title: "Sentinel lines"--an unusual sign of lower lobe contraction.
abstract: Of the various densities occurring in the lower zones of the standard postero-anterior chest radiograph, one sign has been ignored. Coarse linear densities at the bases may be due to adjacent lower lobe contraction. The cause is related to bending or kinking of the lower zone bronchi, usually the superior and inferior branches of the lingular bronchi. The densities are probably due to mucus-filled bronchi or alveolar atelectasis distal to the kink. resulting from poor bronchial drinage, and may indicate more extensive disease. The left lower lobe collapse may not be visible on the chest radiograph but the presence of these densities should alert the observer to the more important associated abnormality.
mesh_terms: D006801:Humans; D008168:Lung / Q000502:physiology; D008171:Lung Diseases / Q000000981:diagnostic imaging*; D011859:Radiography