Hemodynamic Assessment of Bleb Formation in Patient-Specific Intracranial Aneurysms using Computational Fluid Dynamics

Bleb formation is widely recognized as an important morphological indicator of intracranial aneurysm instability and rupture risk. However, the hemodynamic mechanisms associated with bleb development remain incompletely understood. In this study, patient-specific computational fluid dynamics (CFD) simulations were performed to investigate the influence of bleb formation on the hemodynamic environment of intracranial aneurysms. Three aneurysm geometries were reconstructed from medical imaging data and analyzed before and after bleb formation. Blood flow was modeled as a pulsatile, incompressible, laminar, and non-Newtonian fluid using the Casson rheological model, while vessel walls were assumed rigid. The transient Navier–Stokes equations were solved using ANSYS Fluent under physiologically realistic boundary conditions. Key hemodynamic parameters, including wall shear stress (WSS), wall pressure, blood velocity, oscillatory shear index (OSI), and flow streamlines, were evaluated and compared between the original and blebbed aneurysm models. The results demonstrated that the hemodynamic impact of bleb formation strongly depends on aneurysm geometry. In Patient A, bleb formation reduced the mean WSS by approximately 4.1% while increasing the mean sac pressure, velocity, and OSI by 1.7%, 5.9%, and 76.2%, respectively, indicating a substantial alteration of the local flow environment. In contrast, Patients B and C exhibited only minor changes in the averaged hemodynamic parameters following bleb formation, despite maintaining extremely low WSS and high OSI values. Flow visualizations revealed the development of localized recirculation zones and low-velocity vortices within the bleb cavity, resulting in increased flow oscillation and prolonged blood residence time. These disturbed flow conditions may contribute to wall degeneration and aneurysm instability. The findings suggest that blebs act as hemodynamically vulnerable regions characterized by complex flow structures and elevated oscillatory behavior. Patient-specific geometry plays a critical role in determining the extent to which bleb formation alters aneurysm hemodynamics and potentially influences rupture risk.