1668 A Rare Cause of Cyclical Rectal Bleeding: Sigmoid Endometriosis

INTRODUCTION: Endometriosis can frequently involve the bowels with rectosigmoid involvement being the most common. Although serosal infiltration is not uncommon, mucosal involvement is rare, hence presentation with rectal bleeding is rare. Diagnosis without pathology is difficult given symptoms frequently mimic IBS, IBD or malignancy. Here, we present a case of a woman with a history of breast cancer who presented with rectal bleeding ultimately found to have infiltrating sigmoid endometriosis. CASE DESCRIPTION/METHODS: A 40-year-old woman with a history of ER+/PR-/HER2+ breast cancer in remission on maintenance tamoxifen presented with worsening rectal bleeding for one year. Interestingly, hematochezia occurred cyclically every month seemingly coinciding with menses. It was associated with dyschezia, abdominal pain, loose stools, and dysmenorrhea. Hemoglobin and rectal exam were normal. Due to her history of breast cancer, a CT scan was done which demonstrated a focal area of sigmoid wall thickening and luminal narrowing with a 3 cm × 4 cm filling defect. Primary colonic malignancy and metastatic lesions were considered in the differentials. Colonoscopy revealed an area of extreme tortuosity in the sigmoid colon that could not be traversed. Several hypervascular polypoid lesions were noted in the proximal sigmoid colon at the site of narrowing. Cold forceps biopsy of the lesions showed endometriosis on pathology. Immunohistochemical stains positive for CD10 and estrogen receptor further supported the diagnosis. The patient was treated with Goserelin acetate with complete resolution of her rectal bleeding. After a year, she discontinued Goserelin due to side effects of fatigue and joint pains and has been on Danazol suppositories. Surgery was deferred as she did not have colonic obstructive symptoms. DISCUSSION: Here, we report a rare case of sigmoid endometriosis presenting as cyclical rectal bleeding with a lesion that masqueraded as malignancy on CT scan. Gastroenterologists should be aware of this differential in women in their reproductive years and be familiar with its unusual endoscopic appearance. This case also emphasizes good history taking, where the cyclical nature of rectal bleeding coinciding with menses is a clue for diagnosis. While symptoms of colonic endometriosis are typically chronic, late diagnoses can lead to unfortunate sequelae including acute bowel obstructions. Early diagnosis is clinically important to attempt medical therapies before complications necessitate surgical intervention.