Intracranial Aneurysm Morphology and Hemodynamics: A Controlled CFD Study of Aspect Ratio and Neck Size

Abstract

Intracranial aneurysms are bulges in brain arteries that affect up to 5% of the population and can rupture without warning, often leading to fatal or disabling strokes. Current clinical risk assessments rely heavily on aneurysm size, despite evidence that both small and large aneurysms can rupture. Computational fluid dynamics (CFD) offers a way to assess blood flow–related factors linked to rupture, such as Time-Averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT). However, existing CFD studies are often limited by confounding variables in patient-specific geometries, making it difficult to isolate the role of individual shape features. This study aimed to investigate how Aspect Ratio (AR), the height-to-neck-width ratio of an aneurysm, independently influences hemodynamic behavior. Using a generative model (AneuG), 36 anatomically realistic aneurysm models were created with systematically varied AR while keeping neck width constant. Unsteady CFD simulations with pulsatile inflow conditions were conducted in ANSYS Fluent, and key metrics (TAWSS, OSI, RRT) were extracted and analyzed. Results showed that increasing AR consistently reduced TAWSS and moderately increased RRT, both of which are associated with rupture risk. However, AR had no consistent effect on OSI, which appeared to depend more on local flow structures than global shape. These findings suggest that AR is a reliable predictor of certain hemodynamic risks but insufficient to explain complex flow patterns. The study demonstrates that controlled, morphology-driven simulations can clarify how shape affects blood flow, and supports integrating AR into future clinical tools for improved rupture risk assessment.