Pancreatic neuroendocrine tumors (PNETs) may rarely appear as cystic or mixed solid-cystic masses. The endoscopic ultrasound (EUS) morphology and cyst fluid characteristics of these tumors are not well clarified. We retrospectively identified nine adult patients with nine single cystic pancreatic neuroendocrine tumors (CNETs). These nine included 0.67% of the 1344 patients with pancreatic cystic lesions and 9.5% of the 95 confirmed PNETs evaluated over the 12-year study period. At presentation, four patients were asymptomatic and five had known acute pancreatitis (n = 2), MEN-1 syndrome with hypoglycemia (n = 1), and abdominal pain (n = 2). Median maximal tumor diameter was 26 mm (range 20-64 mm). EUS morphology was mixed solid and cystic (n = 4) or cystic alone (n = 5). Cytology from EUS-fine-needle aspiration (FNA) (median 2 passes; range 1-6) demonstrated a PNET, and immunocytochemistry was confirmatory in all patients. Cyst fluid carcinoembryonic antigen (CEA) (n = 4) and amylase (n = 5) ranged from 0.1 to 1.8 ng/ml (normal 0-2.5 ng/ml) and 72 to 1838 U/L (normal 25-161 U/L), respectively. Six patients underwent surgery, and the preoperative diagnosis was confirmed in all.
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