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.
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