Pneumomediastinum (from Greek pneuma - "air", also known as mediastinal emphysema) 's a condition in which air's present in the mediastinum. First described in 1819 by René Laennec, the condition can result from physical trauma or other situations that lead to high pressure within the alveoli of the lung, causing them to burst and leak air into the chest cavity. Presentation Pneumomediastinum's uncommon, it occurs when air leaks from any part of the lung or airways into the mediastinum and… (More on Pneumomediastinum)