Heterogeneity in CT-Based Skeletal Muscle Mass Assessment and Sarcopenia Diagnosis Undermines Comparability in Hepatopancreatobiliary Surgery: A Scoping Review

Background/Objectives: Sarcopenia has emerged as an important prognostic factor in patients undergoing hepatopancreatobiliary (HPB) surgery. However, substantial heterogeneity in assessment methods and diagnostic thresholds limits comparability across studies. The aim of this review is to systematically characterize methodological variability in sarcopenia assessment within HPB surgical literature, quantify dispersion in reported cut-off values, and highlight key areas requiring standardization. Methods: A structured search of PubMed, Scopus, and Web of Science was conducted to identify studies evaluating sarcopenia in adult patients undergoing surgery for benign or malignant HPB diseases. The included studies assessed skeletal muscle mass with computed tomography (CT)-based measures, rather than sarcopenia as defined in contemporary consensus definitions. Data were extracted regarding imaging modality, anatomical landmarks, muscle indices, normalization strategies and diagnostic thresholds. Between-study variability in skeletal muscle index (SMI) thresholds was quantified using the coefficient of variation (CV). Results: Fifty-three studies comprising 11,613 patients met the inclusion criteria. Thirty-four studies assessed CT-defined low skeletal muscle mass using total skeletal muscle area at the third lumbar vertebral level normalized for height, whereas the remaining studies employed heterogeneous methodologies, including psoas-only measurements and alternative vertebral levels. Reported SMI cut-off values ranged from 36.2 to 53.5 cm2/m2 in males and 29.6 to 41.1 cm2/m2 in females. The CV for male and female cut-offs was 10.9% and 7.6%, respectively. Descriptively, lower CV values were observed in Western cohorts (male 6.5%; female 4.2%) than in Eastern cohorts (male 11.0%; female 9.0%); these values were not formally compared statistically. Considerable dispersion persisted irrespective of the threshold source. Conclusions: Despite the predominance of CT-derived L3 SMI assessment, marked methodological heterogeneity remains in HPB sarcopenia research. Variability in anatomical landmarks, normalization methods, and cut-off values limits reproducibility and constrains meta-analytic synthesis. Harmonization of reporting and threshold selection is essential to clarify the prognostic role of sarcopenia in HPB surgery.