INTRODUCTION: Gastric heterotopia is the presence of well-differentiated gastric glands located in a region not anatomically expected. Though often asymptomatic and found incidentally, when symptoms are present, they may be severe leading to complications such as ulceration or bleeding1,2. Gastric heterotopia (GH) has characteristic endoscopic and histologic findings, though since it was first described, it has often been incorrectly undifferentiated from gastric metaplasia. CASE DESCRIPTION/METHODS: A 54-year-old male with history of hypothyroidism and gastroesophageal reflux disease was referred for endoscopy due to persistent reflux despite daily proton pump inhibitor therapy. EGD revealed grade B esophagitis, a 2-3mm gastric body polyp and a 2cm polyp in the duodenal bulb (Figure 1). Pathology review of the stomach polyp revealed a fundic gland-type polyp. Interestingly, the duodenal polyp sample also showed gastric fundic-type mucosa, indicative of gastric heterotopia (Figure 2). DISCUSSION: Though historically described interchangeably, the distinction between gastric heterotopia and metaplasia is critical. Histologically, GH appears as well-differentiated oxyntic glands with full mucosal thickness1,3. GH is congenital, and often found incidentally as a macroscopic lesion on endoscopy4. In contrast, gastric metaplasia (GM) is an acquired microscopic lesion with incomplete gastric glands that resides in a portion of mucosal thickness coalescent with native tissue3,4. It is a reactive process due to local inflammation, often associated with duodenitis, inflammatory bowel disease, hypergastrinemia and H. pylori3-4,6. Analysis by Matsubara et al. suggested that both GM and GH may have metaplastic potential due to GNAS and KRAS mutations, identified in 55% of GM lesions and 28% of GH lesions7. The reported prevalence of GH in the duodenal bulb has varied, ranging between 0.5- 2% of the population4. In the 1970s, post-mortem studies reported incidence of 1-2%5. A 2010 analysis of 28,000 patients reported incidence of GH in 1.9%, and additionally suggested a potential correlation between GH and gastric fundic gland polyps8. Though most cases of GH and GM are benign, investigations have introduced the possibility that a fraction may have neoplastic potential. Thus, accurate identification of these lesions is essential for endoscopists and pathologists, and further studies are needed to assess if routine surveillance for those with GH or GM is indicated.Figure 1.: Polyp in the duodenal bulb seen on endoscopy.Figure 2.: Low-power photomicrograph displaying gastric fundic-type mucosa in the duodenal bulb polyp sample.