Rectal endometriosis masquerading as dissemination in a patient with rectal cancer: report of a case.

A 57-year-old woman was diagnosed as having rectal cancer. A barium enema study showed the apple-core sign at the rectosigmoid colon, and colonoscopy revealed an encircled ulcerated tumor. A laparoscope-assisted resection of the rectum was planned; however, the rectal cancer directly invaded the uterus body. The operation was converted to open surgery. An elastic hard tumor suspected of being peritoneal dissemination at the peritoneal reflection was detected and excised together with the rectum below the peritoneal reflection. A histological examination of this tumor revealed that cystic glands lined by nonmucinous columnar epithelial cells were seen on the serosal side and were embedded in the proper muscle of the rectum. This tumorous lesion was diagnosed as endometriosis.