IntroductionSarcopenia is associated with adverse outcomes in patients with malignancies, it remains unclear whether the sex discrepancy of sarcopenia or muscle loss leads to different prognoses in patients with mass-forming intrahepatic cholangiocarcinoma (MICC).Material and methodsPatients who were pathologically diagnosed with MICC and underwent partial hepatectomy between 2012 and 2019 were recruited. Fat-free muscle areas (FFMA) were defined as areas of bilateral erector spinae muscles on dual-echo T1-weighted gradient-recalled-echo images at the level of radix of the superior mesenteric artery. FFMI (fat-free skeletal muscle index) was calculated by dividing FFMA by individual’s height squared. The prognostic value of FFMI was investigated using Kaplan-Meier method and multivariable Cox regressions in both the entire cohort and sex-specific subgroups.ResultsA total of 157 patients were finally included. Cutoff values for the definition of low FFMI were 14.19 cm2/m2 in males and 11.07 cm2/m2 in females. Patients with low FFMI had significantly shorter overall survival (OS) than those with high FFMI in the entire cohort (19.42 vs 35.29 months, p=0.0067) and male patients (17.25 vs 37.19 months, p=0.006), but not females. Multivariate analyses showed that low FFMI was a significant predictor of OS in the entire cohort (HR 1.725, 95%CI 1.054-2.821, p=0.03) and male patients (HR 2.145, 95%CI 1.113-4.133, p=0.023). No association between FFMI and disease-free survival was found in both the entire cohort and sex-specific subgroups.ConclusionsPreoperative FFMI measured by MRI is a prognostic biomarker for OS in MICC patients, and it is more sensitive in males than in females.