The Spontaneously Diabetic Torii (SDT) rat is a rat model of nonobese
type 2 diabetes mellitus, and
hepatocellular adenomas have not been reported in this model. We report a
hepatocellular adenoma with severe fatty change in a male 42-week-old SDT rat fed a high-fat diet. At necropsy, the animal had a whitish nodular mass of approximately 2 cm in diameter in the right medial lobe. Histologically, the mass was well demarcated from the surrounding tissues, slightly compressing the adjacent hepatic parenchyma and widely compartmented by fibrous connective tissues. The mass consisted of vacuolated
tumor cells resembling hepatocytes with a solid and occasionally trabecular growth pattern. Abundant neutral
lipids, which were positive for fat with
Oil Red O stain and which ultrastructurally had moderately dense material, were contained within the vacuoles of the
tumor cells. Immunohistochemically, the
tumor cells showed an increase in immunoreactivity or number for
Cytokeratin 8/18 and
proliferating cell nuclear antigen but were negative for mesenchymal markers. From these findings, the mass could be distinguished from hepatocellular
hyperplasia and was diagnosed as
hepatocellular adenoma. In rats,
hepatocellular adenoma accompanied by severe fatty change is rare, and this is the first report of a hepatocellular
tumor with severe fatty change in a SDT rat.