A case of duodenal pyloric gland adenoma with high‐grade dysplasia arising from ectopic gastric mucosa

Superficial non-ampullary duodenal epithelial tumor is a rare disease, but its frequency has reportedly been increasing in recent years. We report a case of duodenal pyloric gland adenoma with high-grade dysplasia arising from ectopic gastric mucosa. Esophagogastroduodenoscopy detected a 5-mm raised lesion on the anterior surface of the duodenal bulb. The lesion was diagnosed as gastric foveolar metaplasia with biopsy. A second esophagogastroduodenoscopy was performed 13 years later. The nodule showed a two-stage elevation and a biopsy revealed EGM. The lesion was followed up with EGD almost every year, with enlargement observed each time. Endoscopic submucosal dissection was performed. Histopathological examination revealed pyloric gland adenoma with high-grade dysplasia. Ectopic gastric mucosa was observed in the tumor pathologically and transformation of the EGM into a tumor was followed endoscopically over time.