The white lung field

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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.

4.6 Asbestos plaques

This is the chest film of a 63-year-old man admitted following a gastrointestinal haemorrhage (hence the central venous pressure line) who had been exposed to asbestos whilst working in a naval dockyard. You can see multiple calcified pleural plaques on the inner chest wall.

Pleural plaques represent areas of pleural thickening caused by exposure to asbestos fibres. They may be predominantly soft tissue with small amounts of calcium or be heavily calcified. Isolated pleural thickening is a cause of a localized area of white lung and can be difficult to separate from lung shadows. If you suspect pleural plaques then:

1. Look throughout the lung fields of both lungs. Pleural thickening is easy to identify at the periphery where it appears as a thickened line around the edge of the lung. If you can identify pleural thickening here it makes it more likely that the other areas of whiteness are plaques superimposed over the lung field.

2. Carefully look at the position of the whiteness and compare it to what you know of the anatomy of the lung. If the whiteness follows intrapulmonary structures, for example a lobe of the lung, then it may be originating from the lung itself. If it crosses such structures then it is probably pleural.

3. Compare the distribution of the whiteness to the line of the anterior portion of the ribs. Asbestos plaques are very commonly found running along the line of the anterior portion of the ribs.

4. Look at the distribution of the patches. Pleural plaques are most prevalent in the mid zones and axillary region of the mid chest. They tend to spare the upper zones and costophrenic angles. Look carefully at both lung fields. Pleural plaques are usually bilateral and you should be wary of making this diagnosis if they are present in only one pleural cavity.

5. Look at the diaphragm. Pleural plaques along the diaphragm are often calcified. If you see streaks of dense white material (calcium) running along the diaphragm it implies that pleural plaques are present.

6. Look at the nature of the whiteness. Pleural plaques are patchy in nature as opposed to a pleural effusion which is more uniform. Plaques are sometimes said to have a map-like appearance due to areas of patchy calcification within them. Look at their edge. This should be well defined as opposed to ‘companion shadows’ that have poorly defined margins.

7. Look at old X-rays. Pleural plaques are slow growing and are probably visible on previous X-rays.

4.7 Mesothelioma

This is the chest X-ray of a 68-year-old man with a history of asbestos exposure. He presented with right lateral chest wall pains. The film demonstrates lobulated pleural thickening around the upper, mid and basal right lung, with further pleural thickening evident next to the right side of the mediastinum. CT of a mesothelioma in a different patient is shown on page 71.

Mesothelioma is a malignant tumour of the pleura. The shadowing it causes will have the characteristics of pleural shadowing and some of the characteristics of malignant shadows. If you suspect the whiteness to be mesothelioma then:

1. Look carefully at the spread of the whiteness and determine whether it follows lung boundaries. If it does not, then the whiteness may be pleural in origin.

2. Look at the margins of the whiteness. If they are lobulated in nature, then this suggests malignancy.

3. Look at the upper edge of the whiteness. The main differential is a pleural effusion. A pleural effusion would be unlikely if the upper edge was lobulated and no meniscus was visible.

4. Compare the volume of the affected side. Loss of volume on the affected side may increase your suspicions of a mesothelioma.

Pleural tumours

Primary pleural adenocarcinoma

Pleural sarcoma

Pleural fibromas

Neurofibromas arising paravertebrally or in relation to an intercostal nerve

4.8 Pleural disease on a CT scan

The pleura should not really be visible on a CT scan, since they are so thin. If you see an increased grey area on the inner surface of the chest wall, then suspect that the patient may have pleural disease. Pleural abnormalities are best seen on a spiral CT.

Remember, the pleura is in two layers with a potential space in between. Pleural thickening can affect the visceral (next to the lung) or the parietal (next to the chest wall) pleura. The double layers of pleura run into and out of the fissures of the lung.

If you see increased density around the inner chest wall:

1. Look at the colour of the pleural density on the soft tissue window.

a. Is it grey? The commonest pleural abnormality is pleural fluid. This will appear darker than the muscles of the chest wall. If the pleural density is the same as the chest wall, it is more likely to be pleural thickening.

b. Is it white? This is more likely to be pleural calcification. Pleural plaques often contain very bright white areas where they have calcified.

2. Are the margins of the pleural density smooth or lobulated?

a. Does it have smooth margins? This may be pleural fluid or pleural thickening. Multiple discrete lesions that are short but quite deep are probably pleural plaques.

b. Does it have lobulated margins? This is more likely to be a malignancy.

