Preoperative Psoas Muscle Index and Psoas Attenuation in Patients Undergoing Nephrectomy for Renal Cell Carcinoma: A Retrospective Cohort Study

Background and Objectives: Evidence linking sarcopenia and myosteatosis to oncological outcomes in renal cell carcinoma (RCC) remains inconsistent. We aimed to evaluate whether preoperative psoas muscle measurements are associated with tumor stage, recurrence, and survival in RCC patients undergoing nephrectomy. Materials and Methods: A total of 199 patients who underwent nephrectomy with a diagnosis of RCC between 2018 and 2024 were retrospectively evaluated. Preoperative computed tomography images were used to measure the bilateral psoas muscle area at the L3 vertebral level and Hounsfield unit (HU) values. The psoas muscle index (PMI) was calculated. PMI and psoas HU values were analyzed as continuous variables, as this approach preserves statistical information and avoids misclassification bias inherent to arbitrary dichotomization, particularly given the absence of population-specific validated thresholds for Turkish RCC patients. Tumor stage, metastasis, recurrence, and survival data were analyzed. Results: The mean age of the patients was 60.29 ± 11.62 years, and 67.84% were male. The mean PMI was 5.11 ± 1.54 cm2/m2 while the mean psoas HU value was 38.63 ± 8.95 HU. PMI was significantly higher in patients with advanced-stage (T3 and T4) disease than in those with early-stage (T1 and T2) disease (5.57 ± 1.49 vs. 4.30 ± 1.28, p < 0.001). A positive correlation was found between T stage and PMI (r = 0.396, p < 0.001) and between tumor size and PMI (r = 0.215, p = 0.002). Modest but significant correlations were found between age and both PMI (r = −0.274, p < 0.001) and psoas HU values (r = −0.347, p < 0.001). Conclusions: In this retrospective nephrectomy series, conducted in a cohort inherently enriched for adequate performance status and surgical fitness, PMI showed a positive correlation with pathological T stage and tumor size, intriguingly higher PMI values were observed in patients with advanced T stages. These findings suggest that the role of psoas-based muscle measurements in the prognostication of this subset of RCC patients (advanced disease but candidates for surgical treatment) may be limited.