Local hemodynamics at the rupture point of cerebral aneurysms determined by computational fluid dynamics analysis

Background: Cerebral aneurysms carry a high risk of rupture and so present a major threat to the patient's life. Accurate criteria for predicting aneurysm rupture are important for therapeutic decision-making, and some clinical and morphological factors may help to predict the risk for rupture of unruptured aneurysms, such as sex, size and location. Hemodynamic forces are considered to be key in the natural history of cerebral aneurysms, but the effect on aneurysm rupture is uncertain, and whether low or high wall shear stress (WSS) is the most critical in promoting rupture remains extremely controversial. This study investigated the local hemodynamic features at the aneurysm rupture point.

Methods: Computational models of 6 ruptured middle cerebral artery aneurysms with intraoperative confirmation of rupture point were constructed from 3-dimensional rotational angiography images. Computational fluid dynamics (CFD) simulations were performed under pulsatile flows using patient-specific inlet flow conditions. Time-averaged WSS (TAWSS) and oscillatory shear index (OSI) were calculated, and compared at the rupture point and at the aneurysm wall without the rupture point. We performed an additional CFD simulation of a bleb-removed model for a peculiar case in which bleb formation could be confirmed by magnetic resonance angiography.

Results: All rupture points were located at the body or dome of the aneurysm. The TAWSS at the rupture point was significantly lower than that at the aneurysm wall without the rupture point (1.10 vs. 4.96 Pa, p = 0.031). The OSI at the rupture point tended to be higher than at the aneurysm wall without the rupture point, although the difference was not significant (0.0148 vs. 0.0059, p = 0.156). In a bleb-removed simulation, the TAWSS at the bleb-removed area was 6.31 Pa, which was relatively higher than at the aneurysm wall (1.94 Pa).

Conclusion: The hemodynamics of 6 ruptured cerebral aneurysms of the middle cerebral artery were examined using retrospective CFD analysis. We could confirm the rupture points in all cases. With those findings, local hemodynamics of ruptured aneurysms were quanti-tatively investigated. The rupture point is located in a low WSS region of the aneurysm wall. Bleb-removed simulation showed increased WSS of the bleb-removed area, associated with the flow impaction area. Although the number of subjects in this study was relatively small, our findings suggest that the location of the rupture point is related to a low WSS at the aneurysm wall. Further investigations will elucidate the detailed hemodynamic effects on aneurysm rupture.