What is an empyema?

The term empyema refers to the collection of pus within any anatomical cavity. It is, however, most often used to refer to pus in the pleural space (pleural empyema / empyema thoracis). Other areas of pus collection are usually designated as such, for example empyema of the sinus, referring to collection of pus within the paranasal sinus. A simpler explanation of the term empyema is the collection of pus around the lungs. Interstitial fluid, blood and even lymph can also collect in the pleural space. Read more on fluid around the lungs.


Pus is a combination of inflammatory infiltrate with lymphocytes, cellular debris and microbes. Varying amounts of blood, often degraded, is also present. It may originate from an infection of the pleura (pleuritis), often secondary to a lung infection (pneumonia). Seeding of the pathogen, usually bacteria but sometimes fungi, within the pleural space leads to pus formation and accumulation. Pus may also drain from a neighboring site into the pleural space, as is seen with a ruptured lung abscess and the development of bronchopleural fistula.

Causes of an Empyema

Most cases of an empyema are related to bacterial pneumonia (infection of the lung). Pneumonia tends to cause a pleural effusion – para-pneumonic effusion. This can be uncomplicated (containing exudate), complicated (exudate with high concentrations of neurophils) or empyema thoracis (pus in the pleural space). An empyema associated with bacterial pneumonia, or other lung infections including tuberculosis (TB), is a complication. Early treatment and proper management of pneumonia would reduce the chances of an empyema.

Other causes of an empyema may include spread from a ruptured subphrenic abscess, cardiothoracic surgery, sharp force trauma to the chest, esophageal rupture and following drainage of a pleural effusion (thoracentesis). It may also occur as the infection spreads from the neighboring cavities – peritonitis or mediastinitis.

Signs and Symptoms of an Empyema

An empyema is usually one-sided (unilateral). The pus may fill the entire pleural space or only part of it (loculated). The symptoms of an empyema are not always obvious as it tends to occur in the backdrop of a lung infection. It should be suspected if the symptoms of an infection does not resolve despite treating the primary infection with the suitable antibiotics. Recurrence of a lung infection may also be an indication of undetected empyema. Symptoms of an empyema are similar to that of a pleural effusion and includes :

  • Pleuritic chest pain – worse when breathing in or coughing
  • Dry cough
  • Excessive perspiration,  night sweats
  • Fever with rigors
  • Difficulty breathing – may be absent, mild, moderate or severe
  • Weight loss
  • Malaise


Article reviewed by Dr. Greg. Last updated on March 24, 2011