DOI: 10.1148/rg.255045721
RadioGraphics 2005;25:1255-1276
© RSNA, 2005
MR Imaging of Cardiac Tumors1
Patrick J. Sparrow, MD,
John B. Kurian, MD,
Tim R. Jones, MSc and
Mohan U. Sivananthan, MD
1 From the British Heart Foundation Cardiac MRI Unit, Room 170, D Floor, Jubilee Wing, The General Infirmary, Leeds LS1 3EX, England. Received August 11, 2004; revision requested November 8 and received December 22; accepted January 3, 2005. All authors have no financial relationships to disclose. P.J.S. supported by a grant from the British Heart Foundation.
Address correspondence to M.U.S. (e-mail: gemma.england{at}leedsth.nhs.uk).
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Abstract
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Magnetic resonance (MR) imaging is an important tool in the evaluation of cardiac neoplasms. T1-weighted, T2-weighted, and gadolinium-enhanced sequences are used for anatomic definition and tissue characterization, whereas cine gradient-echo imaging is used to assess functional effects. Recent improvements in pulse sequences for cardiac MR imaging have led to superior image quality, with reduced motion artifact and improved signal-to-noise ratio and tissue contrast. Although there is some overlap in the MR imaging appearances of cardiac tumors, particularly of primary malignancies, differences in characteristic locations and features should allow confident differentiation between benign and malignant tumors. Indicators of malignancy at MR imaging are invasive behavior, involvement of the right side of the heart or the pericardium, tissue inhomogeneity, diameter greater than 5 cm, and enhancement after administration of gadolinium contrast material (as a result of higher tissue vascularity). Concomitant pericardial or pleural effusions are rare in benign processes but occur in about 50% of cases of malignant tumors. MR imaging offers improved resolution, a larger field of view, and superior soft-tissue contrast compared with those of echocardiography, suggesting that knowledge of the MR imaging features of cardiac neoplasms is important for accurate diagnosis and management.
© RSNA, 2005
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- List the clinical features of each type of cardiac tumor including the likely age at presentation and the relative prevalence.
- Describe the MR imaging characteristics of the most common cardiac tumors and how to differentiate probably benign processes from malignant processes.
- Discuss recent developments in MR imaging pulse sequences that have led to improved image acquisition.
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Introduction
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The overall frequency of cardiac tumors is quite low, with an estimated cumulative prevalence of 0.002%–0.3% at autopsy and 0.15% in echocardiographic series (1,2). The majority of primary cardiac tumors are benign; of these, myxoma is by far the commonest, with lipomas and fibromas occurring less frequently. Metastatic involvement of the heart is approximately 40 times more prevalent than primary cardiac tumors. Meta-static spread can be by direct invasion (from adjacent neoplasms such as those of the bronchus and breast), hematologic spread (such as malignant melanoma, lymphoma, or leukemia), or transvenous spread through the great veins (such as renal cell carcinoma or hepatoma). Primary cardiac malignancies are very rare, the majority being sarcomatous in origin. Angiosarcoma is the commonest primary malignancy of adulthood, whereas rhabdomyosarcoma is more prevalent in children.
The initial diagnostic imaging modality likely to be employed in assessment of suspected cardiac neoplasia is the readily available transthoracic echocardiography. This is limited in its imaging capability by several well-described factors such as operator experience, restricted field of view, and unfavorable patient body habitus, potentially leading to incomplete assessment of an invading cardiac mass. Transesophageal echocardiography is not limited by issues of suitable acoustic windows but is an invasive technique and has a relatively narrow field of view, thus offering only limited views of relevant structures, in particular the aortic arch, inferior vena cava, and left ventricular apex. Both echocardiographic techniques are limited in their ability to allow characterization of soft-tissue masses.
Cardiac magnetic resonance (MR) imaging is an established technique in the evaluation of cardiac neoplasia (3–5). It is noninvasive, does not involve radiation, and offers multiplanar imaging without restrictions on the available field of view. This allows accurate confirmation of the presence of a space-occupying lesion, localization and assessment of the extent of involvement, evaluation of the functional impact of the lesion, and tissue characterization. The subsequent information yielded provides an accurate assessment (and staging in case of malignancy) of any cardiac or juxtacardiac mass, emphasizing that cardiac MR imaging has an important role to play not only in diagnosis but also in determination of prognosis and in planning of therapy, including surgical resection.
The advantages of cardiac MR imaging over the more widely accessible echocardiography are improved resolution and soft-tissue contrast, greater ability to allow tissue characterization, and, through its much larger fields of view, an ability to demonstrate involvement of the adjacent mediastinum and lungs in a malignant process. An added advantage is the reproducible views, which allow accurate comparison between examinations to evaluate any changes in size and appearance. Disadvantages include the need for electrocardiographic (ECG) gating, which in the presence of arrhythmia, in particular multiple ectopics, may lead to acquisition artifacts and subsequent image degradation. An important diagnostic limitation of cardiac MR imaging is an inability to demonstrate calcium; although it is adequate for most intracavity lesions, MR imaging should always be combined with either plain radiography or computed tomography (CT) (un-gated will suffice) to assess for the presence of calcium.
In this article, we present selected images of cardiac masses of various etiologies from our own institution, describe the imaging strategies used in their acquisition, and review the cardiac MR imaging characteristics of each tumor type. The cardiac masses discussed include benign tumors, primary malignancies, metastatic involvement, and tumorlike lesions.
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MR Imaging Techniques
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The differentiation of different tissues and normal from abnormal on MR images is based on intrinsic differences in hydrogen proton density and T1 and T2 relaxation properties of the relevant tissues. Consequently, T1- and T2-weighted sequences are used to delineate the morphology and anatomy relevant to the diagnosis of cardiac tumors. Malignant cells are generally larger than normal cells and contain more free intracellular water; in addition, there is more interstitial extra-cellular fluid associated with neoplastic tissue due to an associated inflammatory reaction. Both imply higher free water content in malignant tissue than benign and hence a longer T1 and T2 relaxation time with subsequent inherent contrast between tumors and normal tissue (6).
