Experimental liver cysts induced by 2-acetylaminofluorene.

Liver cyst formation was studied serially in an experimental model in which rats were fed a diet containing 0.02% 2-acetylaminofluorene, a carcinogen, for 6 weeks, followed by a normal diet for 42 weeks. Cysts appeared in the portal tracts at the 12th week, by which time the intrahepatic bile ducts had also proliferated and dilated. Some of the dilated bile ducts were cavernous or multicystic and appeared to represent a transitional form between the bile duct dilation and cystic formation. After 20 weeks cysts were observed in the majority of rats. The number and the size of cysts in the liver increased with time; after 40 weeks, there were up to 20 cysts as large as 15 mm in diameter. Carcinoma or cirrhosis did not develop in this model. Indocyanine green dye injected intravenously did not accumulate in the cysts, which denies the possibility of communication between cysts and the bile duct. Scanning electron microscopy demonstrated that the cysts were composed of a few intercommunicating cavities and were lined with epithelial cells similar to those of the intrahepatic bile duct, which had numerous microvilli and a central cilium. These observations suggest that liver cysts originate in the bile duct.