Feasibility of assessment of skeletal muscle mass on a single cross-sectional image at the level of the fourth thoracic vertebra

Background Skeletal muscle mass (SMM) determined on computed tomography (CT) is emerging as a novel imaging biomarker. Cross-sectional area (CSA) of SMM at the level of the third lumbar vertebra (L3) on abdominal imaging is considered the clinical reference standard for measuring SMM. In certain patient groups, such as those with oncological or non-oncological lung disease like COVID-19, a chest CT may be available while an abdominal CT is not. The purpose of this study was to investigate whether determining SMM on a chest CT is a feasible alternative to abdominal CT.  Research question What is the correlation between SMM measurements at the level of L3 and the level of the fourth thoracic vertebra (Th4)?  Study design and methods  In this study we retrospectively analyzed abdominal and thoracic series of whole-body CT-scans of trauma patients (N = 47) and head and neck cancer patients (N = 194). All abdominal muscles were delineated on a single axial slice at the level of L3. The erector spinae, levator scapulae, rhomboideus minor and major and pectoralis minor and major muscles were delineated on a single axial slice at the level of Th4. CSA of the muscles at Th4 and the L3 level were compared using linear regression, and a multivariate linear regression model was established.  Results Muscle CSA at level Th4 strongly correlates with L3 muscle CSA (r = 0.791, p < 0.05). A multivariate model incorporating the patient characteristics arm positioning, age, sex, and weight achieved a stronger correlation (r = 0.856, p < 0.05). Interpretation: Skeletal muscle CSA measured at the level of Th4 is a feasible alternative to measurements at L3. This allows diagnosing low SMM using clinically available thoracic CT-scans. SMM measurements at the level of Th4 may become a prognostic or triage tool when faced with mechanical ventilator shortage

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