Adult-Onset Focal Nesidioblastosis With Nodular Formation Mimicking Insulinoma

Nesidioblastosis is defined as the neoformation of the islets of Langerhans from the pancreatic ductal epithelium and is recognized as the most common cause of hyperinsulinemic hypoglycemia in infants. We herein report an extremely rare case of adult-onset focal nesidioblastosis with the unusual feature of hyperplastic nodular formation. A 55-year-old woman was admitted to our hospital for a tumor detected in the body of the pancreas by magnetic resonance imaging screening. Laboratory examinations showed a high insulin level in the blood. Contrast-enhanced computed tomography and the selective arterial calcium injection test suggested the presence of multiple insulinomas in the body and tail of the pancreas, and, thus, the patient underwent distal pancreatectomy. A histopathological examination of the tumor in the body of the pancreas showed the nodular hyperplasia of islet-like cell clusters. In addition, many small intralobular ductules and islet cells appeared to be budding from the proliferating ductal epithelium, forming “ductuloinsular complexes”. No other abnormal lesion was detected in the remainder of the pancreas. The histopathological diagnosis was focal nesidioblastosis. The patient has remained free of the recurrence of hypoglycemic episodes for more than 31 months. The present case of rare adult-onset focal nesidioblastosis with hyperplastic nodular formation was preoperatively identified as an apparent pancreatic tumor mimicking insulinoma. Nesidioblastosis and insulinoma need to be considered in cases of hyperinsulinemic hypoglycemia, even in adult patients.