Longitudinal volume evolution of large and giant intracranial aneurysms following endovascular flow diversion.

INTRODUCTION: Large and giant intracranial aneurysms (IAs) pose significant therapeutic challenges due to their complex morphology and high rupture risk. Flow diverters (FD) promote intrasaccular thrombosis, facilitating occlusion. However, the temporal volumetric evolution of FD-treated large and giant IAs remains variable and poorly understood. Here, we sought to assess the temporal volumetric evolution of large and giant aneurysms treated with FD. METHODS: Retrospective single-center study (2018-2022) of aneurysms ≥15 mm treated with FD, with late MRI follow-up. Demographic, morphological and radiological variables (total/patent volumes on T2, TOF hyperintensity, FLAIR edema, T1 contrast enhancement) were collected and analyzed together with complications and occlusion status. RESULTS: Twenty-four patients (median age 64 years, 54% female) were analyzed (saccular 75%, unruptured 96%, anterior circulation 88%). Median follow-up was 41.3 months by MRI and 24.7 months by angiography. Mortality was 17% (4/24), including three fatal post-treatment aneurysm ruptures. After FD treatment, total aneurysm volume did not significantly decrease (-0.86 cm3, p = 0.19) but patent aneurysm volume significantly reduced (-1.15 cm3, p = 0.001), although the individual volume change was heterogenous. Complete occlusion rate was 79%. Aneurysm occlusion was associated with narrower necks (7 vs. 13 mm, p = 0.023) and smaller initial total aneurysm volumes (2.6 vs. 10.6 cm3, p = 0.04). CONCLUSIONS: In large and giant aneurysms treated with FDs, despite high occlusion rates and decreased patent volumes, aneurysm total volume is not similarly reduced. This suggests that the effect of flow diversion is driven mainly by intrasaccular flow cessation and occlusion rather than by measurable volume reduction. Larger studies are needed to confirm our findings.