Masseter muscle parameters can function as an alternative for skeletal muscle mass assessments on cross-sectional imaging at lumbar or cervical vertebral levels

Background: Patients with head and neck cancer are at increased risk of developing low skeletal muscle mass (SMM), which is associated with adverse treatment outcomes and prognosis. Low SMM is most commonly assessed by the skeletal muscle cross sectional area (CSA) at the third lumbar vertebra (L3) or more recently the third cervical vertebra (C3). L3 is not routinely imaged and C3 may be impacted by disease or treatment. As an alternative we analyzed masseter muscle characteristics and their relationship with L3 and C3 skeletal muscle CSA and overall survival (OS).

Methods: In this single-center retrospective study, 99 patients with head and neck cancer who underwent whole body FDG-PET/CT-scans were reviewed. Of these patients, L3 CSA, C3 CSA, masseter CSA, masseter thickness, masseter volume, masseter Hounsfield Unit values, lumbar skeletal muscle index (LSMI), cervical skeletal muscle index (CSMI), and masseter skeletal muscle index (MSMI) were recorded and correlated with each other and with OS.

Results: We included 72 male and 27 female patients. The masseter muscle parameters differed significantly between sexes. The Spearman correlation coefficients for C3 CSA-Masseter volume and L3 CSA-Masseter volume were 0.639 and 0.531 (P<0.001) respectively. In multivariate analysis low MSMI was a predictor of OS (HR 2.227, P=0.009).

Conclusions: There is a moderate to strong association between the masseter muscle volume (MV) and C3 CSA and L3 CSA. MSMI predicts OS. Further research should investigate the relationship between muscle function and masseter muscle parameters and impacting factors on masseter muscle dimensions.