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

Abstract

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.

Keywords: common hepatic duct; computed tomography; cystic duct; endoscopic retrograde cholangiopancreatography; endoscopic ultrasonography; intraductal ultrasound; magnetic resonance imaging; neuroendocrine tumor.

Figure 1. Abdominal computed tomography (CT) imaging findings.

(A) Non-contrast CT showing a 17 mm × 15 mm × 13 mm nodule (arrow) at the confluence of the three bile ducts. (B-E) Dynamic contrast-enhanced CT demonstrating enhancement (arrows), peaking during the portal venous phase. The upstream of bile ducts are dilated (arrowheads).

Figure 2. Abdominal magnetic resonance imaging (MRI) findings.

(A) and (B) The nodule (arrows) shows mildly high signal intensity on T2-weighted imaging (T2WI) and low signal intensity on T1-weighted imaging (T1WI). (C) and (D) The nodule (arrows) exhibits marked diffusion restriction on diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) map (0.63 × 10⁻3 mm²/s). (E) Magnetic resonance cholangiopancreatography (MRCP) shows dilation of the common hepatic duct and intrahepatic bile ducts upstream of the nodule. Bile duct compression by the nodule produces a signal defect (arrowhead).

Figure 3. Fluorine-18-fluorodeoxyglucose positron emission tomography (18F-FDG PET)/CT imaging findings.

(A) Non-contrast CT shows a nodule (arrow) at the confluence of the three bile ducts. A bile duct stent is inserted in the common bile duct (arrowhead). (B) Mild FDG uptake with an SUVmax of 3.5 is observed in the nodule (arrow). The common bile duct stent is also observed (arrowhead).

Figure 4. Findings of endoscopic retrograde cholangiopancreatography (ERCP), endoscopic ultrasound(EUS), and intra-ductal ultrasound (IDUS).

(A) ERCP shows a stenotic lesion at the confluence of the three bile ducts, caused by extrinsic compression resembling a submucosal tumor (arrow). (B) and (C) EUS and IDUS reveal a well-demarcated, smoothly margined nodule with heterogeneous hypoechoic features (arrowheads).

Figure 5. Hematoxylin and eosin (HE)-stained histopathological specimens.

(A) and (B) A well-demarcated, 2 cm yellowish-white nodule (arrows) is observed in the extrahepatic bile duct, just below the cystic duct (arrowhead) orifice. (C)-(F) Tumor cells with mildly pleomorphic, enlarged round nuclei and pale eosinophilic cytoplasm are arranged in trabecular patterns or small clusters (dotted circles).

Figure 6. Immunohistochemical staining.

(A)-(D) Immunostaining was positive for chromogranin A, synaptophysin, CD56, and INSM1 (stained brown).  (E) The Ki-67 labeling index was less than 1%.  (F) Immunostaining was negative for serotonin.