The white lung field

Published on 23/05/2015 by admin

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Last modified 23/05/2015

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CHAPTER 4 The white lung field

4.1 Collapse

Collapse of a lung is an important cause of a white lung on X-ray. When confronted with a white lung it is important to be thorough in looking for the features suggestive of collapse since the presence of collapse indicates possible serious pathology.

Collapse of the lung leads to a loss of volume of that part of the lung and so the normal radiological landmarks will be distorted. To diagnose collapse look at each of these markings carefully and decide whether they are in the correct position. You may need to look at the lateral X-ray as well as the PA.

On the PA film:

1. If possible, compare with previous films – the change may be longstanding and benign and may not require further investigation. Of course, the clinical context must always be considered.

2. Look at the lung fields. The right lung should be larger than the left – if it is not, suspect an area of right-sided collapse.

3. Look at the diaphragms. The right diaphragm is usually higher than the left. Collapse in the left lung may distort this.

4. Look for the horizontal fissure in the right lung (pp. 18, 19). The horizontal fissure on the right should run from the centre of the right hilum to the level of the 6th rib at the axillary line. If this is pulled up it suggests right upper lobe collapse or, if pulled down, right lower lobe collapse.

5. The heart should straddle the midline with one-third to the right and two-thirds to the left. The heart shadow will be deviated to the side of collapse.

6. The heart borders should be distinct. If the lung adjacent to the heart is collapsed then the heart border will appear blurred. If the right heart border is blurred this indicates right middle lobe collapse and if the left is blurred, lingular collapse.

7. The trachea should be central. Collapse of the right or left upper lobes can pull the trachea towards the area of collapse. Again this may be easier to spot by comparing with the patient’s old films.

On the lateral film:

Check the position of the oblique and horizontal fissures (pp. 13 and 14). Any displacement from their normal position suggests collapse. Collapse of any of the lobes of the lung gives a distinct appearance on the X-ray.

Volume loss

A more subtle concept is that of volume loss. Many pulmonary processes, including collapse, may cause progressive amounts of volume change during their evolution. Volume loss will decrease the vascularity of the unaffected part of the lung which will look blacker as a result as this lobe has to over-inflate, so the vessels become more spread out. This is a difficult sign to detect.

1. Right upper lobe collapse. There is an area of whiteness in the upper zone of the right lung (1). The horizontal fissure is elevated, there is an apparent right upper hilar ‘mass’, the trachea is deviated to the right (2) and the ribs over the area of whiteness are closer together than is normal. On the lateral film the increased whiteness in the uppermost part of the chest may be seen.

2. Right middle lobe collapse. This can be difficult to spot. The right diaphragm may be slightly raised (1) and the horizontal fissure (2) may be lower than usual. The upper part of the lower zone may have a hazy white appearance (3) and the heart border is sometimes indistinct. It is easier to detect in the lateral film. There is a triangular area of whiteness with its apex at the hilum (4) and its base running between the sternum and the diaphragm (5).

3. Right lower lobe collapse. There is a whiteness immediately above the diaphragm (1) causing a loss of its outline. On the lateral film there is a white triangle at the lower posterior part of the lung field (2). Note how the outline of the right heart border is maintained.

4. Left upper lobe collapse. This is difficult to spot. Remember that most of the left upper lobe lies in front of, as opposed to above, the left lower lobe. When it collapses it causes a haze to appear over the whole of the left lung field.

The CT image shows the midpoint of the mediastinum shifted to the left (1). The left upper lobe bronchus is filled by a soft tissue density: a tumour. (2). The diagnosis can be easily achieved at bronchoscopy.

5. Left lower lobe collapse. This is easy to miss. The left lower lobe collapses down behind the heart. The left lung field appears much darker than normal and the heart shadow will appear much whiter than normal. If you look carefully you can see a white triangle behind the heart (1). On the lateral film you may see a white triangle at the bottom posterior corner of the lung fields (2) and the vertebral bodies will appear whiter.

