Lung ultrasound: Empyema

Empyema is a purulent pleural effusion.

Seeding of the pleural space by bacteria or rarely fungi is usually from extension from adjacent pulmonary infection. Occasionally haematogenous or lymphatic spread occurs. Iatrogenic inoculation can also introduce infection. Empyema occurs most commonly in the immunosuppressed.

The purulent exudate is often thick and may become located with fibrinous strands and adhesions, and sometimes as associated rind covering the pleural surfaces.

Typical ultrasound features of empyema

The ultrasound appearance of empyema

Echogenic debris within a pleural effusion

• Empyema is characterised typically by an inflammatory exudate, and on ultrasound this appears as echogenic, swirling fluid within a pleural effusion.
• In this case the debris is highly echogenic and very coarse. One would anticipate thick pus, and a small gauge intercostal catheter would be inappropriate. In other cases the debris is far more fine and liquid, with clear swirling demonstrated within the effusion.
• Differential diagnosis of echogenic debris within a pleural effusion includes:
  • Pus – Empyema
  • Blood – Haemothorax
  • Chyle (lymphatic material) – Chylothorax
  • Proteinaceous debris – Exudate of other cause (e.g. malignancy)

Loculations

• Complex thick and thin locations are common within an empyema. Malignant effusions may have a similar appearance.
• Usually clinical features will help to differentiate.

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