Anatomic cardiac T1- and T2-weighted imaging is performed by means of ECG-gated multi-section fast spin-echo (SE) or SE echo-planar imaging techniques (although the latter offer inferior signal-to-noise ratios and have been superseded by fast SE methods) (7,8). As these are fast imaging techniques with multiple SE readouts per repetition, they offer condensed imaging times with reduction in both respiratory and cardiac motion artifact when compared to conventional SE sequences; conversely, they have reduced signal-to-noise ratios and tissue contrast (due to the relatively short repetition and overall acquisition times).
Double inversion-recovery (IR) fast SE imaging with nulling of blood pool signal ("black blood" imaging) gives additional contrast between the pericardial or epicardial fat, myocardium, blood pool, and surrounding tissues (8). This technique involves the addition of two preparatory 180° pulses to a standard fast SE sequence: a spatially nonselective 180° pulse is followed by a section-selective 180° pulse, usually applied immediately after the R wave trigger at end-diastole. This results in all spins outside the section being inverted, while spins within the section undergo both inversions and thus experience zero nutation. Blood flowing into the section undergoes only the nonselective inversion, with the inversion time (ie, time to readout from application of the inversion pulse) selected to the null point of blood (which will vary according to the heart rate but is typically approximately 600 msec at 1.5 T). Conversely, the blood within the section, which has undergone both inversions, moves out of plane between the pre-pulses and readout, as ventricular systole follows immediately after the R wave triggering and readout occurs in the subsequent diastolic period preceding the next R wave. The net result is nulling of signal from the blood pool in the selected section at readout. This technique is dependent on systolic washout of uninverted blood and thus suppression may not be completely effective in regions of slow flow or if flow is predominantly in plane. The selective 180° reinversion pulse thickness is generally set at a greater thickness to the image section, so as to compensate for movement of the left ventricular base toward the apex during systole (15–20 mm) with resultant risk of loss of signal from reinverted myocardium moving out of plane.
Black blood imaging with fat suppression techniques such as triple IR or spectral presaturation with IR (SPIR) can be used to further characterize tumors such as lipomas, assess the extent of tumor spread, or demonstrate the edema associated with aggressive malignant processes (9). In triple IR imaging, an additional selective 180° pulse is applied between the initial nonselective and selective pulse pair and readout, usually in mid to late diastole (approximately at or immediately after the null point of blood). The inversion time of this third pulse is set to the null time of fat. Similarly, with SPIR techniques a section-selective fat saturation pulse is applied as before between the preparatory inversion pulse pair and readout, resulting in suppression of signal from both fat and inflowing blood. Although T2-weighted fast SE imaging can be performed as free-breathing acquisitions, double IR fast SE T1-weighted, T2-weighted, and fat suppression black blood imaging is usually carried out as end-expiratory breath-hold acquisitions.
Administration of gadolinium contrast material is also useful for tissue characterization and improved mass delineation by means of differential enhancement due to variation in tumor vascularity and altered capillary permeability at both dynamic and delayed imaging. Moderate and strong enhancement is more predictive of malignant processes, although mild enhancement will be found in 40%–50% of benign tumors (10). Contrast-enhanced techniques usually more associated with ischemic heart disease, such as fast T1-weighted spoiled gradient-echo first-pass perfusion and delayed enhancement, may also be useful for demonstrating areas of heterogeneous enhancement due to regional variations in vascularity and distribution volumes (ie, areas of necrosis) within a tumor (11–13).
ECG-gated breath-hold bright blood cine gradient-echo sequences are useful for assessment of the mobility of a mass and its functional impact on valves or myocardium and also allow excellent tissue contrast between the mass and blood pool for delineation of the point of attachment of the tumor. Cine spoiled gradient-echo techniques are dependent on inflow of unsaturated blood for signal; as a result, slow or turbulent flow adjacent to a tumor may give areas of low signal intensity, with consequent blurring of the tumor-endocardial border. As masses are generally also of low signal intensity on gradient-echo images, this may lead to overestimation of the size of tumors.
Improvements in magnetic field homogeneity and gradient performance have allowed the recent introduction of segmented k-space steady-state free precession (SSFP) techniques to functional cardiac imaging. These rely less on T2* for signal generation than does spoiled gradient-echo imaging, and tissue contrast is ultimately dependent on the ratio of T2 to T1. This is achieved by short repetition times (typically 3–4 msec as opposed to 7–9 msec for cine spoiled gradient-echo imaging) and the balancing of the gradients along section-selection, phase-encoding, and frequency-encoding axes. This leads to intrinsically high blood pool signal with good contrast between endocardium or a mass and blood (14,15). An added advantage of the reduced repetition time associated with SSFP imaging is shorter breath holds and acquisition times. However, there is the theoretical possibility of tumors with similar T2/T1 ratios to blood being poorly visualized with this technique and as with gradient-echo sequences, there is usually at best only modest tissue contrast between tumors and the adjacent myocardium.
We recommend that a core imaging protocol include vertical long-axis and short-axis SSFP cine images of the left ventricle, a four-chamber stack of SSFP cine images from the diaphragmatic surface to the pulmonary bifurcation, and axial T1-weighted, T2-weighted, fat suppression, and gadolinium-enhanced black blood fast SE images (Tables 1, 2). Additional tailored views such as orthogonal black blood images can be added for individual patients.
