Introduction:
Sarcopaenia is associated with adverse outcomes in patients with malignancies, and it remains unclear whether the sex discrepancy of sarcopaenia or muscle loss leads to different prognoses in patients with mass-forming intrahepatic cholangiocarcinoma (MICC).

Material and methods:
Patients 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 the radix of the superior mesenteric artery. Fat-free skeletal muscle index (FFMI) was calculated by dividing the FFMA by the individual’s height squared. The prognostic value of FFMI was investigated using the Kaplan-Meier method and multivariable Cox regressions in both the entire cohort and in sex-specific subgroups.

Results:
A total of 157 patients were finally included. Cut-off 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 in 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 = 0.030) and in 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.

Conclusions:
Preoperative FFMI measured by MRI is a prognostic biomarker for OS in MICC patients, and it is more sensitive in males than in females.