Causes of emphyema.

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empyema thoracis causes etiology

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Here is a comprehensive summary of the causes of empyema drawn from multiple authoritative surgical and pulmonary textbooks.

Causes of Empyema (Pus in the Pleural Space)

Empyema is a collection of purulent fluid within the pleural space resulting from invasion by pyogenic bacteria, fungi, parasites, or mycobacteria. Microorganisms reach the pleural cavity by several routes:

1. Pneumonia (Most Common Cause)

This is by far the most frequent cause. Up to 50% of pneumonias have an associated pleural effusion, but less than 5% progress to frank empyema. Parapneumonic empyema begins as a sterile reactive effusion, then becomes infected and loculated.

Community-acquired: Streptococcus pneumoniae, anaerobes, beta-hemolytic streptococci
Hospital-acquired: S. aureus (including MRSA) and Klebsiella pneumoniae are more common

In the pre-antibiotic era, S. pneumoniae caused 64% of all empyemas. Today, anaerobic organisms account for up to 75% of cases, often reflecting aspiration pneumonia.

Key anaerobes isolated include Fusobacterium nucleatum, Prevotella species, Peptostreptococcus species, Bacteroides fragilis, and Actinomyces species. - Fishman's Pulmonary Diseases and Disorders, p. 1308

2. Thoracic Surgery / Iatrogenic Causes

Post-operative empyema can follow:

Pneumonectomy (especially right-sided), thoracotomy, or VATS
Bronchopleural fistula formation post-surgery
Risk factors include post-operative ventilator dependence, lower pre-operative haematocrit, and poor pulmonary function

"Postpneumonectomy empyemas are an especially difficult problem as there is no lung tissue to occupy the empty thorax." - Mulholland and Greenfield's Surgery, p. 618

3. Esophageal Perforation / Rupture

Esophageal rupture (Boerhaave syndrome or iatrogenic perforation) allows gastric and oral flora to contaminate the pleural space, causing a rapidly progressive and highly lethal empyema. - Sabiston Textbook of Surgery, p. 2289

4. Penetrating Thoracic Trauma

Direct inoculation of bacteria into the pleural space via stab wounds, gunshot wounds, or contaminated hemothorax (haemopneumothorax that becomes infected). - Sabiston Textbook of Surgery, p. 2287

5. Lung Abscess / Subphrenic Abscess

Rupture of a parenchymal abscess into the pleural space (pyopneumothorax). Subphrenic or hepatic abscesses can spread infection transdiaphragmatically.

6. Tuberculosis

TB empyema, though uncommon, occurs late in the disease in debilitated patients. "Rupture of a cavity into the pleural space usually is catastrophic and often is associated with bronchopleural fistula." - Rosen's Emergency Medicine, p. 3187. It should be suspected in patients from endemic regions.

7. Other Infections from Adjacent Organs

Mediastinitis (spread from mediastinum)
Pancreaticopleural fistula (from severe pancreatitis)
Vertebral osteomyelitis tracking into the chest
Hepatic/subphrenic abscess eroding through the diaphragm
Bronchogenic carcinoma with secondary infection

8. Haematogenous Spread

Bacteraemia from a distant septic focus (e.g., dental abscess, endocarditis) can seed the pleural space, though this is less common.

Stages of Empyema

Understanding the cause is linked to the stage at presentation:

Stage	Fluid	WBC	LDH	pH	Bacteria
Exudative	Thin, elastic	<1,000	<500 IU	>7.3	Absent
Fibrinopurulent	Purulent, inelastic	>5,000	>1,000 IU	<7.1	Present
Organizing	Thick, rigid peel	Varies	Varies	<7.1	Varies

Mulholland and Greenfield's Surgery, Table 80.6

Summary by Route of Infection

Route	Example
Direct extension	Pneumonia, lung abscess, subphrenic abscess, mediastinitis
Direct inoculation	Trauma, surgery, thoracocentesis
Fistula	Bronchopleural, esophageal, pancreaticopleural
Haematogenous	Bacteraemia from distant focus

The leading organisms overall are anaerobes in the community setting and S. aureus / Klebsiella in the hospital setting.

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