Lung abscess

Necrosis of the pulmonary parenchyma caused by microbial infection

Aetiology

• Mostly a complication of aspiration pneumonia

Pathophysiology

• Most common organisms - Peptostreptococcus, Prevotella, Bacteroides, Fusobacterium
  • Others Staph aureus, Klebsiella pneumoniae, Strep pyogenes, Burkholderia pseudomallei, H influenzae type B, Legionella, Nocardia, Actinomyces
  • Immunocompromised - look for Pseudomonas aeruginosa, other aerobic GNB, Nocardia, fungi (Aspergillus, Cryptococcus)
• Typically occurs in a segment of lung that that is dependent in the recumbent position
  • Superior segment of a lower lobe or a posterior segment of the upper lobes

Presentation

• Usually indolent symptoms over weeks to months
• Fever, cough, sputum production
• Chronic systemic disease
• If the cavity spontaneously ruptures into the pleural cavity, treat for empyema or bronchopleural fistula, and lobectomy will usually be required (mortality 1-5%)

Imaging

• CXR - infiltrates with a cavity
• CT indicated if suspected - helps to distinguish between a parenchymal lesion and a pleural collection

Treatment

• Antibiotics
  • Empirical combination
  • Usually beta lactam or carbapenem
  • Can treat for either three weeks or response-dependent
• Bronchoscopy indications
  • Failing medical management
  • High-risk features - symptoms for >3 months prior to treatment or cavities >4-6cm
  • Can be used for either direct drainage or trans-bronchial catheterisation of the cavity
• Surgery
  • Rarely required
  • Indications:
    • Persistent cavity >=2cm and thick-walled
    • Failure to clear sepsis after 8 weeks of medical therapy
    • Haemoptysis
    • Exclusion of cancer