Yellow cytoplasmic mucin in a TP preparation of a Brunner gland hamartoma. Brunner gland hamartoma is a benign proliferation of duodenal submucosal glands. The mucin-secreting gland epithelium is distinguishable from the intestinal surface epithelium by the abundant yellow cytoplasmic mucin content and lobular architecture which stand in contrast to the goblet cells (arrow) and brush border (arrowhead) in the latter (×40; ×63 (inset), oil immersion). TP, ThinPrep®.