3. Is the pleural density very extensive or patchy?

a. Benign pleural thickening and malignant pleural diseases, especially mesothelioma (p. 71), will give a much more diffuse thickening extending over a much greater area of pleura.

b. Pleural plaques are smaller (usually 1–4 cm in length) and well defined. As both pleural plaques and mesothelioma can occur following asbestos exposure, the two may be found together.

4. Look at the position. A small pleural effusion will usually lie against the posterior chest wall as the patient is lying flat for the CT. A larger pleural effusion will surround the lung and compress it, causing some of the outer regions of the lung to become solid. This fluid can track into the fissures.

5. Look at the ‘normal’ pleura. With an empyema, if a contrast-enhanced scan has been performed, as well as the grey fluid the pleura may ‘enhance’ and appear whiter than normal.

4.9 Lung nodule

There is a 3 cm round nodule in the left mid zone. This would need to be investigated as it may represent a small tumour. If bronchoscopy does not provide the answer, the nodule could be biopsied percutaneously under CT guidance.

The term ‘lung nodule’ is used to describe a discrete area of whiteness situated within a lung field. It is less than 3 cm in diameter. It is not necessarily strictly circular. The main worry is that it may represent a carcinoma. Other possibilities are a localized area of consolidation, an abscess or a pleural abnormality. Go through the following steps in assessing the abnormality:

1. Look at the edge of the lesion. A spiculated, irregular or lobulated edge is suggestive of malignancy.

2. Look for areas of calcification. These would be dense white (the same density as bone) and be obviously much denser than the rest of the lesion. Calcification is rare in a malignant lesion and would point you to an alternative diagnosis.

3. Look at the nature of the whiteness. If the lesion is cavitating the centre may be darker than the circumference. If looking at an X-ray film, stand back from the X-ray since a cavity is often easier to see from a distance.

4. Look for an air bronchogram. This is a sign of consolidation and so would be a most unusual finding if the lesion was a tumour.

5. Look for other coin nodules. The presence of more than one strongly suggests metastatic disease.

6. Look for abnormalities peripheral to the lesion. A tumour may cause problems distal to it such as infection causing consolidation or an area of collapse.

7. Look carefully at the rest of the X-ray. Malignant tumours may be associated with mediastinal lymphadenopathy or bone metastasis.

8. Look at old films if available. Tumours grow, and so if the lesion was present on an earlier film compare its size. Some tumours grow slowly, but it is safe to say that if the lesion has not changed over a period of two years or greater it is unlikely to be malignant.

The arrow marks the location of the left oblique fissure. The coin lesion seen on the plain film lies on the oblique fissure and in front of it. The remainder of the CT scan showed no evidence of metastatic disease and no hilar or mediastinal lymph nodes were involved. The patient was referred for a PET scan and subsequently underwent a left upper lobectomy.

Here we can see a nodule with a black centre indicating that it has cavitated. This was proven to be a squamous cell carcinoma.

Causes of solitary pulmonary nodules

Benign tumour, e.g. hamartoma

Malignant tumour, e.g. bronchial carcinoma, single secondary

Infection, e.g. pneumonia, abscess, tuberculosis, hydatid cyst

Rheumatoid nodule

4.10 Cavitating lung lesion

These two films both demonstrate cavitating lung lesions. In the first study there are bilateral thin-walled cavities, some with air–fluid levels. This was due to Wegener’s granulomatosis.

The second film shows a single cavitating mass lesion in the left mid zone. This has a much thicker wall. This lesion was found to be due to a cavitating tumour. The thickness of the wall makes this a more likely diagnosis.

Some coin lesions may cavitate, and if you have identified a coin lesion, it is important to look for the features of cavitation. Therefore:

1. Look at the centre of the lesion and compare it to the periphery. If the centre is darker this points to cavitation.

2. Look for a fluid level. Look for a horizontal line within the lesion. There will be whiteness (fluid) below the line with an area of black (air) above. Fluid levels are common in cavities and their presence should suggest one.

3. Look at the lateral film. Cavities and fluid levels are often easier to see on a lateral, especially when they are posterior or inferior in position.

4. Look at old films. If the lesion is longstanding, it may be possible to see the cavity developing.

If you diagnose a cavitating lesion:

1. Look at the wall of the cavity. It is often said that cavity walls are thicker (> 5 mm) when the lesion is a neoplasm as opposed to an abscess. This rule does not always hold, but the thicker the wall the more likely it is that the lesion is neoplastic.

