Empyema Thoracis

Definition

Empyema thoracis is a collection of pus in the pleural cavity. The pus consists of masses of neutrophils admixed with other leukocytes, bacteria, and cell debris. Volumes can reach 500-1000 mL but are usually smaller and tend to become walled off by fibrosis.

Robbins, Cotran & Kumar Pathologic Basis of Disease
S. Das - A Manual on Clinical Surgery

Stages / Pathogenesis

The evolution of pleural infection passes through three overlapping stages (Murray & Nadel):

Stage	Features	Pleural Fluid
1. Exudative	Rapid sterile fluid outpouring; increased permeability	Low WBC, low LDH, normal glucose and pH
2. Fibropurulent	Bacteria invade; leukocytes, fibrin, and loculations form	Low pH and glucose; high LDH
3. Organizational	Pleural surfaces thicken into a "pleural peel"	Thick pus and cellular debris

Primary empyema (no preceding pneumonia) skips Stage 1 - bacteria invade the pleural space directly via hematogenous spread or oropharyngeal translocation, leading straight to the fibropurulent stage.

Murray & Nadel's Textbook of Respiratory Medicine

Etiology & Risk Factors

Routes of infection:

Contiguous spread from intrapulmonary infection (most common) - parapneumonic
Hematogenous or lymphatic dissemination
Direct transdiaphragmatic spread from subdiaphragmatic or liver abscess (more common on the right)
Esophageal perforation, chest trauma, post-surgical complications, lung transplant complications
Rupture of a peripheral lung abscess into the pleural space

Host risk factors: Diabetes mellitus, alcohol use disorder, intravenous drug use, poor dentition/aspiration, rheumatoid arthritis, immunosuppression, advanced age (incidence 17-20/100,000 in those >65 years).

Microbiology:

Community-acquired: Streptococcus milleri group, Streptococcus pneumoniae, anaerobes (reflecting oropharyngeal flora)
Hospital-acquired: Staphylococcus aureus (including MRSA), Gram-negative organisms (E. coli, Klebsiella, Pseudomonas)

Clinical Presentation

Difficult to distinguish from pneumonia: fever, cough, dyspnea, malaise, pleuritic chest pain (often prolonged)
Many patients with pneumonia develop a parapneumonic effusion without a change in symptoms

Parapneumonic effusion classification:

Type	Criteria
Uncomplicated	Glucose >40 mg/dL, pH >7.2, negative Gram stain/culture, no loculations
Complicated	Glucose <40 mg/dL OR pH <7.2 OR loculated on ultrasound
Frank empyema	Gross pus on aspiration

Diagnosis

Chest X-ray: confirms pleural effusion; may show loculation or shift
Ultrasound: best bedside tool - identifies loculations, guides safe aspiration
CT chest: better delineates loculations, pleural thickening, underlying lung pathology
Thoracocentesis: diagnostic and therapeutic - send for pH, glucose, LDH, protein, Gram stain, culture (aerobic + anaerobic)

Types

Acute empyema: Profound toxaemia and shock with pleural pain; confirmed by needle aspiration and chest X-ray.

Chronic empyema: Walled off by a thick fibrous wall. Causes include mismanagement of acute empyema, bronchiectasis, bronchopleural fistula, tuberculosis, lung abscess, or foreign body. Symptoms are vague - ill health, febrile episodes, malaise. May eventually discharge through a sinus in the chest wall (empyema necessitatis).

TB empyema: High mycobacterial load causes an exaggerated acute inflammatory response with neutrophil leukocytosis and frank pus formation; culture-positive for Mycobacterium tuberculosis.

Treatment

Principles (unchanged since the 1918 U.S. Army Empyema Commission):

Adequate pus drainage with a closed tube (not early open drainage)
Obliteration of the pleural space
Proper nutritional support
Antibiotics

Stage-based approach:

Stage	Management
Exudative	Antibiotics alone usually sufficient
Fibropurulent	Chest tube drainage (intercostal tube thoracostomy); intrapleural fibrinolytics (streptokinase/tPA + DNase) if loculated
Organizational	Surgical: VATS decortication (preferred) or open thoracotomy; thoracoplasty for refractory cases

Tintinalli's Emergency Medicine emphasizes: patients with gross pus or organisms on Gram stain require drainage with thoracostomy tubes. Pleural pH <7.20 is also an indication for tube drainage.

Antibiotics: Cover community organisms empirically (amoxicillin-clavulanate or co-amoxiclav); add MRSA coverage if hospital-acquired; always include anaerobic coverage if aspiration is suspected.

Complications

Bronchopleural fistula
Empyema necessitatis - pus burrows through the chest wall to the subcutaneous tissue
Fibrothorax - dense fibrous adhesions obliterating the pleural space, restricting pulmonary expansion
Septicaemia, metastatic abscess formation

Prognosis / Epidemiology

The incidence has doubled in the United States between 1996 and 2008 (from 3.04 to 5.98 per 100,000). Overall mortality in adults remains ~15-20%, higher in elderly and immunocompromised patients. With modern management (VATS, fibrinolytics), prognosis has significantly improved from the 70% mortality seen with early open drainage pre-1918.

Murray & Nadel's Textbook of Respiratory Medicine
Robbins, Cotran & Kumar Pathologic Basis of Disease
S. Das - A Manual on Clinical Surgery, 13th Edition
Tintinalli's Emergency Medicine

Diagram

Generating Image

Medical diagram of Empyema Thoracis showing: 1. A cross-section of the thoracic cavity with labeled anatomy (lung, pleural space, visceral pleura, parietal pleura, chest wall, diaphragm) 2. Three stages shown in separate panels: - Stage 1 Exudative: sterile fluid accumulation in pleural space, clear fluid - Stage 2 Fibropurulent: bacteria invading, fibrin deposits, loculations forming, yellow-green pus - Stage 3 Organizational: thick pleural peel forming around lung, trapped lung 3. Routes of infection shown with arrows: parapneumonic (from lung), hematogenous, transdiaphragmatic (from subdiaphragmatic abscess), esophageal perforation 4. A small inset showing Empyema Necessitatis - pus burrowing through chest wall 5. Clean, professional medical illustration style with clear labels, color-coded stages, white background

The diagram illustrates:

Thoracic cross-section with key anatomical structures (lung, visceral/parietal pleura, chest wall, diaphragm)
Three stages of empyema development - exudative (sterile fluid), fibropurulent (pus + loculations + fibrin), and organizational (pleural peel trapping the lung)
Routes of infection - parapneumonic (from lung), hematogenous, transdiaphragmatic (from subdiaphragmatic abscess), and esophageal perforation
Empyema necessitatis inset - showing pus burrowing through the chest wall into subcutaneous tissue

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