Intestinal Endometriosis Mimicking Ulcerative Colitis-Associated Neoplasia: A Case Report

Introduction: Intestinal endometriosis is a benign condition characterized by the presence of endometrial tissue within the bowel wall, often mimicking colorectal malignancy. Its coexistence with ulcerative colitis (UC) is rare and can complicate the diagnosis. Case Presentation: A 35-year-old woman with long-standing UC presented with severe diarrhea and rectal bleeding. Colonoscopy revealed severe disease activity with multiple deep ulcerations and a newly developed stricture in the sigmoid colon. Pathological examinations, including bite-on-bite biopsies, showed no evidence of malignancy. However, colitis-associated neoplasia (CAN) could not be completely ruled out because such lesions may primarily involve the deep layers of the colonic wall. Given the severity of disease and concern for possible CAN, a total colectomy was performed. Histopathological and immunohistochemical analysis of the resected specimen ultimately identified intestinal endometriosis as the cause of the stricture. Conclusion: This case underscores the importance of considering intestinal endometriosis in women with UC who develop unexplained colonic strictures, particularly when malignancy cannot be confirmed.