Evaluation of the Significance of Persistent Remnant Filling and Enlargement After Flow Diversion for Intracranial Aneurysms

Background: This study aimed to evaluate the clinical course after flow diversion (FD) treatment with a focus on aneurysms with remnant sac filling, by analyzing angiographic outcomes, aneurysm volume, and clinical events. Methods: We retrospectively reviewed the medical records of 61 patients who underwent FD for intracranial aneurysms between July 2014 and June 2021. Results: The majority of aneurysms (52.5%) were located in the internal carotid artery, with a median diameter of 16.6 mm and neck size of 9.3 mm. Remnant filling was observed in 17 aneurysms (27.9%) more than 18 months after FD, 10 (16.4%) of these aneurysms underwent enlargement, which occurred only in cases with subtotal filling or entry remnant states. Eleven patients experienced major adverse events, and three exhibited unfavorable functional outcomes. The incidence of major adverse events and unfavorable functional outcomes was significantly higher in the aneurysm enlargement group than that in the no-filling or stable remnant filling groups (P < 0.001). Aneurysmal diameter and the presence of incorporated branches were independent predictors of aneurysm enlargement, while the presence of incorporated branches was the only independent predictor of persistent remnant filling. Conclusions: Aneurysm enlargement after FD is not uncommon, particularly when the aneurysm is large, has incorporated vessels, or does not undergo occlusion within 12 months, often culminating in major adverse events and unfavorable functional outcomes. In addition to investigating angiographic results, it is necessary to evaluate the changes in aneurysm size and clinical events when assessing the efficacy of FD.