Distal Bile Duct Metastasis From Rectal Cancer: The Diagnostic Contribution of Intraductal Ultrasonography

A 49-year-old male developed liver dysfunction during chemotherapy for rectal cancer located in the rectosigmoid region. Although magnetic resonance cholangiopancreatography initially indicated sclerosing cholangitis, endoscopic retrograde cholangiopancreatography and intraductal ultrasonography revealed multiple non-contiguous intraductal masses. Histopathological analysis confirmed distal bile duct metastasis from rectal cancer, characterized by papillary intraductal lesions. The distribution and morphology of the tumors suggested implantation via bile flow or hematogenous dissemination through the peribiliary capillary plexus. Extrahepatic bile duct metastasis from colorectal cancer is exceptionally rare and poses significant diagnostic challenges. This report presents a rare case of distal bile duct metastasis detected during chemotherapy for rectal cancer, where endoscopic imaging was instrumental in establishing the diagnosis.