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Lung Abscess

General Considerations

  • Cavitary lung lesions produced by infectious agents
  • They may be consequences of aspiration (most commonly) or pneumonia or they may be secondary to bronchial obstruction, bronchiectasis, bacterial endocarditis or spread of infection from elsewhere in the lung
  • Most abscesses are caused by mouth anaerobes in patients with pre-existing periodontal disease
  • Alcoholics (most commonly), those with seizure disorders leading to aspiration and those with poor dentition are at a higher risk
  • Anaerobes are most frequent cause; most lung abscesses are polymicrobial in etiology
    • Peptostreptococcus
    • Bacteroides
    • Fusobacterium
  • Also
    • Staphylococcus
    • Streptococcus pyogenes
    • Klebsiella
    • Haemophilus influenzae
    • Actinomyces species
  • And, rarely
    • Aspergillus
    • Cryptococcus
    • Histoplasma
    • Blastomyces
    • Coccidioides
    • Mycobacterium

Clinical Findings

  • Typically take 7-14 days from pneumonia to abscess formation, depending on agent
  • Fever
  • Cough
  • Foul-smelling sputum production
  • Hemoptysis
  • Night sweats
  • Anorexia and weight loss

Imaging Findings

  • On conventional radiography
    • Usually single cavity
    • Cavities typically have a
      • Thick-wall (which may become thinner as the surrounding inflammation resolves)
      • Smooth inner margin
      • Air-fluid level
    • More frequent in superior segments of lower lobes or posterior segments of lower lobes
    • Unlike pleural collections, lung abscesses frequently have a fluid level which is approximately the same length on both the frontal and lateral projection
    • About 1/3 may have an associated empyema
  • CT
    • Helpful in differentiating between a lung abscess and an empyema
    • Cavity may be seen as rounded with a thick wall and an air-fluid level
    • Lung abscesses, being intraparenchymal, form an acute angle where they meet the chest wall

Differential Diagnosis


  • Antibiotics for 4-6 weeks or until the chest radiograph shows resolution
  • Percutaneous catheter drainage
  • Surgery, either a lobectomy or pneumonectomy, may be used for patients who fail to respond to medical therapy



  • With proper antibiotic treatment, over 90% are cured
  • Those who are immunocompromised or have a bronchial obstruction have a high mortality rate

Lung abscess

Lung abscess. A single, contrast-enhanced axial CT scan image of the chest shows a large cavitary lesion in the left lower lobe with a relatively thick wall(black arrows). The cavity has a smooth inner margin and an air-fluid level (white arrow). There is inflammatory reaction in the surrounding lung (yellow arrow). Notice the acute angle the abscess makes with the posterior chest wall.

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Lung Abscess

Lung Abscess. There is a thick-walled cavity with a smooth inner margin, located in the left lower lobe. An air-fluid level is present.

Lung Abscess

Lung Abscess. There is a thick-walled cavity with a smooth inner margin (red and white arrows). An air-fluid level is present (black arrow).

Lung Abscess

Lung Abscess. There is a thick-walled cavity (white arrow) with a smooth inner margin (red arrow), located in the right lung.
An air-fluid level is present (black arrow).

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Lung abscess eMedicine Sharma, S. MD, FRCPC