Extra-axial collection (summary)

Dr Jeremy Jones et al.

Extra-axial collections are collections of fluid within the skull, but outside the brain parenchyma. They may be comprised of CSF, blood or pus and may exist in the extradural, subdural or subarachnoid space. 

Reference article

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Summary

  • pathophysiology
    • fluid collection in the extradural, subdural or subarachnoid space
      • blood, e.g. post-traumatic extradural haemorrhage
      • fluid, e.g. chronic subdural haemorrhage
      • pus, e.g. subdural empyema
  • role of imaging
    • determine whether there is an extra-axial collection
    • determine where the collection is:
      • subarachnoid
        • extends down into the sulci
        • extends into the basal cisterns
      • subdural
        • more crescent-like shape
        • may cross sutures
      • extradural
        • lentiform (lens-like) shape
        • don't cross cranial sutures
    • determine whether there is mass effect and:
      • midline shift
      • hydrocephalus
  • radiographic features
    • CT head
      • best initial test, especially in an unwell patient
      • haemorrhage in the acute setting is white
        • as blood ages, it becomes darker (more watery) on CT
      • extra-axial collections are not always blood, e.g. empyema
    • MRI brain
      • may be helpful for further assessment
      • may be easier to determine which space the collection is in
      • using different sequences, it should be possible to determine the type of fluid and narrow the differential diagnosis
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Article information

rID: 51212
Synonyms or Alternate Spellings:

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Cases and figures

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    Case 1: extradural haematoma
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    Case 2: subdural empyema
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    Case 3: chronic subdural haemorrhage (MRI)
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