Introduction: Insulinomas are rare tumors, with an estimated incidence of 0.1–0.4 cases per 100,000 inhabitants, and are almost always functioning, causing limiting symptoms related to hypoglycemia. Initial imaging exams such as computed tomography (CT) and magnetic resonance imaging (MRI) usually identify the lesion; however, in a small percentage of cases they are inconclusive.

Case Report: A 36-year-old female patient presented with episodes of sweating, dizziness, and loss of consciousness, during which hypoglycemia was documented. She also exhibited weight gain due to an increase in both frequency and volume of meals in an attempt to avoid hypoglycemic episodes. After laboratory tests indicated elevated insulin and C-peptide levels, abdominal imaging studies were performed, but no lesions were identified on either CT or MRI. To further investigate the pancreas as the source of symptoms, endoscopic ultrasound (EUS) was performed, revealing a well-defined, heterogeneous, hypoechoic nodular lesion with firm consistency in the pancreatic tail, measuring approximately 23×16 mm. Fine Needle Biopsy was performed during the procedure, and subsequent histopathology and immunohistochemistry demonstrated a well-differentiated neuroendocrine neoplasm producing insulin, confirmed by positivity for Chromogranin A, Synaptophysin, beta-catenin, and insulin.

Discussion: The diagnosis of insulinoma can be challenging, especially when lesions are small and not detectable on traditional imaging modalities. In this case, Endoscopic Ultrasound proved fundamental—not only for localizing the lesion but also for obtaining tissue for analysis and confirming the diagnosis—thus enabling definitive treatment.