DESCRIPTION

A parapneumonic effusion characterized by the presence of pus in the pleural space

EPIDEMIOLOGY

• Occurs following 5% of community-acquired pneumonias
• Usually younger children
• Usually gram-positive bacteria (Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Haemophilus influenzae)

RISK FACTORS

• Usually occurs in healthy children
• Immunodeficiencies
• Malnutrition
• Chronic lung diseases
• Cystic congenital thoracic malformations
• Inhaled foreign body

PATHOPHYSIOLOGY

Pneumonia progresses to empyema over several stages.

• Precollection stage:
  • Pneumonia leads to pleural inflammation.
• Exudative stage:
  • Increased production of clear, free flowing pleural fluid
  • Known as a parapneumonic effusion
• Fibropurulent stage (empyema):
  • Deposition of fibrin which creates loculations within the pleural space
  • Bacteria colonization of the pleural space and the development of turbid fluid and pus
• Organization stage:
  • A thick pleural peel is established which can entrap the lung and cause restrictive lung disease.