Internal carotid aplasia/hypoplasia and intracranial saccular aneurysms: series of three new cases and systematic review of the literature.

BACKGROUND AND PURPOSE: Abnormal arterial flow dynamics and intracranial collateral pathways can be seen in patients with congenital internal carotid artery (ICA) aplasia or hypoplasia. Here we seek to evaluate whether ICA aplasia/hypoplasia is associated with an increased prevalence of intracranial saccular aneurysm relative to carotid rete mirabile. METHODS: We combined our experience of three cases with 148 previous publications to form a retrospective series including 132 cases of ICA aplasia, 33 cases of ICA hypoplasia, and 34 cases of carotid rete mirabile. RESULTS: After excluding cases lacking angiograms, ICA aplasia/hypoplasia was more commonly associated with aneurysm (45/158, 27.8%) compared with rete mirabile (2/34, 5.9%). A significantly greater overall aneurysm prevalence was seen among ICA aplasia/hypoplasia patients age 30 years or older (38/101, 36.6%) than in younger individuals (7/48, 14.6%). CONCLUSIONS: Intracranial saccular aneurysm is more strongly associated with ICA aplasia/hypoplasia than rete mirabile. An increased aneurysm prevalence among older individuals with ICA aplasia/hypoplasia suggests an acquired etiology. Magnetic resonance angiography (MRA) is recommended in the initial evaluation of ICA aplasia/hypoplasia to evaluate for intracranial saccular aneurysm, particularly after the third decade of life.