Definition of Empyema:

Empyema is a collection of pus in the cavity between the lung and the membrane that surrounds it (pleural space).

Causes, incidence, and risk factors:

Empyema is caused by an infection that spreads from the lung and leads to an accumulation of pus in the pleural space. The infected fluid can build up to a quantity of a pint or more, which puts pressure on the lungs, causing shortness of breath and pain.

Risk factors include recent pulmonary (lung) conditions including bacterial pneumonia, lung abscess, thoracic surgery, trauma or injury to the chest, or rarely, a needle inserted through the chest wall to draw off fluid in the pleural space (thoracentesis).