Key points
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In spite of the fact that cardiac tumors are a very rare entity, their diagnosis and clinical management are of paramount importance in the field of cardio-oncology. In addition, confronting with cardiac and paracardiac masses, including neoplastic and nonneoplastic lesions, is not an uncommon diagnostic dilemma in practical cardiology .
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As a general rule in oncology, early accurate diagnosis of tumors could have a great impact on patients’ outcome by selecting a well-timed, appropriate, and efficient treatment. As a result, defining an accurate noninvasive diagnostic imaging modality with high specificity to introduce pertinent criteria for malignancy and differentiate it from the benign and especially from nonneoplastic lesions is of extreme clinical importance in terms of selecting the best therapeutic strategy to achieve the best prognosis and outcome .
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Clinical presentations of cardiac tumors constitute a broad range from an incidental finding during diagnostic imaging evaluation of an irrelevant clinical concern to critical manifestations including systemic embolization or those induced by mass effect such as arrhythmia, syncope, and cardiac tamponade, which are in part dependent on their locations and dimensions and could result in hampering the contractile function regardless of their histopathology .
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Although the histopathological results derived from biopsy are the point of reference for final diagnosis, considering the technical hazards, a presumptive identification of the lesion to precisely localize and to assess its relation to the cardiac structures is of great value. Furthermore, differentiation of malignancy from benignancy, if possible, could have a vital role in planning the forthcoming therapy and management .
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Considering the low incidence, there is not an established diagnostic imaging strategy for suspected cardiac masses. Echocardiography is widely available as the initial modality to detect cardiac masses with a high sensitivity. Nevertheless, several limitations either technically (such as poor acoustic window or difficulty in obese patients) or inherently, in particular for tumor assessment (such as lack of capability to tissue characterization), have been introduced for this modality. As the next step, when the echocardiography findings are inadequate or suspicious, however, cardiac magnetic resonance imaging (MRI), using different sophisticated techniques, is considered as the preferred and reference noninvasive diagnostic method to provide meticulous information on the size and location, structural details, histopathological characterization, and accurate estimation of extent of the mass; nevertheless, even this pivotal modality is susceptible to some limitations such as claustrophobia or contraindication of gadolinium administration in some patients . As an alternative method to MRI and an excessive part of morphological evaluation in some certain individuals, for example in whom with possibility of direct involvement of coronary arteries to define preferable surgical approach, cardiac computerized tomography (CT) enjoying excellent spatial resolution and fast acquisition time with capability to exhibit calcification and fat could be of help in tissue characterization along with providing useful morphologic information about cardiac masses .
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Positron emission tomography (PET) using tumor-targeted radiopharmaceuticals is widely accepted as an invaluable modality of molecular imaging to noninvasively assess variety of oncology issues, introducing acknowledged clinical indications such as tumor diagnosis, prognostic evaluation, clinical management, initial staging, restaging, differentiating benign from malignant lesions ( Fig. 16.1 ), tailoring therapy, detection of recurrence, therapy response assessment, and patient’s outcome study, every one of which depends on the histopathology and clinical status of certain types of cancers . Additionally, by merging molecular information of PET with morphologic data by CT or MRI, the hybrid imaging modalities, PET/CT and PET/MRI, can provide an accurate and efficient tool for many clinical applications of different scenarios in the field of oncology .
Fig. 16.1
Differentiation between neoplastic from nonneoplastic thrombus in patients with positive history of malignancy. Based on the metabolic rate of glucose and as an in vivo biological marker, FDG-PET can reflect the molecular functional state of tissues, which supplies additional information to anatomical imaging . (A) Fused PET/CT; (B) PET; and (C) CT images in a known case of melanoma and liver metastases accompanied with tumor thrombosis through the inferior vena cava up to the right atrium. CT , computed tomography; FDG , fluorodeoxyglucose; PET , positron emission tomography.
Fig. 16.3
Recurrence of tumor. Integrated FDG-PET/CT image: MIP (A) and sagittal section (B), hyperintense 18 FDG uptake illustrating cardiac hypermetabolic lesions ( arrows ) in the left atrium and the anterior mediastinum representing recurrent tumor in a known case of myxofibrosarcoma. CT , computed tomography; FDG , fluorodeoxyglucose; MIP , maximum intensity projection; PET , positron emission tomography.
Adapted from Erdoğan EB, et al. Appearance of recurrent cardiac myxofibrosarcoma on FDG PET/CT. Clin Nucl Med. 2014;39(6):559–560 with permission.
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Despite the fact that a number of specific tracers have been introduced for some specified clinical and research issues, the radiolabeled glucose analogue, F18-fluorodeoxyglucose ( 18 F-FDG), is the most recognized PET radiopharmaceutical in clinical oncology to evaluate the disease and even to change the management decisions and therapeutic courses in many common cancers . Based on the metabolic rate of glucose and as an in vivo biological marker, FDG-PET can reflect the molecular functional state of tissues, which supplies additional information to anatomical imaging and has been reported to be more sensitive than morphological changes while monitoring the treatment (see Boxes 16.2, 16.4 , and 16.5 ).
Box 16.2
FDG-PET/CT in cardiac masses.
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Notwithstanding the fundamental role of FDG-PET/CT in general oncology, given the limited amount of evidence, the clinical contribution of this key imaging modality has not yet been firmly established in the imaging workup of cardiac tumors. Nevertheless, the cumulative body of literature, albeit few in number of cases, has been indicative of incremental value of functional molecular imaging in diagnosis, treatment, and clinical management of this group of rare and complex entity .
