Question: A 26-year-old man was referred to our hospital for an abnormality detected on a computed tomography scan of the abdomen. The patient had no medical or surgical history. He had no abdominal symptoms, such as nausea, vomiting, or abdominal pain. Physical examination was unremarkable. Initial laboratory studies, including routine blood test, carcinoembryonic antigen, and inflammatory markers were within the normal range. The abdominal computed tomography scan showed multiple polyps <2 cm that were confined to the jejunum (Figure A, arrow). Esophagogastroduodenoscopy and colonoscopy were performed, and no additional polyps or lesions were identified. Video capsule endoscopy demonstrated multiple salmon-colored polyps about 2 cm in diameter without any erosion or ulceration on the jejunum (Figure B). To further evaluate the polyps and to acquire biopsy specimens, an enteroscope was inserted orally and introduced to the jejunum under sedation and fluoroscopic guidance. Enteroscopy revealed multiple variable-sized polyps with a smooth-appearing surface, measuring 1–2 cm in the jejunum (Figure C). Based on this information, what is the most likely diagnosis? See the Gastroenterology web site (www.gastrojournal.org) for more information on submitting your favorite image to Clinical Challenges and Images in GI. Histopathologic examination of the biopsy specimens taken from these polyps revealed that the polyp was covered by hyperplastic gastric antrofundic mucosa with well-developed gastric gland (the portion above the red line is the gastric mucosa and that below it is the small intestine mucosa; Figure D). Immunohistochemical staining showed expressed MUC5AC, which is expressed in gastric foveolar epithelial cells of the antrum and the body (Figure E) and MUC6, which is expressed in antral and pyloric mucous glands (Figure F). Finally, the diagnosis was congenital heterotopic gastric mucosa (HGM) of the jejunum. HGM is the presence of mature gastric mucosa in a location where it is not normally found. HGM may occur throughout the gastrointestinal tract from the mouth to the rectum, especially in the upper esophagus and duodenum. It is rarely seen beyond the duodenum, and is usually found in the jejunum, except the Meckel’s diverticulum.1Boybeyi O. Karnak I. Gucer S. et al.Common characteristics of jejunal heterotopic gastric tissue in children: a case report with review of the literature.J Pediatr Surg. 2008; 43: e19-e22Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar HGM can be classified as congenital (heteroplasia) and acquired (metaplasia); however, the mechanism remains unknown. Congenital HGM represents a mixture of pyloric and fundic epithelium without associated disease that can precipitate inflammation. It usually appears as an inlet patch in the upper esophagus (the most common form of HGM), as nodular masses in the duodenum, as part of the mucosa in the Meckel's diverticulum, or as polypoid lesions in the other parts of the small intestine (as in our case).2Yu L. Yang Y. Cui L. et al.Heterotopic gastric mucosa of the gastrointestinal tract: prevalence, histological features, and clinical characteristics.Scand J Gastroenterol. 2014; 49: 138-144Crossref PubMed Scopus (29) Google Scholar In contrast, acquired HGM represents replacement of the native mucosa of any part of gastrointestinal tract by gastric epithelium because of various inflammatory processes, such as inflammatory bowel disease, Barrett's syndrome, celiac disease, postirradiation enteritis, and gastrojejunostomy. Acquired HGM is characterized by pyloric-type epithelium with rare, or absent parietal and chief cells.3Nowak M. Deppisch L. Giant heterotopic gastric polyp in the jejunum.Arch Pathol Lab Med. 1998; 122: 90-93PubMed Google Scholar Because of the variable morphology and size of HGM, it must be differentiated from other neoplasms (such as adenoma, hamartomatous polyp of Peutz-Jeghers syndrome, lipoma, neuroendocrine tumor, or malignant tumors, including carcinoma or lymphoma) and a definitive diagnosis can be established by histopathologic examination of the biopsy specimen containing the gastric mucosa. To date, the natural course of polypoid HGM of the jejunum is unclear, and no guidelines for treatment or surveillance are currently available. HGM is usually clinically silent and does not require treatment (as in the present case); however, surgical intervention can be considered in patients with complications, such as intestinal bleeding, obstruction, or perforation. In summary, although HGM of the jejunum is very rare, it should be considered in the differential diagnosis of jejunal polypoid lesions. Address correspondence to: Dong Hoon Baek, MD, PhD, Department of Gastroenterology, Pusan National University School of Medicine and Biomedical Research Institute, Pusan National University Hospital, 179, Gudeok-ro, Seo-Gu, Busan, 49421, South Korea. e-mail: [email protected]