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 2026;99:863-870.