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Apart from qualitative and visual assessment of metabolic activity, which per se is of ultimate clinical importance in evaluation of tumors, capability of quantification of metabolic activity is the distinctive characteristic of molecular imaging using FDG-PET. Measuring the glucose metabolic activity of lesions could provide valuable data to clarify different aspects of diagnosis, management, and therapy. Standardized uptake value (SUV) is an objective method of metabolic activity quantification in PET imaging, which has most commonly been used in practice so far. This method of quantitative study and its derivatives such as SUVmax, which are practically available in common software, have been widely investigated with excellent results in terms of interoperator reproducibility; these methods of quantification have also provided good results concerning sensitivity and specificity in differentiating malignant from benign lesions .
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The practicality and effectiveness of quantitative metabolic assessment in cardiac masses have been initiated to define the histopathological status of the lesion for planning the treatment strategy as well as for demarcating the target volume in radiation therapy, monitoring early therapeutic response for better estimation of the final results as complete or partial response, stable disease or progression, and ultimately for more accurate estimation of patients’ outcome .
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A universal cutoff value to distinguish benign from malignant lesions has not yet been established, even though different cutoff values for SUVmax have been proposed .
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According to literature, FDG-PET can differentiate benign from malignant cardiac tumors, which could prevent unnecessary biopsies and therapies. Furthermore, it has been used for estimation of the tumor burden as well as for staging the disease, detection of accompanied primary or metastatic extracardiac tumors, assessment of recurrence of tumor ( Fig. 16.3 ), identification of posttreatment residue, evaluation of response to therapy, and finally prediction of patients’ outcome .
Box 16.4
Cardiac uptake of 18 F-FDG.
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For more accurate evaluation of cardiac tumors employing FDG-PET, understanding the mechanism of physiologic uptake and normal distribution pattern of FDG by the heart is crucial. It should be considered that the level of blood glucose as well as that of plasma insulin is the key to proportion of glycolysis and free fatty acid metabolism by the myocardium. To be specific, in a fasting state there is a decrease in myocardial glycolytic metabolism, resulting in diminished 18 F-FDG uptake by the myocytes. Needless to say, the reverse occurs when the blood level of glucose is high, demonstrating high myocardial 18 F-FDG uptake. As a result, to clearly display FDG uptake at the site of neoplastic lesions, a 6-hour fasting is mandatory in order to prevent normal background myocardial uptake as an interfering phenomenon .
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Cardiac 18 F-FDG uptake could normally illustrate a broad spectrum of variants from lack of activity (at fasting state) to focal, regional, or diffuse (in nonfasted and even fasted patients) pattern of myocardial activity. The atria and papillary muscles as well as the basal and anteroapical regions of the left ventricle are responsible for normal focal increased radiotracer uptake of the heart in FDG-PET imaging, while regional cardiac uptake could be attributed to physiologic normal increased activity in posterolateral wall and base of the left ventricle. Moreover, nonneoplastic etiologies could be associated with focal or regional increased 18 F-FDG uptake in the heart, of which atrial fibrillation, prominent crista terminalis, lipomatous hypertrophy of the interatrial septum, epicardial and pericardial fat, cardiac sarcoidosis, endocarditis, myocarditis, and pericarditis have been well known .
Box 16.5
Cardiac tumors.
Neoplastic masses are generally categorized into two major groups of primary and secondary tumors with a far greater prevalence for the latter (about 20–40 times more common than the primaries) .
Metastatic tumors
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Secondary tumors of the heart are estimated to comprise 15%–20% of all cardiac masses. Even though these malignant lesions are not common, by advancing in diagnostic modalities and therapeutic strategies, which is resulting in longer life expectancy of the patients suffering from cancer, the prevalence of secondary tumors is predicted to be increased . While cardiac and pericardial metastatic lesions could originate from almost any malignant tumor ( Fig. 16.6 ), they are mainly arising from melanoma ( Fig. 16.7 ) and carcinoma of the lung ( Fig. 16.8 ), breast, and esophagus as well as from hematologic cancers, leukemia and lymphoma .
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Owing to the fact that metastatic cardiac tumors are commonly in association with widespread metastases and that diagnosis of accompanied extracardiac lesions is crucial in clinical management of patients with cancer, FDG-PET could be of help to evaluate either the cardiac masses in question or the other expected disseminated lesions, simultaneously. Congruently, FDG-PET which is acknowledged for initial staging and evaluation of response to therapy in lymphoma could concurrently disclose the accompanied cardiac involvement, which is not uncommon in non-Hodgkin lymphoma .
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Although malignant melanoma has a significant proclivity for the heart, it is rarely seen in living patients and tumors are often detected in autopsy. The cardiac melanomas usually occur at chambers, more commonly involving the right atrium. They are generally discovered in transthoracic echocardiography (TTE); nevertheless, in some cases TTE fails to recognize the tumor, in which MRI or FDG-PET is supposed to help .
Primary tumors
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Primary cardiac tumors are very rare, more than three-quarters of which are benign in nature originating from the myocardium or pericardium with myxoma as the most common primary cardiac neoplasm. Evidently, malignant primary tumors are exceedingly rare, incorporating a smaller proportion of this rare entity. Sarcomas of different types compose the leading histopathology followed by lymphoma ( Fig. 16.9 ) and mesothelioma ( Fig. 16.10 ) in descending order of occurrence . Sarcomas generally demonstrate high 18 F-FDG uptake ( Fig. 16.11–16.19 ); these aggressive tumors comprise approximately two-thirds of all malignant primaries .
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Paragangliomas are rare neuroendocrine tumors of paraganglionic cells arising from an extraadrenal location. Histopathologically, malignant lesions are not distinguishable from the benign; only local invasion or distant metastases define the malignancy ( Fig. 16.20 ).
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