Association Between Unruptured Intracranial Aneurysms and Downstream Stroke.

Background and Purpose- Case reports suggest that unruptured intracranial aneurysms may serve as a nidus for thrombus formation and downstream embolic stroke. However, few data exist to support an association between unruptured aneurysms and ischemic stroke. Methods- We conducted a within-subjects case-control study of acute ischemic stroke patients prospectively enrolled in the Cornell Acute Stroke Academic Registry who had magnetic resonance imaging of the brain and arterial imaging of the head within 14 days of admission. Reviewers blinded to the study hypothesis ascertained the presence of aneurysms from the neuroradiologist's clinical report of the arterial imaging findings. McNemar test for paired data was used to compare the prevalence of unruptured aneurysms ipsilateral versus contralateral to the side of anterior circulation infarcts. Aneurysms of the anterior communicating artery or in the posterior circulation were not counted in the analysis. Results- Among 2116 patients registered in the Cornell Acute Stroke Academic Registry during 2011 to 2016, 1541 met our inclusion criteria, of whom 176 (11.4%; 95% CI, 9.8-13.0%) had an intracranial aneurysm. The prevalence of aneurysms did not differ on the side ipsilateral versus contralateral to the infarction (risk ratio [RR], 1.2; 95% CI, 0.9-1.5). There was no significant association between aneurysms and ipsilateral stroke in secondary analyses of the 1244 patients with stroke in a single anterior circulation territory (RR, 1.2; 95% CI, 0.8-1.9), the 619 patients with cryptogenic stroke (RR, 1.4; 95% CI, 0.9-2.0), or the 485 patients with cryptogenic stroke in a single anterior circulation territory (RR, 1.7; 95% CI, 0.8-3.3). Results were unchanged when counting only aneurysms >3 mm (RR, 1.2; 95% CI, 0.8-1.9) or 5 mm in diameter (RR, 1.2; 95% CI, 0.9-1.5). Conclusions- Contrary to our hypothesis, we found no significant association between unruptured intracranial aneurysms and ipsilateral ischemic stroke.