Nodular hyperplasia in the liver of the dog: an association with changes in the Ito cell population.

The prevalence and morphological features of hyperplastic nodules in the liver of the dog were studied in a series of 50 consecutive post-mortem examinations. Macroscopically visible nodules were present in 35 of 50 dogs (70%), and the prevalence was related to age. The earliest age at which nodules were found was between 6 and 8 years. They were present in all dogs older than 14 or more years. The lesions were focal, multiple and consistently had evidence of a lobular pattern. There was no liver fibrosis. No direct association between previous drug administration or specific extrahepatic disease was found. Changes in the perisinusoidal fat storing cells (Ito cells) were observed in the dogs in this study. These changes comprised proliferation and hypertrophy and were recorded predominantly in dogs with hepatic nodules. The presence of a ceroid pigment was correlated with these changes. The pigment, together with lipid and macrophages, was present in the form of lipogranulomata. Lipogranulomata were observed in the parenchyma and in the portal areas of dogs with hepatic nodules. These changes may play a role in the pathogenesis of nodular hyperplasia in the liver of the dog.