Nesidioblastosis and endocrine hyperplasia of the pancreas: a secondary phenomenon.

Diffuse endocrine cell proliferation (nesidioblastosis) and islet cell hyperplasia are considered causes of organic hyperinsulinism but have not been distinguished (by histometric or immunohistologic methods) from the normally variable pancreatic islet cell population during development and in adults. Therefore, in this study morphologic, immunohistologic (to detect insulin, glucagon, somatostatin, and pancreatic polypeptide), and morphometric features were evaluated in 1) normal pancreases (from fetal to adult; n = 49); 2) pancreases from patients with nesidioblastosis (n = 5); and 3) tumor-associated pancreases (TAP) from patients with insulin-producing islet cell tumors (n = 8). The study of normal postnatal development revealed that all features of fetal development remain present after birth and that the diagnosis of any diffuse endocrine disorder should therefore be based essentially on quantitative histometric parameters (total endocrine area, islet size distribution, distribution of each endocrine cell type). With these parameters endocrine cell hyperplasia was demonstrated in TAP from adults due to increased numbers of A and D cells. However, in the cases previously diagnosed as pathologic nesidioblastosis, all parameters were within the normal range. Thus, nesidioblastosis does not appear to be a pathologic entity. Careful re-examination of the pancreases, prompted by these data, revealed small islet cell tumors in three of these five cases. It is concluded that the endocrine pancreas can react rapidly, both morphologically and functionally, to changes in hormonal feedback, e.g., islet cell tumors. Therefore, the observation of a diffuse islet cell disorder in a patient with hyperinsulinism should not be considered an indication that an islet cell tumor is not present.