Inclusion Criteria:  Patients with confirmed hyperinsulinemic hypoglycemia, diagnosed by elevated insulin levels during hypoglycemia and/or response to glucagon stimulation. Subjects who failed pharmacological therapy with diazoxide or octreotide. Subjects with signed informed consent by themselves or their parents or legal guardians. Patient's Endocrinologist has determined that the patient cannot be safely managed with standard medical therapy (failed) and surgery is recommended to prevent future episodes of severe hypoglycemia and preserve brain function.  Exclusion Criteria:  Any other major illness or condition that in the investigator's judgment will substantially increase the risk associated with the subject's participation in this study. Patient must not have any contraindication to MRI as evaluated by a standardized MRI safety questionnaire. If MRI is contraindicated, and patient meets inclusion criteria and has no other contraindications study will be conducted in PET/CT scanner. Cases in which surgery will not be considered by parents or guardians.