Intracranial aneurysms occur more frequently at bifurcation sites that typically experience higher hemodynamic stresses.

BACKGROUND: Intracranial aneurysms (IAs) occur more frequently at certain bifurcations than at others. Hemodynamic stress, which promotes aneurysm formation in animal models, also differs among bifurcations, depending on flow and vessel geometry.
OBJECTIVE: To determine whether locations that are more likely to develop IAs experience different hemodynamic stresses that might contribute to higher IA susceptibility.
METHODS: We characterized the hemodynamic microenvironment at 10 sites in or around the circle of Willis where IAs commonly occur and examined statistical relationships between hemodynamic factors and the tendency for a site to form IAs. The tendency for each site to develop IAs was quantified on the basis of the site distribution from systematic literature analysis of 19 reports including 26418 aneurysms. Hemodynamic parameters for these sites were derived from image-based computational fluid dynamics of 114 cerebral bifurcations from 31 individuals. Wall shear stress and its spatial gradient were calculated in the impact zone surrounding the bifurcation apex. Linear and exponential regression analyses evaluated correlations between the tendency for IA formation and the typical hemodynamics of a site.
RESULTS: IA susceptibility significantly correlated with the magnitudes of wall shear stress and positive wall shear stress gradient within the hemodynamic impact zone calculated for each site.
CONCLUSION: IAs occur more frequently at cerebral bifurcations that typically experience higher hemodynamic shear stress and stronger flow acceleration, conditions previously shown to promote aneurysm initiation in animals.