Findings for pneumomediastinum include; streaky lucencies over the mediastinum that extend into the neck,  and elevation of the parietal pleura along the mediastinal borders.

Causes of pneumomediastinum include; asthma, surgery (post-op complication), traumatic tracheobronchial rupture, abrupt changes in intrathoracic pressure (vomiting, coughing, exercise, parturition), ruptured esophagus, barotrauma, and smoking crack cocaine.

Pneumomediastinum should be distinguished from pneumopericardium and pneumothorax. In pneumopericardium, air can be present underneath the heart, but does not enter the neck.