Answer: Chronic pancreatitis

Histology: At low power, this lesion has a lobular architecture. At higher power there are numerous small irregularly shaped glands in a somewhat fibrotic stroma, worrisome for pancreatic adenocarcinoma. However, the glands show minimal cytologic atypia, and often have a “starfish-like” branching pattern. Nuclei do not vary in size between eachother by a ratio of greater than 4:1. There is minimal lymphoplasmacytic infiltration of the pancreas.

Discussion: Pancreatic adenocarcinoma is characterized by a non-lobular, infiltrative growth pattern, nuclear atypia such that nuclei within a gland vary by a factor of 4 in size, perineural invasion, intraluminal necrosis, and location of glands adjacent to blood vessels. Islet cells are resistant to the injurious effects of chronic pancreatitis, and therefore typically remain where the acinar cells have been depleted. Aggregation of islet cells in a background of chronic pancreatitis can mimic of an islet cell neoplasm. However, islet cell neoplasms typically have a pushing border, unlike islet cell aggregation. Lymphoplasmacytic sclerosing pancreatitis features a dense lymphoid infiltrate throughout the pancreas, usually centered upon ducts.