Epicardial fat: Lateral plain film analysis in normals and in pericardial effusion.

Abstract

Before the advent of cinefluoroscopy, the diagnosis of pericardial effusions depended upon the demonstration of enlargement of the cardiac shadow, characteristic water-bottle configuration of the cardiac silhouette, and diminished pulsations of the left cardiac border at fluoroscopy. None of these findings is consistently reliable. Diagnostic pericardiocentesis, C02 cardiograms, and angiography are all definitive but involve certain risks. In 1955 the epicardial fat line in its relationship to pericardial effusions was described both by Torrance (1) and by Kremens (2). Their method of demonstrating the fat stripe by laminagraphy is unreliable, however, due to the long exposure time and motion of the heart. In 1962, Jorgens, Kundel, and Lieber (3) described the cinefluorographic approach using image intensification in cinefluoroscopy, which was considerably more reliable in diagnosing effusions; and since the time of their paper the emphasis in such a diagnosis has been placed upon cinefluoroscopy. It is evident from our experience that, with a good knowledge of the anatomy and relationships of the subepicardial fat, in conjunction with good quality lateral chest radiographs, the diagnosis and exclusion of pericardial effusions can often be made with consistent reliability. In addition, totally unsuspected effusions are often detected. Cross-sectional preparations of the anterior mediastinum near the diaphragm reveal the essential anatomic relationships observable on lateral chest radiographs (Fig. 1). Immediately posterior to the body of the sternum and somewhat laterally placed are the internal mammary vessels with an abundant amount of fat accompanying them. Immediately posterior to this fat lies anterior mediastinal fat, and beneath this lie the parietal and visceral layers of the pericardium, usually separated by a thin film of serous fluid normally present in the pericardial sac. Beneath the visceral pericardium (or epicardium) and slightly to the left of the midline lies the anterior descending branch of the left coronary artery. This vessel also has considerable perivascular fat, as does the right coronary artery, and so the anterior part of the heart is covered with subepicardial fat, often in great abundance. It would appear, therefore, that in a lateral radiograph of the chest these fat plains would be visible and distinguishable from the soft-tissue density of the heart and the bony structure, of the sternum. In addition, the two layers of pericardium will be depicted as a thin line of soft-tissue density interposed between the anterior mediastinal fat in front and the subepicardial fat behind (Fig. 2). In our experience we have noted precisely that relationship in approximately 40 per cent of the routine lateral chest films of patients without pericardial disease.