Coil embolization strategy after flow diverter deployment in patients with intracranial vertebral artery dissection aneurysms: a study from a hemodynamic viewpoint

Flow diverter (FD) deployment combined with coil therapy is effective and considered superior to FD deployment alone for treating large, complex anterior circulation aneurysms. However, the optimal strategy for coil usage in posterior circulation aneurysms, particularly intracranial vertebral artery dissection aneurysms (IVADAs), remains unclear. This study used patient-specific aneurysm models and finite element analysis to determine the ideal packing density (PD) of coils following FD placement in IVADAs. We prospectively analyzed 22 patients with 24 aneurysms, all treated with FD at our hospital. Hemodynamic parameters were analyzed before treatment, after FD alone, and at three different coiling rates (5%, 15%, and 25%) using software simulation. All 22 patients underwent FD procedures to treat IVADAs. FD deployment and additional coil use both reduced the inflow rate at the aneurysm neck, the inflow concentration index, and the mean velocity in the aneurysm. However, compared with FD treatment alone, coils provided a smaller reduction in these parameters. No significant difference in the reduction ratio was observed when the coiling PD increased from 5 to 15% and then to 25%. Further coil addition beyond a 5% PD produced no notable hemodynamic benefits. Adjunct coiling improves the post-FD hemodynamic environment of treated IVADAs. However, dense packing is unnecessary because the intra-aneurysmal hemodynamics tend to stabilize once the PD reaches approximately 5%.