A 14-yr-old boy with a pathogenic MEN1 variant was diagnosed with asymptomatic insulinoma during routine follow-up.

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder attributed to mutations in the MEN1 gene and is characterized by multiple endocrine tumors, including insulinoma. Asymptomatic hyperinsulinemic hypoglycemia and pancreatic nodules were incidentally detected in a 14-yr-old male carrying a pathogenic MEN1 variant. Although insulinoma was suspected, it did not meet Whipple's triad, the classic diagnostic criteria for insulinoma, and some hypoglycemic provocation tests were negative. Selective arterial secretagogue injection (SASI) testing strongly suggested the presence of an insulinoma, and the lesions were surgically excised. The pathological findings were consistent with the SASI test results. Diagnosis of insulinoma based on conventional tests is challenging in some patients with asymptomatic insulinoma, and SASI testing can be useful not only for localization but also for insulinoma diagnosis.