Cardiomegaly, or enlarged heart size on chest radiograph, is a non-specific finding. Besides attributing this appearance to just congestive heart failure, there are many other causes as listed below:1. False positive as in patient with pectus excavatum.
2. Pericardial effusion due to various causes.
3. Cardiomyopathy.
4. Valvular heart disease.
5. Ventricular aneurysm.
6. Mimickers: paraspinal mass or mediastinal mass.
Therefore it is important that adequate history is provided to the radiologist to come to a sensible conclusion.
The picture above shows an obvious enlarged heart which is due to congestive heart failure.
In order estimate the heart size (or cardiothracic ratio/CTR), it is important that the patient take a full breath to fully expand the lungs. Radiographic assessment can be made to assess if the lungs are indeed adequately expanded. A general rule of thumb is that the heart size should not be more than half the width of the greatest transverse diameter of the chest. Nonetheless this is only a rough estimate and should be correlated with the clinical presentation and other tests (eg. echocardiography, ECG etc.).
Some studies have also recommended that CTR of 0.55 to be considered normal for Asia pacific population due to smaller body habitus in this group of people.
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