Hyperplastic and microadenomatous pancreatic neuroendocrine lesions

Hyperplastic lesions of the neuroendocrine cell system of the pancreas have, in certain conditions, the potential to develop into neoplastic lesions. This is particularly the case in the setting of genetically determined and hereditary neuroendocrine tumor syndromes such as multiple endocrine neoplasia type 1 (MEN1) and the recently described glucagon cell adenomatosis (GCA). This chapter discusses the pathology and the molecular changes of the hyperplasia–neoplasia sequence in the pancreas associated with MEN1 and glucagon cell adenomatosis. It also presents the pancreatic changes in insulinomatosis VHL disease. Finally, the pseudohyperplasia of PP-rich islets in the pancreatic head is defined as a physiologic condition clearly differing from the hyperplastic–neoplastic neuroendocrine diseases.