Preoperative BOLD cerebrovascular reactivity correlates with intraoperative STA-MCA bypass flow and influences postoperative CVR improvement

Introduction: The superficial temporal artery-middle cerebral artery (STA-MCA) flow augmentation bypass is effective for treating Moyamoya vasculopathy and selected cases of atherosclerotic large vessel disease. Recently, blood oxygen level-dependent cerebrovascular reactivity (BOLD-CVR) has emerged as a novel tool to assess hemodynamic impairment for patient selection and monitoring. This study investigates whether preoperative BOLD-CVR in the affected vascular territory (i.e. middle cerebral artery (MCA) territory) correlates with intraoperative bypass flow and whether intraoperative bypass flow serves as a predictor of postoperative hemodynamic improvement. Patients and methods: We prospectively included patients with symptomatic cerebrovascular steno-occlusive disease who underwent STA-MCA bypass with pre- and postoperative BOLD-CVR imaging and intraoperative bypass flow measurements. Pearson correlation and multivariable regression models assessed the relationships between preoperative hemodynamic status (i.e. preoperative BOLD-CVR), intraoperative bypass flow, and postoperative BOLD-CVR improvement, adjusting for confounders (type of steno-occlusive disease, age, and cerebrovascular risk factors). Results: Forty-three patients (three receiving bilateral bypass) were included. Despite lack of association ( = 0.08) at univariable analysis, multivariable regression analysis revealed that, after correction for known confounders, preoperative CVR in the affected MCA territory was inversely associated with intraoperative bypass flow. For each 0.1 unit (percentage BOLD signal change/mmHg CO2) decrease in preoperative MCA territory CVR, the predicted bypass flow increased by 14.61 mL/min. Preoperative CVR was also the only significant predictor of postoperative CVR, with higher preoperative BOLD-CVR values linked to greater hemodynamic improvement. Conclusion: The severity of preoperative hemodynamic impairment in the affected MCA territory correlates with the increased need for bypass flow, serving as a potential predictor for intraoperative quantitative bypass flow demand once relevant covariates are accounted for. The STA-MCA bypass appears to deliver optimal flow when the cerebrovascular reserve capacity is not fully exhausted.