Pleural effusion

Pleural effusion, also called hydrothorax, refers to the presence of fluid in the pleural cavity. If visible on a chest radiograph, there are at least 100 mL of fluid.

If there is simultaneous pneumothorax, the condition is called hydropneumothorax.

Etiology and types

• Types according to composition and cause
  • Transudates (hydrothorax/HTX)
    • Heart failure
    • Hypoalbuminaemia
      • Cirrhosis
      • Nephrotic syndrome
  • Exudates
    • Malignancy
    • Pneumonia (thoracic empyema)
    • Haemothorax
    • Chylothorax
• Types according to laterality
  • Bilateral effusions
    • Heart failure
  • Unilateral effusions
    • Pulmonary embolism
    • Trauma
    • Tuberculosis
    • Acute pancreatitis (only left side)

Clinical features

The pleural effusion itself may cause dyspnoea and hypoxaemia. Symptoms of the underlying cause is often present.

Decreased lung sounds and increased dullness on percussion may be felt over the affected area.

Diagnosis and evaluation

Chest radiograph is the first choice if pleural effusion is suspected, although it can't detect effusions < 300 mL. It will show blunting of the costophrenic angle and, if large enough, opacification of parts or of the entire lung. There may be a midline shift toward the contralateral side.Pleural effusion filling the entire pleural cavity causes so-called white-out of the hemithorax, but is very rare.

If there is simultaneous pneumothorax, a horizontal fluid level called an air-fluid level (or "niveau") will be present.

A chest radiograph taken with the patient lying on their side, effusion side down may allow visualisation of small amounts of subpulmonal fluid. This is sometimes called a "Frimann-Dahl image" (according to the lecture, probably a Hungarian term).

Ultrasonography and CT may also be used to visualise pleural effusion. CT is rarely necessary. On ultrasound pleural fluid is seen as hypoechoic or anechoic structures in the costophrenic recess. CT can be used to measure fluid density and therefore assist in the determination of the type of fluid.

If the type of fluid is uncertain, it should be drained with a needle for laboratory examination.

‎