The integrity of the Circle of Willis predicted hemodynamic changes after bypass surgery in Moyamoya disease: a prospective cohort study by 4D flow MRI.

OBJECTIVES

The anatomical completeness of the Circle of Willis (CoW) plays an important role in collateral circulation compensation in patients with moyamoya disease (MMD). This prospective cohort study tested the hypothesis that preoperative CoW integrity influences longitudinal postoperative cerebral hemodynamic adaptation following superficial temporal artery-middle cerebral artery (STA-MCA) bypass, as assessed using 4D flow MRI.

MATERIALS AND

METHODS

45 consecutive patients underwent 4D flow MRI preoperatively (Time Point 1, TP1). Of these, 43 patients underwent short-term postoperative imaging (Time Point 2, TP2), and 23 patients underwent late postoperative imaging (Time Point 3, TP3). Flow, mean velocity (Vmean) and pulsatility index (PI) were measured in major arteries and the bridge artery. Longitudinal hemodynamic changes were analyzed using linear mixed models based on all available repeated measurements. Patients were graded by CoW completeness: Grade 0 (incomplete, n=26), Grade 1 (partial completeness, n=19), Grade 2 (complete, n=0).

RESULTS

In Grade 0 patients, bridge artery flow and Vmean significantly decreased at TP3 (P flow = 0.02, P Vmean = 0.03), while PI increased (P PI = 0.03). These parameters of bridge artery remained stable in Grade 1 patients (all P>0.05). MCA, PCA, and BA hemodynamics showed relative stability in both groups (all P>0.05). Anterior-to-posterior flow ratios increased over time: 1.203 (TP1), 1.491 (TP2), 1.535 (TP3). Operated-side ICA flow was consistently lower than contralateral (P<0.001).

CONCLUSION

STA-MCA bypass induces a sustained redistribution of cerebral blood flow toward anterior circulation, primarily mediated by bridge artery. Incomplete CoW is associated with impaired long-term hemodynamic adaptation, characterized by reduced flow and increased vascular resistance. Preoperative assessment of CoW integrity may therefore aid in predicting postoperative hemodynamic outcomes.