Abstract
An 11-year-old female French Bulldog was presented with a mass at the base of the heart, detected by X-ray and echocardiography. Clinical abnormality included abdominal retention by ascites. Radiation therapy was performed for 5 weeks. The mass volume didn't change during the radiotherapy. The condition became worse and the dog died 6 months after the initial presentation and necropsy was performed. Grossly, the mass, 12.5 × 6.5 × 6.0 cm in size, was found at the base of the heart. Histopathological examination revealed that cardiac mass was composed of alveolar, bundle and diffuse proliferation of neoplastic cells. Most of the neoplastic cells showed a spindle morphology; in some areas small round or polyhedral neoplastic cells were observed. Occasional cartilage metaplasia was seen multifocal in the mass, and it was surrounded by the sarcomatoid proliferation. Electron microscopy revealed a few neuroendocrine granules in the cytoplasm of spindle and polyhedral neoplastic cells. Metastatic cells in the lungs which had not irradiated demonstrated typical morphology of aortic body tumors. Based on these findings, the case was diagnosed as an aortic body carcinoma with sarcomatoid morphology and chondroid metaplasia.