Is this film rotated? If so, in which direction?
Yes, to the right. Note the spinous process of T3 and T4 project over the left clavicular head.
What is the differential diagnosis?
In this case not much, but one should consider 1. consolidation of the right upper lobe; 2. a mass in the medial aspect of the right upper lobe; 3. a mass in on the right side of the superior mediastinum.
What feature makes the diagnosis easy in this case?
The degree of volume loss in the right hemidiaphragm.
Mobile chest x-ray obtained to confirm the position of a nasogastric tube (which is too high, still in the oesophagus) demonstrates collapse of the right upper lobe.