A Rare Neuroendocrine Tumor at the Junction of the Cystic and Common Hepatic Ducts: The Value of a Multimodal Approach in Preoperative Diagnosis.

Neuroendocrine tumors (NETs) of the biliary tract are extremely rare due to a paucity of Kulchitsky cells. While their preoperative diagnosis remains challenging due to the lack of specific diagnostic markers and imaging findings, there have been no detailed reports describing the diagnostic utility of various imaging modalities for bile duct NETs at the junction of the cystic and common hepatic ducts. We report a case of a woman in her 40s who presented with jaundice and elevated hepatobiliary enzymes. Imaging studies identified a 17 mm × 15 mm × 13 mm nodule at the junction of the cystic and common hepatic ducts. Contrast-enhanced computed tomography (CT) demonstrated a well-enhanced nodule from the early phase, while magnetic resonance imaging showed slightly high intensity on T2-weighted images and strong diffusion restriction. Fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography/CT revealed mild 18F-FDG uptake with a maximum standardized uptake value of 3.5. Endoscopic retrograde cholangiopancreatography (ERCP) suggested extramural compression by a submucosal tumor, and endoscopic ultrasonography (EUS) and intraductal ultrasound (IDUS) revealed a well-circumscribed, homogeneous, hypoechoic submucosal nodule. This comprehensive multimodal approach allowed for the inclusion of NET in the preoperative differential diagnosis. The patient underwent cholecystectomy and extrahepatic bile duct resection, and histopathological examination confirmed a World Health Organization grade 1 NET at the junction of the cystic and common hepatic ducts. The patient remains recurrence-free after two years of follow-up. This is the first detailed report demonstrating the potential utility of a multimodal approach, including ERCP, EUS, and IDUS, in the preoperative diagnosis of biliary tract NET at this specific anatomical location, particularly in identifying the characteristic features of a submucosal tumor.