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Benign Tumors
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Myxoma
The majority of myxomas manifest in adulthood between the fourth and seventh decades (16). A minority (7%) of cases will constitute part of an autosomal dominant syndrome known as Carney complex, characterized by myxomas, hyperpigmented skin lesions, and extracardiac tumors such as pituitary adenomas, breast fibroadenomas, and melanotic schwannomas (17–20). The classic triad of symptoms attributed to myxomas include cardiac obstructive symptoms related to obstruction to blood flow, embolic events, and constitutional symptoms such as fever, malaise, and weight loss (21). Macroscopically, the majority are spherical or ovoid lesions with lobular, smooth, or frondlike contours (16,22). Microscopically, myxomas are heterogeneous with cystic areas of polysaccharide-rich myxoid substance, hemorrhage and hemosiderin, fibrosis, and calcification (in 56% of cases). Ninety percent are solitary and atrial in location, with three-fourths seen in the left atrium and 10%–20% in the right atrium. There is a predilection for the interatrial septum, with the majority arising from an area immediately adjacent to the fossa ovalis (16,23). Exceedingly rarely, myxomas may undergo malignant transformation (24,25).
At MR imaging, the vast majority of myxomas will demonstrate heterogeneous signal intensity, which reflects the underlying heterogeneity of the tissue. Myxomatous tissue is hypointense relative to myocardium on T1-weighted images and has high signal intensity on T2-weighted images due to the high extracellular water content; areas of fibrous tissue will be hypointense on both T1-and T2-weighted images (Fig 1). Areas of acute hemorrhage within myxomas will be hypointense on both T1- and T2-weighted images, whereas older areas of hemorrhage with localized methemoglobin formation will be hyperintense on both T1- and T2-weighted images; hemosiderin generally will have low signal intensity on both T1- and T2-weighted images due to pronounced spin dephasing and magnetic susceptibility (26–29).
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Figure 1a. Myxoma of the left atrium in a 70-year-old man who experienced multiple arterial embolic events. (a, b) Axial ECG-gated breath-hold T1-weighted (repetition time msec/echo time msec = 800/38) (a) and T2-weighted (1,600/120) (b) double IR fast SE images show a small myxoma (arrow in a) arising from the posterior wall of the left atrium (LA). The lesion has a heterogeneous appearance on the T1-weighted image (a) and almost homogeneous high signal intensity on the T2-weighted image (b). (c) Axial delayed phase ECG-gated breath-hold T1-weighted IR spoiled gradient-echo image (4.4/1.6, inversion time = 220 msec, 15° flip angle), obtained 20 minutes after administration of gadolinium contrast material, shows heterogeneous intense enhancement of the lesion with areas of delayed enhancement peripherally due to necrosis (arrows). LV = left ventricle.
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Figure 1b. Myxoma of the left atrium in a 70-year-old man who experienced multiple arterial embolic events. (a, b) Axial ECG-gated breath-hold T1-weighted (repetition time msec/echo time msec = 800/38) (a) and T2-weighted (1,600/120) (b) double IR fast SE images show a small myxoma (arrow in a) arising from the posterior wall of the left atrium (LA). The lesion has a heterogeneous appearance on the T1-weighted image (a) and almost homogeneous high signal intensity on the T2-weighted image (b). (c) Axial delayed phase ECG-gated breath-hold T1-weighted IR spoiled gradient-echo image (4.4/1.6, inversion time = 220 msec, 15° flip angle), obtained 20 minutes after administration of gadolinium contrast material, shows heterogeneous intense enhancement of the lesion with areas of delayed enhancement peripherally due to necrosis (arrows). LV = left ventricle.
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Figure 1c. Myxoma of the left atrium in a 70-year-old man who experienced multiple arterial embolic events. (a, b) Axial ECG-gated breath-hold T1-weighted (repetition time msec/echo time msec = 800/38) (a) and T2-weighted (1,600/120) (b) double IR fast SE images show a small myxoma (arrow in a) arising from the posterior wall of the left atrium (LA). The lesion has a heterogeneous appearance on the T1-weighted image (a) and almost homogeneous high signal intensity on the T2-weighted image (b). (c) Axial delayed phase ECG-gated breath-hold T1-weighted IR spoiled gradient-echo image (4.4/1.6, inversion time = 220 msec, 15° flip angle), obtained 20 minutes after administration of gadolinium contrast material, shows heterogeneous intense enhancement of the lesion with areas of delayed enhancement peripherally due to necrosis (arrows). LV = left ventricle.
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Myxomas generally show a heterogeneous pattern of enhancement following administration of gadolinium contrast material, although they occasionally may demonstrate a homogeneous response (4,22,29,30) (Fig 2). The increased signal intensity after contrast material administration may be due to increased vascularity and inflammation, with low-signal-intensity areas corresponding to areas of necrosis (29,31). Cine gradient-echo images will demonstrate the characteristic mobility associated with myxomas with or without prolapse through the mitral valve (best seen on four-chamber horizontal long-axis views); the mass will appear predominantly dark due to the presence of hemorrhage and consequent signal dropout due to the high iron content. On SSFP images, myxomas will be hyperintense relative to myocardium but hypointense relative to the blood pool. However, they occasionally can be isointense relative to the blood pool and thus be easily overlooked (Fig 2).
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Figure 2a. Myxoma of the left atrium in a 37-year-old woman with embolic phenomena of the lower limbs. (a, b) Axial ECG-gated breath-hold T1-weighted double IR fast SE images (632/40) show a large myxoma with a heterogeneous appearance (* in a). The lesion occupies the left atrium (LA), arises from the interatrial septum, and invades through the fossa ovalis into the right atrium (RA) (arrow in b). (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (667/40) shows heterogeneous intense enhancement of the lesion. (d) Four-chamber ECG-gated breath-hold SSFP image (3.2/1.6, 55° flip angle) shows that the myxoma is isointense relative to the blood pool. Arrows = susceptibility artifact due to a thrombus on the surface of the myxoma, LV = left ventricle, RA = right atrium.
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Figure 2b. Myxoma of the left atrium in a 37-year-old woman with embolic phenomena of the lower limbs. (a, b) Axial ECG-gated breath-hold T1-weighted double IR fast SE images (632/40) show a large myxoma with a heterogeneous appearance (* in a). The lesion occupies the left atrium (LA), arises from the interatrial septum, and invades through the fossa ovalis into the right atrium (RA) (arrow in b). (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (667/40) shows heterogeneous intense enhancement of the lesion. (d) Four-chamber ECG-gated breath-hold SSFP image (3.2/1.6, 55° flip angle) shows that the myxoma is isointense relative to the blood pool. Arrows = susceptibility artifact due to a thrombus on the surface of the myxoma, LV = left ventricle, RA = right atrium.
