Safety and Technical Feasibility of Staged Flow Diverter Placement Following Coil Embolization: A Case Series Including Anatomically Challenging Aneurysms

Objective: Flow diverter (FD) stents are a promising treatment option for complex intracranial aneurysms. However, rapid hemodynamic changes, thrombus formation, and complex morphologies can increase rupture risk and pose technical challenges. To address these concerns, a "staged treatment" with initial coil embolization followed by delayed FD placement has been introduced. This study aimed to evaluate its clinical outcomes, safety, and technical feasibility, including in anatomically challenging aneurysms. Methods: A retrospective analysis was conducted on 11 patients with intracranial aneurysms who underwent initial coil embolization followed by FD placement at our institution between 2018 and 2024. The data collected included aneurysm characteristics, number of coils used, initial volume embolization ratio (VER), interval between coil embolization and FD placement, and procedure-related complications. Results: Of the 11 patients, 10 were female. Nine aneurysms were large (>10 mm) and 2 were giant (>25 mm). The median initial VER was 18% and the median interval between coil embolization and FD placement was 79 days. All the FD procedures were technically successful, even in aneurysms for which direct distal navigation was expected to be difficult. No permanent complications or delayed ruptures occurred during the follow-up. At the 12-month follow-up DSA, 81.8% of the patients achieved complete occlusion (O'Kelly-Marotta [OKM] grade D), and all cases were graded as OKM C or higher. All patients had favorable clinical outcomes, with modified Rankin Scale scores of 0 or 1. Conclusion: Staged FD treatment appears to be a safe and effective therapeutic option for treating large, ruptured, or morphologically complex intracranial aneurysms. This approach may serve as a valuable alternative in cases in which primary FD deployment poses a high procedural risk. Moreover, the use of coils in the initial stage may offer a mechanical scaffold that facilitates a more stable and safer FD delivery. Nevertheless, further studies are warranted to determine the optimal coil packing density and timing of the FD placement.