Rectal smooth muscle loss as a predictor of severe postoperative complications in rectal cancer surgery.

The influence of rectal smooth muscle (RSM) mass on the surgical outcomes of rectal cancer surgery remains inadequately understood. This study investigated smooth muscle depletion during rectal cancer surgery, evaluated the perioperative association between skeletal muscle mass and RSM, and assessed the impact of RSM on postoperative complications. This retrospective study analysed 107 patients who underwent rectal cancer surgery, of whom 102 were included in the analysis of postoperative outcomes. Preoperative computed tomography and magnetic resonance imaging scans were utilised to quantify skeletal muscle using the psoas muscle index (PMI) and quantify RSM using the newly established rectal smooth muscle index (RSMI). The RSMI was an independent predictor of severe postoperative complications. The RSMI demonstrated superior predictive accuracy over the PMI for Clavien-Dindo grade III-IV complications, with an area under the curve (AUC) of 0.792 for the RSMI compared with 0.609 for the PMI, and for postoperative ileus, with an AUC of 0.700 for the RSMI versus 0.560 for the PMI. Patients exhibiting reductions in both the PMI and RSMI were significantly more susceptible to skeletal muscle loss 6 months postoperatively. The significant correlation between skeletal muscle and RSM mass underscores the clinical value of the RSMI in predicting postoperative outcomes and informing tailored management strategies.