Solitary Synchronous Biliary Metastasis in Colorectal Adenocarcinoma.

Malignant biliary obstruction can, in rare cases, arise from metastases to the biliary tree from distant primary tumors. This phenomenon often poses a diagnostic challenge, as bile duct metastases may clinically and radiologically mimic primary biliary tumors, such as cholangiocarcinoma. We present a unique case of solitary, synchronous intraductal biliary metastasis in a patient with colorectal adenocarcinoma that led to biliary obstruction. The patient initially presented with a new diagnosis of colon cancer at the hepatic flexure and was found, on cross-sectional imaging, to have biliary obstruction due to an intraductal mass. Initially, the nature of the intraductal lesion was uncertain; however, it was ultimately confirmed through histopathological examination to be metastatic colorectal adenocarcinoma. This case underscores the difficulty of distinguishing metastatic biliary obstruction from primary biliary tumors and highlights the importance of considering metastatic disease in atypical presentations of biliary masses. We discuss several key radiologic and histopathological features that may help differentiate intraductal colorectal adenocarcinoma metastases from primary biliary tumors.