S2538 Colonic Endometriosis Masquerading as a Colonic Mass Diagnosed With Endoscopic Ultrasound

Introduction: Endometriosis is a well-known disorder, which most commonly affects women of reproductive age, whereby uterine tissue grows outside of the uterine cavity. Although rare, the most common extra-pelvic location for implantation is the GI tract, and more specifically, the rectum and sigmoid colon. Moreover, symptoms are misleading, and imaging can be mistaken for colon cancer. We present a rare presentation of a reproductive-aged female with a colonic mass due to an endometrioma, diagnosed by endoscopic ultrasound (EUS). Case Description/Methods: A 40 year-old female with past medical history of dysmenorrhea and menorrhagia presented to her primary care physicians office with complaints of change in bowel habits, left lower quadrant abdominal pain and hematochezia, worse during menstruation. She reported a five-year history of these symptoms, however, worse in the last few months. Labs were normal, Hb 13.5, stool returned occult positive. A colonoscopy was performed with restricted mobility, requiring a pediatric colonoscope to traverse past the sigmoid colon, with extrinsic compression at 20 cm proximal to the anal verge; no frank colon mass identified. A CT A/P was obtained demonstrating a 3.9 cm semi-annular mass-like thickening of the sigmoid colon with associated tubular narrowing of the lumen, suspicious for colon cancer. She subsequently underwent flexible sigmoidoscopy, which again, showed extrinsic compression with mild stenosis measuring 1 cm in length. Rectal EUS with FNA was performed, which revealed a 5 cm partially circumferential submucosal sigmoid mass, originating from the muscularis propria and invading the serosa; cytology revealed the diagnosis of endometriosis. Ultimately, the patient required a laparoscopic sigmoid colon resection as well as robotic total abdominal hysterectomy and bilateral salpingoophrectomy. Discussion: We present a unique case of radiographic diagnosis of a sigmoid colon mass, with endoscopic evaluation revealing a submucosal colonic endometrioma in a patient with no known history of endometriosis. Colonic endometriomas are typically located in the serosa and/or muscularis propria, making superficial biopsies nondiagnostic in the majority of cases. We highlight the importance of utilizing EUS with FNA in cases where endometriomas are suspected, as it provides a safe and noninvasive method to obtain tissue for diagnosis.