S2590 Fluctuating Size of Submucosal Mass in the Sigmoid Colon as a Diagnostic Clue of Colonic Endometriosis

Introduction: Extrauterine endometriosis is a rare condition and occasionally presents as a submucosal mass mimicking GIST. However, until surgical resection is completed, a definitive diagnosis is still challenging. Here we report a case that showed periodic size changes per imaging and colonoscopy and may provide a diagnostic clue for endometriosis in the GI tract mimicking GIST. Case Description/Methods: A 47-year-old woman was initially referred to GI for iron deficiency anemia and intermittent melena. Initial colonoscopy in December 2022 revealed a possible submucosal non-obstructing large mass in the sigmoid colon obstructing one third of the lumen. Biopsies were obtained and pathology revealed benign colonic mucosa. The patient declined surgical intervention as she was clinically and symptomatically improved. A CT abdomen and pelvis in February 2023 revealed a nonobstructive mass of 14mm AP diameter. Subsequent CT imaging in April 2023 demonstrated decreased size at 12mm AP diameter. Repeat colonoscopy in 6 months following the initial showed growth of the mass now obstructing one half of the lumen. The patient underwent surgical resection in May 2023. Follow on pathology demonstrated glandular and stromal infiltration with the muscularis propria, extending from the submucosa, through the muscularis propria, and into the surrounding pericolonic adipose tissue, consistent with endometriosis (Figure 1). Discussion: Intestinal endometriosis is a rare and uncommon etiology of a colonic mass which can mimick GIST. Preoperative diagnosis continues to be a challenge. Here we demonstrate a case that fluctuations in size may be a preoperative diagnostic clue for intestinal endometriosis. We believe that the size of submucosal mass changes during a period of observation by CT imaging and serial colonoscopy may be related to hormonal fluctuations associated with menses. Aligning imaging and colonoscopy findings with the menstrual cycle and changes in hormonal levels with further case control studies may be required to establish a more reliable way to diagnose GI endometriosis. Reference: 1. Tolga Kafadar M, Çaviş T, Sürgit Ö, Köktener A. Endometriosis of the rectosigmoid colon mimicking gastrointestinal stromal tumor. Turk J Surg 2020 Dec 29;36(4):409-412.Figure 1.: Serial colonoscopy and CT imaging.