Subdural haemorrhage (summary)

Jason Chan and Dr Derek Smith et al.

Subdural haemorrhage (SDH) is a collection of blood between the dura and the arachnoid layers of the meninges. They are common and can occur in any age range, usually related to a history of head trauma. Prognosis tends to depend on the extent of the bleed and associated mass effect.

Reference article

This is a summary article; read more in our article on subdural haemorrhage.

  • anatomy
  • epidemiology
    • children: non-accidental injury 1
    • adults: high energy trauma, e.g. road traffic collisions
    • elderly: falls (there may not be a clear history of trauma)
  • presentation
    • acute
      • usually associated with head injury
        • may be associated contusions or extradural haemorrhage
      • underlying vascular malformations
    • subacute or chronic
      • confusion and vague neurological change
      • a classic cause of pseudodementia
      • beware patients on anticoagulants, e.g. warfarin
  • pathophysiology
    • tearing of bridging veins found in the subdural space
    • veins are subject to shearing forces
      • occurs with lower forces in the elderly
  • investigation
    • non-contrast CT head
  • treatment
    • correction of abnormal coagulation
    • discussion with neurosurgical services
    • small subdurals can be observed with repeated CT
    • surgical evacuation of the clot
      • may carry significant mortality and morbidity
  • initial diagnosis
  • assessment of associated mass effect
  • look for an underlying cause
  • suggest further imaging
  • follow up

Subdural haemorrhages are typically unilateral (85%) 4 and follow a crescent-like distribution around the periphery of the brain. They are not limited by sutures and can fill dural reflections (falx cerebri, tentorium).

Non-contrast CT is usually enough to make the diagnosis but contrast can be used in challenging cases, particularly with the different appearances of these bleeds over time.

Acute subdural haemorrhages are hyperdense collections. While many are uniformly hyperdense, up to half can have mixed appearances as (hypodense) unclotted blood, serum or CSF is involved in the collection.

Acute bleeds may be isodense and therefore difficult to identify in patients with anaemia or coagulopathies (including warfarinisation) where it fails to clot. The clotting process causes increased density and failure to clot, therefore, results in an isodense collection.

In the first few weeks after a bleed, the clot and proteins are broken down making the collection appear hypo or isodense. Here, indirect signs of a subdural collection are important to identify, e.g. a gap between the cerebral sulci and skull, mass effect or an apparent ill-defined, thickened cortex.

Isodense subdural collections can be difficult to see if there are identical density to adjacent brain parenchyma. Contrast-enhanced CT is often useful in this instance if MRI is unavailable.

Be aware of the acute isodense SDH in anaemic patients.

Over time, these collections can resolve and leave few products behind with a hypodense region on CT with density similar to CSF 2.

MRI is used to assess the underlying parenchyma. The signal of blood in the subdural haemorrhage change with time and MRI can be used to age a collection.

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Article information

rID: 32796
Synonyms or Alternate Spellings:
  • SDH (summary)
  • Subdural haematoma (summary)

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Cases and figures

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    Figure 1: diagram of subdural bleed
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    Case 1: left chronic SDH
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    Chronic subdural ...
    Case 2: chronic subdural
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    Huge isodense sub...
    Case 3: left isodense SDH
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    Chronic SDH
    Case 4: right chronic SDH
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    Case 5: right acute SDH
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    Case 6: right acute SDH (on warfarin)
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