MR Imaging of Cardiac Masses

Primary Cardiac Angiosarcoma: A Review

Primary cardiac angiosarcoma is a rare and aggressive malignancy originating from the endothelial lining of cardiac blood vessels. This review covers various aspects of the disease, including its pathogenesis, clinical presentation, diagnosis, treatment, and prognosis. The primary characteristic of cardiac angiosarcoma is the rapid growth of abnormal blood vessels that invade the heart muscle, leading to the destruction of healthy tissue. Due to its infiltrative nature and early spread, diagnosing and treating cardiac angiosarcoma present significant challenges. Transesophageal echocardiography (TEE) plays a crucial role in diagnosing cardiac tumors such as angiosarcoma due to its high sensitivity. Additional imaging techniques such as computed tomography (CT) and cardiac magnetic resonance imaging (MRI) help assess tumor anatomy and identify metastases. Histopathological examination and immunohistochemistry are essential for confirming the diagnosis, as they reveal distinct histological features and specific endothelial markers associated with primary cardiac angiosarcoma. Targeted therapies directed at the angiogenic mechanisms and molecular abnormalities hold promise for improving treatment outcomes. Early detection of primary cardiac angiosarcoma remains challenging due to its rarity, and the prognosis is generally poor due to advanced disease at the time of diagnosis. The review emphasizes the importance of a multidisciplinary approach and collaboration among different specialties to optimize the diagnosis, treatment, and follow-up care of patients with primary cardiac angiosarcoma. The ultimate goal is to enhance diagnostic methods and therapeutic approaches by advancing knowledge and promoting further research into this aggressive malignancy.

Cardiovascular magnetic resonance of cardiac tumors and masses

Cardiac masses diagnosis and treatment are a true challenge, although they are infrequently encountered in clinical practice. They encompass a broad set of lesions that include neoplastic (primary and secondary), non-neoplastic masses and pseudomasses. The clinical presentation of cardiac tumors is highly variable and depends on several factors such as size, location, relation with other structures and mobility. The presumptive diagnosis is made based on a preliminary non-invasive diagnostic work-up due to technical difficulties and risks associated with biopsy, which is still the diagnostic gold standard. The findings should always be interpreted in the clinical context to avoid misdiagnosis, particularly in specific conditions (e.g., infective endocarditis or thrombi). The modern multi-modality imaging techniques has a key role not only for the initial assessment and differential diagnosis but also for management and surveillance of the cardiac masses. Cardiovascular magnetic resonance (CMR) allows an optimal non-invasive localization of the lesion, providing multiplanar information on its relation to surrounding structures. Moreover, with the additional feature of tissue characterization, CMR can be highly effective to distinguish pseudomasses from masses, as well as benign from malignant lesions, with further differential diagnosis of the latter. Although histopathological assessment is important to make a definitive diagnosis, CMR plays a key role in the diagnosis of suspected cardiac masses with a great impact on patient management. This literature review aims to provide a comprehensive overview of cardiac masses, from clinical and imaging protocol to pathological findings.

Cardiac papillary fibroelastoma originating from the coumadin ridge and review of literature

Papillary fibroelastomas represent the second most common benign cardiac tumour, secondary only to cardiac myxoma. A majority of patients are asymptomatic on presentation. The most common clinical manifestations include stroke, transient ischaemic attack, myocardial infarction and angina. Echocardiography remains the primary imaging modality for identification of these tumours. The majority of papillary fibroelastomas arise from the valves. Simple surgical excision is the mainstay of treatment, carrying an excellent prognosis. We present an unusual case of cardiac papillary fibroelastoma originating from the coumadin ridge (CR) in a 70-year-old woman. The patient exhibited increasing paroxysms of her atrial fibrillation and was pursuing a MAZE procedure. Preoperatively, a transesophageal echocardiogram revealed a 0.7×1 cm intracardiac mass that had echocardiographic appearance of a fibroelastoma. Surgical resection and MAZE procedures were performed. The gross specimen and histopathology findings were consistent with papillary fibroelastoma. This case reports the seventh documented case of fibroelastoma originating from the CR.

