Cystic cholangiofibrosis of the liver.

We have studied with electron microscope the cysts formed in the liver of rats fed acetylaminofluorene in order to further characterize the lesion and its histogenesis. The cysts were lined by cuboidal and flattened epithelium or both and resembled bile ductular cells. Most of the flattened cells showed adaptive and degenerative changes indicative of pressure atrophy. The cuboidal cells lining the smaller ducts showed ultrastructural signs of activity. Similar "active" cells were seen in the outpouchings of the larger cysts. Our data indicate that the cysts are of cholangiocellular origin. Ultrastructurally the cells forming the cysts showed no signs of anaplasia and represent more likely the end point of bile ductular proliferation than a stage in development of biliary neoplasia.