Background

Collapse of the five lung lobes (right upper, middle and lower, left upper and lower) produces characteristic appearances on a CXR. Interpretation requires a good knowledge of lobar anatomy and of silhouette signs (see Page 5).

Lobar collapses are important as they are a common presentation of bronchial carcinoma (see Chapter 15). Other causes of lobar collapse include any process that obstructs a main bronchus, including mucus plugging in asthmatics and postoperative patients, foreign bodies and ET tubes (these usually cause complete collapse; see Chapter 2).

General radiological features common to all collapses

Remember to use the silhouette sign to your advantage.

A collapsed lobe is of increased density. Remember that edges are only seen on films if two structures of different density are next to each other. In lung collapse a lobe effectively becomes water/soft tissue dense. So if an edge you would expect to see disappears this might help you determine which lobe is collapsed.

For example, in left lower lobe collapse, the left lower lobe is adjacent to the left hemidiaphragm. When this lobe collapses the contour of the left hemidiaphragm is no longer seen.

Collapsed lung is generally homogeneous in density – with no air bronchograms seen.