Submucosal-Predominant (Inverted-Type) Pyloric Gland Adenoma of the Duodenum Mimicking Malignancy

ABSTRACT Duodenal pyloric gland adenomas are uncommon neoplasms that can rarely extend into the submucosa, creating a subepithelial appearance. We present a 69-year-old woman with a history of treated non–small-cell lung cancer who underwent positron emission tomography/computed tomography for oncologic surveillance, which revealed an fluorodeoxyglucose-avid duodenal lesion initially concerning for metastatic disease. Endoscopic ultrasound revealed a well-circumscribed, isoechoic mass confined to the submucosa, and endoscopic resection demonstrated a pyloric gland adenoma. Recognition of this rare, inverted growth pattern is important to distinguish it from malignant or metastatic disease and guide appropriate endoscopic management and surveillance.