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