What is the main finding?
What is the differential diagnosis?
One should consider the possibility of a pericardial effusion or even an anterior mediastinal mass, although in this case both would be most unlikely.
What is the cause of the 'double contour' of the right side of the cardiac outline?
Enlargement of the left atrium, seen as a separate contour.
PA and lateral chest x-rays demonstrate markedly enlarged cardiac silhouette. There is a double contour to the right heart border and splaying of the carina.
The aorta is somewhat ectatic. There are no overt features of congestive cardiac failure at this time.