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AJR Integrative Imaging LIFELONG LEARNING FOR RADIOLOGY |
1 Department of Radiology, Division of Cardiothoracic Radiology, University of
Michigan, B1-132 Taubman Center /0302, 1500 E Medical Center Dr., Ann Arbor,
MI 48109-0302.
2 Department of Cardiology, German Heart Institute, Berlin, Germany.
Received September 29, 2006; accepted after revision November 17, 2006.
Address correspondence to A. K. Attili
(aattili{at}umich.edu).
Keywords: cardiac imaging • cine MRI • heart disease • ischemia
Case History
A 50-year-old old man with known coronary artery disease and two prior anterior myocardial infarctions presents with worsening dyspnea (New York Heart Association class III-IV).
Radiologic Description
Cardiac MRI shows a dyskinetic aneurysmal anterior and apical left ventricular wall on the cine balanced steady-state free precession (b-SSFP) sequence images in diastolic and systolic two-chamber and three-chamber views (Figs. 1A, 1B, 1C, and 1D and supplemental video in three-chamber plane [Fig. S1; see www.arjonline.org]). The contrast-enhanced inversion recovery images (Figs. 1E and 1F) show transmural enhancement of the left ventricular apex and anterior wall, which is indicative of a scar. A dark low-signal-intensity mass is visible adherent to the aneurysmal enhanced and scarred myocardium. The mass is seen as a thickening of the apical myocardium on the cine b-SSFP images and is nearly isointense to the myocardium on this sequence. The left ventricle was dilated and measured 70 mm in end-diastole, and the ejection fraction was reduced at 35%.
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The differential diagnosis in a patient with a cardiac mass includes thrombus, metastases, myxoma, papillary fibroelastoma, and a primary cardiac sarcoma.
Diagnosis
The diagnosis in this patient is a left ventricular mural thrombus in an apical left ventricular aneurysm after anterior myocardial infarction.
Commentary
Cardiac thrombi are the most frequent cardiac masses, being much more common than cardiac tumors.
Thrombus formation in the left ventricle is a well-recognized complication in patients with ischemic heart disease, with an incidence ranging from 5% to 23% after an acute myocardial infarction [1-4]. Its prevalence after myocardial infarction has decreased recently with improved treatment strategies; however, recognition and appropriate treatment remain important because of the risk of systemic embolization. Oral anticoagulation significantly reduces the risk of embolization [5]. Risk factors for developing left ventricular thrombus are infarct location (i.e., anterior myocardial infarction), infarct size and extent, and impairment in global or regional left ventricular function (i.e., ejection fraction < 40%). Most left ventricular thrombi are seen by 2 weeks after an acute myocardial infarction, often attached to the apex or in a discrete aneurysm or dyskinetic ventricular wall [3]. Ventricular thrombus formation is rare in patients with normal ventricular function; however, they may occur in patients with coagulation disorders.
Two-dimensional transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) are the most commonly used techniques for the clinical identification and follow-up of left ventricular thombi. However, false-negative, false-positive, and equivocal findings are not uncommon because of either anatomic abnormalities of the patient, difficulty in discerning the myocardium-thrombus interface, limited near-field resolution of the apex, or difficulty in obtaining images of the true apex. As a result, small nonprotruding mural thrombi may resemble a normal or mildly thickened left ventricular wall, and normal structures such as papillary muscles, anomalous bands, and trabeculae may mimic thrombi. TTE and TEE for the detection or exclusion of left ventricular thrombus may be inconclusive in as many as 46% of patients [6]. Echocardiographic techniques to improve the blood-endocardial interface definition (e.g., harmonic imaging and IV echocardiographic contrast agents) may improve overall diagnostic image quality [7].
Recently, MRI with contrast enhancement has shown promise in the identification of left ventricular thrombus, having greater sensitivity and specificity than TTE and TEE [8-10]. In particular, the delayed contrast-enhanced MRI technique using an inversion recovery pulse to suppress signal of normal myocardium has been shown to be highly beneficial in detecting intracavitary thrombi (which are dark), in addition to being an excellent technique for depicting adjacent myocardial infarction and scarring (which are bright and hyperenhanced). A homogeneous strong enhancement of the left ventricular cavity occurs after the administration of gadolinium, with abnormal intraventricular structures appearing dark in comparison.
Contrast-enhanced inversion recovery MRI allows visualization of small thrombi that are invisible on TEE and cine MRI—for example, smaller than 1 cm and trapped in endocardial trabeculations. The presence of slow and turbulent flow patterns in dysfunctional wall segments and a lack of contrast between the mural thrombus and the adjacent myocardium may cause small thrombi to be invisible on cine MRI, even when using the newer balanced steady-state free precession (b-SSFP) technique [8, 10]. In clinical practice, a combination of cine MRI using the newer b-SSFP technique and contrast-enhanced inversion recovery MRI with a careful analysis of the regions at risk—for example, infarct area, aneurysmal and dysfunctional wall segments of the ventricles, and the atrial appendages—will provide the best guarantee of not missing thrombi.
The other considerations in the differential diagnosis are unlikely for several reasons. Cardiac metastases are more common than primary cardiac tumors; however, they usually occur in patients with widespread malignancy and are rare as an isolated event [11]. A myxoma is the most common primary benign cardiac tumor, which typically occurs in the left atrium and is usually pedunculated and mobile [12]. Angiosarcoma, the most common primary cardiac malignancy, typically involves the right atrium as a heterogeneous infiltrative mass [13]. Papillary fibroelastomas are benign avascular tumors occurring on valve surfaces and typically involve the aortic valve [14]. A thrombus is overall the most frequent cardiac mass; in addition, the presence of adjacent dysfunctional scarred myocardium makes the mural mass most likely to be a thrombus.
Objective
The educational objectives of this teaching article are to describe the typical imaging features of a mural thrombus on contrast-enhanced inversion recovery MRI and to illustrate the value of the technique for depicting small mural thrombi and adjacent myocardial scarring in ischemic heart disease.
Conclusion
A mural left ventricular mass in a patient with ischemic heart disease adherent to an area of scarred and dysfunctional myocardium is most likely to be a thrombus. Contrast-enhanced inversion recovery MRI is a particularly sensitive method for detecting small mural thrombi in ischemic heart disease.
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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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