Hemodynamic analysis of fast and slow aneurysm occlusions by flow diversion in rabbits

Purpose To assess hemodynamic differences between aneurysms that occlude rapidly and those occluding in delayed fashion after flow diversion in rabbits. Methods Thirty-six elastase-induced aneurysms in rabbits were treated with flow diverting devices. Aneurysm occlusion was assessed angiographically immediately before they were sacrificed at 1 (n=6), 2 (n=4), 4 (n=8) or 8weeks (n=18) after treatment. The aneurysms were classified into a fast occlusion group if they were completely or near completely occluded at 4weeks or earlier and a slow occlusion group if they remained incompletely occluded at 8weeks. The immediate post-treatment flow conditions in aneurysms of each group were quantified using subject-specific computational fluid dynamics and statistically compared. Results Nine aneurysms were classified into the fast occlusion group and six into the slow occlusion group. Aneurysms in the fast occlusion group were on average significantly smaller (fast=0.9cm, slow=1.393cm, p=0.024) and had smaller ostia (fast=0.144cm(2), slow=0.365cm(2), p=0.015) than aneurysms in the slow occlusion group. They also had a lower mean post-treatment inflow rate (fast=0.047mL/s, slow=0.155mL/s, p=0.0239), kinetic energy (fast=0.519 erg, slow=1.283 erg, p=0.0468), and velocity (fast=0.221cm/s, slow=0.506cm/s, p=0.0582). However, the differences in the latter two variables were only marginally significant. Conclusions Hemodynamic conditions after flow diversion treatment of cerebral aneurysms in rabbits are associated with the subsequent aneurysm occlusion time. Specifically, smaller inflow rate, kinetic energy, and velocity seem to promote faster occlusions, especially in smaller and small-necked aneurysms. These results are consistent with previous studies based on clinical series.