Imaging of Biliary Tree Abnormalities

Pathologic conditions of the biliary system, although common, can be difficult to diagnose clinically. Challenges in biliary imaging include anatomic variants and the dynamic nature of the biliary tract, which can change with age and intervention, blurring the boundaries of normal and abnormal. Choledochal cysts can have numerous appearances and are important to diagnose given the risk of cholangiocarcinoma potentially requiring surgical resection. Choledocholithiasis, the most common cause of biliary dilatation, can be difficult to detect at US and CT, with MRI having the highest sensitivity. However, knowledge of the imaging pitfalls of MRI and MR cholangiopancreatography is crucial to avoid misinterpretation. Newer concepts in biliary tract malignancy include intraductal papillary biliary neoplasms that may develop into cholangiocarcinoma. New paradigms in the classification of cholangiocarcinoma correspond to the wide range of imaging appearances of the disease and have implications for prognosis. Accurately staging cholangiocarcinoma is imperative, given expanding curative options including transplant and more aggressive surgical options. Infections of the biliary tree include acute cholangitis or recurrent pyogenic cholangitis, characterized by obstruction, strictures, and central biliary dilatation. Inflammatory conditions include primary sclerosing cholangitis, which features strictures and fibrosis but can be difficult to differentiate from secondary causes of sclerosing cholangitis, including more recently described entities such as immunoglobulin G4–related sclerosing cholangitis and COVID-19 secondary sclerosing cholangitis. The authors describe a wide variety of benign and malignant biliary tract abnormalities, highlight differentiating features of the cholangitides, provide an approach to interpretation based on the pattern of imaging findings, and discuss pearls and pitfalls of imaging to facilitate accurate diagnosis.