Effect of coiling on aneurysm neck hemorheology in flow diverter stent-assisted treatment of intracranial aneurysms.

backgroundFlow diverter (FD) stent-assisted coil embolization (FDAC) is widely used for the treatment of wide-necked, large and complex intracranial aneurysms (IA), yet its local hemodynamic effects at the level of blood flow between stent struts remain poorly defined. This study aimed to evaluate the effect of FD deployment and different coil density distributions on between-strut hemodynamics.

methodsComputational fluid dynamics simulations were performed under five conditions: untreated, FD-only, and FD-assisted coiling with three configurations of coil density distribution (Updown, Downstream, and Upstream). Blood flow was modeled as laminar, transient, incompressible, and non-Newtonian using the Carreau-Yasuda rheological model. Primary outcomes were maximum and average shear stress and shear strain rate between FD struts, as well as aneurysm wall shear stress (WSS), viscosity, and Oscillatory Shear Index (OSI).

resultsEight real patient-specific unruptured IA geometries were reconstructed. Stent deployment markedly increased between-strut hemodynamic loading. Maximum between-strut shear stress increased from 22.44 ± 16.38 Pa in the untreated condition to 234.87 ± 211.86 Pa after stenting (p < 0.01), while maximum shear strain rate increased from 6352 ± 4711 s⁻¹ to 67,220 ± 61,525 s⁻¹ (p < 0.01). Coil addition significantly reduced between-strut shear stress and shear strain rate in all configurations relative to FD alone (all p ≤ 0.01), with mean reductions of approximately 49-52%. Downstream and upstream configurations provided significantly greater reduction in maximum between-strut shear stress and strain rate than the Updown configuration (p = 0.031 and p = 0.047, respectively); however, the corresponding omnibus tests were not significant, and these directional differences are therefore reported as exploratory. Coil addition significantly reduced the average aneurysm WSS relative to the FD alone across all configurations (p < 0.01) but did not significantly reduce the maximum WSS relative to the FD alone. Time‑averaged mean and maximum dynamic viscosity increased significantly from normal to FD‑alone (p ≤ 0.031) and further increased markedly after coil deployment (all p ≤ 0.016 vs. FD‑alone), with no significant differences among coil configurations (p ≥ 0.1). OSI did not differ significantly.

conclusionAdjunctive coil placement reduces FD-induced thrombogenic shear stress by approximately 50%; differences among coil-density configurations were modest relative to interpatient variability and should be considered exploratory and hypothesis-generating.