Left ventricular myxosarcoma in a dog

An entire male Neopolitan mastiff, aged two years and eight months, presented with a history of chronic diarrhoea and weight loss. The diarrhoea had been present for approximately 12 months and had progressively worsened, with weight loss developing over an eight-week period prior to presentation. No primary gastrointestinal or metabolic cause for the diarrhoea could be identified. Echocardiography revealed a large, multilocular, cyst-like structure within the pericardium compressing the heart and displacing it to the right. The mass was surgically excised from the left ventricular myocardium. Histopathological examination showed it to be a low-grade malignant myxosarcoma. The dog made a full recovery and was still clinically normal nine months postoperatively, with no evidence of tumour recurrence or metastases. However, 11 months postsurgery, the clinical signs of diarrhoea and weight loss returned. Tumour recurrence with local metastasis was diagnosed and the dog was euthanased 358 days after the original surgery.