Mucinous cholangiocarcinoma featuring a unique microcystic appearance

An autopsy case is presented of a peculiar type of intrahepatic mucinous adenocarcinoma with microcyst formation arising in a 78 year old Japanese man who died of hepatic coma and renal failure 4 months after onset. Macroscopically, the cut surface of the lesion revealed a characteristic honeycomb-like appearance, consisting purely of microcysts, 0.2-0.4 cm in diameter, lined by prolific mucin-producing adenocarcinoma cells. The lesion did not have large cystic space, fibrous capsule, or benign cystadenomatous component other than neoplastic microcyst formation. The carcinoma cells showed various proliferating patterns, such as irregularly shaped nest-like, trabecular, papillary and tubular ones, directly invaded the hepatic parenchyma and portal tract with loose or thick fibrosis, and infiltrated extensively into both intrahepatic and extrahepatic stroma along the vascular structures. From these clinicopathological findings, we consider the present tumor to be a variant of mucinous cholangiocarcinoma with characteristic microcyst formation rather than a type of cystadenocarcinoma.