Intrahepatic cholangiocarcinoma initially diagnosed as adenocarcinoma of unknown primary with hepatoduodenal ligament lymph node metastases: A case report.

Intrahepatic cholangiocarcinoma (iCCA) with regional lymph node metastases, which lacks a well-delineated liver mass, may be misdiagnosed as a carcinoma of unknown primary (CUP) origin. The present study reports the case of a 69-year-old man initially diagnosed with CUP, who was incidentally found to have abdominal lymphadenopathy during ultrasonography (US). The clinical course from the time of lymphadenectomy and CUP diagnosis to iCCA detection after long-term follow-up is reported. A patient with a history of hypertensive renal disease presented with an incidental finding of enlarged abdominal lymph nodes in the perihepatic region on US. Abdominal contrast-enhanced computed tomography (CT) scan and magnetic resonance imaging (MRI) revealed two enlarged lymph nodes in the hepatoduodenal ligament. Exploratory laparotomy and lymphadenectomy were performed for diagnostic and therapeutic purposes, respectively. Poorly differentiated metastatic adenocarcinoma positive for cytokeratin 7 and negative for cytokeratin 20 was identified in two of the 22 lymph nodes. Postoperatively, a positron emission tomography/CT (PET/CT) scan was performed, which failed to locate the primary site. The diagnosis of CUP was confirmed based on clinical, radiological and histopathological characteristics. A sequential abdominal CT scan 48 months after lymphadenectomy revealed a faintly enhancing, intraductal polypoid mass with localized ductal dilatation in liver segment 3. MRI and PET/CT confirmed a mass in the left lobe of the liver. US-guided percutaneous needle biopsy confirmed the presence of moderately differentiated adenocarcinoma. The patient refused surgical treatment because of general weakness caused by Coronavirus disease 2019 infection. The patient received radical radiotherapy and underwent left hepatectomy after recovery of their performance status. Histopathological examination of the surgical specimen demonstrated prevailing fibrosis and mucin accumulation, with scattered cancer cells observed focally in the resected liver specimen owing to the effect of the radiotherapy. Consequently, a definitive diagnosis of primary adenocarcinoma of the intrahepatic bile duct was confirmed. The present report may improve understanding of the pathophysiology and clinical progression of iCCA, with a specific focus on the intraductal growth subtype.