Chest X-ray Anatomy
Lung zones

Key points

  • The lungs are assessed and described by dividing them into upper, middle and lower zones
  • Refer to 'zones' not 'lobes'
  • Compare left with right
  • Compare an area of possible abnormality with the rest of the lung on the same side

For the purpose of description the lungs are divided into zones: upper, middle and lower. Each of these zones occupies approximately one third of the height of the lungs.

The lung zones do not equate to the lung lobes. For example, the lower zone on the right comprises the middle and lower lobes.

Lung zones

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Lung zones

  • Note that the lower zones reach below the diaphragm (dotted white line) – the lungs pass behind the dome of the diaphragm into the posterior sulcus of each hemithorax (asterisks)

Assessing the lung zones

Each zone is compared with its opposite side. If the lungs appear asymmetrical it should be determined if this is due to asymmetry of normal structures, technical factors, such as rotation, or lung pathology.

If there is genuine asymmetry, decide which side is abnormal. Often a dense (whiter) area is abnormal, such as in pneumonia or lung cancer, but some diseases cause reduced density (blacker), such as a pneumothorax. If there is an area that is different from the surrounding areas of the same lung, then this is likely to be the abnormal area.

Some diseases result in bilateral lung abnormalities making comparison of left with right difficult. In these cases it is still important to assess each zone in turn, to avoid missing subtle abnormalities on the background of abnormal lungs.

Page author: Salisbury NHS Foundation Trust UK (Read bio)

Last reviewed: February 2020