Revision 14 for 'Cardiothoracic ratio'

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Cardiothoracic ratio

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.

Radiographic features

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.

Related pathology

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.

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