Well-differentiated neuroendocrine (carcinoid) tumors of the extrahepatic biliary ducts.

Primary, well-differentiated neuroendocrine (carcinoid) tumors of the extrahepatic biliary ducts are an uncommon cause of biliary obstruction. As compared to cholangiocarcinomas, which are more commonly seen at this location, these tumors tend to behave less aggressively, and only one-third metastasize. Tumor size (>2 cm) appears to be the best predictor of aggressive behavior. Surgery is the mainstay of treatment and complete resection offers prolonged disease-free survival. Accurate preoperative diagnosis is therefore important and can be made by examining brush cytology specimens obtained during endoscopic retrograde cholangiopancreatography and/or endoscopic ultrasound-guided fine-needle aspiration. It is important to keep this entity in mind, especially when examining cytologic or small biopsy specimens, so that appropriate immunohistochemical stains can be used to arrive at the correct diagnosis.