4.2 Volume loss

This patient had a pneumonectomy several years ago. The left hemi-thorax is white, and the mediastinum has shifted to the left. The left-sided ribs are also crowded together compared to the right side, and the patient has developed a slight curvature of the spine. The right lung becomes hyperinflated, and some of the lung crosses over the midline.

A pneumonectomy is another cause of a white lung. You should know from the history and your examination that the patient has had a pneumonectomy. Look at the X-ray for the following features:

1. Look at the mediastinum. Look first at the trachea, which should be shifted to the side of the pneumonectomy, then look at the heart border. With a pneumonectomy the heart is often shifted so far that its border is no longer visible.

2. Look at the opposite lung field. Since the mediastinum is shifted the contralateral lung is hyperinflated and so appears darker than usual.

3. Look at the side of the whiteness. You should not be able to see the upper border of the diaphragm on the side of the pneumonectomy.

4. Look carefully at the ribs. If the patient has had a pneumonectomy, ribs would either have been cut or removed during the operation. Therefore look for any rib deformity or note the absence of any rib which would help confirm the diagnosis. The most usual rib to be affected is the 5th.

A very rare cause of a similar appearance is extensive hypoplasia or congenital absence of one lung.

This patient had right upper lobectomy and postoperative radiotherapy. Both of these have led to volume loss in the remaining right lung. The trachea has been pulled to the right as a result. The lung is of increased blackness on the right compared to the left because the remaining lung is hyperinflated.

The right diaphragm has also changed shape, and this appearance is known as diaphragmatic tenting. It looks as though a tent pole has been put underneath to push it upwards.

Tracheal deviation can be the result of it being pushed by a mass lesion in the mediastinum, most often an enlarged thyroid gland, as in the case shown here. The lung volumes in this case are normal, and the ribs and diaphragms are in their normal positions. In the elderly a very tortuous aorta may also lead to tracheal shift.

4.3 Consolidation

This is the appearance of a lobar pneumonia. Notice how the inferior margin of the consolidation is quite straight. This appearance indicates a right upper lobe pneumonia. An air bronchogram (arrow) is visible.

This shows much more widespread consolidation affecting both lungs, especially in the mid to lower zones, and is a bronchopneumonia. An air bronchogram (arrow) is again visible.

Again you can see an area of white lung. Look first at the nature of the whiteness and its border. If it is uniform with a well-demarcated border you are much more likely to be dealing with an area of collapse or a pleural effusion. If the shadowing is not uniform and the border is not so well demarcated the possibilities are consolidation, fibrosis or some other infiltrative condition. It can be difficult to diagnose consolidation so make your way carefully through the following steps:

1. Remember the clinical history. In the presence of a temperature and signs of infection, consolidation is by far the most likely abnormality.

2. Look at old X-rays. Fibrosis is usually a chronic condition and consolidation much more transient. The presence of a similar abnormality on a previous X-ray should lead you to suspect fibrosis rather than consolidation.

3. Look carefully at the nature of the shadowing. In consolidation the alveolar spaces become filled with fluid making them appear white, whereas the airways retain air making them appear black. If you look closely at an area of consolidation you can often make out the small airways as black against a white background – the so-called ‘air bronchogram’.

4. Look at the distribution of the shadowing. Fluid sinks, so consolidation gets denser as one moves down the lung. The shadowing in consolidation will often be denser and more clearly demarcated at its lower border.

If a patient is admitted with pneumonia it is not necessary to repeat the chest X-ray before discharge if they make a satisfactory recovery. For patients who fail to recover, further X-rays are necessary to look for possible complications such as the development of an empyema or pulmonary abscess. For patients ill enough to warrant admission to intensive care, early follow-up X-rays are warranted to ensure that their condition is not progressing.

All patients should be reviewed after 6 weeks. If they have persistent symptoms or signs or are at risk of malignancy (smokers and those over 50 years of age) a follow-up X-ray should be arranged to ensure complete resolution. If there is persistent consolidation at this stage, further investigations should be arranged to exclude malignancy.

