Low-grade Endometrial Stromal Sarcoma Presenting as a Sigmoid Mass

Low-grade endometrial stromal sarcoma (LG-ESS) is a very rare mesenchymal neoplasm of the uterus. LG-ESS can recur or metastasize to extrauterine sites, such as the pelvis, peritoneal cavity, and vagina, but rarely to the lung, liver, heart, bone, and colon. A 42-year-old female patient was transferred from an outside clinic for an evaluation of constipation. EUS revealed a 5 cm hypoechoic lesion with a regular margin, probably arising from the 4th layer (muscular propria) at the sigmoid colon level. CT revealed a 7-cm homogenous enhancing mass lesion at the pelvic cavity and multiple enlarged lymph nodes in the sigmoid mesocolon. The patient underwent an anterior resection, and the diagnosis based on the biopsy result was LG-ESS. After a multidisciplinary discussion, she underwent a bilateral salpingo-oophorectomy. Small nodules found in the endometrium were identified as LG-ESS by a biopsy. This paper reports a case of metastatic LG-ESS presenting as a solitary sigmoid tumor without intrauterine lesions through preoperative examinations and discusses the characteristics of this neoplasm with reference to the relevant literature.