Aneurysm Wall Enhancement and Probability of Instability in Unruptured Intracranial Aneurysms: A Long‐Term Follow‐Up Study

Objective Aneurysm wall enhancement (AWE) may predict aneurysm growth and rupture in the short‐term, but there is a lack of long‐term follow‐up studies. We aimed to determine whether unruptured intracranial aneurysms (UIAs) with AWE have a higher probability of aneurysm instability during long‐term follow‐up compared with those without AWE. Methods For this longitudinal cohort study, we obtained individual patient data from two international cohorts. We included patients with ≥ 1 untreated UIA who underwent gadolinium‐enhanced aneurysm wall imaging and magnetic resonance angiography (MRA) between 2012 and 2016, and had follow‐up imaging and/or had a rupture during follow‐up. The outcome was aneurysm instability, defined as time to growth, morphological change, or rupture during follow‐up. We calculated the 7.5‐year probability of aneurysm instability with 95% confidence interval (CI) with the Kaplan–Meier estimator. We used Cox regression survival analysis to calculate the crude hazard ratio (HR) with corresponding 95% CI of AWE for aneurysm instability, and the HR adjusted for age and aneurysm size at baseline. Results We included 198 patients (median age = 58 years, interquartile range = 50–68, 139 women, 70%) with 224 aneurysms. Aneurysm instability was observed in 15 of 72 aneurysms (21%) with AWE and 13 of 152 aneurysms (9%) without AWE during a median follow‐up duration of 6.8 years (IQR = 3.3–7.9). The 7.5‐year probability of instability was 29.2% (95% CI = 14.5%–41.3%) in aneurysms with AWE and 9.3% (95% CI = 2.9%–15.3%) in aneurysms without AWE (crude HR = 4.29, 95% CI = 1.90–9.72, adjusted HR = 5.06, 95% CI = 2.13–12.02). Interpretation UIAs with AWE have a higher probability of 7.5‐year aneurysm instability compared with those without AWE. ANN NEUROL 2025