[[Cerebral hyperperfusion syndrome]] (CHS) is a common complication after [[direct bypass surgery]] in patients with [[Moyamoya disease]] (MMD). Since preventive measures may be inadequate, Yang et al. assessed whether the [[blood flow]] difference between the [[superficial temporal artery]] (STA) and [[recipient vessel]]s (△BF) and the direct perfusion range (DPR) are related to CHS.