Factors Associated with Aneurysm Occlusion after Flow Diverter Treatment

Flow diverter (FD) treatment has become a central therapeutic option for unruptured intracranial aneurysms and has demonstrated high aneurysm occlusion rates in multiple studies. However, the factors associated with aneurysm occlusion after FD placement remain incompletely understood. This review summarizes current evidence regarding predictors of aneurysm occlusion after FD treatment from 3 perspectives: aneurysm-related factors, procedural/device-related factors, and patient-related factors. The mechanism of FD treatment can be divided into 3 stages: hemodynamic alteration, thrombus formation, and endothelialization. Clinical outcomes are generally favorable for anterior circulation aneurysms, whereas posterior circulation aneurysms, particularly fusiform and dolichoectatic lesions, are associated with lower occlusion rates and higher complication rates. Even when aneurysms remain incompletely occluded at early follow-up, many continue to progress toward complete occlusion over time, and the natural history during the period of incomplete occlusion does not necessarily appear poor. Among aneurysm-related factors, the absence of incorporated branch vessels and smaller aneurysm size are associated with complete occlusion, whereas branch-incorporated aneurysms, bifurcation aneurysms, large aneurysms, long-neck lesions, fusiform aneurysms, partially thrombosed aneurysms, and dolichoectatic aneurysms are associated with incomplete occlusion. Persistent branch-related flow demand, including that seen in fetal posterior communicating artery aneurysms and bifurcation aneurysms represented by basilar tip and middle cerebral artery aneurysms, may interfere with occlusion, although collateral development may reduce this effect in selected cases. Stent malapposition may also impair occlusion when it creates the same compartment between the aneurysm and a nearby branch vessel. Procedural and device-related factors include appropriate sizing and meticulous deployment technique to achieve adequate vessel wall apposition and optimize metal coverage at the aneurysm neck. Adjunctive coiling and straightening of the parent artery after FD placement can also contribute to aneurysm occlusion. Patient-related factors associated with incomplete occlusion include older age, hypertension, and continued anticoagulant therapy, whereas a history of smoking has been reported as a predictor of occlusion. FD treatment provides high efficacy for anatomically challenging unruptured intracranial aneurysms. However, aneurysm-related and patient-related factors associated with difficulty in achieving aneurysm occlusion still remain. Careful preoperative evaluation, appropriate treatment planning, and meticulous postoperative management are therefore essential for maximizing aneurysm occlusion after FD treatment.