Pathologic Classification of Preinvasive Cystic Neoplasms of the Intra- and Extrahepatic Bile Ducts

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In the past few years, there have been significant changes in the way preinvasive neoplastic cysts of the liver are classified. Most of the criteria were adopted from those employed for the pancreas and extrahepatic bile ducts, and accordingly, a counterpart of virtually all entities described in those sites are now also recognized in the liver. Mucinous cystic neoplasms (what used to be called hepatobiliary cystadenoma/cystadenocarcinoma) are now defined by the presence of ovarian-type stroma, and, when defined as such, they occur exclusively in women, mostly in the left lobe, and seldom show carcinomatous changes (5%). Other categories of cystic preinvasive neoplasms (tumoral intraepithelial neoplasms) that occur in the pancreatobiliary tract, namely, intraductal neoplasms, also occur in the liver, and just like their counterparts, they are now regarded in three distinct groups: intraductal papillary neoplasms, intraductal tubulopapillary neoplasms, and intraductal oncocytic papillary neoplasms. The latter is proving to be a highly benevolent tumor type despite its complexity and seemingly aggressive appearance radiographically. Another group of cystic lesions in the liver that can harbor dysplasia (BilIN, preinvasive neoplasia) are congenital/choledochal cysts that exhibit carcinomatous changes in estimated 10% of the cases.