Preoperative CT-Based Segmentation of Psoas Muscle Area and Subcutaneous Fat Tissue: Associations With Perforation and Length of Hospital Stay in Pediatric Appendicitis

Background Acute appendicitis is a leading cause of emergency abdominal surgery in children, and predicting postoperative length of hospital stay (LOS) is important for prognosis and resource planning. This study aims to assess the associations of LOS and appendiceal perforation with preoperative CT-derived measurements of psoas muscle area, attenuation, and subcutaneous fat tissue in children with appendicitis. Methods This retrospective study comprised 170 pediatric patients (< 18 years) surgically diagnosed with appendicitis between January 2022 and October 2025. At the L3-L4 intervertebral disc level, bilateral psoas muscles and subcutaneous adipose tissue were segmented using 3D Slicer. Right, left, and total psoas muscle area (tPMA), psoas muscle mean attenuation, tPMA Z-scores, subcutaneous fat tissue, inflammatory markers (WBC, neutrophils, and CRP), maximum appendiceal diameter, the presence of an appendicolith, appendiceal perforation status, surgical approach, and LOS were recorded. Results Of 170 patients, 51 had perforated appendicitis. Perforation correlated with elevated WBC/neutrophil/CRP levels, increased appendiceal max diameter, a higher incidence of appendicolith, reduced psoas muscle mean attenuation, and extended LOS (median 6.0 vs. 3.0 days; p < 0.001). CRP showed a moderate correlation with LOS (ρ = 0.435), while WBC (ρ = 0.302), neutrophils (ρ = 0.356), appendiceal max diameter (ρ = 0.233), and psoas muscle mean attenuation (ρ=−0.208) showed weak correlations. In multivariable negative binomial regression, perforation (IRR 2.287, p < 0.001) and neutrophil count (IRR 1.018 per 1×10⁹/L, p = 0.039) independently predicted extended LOS. Conclusions There is an association between post-appendectomy LOS and CT-derived psoas muscle attenuation, supporting segmentation-based prognostication and promising future studies.