S1731 Sigmoid Colon Endometriosis Masquerading as Malignancy

Introduction: Endometriosis is the presence of endometrial glands and stroma at extrauterine sites. Bowel endometriosis can be found superficially on the serosa and rarely deeper invading muscularis propria making it difficult to differentiate from malignancy. We present a case of a large sigmoid mass with malignant endoscopic and radiographic features found to be endometriosis on pathology. Case Description/Methods: A 35-year-old female, G1P1, with depression presents with blood and mucus in her stools for one month. She noted increased frequency of formed stools admixed with mucus and bright red blood. She also endorsed left upper quadrant abdominal pain that improved with bowel movements and increased pelvic cramps with her periods. She denied weight loss, pain on defecation, tenesmus, nausea, vomiting, fevers, or chills. Family history was significant for a brother that died from cholangiocarcinoma at age 42. Physical exam demonstrated a soft, non-tender abdomen and a fixed uterus and cervix with palpation of a rectovaginal mass on bi-manual exam. Labs were significant for mild anemia with a hemoglobin of 11.7, CEA of 0.9 and CA-125 mildly elevated at 177. Pelvic ultrasound showed a 4.7 cm left ovarian cyst suggestive of a dermoid cyst. Colonoscopy revealed a polypoid, ulcerated, partially obstructive large mass in the sigmoid colon of malignant appearance. Biopsy of the mass returned as endometriosis involving the colonic mucosa and focal presence of squamous epithelium that was unable to rule out a malignancy. CT chest, abdomen and pelvis with contrast demonstrated an annular sigmoid lesion suggestive of malignancy with no evidence of metastasis. Further evaluation with MRI pelvis showed stage IV endometriosis with widespread involvement of all gynecologic structures. Following a multidisciplinary discussion with colorectal surgery and gynecologic oncology, laparoscopy-guided sigmoid resection along with left salpingo-oophorectomy was performed. Surgical pathology of the excised tissue showed extensive transmural endometriosis in the colonic mucosa with associated hyperplastic changes, as well as surface endometriosis on the ovary and fallopian tube and a mature cystic teratoma formation in the left ovary. Discussion: Intestinal endometriosis is a relatively uncommon entity and can be challenging to distinguish from malignancy. Our case aims to raise awareness for bowel endometriosis as a potential cause for hematochezia in young women with endoscopic or radiographic findings of malignancy.Figure 1.: A computed tomography scan of the abdomen exhibited diffuse fluid-filled dilatation of the colon with wall thickening and peri-colonic haziness, most prominent in the sigmoid colon and rectum. Chronic bilateral hydronephrosis and chronic cystitis were present as well.