PubMed1984
The location and relative size of echo-free spaces observed by cardiac ultrasound have been considered reliable signs for distinguishing pericardial fat from fluid; spaces that are exclusively anterior have been considered to represent fat, while spaces that are exclusively or predominantly posterior have been considered to represent fluid. In the present study, the location and relative size of echo-free spaces in eight patients suggested the diagnosis of pericardial effusion; evaluation by computed tomography or thoracotomy, or both, in six and necropsy in two, however, disclosed that these echo-free spaces--posterior as well as anterior--were exclusively due to fat. Age appeared to be as important a predisposing factor as obesity in the accumulation of excess subepicardial fat. No M-mode or two-dimensional features were found to be reliable in differentiating fat from fluid, although excessive amplitude of the posterior pericardial echo on the M-mode study favored the diagnosis of fat. Thus, the finding of echo-free spaces by cardiac ultrasound, even when the posterior space is isolated or larger than an accompanying anterior space, is not necessarily indicative of pericardial fluid. In elderly patients, in particular, posterior echo-free spaces due to fat may invite an incorrect diagnosis of pericardial effusion or pericarditis. In patients in whom echo-free spaces represent an unexpected finding of cardiac ultrasound examination, computed tomography of the chest may be helpful in establishing whether they are due to fat or fluid.