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BACKGROUND AND PURPOSE: Treatment of intracranial bifurcation aneurysms with flow-diverter stents can lead to caliber changes of the distal vessels in a subacute phase. This study aims to evaluate whether local anatomy and flow disruption induced by flow-diverter stents are associated with vessel caliber changes in intracranial bifurcations. MATERIALS AND METHODS: Radiologic images and demographic data were acquired for 25 patients with bifurcation aneurysms treated with flow-diverter stents. Whisker plots and Mann-Whitney rank sum tests were used to evaluate if anatomic data and caliber changes could be linked. Symmetry/asymmetry were defined as diameter ratio 1 symmetric and diameter ratio 1 asymmetric. Computational fluid dynamics was performed on idealized and patient-specific anatomies to evaluate flow changes induced by flow-diverter stents in the jailed vessel. RESULTS: Statistical analysis identified a marked correspondence between asymmetric bifurcation and caliber change. Symmetry ratios were lower for cases showing narrowing or subacute occlusion (medium daughter vessel diameter ratio 0.59) compared with cases with posttreatment caliber conservation (medium daughter vessel diameter ratio 0.95). Computational fluid dynamics analysis in idealized and patient-specific anatomies showed that wall shear stress in the jailed vessel was more affected when flow-diverter stents were deployed in asymmetric bifurcations (diameter ratio 0.65) and less affected when deployed in symmetric anatomies (diameter ratio 1.00). CONCLUSIONS: Anatomic data analysis showed statistically significant correspondence between caliber changes and bifurcation asymmetry characterized by diameter ratio 0.7 (P .001). Similarly, computational fluid dynamics results showed the highest impact on hemodynamics when flow-diverter stents are deployed in asymmetric bifurcations (diameter ratio 0.65) with noticeable changes on wall sheer stress fields. Further research and clinical validation are necessary to identify all elements involved in vessel caliber changes after flow-diverter stent procedures. Fil: Narata, A. P.. Centre Hospitalier Regional Et Universitaire de Tours; Francia Fil: De Moura, F. S.. Universidade Federal Do Abc; Brasil Fil: Larrabide, Ignacio. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Grupo de Plasmas Densos Magnetizados. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Grupo de Plasmas Densos Magnetizados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina Fil: Perrault, C. M.. University Of Sheffield; Reino Unido Fil: Patat, F.. Universite de Tours; Francia Fil: Bibi, R.. Centre Hospitalier Regional Et Universitaire de Tours; Francia Fil: Velasco, S.. Université de Poitiers; Francia Fil: Januel, A. C.. Centre Hospitalier Universitaire de Toulouse; Francia Fil: Cognard, C.. Centre Hospitalier Universitaire de Toulouse; Francia Fil: Chapot, R.. Alfried Krupp Krankenhaus; Alemania Fil: Bouakaz, A.. Universite de Tours; Francia Fil: Sennoga, C. A.. Universite de Tours; Francia Fil: Marzo, A.. University Of Sheffield; Reino Unido