2. Look carefully at the inside of the cavity. If there appears to be a white ball within it, this is characteristic of an aspergilloma.

Causes of cavitating lung lesions

Cavitation around a pneumonia

Wegener’s disease

Rheumatoid nodules (rare)

4.11 Left ventricular failure (LVF)

This patient presented with an acute cardiac event. At present the pleural spaces are clear but it is common in pulmonary oedema to develop pleural effusions. These are often larger on the right than on the left. Pulmonary upper zone blood vessels are also often dilated, as is shown in this film (arrows). This patient’s film clearly shows ‘bat’s wing’ hilar shadows characteristic of pulmonary oedema. The magnified image of the right lower zone (opposite) shows the horizontal septal lines more clearly (arrowed).

If you suspect heart failure as a cause of a generalized, or localized, area of shadowing then:

1. Look at the size of the heart. The presence of left ventricular dilatation is strongly suggestive of heart failure. In a PA film the maximum diameter of the heart should be less than half that of the maximum diameter of the thorax (the cardiothoracic ratio). If it exceeds this, then there is a cardiac abnormality, such as left ventricular enlargement, and this suggests that the associated shadowing is due to LVF (see Chapter 7 for other causes of an enlarged cardiac shadow). You cannot comment on the size of the heart on an AP portable film since the heart is anterior and will appear magnified. Note also that in acute onset LVF you may not get cardiac enlargement.

2. Look for Kerley B lines. These are caused by oedema of the interlobular septa. They are horizontal, non-branching, white lines best seen at the periphery of the lung just above the costophrenic angle.

3. Compare the size of the upper lobe and lower lobe blood vessels. Take an upper lobe and a lower lobe blood vessel at similar distances from the hilum and compare their widths. The upper should be narrower than the lower. If they are the same size or the upper is wider there is upper lobe blood diversion – the first sign of heart failure. Note that this only applies to an erect film. Upper lobe blood diversion is normal on a supine film and not suggestive of heart failure – a common mistake.

Upper lobe blood diversion is due to lower zone arteriolar vasoconstriction secondary to alveolar hypoxia.

Severe heart failure

Severe pulmonary oedema gives confluent alveolar shadowing which spreads out from the hilum giving a ‘bat’s wing’ appearance. If this is the cause of generalized shadowing then upper lobe blood diversion and Kerley B lines may be present. Look also at the hilum. In pulmonary oedema it may appear distended and the vessels close to the hilum may be blurred.

Severe heart failure vs non-cardiogenic pulmonary oedema

It can be difficult to distinguish non-cardiogenic pulmonary oedema (acute respiratory distress syndrome) from LVF. In non-cardiogenic pulmonary oedema the heart size is likely to be normal (though see 1 above) and there will not necessarily be sparing of the peripheries. (See also Chapter 4.12.)

4.12 Acute respiratory distress syndrome

This 36-year-old man presented with severe upper abdominal pain and was diagnosed as having pancreatitis. Whilst in hospital he became acutely short of breath and required intubation and ventilation. Note the ET tube (arrowed). A chest X-ray was taken which suggested that he had developed the complication of acute respiratory distress syndrome (ARDS). Note that the X-ray shows multiple bilateral white shadows but does not have any signs of left ventricular failure. Unfortunately this man died after 3 weeks of mechanical ventilation on the intensive care unit.

Acute respiratory distress syndrome (ARDS) is defined as respiratory failure in association with a chest X-ray that shows confluent alveolar opacification (whitening) of the lungs that looks like pulmonary oedema.

The other (and far more common) cause of pulmonary oedema is left ventricular failure which is also a cause of respiratory failure. Therefore, if you see a chest X-ray that has bilateral white shadows in the lungs and you suspect ARDS look for the following clues:

1. Look at the distribution of the shadowing. In ARDS it should be present in both lungs – that is part of the definition. Look also at the nature of the shadowing. It is usually fairly ill-defined which means it is difficult to see a clear edge. It may also have the features of consolidation which means that you may be able to see an air bronchogram within it (p. 60).

2. To distinguish ARDS from left ventricular failure:

a. Look at the heart size. In left ventricular failure you would expect the heart to be big. In ARDS it may be normal size.

b. Look again at the distribution of the shadowing. In left ventricular failure it tends to be more central whereas in ARDS it is more peripheral.

c. Look for Kerley B lines (p. 84). Although these do occur in ARDS they are far more common in left ventricular failure.

d. Look for the presence of a pleural effusion. These may be small so look carefully at the edge of the diaphragm for loss of the normal costophrenic angle. Pleural effusions can occur in ARDS but they are much more common in left ventricular failure.

e. Look at old films. A large heart and pleural effusion may have shown on earlier films and may point to left ventricular failure as a more likely diagnosis.

