Letter to the Editor. Intraoperative Cortical Indocyanine Green Extravasation as a Predictor of Cerebral Hyperperfusion following Direct Revascularization for Moyamoya Disease: Impact of Prolonged Observations of Indocyanine Green Videoangiography

Intraoperative Cortical Indocyanine Green Extravasation as a Predictor of Cerebral Hyperperfusion following Direct Revascularization for Moyamoya Disease: Impact of Prolonged Observations of Indocyanine Green Videoangiography."The authors should be commended for addressing the long-standing challenge of intraoperatively identifying blood-brain barrier (BBB) vulnerability in moyamoya disease (MMD) and proposing prolonged late-phase indocyanine green videoangiography (ICG-VAG) as a practical extension of the routine surgical workflow.The demonstrated association between cortical indocyanine green (ICG) extravasation and postoperative cerebral hyperperfusion (CHP) as well as focal vasogenic edema is compelling and biologically plausible.The real-time visualization of BBB dysfunction during revascularization represents a meaningful conceptual advance that may complement existing preoperative perfusion imaging techniques.However, several methodological aspects of the study warrant further consideration.First, cortical ICG extravasation was defined as focal or patchy leakage near the anastomosis site and/or in cortical areas with augmented flow at 5 minutes after ICG injection.According to Forcione et al., ICG enters the extravascular space within 2-10 min post-injection, and its high tissue concentration is confined to brain regions affected by BBB disruption rather than the entire brainx [2].While this supports the use of ICG for assessing BBB injury, it remains unclear whether a single time point is optimal for distinguishing true BBB-related extravasation from delayed intravascular clearance or residual cortical fluorescence.Multi-time-point monitoring would provide more compelling evidence.Furthermore, the study lacks quantitative or semi-quantitative analysis of ICG extravasation.Previous reports have shown that Flow 800 imaging can evaluate peri-anastomotic hemodynamic changes associated with CHP [3,4], and intraoperative laser speckle imaging helps assess cerebral hemodynamics and predict CHP in MMD patients [5].Incorporating Flow 800 or laser speckle data from areas of ICG extravasation could significantly improve inter-observer reproducibility and enhance the generalizability of the findings across institutions.Furthermore, although the authors employed a strictly standardized perioperative management protocol to minimize confounding factors, this uniform approach limits the ability to evaluate whether intraoperative ICG extravasation can guide individualized management beyond postoperative risk stratification.The study convincingly demonstrates an association with CHP; however, it does not address whether intraoperative findings should prompt specific intra-or postoperative interventions.Proposing appropriate interventions and conducting further research in this direction would render the study more comprehensive.Herein, we would like to share our institutional experience.Post-bypass CHP in MMD is primarily attributed to hemodynamic disturbances caused by donor-derived blood flow exceeding the autoregulatory capacity of the recipient cerebral vasculature.Therefore, for patients identified intraoperatively as being at risk of CHP, placing slightly tighter absorbable fine silk ligatures proximal to the superficial temporal artery (STA) anastomosis site can effectively reduce blood flow.Additionally, given that the STA often undergoes compensatory dilatation in the early postoperative period[6], which may increase the risk of CHP, for patients without evident signs of CHP intraoperatively, placing adjustable ligatures matching the vessel diameter can help control postoperative flow augmentation, thereby facilitating a stable perioperative course.In conclusion, Ito et al. present an important and thought-provoking study that advances intraoperative assessment of BBB dysfunction in MMD.Addressing the methodological issues discussed above may further strengthen the clinical applicability and translational impact of late-phase ICG-VAG.