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AJR Integrative Imaging LIFELONG LEARNING FOR RADIOLOGY |
1 Department of Radiology, University of Michigan, 1500 E Medical Center Dr.,
Ann Arbor, MI 48109.
2 Department of Cardiology, German Heart Center, Berlin, Germany.
Received June 6, 2006; accepted after revision October 4, 2006.
This Radiological Reasoning article is available for SAM credit and
CME credits when completed with the additional educational material provided
in "Imaging of Cardiac Masses and Myocardial Disease: Self-Assessment
Module." See page
S21 for
details.
OBJECTIVE
An older man with a history of urothelial cancer presented with an incidental right atrial mass. Cardiac MRI showed a pedunculated right atrial mass that was homogeneous and of intermediate signal intensity on T1- and T2-weighted images. No signal drop-out was seen on fat-suppressed images. The mass did not exhibit enhancement on the first-pass perfusion and delayed contrast-enhanced images.
CONCLUSION
A myxoma is the most common benign primary intracavitary cardiac mass. Although the MRI features are not pathognomonic, certain features such as location, presence of a stalk, and noninfiltrating nature may help to distinguish a myxoma from other intracavitary masses such as a thrombus, metastases, and primary cardiac malignancy. The final pathologic diagnosis was a right atrial myxoma.
Keywords: atrium • cardiac imaging • MRI
Case History
A 66-year-old asymptomatic man with a history of bladder cancer is found to have a cardiac mass during a routine cardiac evaluation that includes echocardiography. Cardiac MRI was performed to further evaluate the mass.
Cardiac MRI
A comprehensive cardiac MR evaluation, including cine bright blood imaging (using balanced steady-state free-precession [b-SSFP]), T1- and T2-weighted black blood imaging, T1-weighted fat-suppressed imaging, first-pass perfusion imaging, and delayed contrast-enhanced T1-weighted imaging, was performed (Figs. 1A, 1B, 1C, 1D, 1E, 1F, and 1G). A mobile pedunculated mass is seen in the right atrium attached by a long narrow stalk to the posterolateral wall of the right atrium (Figs. 1A and S1 [see www.arjonline.org for Fig. S1]). No tricuspid valve dysfunction is seen. The mass is of homogeneous intermediate signal intensity on T1- and T2-weighted images with no signal loss on the fat-suppressed T1-weighted images. No significant enhancement is seen on the first-pass perfusion and delayed contrast-enhanced T1-weighted images.
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A major application of cardiac MRI is in the characterization of cardiac and paracardiac masses with regard to localization, extent, and tissue composition. In comparison with echocardiography, MRI offers several advantages, such as a large unrestricted field of view, superior soft-tissue contrast, operator independence, and consistent reproducibility. A comprehensive MR protocol for the evaluation of a cardiac mass should consist of ECG-gated cine bright blood sequences, T1- and T2-weighted black blood prepared sequences, and gadolinium-enhanced sequences using a variety of imaging planes. Cine bright blood imaging using segmented k-space b-SSFP techniques enables assessment of the mobility of a mass, its functional impact on valves or myocardium, and delineation of the point of attachment. Tissue contrast in the b-SSFP sequence is ultimately dependent on the ratio of T2 to T1 relaxation times leading to intrinsically high blood pool signal with good contrast among endocardium, blood pool, and a mass. A combination of T1- and T2-weighted black blood prepared fast spin-echo imaging with and without fat suppression provides information on the tissue composition of a mass in addition to allowing excellent anatomic evaluation. 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 capillary permeability at both dynamic first-pass perfusion and delayed imaging.
The differential diagnosis for this pedunculated mass in the right atrium, in order of likelihood, is myxoma, thrombus, metastases, and a primary malignant cardiac tumor.
Myxomas are the most frequent intracavitary primary neoplasm of the heart. Although the preferential location is the left atrium in 75% of cases, 20% of myxomas occur in the right atrium [1]. The clinical presentation can be nonspecific; asymptomatic incidentally discovered masses are often reported. Morphologically, the smooth contour of the mass and its stalk favors the diagnosis of a myxoma. The MR signal characteristics of a myxoma depend on its tissue composition, with most myxomas showing heterogeneous signal intensity and enhancement because of the varying components of myxoid, hemorrhagic, cystic, calcified, ossified, and fibrous tissue [2]. In a typical case, the signal intensity increases on T2-weighted images with heterogeneous enhancement after contrast administration. The MR signal and enhancement characteristics are atypical in this case because the mass is homogeneous and does not show significant first-pass and delayed enhancement. Nevertheless, myxomas have a broad range of tissue compositions, and the behavior of the mass on MRI reflects its composition. The absence of signal suppression on the fat-saturated sequence excludes a significant fatty component, as in a lipoma.
