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 |
Most clinically indicated CMR images are obtained on 1.5T field strength magnets, though in recent years 3T imaging has been making a significant advance in quality and availability. The signal intensity of a neoplastic lesion is dependent on the tissue morphology and CMR parameters employed to obtain the images. Fig. 14.4 illustrates a CMR protocol recommended for the evaluation of cardiac masses . Axial plane images with T1-weighted (T1W) and T2-weighted (T2W) sequences are used for native tissue characterization and are the first step in CMR evaluation. In recent years, the evolution of CMR parametric mapping has provided us with the ability to quantify myocardial tissue alterations based on T1, T2, and T2*(star) relaxation times and extracellular volume (ECV) measurements . In turn, these values can be used in conjunction with qualitative T1W and T2W images in differentiating between cardiac tumors. For instance, a hypointense mass on T1W (or low T1 on T1 mapping) may represent a calcified tumor, meanwhile, hyperintensity on T1W images (high T1 on T1 mapping) can be seen in masses with high-fat content (e.g. lipomas and liposarcomas), hemorrhagic or highly vascularized tumors (e.g. angiosarcoma and hemangioma), as well as in melanomas ( Table 14.5 ). On T2W images, highly vascularized tumors such as angiosarcoma present with hyperintense signal (high T2 on T2 mapping), in contrast to fibrous tumors which are hypointense (low T2 on T2 mapping). Importantly, the most common benign primary tumor, cardiac myxoma, also presents as bright/hyperintense on T2W and with high values on T2 mapping and in instances may present a diagnostic challenge ( Fig. 18.8 ).
In contrast to qualitative assessment on T1W and T2W images, mapping permits quantification and may allow visualization of the disease process related to intra- and extracellular disturbances. Though current clinical evidence is scarce, mapping techniques can be used to characterize masses, pericardial effusion, and fatty lesions within the heart. For example, vascularized tumors with high water content have long T1 and T2 relaxation times, while they have low T1 values postcontrast update due to significant gadolinium contrast uptake . Although significant advances have been made in parametric mapping techniques, future research and validation are needed before routine clinical application for diagnoses of cardiac tumors. When describing T1W and T2W imaging with hyperintense or hypointense findings for various tumors, this information can also be obtained using T1 and T2 mapping.
Steady-state free precession (SSFP) technique is a valuable sequence to assess the relationship between the tumor with the myocardium, pericardium, blood pool, valves, and adjacent tissues. Assessment of tumor movement with respect to normal cardiac structure during cardiac cycle provides information on tumor attachment and whether tumor growth is invasive. Additionally, the hemodynamic effects on cardiac pumping and valvular function can be evaluated by cine SSFP images. Also, phase contrast flow imaging can be used to quantify hemodynamic effects with, e.g. increases in flow velocity if the tumor is affecting ejection or filling of blood.
Beyond native tissue characteristics, gadolinium contrast infusion can be employed to discern cardiac masses from normal cardiac structure through first-pass perfusion and late gadolinium enhancement (LGE). First-pass perfusion is conducted with dynamic imaging during infusion of contrast and is an important method to identify tumor vascularity and presence of necrosis. Masses such as hemangioma and to a lesser degree angiosarcoma tend to show early enhancement after contrast infusion and are easily distinguishable from other lesions . As malignant tumors frequently cause tissue necrosis by obliteration of capillary beds, first-pass perfusion images may exhibit dark central areas (necrosis) with hyperenhancement of the surrounding tissue, an important diagnostic measure to differentiate benign from malignant tumors. Late gadolinium enhancement (LGE) sequences are obtained 10 min postcontrast administration. Benign cardiac masses more often present as markedly homogeneous enhancing lesions (with the exception of myxoma), while malignant tumors present heterogeneous contrast enhancement due to extensive vascularity and necrosis. To discriminate normal myocardium from neoplastic masses, the inversion time is set to null normal cardiomyocytes as the exact inversion time varies depending upon patient physiology, timing postcontrast administration, and type of sequence.
Primary malignant tumors
Cardiac sarcomas
Cardiac sarcomas are the most common primary malignant tumor of the heart and together represent more than two-thirds of all malignant primary tumors . Cardiac sarcomas occur mainly in adulthood, usually between the third and fifth decades of life, and are often asymptomatic until advanced with dismal prognostic results . Many subtypes have been described based on histological characteristics (e.g., angiosarcoma, rhabdomyosarcoma, fibrosarcoma, leiomyosarcoma, liposarcoma, synovial sarcoma, intimal sarcoma, myxofibrosarcoma, and undifferentiated pleomorphic sarcomas) which largely share imaging appearances ( Table 14.1 ). Angiosarcomas are the most common subtype in adulthood, accounting for approximately 40% of all cardiac sarcomas, while rhabdomyosarcomas are the most common in the pediatric population .
