# Dynamic evolution of postoperative hemodynamics in moyamoya angiopathy: a quantitative assessment of 4D Flow MRI and prognostic relevance

## TL;DR

This study uses 4D Flow MRI to track blood flow changes in moyamoya angiopathy patients after surgery, showing how these changes relate to recovery and brain blood supply improvement.

## Contribution

The study introduces 4D Flow MRI as a tool to assess long-term hemodynamic changes and their clinical relevance in moyamoya angiopathy patients.

## Key findings

- Contralateral carotid siphon velocity increased significantly one week post-surgery.
- Both carotid siphons showed reduced flow at one-year follow-up, correlating with improved cerebral perfusion and collateralization.
- No hemodynamic changes were observed in patients with poor collateral development (Matsushima grade C).

## Abstract

The hemodynamic mechanisms underlying revascularization efficacy in moyamoya angiopathy (MMA) and their prognostic implications remain incompletely characterized. This study leverages four-dimensional flow magnetic resonance imaging (4D Flow MRI) to investigate longitudinal hemodynamic changes at the carotid siphons of MMA patients undergoing revascularization, and to evaluate their association with surgical outcomes.

A prospective cohort of 35 consecutive MMA patients undergoing unilateral revascularization was enrolled at West China Hospital from July 2018 to January 2020. Using 4D Flow MRI, hemodynamic parameters, including mean/maximum flow, velocity, and wall shear stress, were quantified in the ipsilateral and contralateral carotid siphons at three timepoints: baseline, 1-week postoperative, and 1-year follow-up. Repeated-measures analysis of variance with Bonferroni correction was employed to compare longitudinal changes and correlate findings with 1-year clinical (excellent, good, and poor) and imaging (cerebral perfusion status and Matsushima collateralization grade) outcomes.

Baseline and 1-week postoperative assessments revealed that only velocity within contralateral carotid siphon significantly increased (mean velocity: from 20.52 [15.34–28.78] cm/s to 23.70 [16.01–39.06] cm/s, p = 0.026; maximum velocity: from 29.26 [19.68–38.39] cm/s to 33.22 [20.99–50.95] cm/s, p = 0.001). However, both carotid siphons demonstrated significant reductions in mean and maximum flow (ipsilateral: mean flow from 1.92 [0.65–3.53] mL/s to 1.31 [0.58–2.87] mL/s, p = 0.043, maximum flow from 2.61 [0.93–4.95] mL/s to 1.97 [0.89–3.90] mL/s, p = 0.036; contralateral: mean flow from 2.87 [0.91–4.12] mL/s to 2.14 [0.81–3.78] mL/s, p = 0.010) at 1-year follow-up. Lower contralateral siphon flow at follow-up correlated with “good” (but not “excellent”) clinical outcomes. Reduced flow in both siphons was associated with improved cerebral perfusion and robust collateralization (Matsushima grades A/B), whereas no changes were observed in patients with poor collaterals (Matsushima grade C).

4D Flow MRI reveals delayed, bilateral hemodynamic remodeling in MMA at 1-year post-revascularization. These changes correlate with clinical improvement, enhanced perfusion, and collateral development, underscoring the technique utility in monitoring long-term cerebrovascular adaptation.