If you are certain that the chest X-ray suggests a diagnosis of ARDS then look for clues as to the cause. There are many causes of ARDS (see Box on p. 89) and most can only be picked up by history and examination. However, an asymmetrical distribution of the shadowing, i.e. significantly more shadowing in one lung than the other, may point to lung injury as a cause. Chest X-rays taken just before the development of ARDS may show an obvious pneumonia.

4.13 Bronchiectasis

This film shows a localized area of bronchiectasis in the right lower lobe which has resulted from earlier pertussis infection. In the lower lobe you can see a cluster of typical ring shadows giving a ‘bunches of grapes’ appearance (1) together with bronchial wall thickening seen side-on, which gives two thick parallel lines, known as tramline shadows (2).

Bronchiectasis can be difficult to diagnose on a plain chest X-ray. If you suspect it as a cause of increased shadowing then look for the following features:

1. Ring shadows. These look like rings and are any size up to 1 cm in diameter. They can be single but usually occur in groups giving a ‘bunches of grapes’ appearance. Ring shadows represent diseased bronchi seen end on.

2. Tramline shadows. Look for these towards the periphery of the lung. They consist of two thick white parallel lines separated by black. It is common to get parallel lines close to the hilum in the normal chest X-ray but these lines are hairline in nature. True tramline shadowing is thicker and is not necessarily close to the hilum. Tramline shadows are diseased bronchi seen side on.

3. Tubular shadows. These are solid thick white shadows up to 8 mm wide. They represent bronchi filled with secretions seen side on. They are not common but their presence suggests bronchiectasis.

4. Glove finger shadows. These represent a group of tubular shadows seen head on and look like the fingers of a glove – hence the name!

The presence of any of these features suggests the possibility of bronchiectasis. A normal chest X-ray does not, however, exclude the diagnosis and CT scanning is the most sensitive diagnostic test available.

The HRCT scan and bronchiectasis

Although bronchiectasis can be diagnosed on a plain chest X-ray, in half the patients the X-ray is normal. Therefore, if you suspect bronchiectasis and the chest X-ray is normal, you will need to undertake a high-resolution CT (HRCT) scan. An HRCT scan may also give you clues as to the cause of the bronchiectasis and will give you a much more accurate picture of the extent of disease.

To diagnose bronchiectasis on HRCT scanning you need to identify areas in which the bronchi are dilated. There are a number of ways of doing this. Look at the lung windows:

1. Look in the periphery of the lung, where the airways are round. Compare the airway diameter here to that of the neighbouring blood vessels. If the diameter of the airway is larger than that of the neighbouring blood vessel, then it is dilated. The airway is usually patent so will have a black hole in the middle whereas the blood vessel is solid white.

2. Look in the middle third of the lung fields. The airways here can be seen along their long axis, and the airway walls should normally taper over 2 cm. If there is no tapering, this is a sign of more proximal airway dilatation.

3. Look for areas of mucus plugging. These are airways in which the lumen has been blocked by mucus. The normal airway has the appearance of a white ring (the airway wall) surrounding a black hole (the air within the airway). When the airway is plugged it has a solid appearance – the plug, being mucus, may have a lower density (be darker) than the airway wall when you look at the mediastinal windows. Occasionally it is not clear whether these structures are impacted airways or blood vessels since both may appear white.

4. Look at the lung parenchyma around the airways, since changes in the lung occur around bronchiectatic airways. These changes include:

• areas of collapse, known as atelectasis

• areas of very small airway plugging, known as ‘tree in bud’

• larger patches of consolidation.

The HRCT scan may also give some clues as to the cause of the bronchiectasis. The radiologist will look at the distribution of the changes to give an indication of the possible aetiology. For example:

• If it is localized to one lobe or one segment of lung it could be due to an obstructive lesion which would require further investigation by a contiguous CT scan and a bronchoscopy to find the cause.

• Proximal bronchiectasis is often seen in allergic bronchopulmonary aspergillosis (ABPA).

• Cystic fibrosis causes widespread bronchiectasis often more marked in the upper zones, with some sparing of the lung bases.

