Pneumothorax (summary)

Last revised by Calum Worsley on 30 Oct 2021
This is a basic article for medical students and other non-radiologists

Pneumothorax (pl: pneumothoraces) describes gas within the pleural space. This may occur because of a number of reasons and may be spontaneous. Patients will not always be symptomatic and treatment will depend on the cause. Pneumothoraces may be small or very large. The larger the pneumothorax, the more likely it is to cause symptoms.

Reference article

This is a summary article; read more in our article on pneumothorax.

  • pathophysiology
  • investigation
    • erect chest x-ray
      • will show most pneumothoraces
    • CT chest
      • will show tiny pneumothoraces not shown on chest x-ray
        • these are often incidental and asymptomatic
      • not used for assessment of pneumothoraces unless complex

A pneumothorax is seen as a region of lucency (dark) around the edge of the lung. This is difficult to see because the lung itself is black too. They are more easily seen on erect chest x-rays as the free air typically rises up to the apex above the lung, making it more visible.

Tips to help to find pneumothoraces include:

  • the lung edge
    • you should not be able to see the lung edge
    • if you can, the region peripherally is likely a pneumothorax
  • absence of vessels
    • the lung should have vessels running through it
      • these are white branching structures on the x-ray
    • if there are not vessels, there may be a pneumothorax

If both these findings occur, measure how deep the pneumothorax is and check whether there is any mediastinal shift.

Pneumothorax on supine or portable chest x-rays can be much more subtle unless they are very large, as the free air rises to the front of the chest with the lung behind it, so there is less likely to be an obvious gap between the lung and chest wall. Read more in our article on pneumothorax in supine projection.

Pneumothoraces on CT are rims of gas (black) around the edges of the lung which may track up the fissures. Very small pneumothoraces can be detected.

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Cases and figures

  • Case 1: pneumothorax
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  • Case 2: left pneumothorax
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  • Case 3: right pneumothorax
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  • Case 4: pneumothorax at CT
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  • Case 5
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  • Case 6
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