Multislice or spiral single-slice CT scans in the axial plane after contrast enhancement are used to identify and determine the extent of masses (Fig. 35-1). For this evaluation, ECG-gated multislice CT acquisitions are not necessary. However, ECG-gated multislice CT is now sometimes used especially for evaluation of an intracardiac mass. Collimation is usually 1.25 to 2.5 mm. Retrospective reconstruction of volumetric data in the sagittal or coronal plane may be useful. Reconstructions in the sagittal and coronal planes are done routinely using the multislice axial data usually with slice thickness of 1.25 mm or less. Positron emission tomography/CT can also be used to indicate the likely malignant nature of intracardiac and paracardiac tumors (Fig. 35-2).

ECG-gated transaxial T1-weighted spin-echo (SE) images of the entire thorax are initially acquired for the evaluation of suspected cardiac or paracardiac masses. In addition, such images are frequently acquired in the sagittal or coronal plane to delineate the regions that are displayed suboptimally in the transaxial plane, such as the diaphragmatic surface of the heart. Coronal images facilitate the evaluation of masses involving the aortopulmonary window and pulmonary hili, and mediastinal masses that extend through the cervicothoracic junction. The wide field of view afforded by sagittal and coronal images can readily display the extent of tumors (Figs. 35-3 and 35-4). Contrast between intramural tumor and normal myocardium may be low on nonenhanced T1-weighted images. Transaxial T2-weighted SE images are acquired to enhance the contrast between myocardium and tumor tissue, which usually has a longer T2 relaxation time, and to delineate possible cystic or necrotic components of a mass. The comparison of signal intensities of a mass lesion on T1-weighted and T2-weighted images may to a certain degree allow for tissue characterization. For example, lipomas have relatively high signal intensity on T1-weighted images and moderate signal intensity on T2-weighted images. Cystic lesions (filled with simple fluid) have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (Fig. 35-5). The administration of Gd-DTPA (gadolinium diethylenetriamine pentaacetic acid) usually improves the contrast between tumor tissue and myocardium on T1-weighted images and may facilitate tissue characterization. Hyperenhancement of tumor tissue with MR contrast agents indicates either an enlarged extracellular space of tumor tissue in comparison with normal myocardium (Fig. 35-6) or a high degree of vascularization of the mass. Application of a fat-saturation sequence, which vitiates the bright signal of fat, is effective for the tissue characterization of lipomas (Fig. 35-7).

In patients with cardiac tumors, cine MRI provides valuable information regarding the movement of the cardiac mass relative to cardiovascular structures. Because cine MR images are acquired with gradient-echo or steady-state free precession (SSFP) sequences, a different contrast is obtained than with the SE technique. On SE images, flowing blood appears with low signal intensity, whereas gradient-echo or SSFP images display the blood pool with high signal intensity. Most studies using white blood imaging now use some form of SSFP sequence.

Myxoma is the most common benign cardiac tumor. It is located in the left atrium in 75% of cases and in the right atrium in 20% of cases. Multiple atrial myxomas may occur rarely, especially in Carney’s syndrome. This tumor is usually spherical, but the shape may vary during the cardiac cycle because of its gelatinous consistency. Left atrial myxomas are typically attached by a narrow pedicle to the area of the fossa ovalis (Fig. 35-9, A). Infrequently, myxomas have a wide base of attachment to the atrial septum (see Fig. 35-9, B). However, a wide mural attachment is more frequently encountered with malignant tumors. The extent of attachment may be difficult to assess for large tumors, which fill nearly the entire cavity so that they are compressed against the septum (Fig. 35-9, B). As a result, the tumor appears to have broad contact with the atrial septum on static MR images. Myxomas can grow through a patent foramen ovale and extend into both atria, a condition that has been described
as a “dumbbell” appearance. Cine MRI permits an evaluation of tumor motion and may help to identify the site and length of attachment of the tumor to the wall or walls of the cardiac chambers. With this technique, myxomas have been shown to prolapse through the funnel of the atrioventricular valve (Fig. 35-10) or into the corresponding ventricle during diastole. Rarely, myxoma can have a wide point of attachment to ventricular endocardium (Figs. 35-11 and 35-12).

Usually, myxomas display intermediate signal intensity (isointense to the myocardium) on T1-weighted SE images. On T2-weighted SE images, myxomas usually have higher signal intensity than myocardium. However, myxomas with very low signal intensity have also been observed. Fibrous stroma, calcification, and the deposition of paramagnetic iron following interstitial hemorrhage can reduce the signal intensity of the tumor on T2-weighted SE images. Rarely, myxomas have been reported to be invisible on SE images because of a lack of contrast with the dark blood pool. Such tumors can be delineated with cine MRI, on which they appear with high contrast against the surrounding bright blood. Most myxomas show increased signal intensity after the administration of Gd-DTPA on T1-weighted images (Fig. 35-13) and on delayed gadolinium-enhanced images, which is probably secondary to an increased interstitial space and, therefore, a larger distribution volume of the contrast agent within the tumor than in normal tissue.

Lipomas are reported to be the second most common benign cardiac tumor in adults but may actually be the most common. If the mass projects into the right atrium, it is called a lipoma, while lipomatous hypertrophy is confined to the atrial septum. They may occur at any age but are encountered most frequently in middle-aged and elderly adults. Lipomas consist of encapsulated mature adipose cells and fetal fat cells. The tumor consistency is soft, and lipomas may grow to a large size without causing symptoms. Lipomas are typically located in the right atrium (Fig. 35-14) or atrial septum. They arise from the endocardial surface and have a broad base of attachment. Lipomas have the same signal intensity as subcutaneous and epicardial fat on all MRI sequences. Because fat has a short T1 relaxation time, lipomas have high signal intensity on T1-weighted images, which can be suppressed with fat-saturating pulse sequences (see Fig. 35-14). Usually, they appear with homogeneous signal intensity but may have a few thin septations. They do not enhance after the administration of contrast. On T2-weighted images, lipomas have intermediate signal intensity.