Pleural Effusion


  • 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)


  • 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)


  • 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)

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: