Key points
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Cardiac magnetic resonance (CMR) is the gold standard noninvasive imaging modality to assess tissue characteristics in vivo which gives it a unique advantage in discriminating benign cardiac masses from malignant tumors. CMR also provides visualization of tumor invasion, hemodynamic effects, and location relative to surrounding cardiac and extracardiac structures. These features make CMR an essential tool for diagnosis and management of cardiac tumors.
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The following sequences form part of a comprehensive CMR exam: cine imaging (e.g. balanced steady state free precession (bSSFP)), T1/T2-weighted black-blood (BB) images, T1/T2 mapping, first-pass perfusion, and delayed enhancement imaging. The characteristics of the tumor are often described as hyper/iso/hypo-intense, meaning higher, equal to, or lower signal intensity compared to normal myocardium. For instance, the extensive vascular networks associated with malignant tumors often present as hyperintense on first-pass perfusion and on late gadolinium enhancement (LGE) images. The high volume of intracellular free water content in malignant tumors and the frequently observed surrounding edema may lead to longer T1 and T2 relaxation times. At the same time, necrosis and hemorrhage within the tumor often result in heterogeneous signal on T1W and T2W BB images. The newer T1 and T2 mapping techniques provide quantitative T1 and T2 values, instead of the relative grayscale obtained through T1W and T2W BB imaging, providing an opportunity to further advance the diagnosis of malignant cardiac tumors.
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CMR limitations include absolute and relative contraindications for imaging in patients with devices that are not MR compatible (e.g., noncompatible pacemakers, internal defibrillators, mechanical circulatory support devices, etc.). Breath-holds are often used in clinical protocols and patients that cannot hold their breath often have decreased image quality. Similarly, the need for ECG gating makes CMR a challenge in patients with irregular heart rhythm as it can lead to acquisition artifacts and poor image quality.
Abbreviations
2CH
2-chamber
4CH
4-chamber
BB
black blood
bSSFP
balanced steady-state free precession
CMR
cardiovascular magnetic resonance imaging
CNS
central nervous system
CT
computed tomography
FPP
first-pass perfusion
FS
fat saturation
FSE
fast spin echo
LGE
late gadolinium enhancement
LV
left ventricle
RV
right ventricle
SAX
short-axis
SSFP
steady-state free precession
T1W
T1 weighted
T2W
T2 weighted
TEE
transesophageal echocardiography
TTE
transthoracic echocardiography
Introduction
Cardiac masses entail a heterogeneous group of disorders that can be broadly divided into benign and malignant tumors. Malignant cardiac tumors are exceedingly rare (compared to benign masses) and often present with significant diagnostic and therapeutic challenges. Cardiac magnetic resonance (CMR) imaging has emerged as a key noninvasive technique in their evaluation, primarily due to the superior tissue characterization without ionizing radiation exposure. Moreover, CMR provides visualization of cardiac tumor extension/invasion, relationship with surrounding cardiac and extracardiac structures, and the evaluation of hemodynamic effects. Malignant tumors can be further divided into primary and secondary cardiac malignancies ( Table 14.1 ). Among malignant primary cardiac tumors, the most common are sarcomas which account for about 75% of the cases, while primary cardiac lymphomas, mesotheliomas, neuroendocrine tumors, and others account for the remainder 25% of cases ( Table 14.1 ) . Secondary tumors can invade the heart by direct extension (e.g. pleural mesothelioma), intracavitary spread (e.g. renal cell carcinoma via inferior vena cava or lung carcinoma via pulmonary veins), and hematogenous or lymphatic, metastatic spread. The reports about the prevalence of cardiac metastases vary widely, from 2% to up to 18%; however, these estimates are largely based on autopsies and may not reflect the cases seen in cardiac imaging centers .
