Adult endogenous hyperinsulinaemic hypoglycaemia The most common form of functional neuroendocrine tumours of the pancreas are insulin producing pancreatic neuroendocrine tumors (IPPNET). These tumors are rare and have an incidence of 1-4 newly diagnosed cases per 1 million per year and are malignant in about 10% of the cases. Another cause of AHH is nesidioblastosis, or adult beta cell hyperplasia. It is difficult to exactly determine the incidence of the disease, but it appears that in approximately 5% of the cases of AHH nesiodioblastosis may be the underlying pathology, while IPPNET are responsible for the majority of the cases. The pathophysiological cause of nesidioblastosis is not well understood, but the rising incidence of the AHH as a consequence of gastric bypass surgery for morbid obesity (although often reversible in these patients) may suggest an association with metabolic and hormonal changes.