Primary Well-Differentiated Neuroendocrine Tumor of the Perihilar Bile Duct Mimicking Cholangiocarcinoma

Primary neuroendocrine tumors (NETs) of the biliary tract are exceptionally rare and may closely mimic cholangiocarcinoma (CCA).A 73-year-old woman with previous cholecystectomy presented with abdominal discomfort and biliary dilatation.Magnetic resonance imaging (MRI)/magnetic resonance cholangiopancreatography (MRCP), endoscopic ultrasonography (EUS), endoscopic retrograde cholangiopancreatography (ERCP), and computed tomography (CT) all demonstrated a hilar lesion causing predominantly right-sided biliary obstruction and were considered highly suspicious for perihilar CCA (pCCA); serum carbohydrate antigen 19-9 was 230 U/mL.Endoscopic retrograde cholangiopancreatographydirected forceps biopsy and brush cytology were negative for malignancy.The patient underwent right hepatectomy with en bloc extrahepatic bile duct resection, regional lymphadenectomy, and Roux-en-Y hepaticojejunostomy.Histopathology unexpectedly demonstrated a 4.3 cm well-differentiated grade 2 NET arising in the right and common hepatic duct walls, with a Ki-67 index of 5%, negative margins, and no nodal metastases (0/4).The tumor showed an intramural growth pattern with preserved overlying biliary epithelium, providing a plausible explanation for the negative endoluminal samples.DOTATATE PET/CT at six months showed no abnormal uptake, and the patient remains recurrence-free at eight months.This case highlights the diagnostic challenge of primary hilar biliary NETs and the limitations of superficial endoluminal sampling.