BACKGROUND AND PURPOSE: EL associated with ruptured aneurysms is higher than that for unruptured aneurysms. In this study, the effect of arterial morphologic variation of bifurcation aneurysms on EL was investigated in idealized models of middle cerebral artery aneurysms.

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Morphological characteristics associated with cerebral aneurysm formation can be used to assess aneurysm rupture. This study investigated hemodynamic effects resulting from change in the parent artery diameter of bifurcation type aneurysm. Computational fluid dynamic (CFD) analysis was performed on middle cerebral artery (MCA) models with various parent artery diameters. Calculations were performed with steady flow rate (125 ± 12.5 ml/min) at the parent artery inlet. Energy loss (EL) was calculated from pressure and kinetic energy obtained from flow velocity. The results indicate that the high wall shear stress (WSS) and EL occurs in model with the smallest parent vessel compared to the other models for all three inflows. Results also showed that 10% variation of inflow results in average of 23 ± 2.9% changes in WSS and 25.5 ± 0.5% changes in energy loss. These results demonstrated that for CFD analysis of MCA bifurcation type aneurysm, upstream parent vessel and inflow evaluation for individual patient is essential.

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Surgical decisions on treatment of cerebral aneurysms are based predominantly on aneurysm size. This study has assessed the influence of parent vessel geometry on intra-aneurysmal flow patterns and mass flow rate using computational fluid dynamics and finite element modeling of straight and curved vessels feeding saccular aneurysms of varying size and aspect ratio. Simulation results have shown that aneurysms of similar shape and size but with curved parent vessels can have more than 2 fold increase in flow rate, with markedly different flow velocity patterns and development of secondary flows. These are significant hemodynamic factors that can contribute to increased risk of aneurysm rupture, in addition to aneurysm size. The dependency of parent vessel geometry is a function of aneurysm aspect ratio and shows minimal dependency at an aspect ratio of 1.68. These findings could be used for improved quantification of risk of rupture of cerebral aneurysms detected from clinical imaging modalities and to aid surgical decision making.