S3968 Heterotopia in Hindsight: A Stomach Where It Shouldn’t Be

Introduction: Gastric heterotopia (GH) refers to the presence of gastric mucosa outside its normal anatomic location. While GH is most commonly observed in the esophagus and duodenum, its occurrence in the rectum is exceedingly rare, with limited case reports and unclear clinical implications. Though often asymptomatic, GH has been associated with rectal bleeding, abdominal pain, and potential malignant transformation. Case Description/Methods: A 45-year-old woman with a history of asthma, Graves’ disease, and migraines underwent a routine screening colonoscopy. She reported intermittent constipation managed with docusate but denied hematochezia, abdominal pain, weight loss, or family history of colorectal cancer. Physical exam and labs were unremarkable. Colonoscopy revealed, a 5 mm sessile serrated polyp in the cecum, 2 mm tubular adenoma in the ascending colon, and a 4 cm patch of erythematous, friable, and nodular area with polypoid features in the rectum. Histopathology of the rectal lesion showed gastric oxyntic mucosa within benign rectal mucosa, consistent with gastric heterotopia. The patient was asymptomatic and was advised to repeat colonoscopy in 5 years. Discussion: Rectal GH is an exceptionally rare finding, believed to arise from aberrant embryologic differentiation or post-inflammatory metaplasia. It is most frequently identified incidentally, but symptoms—when present—can mimic colorectal neoplasia. Importantly, while GH is generally benign, cases of dysplasia and even adenocarcinoma arising within ectopic gastric mucosa have been reported, warranting long-term surveillance in some patients. Interestingly, gastric heterotopia expresses functional parietal cells, capable of acid secretion. In the rectum, this may cause local irritation, inflammation, and ulceration, possibly explaining bleeding or tenesmus in symptomatic patients. Moreover, GH has been associated with overexpression of mucin genes (MUC5AC and MUC6), which may play a role in mucosal protection but could also contribute to neoplastic potential. With fewer than 30 reported rectal GH cases in the literature, this case adds to the growing body of knowledge suggesting that these lesions, though rare, should not be overlooked. Greater awareness and histologic recognition are essential to differentiate them from malignancy and to guide appropriate management.