PT54 - SEX DIFFERENCES IN THE ASSOCIATION BETWEEN L1 ILIOPSOAS MUSCLE QUALITY AND POST-CYSTECTOMY LENGTH OF STAY

PT54

SEX DIFFERENCES IN THE ASSOCIATION BETWEEN L1 ILIOPSOAS MUSCLE QUALITY AND POST-CYSTECTOMY LENGTH OF STAY

T. Boucher^1,2,*, N. Tetlow^2,3, A. Dewar², S. Kerneis², A. Fung², P. Arina², G. Batum², J. Whittle^2,3, E. B. Mazomenos¹

¹UCL Hawkes Institute, Department of Medical Physics and Biomedical Engineering, ²Department of Targeted Intervention, Centre for Perioperative Medicine, Human Physiology and Performance Laboratory (HPPL), University College London, ³Department of Anaesthesia and Perioperative Medicine, University College London Hospitals, London, United Kingdom

Rationale: Sarcopenia, characterised by decreased muscle mass and quality, predicts poor surgical outcomes. Muscle radiodensity on CT assesses muscle quality (myosteatosis), but its association with outcomes like length of stay (LOS) may differ by sex. We hypothesised that L1 iliopsoas radiodensity predicts post-cystectomy LOS differently in males versus females.

Methods: Pre-cystectomy CT scans from 91 patients (63 males) were analysed using a machine learning model [1] quantifying mean Hounsfield Units (HU) of the right iliopsoas muscle at L1. Sex-stratified analyses compared LOS using Mann-Whitney U tests based on myosteatosis defined by sex-specific medians (males: ≤38.1 HU; females: ≤46.3 HU) and a fixed threshold (≤40 HU). Multivariate ordinary least squares (OLS) regression assessed the independent association of L1 HU with LOS, testing for sex interactions.

Results: Sex significantly modified the relationship between L1 iliopsoas HU and LOS (sex×HU interaction p=0.031). In males: Myosteatosis defined by the fixed threshold was associated with significantly longer LOS (13.9±8.9 vs 9.7±5.2 days, p=0.029), with a similar trend for the median split (p=0.062). Higher L1 HU remained independently associated with shorter LOS in multivariate analysis (β=-0.10 days/HU, p=0.004). In females: L1 iliopsoas HU showed no significant association with LOS using threshold or regression analyses.

Conclusion: L1 iliopsoas radiodensity is a significant, independent predictor of post-cystectomy LOS in males, but not in females. These sex differences highlight the importance of stratified analysis when using myosteatosis as a prognostic indicator.

References: [1]Boucher T, et al. KEVS: Enhancing Segmentation of Visceral Adipose Tissue in Pre-Cystectomy CT with Gaussian Kernel Density Estimation. 2025. Int J Comput Assist Radiol Surg. 2025; In press. Preprint available: https://doi.org/10.48550/arXiv.2503.22592 

Disclosure of Interest: None declared