Impacts of Flow Diversion on Vascular Remodeling in ACOM and Basilar Tip Aneurysms

Flow diversion is an established treatment for complex and wide‐necked intracranial aneurysms, promoting aneurysm thrombosis and durable vessel reconstruction through redirected flow and endothelialization. The placement of flow‐diverting stents (FDSs) often necessitate “jailing” branch vessels to achieve adequate aneurysm exclusion. This approach alters regional hemodynamics, potentially prompting compensatory remodeling in cerebral vasculature to preserve perfusion. While this mechanism of collateral recruitment and vascular adaptation is encountered in clinical scenarios, it remains insufficiently studied. This study investigates the hemodynamic and structural remodeling of contralateral and collateral arteries following the jailing of vessels by flow‐diverting stents in cases involving bifurcation aneurysms. The goal of this study is to characterize patterns of vascular reconfiguration and better understand compensatory mechanisms supporting distal perfusion after intentional branch vessel jailing. A retrospective analysis was performed on 87 patients treated with flow diversion for ACOM, A1/A2 segment, or basilar tip aneurysms between June 2020 and May 2025. Vascular remodeling was assessed by measuring diameter changes in collateral vessels (contralateral A1 for ACOM aneurysms, or contralateral PCOM relative to jailed P1 in cases of basilar terminus aneurysms) on pre‐ and 6‐month post‐operative imaging. Diameter measurements were averaged across three points along the vessel to reduce variability. Pre‐treatment diameters were obtained from DSA or, when unavailable, CTA with MIP reconstructions. Post‐treatment measurements were derived exclusively from the 6‐month follow‐up DSA. Patients with missing imaging were excluded. Paired t ‐tests were used to compare vessel diameters, with a subgroup analysis performed for ACOM aneurysms for consistency. 45 patients (28 ACOM, 11 Basilar tip, and 2 A1/A2 aneurysms) with both pre‐operative and post‐operative imaging were included in our analyses. Treatment with flow diversion was associated with increased contralateral vessel diameter on 6‐month post‐operative imaging compared to baseline imaging. On average, post‐operative vessel diameters (1.85 mm ± 0.65) were 0.1 mm larger than pre‐operative vessels (1.72 mm ± 0.74, p = 0.006).In the ACOM subgroup, the contralateral A1 segment increased by 0.16 mm (95% CI: 0.015‐0.31, p = 0.032). Multivariate analysis identified age as a significant predictor of remodeling magnitude, with older patients showing greater pre‐ to post‐interventional diameter change ( p = 0.033). Collateral vessels supplying jailed territories after flow diversion for bifurcation aneurysms demonstrated measurable diameter increases at 6 months, suggesting compensatory reconfiguration of the Circle of Willis. These findings provide preliminary evidence that intentional branch vessel jailing may be tolerated in select cases, as collateral pathways appear capable of maintaining distal perfusion. Specifically, vessels arising from the ACoM or other bifurcation points may tolerate flow diversion with less risk, given the compensatory remodeling observed within the Circle of Willis. Limitations include low resolution of pre‐operative CTA, which introduces variability in vessel measurements—particularly given the small observed diameter change (∼0.1 mm). Comparisons between pre‐operative CTA and post‐operative DSA may further contribute to measurement error. Additionally, the modest sample size limits statistical power. Future studies should pre‐emptively incorporate standardized imaging, ideally pre‐ and post‐operative DSA for reliability.