Association of preoperative CT-diagnosed low skeletal muscle mass with postoperative complications after radical cystectomy

Radical cystectomy (RC) carries high postoperative complication rates. Most prior studies on sarcopenia and RC outcomes use Western-derived or 2019 AWGS SMI cut-offs, which may misclassify Asian patients and cause result heterogeneity. This study aimed to evaluate the association between CT-diagnosed low skeletal muscle mass (using Chinese population-specific SMI thresholds aligned with the 2025 AWGS framework) and 30-day postoperative complications in NAC-naïve bladder cancer patients undergoing RC. This retrospective cohort study was conducted on 198 patients who underwent RC without neoadjuvant chemotherapy at the Second Affiliated Hospital of Anhui Medical University from January 2018 to April 2025. Low skeletal muscle mass was defined as a skeletal muscle index (SMI; total skeletal muscle area at L3/height²) of < 43.13 cm²/m² for men and < 37.81 cm²/m² for women, based on abdominal CT obtained within 30 days preoperatively. Patients were divided into the low-SMI group ( n = 85) and non-low-SMI group ( n = 113). Baseline clinical characteristics, perioperative indicators, and 30-day postoperative complications were compared between the two groups. The primary endpoint was Clavien-Dindo grade II or higher complications. Univariable and multivariable logistic regression analyses were performed, with bootstrap internal validation. Overall, 85 patients (42.9%) were classified as low SMI. Low-SMI patients had significantly higher rates of overall complications (52.9% vs. 26.5%, P < 0.001) and grade II complications (41.2% vs. 21.2%, P = 0.002). In the perioperative multivariable model, low SMI (OR = 3.04, 95% CI 1.43–6.45, P = 0.004) and operative time (OR = 1.01 per minute, 95% CI 1.00–1.01, P = 0.004) were independent risk factors for grade II+ complications (AUC = 0.722). Bootstrap validation confirmed model robustness. Preoperative low skeletal muscle mass, defined by Asian-specific SMI cut-offs, is an independent risk factor for postoperative complications in NAC-naïve RC patients. Combining preoperative muscle assessment with intraoperative efficiency optimization may improve risk stratification; prospective validation is warranted.