Primary Pulmonary Chondrosarcoma in a Bitch

Background: Primary lung neoplasms are uncommon in veterinary medicine, and when they develop, they are more frequently observed to be of epithelial origin. Although chondrosarcomas are the second most diagnosed type of neoplasm in dogs at skeletal sites, their development in extraskeletal tissues, including the spleen, aorta, heart, tongue, peritoneum, and lungs, corresponds to approximately only 1% of cases. Therefore, the occurrence of primary pulmonary chondrosarcoma is considered very rare in domestic animals. Considering the rare occurrence and scarcity of data regarding its development, the present report describes the clinical and pathological aspects of a case of primary pulmonary chondrosarcoma in a bitch. Case: A 8-year-old mixed-breed bitch, weighing 14.2-kg, was examined at one private veterinary clinic with the principal complaint of prolonged respiratory distress and resistance to exercise. Clinical evaluation revealed tachypnea with expiratory dyspnea due to intense pleural effusion, tachycardia, and diffusely pale mucous membranes. Thoracocentesis was performed with drainage of 1000 mL of modified transudate, and fluid cytology, blood count, and chest radiography were performed. Cytological analysis of the thoracic fluid did not identify neoplastic cells, the blood count showed intense regenerative anemia, and the radiograph showed an extensive area of consolidation in the left caudal lung lobe, compatible with neoplasia. The results of the tests performed, in addition to the evolution of the clinical picture and the impossibility of performing the indicated surgical intervention, culminated in the patient's unfavorable prognosis, followed by euthanasia, necropsy, and histopathological evaluation of the collected material. Necropsy revealed a white neoplastic formation with reddish areas and firm consistency that diffused into the parenchyma of the left caudal lung lobe with invasion of the rib cage, fracture of the fifth and sixth left ribs, diaphragmatic metastasis, intense hydrothorax, and moderate hydroperitoneum. Microscopically, in the histological sections of the lung and diaphragm, poorly differentiated mesenchymal cells with moderate anisocytosis and anisokaryosis and interspersed with them, moderately differentiated chondrocytes surrounded by chondroid matrix, moderate anisocytosis and anisokaryosis, and a low mitotic index culminated in the diagnosis of primary pulmonary mesenchymal chondrosarcoma. Discussion: Malignant epithelial neoplasms were suspected; however, the histopathological features observed were compatible with primary pulmonary chondrosarcoma. The characteristics of the fluid collected through thoracentesis led to its classification as a modified transudate, which is often associated with neoplastic and hemorrhagic processes; both alterations were present in this case. The diagnosis of primary pulmonary chondrosarcoma was established based on the histopathological findings since the cell type and distribution observed in the present case were compatible with the typical pattern observed in extraskeletal chondrosarcomas. An unfavorable prognosis is common in cases of primary or metastatic lung neoplasm since, in most cases, the condition is identified in the advanced stages of the disease, making therapeutic management challenging. Given the increase in the number of dog deaths due to neoplasms in recent years, this case report may contribute to a better understanding of the biological behavior of pulmonary chondrosarcoma and assist in the choice of treatment to be adopted when required. Keywords: dog, malignant neoplasm, mesenchymal; extra skeletal, respiratory system, pathology.