Filling defects in an atrial cavity may be due to bland thrombus, tumor thrombus, an atrial myxoma, a metastasis and lymphoma. The commonest primary atrial tumor is a myxoma.
Tumor thrombus can be differentiated from bland thrombus using CT arteriography or FDG PET imaging.
Atrial metastasis is uncommon, the primary site maybe melanoma or a primary renal cancer.
Atrial thrombus resulting from IVC extension is most commonly seen when a renal cancer involves the renal vein and IVC.
Primary leiomyosarcoma of the IVC may also involve the right atrium.