Nesidioblastosis is a controversial medical term for hyperinsulinemic hypoglycemia attributed to excessive insulin production by pancreatic beta cells that have an abnormal microscopic appearance. The term was coined in the first half of the 20th century. The abnormal microscopic features of the tissue included the presence of islet cell enlargement, pancreatic islet cell dysplasia, beta cells budding from ductal epithelium, and islets close to ducts.