Clinical introduction A 66-year-old asymptomatic patient underwent a routine transthoracic echocardiogram prior to commencement of clozapine, and was found to have a mobile echogenic structure in the right atrium, which was later confirmed on transoesophageal echocardiogram to be adjacent to the insertion of inferior vena cava.

Follow-up cardiovascular MRI (CMR) revealed a mobile, avascular 2.1×2.2 cm² mass with regular and smooth borders, adjacent to the eustachian valve (Figure 1 panel A: coronal view; online supplementary movie 1). Late gadolinium enhancement (LGE; panel B) demonstrated heterogeneity, and T1-imaging demonstrated mild hyperintensity (panel C). There was no evidence of obstructive haemodynamic compromise.

The mass was subsequently resected, and the histology (H&E staining, magnification ×100) is shown in panel D.

Question The diagnosis of this mass is:

1. Aberrant liver

2. Angiosarcoma

3. Atrial myxoma

4. Renal cell carcinoma

5. Thrombus