Empyema vs pleural effusion

An empyema can resemble a pleural effusion and can mimic a peripheral pulmonary abscess, although a number of features usually enable distinction between the two (see empyema vs. lung abscess). Features that help distinguish a pleural effusion from an empyema include:

Empyemas usually:

  • form an obtuse angle with the chest wall
  • unilateral or markedly asymmetric whereas pleural effusions are (if of any significant size) usually bilateral and similar in size 4.  
  • lenticular in shape (biconvex), whereas pleural effusions are crescentic in shape (i.e. concave towards the lung)

Features suggestive of an empyema include:

  • enhancing thickened pleura (see split pleura sign) whereas pleural effusion has thin imperceptible pleural surfaces
  • locules of gas absent unless recent thoracocentesis
  • obvious septations
  • associated consolidation
  • associated adjacent infection (e.g. subdiaphragmatic abscess)
  • pH <7.0
  • glucose level <40mg/dL 4
  • white cells or organisms present
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Article information

rID: 8670
System: Chest
Tag: vs
Synonyms or Alternate Spellings:
  • Pleural empyema vs pleural effusion
  • Thoracic empyema vs pleural effusion
  • Pleural effusion vs thoracic empyema
  • Pleural effusion vs empyema
  • Pleural effusion vs pleural empyema

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