7
B - Breathing

How to review the lungs

A general rule is that black = air and white = no air. There are five main areas to look at.

1. Are the lungs uniformly expanded?
2. Compare the lung fields and look for white areas (opacities):
   • compare left apex with right apex;
   • compare left upper zone with right upper zone;
   • compare left mid zone with the right mid zone;
   • compare the left lower zone with the right lower zone.
3. Look around the edges of each lung.
4. Look at the costophrenic angles.
5. Look for the following four silhouettes (outlines) (Figure 7.1):
   1. Right heart border. Loss of definition of the right heart border silhouette indicates a loss of air in the middle lobe (due to collapse or consolidation).
   2. Left heart border. Loss of definition of the left heart border silhouette indicates a loss of air in the lingula (part of the left upper lobe).
   3. Right hemidiaphragm. Loss of definition of the right hemidiaphragmatic silhouette indicates a loss of air in the right lower lobe (due to collapse or consolidation), or that there is something between the diaphragm and the right lower lobe (e.g. pleural fluid).
   4. Left hemidiaphragm. Loss of definition of the left hemidiaphragmatic silhouette indicates a loss of air in the left lower lobe (due to collapse or consolidation), or that there is something between the diaphragm and the left lower lobe (e.g. pleural fluid).

Figure 7.1 The four silhouettes. The right heart border (red), left heart border (yellow), right hemidiaphragm (purple), and left hemidiaphragm (pink).

Note: It is normal to see all four silhouettes as there should be air in the lobes adjacent to each these four areas. If there is an opacity in the lobe adjacent to one of these areas (e.g. consolidation or collapse), then the crisp silhouette is lost and this is called the 'silhouette sign' (Figure 7.2). Because the 'silhouette sign' refers to the loss of one of the above silhouettes, it may be more accurate to call it the 'loss of silhouette sign' or 'loss of outline sign'.

Figure 7.2 Diagrammatic representation of the silhouette sign. Image 1 (left) shows a normal crisp silhouette. Image 2 (right) shows the 'silhouette sign'. As you can see the 'silhouette sign' refers to loss of definition/blurring of the normal crisp silhouette.

What to look for

Chest X-rays do not show many specific diseases (e.g. pneumonia, primary lung malignancy, etc.), only signs of pathology, which can give a clue to the underlying disease process. The following are a list of pathologies and signs that you should know.

• Consolidation/airspace opacificationp.29
• Air bronchogramp.31
• Collapse (atelectasis) overviewp.32
  • right upper lobe collapsep.33
  • middle lobe collapsep.34
  • right lower lobe collapsep.36
  • left upper lobe collapsep.37
  • left lower lobe collapse?p.39
  • complete lung collapsep.40
• Pneumonectomyp.41
• Solitary mass lesionp.44
• Multiple mass lesionsp.47
• Cavitating lung lesion?p.48
• Fibrosisp.50
• Pneumothorax?p.53
• Tension pneumothoraxp.55
• Hydropneumothoraxp.56
• Pleural effusionp.57
• Pulmonary oedemap.60
• 'Bat's wing' pattern opacificationp.61
• Septal linesp.64
• Asbestos-related lung diseasep.65
  • benign pleural diseasep.65
  • asbestosisp.66
  • mesotheliomap.66

Consolidation/airspace opacification

Consolidation (also known as airspace opacification) is the replacement of alveolar air by fluid, cells, pus, or other material (Figure 7.3). Pneumonia is by far the most common cause of consolidation. It is also sometimes seen in primary TB.

Figure 7.3 Diagrammatic representation of three normal alveoli (left image) and consolidation (green) within the three alveoli (right image).

Features of consolidation on a chest radiograph

• Heterogenous or patchy opacification: the opacification is non-uniform and the border is not well demarcated (it sometimes looks fluffy).
• Lobar or segmental distribution: the opacification usually corresponds anatomically to a lobe or lung segment.
• Air bronchogram (see p. 31): the presence of an air bronchogram would confirm that the density (fluid/pus) was in the alveoli and not the larger airways. Bronchial breathing on auscultation is the clinical sign of an air bronchogram.
• No loss of lung volume: lung volumes may actually increase in the early stages of consolidation. In later stages there can be a small loss of lung volume due to secretions obstructing airways; however, as a general rule, there is no significant loss of lung volume in consolidation.

Note: Remember the clinical history. In the presence of a temperature and signs of infection, consolidation is by far the most likely abnormality. Also compare with previous radiographs - the presence of a similar abnormality on a previous radiograph should lead you to suspect fibrosis rather than consolidation.

Example 1: Figure 7.4

Figure 7.4 Consolidation in the lingula (green). There is heterogenous airspace opacification in the left lower zone and no loss of lung volume. The left hemidiaphragm can be clearly seen, however the left heart border is poorly defined (silhouette sign); therefore, the pathology is in the lung adjacent to the left heart border, i.e. the lingula of the left upper lobe.

Example 2: Figure 7.5

Figure 7.5 Consolidation (green) in the middle lobe and left lower lobe. There is heterogenous airspace opacification in the right and left lower zones and no loss of lung volume. We know the consolidation on the right side is in the middle lobe as there is loss of definition of the right heart border (silhouette sign) and the superior border is the horizontal fissure (marked with a white dashed line). We know the consolidation on the left side is in the left lower lobe as there is loss of definition of the left hemidiaphragm (silhouette sign), yet the left heart border is still clearly visible.

Example 3: Figure 7.6

Figure 7.6 Consolidation (green) in both lungs with moderate sparing of the right upper zone (which appears darker than the rest). There is heterogenous airspace opacification, no loss of lung volume, and air bronchograms seen in both lungs. You can also see an endotracheal tube (white arrowheads), ECG leads (white dashed lines), nasogastric tube in situ, and other overlying tubing.

Air bronchogram

An air bronchogram is the radiographic appearance of an air-filled bronchus that is surrounded by fluid-filled or solid alveoli.

• It can appear when there is consolidation (e.g. pneumonia) or pulmonary oedema in the surrounding alveoli.
• Sometimes it is a good prognostic sign as it shows that secretions are able to exit from the consolidated region via the bronchus.

Note: The air bronchogram is the radiological equivalent of bronchial breathing on clinical examination.

Example 1: Figure 7.7

Figure 7.7 This is the same radiograph as Figure 7.6 and is a good example of an air bronchogram caused by severe bilateral consolidation. The air bronchogram is marked in grey on the inferior radiograph. You can also see an endotracheal tube, ECG leads, nasogastric tube in situ, and other overlying tubing.

Collapse (atelectasis) overview

Collapse is failure of all or part of the lung to expand due to loss of air in the alveoli.

• Lobar collapse refers to collapse of a particular lobe of the lung.
• Lung collapse refers to collapse of a whole lung.

General features of collapse on a chest radiograph include:

• An increase in density, representing lung devoid of air (whiteness).
• Signs indicating decreased lung volume, such as:
  • displacement of mediastinum/trachea towards the collapsed lung;
  • elevation of the hemidiaphragm;
  • compensatory over-inflation of adjacent lobes or opposite lung.

Note: When looking at a white lung, it is important to be thorough in looking...