Abstract
Bile duct communication (BDC) and ovarian-like stroma (OS) have been believed to be key findings for the differentiation of intraductal papillary neoplasm of the bile duct (IPNB) and mucinous cystic neoplasm (MCN). However both have their problems as diagnostic criteria. BDC is sometimes difficult to detect both by images and by pathological examination. True character of OS has not yet been clarified at present. It can be ectopic ovary or fibroblast, It is also controversial whether IPNB and MCN are different entities or different subtypes. The concept of different entities denies the presence of intermediate condition between IPNB and MCN. By contrast, the concept of different subtypes means the presence of intermediate condition. The histological classification of biliary intraepithelial neoplasia (BilIN) is very useful to express the grade of atypia of epithelial tumors of bile duct. However, it is not sufficient to solve the problems of difficult lesions by itself. There exists overlapping zone between malignant lesion with low grade atypia and benign lesion with high grade atypia. These serious problems should be solved by specialists of bile duct disease in the future. Finally, supplemental comments were described on the histological explanation of general rules for surgical and pathological studies on cancer of the biliary tract.
