Nodular hyperplasia of the liver in the beagle dog.

Gross and light microscopic features of focal nodular hyperplasia of the liver were investigated in beagle dogs used for the study of the long-term effects of low-dose, whole-body, 60Co gamma radiation. The nodules were morphologically similar in the irradiated and unirradiated dogs. Microscopically, and normal lobular architecture, although retained, often was distorted. Hepatocytes in the nodules often were vacuolated and the distribution of vacuolated cells varied from focal to diffuse. There were more hepatocytes per unit area within nodules than in the adjacent parenchyma. Nodule hepatocytes were more variable in size. A lower proportion were binucleate and a higher proportion were in mitosis. The cells in the nodules contained less hemosiderin. The incidence of hyperplastic nodules was directly related to age but not to sex, was higher in irradiated dogs than in controls. Nodular hyperplasia occurred in association with primary hepatocellular neoplasms in only two dogs.