Key points
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Cardiac magnetic resonance (CMR) is a robust technique in the evaluation of cardiac mass.
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The advantage of CMR includes the large field of view, superior tissue contrast, multiplanar reconstruction, and unique ability to discriminate tissue characteristics.
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CMR core protocol for assessment of cardiac mass includes cine SSFP, T1-W, T2-W, first pass perfusion, postcontrast T1-W, and late gadolinium enhancement (LGE) sequences.
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Strong early contrast enhancement on postcontrast T1-weighted images is more suggestive of a malignant, highly vascular lesion, although mild contrast enhancement is still seen in 40%–50% of benign tumors.
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Secondary cardiac tumors (metastasis) are more common than primary benign cardiac masses.
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Myxoma is the most common primary benign cardiac mass.
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Lipoma is the second most common primary cardiac tumor.
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The most common primary benign cardiac tumors in pediatric patients are rhabdomyoma and fibroma.
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The left atrium is the most common chamber is involved by primary benign cardiac mass.
CMR protocols for cardiac and paracardiac masses, including thrombous
A core protocol for the MR imaging assessment of cardiac masses and tumors mention, follow. However, cardiac masses vary widely and therefore any standardized protocol needs to be tailored to the specific mass lesion.
- 1.
LV structure and function
- 2.
T1w FSE—slices through the mass and surrounding structures (number of slices depends on size of the mass)
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T2w FSE with fat suppression (optional—without fat suppression)—through the mass and surrounding structures as earlier
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First-pass perfusion module with slices through mass
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Repeat T1w FSE with fat suppression (early after GBCA)
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Optional—Repeat selected bSSFP cine images postcontrast
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LGE
- a.
Images with the TI set to null thrombus (approximately 500–550 ms at 1.5 T, 850–900 ms at 3 T) will help differentiate thrombus from the tumor as well as delineate thrombus surrounding or associated with tumors
- b.
Serial imaging can help distinguish hypoperfused tumor necrotic core from thrombus
- a.
Tissue characteristics
In MR imaging, the relative signal intensity from a particular tissue depends principally on its proton density and the T1 and T2 relaxation times. Different tissues have different T1 and T2 relaxation times owing to different internal biochemical environments surrounding protons. By weighting images to emphasize on either T1- or T2-based contrast, MR imaging can exploit differences in signal intensity to discriminate between different tissue types ( Table 1 ). Neoplastic cells tend to be larger than normal cells, contain more free intracellular water, and are usually associated with surrounding inflammatory reactions and increased interstitial fluid. Because water molecules are small and move so rapidly for an efficient relaxation, the higher free water content of the malignant tissue, as well as other changes in tissue composition, leads to prolonged T1/T2 relaxation times and thus an inherent contrast between tumors and normal tissue . In addition, tumors containing fibrotic or lipomatous material show characteristic signal intensity patterns on MR images ( Table 1 ) .
| Cardiac mass | T1-weighted a | T2-weighted a | After contrast administration |
|---|---|---|---|
| Myxoma | Isointense | High | Heterogeneous |
| Lipoma | High | High | No enhancement |
| Fibroma | Isointense | Low | hyperenhancement |
| Rhabdomyoma | Isointense | Iso to high intense | No or minimal |
| Fibroelastoma | Isointense | High | No enhancement |
| Paraganglioma | Hypo to Isointense | High | Strong enhancement |
| Hemangioma | Isointense | High | Hyperenhancement |
a T1- and T2-weighted imaging signal intensity is given relative to myocardium.
T1-weighted imaging. Targeted black-blood T1-weighted FSE images (e.g., pulse sequence parameters at our department: 1000/40; flip angle, 90°; section thickness, 6–8 mm, no gap; matrix, 512*512) in the optimal imaging planes defined earlier are acquired to cover the entire mass, with and without a fat saturation prepulse. Acquisition of T1-weighted images can be repeated after the intravenous injection of gadolinium-based contrast agent for further tissue characterization. Strong early contrast enhancement on postcontrast T1-weighted images is more suggestive of a malignant, highly vascular lesion, although mild contrast enhancement is still seen in 40%–50% of benign tumors. Differential enhancement due to variation in tumor vascularity and altered capillary permeability allows some discrimination between the various tumor types as will be discussed in their individual section later .
T2-weighted imaging. Prior to the administration of contrast material, T2-weighted images should be acquired in the same imaging planes as T1-weighted images. These T2-weighted FSE images are acquired with breath hold, preferably triple inversion recovery with blood and fat suppression (e.g., pulse sequence parameters at our department: 2000/100; flip angle, 90°; inversion time, 160 msec; section thickness, 6–8 mm, no gap; matrix, 192*192), and can be used to detect regions of edema or liquefactive necrosis in the mass, which demonstrate high signal intensity, or regions of coagulative necrosis, which have low signal intensity . The presence of hemorrhage or thrombus also affects T2-weighted signal intensity depending on their chronicity.
First-pass perfusion and delayed enhancement imaging
After infusion of gadolinium chelate, first-pass rest perfusion imaging (based on a T1-weighted gradient echo sequence) of the tumor followed by 10–15 min delayed enhancement imaging (based on a T1-weighted inversion recovery sequence) assess lesion vascularity. Considerable first-pass enhancement is a typical feature for highly vascular tumors such as hemangioma or angiosarcoma. The presence of late phase gadolinium enhancement (LGE) implies delayed contrast washout from the lesion, usually as the result of extracellular space expansion or necrosis . LGE can be seen with both benign and malignant lesions. Benign tumors like fibroma usually display uniform LGE whereas tumors with a more heterogeneous composition like myxoma or angiosarcoma (containing a mixture of tumor tissue, necrosis, and foci of hemorrhage) usually show patchy areas of LGE.
Myxoma
Myxomas are the most common type of primary cardiac tumor (50%) and usually occur in the fourth to seventh decade of life. They are typically solitary, vary in size from 1 to 15 cm, and have a predilection for the interatrial septum near the fossa ovalis. Approximately 75% occur in the left atrium, 20% in the right atrium, and 5% concomitantly in both sides, either involving the atrium, ventricle, or mitral valve. They are generally well defined, smooth, lobular or oval, and often pedunculated. On MR images, they appear isointense on T1-weighted images and have higher signal intensity on T2-weighted images owing to the high extracellular water content ( Figs. 13.2–13.4 ). Regions of acute hemorrhage within myxomas appear hypointense on both T1- and T2-weighted images, while the older ones appear hyperintense as the hemoglobin becomes deoxidized to methemoglobin . Cine imaging is very useful in the workup of myxomas as they are highly mobile, occasionally prolapsing through the mitral valve causing an obstruction. With SSFP cine techniques, myxomas appear hyperintense relative to the myocardium but hypointense relative to the blood pool (Movie [online]).
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