Introduction: Colorectal cancer is the third most commonly diagnosed cancer worldwide, and its incidence is rising in developing countries. Studies have shown an association between sarcopenia and various poor short-term outcomes in cancer patients who underwent surgery. In
this case study, we sought to highlight the importance of a modern prognostic factor, the psoas muscle index (PMI), in colorectal cancer. Case Presentation: We present the case of a 59-yearold male patient with sigmoid cancer. We calculated the PMI as the sum of the areas of the left and right psoas muscle at the level of the L3 vertebra, divided by the square of the patient’s height, using computed tomography measurements. We also measured the density of the proas muscles. Prior to surgery, the left psoas muscle had an area of 14.52 cm2, and the right 14.54 cm2, with a PMI of 9.4967 cm2/m2. The mean density of the psoas muscles was 43.60 UH. The surgery consisted in a rectosigmoid resection with termino-terminal colorectal anastomosis. The histopathological examination confirmed moderately differentiated adenocarcinoma, stage IIIB (pT3N1M0). The patient left the hospital eight days after surgery in good general condition. Longterm follow-up was performed by phone and CT scans at 1, 6, and 12 months. Conclusions: CTmeasured PMI may be a potential prognostic imaging marker in patients with colorectal cancer that can be easily and routinely assessed preoperatively.