Obstructive right ventricular outflow tract myxosarcoma in an adult dog

An 8-year-old female spayed German Shepherd cross was presented for acute onset of respiratory distress. Four days before presentation, the owner noticed a reduced appetite and reluctance to move. Clinical examination identified muffled lung sounds and a left base, diamond-shaped systolic murmur graded 4/6. Echocardiography identified pleural and pericardial effusion, ascites and a myxoid mass (39 mm/18.9 mm) obstructing the right ventricular outflow tract and interfering with the pulmonary valve function. Given the poor prognosis, the dog was euthanatised, and a postmortem examination was performed. Grossly, a mass with a heterogeneous appearance was identified below the pulmonary valve leaflets. Based on histopathological and immunohistochemical findings, a diagnosis of intracardiac myxosarcoma affecting the subvalvular region of the pulmonary artery was made. To the author's knowledge, this is the first report of right ventricle out flow tract myxosarcoma in the canine species.