Concurrent Adult-Onset Diffuse β-Cell Nesidioblastosis and Pancreatic Neuroendocrine Tumor: A Case Report and Review of the Literature.

Nesidioblastosis is an uncommon cause of organic persistent hyperinsulinemic hypoglycemia in adults. We report a case of adult-onset diffuse β-cell nesidioblastosis in a 49-year-old woman who was status-post Roux-en-Y gastric bypass and distal pancreatectomy for a well-differentiated pancreatic neuroendocrine tumor. While the neuroendocrine tumor was suspected to be an insulinoma, persistent hypoglycemia postoperatively suggested either incomplete resection or a second pancreatic neoplasm. Completion pancreatectomy revealed islet β-cell hyperplasia and nuclear pleomorphism consistent with β-cell nesidioblastosis. The patient's blood glucose levels normalized after completion pancreatectomy. While β-cell nesidioblastosis and insulinomas can coexist in the same patient, pathologists should be aware of β-cell nesidioblastosis as a potential cause for hyperinsulinemic hypoglycemia and should exclude it in patients who have not shown definitive clinical response after surgical excision of a pancreatic neuroendocrine tumor.