A 55-year-old man who is extremely obese reports weakness, sweating, tachycardia, confusion, and headache whenever he fasts for more than a few hours. He has prompt relief of symptoms when he eats. These symptoms are most suggestive of which of the following disorders?

Tumors arising from the pancreatic b cells give rise to hyperinsulinism. Seventy-five percent of these tumors are benign adenomas and in 15% of affected patients the adenomas are multiple. Symptoms relate to a rapidly falling blood glucose level and are due to epinephrine release triggered by hypoglycemia (sweating, weakness, tachycardia). Cerebral symptoms of headache, confusion, visual disturbances, convulsions, and coma are due to glucose deprivation of the brain. Whipple's triad summarizes the clinical findings in patients with insulinomas: (1) attacks precipitated by fasting or exertion; (2) fasting blood glucose concentrations below 50 mg/dL; (3) symptoms relieved by oral or intravenous glucose administration. These tumors are treated surgically and simple excision of an adenoma is curative in the majority of cases.