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Figure 2c. Myxoma of the left atrium in a 37-year-old woman with embolic phenomena of the lower limbs. (a, b) Axial ECG-gated breath-hold T1-weighted double IR fast SE images (632/40) show a large myxoma with a heterogeneous appearance (* in a). The lesion occupies the left atrium (LA), arises from the interatrial septum, and invades through the fossa ovalis into the right atrium (RA) (arrow in b). (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (667/40) shows heterogeneous intense enhancement of the lesion. (d) Four-chamber ECG-gated breath-hold SSFP image (3.2/1.6, 55° flip angle) shows that the myxoma is isointense relative to the blood pool. Arrows = susceptibility artifact due to a thrombus on the surface of the myxoma, LV = left ventricle, RA = right atrium.
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Figure 2d. Myxoma of the left atrium in a 37-year-old woman with embolic phenomena of the lower limbs. (a, b) Axial ECG-gated breath-hold T1-weighted double IR fast SE images (632/40) show a large myxoma with a heterogeneous appearance (* in a). The lesion occupies the left atrium (LA), arises from the interatrial septum, and invades through the fossa ovalis into the right atrium (RA) (arrow in b). (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (667/40) shows heterogeneous intense enhancement of the lesion. (d) Four-chamber ECG-gated breath-hold SSFP image (3.2/1.6, 55° flip angle) shows that the myxoma is isointense relative to the blood pool. Arrows = susceptibility artifact due to a thrombus on the surface of the myxoma, LV = left ventricle, RA = right atrium.
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The main differential diagnoses for myxoma include atrial thrombus or papillary fibroelastoma. It can be difficult to differentiate thrombus from a myxoma on MR images because both may have a heterogeneous appearance with areas of calcification; however, myxomas are more likely to arise anteriorly from the interatrial septum, whereas thrombus is more likely located posteriorly in the left atrium. In addition, myxomas will enhance with gadolinium contrast material, whereas thrombus, in most cases, should not (3,31). Papillary fibroelastomas tend to be much smaller and demonstrate different signal intensity characteristics.
Lipoma
Lipomas are the second most common benign cardiac tumor (16). They are encapsulated collections of adipose cells and can manifest in a wide age group. Many are discovered incidentally, but some can manifest due to symptomatic obstruction to blood flow or compression of the ventricles, especially if they have arisen in the pericardial space (32–34). They may arise in both an epicardial and endocardial location, although the majority appear to be subepicardial, expanding into the pericardial space. (It is hypothesized that many pericardial lipomas originate in the atrio-ventricular grooves.)
Lipomas have specific MR imaging characteristics, with homogeneous high signal intensity on T1-weighted images, slightly less high signal intensity on T2-weighted images, and signal suppression on fat-saturated images (Fig 3). The signal intensity is similar to that of adjacent subcutaneous or mediastinal fat. Septations may be visible, but soft-tissue components should not (35). They do not enhance after contrast material administration.
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Figure 3a. Pericardial lipoma in a 68-year-old woman. (a, b) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar (667/25) (a) and T2-weighted double IR fast SE (2,000/120) (b) images show a lipoma (arrows in a). The lesion appears bright on both images; note the brighter appearance of fat on the fast SE T2-weighted image (b) than would be expected on a standard SE image. * in a = adipose tissue in the right atrioventricular groove, LA = left atrium, RAA = right atrial appendage. (c) Axial ECG-gated breath-hold T1-weighted spectral presaturation IR image (667/15) shows equivalent suppression of signal in the lipoma and in the mediastinal and subcutaneous fat.
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Figure 3b. Pericardial lipoma in a 68-year-old woman. (a, b) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar (667/25) (a) and T2-weighted double IR fast SE (2,000/120) (b) images show a lipoma (arrows in a). The lesion appears bright on both images; note the brighter appearance of fat on the fast SE T2-weighted image (b) than would be expected on a standard SE image. * in a = adipose tissue in the right atrioventricular groove, LA = left atrium, RAA = right atrial appendage. (c) Axial ECG-gated breath-hold T1-weighted spectral presaturation IR image (667/15) shows equivalent suppression of signal in the lipoma and in the mediastinal and subcutaneous fat.
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Figure 3c. Pericardial lipoma in a 68-year-old woman. (a, b) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar (667/25) (a) and T2-weighted double IR fast SE (2,000/120) (b) images show a lipoma (arrows in a). The lesion appears bright on both images; note the brighter appearance of fat on the fast SE T2-weighted image (b) than would be expected on a standard SE image. * in a = adipose tissue in the right atrioventricular groove, LA = left atrium, RAA = right atrial appendage. (c) Axial ECG-gated breath-hold T1-weighted spectral presaturation IR image (667/15) shows equivalent suppression of signal in the lipoma and in the mediastinal and subcutaneous fat.
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The main differential diagnosis is lipomatous infiltration of the interatrial septum. This is characterized by infiltration of adipocytes between the atrial muscle cells and is defined as any deposit of fat in the atrial septum exceeding 2 cm in transverse diameter (Fig 4). They are unencapsulated and occur in older overweight patients who frequently are in atrial fibrillation. At imaging, it again will demonstrate the well-described high-signal-intensity characteristics of fat with sparing of the fossa ovalis and a consequent dumbbell shape (36). A large proportion of patients will demonstrate an increase in mediastinal and epicardial fat associated with the lesion.
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Figure 4a. Lipomatous infiltration of the interatrial septum in a 69-year-old woman with atrial fibrillation in whom an atrial mass was noted at transthoracic echocardiography. (a) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar image (800/25) shows a mass (arrows) with signal intensity similar to that of the subcutaneous and mediastinal fat. This is the classic appearance of lipomatous infiltration of the interatrial septum (although the mass is not dumbbell shaped). LA = left atrium, RA = right atrium, RV = right ventricle. (b) Axial T1-weighted spectral pre-saturation with IR fat-suppressed image (800/25) shows suppression of signal in the mass. AA = aorta.
