Wall shear stress association with rupture status in volume matched sidewall aneurysms

Flow induced tangential wall shear stress (WSS) is thought to be involved in aneurysm formation, growth, and rupture. Low WSS was previously associated with rupture, but definitive quantitative analyses remain scant as larger aneurysms are associated with lower WSS regardless of rupture status, and ruptured aneurysms are larger than unruptured aneurysms. Here, the intra-dome WSS was evaluated on 18 internal carotid artery aneurysms, volume matched as ruptured/unruptured pairs in order to remove the confounding effect of size dependence.

Computational fluid dynamic simulations were performed and WSS was evaluated at peak systole, end diastole, and as time averaged over the cardiac cycle. WSS logarithmic scaling was applied to refine value discrimination at extrema. Ruptured/unruptured lesions were statistically evaluated using pairwise t test analysis. The effect of size on WSS was evaluated in parametric models.

In parametric data, there was a statistically significant negative correlation between volume and WSS values. In patient data, mean WSS was not statistically significant but low range WSS values were significantly lower for ruptured aneurysms, regardless of WSS evaluation (time averaged, peak systole, end diastole). Statistically, logarithmic WSS performed better than WSS, with minimum logarithmic WSS at end diastole being the best rupture status discriminator (p=0.001, area under the curve=0.98). Higher range and maximal WSS were not significantly significant.

Aneurysm size is a confounding factor to WSS rupture discrimination, and volume matched analysis is necessary for unbiased evaluation. While these results lend support to the hypothesis that lower WSS induces wall changes which may be associated with rupture, it raises questions regarding the extent of this association, which requires further exploration.