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.