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Figure 4b. Lipomatous infiltration of the interatrial septum in a 69-year-old woman with atrial fibrillation in whom an atrial mass was noted at transthoracic echocardiography. (a) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar image (800/25) shows a mass (arrows) with signal intensity similar to that of the subcutaneous and mediastinal fat. This is the classic appearance of lipomatous infiltration of the interatrial septum (although the mass is not dumbbell shaped). LA = left atrium, RA = right atrium, RV = right ventricle. (b) Axial T1-weighted spectral pre-saturation with IR fat-suppressed image (800/25) shows suppression of signal in the mass. AA = aorta.
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Papillary Fibroelastoma
Reports of the frequency of papillary fibroelastomas vary, but they would seem to be approximately equivalent to lipoma in prevalence (16, 23). Over 90% occur on cardiac valves, making them the commonest neoplasm of the valves (37). Many are asymptomatic, and symptoms if present are usually related to embolic events. There appears to be a slight predilection for the left-sided valves, but this may reflect the more symptomatic nature of systemic embolism, leading to a greater detection rate (38). Macroscopically, they are quite small, usually being less than 1.5 cm in diameter, and are attached to the endocardium by a short thin stalk. They occur on the atrial surface of the atrioventricular valves and aortic surface of the semilunar valves. Microscopically, they consist of avascular connective tissue lined by endothelium (39).
There are very few descriptions of the appearance of fibroelastoma on MR images; the few that exist describe its appearance on cine gradient-echo images alone, where it appears as a hypo-intense mobile mass (40,41) (Fig 5). Capturing meaningful images on static fast SE images is difficult given the small size of the tumors and their inherent mobility, as they are attached to a mobile valve leaflet.
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Figure 5a. Papillary fibroelastoma of the mitral valve in an 80-year-old woman who presented with embolic events. Diastolic (a) and systolic (b) coronal vertical long-axis ECG-gated breath-hold cine gradient-echo images (8.1/4.9, 35° flip angle) and axial four-chamber image (7.8/4.6, 35° flip angle) (c) show a pedunculated low-signal-intensity mass (arrow) arising from the atrial surface of the posterior mitral leaflet. Note the absence of a turbulent jet in the left atrium on the systolic image (b); this finding implies that there is no significant associated mitral regurgitation. LV = left ventricle.
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Figure 5b. Papillary fibroelastoma of the mitral valve in an 80-year-old woman who presented with embolic events. Diastolic (a) and systolic (b) coronal vertical long-axis ECG-gated breath-hold cine gradient-echo images (8.1/4.9, 35° flip angle) and axial four-chamber image (7.8/4.6, 35° flip angle) (c) show a pedunculated low-signal-intensity mass (arrow) arising from the atrial surface of the posterior mitral leaflet. Note the absence of a turbulent jet in the left atrium on the systolic image (b); this finding implies that there is no significant associated mitral regurgitation. LV = left ventricle.
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Figure 5c. Papillary fibroelastoma of the mitral valve in an 80-year-old woman who presented with embolic events. Diastolic (a) and systolic (b) coronal vertical long-axis ECG-gated breath-hold cine gradient-echo images (8.1/4.9, 35° flip angle) and axial four-chamber image (7.8/4.6, 35° flip angle) (c) show a pedunculated low-signal-intensity mass (arrow) arising from the atrial surface of the posterior mitral leaflet. Note the absence of a turbulent jet in the left atrium on the systolic image (b); this finding implies that there is no significant associated mitral regurgitation. LV = left ventricle.
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The main differential diagnosis would be a vegetation or thrombus. Vegetations are usually associated with destruction of valvular leaflets and associated valvular incompetence, whereas fibroelastomas may not necessarily have a functional impact on the valve, as they are typically located away from the free edges (42). The clinical presentation of vegetations associated with bacterial endocarditis will also differ, typically being a syndrome of fever, murmurs, embolic events, and small vessel vasculitis. Myxomas can also occur on valves, but these are slightly larger and will have the same MR imaging characteristics described previously (37,40).
Fibroma
Fibroma is a neoplasm primarily of infants and children, being the second most common in this age group. One-third are asymptomatic and are detected incidentally, but they may also manifest with heart failure and ventricular arrhythmias. Macroscopically, they are solid tumors that arise within the myocardium and may grow to a size that obliterates the cavity. Microscopically, they are composed of fibroblasts; calcification is a common feature, although hemorrhage, cystic change, or necrosis usually is not (43). They are generally isointense or hypointense on T1-weighted images and homogeneously hypointense on T2-weighted images (10,44,45). Appearances after administration of gadolinium contrast material can demonstrate differing patterns, with both nonenhancement and an enhancing or isointense rim with a hypointense core reflecting reduced vascularity having been described (3,45,46).
Hemangioma
Hemangiomas are benign vascular tumors that can affect a wide age group, accounting for approximately 5%–10% of benign tumors (16). The commonest presentation is dyspnea on exertion, but a proportion are asymptomatic (47). They can occur in any chamber and histologically can be capillary, cavernous, or arteriovenous in nature. At MR imaging, they will be heterogeneously isointense or hypointense on T1-weighted images and usually hyperintense on T2-weighted images, although a heterogeneous appearance with low-signal-intensity areas on T2-weighted images has also been described. An inhomogeneous hyperintense enhancement pattern has been reported after administration of gadolinium contrast material (46,48–50).