Intracardiac melanoma metastases on 18F-FDG PET-CT-a case report and review of literature with imaging features

Cutaneous malignant melanoma is one of the few malignancies that can metastasize to the heart. It is important not to miss cardiac metastases on imaging as they are often clinically asymptomatic, but if present and undiagnosed could lead to significant cardiac compromise, arrhythmias, congestive heart failure, cardiac tamponade or transient ischaemic attacks.

Identifying intracardiac metastases on imaging often requires a multimodality approach as they can evade detection due to cardiac motion artefact; be confused with intracardiac thrombus, or be misinterpreted as a normal/anatomical finding.

We present an interesting case report of asymptomatic intracardiac melanoma metastases, initially identified on staging 18-fludeoxyglucose positron emission tomography-CT and eventually confirmed on cardiac MRI. The latter was able to differentiate myocardial metastases from tumour thrombus. We also review the relevant literature.

Cardiac melanoma: Retrospective review of a rare disease at the Mayo clinic (1988-2015)

BACKGROUND

Melanoma metastasizing to the heart (cardiac melanoma) is a rare entity that has been described only in autopsy studies or isolated pre-mortem case reports. We aim to better characterize cardiac melanoma, and describe its presenting features, imaging findings, and disease course with a case series collected over nearly 30years.

METHODS

We performed a retrospective review of all patients diagnosed with cardiac melanoma at the Mayo Clinic from 1988 to 2015. Qualitative analysis was performed on patient demographics, clinical history, and imaging modalities.

RESULTS

11 patients (7 male, median age 63years) were identified with cardiac melanoma. Shortness of breath (64%) was the most common presenting symptom. Transthoracic echocardiography (TTE) was utilized in the assessment of all patients though it failed to identify 20% of masses that were seen on fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) or cardiac magnetic resonance (CMR). The majority of masses were located within the cardiac chambers (46% right atrium, 18% right ventricle, 18% left atrium), and 36% appeared mobile on TTE. Patients lived for a median of 68months (interquartile range [IQR] 14-143months) after the initial diagnosis of primary melanoma, and only 12months (IQR 2-150months) after diagnosis of cardiac melanoma.

CONCLUSION

Echocardiography can generally identify most cases of cardiac melanoma, though it misses one-fifth of masses seen on FDG PET/CT or CMR. Cardiac melanoma is associated with a poor prognosis.

Multimodal imaging of the tricuspid valve: normal appearance and pathological entities

The tricuspid valve, which is the atrioventricular valve attached to the morphological right ventricle, is affected by a wide range of pathological processes. Tricuspid valve diseases are now increasingly recognized as a significant cause of morbidity and mortality. Echocardiography is the most widely available and, hence, the first-line imaging modality used in the evaluation of tricuspid valve disorders; however, CT and MRI are also increasingly used for further evaluation and characterization of these entities. In this article, we first review the normal anatomy and embryology of the tricuspid valve, followed by a discussion of the role of multiple imaging modalities in the evaluation of tricuspid valve abnormalities. We then review and illustrate the imaging appearance of several congenital and acquired tricuspid valve abnormalities.

Main Messages

• Tricuspid valve diseases have a significant impact on morbidity and mortality.

• CT and MRI are increasingly used in the evaluation of tricuspid disorders.

• CT and MRI help in diagnosis, functional evaluation, pre-surgical planning and post-surgical follow-up.

• The most common cause of tricuspid regurgitation is functional.

Noise behavior of MR brain reconstructions using compressed sensing

Compressed sensing (CS) has demonstrated great potential to reconstruct high quality MR images from undersampled k-space data. However, successful application of CS in clinic is still limited by many factors. One of the key factors is that the noise behavior in CS reconstructions remains largely unexplored. The main objective of this work is to analyze the noise behavior of MR reconstructions using CS method with different reduction factors. Our work focuses on brain CS-MRI reconstructions using non-linear conjugate gradient (NLCG) solvers. After reconstruction, the noise behavior is characterized using the MP-Law method. The results show that the spatial noise distributed non-uniformly, and the noise variance from CS reconstruction increases with reduction factors. A kind of fitting model is given, which can be used to predict the noise behavior parameter for different reduction factors, and the noise amplification factor maps are shown to prove the denoising capability of CS reconstruction. The results provide a qualitative and quantitative understanding of the noise behavior in CS-MRI with different reduction factors.

