Aneurysm flow dynamics: alterations of slipstream flow for neuroendovascular treatment with liquid embolic agents.

BACKGROUND AND PURPOSE The main issue with use of a liquid embolic agent is one of safety. To determine and improve the efficacy of potential neuroendovascular treatment regimens, particularly the use of liquid embolic agents, we evaluated the changes in aneurysm flow dynamics resulting from alterations of parent vessel flow. METHODS We created silicone replicas of a laboratory-created aneurysm model and a basilar artery aneurysm cast from a human cadaver. Replicas were placed in a circuit of pulsatile non-Newtonian fluid, and flows were adjusted to simulate human physiologic flow velocity, profile, and volume. Individual fluid slipstreams were opacified with isobaric dyes. Images were obtained of the unaltered vascular replica; after placement of a nondetachable balloon in the parent vessel at multiple locations proximal to, across, and distal to the aneurysm neck; and after placement of a stent across the aneurysm neck. Aneurysms were then occluded with a cyanoacrylate liquid embolic agent in association with each device. RESULTS In the unaltered replica, flow entered the distal aneurysm neck and impacted against the distal lateral aneurysm wall. Disturbed, but nonturbulent, flow then continued along the aneurysm wall in a vortex pattern and exited at the proximal aspect of the aneurysm neck. With the balloon partially inflated in the parent vessel, the slipstream velocity increased. This resulted in more rapid flow in the aneurysm sac, a less favorable condition for deposition of liquid embolic material. The effect was more pronounced with greater degrees of balloon inflation (resulting in greater parent vessel narrowing) and when the balloon was proximal to the aneurysm neck compared with more distal parent vessel positioning. Only with complete occlusion of the parent vessel lumen, either proximal to, across, or distal to the aneurysm sac, was there intraaneurysmal flow reduction (ie, stasis), a more favorable condition for liquid embolic material deposition. Also, with the balloon positioned across the aneurysm neck, not only did the liquid agent remain in the aneurysm sac, but also the surface could be molded to re-create a normal parent vessel lumen. A stent placed across the aneurysm neck caused the slipstreams to lose their coherence as they passed through the stent mesh. This prevented slipstream impact against the aneurysm sidewall and decreased the intraaneurysmal fluid velocity. During deposition of liquid embolic agent through the stent sidewall into the aneurysm sac, the stent mesh appeared to provide a barrier to passage of the embolic agent into the adjacent parent vessel, also a more favorable condition for liquid embolic material deposition. CONCLUSION Knowledge of aneurysm flow dynamics and the changes incurred after endovascular parent vessel flow alteration provides a basis for safer aneurysm obliteration by using a liquid embolic agent with a neurointerventional technique.