What is the main finding and what is the likely cause?
Enlargement of the cardiac silhouette. The size and shape suggest the diagnosis of a pericardial effusion.
What can be done at the time of interpreting this x-ray which is often helpful in supporting the diagnosis?
Review previous films. Frequently you will find a recent chest x-ray demonstrating a much smaller cardiac outline. Rapid enlargement is unlikely to represent cardiomegaly.
Front chest x-ray demonstrates marked enlargement of the cardiac outline. This was due to pericardial effusion and is a good example of the water bottle sign. This refers to the shape of the cardiac silhouette on erect frontal chest x-rays in patients who have a very large pericardial effusion. The fluid, often measuring a litre or more, causes the pericardium to sag mimicking an old-fashioned water bottle sitting on a bench. Typically the effusion has accumulated over many weeks (e.g. in patients with malignancy) and the pericardium has gradually stretched.