Abstract
An abdominal mass may present with a myriad of symptoms resulting from compression of surrounding organs. A major clinical challenge with practical implications is accurate preoperative identification of the origin of the mass. Here, we present the case of a 29-year-old female patient with abdominal distension and shortness of breath for approximately 6 weeks before presentation. A large abdominal mass compressing the surrounding organs was observed on abdominal x-ray and computed tomography of the abdomen and pelvis. Preoperative imaging was unable to identify the organ of origin; pathologic and histologic analyses of the tumor ultimately identified a rare, massive intra-abdominal endometrioma, freely floating within the peritoneum and fed by an omental blood supply. This case highlights the importance of considering an atypical presentation of endometriosis in women of reproductive age with abdominal complaints.