Cardiac tumor versus thrombus differentiation: Role of cardiac magnetic resonance imaging

Given the current tremendous advancements in cardiac imaging, the early detection and an accurate noninvasive etiological diagnosis of a cardiac mass is now not only imperative but possible. We report 2 interesting, related, and clinically challenging cases that highlight the role of cardiac magnetic resonance imaging (CMR) for assessment of an intracardiac mass.

Case 1

A 61-year-old male recently diagnosed with a left renal cell carcinoma and renal vein thrombosis was found to have a right ventricular (RV) apical mass on a computed tomography (CT) of the abdomen. Initially, this was thought to be an RV thrombus due to a previous history of renal venous thrombosis. Warfarin anticoagulation was initiated. Cardiac magnetic resonance imaging was performed to further evaluate for potential inferior vena cava (IVC) extension of the suspected RV mass.

Cardiac imaging

A large, irregular mass (approximately 4 cm x 2 cm x 6 cm) filling the RV apex, restricting RV wall motion, and extending into the mid-RV cavity was seen on steady-state free precession cine CMR (Figure 1). The mass traversed the anterior pericardial space with the presence of a pericardial effusion (Figure 2, dark area anterior to the mass). It was isointense with the myocardium on precontrast T1-weighted image (Figure 2). It was hyperintense on precontrast T2-weighted image (Figure 3) and had increased vascularity along with heterogeneous areas of hyperenhancement with gadolinium contrast (Figure 4). These CMR findings were consistent with a soft-tissue vascularized mass that breached multiple tissue planes and an accompanying pericardial effusion diagnostic of a malignant neoplasm and not a thrombus. More importantly, there was no obvious evidence of a mass in the right atrium or in the IVC.

Figure 1. Steady-state free precession cine

4-chamber cardiac magnetic resonance

image showing the large, irregular, hypo-

intense, right ventricular mass (white arrows)

filling the apical cavity with extension

anteriorly into the pericardial space.

Figure 2. Precontrast T1-weighted breath-

hold 4-chamber view demonstrating a large

iso-intense right ventricular mass (black

arrows). An area of dark space anterior to the

mass in the pericardial space indicates the

presence of a pericardial effusion.

Figure 3. Precontrast T2-weighted breath-

hold short axis image of both ventricles

showing the hyperintense signal of the right

ventricular mass (black arrows) and increased

signal intensity (bright white area) posteriorly

that is the presence of pericardial effusion.

Figure 4. Postcontrast heterogeneous areas

of lack of enhancement (red line) from

necrosis and increased enhancement (black

arrows) from increased tumor perfusion or

vascularity of the right ventricular mass.

Clinical follow-up

Subsequently, the anticoagulation therapy was discontinued. The patient was hospitalized a few days later for a large pericardial effusion and cardiac tamponade that required an emergent surgery. The biopsy of the mass during surgery confirmed the presence of poorly differentiated high-grade malignant cells consistent with metastatic renal cell carcinoma.

Case 2

A 36-year-old female with ulcerative colitis, chronic anemia, status post-proctocolectomy, and a history of total parenteral nutrition via a central venous catheter for several months was admitted to the hospital for symptoms of worsening dyspnea. A transthoracic echocardiogram (TTE) upon admission demonstrated a large, mobile right atrial (RA) mass. In view of her history of prolonged central venous access this was thought to be a thrombus and warfarin anticoagulation was initiated. Follow-up transesophageal echocardiography (TEE) in 2 months (Figure 5) and repeat TTE's at 3 and 8 months after her initial presentation on therapeutic anticoagulation showed that the mass was unchanged in size. Hence, an alternative diagnosis to a thrombus, such as a benign neoplasm, was considered and a CMR was performed.

Figure 5. Transesophgeal echocardiography

image showing the large irregular shaped,

mobile right atrial mass attached to the atrial

free wall.

Figure 6. Steady-state free precession cine

image of the right atrium (RA) and both the

inferior (IVC) and superior vena cava (SVC).

A large, irregular, hypodense (compared to

white blood in RA) mass (labeled) without

extension into either the IVC or the SVC is

noted.

Cardiac imaging

Cardiac magnet resonance imaging demonstrated a large, irregular, mobile, RA mass measuring 2.8 cm x 2.0 cm x 3.3 cm, contained completely within the RA (without extension into the IVC or the superior vena cava. The mass attached to the anterior aspect of the RA free wall (Figure 6) separate from the tricuspid valve. The mass demonstrated a central core of hyperintensity on precontrast T1-weighted image (Figure 7) and no signal on T2-weighted image; and no immediate enhancement with gadolinium contrast. However, a central core of heterogenous enhancement with areas of signal void (likely due to calcification) with a peripheral ring of hypointense halo (Figure 8) was seen on delayed contrast inversion recovery image. Constellation of these CMR findings was consistent with an atypical or chronic thrombus and unlikely to be a soft-tissue tumor.

