BackgroundIn aneurysmal subarachnoid hemorrhage patients with multiple intracranial aneurysms (aSAH-MIA patients), the risk of secondary unruptured intracranial aneurysms is inconsistent. This study aimed to explore the risk of unruptured aneurysms in Chinese aSAH-MIA patients.MethodsThe medical records and angiographic images of aSAH-MIA patients from eight cerebrovascular centers in China were retrospectively reviewed and analyzed. Patients with a single unruptured intracranial aneurysm (UIA) and no prior aSAH were used as controls. Propensity score matching (PSM) was employed to balance the differences in age, gender, aneurysm size, aneurysm site, and follow-up duration between the two groups.ResultsThe study included 267 unruptured aneurysms from 204 aSAH-MIA patients and 769 single UIA. After PSM, 201 aneurysms were enrolled in the aSAH-MIA group and 201 aneurysms in the control group. The mean follow-up was 2.2 years. Thirty-four aneurysm instability events (28 growth and 6 rupture, 16.9%) occurred during follow-up in the aSAH-MIA group and 16 instability events (13 growth and 3 rupture, 8%) occurred in the control group. Risk factors for aneurysmal instability were aneurysm irregularity (OR 2.53; 95% CI 1.18 to 4.31), higher size ratio (OR 1.23; 95% CI 1.37 to 4.39), and middle cerebral artery location (OR 1.86; 95% CI 1.03 to 3.17). The risk of aneurysmal instability was substantially elevated in the aSAH-MIA group (HR 2.07; 95% CI 1.12 to 3.02).ConclusionsUnruptured aneurysms in Chinese aSAH-MIA patients exhibited higher risks of growth and rupture than in patients with a single UIA. Middle cerebral artery location, higher size ratio and irregular shape were associated with higher risk of growth or rupture.