Abstract Details Title High Preoperative Neutrophil to Lymphocyte Ratio is Associated with Unfavorable Clinical Outcome in Moyamoya Disease Patients Undergoing Combined Revascularization Surgery Topic Cerebrovascular Disease and Interventional Neurology Presentation(s) P9 - Poster Session 9 (5:00 PM-6:00 PM) Poster/Presentation Number 4-021 Objective This study aimed to investigate an association between the high preoperative NLR and unfavorable clinical outcome following combined revascularization surgery in Moyamoya disease (MMD) patients Background A high preoperative neutrophil-to-lymphocyte ratio (NLR) has been associated with poor postoperative prognosis in various diseases. Design/Methods This retrospective study analyzed 885 adult MMD patients who underwent combined revascularization surgery between January 2005 and February 2025. Patients were categorized into high (n = 331) and low (n = 554) preoperative NLR groups based on the optimal cut-off value derived from receiver operating characteristic analysis. The primary outcome was the incidence of unfavorable clinical outcome, defined as a modified Rankin Scale score ≥ 3 at hospital discharge. Propensity score–based inverse probability weighting (IPW) was used to adjust for potential confounders. Results The high preoperative NLR (≥ 2.01) group showed a higher incidence of unfavorable clinical outcome than the low preoperative NLR (< 2.01) group, before (11.8% vs. 2.0%, P < 0.001) and after (9.4% vs. 3.5%, P < 0.001) IPW, respectively. Also, a high preoperative NLR was an independent predictor of unfavorable clinical outcome before (odds ratio [95% CI]: 1.18 [1.04–1.35], P = 0.010) and after (1.24 [1.07–1.44], P = 0.006) IPW, respectively. The area under the curve of preoperative NLR for predicting unfavorable clinical outcome was 0.71 (0.64–0.77, p < 0.001). Conclusions A high preoperative NLR was associated with unfavorable clinical outcome at hospital discharge in MMD patients undergoing combined revascularization surgery Authors/Disclosures Hee-Pyoung PARK, MD PRESENTER Dr. PARK has nothing to disclose.