Pleural effusion

A pleural effusion is excess fluid between the visceral and parietal pleura. Light's criteria separate transudates (heart failure, cirrhosis, nephrotic syndrome) from exudates (pneumonia, malignancy, tuberculosis, pulmonary embolism).

Clinical presentation

Breathlessness, reduced expansion, stony dullness to percussion and absent breath sounds at the base. Small effusions are often silent.

Radiographic features

Plain radiograph

• Blunting of the costophrenic angle — around 200 ml is needed on an erect PA film, less on the lateral view
• A meniscus: a concave upper border that rises laterally
• Large effusions cause opacification of the hemithorax and push the mediastinum away
• Supine films show a hazy veil over the hemithorax with preserved vessels
• Lateral decubitus films show free fluid layering along the dependent chest wall

Ultrasound

The most sensitive bedside test. It shows anechoic or echogenic fluid, septations that suggest an exudate or empyema, and guides safe aspiration.

CT

Shows loculation, pleural thickening and enhancement (the split pleura sign of empyema) and the underlying cause.

Treatment and prognosis

Treat the cause. Diagnostic aspiration with protein, LDH, pH, microscopy and cytology guides further management; infected or symptomatic effusions are drained.

Differential diagnosis

• Lower lobe collapse or consolidation
• Elevated hemidiaphragm
• Pleural thickening or mass