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Lung Abscess

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Overview

An abscess is a localised collection of pus within the lung leading to the formation of a cavity. This differs from an empyema, where the collection of pus occurs in a pre-existing normal anatomical cavity.

Causes

  • Bacterial infection:
    • Staphylococcus aureus
    • Klebsiella pneumoniae
    • Pseudomonas aeruginosa
    • Tuberculosis
  • Aspiration (e.g. inhalation of a foreign body)
  • Haematogenous (e.g. secondary to infective endocarditis) 
  • Extension of a hepatic abscess
  • Lung cancer
  • Severe or incompletely-treated pneumonia
  • Trauma

Risk Factors

  • Risk factors for gastric aspiration (e.g. strokes leading to dysphagia)
  • Pneumonia
  • Diabetes mellitus
  • Immunodeficiency
  • Severe dental disease
  • Excess alcohol consumption
  • Drug misuse
  • Underlying respiratory diseases e.g. COPD, bronchiectasis

Presentation

The signs and symptoms are similar to pneumonia; however, they usually develop over weeks and develop more insidiously. Features are:

  • Fever
  • Productive cough – often copious amounts of foul-smelling sputum are produced
  • Pleuritic chest pain
  • Constitutional symptoms – weight loss, night sweats, malaise
  • Dyspnoea
  • Some patients may have haemoptysis
  • Finger clubbing may be seen in chronic cases

Differential Diagnoses

Empyema

  • There may be no way to differentiate them clinically
  • Thoracic ultrasound shows echogenic, loculated, or septated empyema

Pneumonia

  • There may be no way to differentiate them clinically
  • Chest x-ray shows consolidation but no effusion

Pleural effusion

  • There may be no way to differentiate them clinically
  • Chest x-rays show effusions with a clear fluid level

Investigations

All patients

  • Chest x-ray:
    • Shows focal consolidation with central cavitation and an air-fluid level
  • Blood cultures:
    • May show causative organism and should ideally be taken before antibiotics are given, but do not delay treatment
  • Sputum cultures:
    • May show causative organism

Management

All patients

  • 1st-line: IV antibiotics and sepsis six if necessary
  • Drainage may be necessary or surgery

Complications

  • Empyema
  • Complications from haematogenous spread (e.g. abscesses in other locations)
  • Haemoptysis

Prognosis

  • The cure rate is around 90% with antibiotic therapy
  • The prognosis is worse with factors such as increasing age and the presence of other comorbidities

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