Flow diverter mechanism influenced by concurrent processes: progressive neck coverage and intrasaccular thrombus formation

Background Although good long-term outcomes have been obtained in the treatment of intracranial aneurysms with flow-diverting devices, aneurysms are not immediately occluded, and many remain incompletely occluded for a long time necessitating re-treatment. Improving devices and treatment outcomes requires detailed understanding of the mechanisms leading to quick and complete aneurysm occlusion after device implantation. Methods In this work, a series of seven aneurysms with persistent high-speed flow after flow diverter deployment were analyzed with computational models that include fibrin production and adhesion to the device struts and subsequent flow alteration due to fibrin accumulation. Four of the seven aneurysms were completely occluded at 3 months despite having high-flow conditions immediately after treatment. The remaining three aneurysms were incompletely occluded for at least 6 months. Results Significantly more fibrin accumulation and neck coverage (P=0.0209) was observed in the aneurysms that were completely occluded at 3 months compared with those that remained incompletely occluded. This larger fibrin accumulation resulted in larger inflow jet disruption and mean aneurysm velocity reductions (p=0.0209), creating in these aneurysms hemodynamic environments more favorable for fast complete occlusions. Conclusions Fibrin production induced by high-flow shear stress and adhesion to the device wires can result in some cases with persistent high-speed flow after device deployment in neck coverage and substantial inflow jet obstruction that may explain why these aneurysms were quickly completely occluded.