Finally, when looking at the scan, you should note the extent of the disease. Mild bronchiectasis is a relatively common finding on HRCT and may not necessarily be the cause of the patient’s symptoms. Interpret the scan in the context of the clinical history and make sure that you discuss the images with a radiologist.

Some causes of bronchiectasis

Structural, e.g. obstruction (carcinoma, foreign body)

Infection, e.g. childhood pertussis or measles, tuberculosis, pneumonia

Immune, e.g. hypogammaglobulinaemia, allergic bronchopulmonary aspergillosis

Congenital, e.g. cystic fibrosis

4.14 Fibrosis

This patient has pulmonary fibrosis and as there is no known predisposing cause it is termed cryptogenic fibrosing alveolitis (CFA). The film demonstrates a fine meshwork pattern over the lungs which is worse in the periphery of the lungs, especially at the lung bases. In very severely affected areas a denser meshwork produces a ‘honeycomb’ appearance.

Fibrosis is one of the rarer causes of white lung and you need to differentiate it from consolidation or oedema which is far more common. If you suspect fibrosis:

1. Look at old X-rays if possible. Fibrosis is a fairly chronic process so if present a while ago it is more likely to be fibrosis than consolidation or oedema.

2. Look at the distribution of the shadowing. This may help differentiate fibrosis from oedema since the latter is more likely to be bilateral, basal and peripheral. Shadowing that is bilateral and basal could be either oedema or fibrosis. Shadowing that is mid zone or apical is more likely to be fibrosis.

3. Look at the size of the lungs. Fibrosis may cause shrinkage of the lungs which will not be caused by consolidation or oedema. The presence of small lungs points strongly to fibrosis.

4. Look at the shape of the mediastinum. Since fibrosis causes shrinkage of the lungs it will pull the mediastinum and distort the outline.

5. Look at the nature of the shadowing. Pulmonary fibrosis gives reticular-nodular shadowing which simply means a meshwork of lines that combine to form nodules and ring shadows of about 5 mm in diameter. Sometimes the meshwork is very fine giving a ground-glass appearance, said to look like a thin veil over the lung. Later it gives a more coarse appearance and is said to look like a honeycomb. Compare this appearance to that of pulmonary oedema (p. 82) or consolidation (p. 58) and you will see that it is quite distinctive, although in fact it is the other features of fibrosis outlined above that are often the most useful in making the diagnosis.

6. Look at the heart border and diaphragm. Both of these may appear blurred if fibrosis is present.

7. Look at the vascular markings. These become less distinct in areas of fibrosis. This is due to the development of numerous small areas of lung collapse.

The HRCT scan and pulmonary fibrosis

HRCT is the established test for patients with pulmonary fibrosis. It is a more sensitive and specific test than a plain chest X-ray. If there is clinical suspicion and the patient has a normal X-ray you should still order a HRCT. The scan will demonstrate the distribution and character of fibrosis. This can give valuable clues as to its aetiology and is a sensitive way to follow disease progression.

You will be ordering the scan to give you details of any lung parenchymal changes. Therefore you will need to order a high-resolution scan so that you can see the fine detail of the lung architecture.

On the CT image the small black holes around the lung edges are the honeycomb pattern. Another feature seen on CT is that the fibrosis causes changes in other structures in the lung, for instance the airways are pulled apart and the usual smooth curve of the fissure is lost.

Confirming fibrosis

1. Look at the surface of the pleura. One of the first changes is the development of small irregular lumps on the pulmonary surface of the pleura.

2. Look for septal lines. These are thin white lines, 1–2 cm in length, that are perpendicular to the pleura.

3. Look at the bronchi. In pulmonary fibrosis there is a lot of inflammation in the lung around the airway, and this can pull the airway walls apart. Unlike in bronchiectasis, the walls do not appear thickened. This is known as traction airway change.

4. Look for very small lung nodules that can occur. They may be well defined or be slightly hazy in their appearance. In sarcoidosis nodules may coalesce in the lung to form masses and they may also be seen along the fissures, known as ‘beading’.

5. The meshwork of lines in the lung periphery may give rise to a ‘honeycomb’ appearance. This occurs late on in the fibrotic process and consists of areas of black air surrounded by a thicker white border.

