The Roentgen Appearance of Lobar and Segmental Collapse of the Lung

Abstract

Diagnosis of collapse of individual lobes or segments of lobes requires criteria additional to those which are necessary in collapse of an entire lung or the major part thereof (7, III). Besides the well recognized signs, therefore, the roentgenologist must look for any change from normal in the position of the hili and in the position and contour of the septa, and for rearrangement of the vascular shadows. Collapse of a lower lobe occurs rather frequently, but it is often overlooked or misinterpreted because the shadow of increased density does not stand out as clearly as in other pathologic. processes, such as consolidation. The shadow may be small and so located that it is hidden by overlying structures, as by the mediastinum and diaphragm on the posteroanterior roentgenogram and the spine on the lateral roentgenogram. Roentgenologically, the two lower lobes are essentially alike both in structure and position, so that the appearance of collapse of the whole lobe or of its segments is similar on the two sides. One important difference is that disease processes in the left lower lobe are often obscured by the heart shadow, but with the technic previously described (7, r) this difficulty is overcome. In the 600 cases studied, the left lower lobe was more frequently involved than the right, the left being collapsed in 262 cases and the right in 156. In the majority of instances, it is possible, with satisfactory technic, to demonstrate the location of the septa which bound the individual lobes (7, II). Roughly, each major septum runs from the level of the fifth thoracic vertebra posteriorly to a point near the anterior portion of the diaphragm. The pulmonary structures seen posterior to the greater septa represent the lower lobes. On the right side a fair portion of the lower lobe is behind both the upper and middle lobes, while on the left, the upper lobe and its lingular portion lie in front of the lower lobe. The remainder of the lower lobes lies below the shadow of the dome of the diaphragm. It is evident, therefore, that in the postero-anterior projection essentially the entire lower lobe on each side is either superimposed on shadows of the adjoining lobes or is obscured by the diaphragm. Frequently the first evidence to suggest a decrease in size of a lower lobe is the demonstration on the lateral roentgenogram of change in the normal position of a major septum, which appears to lie further posteriorly than usual. Shortly after this becomes evident, it is observed that a large number of the pulmonary markings of the lower lobe tend to radiate from the hilus downward and posteriorly just anterior to the spine, where they fan out anteriorly and posteriorly in gentle curves.