mALIgNANT mESENCHYmOmA Of THE AORTIC VALVE IN A dOg

Summary: A malignant mesenchymoma of the aortic valve with an infiltrative growth into the myocardium in an 8-year-old intact male German shepherd is presented. Macroscopically, the aortic valve leaflets were markedly thickened, yellowishgrey and rough, with rounded edges, a rubbery consistency and greyish and smooth cut surface. Approximately 90% of the valve tissue was altered. Microscopically, alteration consisted predominantly of liposarcomatous, fibrosarcomatous and leiomyosarcomatous components and a focus of chondrosarcomatous cells. Focally, liposarcomatous cells infiltrated the myocardial muscle fibres. Mitoses were rare. Histopathologically, malignant mesenchymoma of the aortic valve was diagnosed. The diagnosis was confirmed by immunohistochemistry. A strong diffuse positive reaction for vimentin and a negative reaction for desmin were observed in all neoplastic components. In leiomyosarcomatous component a strong positive reaction for smooth muscle actin (SMA) was detected multifocally. Severe dilatation of all heart chambers, mild endocardiosis of the mitral and tricuspidal valves, severe congestion of the liver, spleen, kidneys and lungs with severe pulmonary oedema, moderate ascites and mild hydrothorax were also observed. We conclude that the dog died of chronic heart failure induced by malignant mesenchymoma of the aortic valve and endocardiosis of the mitral and tricuspidal valves. Malignant mesenchymomas are uncommon tumours in animals and humans, rarely reported in dogs. To the best of our knowledge, this is the first report of a malignant mesenchymoma of the aortic valve with an infiltrative growth into the myocardium in animals.