A Variation on a Rare Diagnosis: Rectosigmoid Endometriosis

CASE REPORT Endometriosis is defined as the development and presence of endometrial tissue outside the uterus.1 It may affect the rectosigmoid junction, mimicking cancer.2 The gold standard for diagnosis of endometriosis is laparoscopy with histological identification. Estrogen receptor, CD10, and PAX8 may be identified.3,4 Endoscopic visualization is possible, however, diagnostically unreliable for this condition.5 A 50-year-old menopausal woman with a history of chronic low back pain and nephrolithiasis presented for screening colonoscopy. An 18-mm polypoid-like lesion was found in the proximal rectum (Figure 1). The polyp was multilobulated and nodular in appearance. The base was hard and did not lift with saline injection. Biopsy revealed rectal mucosa with multiple lymphoid aggregates and hyperplastic changes without adenoma. Because of the atypical nature of this lesion, a repeat flexible sigmoidoscopy was performed 7 months later to better sample and resect this region (Figure 1). Pathology revealed endometriosis with entrapped colonic crypts. The estrogen receptor, CD10, and PAX8 were noted, confirming the diagnosis of endometriosis. She had no history of endometriosis, and this was her initial diagnosis. She subsequently followed up with gynecology but never exhibited symptoms. She was given a 10-year screening interval because this lesion has no malignant potential.Figure 1.: (A) Mucosal findings on initial colonoscopy. (B) Mucosal changes on follow-up flexible sigmoidoscopy. (C) Rare glands with ciliated epithelium strongly positive for ER. Note the cellular stroma, positive for ER (blue arrow) and CD10 (not shown). (D) The same gland also positive for PAX8.It is not known whether this case represents postmenopausal endometriosis or results from lesions established during her reproductive years. The loss of the estrogen drive with menopause likely stopped the lesion from growing, preventing it from becoming an obstructing mass. She is not obese or on hormone therapy, 2 factors that can cause postmenopausal endometriosis.6 This case is unique and notable because we report an incidentally found rectosigmoid endometrial lesion on screening colonoscopy in an asymptomatic menopausal female patient. DISCLOSURES Author contributions: S. Engman: composed and edited the manuscript. F. Puello: edited manuscript. DA Labowitz: identified patient and edited manuscript. TT Ha Lan: took histological images and performed staining and helped to craft the image description. S. Engman is the article guarantor. Financial disclosure: None to report. Informed consent was obtained for this case report.