Answer: Pyloric adenoma with high-grade dysplasia

Histology: Sections show a branching papillary structure lined by gastric type mucosa with ares showing intestinal metaplasia. Focal metaplastic spindle-squamoid morules are also noted. These low grade adenomatous areas are intermixed with solid sheets and cribriform areas where the cells have enlarged overlapping nuclei with more open chromatin and small nucleoli consistent with high grade dysplasia. The background gallbladder is benign and shows mild acute inflammation. The cystic duct margin is free of adenoma. One lymph node was identified and was negative for tumor. A small fibrovascular core consistent with a narrow stalk typical of this type of adenomas is identified. Immunostains performed in our laboratory demonstrate that the neoplastic cells are MUC-6 positive, while a MUC-2 and CDX-2 stain is focally positive and highlights the areas of intestinal metaplasia. A beta-catenin stain is also positive (nuclear labeling). This staining pattern is characteristic of pyloric adenoma.

Discussion: Adenomas of the gallbladder arise from the surface epithelium and can be classified as tubular pyloric gland type or intestinal type, and papillary adenoma intestinal type or biliary type, and as tubulopapillary type. Pyloric gland adenomas can have variably amount of intestinal metaplasia and show high grade dysplasia. Metaplastic changes are common and include squamouid morules, mucous cell and Paneth cell metpalsia. Pyloric gland adenomas maybe mistaken for heterotopic gastric mucosa, however, the latter contains fundic type glands with chief cells and parietal cells.