of other lobes may result in increased transradiency of adjacent areas of the lung.
Right upper lobe collapse is relatively easy to spot on a plain chest X‐ray; there is an area of increased density in the upper medial aspect of the right hemithorax with elevation of the horizontal fissure and right hilum. In right middle lobe collapse there may be little to see on a PA X‐ray apart from lack of definition of the right heart border. This is a useful sign that helps to distinguish it from right lower lobe collapse where the right border of the heart remains clearly defined. In right lower lobe collapse there is also a triangular opacity in the right lower zone (usually medially) pointing to the hilum and the medial aspect of the right hemidiaphragm is obscured. The left upper lobe collapses anteriorly, becoming a thin sheet of tissue up against the anterior chest wall. It appears like a veil, most obvious superiorly and fading inferiorly. Left lower lobe collapse is manifest as a triangular area of increased density behind the heart shadow, often with a shift of the heart shadow to the left and increased transradiency of the left hemithorax because of compensatory expansion of the left upper lobe (see Fig. 4.4). Collapse is a sinister sign often indicating an obstructing carcinoma that may be confirmed by bronchoscopy.
Figure 4.1 Diagram of chest X‐ray (PA view). The right hemidiaphragm is 1–3 cm higher than the left (a) and on full inspiration it is intersected by the shadow of the anterior part of the sixth rib (b). The trachea (c) is vertical and central or very slightly to the right. The horizontal fissure (d) is found in the position shown and should be truly horizontal. It is a very valuable marker of change in volume of any part of the right lung. The left border of the cardiac shadow comprises (e) aorta; (f) pulmonary artery; (g) concavity overlying the left atrial appendage; (h) left ventricle. The right border of the cardiac shadow (i) is formed by the right atrium, the superior vena cava entering superiorly and the inferior vena cava which is often seen at its lower margin.
Consolidation
Air in the lungs appears black on X‐ray. Consolidation appears as areas of opacification sometimes conforming to the outline of a lobe or segment of lung in which the air has been replaced by an inflammatory exudate (e.g. pneumonia), fluid (e.g. pulmonary oedema), blood (e.g. pulmonary haemorrhage) or tumour (e.g. carcinoma with lepidic growth). Bronchi containing air passing through the consolidated lung are sometimes clearly visible as black tubes of air against the white background of the consolidated lung: air bronchograms (see Fig . 17.2). Structures such as the heart, mediastinum and diaphragm are usually clearly outlined as a silhouette on an X‐ray because of the contrast between the blackness of aerated lung and the whiteness of these structures. When there is abnormal shadowing in the lung adjacent to these structures, there is loss of the sharp outline, and this is often referred to as the silhouette sign although it is the absence of the expected silhouette that indicates an abnormality (Fig. 4.6).
Figure 4.2 Diagram of chest X‐ray (lateral view). (a) Trachea. (b) Oblique fissure. (c) Horizontal fissure. It is useful to note that in a normal lateral view, the radiodensity of the lung field above and in front of the cardiac shadow is about the same as that below and behind (x). Ao, aorta.
Pulmonary masses
Various descriptive terms such as ‘rounded opacity’, ‘nodule’ or ‘coin lesion’ are used to refer to pulmonary masses. Carcinoma of the lung is the most important cause of a mass on chest X‐ray but several other diseases may cause a similar appearance (Table 4.1, Fig. 4.7). Features such as cavitation, calcification, rate of growth, the presence of associated abnormalities (e.g. lymph node enlargement) and whether the lesion is solitary or whether multiple lesions are present may provide clues to diagnosis. However, these features are often not reliable indicators of aetiology, and the X‐ray appearances must be interpreted in the context of all the clinical information. Further investigations such as computed tomography (CT) and biopsy (bronchoscopic, percutaneous, surgical) are often necessary.
Figure 4.3 Radiographic patterns of lobar collapse. Collapsed lobes occupy a surprisingly small volume and are commonly overlooked on the chest X‐ray. Helpful information may be provided by the position of the trachea, the hilar vascular shadows and the horizontal fissure. LLL, left lower lobe; LUL, left upper lobe; RLL, right lower lobe; RML, right middle lobe; RUL, right upper lobe.
Cavitation
Cavitation is the presence of an area of radiolucency within a mass lesion. It is a feature of bronchial carcinoma (particularly squamous carcinoma) (Fig. 4.8), tuberculosis, lung abscess, pulmonary infarcts, granulomatosis with polyangiitis (GPA) and some pneumonias (e.g. Staphylococcus aureus, Klebsiella pneumoniae).
Figure 4.4 Left lower lobe collapse. The left lower lobe has collapsed medially and posteriorly and appears as a dense white triangular area behind the heart close to the mediastinum. The remainder of the left lung appears hyperlucent because of compensatory expansion. Bronchoscopy showed an adenocarcinoma occluding the left lower lobe bronchus.
Figure 4.5 Left lung collapse. There is complete opacification of the left hemithorax with shift of the mediastinum to the left. Bronchoscopy showed a small cell carcinoma occluding the left main bronchus.
Figure 4.6 The silhouette sign, showing abnormal lung shadowing in the left lower zone. Where the sharp outline of mediastinal structures or diaphragm is lost because of normal lung opacification, it can be concluded that the shadow is immediately adjacent to the structure (and vice versa). In example (a), the shadow must be anterior and next to the heart as the sharp outline of the heart is lost. In (b), it must be posterior, as the heart outline is preserved.
Table 4.1 Causes of pulmonary masses
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NeoplasticPrimary bronchial carcinomaMetastatic
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