Angiosarcoma
Angiosarcomas commonly present in the right atrium, manifesting with symptoms of right-heart failure, hemorrhagic pericardial effusions, and metastatic invasion . Histologically, angiosarcomas present with widespread infiltrative anaplastic cells derived from blood vessels, often highly vascularized with pleomorphic mitotic figures and areas of extensive hemorrhage and necrosis ( Table 14.1 ). These tissue characteristics may be seen on CMR imaging as heterogeneous T1W and T2W signal intensity, in part due to tissue necrosis and hemorrhage. On LGE images heterogeneous enhancement may be seen as a result of central necrosis (hypointense) and fibrotic margins (hyperintense) ( Fig. 14.6 ).
Rhabdomyosarcoma
Rhabdomyosarcomas are malignant tumors of striated muscle and are the most common pediatric cardiac malignancy . Unlike other cardiac sarcomas, these tumors arise from the myocardium and frequently affect multiple sites within the heart, frequently involving the valves. Often times they grow to be > 10 cm in diameter, and as described in Table 14.1 , they are made up of rhabdomyoblasts containing glycogen and expressing desmin, myoglobin, and myogenin . CMR findings of this tumor typically include isointensity on T1W and hyperintensity on T2W images, with diffuse enhancement after contrast administration. Depending on the extent of central necrosis and the volume of necrotic tissue, regions of hypointensity may be present at the center of the mass.
Leiomyosarcoma
Primary cardiac leiomyosarcomas are the second most common type of cardiac sarcomas in adult patients, accounting for 8% to 9% of all cardiac sarcomas . They are known to mimic myxomas and have a predilection for the posterior left atrium, pulmonary vein, and mitral valve. Leiomyosarcoma often presents as a sessile mass on SSFP cine images with a gelatinous base . They arise from smooth muscle and as mentioned before, they have the propensity to involve the valves ( Table 14.1 ). Leiomyosarcoma, as opposed to angiosarcomas, is characterized by slow and asymptomatic growth. Due to the oligosymptomatic course, they are usually diagnosed in advanced stages. CMR imaging descriptions are scarce due to the rarity of the condition, but it is commonly described as isointense or hypointense on T1W images, and hyperintense on T2W images . Diffuse enhancement is frequently observed after administration of gadolinium contrast.
Osteosarcoma
Primary cardiac osteosarcomas are extremely rare, making up 3% to 9% of primary cardiac sarcomas . As opposed to metastatic osteosarcomas that frequently involve the right atrium, primary cardiac osteosarcomas predominantly involve the left atrium which makes it easy to be mistaken for myxomas. However, presence of dense calcification, wide-based attachment, and location away from fossa ovalis with frequent invasive behavior can be helpful in differentiation. They may have osteo-, chondro-, or fibro-blastic substances with atypical spindle or ovoid cells . This tumor is best seen on computed tomography (CT) as low attenuated masses with dense calcifications will not be seen on CMR. (For details of CT imaging in malignant masses, we direct the reader to Chapter 12 .) On CMR imaging, osteosarcomas tend to be heterogeneously hypointense on T1W and hyperintense on T2W images .
Primary cardiac lymphoma
Primary cardiac lymphomas are rare tumors and when found, they most often fall in the category of aggressive large B-cell lymphoma, a subtype of non-Hodgkin lymphoma (NHL). It is much more common for extracardiac NHL to metastasize to the heart, and approximately 25% of all patients with disseminated disease have evidence of heart involvement . Primary cardiac lymphomas are more frequently seen in immunocompromised individuals and are strictly confined to the heart and/or pericardium . They have the tendency to involve the right side of the heart, in particular the right atrium, and frequently involve multiple structures . The pericardium is involved in approximately about one-third of reported cases and superior vena cava involvement is seen in up to 25% of all cases . Microscopically, they consist of malignant lymphoid cells with firm nodules of homogeneously appearing tissue, without apparent hemorrhage or necrosis . On CMR imaging, primary cardiac lymphomas are commonly hypointense on T1W and hyperintense on T2W ( Fig. 14.7 ). On first-pass-perfusion, lymphomas often rapidly enhance while the appearance on LGE sequences may vary from homogeneous to heterogeneous enhancement. Postcontrast images also help delineate presence of pericardial nodularity, inflammation, and enhancement. Primary cardiac lymphomas may have adjacent thrombi that are seen as absence of enhancement on LGE sequences ( Fig. 14.8 ).
