The frontal and lateral chest x-rays show pneumomediastinum.
There is a ‘continuous diaphragm sign’ on the frontal view.
The lateral chest x-ray shows ‘ ring around the artery sign’
Continuous diaphragm sign is seen because of the air trapped posterior to the pericardium, giving the appearance of continuous collection of air.
Air around the right pulmonary artery on the lateral chest x-ray causes the ring around the artery sign.
Reference: Grainger & Allison’s Diagnostic Radiology, 6th edition.