Rhabdomyoma
Rhabdomyoma is the commonest benign cardiac tumor of childhood, although it rarely will be found in early adulthood. Up to 50% of these hamartomas are associated with index cases of tuberous sclerosis. The majority of patients are asymptomatic, and most of these rhabdomyomas will spontaneously regress. However, some may produce life-threatening cardiac failure due to left ventricular outflow tract obstruction or arrhythmias, and these will require surgical resection. They originate within the myocardium, typically in the ventricles, and may be multiple in up to 90% of cases. They will be isointense to marginally hyperintense to myocardium on T1-weighted images and hyperintense on T2-weighted images (46,51,52). They may be hypointense to myocardium after contrast material administration (46).
Other extremely rare tumors include paragangliomas and teratomas.
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Primary Malignancies
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Angiosarcoma
Angiosarcoma is the commonest primary cardiac malignancy of adulthood, representing 37% of all cases. It is a malignant tumor of mesenchymal cells characterized by ill-defined anastomotic vascular spaces lined by atypical endothelial cells (16). The tumor typically involves the right atrium, and so presenting symptoms are related to obstruction to right cardiac filling and pericardial tamponade. Presentation is late, and frequently there are metastases at the time of diagnosis, particularly to the lung (53). Macroscopically, they will be large grossly hemorrhagic infiltrative masses with areas of necrosis.
These attributes are reflected on MR images, which typically demonstrate a large heterogeneous mass involving the right atrium with or without pericardial involvement (characterized by disruption of fat planes, pericardial thickening, or nodularity with the possible addition of a hemorrhagic pericardial effusion). The tumor will have a heterogeneous appearance on T1-weighted images with areas of intermediate, low, and high signal intensity, reflecting tumor tissue, necrosis, and the presence of methemoglobin (Figs 6, 7). Angiosarcomas have a heterogeneous predominantly hyperintense appearance on T2-weighted images (54,55). They demonstrate a heterogeneous enhancement pattern after administration of gadolinium contrast material, with marked surface enhancement (a sun ray appearance has also been described) and central areas of necrosis (5,54,56,57). On SSFP images, they will be predominantly hyperintense relative to myocardium, with areas of high and low signal intensity within the mass corresponding to hemorrhage and necrosis, respectively.
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Figure 6a. Primary cardiac angiosarcoma in a 25-year-old woman with leg swelling, abdominal pain, bloating, and dyspnea. (a) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar image (600/25) shows a large heterogeneous mass (straight arrows) arising from the right atrial free wall. The mass is predominantly isointense relative to the myocardium but has some areas of increased signal intensity (curved arrow), which are most likely due to localized hemorrhage. LV = left ventricle, RV = right ventricle. (b, c) Axial ECG-gated breath-hold T2-weighted double IR fast SE (1,895/120) (b) and fat-suppressed T2-weighted spectral presaturation with IR (1,895/120) (c) images show the large, hyperintense, water-rich mass. Note the presence of a concurrent left pleural effusion (* in b).
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Figure 6b. Primary cardiac angiosarcoma in a 25-year-old woman with leg swelling, abdominal pain, bloating, and dyspnea. (a) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar image (600/25) shows a large heterogeneous mass (straight arrows) arising from the right atrial free wall. The mass is predominantly isointense relative to the myocardium but has some areas of increased signal intensity (curved arrow), which are most likely due to localized hemorrhage. LV = left ventricle, RV = right ventricle. (b, c) Axial ECG-gated breath-hold T2-weighted double IR fast SE (1,895/120) (b) and fat-suppressed T2-weighted spectral presaturation with IR (1,895/120) (c) images show the large, hyperintense, water-rich mass. Note the presence of a concurrent left pleural effusion (* in b).
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Figure 6c. Primary cardiac angiosarcoma in a 25-year-old woman with leg swelling, abdominal pain, bloating, and dyspnea. (a) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar image (600/25) shows a large heterogeneous mass (straight arrows) arising from the right atrial free wall. The mass is predominantly isointense relative to the myocardium but has some areas of increased signal intensity (curved arrow), which are most likely due to localized hemorrhage. LV = left ventricle, RV = right ventricle. (b, c) Axial ECG-gated breath-hold T2-weighted double IR fast SE (1,895/120) (b) and fat-suppressed T2-weighted spectral presaturation with IR (1,895/120) (c) images show the large, hyperintense, water-rich mass. Note the presence of a concurrent left pleural effusion (* in b).
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Figure 7a. Primary cardiac angiosarcoma in a 55-year-old man with weight loss, dyspnea, and peripheral edema. (a) Axial ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows a large, heterogeneous, isointense mass that originates in and almost completely obliterates the right atrium. The mass contains subtle areas of increased signal intensity (arrows), which are due to hemorrhage. (b) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,538/120) shows that the mass (arrows) is heterogeneously hyperintense with areas of low signal intensity, which correspond to necrotic areas. CS = coronary sinus, IVC = inferior vena cava, RV = right ventricle. (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows marked enhancement of the mass with obvious areas of poor enhancement (*), which are due to focal necrosis. (d) Axial four-chamber ECG-gated breath-hold SSFP image (3/1.5, 55° flip angle) shows the angiosarcoma as a large slightly hyperintense mass arising from the right atrial free wall. LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle.
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Figure 7b. Primary cardiac angiosarcoma in a 55-year-old man with weight loss, dyspnea, and peripheral edema. (a) Axial ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows a large, heterogeneous, isointense mass that originates in and almost completely obliterates the right atrium. The mass contains subtle areas of increased signal intensity (arrows), which are due to hemorrhage. (b) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,538/120) shows that the mass (arrows) is heterogeneously hyperintense with areas of low signal intensity, which correspond to necrotic areas. CS = coronary sinus, IVC = inferior vena cava, RV = right ventricle. (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows marked enhancement of the mass with obvious areas of poor enhancement (*), which are due to focal necrosis. (d) Axial four-chamber ECG-gated breath-hold SSFP image (3/1.5, 55° flip angle) shows the angiosarcoma as a large slightly hyperintense mass arising from the right atrial free wall. LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle.
