Incomplete Circle of Willis predicts impaired long-term hemodynamic adaptation after bypass surgery in Moyamoya disease

Incomplete Circle of Willis (CoW) predicted impaired long-term hemodynamics after STA-MCA bypass in Moyamoya disease: bridge artery flow decreased at late follow-up (P=0.02) while pulsatility index increased (P=0.03), suggesting higher vascular resistance. Preoperative CoW gradi…

• Prospective cohort study of 45 patients (26 with incomplete CoW, 19 with partial CoW; none with complete CoW) assessed by 4D flow MRI at preop, short-term, and late postop.
• Anterior-to-posterior flow ratios increased over time (1.203 at preop, 1.491 at short-term, 1.535 at late), indicating sustained anterior redistribution; operated-side ICA flow was consistently lower than contralateral (P<0.001).
• Limitations: small sample size, single-center, only 23 patients with late follow-up, and no complete CoW group for comparison.

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