A case of pyloric gland adenoma with high-grade dysplasia in the duodenum arising from heterotopic gastric mucosa observed over 5 years.

Pyloric gland adenoma (PGA) in the duodenum is a rare gastric phenotype duodenal neoplasm. Although heterotopic gastric mucosa in the duodenum has been recognized as a benign lesion, it is a potential precursor of PGA and gastric phenotype adenocarcinoma. Herein, we present a case follow-up of endoscopic and histological changes in the PGA in the duodenum from low-grade to high-grade dysplasia. PGA was considered to arise from the heterotopic gastric mucosa, because the heterotopic gastric mucosa was observed in the initial examination. It is difficult to distinguish heterotopic gastric mucosa from PGAs, both endoscopically and histologically. This increase in size may be useful for their differentiation. Therefore, endoscopists should not underestimate the growth of the heterotopic gastric mucosa compared to that in the previous examination.