Introduction: Hemodynamic forces, including flow-induced tangential wall shear stress (WSS), are thought to be involved in aneurysm formation, growth and rupture. We aimed to evaluate the pattern and distribution of intra-dome WSS in a set of volume-matched ruptured and unruptured sidewall aneurysm pairs in order to remove the confounding effect of aneurysm size-dependence.
Methods: Ruptured aneurysms were volume-matched to unruptured aneurysms at similar locations resulting in nine pairings. Computational fluid dynamic simulations were performed on all models and WSS distribution statistics were computed. WSS was evaluated at peak-systole and end-diastole, and as time-averaged during the entire cardiac cycle. Logarithmic transformation of WSS was also performed to refine value discrimination at extrema. Differences among size-matched ruptured-unruptured lesions were evaluated using pairwise t-test analysis. Parametric models constructed using solid modeling were used to evaluate the effect of aneurysm size and presence of bleb on the dome on WSS.
Results: Analysis on parametric models show there is a statistically significant negative correlation between volume and WSS values. On the patient dataset, low-range WSS values were significantly lower for ruptured compared to unruptured aneurysms, regardless of WSS evaluation (time-averaged, peak-systole, end-diastole). Statistics of logarithmic WSS performed better than WSS statistics, with minimum logarithmic WSS at end-diastole being best at discriminating rupture status (p=0.002, AUC=0.96). Regardless of evaluation, higher range and maximal WSS were not significantly different between ruptured and unruptured counterparts. Bleb presence was not found to correlate with rupture status (p=0.31). Although bleb presence was found to lower the minimum WSS values, it did not translate in statistical significance between aneurysms with blebs compared to aneurysms without blebs.
Conclusions: Aneurysms size acts as confounding factor to WSS discriminative performance and volume-matched analysis is necessary for unbiased WSS evaluation. When compensating for size-dependent variation, very low-range WSS emerges as best for its association with rupture status, in contrast to mean and high-range values. These findings lend support to the hypothesis that lower WSS is associated with wall changes and rupture by a mechanism that needs further exploration.
Patient Care: It is hoped that understanding the link between low wall shear stress and aneurysm development and rupture may serve as a potential diagnostic tool for aneurysm rupture risk stratfication.
Learning Objectives: 1) Understand the role of mechanical forces in the aneurysm dome
2) Appreciate the link between low wall shear stress and ruptured status in sidewall cerebral aneurysms
3) Understand the importance of volume matching aneurysm dome size when evaluating the role of wall shear stress and its link to aneurysm rupture