Primary hepatic fibrosarcoma in a wistar rat (Rattus norvegicus)

Abstract

Soft tissue sarcomas are a heterogeneous group of malignant neoplasms with different morphological patterns of mesenchymal lineage. This type of neoplasm is most commonly found in the subcutaneous tissue but is rare in solid organs, such as the liver and kidneys. This paper describes the main anatomopathological alterations in the liver of a Wistar rat (Rattus norvegicus) with soft tissue sarcoma. A two-year-old male pet Wistar rat was referred to the Laboratory of Veterinary Pathology at the Federal University of Fronteira Sul. The owner reported apathy and the animal died during physical examination. At necropsy, 10 ml of a reddish liquid was found in the thoracic cavity. The left lateral liver lobe contained a 5-cm mass of heterogeneous surface composed of whitish parenchyma and red multifocal lesions extending to the surface of the liver. Moreover, whitish dotted spots intercalated with dark and more friable spots were found in the whole left lateral liver lobe. Histopathological evaluation of the nodule revealed the formation of spindle cells in parallel bundles with slightly eosinophilic cytoplasm, elongated nucleus, hyperchromatic to granular chromatin, and inconspicuous nucleolus. Extracellular matrix and mineralization were also observed. An area with proliferation of spindle cells with elongated cytoplasm, round to oval nuclei, sometimes hyperchromatic, consistent with cells found in the liver was noted in the mesenteric lymph node and omental node. Masson Trichrome staining revealed tumor cells stained in blue. Immunohistochemistry was performed and revealed positive staining for vimentin and negative for pan-cytokeratin, S100, desmin and factor VIII. Thus, the histological, histochemical and immunohistochemical evaluations suggested hepatic fibrosarcoma. This report showed the histological and immunohistochemical findings of a poorly described tumor in a Wister rat in veterinary literature.