Flow Redistribution in Circle of Willis Branches After Flow Diversion: Impetus for Vascular Remodeling?

Flow diverters (FDs) can induce vascular remodeling in nontarget branches of the circle of Willis (CW), yet the hemodynamic drivers of these changes remain unclear. Using in vitro CW models, flow rate alterations were quantified across both target and contralateral CW branches after FD deployment.

Four 3-dimensional-printed CW models were created (standard and hypoplastic variants) and integrated into a physiological pulsatile flow loop. Flow rates and pressures were recorded in all major branches before and after sequential deployment of 3 concentric FDs. Eight experiments were performed across the 4 models to capture anatomy-dependent hemodynamic responses.

Across all 4 FD configurations, deployment produced significant flow redistribution both in the covered branch and in remote CW vessels. Covered vessels showed progressive flow reductions of up to 14% after 3 FDs, particularly in hypoplastic anatomies. Importantly, contralateral and collateral pathways also demonstrated measurable redistribution: contralateral anterior cerebral artery flow decreased by up to 4.7%, middle cerebral artery flow increased by 2% to 5%, and posterior cerebral artery flow shifted by 3% to 8% depending on the FD location. Several of these compensatory changes reached statistical significance despite occurring in branches not directly covered by the device, underscoring the CW's sensitivity to localized resistance changes.

FD placement produced significant, anatomy-dependent changes in branch flow rate and pressures. Hypoplastic models exhibited more pronounced redistribution patterns than standard CW anatomy, highlighting the role of baseline vessel diameter. These findings support a mechanistic explanation for clinically reported post-treatment vascular remodeling.