| Primary cardiac tumors | Morphologic characteristics | Histopathologic characteristics | Treatment considerations and prognosis |
|---|---|---|---|
| Cardiac sarcomas | |||
| Angiosarcoma | Invasive, sessile, and lobular | Present with myocardial infiltration, often highly vascularized with pleomorphism, mitotic figures, and areas of necrosis | When possible, surgical resection is recommended and is often considered to treat hemodynamic consequences and reduce tumor burden. Systemic chemotherapy and less often radiation therapy may be considered Poor prognosis with aggressive course |
| Undifferentiated sarcoma | Large, irregular, intracavitary mass | Typical spindle and polygonal cells, filled with eosinophilic cytoplasm | |
| Osteosarcoma | Invasive, sessile, lobular | Spindle cell lesions with malignant fibrous histiocytoma, microscopic foci areas of osteosarcoma, and chondrosarcoma in the spindle regions | |
| Leiomyosarcoma | Invasive, sessile, lobular | Blunt nuclei with bundles of spindled cells, areas of necrosis, mitotic cells with epithelioid regions | |
| Synovial cell sarcoma | Protruded mass with irregular, gelatinous appearance | Monophasic: Only contains spindle cells, no epithelial cells Biphasic: contains both epithelial and spindle cells | |
| Intimal sarcoma | Invasive, arising from large blood vessels and heart | Spindle and pleomorphic cells with myxoid area | |
| Fibrous histiocytoma sarcoma (pleomorphic and undifferentiated high grade) | Invasive, knoblike lesion |
| |
| Rhabdomyosarcoma | Invasive, lobular | Embryonal type with rhabdomyoblasts containing abundant glycogen and expressing desmin, myoglobin, and myogenin | |
| Primary cardiac lymphoma | Lobular, multiple lesions | Commonly diffuse large B-cell lymphoma. Other variations include Burkitt lymphoma, T-cell lymphoma, and low-grade B-cell lymphoma | Chemotherapy and immunotherapy, no role for surgery |
| Pericardial mesothelioma | Pericardial effusion and a tumor encasing the heart | Combination of epithelial or sarcomatous lesions, and/or biphasic | Highly aggressive with poor prognosis Palliative management |
| Secondary cardiac tumors | Smooth surface, often multiple lesions | Varies depending on the primary disease | Cardiac involvement confers a similar prognosis to stage IV cancer Management directed toward primary disease |
| Metastatic melanoma | Smooth surface, often multiple lesions | Malignant epithelioid cells with prominent nucleoli and frequent mitoses | Systemic therapy with targeted therapy per clinical guidelines |
In this chapter we describe current clinical indications for CMR and detailed CMR imaging protocol recommended for the comprehensive assessment and management of cardiac tumors. We then provide examples of applied CMR imaging and specific CMR findings with primary and secondary cardiac tumors.
Role of CMR imaging in establishing the diagnosis
The initial identification and evaluation of a cardiac mass most often starts with the readily available transthoracic echocardiogram (TTE). Echocardiographic findings, in turn, frequently represent an indication for CMR to (a) confirm abnormal cardiac mass (vs normal anatomical structure as described in Table 14.2 ) and (b) further differentiate between benign, malignant, and nontumorous masses (e.g. thrombus). CMR imaging protocols can be employed to evaluate hemodynamics, morphology, pericardial invasion, size, location, homogeneity, and signal characteristics of cardiac masses, and thus aid in differentiation between benign and malignant tumors . Features concerning for malignancy include large tumor size, involvement of the pericardium and the right heart, tissue heterogeneity, and high extracellular volume (ECV) determined by T1 mapping before and after gadolinium contrast infusion. A position paper published in 2020 by the Society of Cardiovascular Magnetic Resonance (SCMR) outlines clinical indications for the use of CMR in the evaluation and management of cardiac masses . Beyond diagnosis and differentiation of malignant masses, CMR is recommended for guidance of surgical therapy, assessment of treatment effect, as well as posttreatment surveillance ( Table 14.3 ) .
| Anatomical structure | Comments |
|---|---|
| Crista terminalis | Seen as a protuberance in the right atrium, may be perceived as angiosarcoma or primary cardiac lymphoma |
| Eustachian valve | Frequently observed in the right atrium |
| “Coumadin ridge” | Lies in the left atrium, in between the left atrial appendage and the left superior pulmonary vein |
| Chiari network | Occasionally seen in the right atrium near the entry site of inferior vena cava and coronary sinus |
| Moderator band | Seen in the right ventricle |
| False tendons of LV | Seen in the left ventricle |
| CMR indications | Level of evidence |
|---|---|
| I. Suspected cardiac mass | I |
| II. Differentiation between benign, malignant, and nontumorous masses | I |
| III. Guide surgery and/or biopsy if this is deemed appropriate | I |
| IV. Follow-up of benign cardiac tumors that do not require urgent intervention for changes over time | I |
| V. Evaluation of tumor resection/debulking, monitoring recurrence after surgery, and regression or progression after chemotherapy or radiotherapy | I |
| VI. Extracardiac extension of cardiac tumors or cardiac extension of tumors originating from surrounding structures | I |
| VII. Impact of cardiac masses on hemodynamics | I |
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