Intrapulmonary effusion. Effect of expiration on the pseudodiaphragmatic contour

The pseudodiaphragmatic contour of infrapulmonary effusion may differ from the contour of an elevated hemidiaphragm in the frontal view in that its medial portion is straight and shows a gradual inclination upward and laterally from the cardiac shadow, so that its apex is located more laterally. Previous studies have indicated that this configuration is seen only in about 50% of cases of infrapulmonary effusion. Using expiration radiographs, it is possible to routinely demonstrate this characteristic pseudodiaphragmatic contour. This study provides an additional sign of infrapulmonary effusion and aids in the explanation of the pseudodiaphragmatic contour.