid CTA scans performed between January 2023 and January 2024 was conducted. Adult patients (≥ 18 years) were included; cases with severe artifacts, vasculitis, or traumatic dissection were excluded. Images were reviewed for ICA anomalies, collateral circulation, and associated neurovascular findings such as aneurysms.

Results: Five cases (0.26%) of ICA agenesis or hypoplasia were identified, including one bilateral case. All were asymptomatic and showed no signs of infarction or encephalomalacia. Two cases had saccular aneurysms - one in the contralateral ICA and one in the basilar artery. Two ICA fenestrations were found: one in the supraclinoid and one in the cavernous segment. One of these was associated with an ipsilateral aneurysm. Collateral flow was mainly through a hypertrophic posterior communicating artery, with additional input from the anterior communicating artery in some cases.

Conclusions: Although ICA anomalies are uncommon, accurate recognition is essential for proper surgical planning and avoiding misdiagnosis. High-resolution CTA plays a key role in detecting these rare variants and related aneurysms, ultimately aiding clinical decision-making. Further research into their embryological origins and hemodynamic consequences is warranted.