• Definition

    Empyema is a collection of pus in the space between the lung and the inner surface of the chest wall (pleural space).

    Causes, incidence, and risk factors

    Empyema is usually caused by an infection that spreads from the lung. It leads to a buildup of pus in the pleural space.

    There can be a pint or more of infected fluid. This fluid puts pressure on the lungs.

    Risk factors include:

    • Bacterial pneumonia
    • Chest surgery
    • Lung abscess
    • Trauma or injury to the chest

    In rare cases, empyema can occur after a needle is inserted through the chest wall to draw off fluid in the pleural space for medical diagnosis or treatment (thoracentesis).