What is the etiology of mediastinitis?

Etiology of Mediastinitis

Mediastinitis is primarily caused by three major mechanisms: post-sternotomy infections, esophageal perforations, and descending necrotizing infections from oropharyngeal sources. These distinct etiologies determine both the microbiology and appropriate management approaches.

Primary Etiologies

1. Post-Sternotomy Mediastinitis

• Most common cause in modern clinical practice 1
• Occurs as a complication of cardiac and thoracic surgical procedures
• Incidence: 0.4-5% following cardiac revascularization surgery 2
• Mortality: 16.5-47% 2
• Predominant pathogens:
  • Staphylococcus aureus (most common)
  • Nasal colonization with S. aureus is a significant risk factor 3
  • Coagulase-negative staphylococci

2. Esophageal Perforation

• Second most common cause of acute mediastinitis 2
• Etiologies include:
  • Iatrogenic injury (most common)
  • Traumatic perforation
  • Spontaneous rupture (Boerhaave syndrome)
• Predominant pathogens:
  • Polymicrobial infections
  • High proportion of anaerobes
  • Common oropharyngeal flora 1, 2
• Mortality: 20-60% depending on time to diagnosis 2

3. Descending Necrotizing Mediastinitis

• Originates from infections in the head and neck region
• Sources include:
  • Odontogenic infections (60% of cases) 2
  • Pharyngeal infections
  • Cervical infections
• Predominant pathogens:
  • Beta-hemolytic streptococci (71.5% of cases) 2
  • Mixed aerobic and anaerobic bacteria

4. Less Common Etiologies

Infectious Causes:

• Direct extension from adjacent infections:
  • Mediastinal lymph node infections
  • Empyema
  • Infectious pericarditis
  • Paravertebral abscess 3
• Hematogenous spread:
  • Septic emboli from bacterial endocarditis
  • Hematogenous dissemination in sepsis or IV drug use 3
  • Rare cases of hematogenous spread from skin infections 4

Specific Infectious Agents:

• Bacterial:
  • Staphylococcus aureus (including MRSA)
  • Salmonella species
  • Pneumococcus
  • Escherichia coli
  • Treponema pallidum (syphilitic aortitis) 3
• Fungal:
  • Histoplasma capsulatum (causing granulomatous or fibrosing mediastinitis) 3, 5
  • Candida species
  • Aspergillus species 3, 1
• Mycobacterial:
  • Mycobacterium tuberculosis (tuberculous aortitis) 3

Classification of Mediastinitis

Acute Mediastinitis

• Rapid onset
• High mortality without prompt intervention
• Includes:
  • Acute necrotizing mediastinitis
  • Post-sternotomy mediastinitis 6

Chronic Mediastinitis

• Subdivided into:
  • Granulomatous mediastinitis: Active inflammation of mediastinal lymph nodes
  • Fibrosing/sclerosing mediastinitis: End-stage fibrotic reaction to past infection 6, 5
• Often associated with fungal infections (particularly histoplasmosis) 3, 5

Clinical Implications

The etiology of mediastinitis directly impacts treatment approach:

• Post-sternotomy infections require surgical debridement and anti-staphylococcal antibiotics
• Esophageal perforations need broad-spectrum coverage for oropharyngeal flora including anaerobes
• Descending necrotizing mediastinitis requires drainage of the primary focus and broad-spectrum antibiotics

Understanding the specific etiology is crucial for selecting appropriate antimicrobial therapy and determining the need for surgical intervention, which significantly impacts mortality outcomes 7.