What do you see when you take a look at this Chest radiograph? It isn’t immediately noticeable (and was read as normal), and is a good reminder of why you should always check your own films, and why a systematic read is important. If all you were looking for was “r/o PNA/PTX” you could easily miss the subcutaneous air, as well as the subtle border around the cardiac silhouette which should raise you concern for atraumatic pneumomediastinum.
This is a relatively uncommon diagnosis which often presents with: chest pain, dyspnea, and cough. Physical exam is often unremarkable, though subcutaneous emphysema can occasionally cause crepitus. Substantial air can also cause Hamman’s Sign (a crunching, rasping sound, synchronous with the heartbeat).
Most often, pneumomediastinum is a sequelae of asthma. Alevolar ruptures during asthma attacks can cause air leaks which can leak into the mediastinum (one that is contiguous with the pleural space would cause both pneumothorax and pneumomediastinum). These cases are often self limited, and can be treated conservatively with rest and analgesics (there are rare cases of asthma-induced pneumomediastinum progressing to tension pneumomediastinum; the literature on this phenomenon is sparse with barely more than a dozen reported cases)
The dreaded and most severe cause of pneumomediastinum, however, is Boerhaave Syndrome, or esophageal rupture. This is a critical diagnosis that must not be missed; a water-soluble (ie, not barium) swallow study is the diagnostic test of choice. If clinical suspicion is high, be sure to have prophylactic antibiotics administered while awaiting confirmatory testing.