Small-cell Neuroendocrine Carcinoma of the Extrahepatic Bile Duct: A Rare Case Report

Neuroendocrine carcinoma (NEC) arising from the extrahepatic bile duct is extremely rare and commonly mistaken for cholangiocarcinoma. Therefore, NEC of the bile duct is difficult to diagnose preoperatively. Previously reported cases were resected with a diagnosis of cholangiocarcinoma and diagnosed with NEC after surgery. This paper reports an 84-year-old female with small-cell NEC of the extrahepatic bile duct, confirmed by a biopsy from an ERCP, with a review of the relevant literature. Contrast-enhanced abdomen computed tomography and magnetic resonance cholangiopancreatography revealed an approximately 1.7 cm enhancing intraductal mass in the proximal common bile duct with dilatation of the upstream bile duct. ERCP showed a long strictured segment in the proximal common bile duct with bile duct dilatation. A biopsy was performed at the site of the stricture. Histological examinations and hematoxylin-eosin staining showed the solid proliferation of small tumor cells with irregularly shaped hyperchromatic nuclei. Immunohistochemical examinations showed that the tumor cells were positive for CD56 and synaptophysin. Small-cell NEC of the extrahepatic bile duct was confirmed based on the histology and immunohistochemistry findings. The patient and their family denied treatment because of the patient's old age.