The Roentgen Appearance of Lobar and Segmental Collapse of the Lung

Abstract

Collapse of the right middle lobe of the lung occurs frequently, and is still confused with interlobar effusion (1). The location of the middle lobe, between the greater and the lesser fissures of the right lung, explains the original mistaken roentgenologic interpretation of these two processes. On the roentgenogram, the pulmonary fissures appearing as lines, or septa (4, n), are now recognized as boundaries of the various lobes. The minor septum and approximately the lower half of the right major septum bound the middle lobe. In collapse of this lobe the septa tend to come closer together as the lobe decreases in size, and the final shadow of increased density may simulate that of interlobar effusion which would, if present, lie in the same plane. The shape of the shadow cast by interlobar effusion, however, is different, and very rarely is a proved case seen without fluid elsewhere in the pleural cavity. At the present time, the diagnosis of collapse of the middle lobe can be made accurately if certain definite characteristic signs are looked for, and if their importance is recognized. Collapse of the right middle lobe, or of one of its segments, occurred in 26 per cent of the group of 600 cases of collapse studied. It is our purpose to discuss in detail the roentgenologic appearance of the pulmonary abnormalities which distinguish collapse of the middle lobe, or of its segments, and the most satisfactory means of demonstrating them. The middle lobe lies in the antero-inferior portion of the right chest, making up essentially all of the pulmonary tissue adjoining the right border of the heart as seen on the roentgenogram. It is demarcated by two septa, the minor running more or less horizontally and the major running downward and anteriorly, as previously described (4, ii). The bronchus to the right middle lobe arises from the right main bronchus at the level of the origin of the bronchus to the dorsal division of the right lower lobe. The middle lobe bronchus immediately divides into two branches, the anteromedian which supplies the segment of the lobe adjoining the right border of the heart, and the posterolateral, which supplies the segment lying adjacent to the upper lobe and the anterolateral chest wall. Complete obstruction of the bronchus to the right middle lobe causes the lobe to decrease markedly in size, and roentgenologically to assume a somewhat pyramidal shape with its base against the right border of the heart and its apex extending toward the lateral chest wall. Since the general plane of the middle lobe is more or less oblique, running from the hilus anteriorly and inferiorly to the lower fourth of the anterior chest wall, the ordinary postero-anterior roentgenogram does not catch it entirely in profile, and thus the fact that it is the site of a disease process may not become apparent until some other abnormality is observed—that is, loss of definition of the right border of the heart.