6. Look for a ground glass density in the lung. This has a very specific appearance. There is abnormal increased whiteness in the lung. Look at the blood vessels – with ground glass shadowing the blood vessels must still be visible. If they cannot be seen then that area of lung is said to be consolidated (another cause of increased whiteness in the lung). Ground glass density tends to be unevenly distributed through the lung – it may affect particular zones of the lung or occur in smaller discrete areas. Ground glass density may represent very fine fibrotic change which is below the resolution of the scanner to demonstrate more clearly or conversely be due to transient abnormalities such as infection or fluid within the lung. If seen in isolation it is difficult to be certain of its significance, but if seen with the other features described above it is consistent with an interstitial fibrosis.

Determining aetiology

A radiologist may be able to determine the aetiology of pulmonary fibrosis by careful examination of the HRCT images. They will look for a number of clues, for example:

1. The distribution of the fibrotic changes.

a. Idiopathic pulmonary fibrosis, fibrosis secondary to connective tissue disease, and asbestosis are characterized by their patchy distribution and by the presence of subpleural, predominantly basal, fibrotic changes.

b. Sarcoidosis causes changes predominantly in the mid zones and around the hila.

2. The appearance of the interlobular septa. In lymphangitis carcinomatosis there is irregular thickening of the interlobular septa. Some nodular deposits can also be seen on the pleura, but the distribution is not usually the same as that of sarcoidosis.

3. The appearance of the pleura. In asbestos lung diseases the pulmonary fibrosis is often accompanied by changes to the pleura, notably pleural thickening and calcified pleural plaques.

4. Mediastinal changes.

a. In sarcoidosis the scan may confirm bilateral hilar lymphadenopathy.

b. Fibrosing alveolitis is often accompanied by lymph node enlargement in the mediastinum.

The HRCT scan can accurately determine the aetiology of interstitial lung disease. However, this accuracy is highly dependent on the skill of the interpreter and so it is vital that these scans are assessed by experienced radiologists.

4.15 Chickenpox pneumonia

This film of a woman admitted with an acute abdomen shows the typical appearance of old chickenpox pneumonia. You can see numerous bilateral calcified intrapulmonary nodules.

Chickenpox pneumonia in adulthood can cause the development of numerous calcified nodules. To determine whether this is a likely diagnosis:

1. Look at the distribution of the nodules. In chickenpox pneumonia they tend to be in the lower and mid zones.

2. Look at the density of the nodules. They are calcified and so should be very white in appearance.

3. Look at their size. They are usually less than 3 mm in diameter.

Causes of numerous calcified nodules

Infection, e.g. TB, histoplasmosis, chickenpox

Inhalation, e.g. silicosis

Chronic renal failure

Lymphoma following radiotherapy

Chronic pulmonary venous hypertension in mitral stenosis

4.16 Miliary shadowing

This is the chest film of a 32-year-old man with immunodeficiency. It shows the typical miliary shadowing characteristic of tuberculosis (TB). There is also soft shadowing in the left apex consistent with TB.

The lungs have a spotted appearance. This may be due to miliary shadowing. The normal lung can sometimes have a mottled appearance. This can be especially so in obese patients. To distinguish between miliary shadowing and normal lung:

1. Look at the distribution of the shadowing. Look carefully at the periphery. If the shadowing is present in the periphery it is far more likely to be pathological. Sometimes normal vasculature can mimic interstitial shadowing but this usually occurs only towards the centre of the lung fields.

2. Move close to the X-ray and carefully examine the shadowing. With miliary shadowing the opacities should be discrete. Noise from overlying soft tissue can appear more fuzzy.

3. Compare a few of the opacities with one another. If the shadowing is miliary they should be of a similar density and size.

If you feel the shadowing is miliary then look for clues as to its cause. Likely possibilities are miliary TB, sarcoid or malignant miliary metastasis:

1. Look again at the distribution. With miliary TB the opacities are most profuse in the upper zone, with sarcoid they are most profuse in the perihilar and mid zones, and with miliary metastases there may be more opacities in the lower zone.

2. Look at the density. High density, very white shadows are likely to be dust related industrial disease or calcified TB. Less dense changes could be multiple secondaries, sarcoid or any of the other causes of miliary mottling.

3. Look at the rest of the X-ray for signs of other disease processes. Look at the hilum. Unilateral hilar enlargement suggests TB and bilateral hilar enlargement sarcoidosis. Look at the upper part of the mediastinum for thyroid enlargement which could suggest secondaries from a thyroid carcinoma. Look at the apices for subtle cavitating lesions suggestive of TB. Note, however, that the presence of apical shadowing, although suggestive of TB, is in fact very rare in patients with miliary spread.

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