Mass General Hospital
OCTOBER 2010
ISSUE 30

 
 
Epicardial and Mediastinal Fat Mimicking Pericardial Effusion
James Woo, MD, Leila Khorashadi, MD, Vikram Venkatesh, MD, John Lichtenberger, MD, Jonathan Passeri, MD, Hector M. Medina, MD, MPH, Suhny Abbara, MD, Fred Holmvang, MD
 
  Clinical History
A 48-year-old obese woman with a body mass index (BMI) of 31, a history of systemic lupus erythematosus (SLE), and a history of hypothyroidism presented with several months of progressive exertional dyspnea. Three transthoracic echocardiograms (TTE) reports over the past decade, the last obtained three years ago, had noted the presence of a small chronic pericardial effusion (PE). A repeat TTE (Figure 1) was performed and the possibility of excess epicardial and mediastinal fat rather than a PE was raised. Cardiac MRI (Figures 2 and 3) was performed to confirm the presence of excess fat.

Findings
MR confirmed the presence of fat in the epicardial space and mediastinum, as noted by the presence of a diffuse thick band of T1 and T2 hyperintense signal around the heart which lost signal on the fat-saturated images. No mass effect on the cardiac chambers or great vessels was identified.

Figure 1:  Echocardiographic off-axis short-axis image demonstrates heterogeneous, predominantly hypoechoic material in the epicardial space (asterisks) and mediastinum (arrows), separated by pericardium (arrowheads). LV, left ventricle; RV, right ventricle; ^, RV free wall.
Figure 1
Figure 2:  Axial T1 image demonstrates homogeneous hyperintensity throughout the epicardial space (asterisks) and mediastinum (arrows), separated by pericardium (arrowheads).
Figure 2
Figure 3(A,B):  (A) Short-axis T2 weighted image demonstrates relatively homogeneous T2 hyperintensity throughout the epicardial space (asterisks). The thick arrow shows subcutaneous fat, the thin arrow points to mediastinal fat, and the arrowhead indicates the pericardium. (B) Short-axis T2 fat-saturation image shows uniform signal loss.
Figure 3A
Figure 3(A,B):  (A) Short-axis T2 weighted image demonstrates relatively homogeneous T2 hyperintensity throughout the epicardial space (asterisks). The thick arrow shows subcutaneous fat, the thin arrow points to mediastinal fat, and the arrowhead indicates the pericardium. (B) Short-axis T2 fat-saturation image shows uniform signal loss
Figure 3B

(Click on images to enlarge)

Figure 1: Echocardiographic off-axis short-axis image demonstrates heterogeneous, predominantly hypoechoic material in the epicardial space (asterisks) and mediastinum (arrows), separated by pericardium (arrowheads). LV, left ventricle; RV, right ventricle; ^, RV free wall.

Figure 2: Axial T1 image demonstrates homogeneous hyperintensity throughout the epicardial space (asterisks) and mediastinum (arrows), separated by pericardium (arrowheads).

Figure 3(A,B): (A) Short-axis T2 weighted image demonstrates relatively homogeneous T2 hyperintensity throughout the epicardial space (asterisks). The thick arrow shows subcutaneous fat, the thin arrow points to mediastinal fat, and the arrowhead indicates the pericardium. (B) Short-axis T2 fat-saturation image shows uniform signal loss.


Discussion
Diffuse, excess epicardial and mediastinal fat may be idiopathic or secondary to obesity, Cushing disease or exogenous steroid use1. In this case, excess epicardial and mediastinal fat was likely related to patient obesity and a history of hypothyroidism. Excess epicardial and mediastinal fat can mimic pericardial effusion and/or pericardial masses2,3. In addition, excess fat can also have mass effect with or without hemodynamic significance.

Reports of pericardial fat in the literature have predominantly pertained to pericardial lipomas rather than unencapsulated, diffuse fat. On echocardiography, intracardiac lipomas are generally hyperechoic while subepicardial lipomas usually appear relatively hypoechoic and may be misinterpreted as pericardial fluid. Both CT and MRI are useful in localizing and characterizing epicardial fat, mediastinal fat, and lipomatous tumors.


 
 
REFERENCES
1. Hsu YM, Yao NS, Liu JM. Steroid-induced mediastinal lipomatosis with radiographic features of pericardial effusion. Am J Emerg Med 2000;18(3):346-8
2. Srivastava AK, Agarwal AK, Kapoor A, Tiwari P, Pandey R.  Diffuse Cardiac Lipomatosis Presenting as Recurrent Pericardial Effusion.  Asian Cardiovasc Thorac Ann 2000;8:381-3
3. Yousem D, Traill TT, Wheeler PS, Fishman EK. Illustrative Cases in Pericardial Effusion Misdetection: Correlation of Echocardiography and CT. Cardiovasc Intervent Radiol 1987;10:162-7
   

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Suhny Abbara, M.D.
MGH Department of Radiology
Wilfred Mamuya, M.D., Ph.D.
MGH Division of Cardiology

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