The black lung field

Published on 23/05/2015 by admin

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Last modified 23/05/2015

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CHAPTER 5 The black lung field

5.1 Chronic obstructive pulmonary disease 106
5.2 Pneumothorax 110
5.3 Tension pneumothorax 112
5.4 Pulmonary embolus 114
5.5 Mastectomy 119

5.1 Chronic obstructive pulmonary disease (COPD)

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This is the chest film of a patient with chronic obstructive pulmonary disease. The lungs look larger in volume than normal. The diaphragms are rather flattened. The right upper zone and many areas of the left lung are abnormally black. In these areas the blood vessels are difficult to see or are very thinned. This is because these regions of lung have developed emphysema.

The CT section shows how the lung contains black holes (1) and thin thready blood vessels (2).

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When trying to decide the cause of bilateral black lungs you need to:

1. Check the penetration. Look at the vertebral bodies behind the heart. Remember that in a good quality X-ray the vertebral bodies become harder to see behind the heart shadow. If they are too clearly seen the film is over penetrated making the lungs appear black.

If you are satisfied with the technical quality of the film then the most likely cause is COPD. COPD is associated with large lungs due to air trapping and the development of bullae. You therefore need to:

1. Look at the shape of the diaphragm. In COPD the diaphragms are flat or even scallop shaped instead of concave upwards. This is a more reliable sign of hyperexpansion than rib counting.
2. Count the number of ribs you see anteriorly. If the lungs are enlarged you should be able to count more than seven. Be careful, however, because you can sometimes count more than seven ribs in normal patients if they are tall and slim.
3. Look at the shape of the heart. The enlarged thorax of COPD appears on the X-ray to elongate and narrow the heart, elevating the lower border. The heart, instead of sitting on the diaphragm, often appears to ‘swing in the wind’. It will also appear small unless there is also an element of cardiac failure in which case it will be normal in size or large.
4. Look for bullae. These are densely black areas of lung, usually round, surrounded by fine curvilinear shadows. Bullae distort the surrounding vasculature so to help find them look out for areas of distortion of vascular markings.
5. Look at the distribution of lung markings. The black lungs of COPD are due to reduced size of blood vessels. The lung markings are reduced bilaterally and fan out in straight lines from the hilum, starting off chunky but stopping two-thirds of the way out – peripheral pruning.

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Cigarette smoking causes damage to the parenchyma of the lung. Cigarette smoke in a room tends to float upwards, and similarly smoking related lung damage tends to occur in the upper lungs. This image shows how the normal smooth lung texture has been destroyed with the formation of air cysts (bullae – 1) and small black holes in the lung (centrilobular emphysema – 2). The blood vessels through these areas can also become very narrowed, as the body will not perfuse areas of the lung where gas exchange is significantly impaired.

5.2 Pneumothorax

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This patient has a left-sided pneumothorax with partial collapse of the left lung. The outer left lung field is black. You can see the lung edge (arrowed).

When you see a unilateral black lung you need to:

1. Check the technical quality of the film. A rotated film may make one side less dense than the other.
2. Determine which side is abnormal. This is usually easy since the side with reduced lung markings will be the abnormal side.

You must now decide the cause of the blackness. Lung markings are made up of bronchi and blood vessels and it is their absence that makes the lung look black. Vascular shadows will disappear if the lung is replaced by air, which will occur with a pneumothorax or bullous or cystic lung disease or if the vessels are deprived of blood as in a pulmonary embolus. Therefore think pneumothorax, bullae/cyst or pulmonary embolism and:

1. Look for a lung edge. In a pneumothorax you will see the edge of lung which is not normally seen. Look carefully at the upper zone where air will accumulate first. Your eye is trained to see horizontal lines better than vertical so it is sometimes easier to detect the lung edge with the X-ray turned on its side.
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