Empyema may be classified according to the etiology, anatomical location, and pathological course of the disease.^[1] Primary thoracic empyema occurs most commonly as iatrogenic empyema without associated pneumonia whereas secondary empyema happens more commonly secondary to pneumonia. Empyema necessitans is a spontaneous discharge of an empyema that has burrowed through the parietal pleura into the chest wall to form a subcutaneous abscess that may eventually rupture through the skin.^[2][3] Empyema is mostly caused by bacteria. It may be tuberculous or nontuberculous. Tuberculous empyema is the most common cause of empyema necessitans with majority of affected patients being immunocompromised.^[4][5] There are 3 stages of empyema which are important in terms of the laboratory findings. These are exudative, fibrinopurulent and organizing.^[6]

Empyema may be classified according to the etiology, anatomical location/organ, and pathological course of the disease as follows:^[1]

Primary empyema occurs most commonly as iatrogenic empyema without associated pneumonia whereas secondary empyema happens more commonly secondary to pneumonia.

Empyema necessitans is a spontaneous discharge of an empyema that has burrowed through the parietal pleura into the chest wall to form a subcutaneous abscess that may eventually rupture through the skin.^[2][3]

Tuberculous empyema is the most common cause of empyema necessitans. This disease can be found in patients with impaired immunity or who are immunocompetent however majority of patients affected are immunocompromised.^[4][5]

Empyema may be classified according to the stage of the disease as follows:^[7]

• Exudative

In the exudative stage, the pus accumulates, and initial sterile fluid becomes infected with fluid characteristics of;

• • Glucose>60
  • pH>7.2
  • LDH<500

• Fibrinopurulent

During this stage, bacteria multiplies with increase in polymorphs and fibrin deposition on both pleural surfaces with fluid characteristics of;

• • glucose<40
  • pH <7.2
  • LDH>1000

• Organizing

This stage is characterized by loculations, inelastic membranous peel, and lung entrapment as a result of scarring of the pleural space.^[6]