|Classification and external resources|
A CT scan showing air in the mediastinum
Pneumomediastinum (from Greek pneuma - "air", also known as mediastinal emphysema) is a condition in which air is present in the mediastinum. First described in 1819 by René Laennec, the condition can result from physical trauma or other situations that lead to air escaping from the lungs, airways or bowel into the chest cavity.
Pneumomediastinum is uncommon and occurs when air leaks into the mediastinum. The diagnosis can be confirmed via chest X-ray showing a radiolucent outline around the heart and mediastinum or via CT scanning of the thorax.
It is most commonly caused by:
- Oesophageal rupture, for example in Boerhaave syndrome
- Asthma 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:
It can be induced to assist thoracoscopic surgery. It can be caused by a pulmonary barotrauma resulting when a person moves to or from a higher pressure environment, such as when a SCUBA diver, a free-diver or an airplane passenger ascends or descends.
In rare cases, pneumomediastinum may also arise as a result of blunt chest trauma (e.g car accidents, fights, over pressure of breathing apparatus), while still evolving in the same fashion as the spontaneous form.
Pneumomediastinum is most commonly seen in otherwise healthy young male patients and may not be prefaced by a relevant medical history of similar ailments.
Signs and Symptoms
The main symptom is usually severe central chest pain. Other symptoms include laboured breathing, voice distortion (as with helium) and subcutaneous emphysema, specifically affecting the face, neck, and chest. Pneumomediastinum can also be characterized by the shortness of breath that is typical of a respiratory system problem. It is often recognized on auscultation by a "crunching" sound timed with the cardiac cycle (Hamman's crunch). Pnemomediastinum may also present with symptoms mimicking cardiac tamponade as a result of the increased intrapulmonary pressure on venous flow to the heart 
The tissues in the mediastinum will slowly resorb the air in the cavity so most pneumomediastinums are treated conservatively. Breathing high flow oxygen will increase the absorption of the air. If the air is under pressure and compressing the heart, a needle may be inserted into the cavity, releasing the air. Surgery may be needed to repair the hole in the trachea, esophagus or bowel.
If there is lung collapse, it is imperative the affected individual lies on the side of the collapse, although painful, this allows full inflation of the unaffected lung.
- Laënnec RTH. De l’auscultation médiate ou Traité du Diagnostic des Maladies des Poumon et du Coeur. 1st ed. Paris: Brosson & Chaudé; 1819.
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- Dr. Richard Moon, Diver's Alert Network Vice President and Medical Director, http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=40
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