4.4 Pneumocystis carinii (jiroveci) pneumonia (PCP)

This patient is on long-term immunosuppression following renal transplant. He presented with a week-long history of a dry cough and increasing breathlessness. Following bronchoscopy and lavage he was diagnosed with Pneumocystis pneumonia, an organism recognized to cause pneumonia in immune compromise from many causes.

The film shows vague white shadowing around the hilum. There is also enlargement of the right hilum from lymphadenopathy.

Pneumocystis carinii pneumonia (PCP) can be difficult to diagnose on a chest X-ray and in 10% of patients with PCP the chest X-ray is normal. It is something to suspect if a patient presents with shortness of breath and hypoxia which are out of proportion to a relatively normal looking chest X-ray.

If you suspect that the chest X-ray shadowing may be due to PCP then look for the following features:

1. Look at lung volumes. Very early PCP may be suspected when both lungs show reduced volume. Look for an old chest X-ray. If there is one, compare the lung volumes to a chest X-ray taken when the patient was well.

2. Look at the area around the hilum. In PCP there is often white shadowing in this region. This can be very vague. You can best appreciate it by looking at the blood vessels as they come away from the hila. In PCP the blood vessels will appear less well defined than normal.

3. Look for peribronchial cuffing. This is best seen in airways that are seen ‘end-on’ and is due to fluid seen as increased whiteness within the walls of the airways. This gives the wall of the airway a thickened or fuzzy appearance, with a central hole, rather like a well-sucked ‘Polo’ mint.

4. Look for large areas of whiteness extending throughout the lung fields. These may develop as the disease progresses and represent large areas of consolidation. Typically, in PCP the whiteness does not extend to the apices or affect the costophrenic angles.

4.5 Pleural effusion

This pair of films shows the varied appearances of pleural effusions. The first film shows a small left effusion filling the costophrenic angle. It has a curved upper margin.

The second film shows a much larger right pleural effusion. The fluid now encases the lung and the increased whiteness can be seen around the apex of the lung. Compare this almost totally white lung with the appearance following a pneumonectomy. In the case of a large pleural effusion, the mediastinum may be pushed away from the midline by the large volume of fluid.

If you see an area of whiteness at the base of a lung then the possible causes are a pleural effusion, a raised hemidiaphragm and an area of consolidation or collapse. You need to determine which of these it is.

1. Look closely at the texture of the whiteness. Consolidation usually causes more heterogeneous shadowing, typically with the presence of an air bronchogram. Look carefully for an air bronchogram (p. 60) since its presence will point to consolidation rather than a pleural effusion.

2. Look at the shape of the upper border of the shadowing. Fluid will have a meniscus so the upper outer border of an effusion will be concave.

3. To differentiate an effusion from a raised hemidiaphragm look again at the shape of the upper border. The upper border of an effusion will peak much more laterally than you would expect the diaphragm to do. This is a matter of looking at lots of X-rays.

4. Look for mediastinal shift. It can be difficult to differentiate an effusion from lung collapse. Collapse usually causes mediastinal shift towards the white lung field so the absence of shift suggests the presence of an effusion. Remember, however, that collapse can accompany an effusion so that, although the absence of shift implies an effusion, its presence does not exclude it.

5. A lateral view is often helpful since the meniscus on a lateral can be much more obvious. Look for the presence of a meniscus which, often on the lateral, is seen to extend up into one of the fissures.

6. If you diagnose an effusion look on the X-ray for possible causes. Check the size of the heart (a large heart points to heart failure) and look at the hilum for possible enlargement. Look at the visible parts of the lung fields for obvious masses and check the bones for signs of metastasis. Look very carefully at the apices of the lungs for tumours and TB.

7. To confirm the presence of pleural fluid request an ultrasound of the chest. This is particularly important if you plan to aspirate the effusion or put in a chest drain.

Some causes of a pleural effusion

Transudate < 30 g/l of protein

Heart failure, e.g. congestive cardiac failure, pericardial effusion

Liver failure, e.g. cirrhosis

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