46 year-old female admitted for TIA.

Figure 1: There is a 5 x 4 cm mass that demonstrates high T2-weighted signal protruding through the mitral valve into the left ventricle.

Figures 2 and 3: There is a 5 x 4 cm low T1-weighted mass that appears as a filling defect in the left atrium.

Left atrial myxoma.

The most common cardiac tumors are metastases and include melanoma, lung cancer, breast cancer, and lymphoma. Primary cardiac tumors are rare. Benign cardiac tumors make up the majority of these lesions, and include cardiac myxoma (most common primary cardiac neoplasm), papillary fibroelastoma, rhabdomyoma, fibroma, lipoma, and paraganglioma. Malignant cardiac tumors account for 25% of the primary cardiac neoplasms, and include sarcoma (second most common primary cardiac neoplasm) and lymphoma. Cardiac tumors commonly present as intracavitary, mural, or epicardial focal masses. These tumors may demonstrate invasive features or may involve the heart diffusely. Pericardial neoplasms can also affect the heart and may mimic cardiac tumors. The two most common pericardial tumors are teratoma and malignant mesothelioma.

Cardiac myxoma, a benign neoplasm, is an endocardial mass usually arising from the fossa ovalis of the interatrial septum. The majority of cardiac myxomas are found in the left atrium, less commonly in the right atrium, and rarely in the ventricles. Left atrial myxomas commonly cause mitral valve obstruction with dyspnea and orthopnea or heart failure. Right atrial myxomas can obstruct the tricuspid valve and cause symptoms of right-heart failure. However, approximately 20% of patients with cardiac myxomas are asymptomatic.

Cardiac myxomas are endocardial-based masses that do not infiltrate the underlying tissues. Irregularly-shaped tumors have an increased tendency to form thrombi and embolize (as seen in this case). The majority of cardiac myxomas are attached to the endocardium via a broad-based or pedunculated stalk.

The radiographic features of cardiac myxomas reflect the location of the tumor. Left atrial myxomas typically demonstrate evidence of mitral valve obstruction including left atrial enlargement and pulmonary venous hypertension. Right atrial myxomas often demonstrate tumor calcification and cardiomegaly.

On MRI, myxomas appear as ovoid, lobular masses with heterogeneous signal intensity. Multiplane and gradient-recall echo (GRE) images can usually accurately display the point of attachment to the endocardial surface. On T1-weighted images, the majority of myxomas are isointense (some can be hyperintense) relative to the adjacent myocardium which has intermediate signal intensity. Heterogeneous enhancement with intravenous gadolinium-based contrast is thought to result from the cellular matrix or inflammation within the tumors. Non-enhancing areas likely represent cyst or areas of tumor necrosis. Myxomatous components appear low on T1-weighted and high on T2-weighted sequences. Tumor calcification manifests as a low signal intensity, and subacute hemorrhage displays high signal intensity of both T1- and T2-weighted images. Cine GRE studies are helpful in demonstrating tumor motion and prolapse across an atrioventricular valve. Myxomas can appear dark on GRE imaging possibly due the high iron content of these lesions.

References:

1. Grebenc M.L., Rosado de Christenson M.L., Burke A.P., Green C.G., and Galvin J.R. Primary Cardiac and Pericardial Neoplasms: Radiologic-Pathologic Correlation. Radiographics 2000; 20: 1073-1103.
2. Araoz P.A., Eklund H.E., Welch T.J., and Breen J.F. CT and MR Imaging of Primary Cardiac Malignancies. Radiographics 1999 Nov-Dec; 19(6): 1421-34.