A 30 year old woman was admitted to our hospital because of shortness of breath and general fatigue that developed progressively. Transthoracic and transoesophageal echocardiography demonstrated an abnormal mass located just proximal to the pulmonary valve and occupying the right ventricular outflow tract. The magnetic resonance images in transverse (left) and sagittal (right) views also showed a huge mass of heterogenous density in the right ventricular outflow tract. A moderate amount of pericardial effusion was noted. The increase in size of the right ventricle with presence of the flattened ventricular septum suggested increased right ventricular pressure. In the sagittal view (right) part of the mass seemed to invade the ventricular free wall extensively, suggesting the possibility of a malignant tumour. As a result, the right ventricular outflow tract and part of the pulmonary artery was extensively resected and reconstructed. Histology from the resected mass confirmed that the tumour consisted of an osteosarcoma that commonly occurs in the left atrium and frequently demonstrates calcification, although the magnetic resonance image did not show the calcified lesion. Magnetic resonance imaging can help to differentiate malignant from benign tumours by revealing certain features—such as a broad base of attachment as shown in this case—probably better than conventional echocardiography.

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