Intraoperative transit-time flowmetry of the superficial temporal artery directly predicts and may mitigate risk of postoperative hyperperfusion syndrome in moyamoya bypass surgery

Objective To obtain perioperative cerebral blood flow measurements and assess the role of intraoperative blood flow evaluation in predicting postoperative complications. Methods We conducted a retrospective analysis of 102 cases of extracranial-intracranial (EC-IC) bypass surgery performed for flow augmentation in patients with moyamoya disease. The study monitored blood flow in the donor artery, graft vessels, and recipient artery at various stages. We measured superficial temporal artery (STA) flow during the perioperative period using a transit time ultrasonic flowmeter and Doppler ultrasound for real-time monitoring. A modified MBC scale was developed to evaluate the vascular network of the middle cerebral artery (MCA). STA flow measurements and the modified MBC scale were analyzed for their correlation with the incidence of cerebral hyperperfusion syndrome (CHS). Results A total of 102 hemispheres underwent revascularization through EC-IC bypass, comprising 69 direct bypass cases and 33 combined bypass cases. We observed fluctuations in donor vascular flow during the perioperative period. The STA flow increased post-anastomosis, stabilizing at an elevated level thereafter. Specifically, the STA in situ flow measured 7.06 ± 3.30 mL/min, while the STA-Cut flow was 59.75 ± 37.49 mL/min. The flow following STA anastomosis was 36.07 ± 22.59 mL/min. Prior to the anastomosis of the bonnet aponeurosis and skin, STA flow was recorded at 35.14 ± 22.93 mL/min. Postoperative STA flow on day one was 111.91 ± 62.06 mL/min, and on day seven it was 104.47 ± 64.93 mL/min. Notably, 12.74% of patients developed CHS. Logistic regression analysis indicated that the occurrence of CHS was significantly correlated with STA-Cut flow, suggesting that lower flow rates are associated with a higher likelihood of CHS. Additionally, surgical approach and the MBC scale were also related to the incidence of CHS. Conclusion The transit time flow (TTF) measurements indicate that the superficial temporal artery (STA) transitions from a low-flow vessel in situ to a medium- to high-flow graft vessel immediately after anastomosis. The variability in flow within the graft vessel plays a significant role in the occurrence of postoperative hyperperfusion syndrome.