A Masked Diagnosis: Sigmoid Endometriosis.

Serosal involvement in intestinal endometriosis is relatively common, and patients often present with nonspecific gastrointestinal symptoms; however, presentation with deeper mucosal infiltration and rectal bleeding is rare. We report a case of a 40-year-old woman with a history of breast cancer in remission who presented with periodic rectal bleeding and abdominal pain. Computed tomography scan showed sigmoid lesions concerning for metastatic disease. Colonoscopy showed hypervascular sigmoid lesions which were confirmed to be endometriosis on histopathology. This case highlights endometriosis as a rare differential to be considered in young women with abnormal bowel imaging or catamenial rectal bleeding.