The Complementary Role of Size and Morphology in Predicting Intracranial Aneurysm Rupture: An Intrapatient Matched Study

Background: Managing patients with multiple intracranial aneurysms remains challenging, both for identifying the ruptured aneurysm in the acute phase and for deciding whether to treat unruptured bystanders later. As traditional risk scores rely largely on aneurysm size, this study used an intrapatient matched design to better assess the anatomical determinants of rupture beyond patient-specific factors. Methods: A retrospective analysis was conducted on 55 patients harboring a total of 136 intracranial aneurysms. To inherently control systemic risk factors, the ruptured index aneurysm was directly compared against the unruptured bystanders within the same individual. A generalized linear mixed model was utilized to evaluate morphological predictors of rupture. Results: After adjusting for topography, absolute dome width emerged as a strong independent predictor of intrapatient rupture (odds ratio [OR] 1.56, 95% confidence interval [CI]: 1.12–2.18, P = 0.008), alongside the macroscopic presence of blebs (OR 7.27, 95% CI: 1.65–32.06, P = 0.009). Conversely, the size ratio and neck size lost their statistical significance (P = 0.697 and P = 0.567, respectively). Topographically, aneurysms located at the anterior and posterior communicating arteries exhibited the highest propensity for rupture (74% and 69%, overall effect P = 0.002), with significantly higher odds of rupture compared to the middle cerebral artery baseline (OR 9.83 and OR 8.99, respectively). Conclusions: The propensity for aneurysm rupture within the same patient is associated with a combination of absolute volumetric growth (width) and focal morphological instability (blebs). Topographically, high-flow bifurcations such as anterior communicating artery and posterior communicating artery carry the highest risk. The decision-making process for treating unruptured bystander aneurysms should comprehensively integrate both absolute size thresholds and local wall irregularities.