  Cerebral aneurysm progression is a result of a complex interplay of the
biomechanical and clinical risk factors that drive aneurysmal growth and
rupture. Subjects with multiple aneurysms are unique cases wherein clinical
risk factors are expected to affect each aneurysm equally, thus allowing for
disentangling the effect of biomechanical factors on aneurysmal growth. Towards
this end, we performed a comparative computational fluid--structure interaction
analysis of aneurysmal biomechanics in image-based models of stable and growing
aneurysms in the same subjects, using the cardiovascular simulation platform
SimVascular. We observed that areas exposed to low shear and the median peak
systolic arterial wall displacement were higher by factors of 2 or more and
1.5, respectively, in growing aneurysms as compared to stable aneurysms.
Furthermore, we defined a novel metric, the oscillatory stress index (OStI),
that indicates locations of oscillating arterial wall stresses. We observed
that growing aneurysms were characterized by regions of combined low wall shear
and high OStI, which we hypothesize to be associated with regions of collagen
degradation and remodeling. Such regions were either absent or below 5% of the
surface area in stable aneurysms. Our results lay the groundwork for future
studies in larger cohorts of subjects, to evaluate the statistical significance
of these biomechanical parameters in cerebral aneurysm growth.
