RESUMO
Mesothelioma is a primary neoplasia of body cavities, of rare occurrence , with origin in the mesenchymal cells lining serosal surfaces. The most frequent location of this neoplasias is the pleura, followed by the peritoneum and occasionally, the pericardium. The disease can be present in a benign way, through polyps or isolated nodules, or in a malignant way, spreading over the whole mesothelium. The present work reports a case of one female English cocker spaniel, 5 year-old, with history of breathing difficult and increased abdominal volume. Clinical examination revealed dispnea and ascitis; cardiopulmonar ausculation revealed muffling of heart murmurs. Thoracic X-ray was suggestive of severe pelural effusion. In the electrocardiogram, milivoltage suppresion was observed, without any rhythm alteration or other pathological finding. Thoracocenteses revealed mesothelial cells. The treatment was conducted in order to decrease the pleural and abdominal effusion. The animal died after 40 days of treatment. At necropsy large amount of liquid was verified in the thoracic cavity and a smaller volume in the abdomen; it was observed countless nodules varying in diameter from 5 mm to 3 cm, located in the thoracic and abdominal wall lining , diaphragm, omentum and subcutaneous tissue. The histopathologic exam confirmed the diagnosis of malignant mesothelioma.