Hepatic extraskeletal chondroblastic osteosarcoma with unusual angioinvasion of the caudal vena cava in a dog.

Abstract

Extraskeletal osteosarcomas are rare malignant mesenchymal neoplasms that are able to directly produce osteoid, without requiring a cartilage template. The extraskeletal localization indicates that these neoplasms are not associated with pre-existing skeletal elements or periosteum. We describe the gross and histological findings of a 4-year-old male Rottweiler that presented with an extraskeletal chondroblastic osteosarcoma (also known as osteosarcoma of the chondroblastic subtype) originating from the liver and extending into the lumen of the caudal vena cava, passing through the right atrium and terminating in the right ventricle of the heart immediately below the pulmonary valve. In the liver, predominantly fusiform cells grew in loosely packed streams and whorls. In the vena cava, the neoplasm was multilobular with polygonal neoplastic cells scattered within lacunae in a chondroid matrix. In the cardiac lumen, neoplastic cells produced osteoid that showed multifocal mineralization. Immunohistochemical staining showed no cytokeratin and variable S-100 protein and vimentin immunoreactivity. To the best of our knowledge, this is the first report of a chondroblastic osteosarcoma arising in the liver and showing such extensive and unusual extension into the vasculature.