Atypical chondroblastic osteosarcoma in the axial skeleton in a dog

Abstract

Osteosarcoma is the most common malignant bone tumor in dogs, most frequently affecting middleto old-aged animals. It is a tumor of mesenchymal origin with great potential for the development of metastases, and is characterized by its aggressive and invasive behavior. In the axial skeleton, primary osteosarcoma is rare but may occur in the ribs, sternum, vertebrae and skull. This paper reports an atypical case of primary chondroblastic osteosarcoma of the rib with esophageal metastasis in a dog. The patient had muffled heart sounds on auscultation, expiratory dyspnea, and severe dehydration. Thoracic radiography showed generalized enlargement of the heart silhouette, suggestive of pericardial effusion. Because of a suspicion of intrathoracic neoplasia and the poor general state of the patient, euthanasia was advised. Necropsy revealed a neoplastic mass within the thoracic cavity, adhered to a rib and the sternum and pericardial sac, in addition to a metastatic mass in the esophagus. Histopathological examination confirmed the diagnosis of this neoplasia. This report describes an unusual case of primary chondroblastic osteosarcoma of the rib in a dog with metastasis in the esophagus. It is considered unusual because of the location of the tumoral mass inside the thoracic cavity and external adhesion to the pericardial sac.