Serotonin-positive neuroendocrine neoplasm with pancreatic ductal dilation in which cytological immunostaining contributed to the diagnosis.

A 52-year-old man was transported via an ambulance because of syncope and the passage of tarry stools, which had been noted the previous day. He was diagnosed with upper gastrointestinal bleeding from a gastric ulcer and underwent endoscopic hemostasis. Prior to endoscopy, abdominal computerized tomography performed for gastrointestinal bleeding revealed pancreatic duct dilation. After discharge, abdominal imaging revealed a strongly enhancing tumor (5 mm) with caudal pancreatic duct dilation. Endoscopic retrograde pancreatography revealed that the main pancreatic duct was interrupted at the body. Pancreatic juice cytology was class III, and additional immunostaining were positive for chromogranin A, synaptophysin, and serotonin, suggesting a pancreatic neuroendocrine neoplasm (NEN). Distal pancreatectomy was performed and a yellowish-white solid lesion was found in the pancreatic duct. Pathological examination revealed narrowing of the pancreatic duct, extensive stromal fibrosis, and proliferation of tumor cells with small round nuclei and eosinophilic vesicles. Furthermore, the immunostaining findings of the resected specimen corresponded with those of the cytology. A diagnosis of NEN G1 (WHO classification) with Ki-67 index < 1% was made. Imaging of the pancreatic duct tend to be normal or show no involvement of the duct in pancreatic neuroendocrine neoplasms; however, there have been a few reports of stenosis due to fibrosis around the pancreatic duct. Serotonin positivity was previously documented to be significantly higher in patients with fibrosis. In lesions with pancreatic ductal stenosis, the addition of immunostaining to pancreatic juice cytology was thought to be useful in differentiating pancreatic cancer from pNEN.