Subarachnoid Haemorrhage - SAH


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.