Chest x-ray abnormalities

Lung abnormalities

Lung zones

Assess the lungs by comparing the upper, middle and lower lung zones on the left and right. Asymmetry of lung density is represented as either abnormal whiteness (increased density), or abnormal blackness (decreased density). Once you have spotted asymmetry, the next step is to decide which side is abnormal. If there is an area that is different from the surrounding ipsilateral lung, then this is likely to be the abnormal area.


If the alveoli and small airways fill with dense material, the lung is said to be consolidated. It is important to be aware that consolidation does not always mean there is infection, and the small airways may fill with material other than pus (as in pneumonia), such as fluid (pulmonary oedema), blood (pulmonary haemorrhage), or cells (cancer). They all look similar and clinical information will often help you decide the diagnosis.

Air bronchogram

If an area of lung is consolidated it becomes dense and white. If the larger airways are spared, they are of relatively low density (blacker). This phenomenon is known as air bronchogram and it is a characteristic sign of consolidation.

Key points

  • Compare the left and right upper, middle and lower lung zones
  • Decide which side is abnormal
  • Compare an area of abnormality with the rest of the lung on the same side
  • The whiter side is not always the abnormal side
  • Remember many lung diseases are bilateral and symmetrical
Consolidation with air bronchogram
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Consolidation with air bronchogram

  • The left middle zone is white
  • Dark lines through the area of white are a good example of air bronchogram

Clinical information

  • The patient had a high temperature and a productive cough


  • Pneumonia - consolidation with pus

Differential diagnosis of consolidation

  • Pneumonia - airways full of pus
  • Cancer - airways full of cells
  • Pulmonary haemorrhage - airways full of blood
  • Pulmonary oedema - airways full of fluid

Small lung zone abnormalities

Careful comparison of the lung zones can lead to noticing smaller abnormalities which may otherwise be ignored.

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Unilateral middle zone abnormality

  • The middle zones are asymmetrical
  • There is a small irregular opacity on the right
  • This opacity contains a dark area - cavity
  • Other areas of the lungs are normal

Clinical information

  • This patient had a history of intravenous drug abuse and presented with a high fever


  • Septic embolus

Differential diagnosis of lung cavities

  • Lung abscess - TB, Klebsiella or Staph aureus
  • Lung cancer
  • Septic embolus - infected thrombus
  • Fungal infection - if immunocompromised
  • Granulomatosis with polyangiitis

Bilateral lung abnormalities

Comparing sides does not always give the answer. The lungs may be abnormal on both sides and so awareness of the normal appearances of lung parenchyma becomes more important.

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Bilaterally abnormal lung zones

  • Multiple bilateral lung nodules
  • Symmetrical distribution
  • More nodules at the lung bases

Clinical information

  • Shortness of breath, weight loss and clinically suspected underlying malignancy


  • Pulmonary metastases

Unilateral low density

If there is asymmetry of the lungs, sometimes it is the dark (less dense) area that is abnormal.

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Unilateral black lower zone

  • Asymmetrical lower zones
  • Left darker than right
  • Lung hyperexpansion

Clinical information

  • Chronic smoker with increasing shortness of breath


  • Chronic obstructive pulmonary disease with a large left lower zone lung bulla

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