Subarachnoid Haemorrhage – SAH
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This is bleeding into the subarachnoid space.
The classical sign is a sudden onset intense headache (“feel like I’ve been hit on the back of the head Doc”).
The bleeding occurs as the result of rupture of aneurysm (80%) and AV malformations (15%). In the remainder of cases, no cause can be identified.
  • Trauma is also a major cause, but is not considered true SAH.

Epidemiology and Aetiology

Signs and Symptoms

  • Sudden onset severe headache, often at the back of the head
  • Neck stiffness – Kernig’s sign may be present after 6 hours (due to chemical meningitis), or in massive bleeds it may occur sooner due to herniation of the cerebellar tonsils (due to raised ICP).
    • Sometimes the chemical meningitis can cause vomiting and extensor plantar responses after 24hrs
  • Impaired consciousness (drowsiness / coma) – usually occurs very shortly after the onset of symptoms, but can occur several hours later.
  • Cranial nerve signs
  • Hemiplegia
    • CNS deficits can become permanent within minutes. If it lasts more than several hours it is highly unlikely to ever resolve.
  • Sentinel headache – is experienced by about 6% of patients, and is a prodromal headache thought to be the result of a small leak before rupture of an aneurysm or malformation.


Mortality (%)
Neck stiffness, cranial nerve lesions
 ± Drowsiness
± Hemiplegia
Prolonged coma


  • Overall mortality is 35-50%
    • About 30% die within a few days, and another 10-15% within a few weeks.
  • Most patients die within 1 month
  • After 1 month, 90% of patients will survive >1 year
  • Prognosis is worse with aneurysm, better with AMV, and best when no lesion is detected (presumably the lesion was small, and has healed in these instances).


  • The period of haemorrhage is actually very short – and it normally stops bleeding by itself.
  • After the initial haemorrhage, patients are at risk from vasospasm. This can causes ischaemia, which can result in secondary brain damage and further neurological signs.
    • 25% of patients will have signs of TIA / stroke after SAH as a result of vasospasm
    • Brain oedema and risk of vasospasm is greater between 72hrs and 10 days
  • Secondary acute hydrocephalus often occurs
  • Re-bleeding is VERY COMMON and usually occurs within 7 days. The risk thereafter is about 3% / year


Diagnosis is by CT, or if this is normal with a high sense of suspicion, CSF.

CT – is able to detect >90% of lesions within 48 hours of onset of symptoms.

  • Often star shaped lesion on CT – or the blood fills in giral patterns around the brain the ventricles
  • If CT is negative, but SAH is highly suspected, consider :

Lumbar puncturecontraindicated in raised ICP – so be careful! – Several features:

  • Blood – detected via the presence of bilirubin. Previously, people would use the level of RBCs as an indicator, however, it is unreliable to use the rule: if blood remains constant in 3 separate samples = SAH, if blood declines = tap trauma.
  • Xanthochromia – yellow appearance of CSF if it is left to stand for a few hours


  • Get specialist help! – call the Medical Registrar, the Neurosurgeon on call, and depending on GCS, call the anaesthetist. (Patients are unable to maintain a competant airway at GCS <8)
  • Stablise the patient haemodynamically
  • Many patients require ICU treatment
  • Neurosurgical interventions are limited, but in severe cases, a drain may be placed.
  • After the acute presentation, the patient may have their aneurysm clipped or coiled to prevent further bleeds


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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