A Case Report of Insulinoma Presenting with Seizures and Localized on Endoscopic Ultrasound

Insulinomas are rare functioning neuroendocrine (NEN) tumors. Up to 10% of insulinomas are associated with multiple endocrine neoplasia 1 (MEN1). Most of the tumors present with symptomatic hypoglycemia. Several non-invasive and invasive techniques are used to localize the lesion. We present a case of insulinoma presenting with seizure episodes with negative results on non-invasive imaging diagnosed and localized with endoscopic ultrasound. A 36-year-old male was brought by ambulance to the emergency department with an episode of generalized tonic-clonic seizures. He had been previously healthy and did not have family history of neuro-endocrine tumors. At the time of the attack, the patient's blood glucose checked via point-of-care testing was 28.8 (70-99 mg/dL). He was given IV dextrose. Physical examination after the patient regained consciousness was completely unremarkable. Hypoglycemia workup revealed a normal morning cortisol level of 281 (138-689 nmol/L). Insulin level was 62.4 mcunit/ml (2.36-24.9), and c-peptide was 8.13 (1.1-4.4 ng/mL) consistent with hyperinsulinemia. Magnetic resonance cholangiopancreatography (MRCP), fluorine-18-l-dihydroxyphenylalanine whole-body positron emission tomography scan (NM 18F-DOPA whole-body PET scan), and gallium Ga 68 dodecanetetraacetic acid (Ga-68 DOTATATE) scan were normal and did not reveal any pancreatic lesion consistent with insulinoma. Due to high suspicion of insulinoma and negative non-invasive imaging, an endoscopic ultrasound (EUS) was performed, which showed a hypoechoic homogenous mass lesion sized 13 × 9 mm in the proximal body/neck of the pancreas. A fine needle biopsy (FNA) via EUS was performed. Histopathology showed a well-differentiated neuroendocrine tumor, consistent with Grade 1 insulinoma (T1N0M0). The patient underwent a distal pancreatectomy and splenectomy. In cases of high clinical and biochemical suspicion of insulinoma but negative non-invasive imaging, invasive modalities should be used to localize the culprit lesion.