Ultrastructure of hepatocellular neoplasms in aflatoxin B1 (AFB1)-initiated rainbow trout (Oncorhynchus mykiss).

The fine structure of hepatocellular neoplasms from aflatoxin B1 (AFB1)-initiated rainbow trout was studied by transmission electron microscopy. Large, usually uniform hepatic nuclei, large nucleoli, abundant, dilated rough-surfaced endoplasmic reticulum, and reduced glycogen storage were common findings in both hepatocellular adenomas and hepatocellular carcinomas. In addition, the presence of poorly developed microvilli in the space of Disse and in bile canaliculi, the occurrence of few or no bile preductule cells and a striking increase in the size and number of intercellular spaces characterized hepatocellular carcinomas. The three latter characteristics of hepatocellular carcinomas suggest loss of inter-relationships between hepatocytes and the microvascular system (sinusoids), between hepatocytes and the biliary system, and between individual hepatocytes, respectively. With respect to these parameters, adenomas were more similar to normal liver than to carcinomas.