Pancreatic Neuroendocrine Tumor Leading to a Diagnosis of Multiple Endocrine Neoplasia Type 1

Pancreatic neuroendocrine neoplasms are rare but occasionally encountered. They are generally highly vascularized solid tumors, often round in shape with clear boundaries, defined contours, and a homogeneous internal structure. However, they can also present with atypical features, such as cystic degeneration, hemorrhage, calcification, and fibrosis, making diagnosis difficult in some cases. They are also known as comorbidities of multiple endocrine neoplasia type 1 (MEN1). This report describes a case in which endoscopic ultrasound (EUS) led to a diagnosis of MEN1. A 50-year-old man was referred to our hospital for examination of a mass in the pancreatic body. An EUS-guided fine-needle biopsy was performed, and a histological diagnosis of neuroendocrine tumor (NET) was made. In addition, the NET was also identified in the duodenum. Serum calcium and parathyroid hormone levels were elevated. Examination of the parathyroid and pituitary glands revealed concurrent hyperparathyroidism and a pituitary adenoma, confirming the diagnosis of MEN1, including a NET in the duodenum.