The main causes of pneumomediastinum are
Alveolar rupture with dissection of air into the interstitium of the lung with translocation to the mediastinum
Esophageal perforation
Esophageal or bowel rupture Acute Perforation of the Gastrointestinal Tract Any part of the gastrointestinal tract may become perforated, releasing gastric or intestinal contents into the peritoneal space. Causes vary. Symptoms develop suddenly, with severe pain followed... read more
with dissection of air from the neck or the abdomen into the mediastinum
Tension pneumomediastinum with compression of mediastinal structures is rare.
The primary symptom is substernal chest pain which can, on occasion, be severe.
Physical examination may show subcutaneous emphysema, usually in the suprasternal notch, along with a crunching or clicking noise synchronous with the heartbeat; this noise is best heard over the heart when the patient is in the left lateral decubitus position (Hamman sign).
The diagnosis is confirmed by chest x-ray, which shows air in the mediastinum.
The cause of pneumomediastinum must be identified to rule out esophageal perforation, which requires hospitalization and treatment.
Treatment of Pneumomediastinum
Usually unnecessary
Treatment usually is not necessary, although tension pneumomediastinum with compression of mediastinal structures can be relieved with needle aspiration, leaving the needle open to the atmosphere as is done with tension pneumothorax Pneumothorax (Tension) Tension pneumothorax is accumulation of air in the pleural space under pressure, compressing the lungs and decreasing venous return to the heart. (See also Overview of Thoracic Trauma.) Tension... read more 
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Hospital admission is required if pneumomediastinum is secondary to esophageal or bowel rupture but not necessarily if secondary to alveolar rupture.
