Increased cardiothoracic ratio (summary)

Dr Jeremy Jones et al.

Increased cardiothoracic ratio describes widening of the cardiac silhouette on a chest radiograph. This is only of use when making assessment of a PA chest x-ray since the AP chest x-ray causes artefactual magnification of the heart and the cardiothoracic ratio is altered.

Reference article

This is a summary article; read more in our article on increased cardiothoracic ratio.

  • pathophysiology
    • enlargement of the heart
      • may be global or specific chamber enlargement
  • investigation
    • PA chest x-ray
      • cardiothoracic ratio over 50% describes cardiomegaly
    • AP chest x-ray
      • the cardiomediastinum is magnified
        • increased cardiothoracic ratio is less specific
Plain radiograph

On a PA radiograph, measure the cardiac silhouette at its widest and the thoracic cavity at its widest point (inside of the ribs). Divide the cardiac dimension by the thoracic dimension to get the cardiothoracic ratio (CTR). 

On a PA chest x-ray this should be less than 50% in adults.

Medical student radiology curriculum
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Article Information

rID: 51429
Systems: Chest, Cardiac
Synonyms or Alternate Spellings:

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Cases and Figures

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    Normal cardiothor...
    Case 1: normal
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    Cardiothoracic ra...
    Case 2: increased CTR (cardiomegaly)
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