Imaging mimickers of cholangiocarcinoma in the extra-hepatic biliary tree: a pictorial review with diagnostic clues.

Distal and perihilar biliary strictures and intraductal lesions frequently trigger immediate concern for cholangiocarcinoma (CCA). However, a broad spectrum of benign, inflammatory, infectious, vascular, and extrinsic processes can produce overlapping imaging appearances. Typical CCA of the common bile duct (CBD) commonly manifests as a long, irregular, asymmetric stricture with conspicuous mural thickening and progressive enhancement. These lesions may be accompanied by periductal soft tissue and vascular encasement. In contrast, mimickers more often demonstrate short, smooth, symmetric narrowing; obstructive causes such as stones or periampullary diverticula; extrinsic compression such as lymphadenopathy or portal cavernoma; inflammatory patterns with interval improvement; congenital ductal ectasia; or characteristic systemic/infectious findings. Careful pattern recognition on MRCP and contrast-enhanced MRI and CT integrating stricture morphology, enhancement behavior, vascular relationships, and temporal evolution provide a reliable framework to distinguish malignant CBD cholangiocarcinoma from benign mimics. This review presents a structured approach to differentiate CBD cholangiocarcinoma from key mimickers using MRI/MRCP and CT.