Cardiothoracic ratio

Dr Dan J Bell and A.Prof Frank Gaillard et al.

The cardiothoracic ratio (CTR) aids in the detection of enlargement of the cardiac silhouette, which is most commonly from cardiomegaly but can be due to other processes such as pericardial effusion

Some report CTR as a percentage, however this is strictly incorrect, as it is a ratio.

The CTR is measured on a PA chest x-ray, and is the ratio of maximal horizontal cardiac diameter to maximal horizontal thoracic diameter (inner edge of ribs / edge of pleura). A normal measurement should be ≤0.5.

It should be noted that this measurement is a coarse marker of disease 4. If the patient is symptomatic then echocardiography is required but the yield of echocardiography is low if performed just for an increased CTR 3.

In some situations, an increased cardiothoracic ratio on a PA radiograph may be a result of a prominent epicardial fat pad and/or due to expiration rather than cardiomegaly.

Chest x-ray
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Article information

rID: 15283
System: Chest
Section: Approach
Synonyms or Alternate Spellings:
  • Cardio-thoracic ratio
  • Cardiothoracic ratio (CTR)
  • CTR

Cases and figures

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    Normal cardiothor...
    Figure 1: normal
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    Cardiothoracic ra...
    Figure 2: enlarged
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    Case 1: cardiomegaly
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    Case 2: pericardial effusion
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