Figure 7. Precontrast T1-weighted breath hold

4-chamber view demonstrating a hyperintense

right atrial mass (white arrow).

Figure 8. Postcontrast delayed enhancement

inversion recovery 4-chamber image showing

the central core of heterogeneous

enhancement, with hypointense (dark areas,

white line) regions; and a peripheral ring of

hypointensity halo (white arrow) from the right

atrial mass.

Clinical follow-up

In view of the patient's chronic anemia requiring frequent blood transfusions (with an increased risk of bleeding from chronic anticoagulation) in the setting of an unyielding RA mass that had an embolic risk, she underwent an uneventful surgical excision of the mass. The final pathology of the mass confirmed the presence of an unorganized, focally calcified thrombus with an underlying thickened endocardium.

Discussion

Echocardiography, cardiac CT, CMR, and (rarely) X-ray angiography are among the modalities presently used to evaluate patients with an intracardiac mass.^1-3 Although each modality has its own advantages and limitations, TTE and (at times) TEE are the most commonly used imaging techniques for detecting the location, size, and mobility of an intracardiac mass.⁴ However, TTE and TEE cannot routinely describe the tissue composition or provide definitive etiology of a mass.⁴ On the other hand, CMR has excellent spatial resolution and superior soft-tissue contrast, providing the ability to characterize tissue composition.⁵ Cardiac magnetic resonance imaging is also capable of assessing the precise cardiac and extracardiac anatomic and physiological effects of the mass.^4-6 These unique attributes make CMR an ideal second-line noninvasive imaging tool to further evaluate a cardiac mass.

The differential diagnoses of an intracardiac mass mainly include thrombus, tumor, or vegetation. It is also important to promptly recognize some of the anatomical variants that may mimic a cardiac mass, such as the Eustacian valve, Chiari network, crista terminalis, pectinate muscles, RV moderator band, or an interatrial septal aneurysm. In general, these normal variants more often involve the right-sided chambers and are found as an incidental finding. Furthermore, so called "pseudotumors," such as a coronary or an aortic aneurysm, lipomatous hypertrophy of interatrial septum, a hiatal hernia, or a catheter/pacemaker lead may mimic a cardiac mass on a TTE.^3-6 Similarly, potential false positive appearances from an echo artifact, such as the near field clutter, reverberations, or a side-lobe artifact could be mistaken for a mass. The major advantages of a CMR include the larger field of view of both cardiac and extracardiac structures, multiplanar 3-dimensional imaging, excellent inherent natural tissue contrast, and the ability to characterize tissues with increased water, fat, or soft-tissue contents by their varying degrees of magnetized T1- or T2-weighted relaxation times. Gadolinium contrast enhancement patterns of increased capillary perfusion help to study the extent of vascularity of a mass.^5,6

Cardiac thrombi are more frequent than tumors and prompt recognition and appropriate treatment is important. Although the primary screening modality may be a TTE, equivocal findings are not uncommon; as in our second case.^7,8 Typically, both recent thrombus (< 2-3 weeks) and a chronic (> 3 weeks) organized thrombus demonstrate increased signal intensity on T1-weighted image due to oxyhemoglobin or deoxyhemoglobin and lower signal intensity on gradient echo cine images, and neither should demonstrate gadolinium contrast enhancement. Chronic thrombi have uniformly low signal on T2-weighted images compared with a tumor.^9,10 An organized clot, however, may demonstrate intermediate, heterogeneous areas of enhancement that may be mistaken for a cardiac tumor such as a myxoma.^10,11 Primary benign cardiac tumors such as lipoma, rhabdomyoma, or a fibroma and a hemangioma have variable heterogeneity and signature tissue characteristics that are typical for the individual tumor on CMR imaging.^4-6

The majority of malignant cardiac tumors are metastatic in nature and 20-40 times more common than primary cardiac tumors; these include those occurring through direct invasion (lung and breast), lymphatic spread (lymphomas and melanomas); and hematogenous spread (renal cell carcinoma).^1,12 Cardiac involvement of renal cell carcinoma occurs more often occur by contiguous spread via the inferior vena cava into the right-sided chambers; an isolated right ventricular metastasis, as noted in our case, is a rarer occurrence.^13,14 In both of these cases, CMR provided a more definitive diagnosis of the cardiac mass and helped plan appropriate therapeutic strategies for the patients.