In-vitro investigation of the influence of aneurysmal sac morphology on the hemodynamics of cerebral aneurysms treated with flow diverting stents

Flow diverting stents (FDS) are a common cerebral aneurysm treatment. These high-porosity meshes aim at reducing flow into the aneurysm, promoting re-endothelization, and leading to the formation of a stable thrombus filling the aneurysmal sac. 25% of procedures fail, requiring follow-up and re-treatment. We investigate the effect of the aneurysm geometry on the efficacy of FDS at reducing flow into the aneurysm, via Stereo Particle Image Velocimetry (2D-3C PIV) measurements in 12 idealized aneurysm flow phantoms. Parent vessel curvature, neck size and sac aspect ratio were varied. These models were set up in a flow loop, before and after treatment, at physiological flow rates, corresponding to different Dean and Womersley numbers. A single counter-rotating vortex, whose circulation correlates with the Dean number, was observed for all untreated aneurysms. Aspect ratio variations yielded different post-treatment flow patterns: inversion of vorticity during the cycle, counter-, co-rotating vortex. Depending on the shape, the post-treatment circulation ranged from 65% to only a few % of the pre-treatment value. This study highlights the influence of some parameters: high impact of the morphology and negligible for Wo, helping to predict better the risk of treatment failure.