Aneurysm Inflow-Angle as a Discriminant for Rupture in Sidewall Cerebral Aneurysms

Background and Purpose— The ability to discriminate between ruptured and unruptured cerebral aneurysms on a morphological basis may be useful in clinical risk stratification. The objective was to evaluate the importance of inflow-angle (IA), the angle separating parent vessel and aneurysm dome main axes. Methods— IA, maximal dimension, height–width ratio, and dome–neck aspect ratio were evaluated in sidewall-type aneurysms with respect to rupture status in a cohort of 116 aneurysms in 102 patients. Computational fluid dynamic analysis was performed in an idealized model with variational analysis of the effect of IA on intra-aneurysmal hemodynamics. Results— Univariate analysis identified IA as significantly more obtuse in the ruptured subset (124.9°±26.5° versus 105.8°±18.5°, P =0.0001); similarly, maximal dimension, height–width ratio, and dome–neck aspect ratio were significantly greater in the ruptured subset; multivariate logistic regression identified only IA ( P =0.0158) and height–width ratio ( P =0.0017), but not maximal dimension or dome–neck aspect ratio, as independent discriminants of rupture status. Computational fluid dynamic analysis showed increasing IA leading to deeper migration of the flow recirculation zone into the aneurysm with higher peak flow velocities and a greater transmission of kinetic energy into the distal portion of the dome. Increasing IA resulted in higher inflow velocity and greater wall shear stress magnitude and spatial gradients in both the inflow zone and dome. Conclusions— Inflow-angle is a significant discriminant of rupture status in sidewall-type aneurysms and is associated with higher energy transmission to the dome. These results support inclusion of IA in future prospective aneurysm rupture risk assessment trials.