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Figure 7c. Primary cardiac angiosarcoma in a 55-year-old man with weight loss, dyspnea, and peripheral edema. (a) Axial ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows a large, heterogeneous, isointense mass that originates in and almost completely obliterates the right atrium. The mass contains subtle areas of increased signal intensity (arrows), which are due to hemorrhage. (b) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,538/120) shows that the mass (arrows) is heterogeneously hyperintense with areas of low signal intensity, which correspond to necrotic areas. CS = coronary sinus, IVC = inferior vena cava, RV = right ventricle. (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows marked enhancement of the mass with obvious areas of poor enhancement (*), which are due to focal necrosis. (d) Axial four-chamber ECG-gated breath-hold SSFP image (3/1.5, 55° flip angle) shows the angiosarcoma as a large slightly hyperintense mass arising from the right atrial free wall. LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle.
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Figure 7d. Primary cardiac angiosarcoma in a 55-year-old man with weight loss, dyspnea, and peripheral edema. (a) Axial ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows a large, heterogeneous, isointense mass that originates in and almost completely obliterates the right atrium. The mass contains subtle areas of increased signal intensity (arrows), which are due to hemorrhage. (b) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,538/120) shows that the mass (arrows) is heterogeneously hyperintense with areas of low signal intensity, which correspond to necrotic areas. CS = coronary sinus, IVC = inferior vena cava, RV = right ventricle. (c) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (769/38) shows marked enhancement of the mass with obvious areas of poor enhancement (*), which are due to focal necrosis. (d) Axial four-chamber ECG-gated breath-hold SSFP image (3/1.5, 55° flip angle) shows the angiosarcoma as a large slightly hyperintense mass arising from the right atrial free wall. LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle.
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Undifferentiated Sarcoma
Undifferentiated sarcomas are sarcomas with no specific histologic markers. The prevalence among cardiac malignancies varies, but it is at least the second most common primary malignancy, with a reported prevalence of 24%–37.5%. It is a tumor predominantly of adulthood, typically manifesting in the fourth or fifth decade with symptoms of dyspnea, chest pain, and weight loss (16,58). At least 80% of tumors will arise in the left atrium, although they can also involve the cardiac valves (59). Descriptions of MR imaging appearances are scarce, but like many other primary cardiac sarcomas, it appears as an isointense irregular mass infiltrating the myocardium (60).
Rhabdomyosarcoma
Rhabdomyosarcoma is the commonest primary cardiac malignancy of childhood. It is a malignancy of striated muscle. There are two distinct histologic types: embryonal types, which occur mainly in children and adults, and a pleomorphic variety, which are much less frequent and occur in adulthood (16). There is no specific chamber from which they arise, but they are more likely than any other primary cardiac sarcomas to involve the valves and may manifest with multiple sites of involvement (1). The presentation will depend on the area of involvement, but as with other cardiac sarcomas, congestive heart failure is common. They will be isointense to myocardium on T1-weighted images and demonstrate more or less homogeneous enhancement after contrast material administration, although there may be areas of low signal intensity due to central necrosis within the tumor (Fig 8) (5,60–62).
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Figure 8a. Primary cardiac rhabdomyosarcoma in a 71-year-old man with weight loss, sweating, and worsening dyspnea. (a, b) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar images (923/25) (b obtained cephalad to a) show an isointense mass arising from the myocardial wall of the right ventricular outflow tract (arrow in a) with a large cavitating metastasis in the apical segment of the left lower lobe (arrow in b). (c) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,846/120) shows that the mass (arrow) has a more heterogeneous appearance, with areas of high signal intensity. (d) Sagittal ECG-gated breath-hold cine gradient-echo image (8/4.8, 35° flip angle) shows that the mass (arrowheads) is isointense relative to the adjacent infiltrated myocardium. The arrow indicates the pulmonary metastasis. LV = left ventricle.
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Figure 8b. Primary cardiac rhabdomyosarcoma in a 71-year-old man with weight loss, sweating, and worsening dys-pnea. (a, b) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar images (923/25) (b obtained cephalad to a) show an isointense mass arising from the myocardial wall of the right ventricular outflow tract (arrow in a) with a large cavitating metastasis in the apical segment of the left lower lobe (arrow in b). (c) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,846/120) shows that the mass (arrow) has a more heterogeneous appearance, with areas of high signal intensity. (d) Sagittal ECG-gated breath-hold cine gradient-echo image (8/4.8, 35° flip angle) shows that the mass (arrowheads) is isointense relative to the adjacent infiltrated myocardium. The arrow indicates the pulmonary metastasis. LV = left ventricle.
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Figure 8c. Primary cardiac rhabdomyosarcoma in a 71-year-old man with weight loss, sweating, and worsening dys-pnea. (a, b) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar images (923/25) (b obtained cephalad to a) show an isointense mass arising from the myocardial wall of the right ventricular outflow tract (arrow in a) with a large cavitating metastasis in the apical segment of the left lower lobe (arrow in b). (c) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,846/120) shows that the mass (arrow) has a more heterogeneous appearance, with areas of high signal intensity. (d) Sagittal ECG-gated breath-hold cine gradient-echo image (8/4.8, 35° flip angle) shows that the mass (arrowheads) is isointense relative to the adjacent infiltrated myocardium. The arrow indicates the pulmonary metastasis. LV = left ventricle.
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Figure 8d. Primary cardiac rhabdomyosarcoma in a 71-year-old man with weight loss, sweating, and worsening dys-pnea. (a, b) Axial ECG-gated non–breath-hold T1-weighted SE echo-planar images (923/25) (b obtained cephalad to a) show an isointense mass arising from the myocardial wall of the right ventricular outflow tract (arrow in a) with a large cavitating metastasis in the apical segment of the left lower lobe (arrow in b). (c) Axial ECG-gated breath-hold T2-weighted double IR fast SE image (1,846/120) shows that the mass (arrow) has a more heterogeneous appearance, with areas of high signal intensity. (d) Sagittal ECG-gated breath-hold cine gradient-echo image (8/4.8, 35° flip angle) shows that the mass (arrowheads) is isointense relative to the adjacent infiltrated myocardium. The arrow indicates the pulmonary metastasis. LV = left ventricle.
