Polypoid Endometriosis Presenting as a Colonic Mass

A 58-year-old woman with a history of chronic diarrhea and post-menopausal uterine bleeding underwent a routine colonoscopy for colon cancer screening, which demonstrated a large, nearly obstructing mass extending from the proximal rectum into the distal sigmoid colon (Figure 1). The colonoscope could be traversed proximally, and the remainder of the examination was normal. Biopsies from the lesion demonstrated granulation tissue and endometrial-type glands and stroma. Immunohistochemical stains showed CK7, PAX8, vimentin, estrogen and progesterone receptor–positive glands and stroma, consistent with endometriosis. No malignancy was identified even on deeper histologic sections. Due to the size of the mass, malignancy could not be excluded based on sampling. Her carcinoembryonic antigen (CEA) level was normal (3.9 ng/mL). A contrast-enhanced computed tomography (CT) scan of the abdomen and pelvis showed an enlarged heterogeneously enhancing uterus, rectosigmoid thickening with heterogeneous enhancement, and multiple similarly enhancing nodular soft tissues in the sigmoid mesentery and perirectal fat. CT scan of the chest did not show any evidence of metastatic disease