Intrahepatic biliary proliferations: histopathology and potential immunohistochemical markers.

•Intrahepatic biliary proliferations represent a spectrum varying from reactive to malignant entities. •Clinical and imaging patterns may be similar, requiring histopathological and immunohistochemistry for precise diagnosis. Intrahepatic biliary proliferations represent a spectrum from reactive (ductular reaction, some with atypical architecture), hamartomatous (von Meyenburg complex), benign (bile duct adenoma) and precursor/borderline entities (biliary intraepithelial neoplasia, intraductal papillary neoplasm of the bile duct) to fully malignant (cholangiocarcinoma) neoplasms. Clinical pictures and even imaging patterns may be similar, requiring refined studies aiming at histopathological and immunohistochemistry for more precise diagnosis, essential for correct patient management. This article discusses updated concepts and definitions of most relevant entities aiming more specifically at the differential diagnosis in practice, focusing on morphology and immunohistochemistry, with a discussion of potential markers to help distinguishing between benign and malignant lesions.