It is most commonly caused by: •
Esophageal rupture, for example in
Boerhaave syndrome •
Asthma,
crack cocaine use or other conditions leading to alveolar rupture •
Bowel rupture, where air in the abdominal cavity tracts up into the chest. It has also been associated with: •
Mycoplasma pneumoniae pneumonia •
obesity It can be induced to assist thoracoscopic surgery. It can be caused by a pulmonary
barotrauma induced by a person moving from a higher to a lower pressure environment, such as when a
scuba or surface-supplied diver, a
free-diver after , or an
airplane passenger ascends. In the case of scuba and surface supplied divers, the diver breathes gas at ambient pressure, and if this is not able to escape freely during ascent, the pressure difference will cause it to expand, and may rupture the lung tissues (
pulmonary barotrauma), and escape to a variety of places, one of which can be the mediastinum. A diver with symptoms of mediastinal emphysema may also have any combination of
arterial gas embolism,
pneumothorax and
subcutaneous or
pulmonary interstitial emphysema. Factors which may prevent free escape of the compressed breathing gas include holding the breath or respiratory obstructions such as cysts, mucus plugs, or scar tissue. Pneumomediastinum is most commonly seen in otherwise healthy young male patients and may not be prefaced by a relevant medical history of similar ailments. ==Diagnosis==