What is Empyema?
Empyema is defined as the presence of pus in the pleural space, representing a severe complication of pleural infection that typically requires both antibiotic therapy and drainage procedures. 1, 2
Core Definition and Pathophysiology
Empyema represents the most advanced stage of pleural infection, characterized by:
- Frank pus accumulation in the thoracic cavity, which may be defined by gross purulent appearance, white blood cell count >50,000 WBCs/μL, or positive bacterial culture 1, 3
- Progression through three distinct stages: exudative (clear fluid with low white cell count), fibropurulent (fibrin deposition with septation and loculation formation), and organizational (fibroblast infiltration creating thick, non-elastic "peel") 1, 4
- Overwhelmed lymphatic drainage capacity when inflammation from pneumonia extends to the pleural surface, triggering increased capillary permeability 4
Clinical Context and Epidemiology
Empyema most commonly develops as a complication of bacterial pneumonia, though it can also result from penetrating chest injuries, surgical procedures, or tuberculosis 2:
- Occurs in 2-12% of children with community-acquired pneumonia and up to 50% of cases caused by typical bacteria including Streptococcus pneumoniae, Staphylococcus aureus, and β-hemolytic streptococci 3, 1
- Incidence in children is approximately 3.3 per 100,000, with higher rates in boys, infants, and young children, particularly during winter and spring 1
- Associated with significant morbidity and mortality (7-33% in adults, potentially exceeding 50% in elderly patients or those with comorbidities like malignancy, diabetes, or alcohol abuse) 5
Key Clinical Features
Patients with empyema typically present with:
- Prolonged fever despite antibiotic therapy (>48 hours) 1, 3
- Chest pain and abdominal pain 1, 3
- Physical examination findings including dullness to percussion, diminished breath sounds, and altered quality of breath sounds over the effusion 1, 3
Diagnostic Approach
Chest radiography should be used to confirm pleural fluid presence, with ultrasound as the gold standard for characterization 1:
- Ultrasound has 92% sensitivity and 93% specificity for detecting effusions and is superior to CT for identifying internal characteristics like fibrin strands and septations 1
- Frankly purulent or turbid/cloudy pleural fluid on sampling mandates prompt chest tube drainage 3
- Pleural fluid analysis should include Gram stain, culture, pH measurement (pH <7.2 indicates need for drainage), glucose, LDH, and cell count with differential 6, 3
Management Principles
Treatment must be adapted to the stage of disease 4:
- Stage 1 (Exudative): Antibiotics alone may be sufficient 4
- Stage 2 (Fibropurulent) and Stage 3 (Organizational): Require chest tube drainage in addition to antibiotics 4
- Organized empyema with symptomatic trapped lung: Requires formal thoracotomy and decortication for proper lung re-expansion 4
Critical Pitfalls
- Delaying drainage when indicated by fluid characteristics (purulent appearance, pH <7.2, positive Gram stain/culture) leads to increased morbidity 6
- Failure to recognize progression to the organizational stage can result in fibrothorax requiring major surgical intervention 4
- Rare complications include empyema necessitans (extension through chest wall to skin), bronchopleural fistula, and lung abscess 1, 7