A 72-year-old man who had suffered several episodes of syncope was diagnose
d as having hyperinsulinemic hypoglycemia. Although imaging studies and per
cutaneous transhepatic portal venous sampling did not reveal the existence
of any tumors in the pancreas, distal pancreatectomy was performed because
the possibility of a small pancreatic endocrine tumor could not be complete
ly rejected. External examination of the surgically removed pancreas did no
t reveal any tumors. Microscopically, the pancreas exhibited diffuse islet
cell hyperplasia without nesidioblastosis. The patient remains euglycemic a
nd has tolerated 24-hour fasting without any medication for a period of 10
months after the operation.