Subarachnoid haemorrhage (summary)

Jason Chan and Dr Derek Smith et al.

Subarachnoid haemorrhage (SAH) is bleeding into the subarachnoid space. This is usually found centrally (around the circle of Willis) but can occur in other parts of the brain.

Reference article

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

  • anatomy
  • epidemiology
    • older middle-age, typically < 60
    • 3% of strokes and 5% of stroke-deaths
  • presentation
    • headache - described as "thunderclap"
    • neck stiffness (not specific)
    • acute confusion, neurological signs or reduce conscious level
    • ECG changes (ischaemic) or rhythm changes (Torsades)
  • pathophysiology
    • 85% rupture of intracranial aneurysm
    • vascular malformations
    • trauma
  • investigation
    • non-contrast CT head or initial assessment
    • if signs of subarachnoid haemorrhage, CT angiogram
    • lumbar puncture (looking for xanthochromia >12 h after symptoms)
  • treatment
    • depends on the cause but there are general principles
      • high fluid intake (>3500 ml/day) to prevent vasospasm
      • calcium channel blockers (nimodipine) to dilate vessels
      • early neurosurgical discussion
    • aneurysms can be coiled or clipped
  • primary diagnosis, e.g. after assessment for acute onset headache
  • determination of cause (e.g. aneurysm), e.g. CT angiography 
  • characterisation of aneurysm, e.g. catheter angiography
  • as part of treatment, e.g. interventional coiling
  • follow up 

CT scanning is the first-line imaging modality for the investigation of acute subarachnoid haemorrhages because it is fast, relatively cheap and widely available. Imaging findings, in combination with the GCS, can be used to classify bleeds.

Positive findings on CT are marked by hyperdense material in the subarachnoid space. This is usually seen in the basal cistern where the circle of Willis and underlying aneurysms lie but can be in other areas including the Sylvian fissure, lateral ventricles or interpeduncular cistern.

When a spontaneous subarachnoid haemorrhage is detected, a CT angiogram (with intravenous contrast) can be performed to look for an aneurysmal cause.

Subarachnoid blood may be demonstrated using certain sequences, but is not the first-line investigation. It can be very helpful to assess the underlying brain parenchyma in traumatic cases or used when performing MR angiography.

Angiography can be used to further investigate aneurysms or any underlying abnormalities. This study can be done by CTA, MRA or DSA (catheter angiography) - (case 4).

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Cases and figures

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    Figure 1: subarachnoid haemorrhage (diagram)
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    Case 1: traumatic SAH
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    Case 2: subarachnoid haemorrhage
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    Case 3: subarachnoid haemorrhage
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    Case 4: angiogram with PCOM aneurysm and vasospasm
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