Adult-Onset Nesidioblastosis Mimicking Insulinoma in a Patient with Type 2 Diabetes Mellitus: A Case Report

Nesidioblastosis represents a rare cause of endogenous hyperinsulinemic hypoglycemia in adults, characterized by diffuse or focal proliferation of pancreatic β-cells. It often mimics insulinoma clinically and radiologically, and therefore, its differential diagnosis is quite difficult in the preoperative period. A case of adult nesidioblastosis mimicking insulinoma is presented. A 59-year-old man with a 13-year history of type 2 diabetes mellitus presented with recurrent hypoglycemic episodes manifested by sweating, palpitations, and confusion, despite cessation of antidiabetic therapy for 2 months. During a prolonged fasting test, hypoglycemia accompanied by inappropriately elevated insulin and C-peptide concentrations confirmed endogenous hyperinsulinemia. Contrast-enhanced abdominal computed tomography (CT) and magnetic resonance imaging failed to reveal a pancreatic lesion. Gallium-68 DOTATATE positron emission tomography (68Ga-DOTATATE PET) demonstrated a focal area of increased uptake, approximately 1 cm in size, in the pancreatic uncinate process, suggesting a preliminary diagnosis of insulinoma. The patient underwent Whipple surgery, during which no macroscopic tumor was identified. Histopathological examination revealed ductuloinsular complexes, islet cell hyperplasia, and nuclear enlargement, and the findings were evaluated as compatible with focal nesidioblastosis. This case emphasizes the diagnostic complexity of differentiating nesidioblastosis from insulinoma and underscores the essential role of histopathological and immunohistochemical analyses for establishing a definitive diagnosis.

Cite this article as: Bozdoğan ME, Kü.ük ŞD, Dilli MŞ, Acıbucu F, Aşut E. Adult-onset nesidioblastosis mimicking insulinoma in a patient with type 2 diabetes mellitus: A case report. Endocrinol Res Pract. 2026;30(3):209-212.