What is the etiology of a mediastinal abscess?

Etiology of Mediastinal Abscess

Mediastinal abscesses most commonly result from contiguous spread from adjacent infections, esophageal perforation, post-surgical complications, or hematogenous spread of bacteria to the mediastinum. 1

Primary Causes

1. Esophageal Perforation

• Most frequent cause of mediastinal abscess 2
• Mechanisms include:
  • Iatrogenic injury during procedures
  • Traumatic perforation
  • Spontaneous perforation (Boerhaave syndrome) after forceful vomiting or straining 3
  • Foreign body ingestion
  • Malignancy

2. Post-Surgical Complications

• Currently the most common cause in developed countries 1
• Occurs after:
  • Cardiac surgery with sternotomy
  • Thoracic procedures
  • Esophageal surgery

3. Extension from Adjacent Infections

• Descending necrotizing mediastinitis from:
  • Odontogenic infections
  • Deep neck infections
  • Pharyngeal/retropharyngeal abscesses 4
  • Peritonsillar abscesses

4. Other Causes

• Infected mediastinal lymph nodes (tuberculous or histoplasmosis) 5
• Trauma with direct introduction of bacteria
• Perforated bronchus or trachea
• Extension from lung abscess 5
• Rare causes:
  • Eosinophilic esophagitis with perforation 6
  • Infected aortic aneurysm 5
  • Intravenous drug use with hematogenous spread

Microbiology

• Typically polymicrobial infections
• Common pathogens:
  • Streptococcal species
  • Staphylococcus aureus
  • Anaerobes (particularly Bacteroides species) 4
  • Gram-negative bacteria
  • In specific cases: fungal (Candida, Aspergillus) or mycobacterial organisms 5

Pathophysiology

The development of mediastinal abscess follows a predictable pattern:

1. Initial contamination of mediastinal space
2. Bacterial proliferation facilitated by:
   • Negative intrathoracic pressure
   • Rich vascular and lymphatic supply
   • Loose connective tissue allowing spread
3. Synergistic bacterial growth leading to abscess formation 4
4. Progression to systemic infection and septic shock if untreated

Risk Factors

• Male gender
• Alcohol use
• Immunocompromised states
• Diabetes mellitus
• Malnutrition
• Advanced age
• Recent instrumentation or surgery

Clinical Pearls and Pitfalls

• Mediastinal abscess can rapidly progress to life-threatening sepsis
• Early diagnosis is critical as mortality remains high (approximately 40% for descending necrotizing mediastinitis) 4
• Consider mediastinal abscess in patients with:
  • Persistent fever after upper respiratory infection
  • Chest pain with signs of infection
  • Widened mediastinum on chest imaging
  • Dysphagia, odynophagia, or dyspnea with fever
• Never underestimate a "simple sore throat" that presents with neck edema or subcutaneous emphysema, as this may represent early spread of infection to the mediastinum 4

Understanding the etiology of mediastinal abscess is essential for prompt diagnosis and appropriate management to reduce the significant morbidity and mortality associated with this condition.