Basilar Apex Aneurysms in the Setting of Carotid Artery Stenosis: Case Series and Angiographic Anatomic Study

Background: Intracranial aneurysms (IAs) are life-threatening lesions known within the literature to be found incidentally during routine angiographic workup for carotid artery stenosis (CAS). As IAs are associated with vascular shear stress, it is reasonable to expect that altered flow demands within the anterior circulation, such as with CAS, increase compensatory flow demands via the Circle of Willis (COW) and may induce similar stress at the basilar apex. Objective: We present a series of nine unruptured basilar apex aneurysms (BAA) with CAS and a comparative radiographic analysis to BAA without CAS. Methods: Twenty-three patients with BAA were retrospectively identified using records from 2011 to 2016. CAS by North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria, morphology of BAA, competency of COW, and anatomic relationships within the posterior circulation were examined independently by a neuroradiologist using angiographic imaging. Results: Nine (39%) of the twenty-three BAA patients had CAS, with six having stenosis ≥50%. Four (67%) of the patients with ≥50% CAS demonstrated aneurysm flow angles contralateral to the side with highest CAS. Additionally, the angle between the basilar artery (BA) trajectory and aneurysm neck was observed to be smaller in patients with ≥50% CAS (61 vs 74 degrees). No significant differences in COW patency, posterior circulation morphology, and degree of stenosis were observed. Conclusion: Changes in the cervical carotid arteries may lead to blood flow alterations in the posterior circulation that increase the propensity for BAA formation. Posterior circulation imaging can be considered in CAS patients to screen for BAA.