Left ventricular thrombus in a patient with cutaneous T-cell lymphoma, hypereosinophilia and Mycoplasma pneumoniae infection - a challenging diagnosis: a case report

Differential diagnoses of cardiac masses include primary benign and malignant neoplasms, secondary neoplasms, and non-neoplastic masses, such as thrombi. Owing to different therapeutic approaches and the way these affect the prognosis, the early and correct diagnostic determination of the etiology of a cardiac mass is of utmost importance and essential for the appropriate management of patients.

We report a case of a 52-year-old woman with a left ventricular mass in the setting of a recent Mycoplasma pneumoniae infection and a medical history of cutaneous T-cell lymphoma and hypereosinophilia. Imaging findings were consistent with both an infiltrative process of the lymphoma and a cardiac thrombus. An estimated very high risk for embolization led to the indication for open-heart surgery for the removal of the cardiac mass. Histopathological examination confirmed the presence of a thrombus; there were no signs of malignancy. The patient was discharged 11 days after surgery in good general condition and is now in outpatient care for follow-up and further management.

This case highlights possible challenges in the diagnostic assessment of cardiac masses and their management in a patient with several underlying diseases and a complex medical history.

MRI assessment of cardiac tumours: part 1, multiparametric imaging protocols and spectrum of appearances of histologically benign lesions

Cardiac magnetic resonance imaging (MRI) is the reference standard technique for assessment and characterization of a suspected cardiac tumour. It provides an unrestricted field of view, high temporal resolution and non-invasive tissue characterization based on multi-parametric assessment of the chemical micro-environment. MRI exploits differences in hydrogen proton density in conjunction with T1 and T2 relaxation properties of different tissues to help differentiation normal from abnormal and benign from malignant lesions. In this article we review specific cardiac MRI techniques, tumour protocol design and the appearance of the spectrum of histologically benign tumours.

Magnetic resonance imaging using gadolinium-based contrast agents

The purpose of this article was to review the basic properties of available gadolinium-based magnetic resonance contrast agents, discuss their fundamental differences, and explore common and evolving applications of gadolinium-based magnetic resonance contrast throughout the body excluding the central nervous system. A more specific aim of this article was to explore novel uses of these gadolinium-based contrast agents and applications where a particular agent has been demonstrated to behave differently or be better suited for certain applications than the other contrast agents in this class.

Medical and surgical management of primary cardiac tumours in infants and children

Primary cardiac tumours in infants and children are extremely rare, with an estimated incidence of 0.2% according to echocardiographic studies. Owing to their rarity, there is very little literature available, and most knowledge is based on collections of case reports. Therefore, we reviewed retrospectively our 27 years of clinical experience on the overall management of cardiac tumours among children in order to improve not only our knowledge but also to provide others with information about the incidence, clinical presentation, management, and long-term outcome of this rare disease. Between April, 1982 and April, 2009, 52 children were diagnosed with cardiac tumours at our Institution. Medical records and follow-up echocardiographic evaluations were studied. The diagnosis was prenatal in 35% of the patients. The most frequent tumour types were rhabdomyomas (61.5%), fibromas (15.4%), and myxomas (5.8%). There were no cases of primary malignant tumours. All diagnoses were achieved using two-dimensional echocardiography, and for 12 patients a pathological analysis was carried out. A total of 41 patients (79%) were managed medically, whereas 11 (21%) patients underwent surgical treatment. At a mean follow-up of 7.2 ± 5.4 years, two patients died of complications related to cardiac transplantation; all the remaining patients are in excellent clinical condition. In conclusion, cardiac tumours in paediatric practice are usually clinically and histologically benign. Only a few cases need surgery. Up to one-third of the cardiac masses are detectable prenatally. Rhabdomyoma is the most common histotype, followed by fibroma and myxoma. The long-term prognosis is generally good.

