Catamenial rectal bleeding as a manifestation of rectosigmoid endometriosis in a young woman: a case report and literature review

Bowel endometriosis is a manifestation of deep endometriosis that most commonly involves the rectum and sigmoid colon. Diagnosis can be challenging because disease involvement usually predominates in the outer layers of the bowel wall, while endoscopic findings may be normal or nonspecific. We report the case of a 21-year-old woman with a three-year history of recurrent catamenial rectal bleeding, an unrevealing initial gynecologic evaluation, and a previous colonoscopy without relevant abnormalities. Because bleeding persisted, repeat colonoscopy was performed and showed edema and loss of the vascular pattern in the rectum and sigmoid colon. Rectosigmoid biopsies demonstrated glandular structures extending toward the submucosa that were morphologically compatible with endometriosis. Clinicopathologic correlation established the diagnosis of bowel endometriosis. This case highlights the importance of considering rectosigmoid endometriosis in reproductive-aged women with cyclic rectal bleeding, even after a previous negative endoscopic evaluation, and illustrates that colonoscopic biopsy may establish the diagnosis when mucosal or submucosal involvement is present.