Atypical Distribution of Pleural Effusions

Abstract

CERTAIN conceptions about the distribution of fluid in the pleural cavity have been maintained since the earliest studies in physical diagnosis. The development of the roentgen examination of the chest has served, in some respects, to substantiate these conclusions. There is a general idea, expressed in most textbooks, in the literature, and widely held by roentgenologists and physical diagnosticians, that liquids in the pleural cavity, in the absence of pneumothorax, take on a fairly definite, uniform appearance on roentgen examination. This appearance is described, typically, as a dense shadow which, in the early stages of an effusion, obliterates the normal aeration of the costophrenic angle; as the fluid increases, the shadow extends medially over the diaphragm and upward along the periphery of the chest. The upper surface of this density is concave, and the shadow rises higher in the lateral and posterior than in the medial or anterior portions of the thorax. When a massive effusion is present the entire hemithorax is dense so that there are no levels or surfaces and obviously no possible differences in position. The position of the fluid in the latter type of effusion requires no discussion. In the cases in which the effusion does not completely fill the pleural cavity, the description given above will probably hold true, in the majority of instances, if the roentgen examination is made in the usual upright position. Contrary to much opinion in the literature, a change in position of the patient will, in the greater number of cases, produce a distinct change in the position of the fluid; not, however, to the same extent as would occur if gravity were the only factor involved. This has been abundantly proved by the author (3 and 4) and others in previous papers. The shifting occurs whether the fluid is exudative or transudative in nature. A change in the position of the patient from upright to supine (Fig. 1) may cause the shadow of the fluid to change from the typical appearance described above, to a thin density throughout the chest. If the patient is placed in the lateral decubitus position, a postero-anterior exposure being made, the upper surface of the fluid may appear quite flat rather than concave, and the dense shadow of the fluid will occupy largely the inferior costal gutter. The cases in which no change in position of the fluid occurs are invariably exudative in type; they are either of long standing so that adhesions have formed, or of more recent origin with pus of a thick fibrinous character. Aside from this shifting with change in position, however, there is a group of cases in which the fluid, even in the upright position, presents an appearance which is radically different from the usual picture described above. In such patients there are so many variations in the position of the fluid, and in the appearance of its upper surface, that interpretation of the roentgenograms may be difficult and diagnostic error may result.