Pericardial disease: value of CT and MR imaging

The pericardium represents an important focus of morbidity and mortality in patients with cardiovascular disease. Fortunately, in recent years knowledge regarding this enigmatic part of the heart and the diagnosis of related diseases has substantially advanced. To a large extent, this can be attributed to the availability of several noninvasive cardiac imaging modalities. Transthoracic echocardiography, which combines structural and physiologic assessment, is the first-line technique for examination of patients suspected of having or known to have pericardial disease; however, cardiac computed tomography (CT) and magnetic resonance (MR) imaging are becoming increasingly popular for the study of this part of the heart. Modern multidetector CT scanners merge acquisition speed and high spatial and contrast resolution, with volumetric scanning to provide excellent anatomic detail of the pericardium. Multidetector CT is by far the modality of choice for depiction of pericardial calcifications. MR imaging is probably the best imaging modality for the acquisition of a comprehensive view of the pericardial abnormalities. MR imaging combines cardiac and pericardial anatomic assessment with tissue characterization and appraisal of the effects of pericardial abnormalities on cardiac performance. This review aims to elucidate the role of the pericardium and its interaction with the remainder of the heart in normal and pathologic conditions. It focuses on the rapidly evolving insights regarding pericardial disease provided by modern imaging modalities, not infrequently necessitating reconsideration of evidence that has thus far been taken for granted.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13121059/-/DC1.

PET/MR imaging: technical aspects and potential clinical applications

Instruments that combine positron emission tomography (PET) and magnetic resonance (MR) imaging have recently been assembled for use in humans, and may have diagnostic performance superior to that of PET/computed tomography (CT) for particular clinical and research applications. MR imaging has major strengths compared with CT, including superior soft-tissue contrast resolution, multiplanar image acquisition, and functional imaging capability through specialized techniques such as diffusion-tensor imaging, diffusion-weighted (DW) imaging, functional MR imaging, MR elastography, MR spectroscopy, perfusion-weighted imaging, MR imaging with very short echo times, and the availability of some targeted MR imaging contrast agents. Furthermore, the lack of ionizing radiation from MR imaging is highly appealing, particularly when pediatric, young adult, or pregnant patients are to be imaged, and the safety profile of MR imaging contrast agents compares very favorably with iodinated CT contrast agents. MR imaging also can be used to guide PET image reconstruction, partial volume correction, and motion compensation for more accurate disease quantification and can improve anatomic localization of sites of radiotracer uptake, improve diagnostic performance, and provide for comprehensive regional and global structural, functional, and molecular assessment of various clinical disorders. In this review, we discuss the historical development, software-based registration, instrumentation and design, quantification issues, potential clinical applications, potential clinical roles of image segmentation and global disease assessment, and challenges related to PET/MR imaging.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13121038/-/DC1.

CT and MR imaging of the aortic valve: radiologic-pathologic correlation

Valvular disease is estimated to account for as many as 20% of cardiac surgical procedures performed in the United States. It may be congenital in origin or secondary to another disease process. One congenital anomaly, bicuspid aortic valve, is associated with increased incidence of stenosis, regurgitation, endocarditis, and aneurysmal dilatation of the aorta. A bicuspid valve has two cusps instead of the normal three; resultant fusion or poor excursion of the valve leaflets may lead to aortic stenosis, the presence of which is signaled by dephasing jets on magnetic resonance (MR) images. Surgery is generally recommended for patients with severe stenosis who are symptomatic or who have significant ventricular dysfunction; transcatheter aortic valve implantation (TAVI) is an emerging therapeutic option for patients who are not eligible for surgical treatment. Computed tomography (CT) is an essential component of preoperative planning for TAVI; it is used to determine the aortic root dimensions, severity of peripheral vascular disease, and status of the coronary arteries. Aortic regurgitation, which is caused by incompetent closure of the aortic valve, likewise leads to the appearance of jets on MR images. The severity of regurgitation is graded on the basis of valvular morphologic parameters; qualitative assessment of dephasing jets at Doppler ultrasonography; or measurements of the regurgitant fraction, volume, and orifice area. Mild regurgitation is managed conservatively, whereas severe or symptomatic regurgitation usually leads to valve replacement surgery, especially in the presence of substantial left ventricular enlargement or dysfunction. Bacterial endocarditis, although less common than aortic stenosis and regurgitation, is associated with substantial morbidity and mortality. Electrocardiographically gated CT reliably demonstrates infectious vegetations and benign excrescences of 1 cm or more on the valve surface, allowing the assessment of any embolic complications.

