Isolated muscle metastasis revealing colorectal cancer recurrence.

Colorectal cancer is the first digestive cancer in terms of incidence, and the most common metastatic sites are the liver, lungs and peritoneum. Skeletal muscle metastases are exceptional, accounting for less than 1% of cases. Their rarity may be explained both by the biological characteristics of skeletal muscle and by the frequent underdiagnosis of this unusual metastatic site. We report here the case of a 68-year-old woman diagnosed with sigmoid adenocarcinoma who underwent immediate surgery with recto-sigmoid resection followed by adjuvant chemotherapy. Two years later, she presented with two painless abdominal masses, one located in the right flank and the other in the left subumbilical region. Thoraco-abdominopelvic CT revelated two intra-muscular lesions in the rectus abdominis muscle. No other metastatic sites were detected. Abdominal MRI confirmed the suspicious nature of the muscle masses, and the diagnosis of muscle metastases of colorectal origin was confirmed by biopsy.