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Osteosarcoma
Osteosarcomas are again quite rare, making up approximately 9% of primary cardiac sarcomas. Unlike metastatic osteosarcoma, primary osteosarcoma occurs predominantly in the left atrium. They may have osteo-, chondro-, or fibroblastic differentiation. Many will have dense calcification but may in the early stages of development be mistaken for myxomas, given the left-sided location and presence of calcification. However, a broad base of attachment, location away from the fossa ovalis, and potential signs of invasive behavior should raise the suspicion of this sarcoma. No comprehensive description of the MR imaging appearance exists, but it appears to be heterogeneously hypointense on T1-weighted images and hyperintense on T2-weighted images (63,64). CT is recommended in all suspected cases of osteosarcoma to confirm the presence and specific pattern of calcification.
Leiomyosarcoma
Leiomyosarcoma is a malignant tumor arising from smooth muscle and constitutes only 1% of all primary cardiac tumors. It has a predilection for the left atrium, and the commonest manifestation is dyspnea and cardiac failure from mitral obstructive symptoms. They can be multiple in 30% of cases. MR imaging descriptions are infrequent, but it appears to be isointense or hypo-intense to myocardium on T1-weighted images, hyperintense on T2-weighted images, and markedly enhancing with gadolinium contrast material (65–67).
Primary Cardiac Lymphoma
Primary cardiac lymphomas are exceedingly rare, are typically of the non-Hodgkin B-cell type, and are confined to the heart or pericardium. They usually occur in immunocompromised patients but are not restricted solely to this group (16,68). Presentation is with rapidly worsening heart failure, obstructive symptoms, or arrhythmias. The prognosis is invariably poor, although there have been reported remissions with chemotherapy (69). They most commonly involve the right side of the heart, in particular the right atrium, with frequent involvement of more than one chamber and invasion of the pericardium. Microscopically, they consist of firm nodules of homogeneous-appearing tissue; they do not seem to be prone to large areas of hemorrhage or necrosis. At MR imaging, they are isointense on T1-weighted images and heterogeneously hyperintense on T2-weighted images; they demonstrate heterogeneous enhancement after administration of gadolinium contrast material, with areas of low enhancement in the center of the lesion compared to the periphery (10,54,70,71).
Pericardial Mesothelioma
Pericardial mesothelioma is defined as a mesothelioma arising from mesothelial cells of the pericardium and does not include mesotheliomas invading from the pleura. No definite causal relationship with asbestos exposure has been identified, possibly due to the relative rarity of the lesion. The tumor usually forms multiple coalescing masses that envelop the pericardial space with subsequent obliteration of the pericardial space. However, frank invasion of the adjacent epicardium is rare. There are few descriptions of the MR imaging appearance, but it appears to be homogeneously isointense on T1-weighted images, heterogeneous on T2-weighted images due to areas of necrosis, and markedly enhancing with gadolinium contrast material (54,72,73).
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Metastatic Involvement
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Secondary malignancies involving the heart are 20–40 times more frequent than primary cardiac neoplasms. In autopsy studies, patients with known malignant neoplasms will have cardiac metastatic involvement in 10%–12% of cases (74,75). The commonest primary neoplasm is bronchogenic carcinoma, followed by lymphomas, leukemia, and carcinomas of the breast and esophagus. The commonest site of involvement is the pericardium with or without invasion of the underlying myocardium. In approximately one-third of patients with cardiac involvement, death will be directly attributable to the metastases as a result of pericardial tamponade, congestive cardiac failure, or coronary artery invasion (76). Involvement in many cases may go unnoticed, but abject manifestations are most commonly due to pericardial effusions and the associated impairment of right cardiac filling that results. Presenting symptoms may include shortness of breath, chest wall pain, and peripheral edema. As with other cardiac malignancies, arrhythmias may also be a feature.
Spread is primarily via retrograde propagation through mediastinal lymphatics, leading to implantation in the epicardial myocardium. Given that most of the lymphatic drainage of the pericardium occurs via visceral pericardial channels to the region of the aortic root, infiltration by tumors in this region can lead to development of symptomatic pericardial effusions. Other tumors such as melanomas and occasionally sarcomas may spread hematogenously to the myocardium (Fig 9). Direct extension and invasion may occur with bronchial, breast, and esophageal tumors due to their proximity to the heart (Fig 10). Direct transvenous extension can also occur with renal cell carcinoma, hepatoma, and adrenal adenocarcinoma; the tumor mass may be a combination of malignant tissue and thrombus (Fig 11). Enhancement patterns after administration of gadolinium contrast material may be helpful in differentiating bland thrombus from combined thrombus and tumor; tumor would be expected to show heterogeneous enhancement, whereas bland thrombus should not.
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Figure 9a. Metastases from an abdominal islet cell tumor in a 72-year-old woman with chest pain and palpitations. (a) Axial ECG-gated breath-hold T1-weighted double IR fast SE image (706/38) shows a hyperintense mass (arrow) infiltrating the interatrial septum. LV = left ventricle, RA = right atrium, RV = right ventricle. (b) Coronal ECG-gated breath-hold T2-weighted double IR fast SE image (1,412/100) shows extensive infiltration of the right side of the heart by a hyperintense tumor mass (arrows). Note the large skeletal metastasis in the neck of the right humerus (*). (c) Axial four-chamber ECG-gated breath-hold SSFP image (3/1.5, 55° flip angle) shows the metastasis in the interatrial septum (black arrow) and a metastasis in the lateral wall of the left ventricle (LV) (white arrow). Note that the tumors are isointense relative to the adjacent myocardium. LA = left atrium, RA = right atrium. (d) Axial gadolinium-enhanced ECG-gated breath-hold T1-weighted double IR fast SE image (706/38) shows heterogeneous enhancement of the metastases noted in c (arrows).
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Abstract
LEARNING OBJECTIVES FOR TEST...