Isolated cardiac involvement of Rosai-Dorfman disease

Rosai-Dorfman disease is a rare and multisystem disorder of unknown etiology. It commonly presents as cervical lymph node enlargement, but extranodal involvement may be presented in one-third of the cases. Usually, the clinical course of Rosai-Dorfman disease is benign but it can be malignant, both clinically and pathologically. Herein, we present an isolated cardiac case of extranodal Rosai-Dorfman disease without lymphadenopathy that involves the left ventricle in a symptomatic adult patient and a description of cardiac magnetic resonance imaging findings of this disease.

Pericardial disease--anatomy and function

Imaging of patients with suspected or known pericardial disease remains challenging. Echocardiography is the first-line investigation for pericardial disease but it has specific limitations in terms of its abilities to visualise the pericardium fully and to identify extracardiac pathology. Cardiac cross-sectional imaging by both MRI and CT has developed significantly and now has an important role in the investigation of pericardial disease. This article examines the appearances of both healthy and diseased pericardium using CT and MRI. The typical imaging findings across a wide range of conditions are illustrated and the roles of CT and MRI are reviewed. The relative merits and weaknesses of each modality are explored and the specific functional techniques that are available are introduced.

Imaging sarcomas of the great vessels and heart

Primary sarcomas of the aorta, pulmonary artery, superior vena cava, inferior vena cava, and the heart are rare neoplasms. Aortic sarcomas are broadly categorized as either primarily luminal or primarily mural, with luminal sarcomas more likely to be misdiagnosed as thrombus. Pulmonary artery sarcomas are often mistaken for pulmonary embolism both clinically and at imaging. Vena caval sarcomas appear as intraluminal or extraluminal masses connecting to or filling the veins. The most common are leiomyosarcomas of the inferior vena cava. Primary sarcomas of the heart are rare and usually appear as heterogeneous aggressive masses.

Cardiac imaging: Part 1, MR pulse sequences, imaging planes, and basic anatomy

OBJECTIVE

MRI is a well-established modality for evaluating congenital and acquired cardiac diseases. This article reviews the latest pulse sequences used for cardiac MRI. In addition, the standard cardiac imaging planes and corresponding anatomy are described and illustrated.

CONCLUSION

Familiarity with the basic pulse sequences, imaging planes, and anatomy pertaining to cardiac MRI is essential to formulate optimal protocols and interpretations.

Cardiovascular magnetic resonance in heart failure

Imaging has a central role in the evaluation of patients with heart failure (HF). Cardiovascular magnetic resonance (CMR) is rapidly evolving as a versatile imaging modality that often provides additional information to echocardiography in patients with suspected or known HF. CMR is the only imaging modality that has the ability to assess, without exposure to ionizing radiation, cardiac function, structure (tissue characterization), perfusion, and viability. Moreover, magnetic resonance spectroscopy techniques can assess the pathophysiologic role of deranged cardiac energetics in HF. In this review we discuss the role of CMR in the evaluation of patients with HF giving particular emphasis to recent developments and the additional information that can be obtained with this imaging modality, over and above standard echocardiography.

CT and MR imaging of the mitral valve: radiologic-pathologic correlation

Computed tomography (CT) and magnetic resonance (MR) imaging are increasingly important adjuncts to echocardiography for the evaluation of mitral valve disease. The mitral valve may be involved in various acquired or congenital conditions with resultant regurgitation or stenosis, and many of these conditions can be identified with CT or MR imaging. In addition, CT is useful for detecting and monitoring postoperative complications after mitral valve repair or replacement. As the use of CT and MR imaging increases, awareness of the CT and MR imaging appearances of the normal mitral valve and the various disease processes that affect it may foster recognition of unsuspected mitral disease in patients undergoing imaging for other purposes. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.306105518/-/DC1.

Primary cardiac angiosarcoma arising from the interatrial septum: magnetic resonance imaging appearances

We present a case of primary cardiac angiosarcoma arising from the interatrial septum that had imaging features overlapping with those of right atrial myxoma. The mass was initially discovered on a thoracic CT study. Further evaluation with echocardiography was limited by poor acoustic windows and cardiac magnetic resonance (CMR) imaging was performed prior to surgical resection. CMR provided a detailed morphological assessment; imaging features included a frond-like surface architecture, a narrow attachment point at the interatrial septum, mild signal hyperintensity compared with that of myocardium on T(1) weighted sequences, patchy foci of delayed gadolinium enhancement and a haemorrhagic pericardial effusion. To the best of our knowledge, this is the first reported case of angiosarcoma arising from the interatrial septum that has undergone evaluation with CMR.

