Clinical PET imaging of insulinoma and beta-cell hyperplasia

Persistent hyperinsulinemic hypoglycemia (PHH) is caused by solitary benign insulinoma or hyperplasia of pancreatic beta cells. In infants, PHH is caused by functionally defective hyperplastic beta cells, which are either diffusely or focally distributed in the pancreas. In adults, insulinoma is the most common cause of PHH, but recently, an increasing number of beta-cell hyperplasias has been reported among adults. The cause of adult beta-cell hyperplasia is not known. Whether the increased use of bariatric surgery in the treatment of severe obesity plays a role here is under investigation. Accurate localization of disease focus in both insulinoma and focal beta-cell hyperplasia provides an important support for surgery, especially as the use of laparoscopic surgery has increased. Conventional imaging of these challenging pancreatic lesions has evolved during recent years, but current imaging methods still lack sufficient sensitivity or are invasive. In most pancreatic NETs, the usefulness of positron emission tomography (PET) with fluorine-labeled fluorodeoxyglucose ([(18)F]FDG) for lesion detection is limited because of the low glucose turnover of these tumors. Based on the capacity of pancreatic beta cells to take up and decarboxylate amine precursors, several investigators have studied patients with pancreatic NETs using aminoacid precursors, such as [(18)F]dihydroxyphenylalanine (DOPA) and [(11)C]hydroxytryptophan (5-HTP), in an attempt to increase the sensitivity of PET scanning. Another characteristic of NETs is the expression of somatostatin receptors, and thus encouraging studies with somatostatin receptor imaging with [(18)Ga]-labeled somatostatin analogs have emerged as a new interesting imaging tool for the diagnosis of pancreatic NETs. This article provides an overview of our experiences and the current literature on PET imaging in patients with PHH caused by insulinoma or beta-cell hyperplasia.