S2356 Hiding in Plain Sight: A Challenging Case of Obscure GI Bleeding Due to Appendiceal Endometriosis in a Postmenopausal Female Patient

Introduction: Endometriosis is the growth of endometrial tissue outside of the uterine lining. It commonly presents in females with symptoms of dysmenorrhea, dyspareunia, and infertility. Postmenopausal appendiceal endometriosis is extremely rare and can present with a wide range of symptoms making diagnosis challenging. Herein, we present a case of obscure GI bleeding in a postmenopausal female due to appendiceal endometriosis. Case Description/Methods: A 69-year-old White female patient with history of recurrent venous thromboembolism on Apixaban initially presented to the emergency room complaining of maroon colored stool without associated abdominal pain. She underwent EGD and colonoscopy which revealed mild gastritis and sigmoid colon diverticulosis, respectively. Apixaban was subsequently discontinued due to bleeding. She later presented with similar symptoms and associated iron deficiency anemia. She underwent video capsule endoscopy which showed a duodenal polyp. Repeat EGD was performed, and a 2 cm tubular adenomatous polyp was resected. Shortly after discharge, she had an acute non-ST elevation myocardial infarction and was placed on dual antiplatelet therapy (DAPT). She had episodes of intermittent GI bleeding, however, CTA of the abdomen, tagged RBC scan, technetium-99 scan, and mesenteric angiogram failed to identify a source of bleeding. Repeat CTA of the abdomen ultimately revealed a suspicious area in the cecum warranting further evaluation with high risk provocative angiogram, however, the decision was made to initially proceed with a colonoscopy which revealed active bleeding at the appendiceal orifice. The patient underwent an uncomplicated laparoscopic appendectomy. Histopathology confirmed the diagnosis of appendiceal endometriosis with estrogen receptor and PAX-8 positivity. Discussion: Our patient presented with recurrent episodes of GI bleeding with unclear etiology. Exhaustive diagnostic imaging and procedural studies were obtained to eventually establish the source of bleeding. The diagnosis of appendiceal endometriosis requires tissue sample for pathology. The management is primarily surgical, as resection of the appendix results in symptomatic relief for the patient. Repeating colonoscopy prior to high risk provocative angiogram and maintaining a high index of suspicion of endometriosis by treating gastroenterologists should be always considered. In our patient, appendectomy led to complete resolution of her bleeding, and we resumed DAPT safely for her coronary artery disease.Figure 1.: Colonoscopy images showing bleeding from the appendiceal orifice (A,B). H&E staining showing endometrial type glands in the appendiceal wall (C,D). Immunohistochemistry images showing positive estrogen receptor (E) and PAX-8 (F) staining.