Cardiac thrombi are overall the most frequent cardiac masses, mainly resulting from regional or global impaired wall motion (e.g., after myocardial infarction or in dilated cardiomyopathy) or from arrhythmia (atrial fibrillation) [3]. Thrombi arising in the right atrium are rare and are usually found in patients with central venous lines or patients having enlarged cavities—for example, dilated cardiomyopathy. The patient has no risk factors for right atrial thrombi. The signal intensity characteristics of a thrombus can vary considerably depending on its age, its hemosiderin content, and calcification processes. The delayed enhancement technique is particularly sensitive for detecting thrombi, which are seen as dark structures surrounded by contrast-enhanced blood [4]. Chronic organized thrombi may show gadolinium enhancement.
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Primary malignant cardiac tumors are rare and can be divided into three major groups: sarcomas, lymphomas, and mesotheliomas. Of these, mesothelioma arises in the pericardium and is clearly not the case in this patient. Soft-tissue sarcoma is the most common primary malignant neoplasm of the heart. There are several subtypes of cardiac sarcoma, with angiosarcoma being the most common in adults. Other subtypes include rhabdomyosarcoma, malignant fibrous histiocytoma, undifferentiated, and fibrosarcoma.
Most cardiac angiosarcomas arise in the right atrium and present as single or multiple nodules, filling the right atrium or infiltrating the myocardium and pericardium [2]. Angiosarcomas usually appear on MRI as heterogeneous masses consisting of nodular areas of high signal interspersed with areas of intermediate signal (cauliflower appearance). There is usually heterogeneous enhancement.
The lack of enhancement on dynamic first-pass perfusion and delayed images does not favor a malignant primary or secondary cardiac tumor, which would be expected to be well vascularized and to exhibit enhancement.
Primary cardiac lymphomas are rare; metastatic involvement of the heart with malignant lymphoma is more common [5]. Typical presentations include pericardial effusion and infiltrative masses, neither of which is present in this patient.
In summary, the well-defined homogeneous noninfiltrating pedunculated mass in the right atrium in this patient favors a benign lesion over a malignant entity. A thrombus is unlikely in view of the location and the absence of significant risk factors. A myxoma is the most likely diagnosis. Definitive diagnosis and management will involve surgical resection.
Clinical Management
The mass was surgically resected. The final pathologic diagnosis was a myxoma (Fig. 2).
Commentary
As exhibited in our patient, cardiac myxomas frequently present as an incidental finding on echocardiography performed for reasons other than mass detection. However, there are situations in which myxoma can be suspected on clinical grounds alone. Radiologists should be familiar with these clinical signs when consulting with clinicians from other specialties.
There are three major categories of clinical presentation [7]. Patients can present with a clinical picture of peripheral embolism, manifestations of valve obstruction, or constitutional symptoms. Embolic phenomena are a common presentation of myxoma, usually related to tumors of the left atrium, with distal arterial occlusive symptoms such as visual loss, coronary event, or acute lower extremity arterial obstruction. Emboli from right atrial myxomas are usually silent clinically. Myxomas can also obstruct the tricuspid or mitral valves, leading to clinical signs that include dyspnea, pulmonary edema, or manifestations of right heart failure. General symptoms such as fever, fatigue, arthralgia, and weight loss can occur associated with myxoma. Symptoms and laboratory abnormalities such as anemia and elevated sedimentation rate have also been reported. These clinical findings can mimic paraneoplastic, inflammatory, and autoimmune diseases. Myxomas can also be familial in origin, sometimes associated with a specific clinical syndrome [8]. Carney's syndrome consists of the clinical combination of abnormal pigmentation, cutaneous myxomas, and endocrine overactivity. Familial myxomas tend to be multiple.
Once a patient has been referred for imaging and found to have an intracavitary mass, the differential diagnosis includes thrombus, myxoma, and primary benign and malignant neoplasms. The location and physical appearance of the lesion are the most important distinguishing features, although tissue characterization with MRI can be helpful in some cases. When the intracavitary mass is on a stalk or attached to the interatrial septum, myxoma becomes the diagnosis of first choice. Myxoma is excluded when a lesion is "layered" against the wall of the chamber (thrombus), or when the myocardium is invaded (malignant neoplasm).
When the diagnosis cannot be made on the anatomic features alone, tissue characterization can sometimes be helpful. For example, intracavitary lipomas can be firmly diagnosed by visualization of a high signal on T1-weighted images with signal suppression on fat-saturated sequences. However, differentiating clot from myxoma can be difficult on the basis of MRI tissue characterization [9]. Visualizing enhancement after contrast injection can help in distinguishing myxomas from nonenhancing thrombus. When the differentiation between clot and myxoma cannot be made with confidence, follow-up imaging after a suitable time interval, with concomitant anticoagulation therapy to see if the "tumor" resolves, can sometimes lead to a diagnosis of thrombus without resorting to open heart surgery [10].
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  A. K. Attili and F. S. Chew Imaging of Cardiac Masses and Myocardial Disease: Self-Assessment Module Am. J. Roentgenol., June 1, 2007; 188(6_Supplement): S21 - S25. [Abstract] [Full Text] [PDF]
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