Pleural Effusion

Background

• Principally a radiological diagnosis
• Accumulation of serous fluid within the pleural space
  • Can appear similar to empyema or haemothorax (pus or blood, respectively in the pleural space- see below for differences)

Pathophysiology/Aetiology

• Transudates
  • Transudates are usually bilateral on CXR
  • Usually resulting from increased hydrostatic or decreased osmotic pressures
  • Causes of transudate (protein <30g/l; LDH typically <200IU/l) include organ failures
    • Heart failure
    • Nephrotic syndrome
    • Liver failure
    • Other causes include hypothyroidism and Meig’s syndrome (ovarian tumours causing right sided pleural effusion)
• Exudates
  • exudates are typically unilateral
  • usually a result of increased microvascular pressure due to disease of the pleura or adjacent lung
  • Causes of exudates (protein >30g/l; LDH usually >200IU/l) include
    • Infection (pneumonia; TB)
    • Inflammation (Rheumatoid/SLE)
    • Infarction
    • Malignancy
    • Pancreatitis

Clinical Presentation/Assessment

• Try and determine an underlying cause i.e.
  • Infection- SOB, cough, sputum, chest pain, fever
  • Malignancy- SOB, cough, weight loss, night sweats, smoking history
  • Heart Failure- SOB, chest pain, oedema,
• The side of a unilateral effusion may give a clue
  • Left
    • Pancreatitis; Dressler’s syndrome (transudative); distal thoracic duct obstruction
  • Right
    • Heart or liver failure; ovarian malignancy; proximal thoracic duct obstruction
• Symptoms/signs specifically of pleural effusion include
  • Chest pain (pleuritic)
  • Cough
  • Occasionally SOB
  • Dullness to percuss (and decreased vocal resonance/whispering pectoriloquy)
  • Pleural rub, decreased air entry (possible crackles above the effusion)

Investigation

• CXR
  • Classical appearance is a curved shadow at the lung base (meniscus sign), blunting of the costophrenic angle and ascending towards the axilla (tracking up the chest wall)
  • Other signs may include
    • blunting of the cardiophrenic angle
    • fluid within the horizontal or oblique fissures
    • mediastinal shift can occur with large effusions
  • NB Lateral and (moreso) lateral decubitus films may show fluid more clearly and earlier than PA view
• USS (greater sensitivity for effusion)

Suspect an empyema if the shadow forms an obtuse angle with the chest wall; markedly asymmetrical bilateral shadows; lenticular (lens) shaped rather than crescent shape.  There is also more likely to be associated consolidation and features of infection.
NB It is almost impossible to differentiate effusion from haemothorax.

• From radiological diagnosis, further investigation depends on whether the effusion is unilateral and whether an underlying cause (or suspicion of transudate/exudate) is present
  • A transudative unilateral effusion with a clinically apparent underlying cause e.g. organ failure, requires no further investigation and should be treated
  • A unilateral effusion with no apparent cause:
    • USS-guided pleural aspiration for cytology, protein, LDH, pH (acidity suggests infection), microscopy, culture and sensitivity; AAFB stains and culture
      • + haematocrit for haemothorax; cholestrol for chylothorax; glucose and complement if rheumatoid suspected; amylase if pancreatitis
  • A unilateral effusion with underlying infective cause requires pleural tap (USS guided)
  • NB A bilateral effusion (presumably transudative) does not require aspiration unless it fails to respond to treatment
• Fluid analysis (and Light’s criteria)
  • In general >30g protein/l suggests exudate and <30g/l suggests transudate
  • If 25-35g/l, use Light’s criteria for accuracy
    • For exudate- one or more of
      • Pleural fluid protein / serum protein >0.5
      • Pleural fluid LDH / serum LDH >0.6
      • Pleural fluid LDH > two thirds the upper limit normal serum LDH
  • + other tests
    • Blood suggests malignancy (as can cytology- although this can be negative and requires repeating in ~40% of malignant effusions) or infarction
    • Low pH suggests
      • Pleural infection and empyema (also low glucose)
      • Rheumatoid/SLE effusion
      • TB
      • Malignancy
      • Oesophageal rupture
      • NB A low pH is an indication for tube drainage
    • Low glucose- rheumatoid and tuberculosis
    • Raised amylase- pancreatitis; oesophageal perforation
    • Heavy blood staining- mesothelioma; PE; TB
• If other tests do not suggest a diagnosis, CT thorax +/- biopsy (USS/CT guided or thoracoscopy)