Pleural fluid (summary)

Dr Craig Hacking and Dr Jeremy Jones et al.
This is a basic article for medical students and other non-radiologists

Pleural fluid describes fluid within the pleural space. Fluid may be simple fluid, pus, haemorrhage and therefore is a broad description that includes, but not synonymous with pleural effusion. Pus in the pleural space may become loculated and in some cases, may have solid elements.

Reference article

This is a summary article; we do not have a more in-depth reference article.

  • pathophysiology
    • fluid within the pleural space
    • causes
      • simple fluid: pleural effusion
        • high protein: exudate, e.g. infection
        • low protein: transudate, e.g. pulmonary oedema
      • pus
      • haemorrhage
  • common pathology

chest x-ray | chest ultrasound | CT chest

  • role of imaging
    • is there a pleural effusion?
      • a chest x-ray is first line test
      • US and CT are more sensitive and specific but not always required
    • are there other features that suggest a cause?
      • air-space opacification in pneumonia or heart failure
      • cardiomegaly in heart failure
      • focal lung lesion or collapse in lung cancer
    • is it complex (septations or loculations)?
      • ultrasound is best, but CT may help
    • is it infected (enhancement)? 
      • CT is best; ultrasound is less sensitive
    • what is the best way to drain it?
      • ultrasound is helpful - most drainage will be ultrasound-guided
  • radiographic features
    • chest x-ray
      • unilateral opacification without volume loss or air bronchograms
        • usually basal
      • blunting of the costophrenic angle 
        • this may be the only sign in smaller effusions
        • if it can be seen on a chest x-ray, it measures 300-500 ml
    • ultrasound
      • fluid is dark (hypoechoic) on ultrasound
        • the underlying lung may be consolidated
      • additional features:
        • septations: parapneumonic effusion or early empyema
        • loculation: established pleural infection
        • thick turbid fluid with echogenic material: empyema
    • CT chest
      • the volume required for detection is much smaller than CXR
      • fluid on CT is an intermediate density: 0-30 HU
        • the density may help to determine the type of fluid
          • simple fluid will have a lower HU than blood
      • if IV contrast is given, enhancement may point to an infective cause
Medical student radiology curriculum
Share article

Article information

rID: 51425
System: Chest
Synonyms or Alternate Spellings:

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    Case 1: right pleural effusion
    Drag here to reorder.
  • Drag
    Case 2: simple pleural effusion
    Drag here to reorder.
  • Drag
    Case 4: empyema with enhancing margins
    Drag here to reorder.
  • Drag
    Case 3: haemothorax with increased density
    Drag here to reorder.
  • Updating… Please wait.

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.