Empyema

An empyema, also known as a pyothorax, is a collection of pus within the pleural cavity. It must be differentiated from an abscess, which is a collection of pus in a newly formed cavity. Most empyemas arise from an infection within the lung (pneumonia), often associated with parapneumonic effusions.

There are 3 stages: exudative, fibrinopurulent and organizing. In the exudative stage, the pus accumulates. This is followed by the fibrinopurulent stage in which there is loculation of the pleural fluid (the creation of grapelike pus pockets). In the final organizing stage, scarring of the pleural space may lead to lung entrapment.