S3973 Endometriosis Presenting as Colon Mass With Stricture

Introduction: Colonic endometriosis is an uncommon diagnosis that can be difficult to make endoscopically. The clinical presentation of colonic endometriosis usually includes symptoms that overlap with colorectal cancer. Here, we present an unusual case of endometriosis that presented as a sigmoid colon mass with stricture. Case Description/Methods: A 41-year-old woman patient presented with history of lower abdominal cramping on the left side with rectal bleeding. The patient has a vague history of mild ulcerative colitis. No weight loss or loss of appetite is reported. Computed tomography scan showed an area of soft tissue thickening in the sigmoid colon concerning for neoplasm. Colonoscopy showed grade 2 internal hemorrhoids and a 3 cm fibrotic lesion with stricture at 30 cm from the anal verge. Biopsy of the mass showed colonic mucosa with fibrosis and was negative for malignancy. The patient underwent partial surgical resection of the sigmoid colon. Gross evaluation of the specimen revealed a 5 cm fibrotic mass in the colon wall. Histologic examination revealed endometrial glands and endometrial stromal cells involving the submucosa and muscularis layers, consistent with endometriosis. Immunostains showed that the stromal cells are positive for CD10, consistent with endometrial stroma. Estrogen receptor was positive in both endometrial glands and stromal cells. Discussion: Endometriosis of the colon can mimic colorectal cancer clinically and endoscopically. Histologic examination is necessary to confirm the diagnosis of endometriosis.