Biliary intraepithelial neoplasia: a case with benign biliary stricture

Intrahepatic and extrahepatic cholangiocarcinomas develops through a multistep carcinogenesis sequence and they are preceded by precursor lesions. Precursors of malignant neoplasm are identified in various organs including uterine cervix, gastrointestinal tract and breast. Identification of these precursor lesions are important in that they need minimal treatment or they are good indicator of disease progression or recurrence. In the intrahepatic and extrahepatic biliary tract, precursor lesions of malignancy are defined as follows; biliary intraepithelial neoplasia (BilIN), intraductal papillary neoplasm, mucinous cystic neoplasm, and adenoma. BilIN is characterized by atypical epithelial cells with multi-layering of nuclei and micropapillary projections into the lumen of bile duct. In contrast to intraductal papillary neoplasm which is characterized by papillary proliferation of epithelial cells with fibrovascular stroma and mucin production, BilIN tend to be a microscopic lesion. Mucinous cystic neoplasm is usually cystic lesions and has distinguishing clinicopathologic findings such as subepithelial stroma resembling ovarian stroma and predominant occurrence in adult female. Adenomas are commonly encountered in extrahepatic bile ducts and divided into tubular, papillary and tubulopapillary on the basis of growth pattern. CASE SUMMARY