[Mediastinal cysts: clinical approach and treatment]

Mediastinal cysts (MC), mainly from embryonic origin, are benign and rare malformative lesions, gathering several varieties according to tissue origin. Diagnosis is mostly obtained thanks to tomodensitometry performance and sometimes by magnetic resonance imaging. It may be more difficult in some atypical topographies and in case of bulky MC. The most frequent, springing from division abnormality from embryonic foregut ("foregut cysts" in English literature), are primarily bronchogenic cysts (50 to 60 % of MC), which are symptomatic in 30 to 80 % of cases. Coelomic cysts, lined by a mesothelium, result from embryologic abnormality by incomplete fusion of mesenchymal coelomic lacunae. Rarely symptomatic, excepted in cases of very large cysts, they are mainly pleuropericardic cysts (PPC) that represent 30 % of MC. Thymic cysts, around 15 % of MC, are most often asymptomatic. Cystic lymphangiomas (CL) are congenital lymphatic malformations more frequent and symptomatic in children. Diagnosed in older patients, they are most often acquired and asymptomatic. The only radical and definitive treatment is complete surgical resection of the cyst. It allows suppression of symptoms, procurement of a formal diagnosis and prevention of complications. This resection, generally indicated for all symptomatic cysts, large-sized even asymptomatic and in case of non formal diagnosis, is now recommended for all kinds of cysts except for asymptomatic PPC. This strategy is justified considering morbidity and mortality rising rates in patients treated by surgical resection at time of local complications of the cyst. Surgery is commonly performed by videothoracoscopy or by video-assisted mini-thoracotomy, mainly for PPC and CL. The more conventional thoracotomy is performed in surgery for cysts, which are adhesive to nearby structures. PPC just need a simple follow-up, and surgery is required only in case of symptoms and increasing size. In total, surgical indications for MC are large and accepted because of null postoperative mortality and very low rate of morbidity thanks to mini-invasive surgery. This militates for early surgery, without waiting for cystic complications leading to peroperative difficulties and increasing risks. This review presents the characteristics of those different cysts and the strategies currently acknowledged for the treatment.

The role of cardiovascular magnetic resonance imaging in heart failure

Noninvasive imaging plays a central role in the diagnosis of heart failure, assessment of prognosis, and monitoring of therapy. Cardiovascular magnetic resonance (CMR) offers a comprehensive assessment of heart failure patients and is now the gold standard imaging technique to assess myocardial anatomy, regional and global function, and viability. Furthermore, it allows assessment of perfusion and acute tissue injury (edema and necrosis), whereas in nonischemic heart failure, fibrosis, infiltration, and iron overload can be detected. The information derived from CMR often reveals the underlying etiology of heart failure, and its high measurement accuracy makes it an ideal technique for monitoring disease progression and the effects of treatment. Evidence on the prognostic value of CMR-derived parameters in heart failure is rapidly emerging. This review summarizes the advantages of CMR for patients with heart failure and its important role in key areas.

Cardiovascular magnetic resonance in pericardial diseases

The pericardium and pericardial diseases in particular have received, in contrast to other topics in the field of cardiology, relatively limited interest. Today, despite improved knowledge of pathophysiology of pericardial diseases and the availability of a wide spectrum of diagnostic tools, the diagnostic challenge remains. Not only the clinical presentation may be atypical, mimicking other cardiac, pulmonary or pleural diseases; in developed countries a shift for instance in the epidemiology of constrictive pericarditis has been noted. Accurate decision making is crucial taking into account the significant morbidity and mortality caused by complicated pericardial diseases, and the potential benefit of therapeutic interventions. Imaging herein has an important role, and cardiovascular magnetic resonance (CMR) is definitely one of the most versatile modalities to study the pericardium. It fuses excellent anatomic detail and tissue characterization with accurate evaluation of cardiac function and assessment of the haemodynamic consequences of pericardial constraint on cardiac filling. This review focuses on the current state of knowledge how CMR can be used to study the most common pericardial diseases.