subarachnoid haemorrhage

Last edited 12/2022 and last reviewed 12/2022

Subarachnoid haemorrhage (SAH) accounts for about 5% of strokes with an annual incidence of 2 to 20 per 100,000 per year

• in around 80% of people, the bleed arises from rupture of an intracranial arterial aneurysm
  
  
• aneurysmal subarachnoid haemorrhage is slightly more common in women than men, and can occur across a wide range of ages with a median age at presentation between 50 and 60 years
  • prevalence of aneurysms in the general population is roughly 2-5%, (2) greater in those with family history of aneurysms, and/or personal history of Ehlers-Danlos or polycystic kidney disease
  • factors associated with the risk of rupture include
    • hypertension,
    • tobacco use,
    • excessive alcohol use,
    • sympathomimetic drugs,
    • Black race,
    • Hispanic ethnicity,
    • and aneurysmal size > 10 millimeters (mm)
  • aneurysmal SAH is more common in women and in patients 40-60 years old (2)
    
    
• occasionally, the arachnoid layer gives way and a subdural haematoma develops
  
  
• main symptom of subarachnoid haemorrhage is a sudden and severe 'thunderclap' headache
  • 'thunderclap' headache (a sudden severe headache, typically peaking in intensity within 1 to 5 minutes) is a red-flag symptom of subarachnoid haemorrhage (1)
    • thunderclap headache is associated with other conditions or causes such as migraine, cough, coitus or exertion
    • most people with a thunderclap headache do not have a subarachnoid haemorrhage, but this should not deter further investigation if subarachnoid haemorrhage is suspected
      
      
  • other possible symptoms include neck stiffness, altered consciousness or seizures
  • is more easily diagnosed in people presenting with severe symptoms, unconsciousness or sudden onset acute headache but some people with subarachnoid haemorrhage present with less severe or non-specific symptoms and signs
    
    
• urgent investigation to confirm a diagnosis of subarachnoid haemorrhage facilitates treatment to prevent rebleeding from the ruptured aneurysm and reduces disability and death

When carrying out an initial assessment in a person who presents with unexplained acute severe headache:

• have a high index of suspicion for subarachnoid haemorrhage

• take a careful history to establish the rate of onset and time to peak intensity of the headache

On initial presentation, the one-year mortality of untreated SAH is up to 65% (2)

• with appropriate diagnosis and treatment, mortality can be reduced to 18%

Refer people with suspected subarachnoid haemorrhage seen outside of acute hospital settings to an emergency department immediately for further assessment

Refer the person for an urgent non-contrast CT head scan if review in secondary care by a senior clinical decision-maker confirms unexplained thunderclap headache, or other signs and symptoms that suggest subarachnoid haemorrhage. Be aware that the diagnostic accuracy of CT head scans is highest within 6 hours of symptom onset.

Reference:

• NICE (November 2022).Subarachnoid haemorrhage caused by a ruptured aneurysm: diagnosis and management
• Marcolini E, Hine J. Approach to the Diagnosis and Management of Subarachnoid Hemorrhage. West J Emerg Med. 2019 Mar;20(2):203-211.