SUBARACHNOID HEMORRHAGE

Definition and etiology of subarachnoid hemorrhage

Created 29/03/2021, last revision 21/04/2023

Definition, epidemiology

• subarachnoid hemorrhage (SAH) is a clinical syndrome resulting from bleeding into the subarachnoid space (the area between the arachnoid membrane and the pia mater surrounding the brain)
• the most common cause of SAH is head trauma (traumatic SAH)
• non-traumatic SAH is often caused by rupture of a cerebral aneurysm (~80%) or, less frequently, due to arteriovenous malformation (AVM)
  • aneurysms are acquired lesions related to hemodynamic stress on the arterial walls at bifurcations and bends
  • aneurysmal SAH is a cause of 3-8% of all strokes; aneurysms 5-15 mm in size are the most common aneurysm to rupture
  • unruptured aneurysms are found in 0.3-5% of the population, multiple in 15-20% of cases
• the annual incidence of aneurysmal SAH is race-, sex-, and age-related
  • reported rates vary between 10 and 26 cases per 100,000 population
  • the incidence of SAH in women is higher than in men (ratio of 3 to 2)
  • incidence increases with age 
    • the peak at the age of 40-65 years (80% of SAH)
    • only 15% occur in people aged 20-40 years and  5%  in people < 20 years of age
      
    • SAH is rare in children
• SAH may have an unfavorable prognosis (reported percentages vary in the literature):
  • 5-15% of patients die before arriving at the hospital
  • 30% have initially severe deficits  (Hunt-Hess 4-5)
  • about 2/3 have a mild deficit initially; 50% deteriorate soon  (spasms, rebleeding, surgery, and other complications)
  • 10-20% of those admitted to hospital die within 24 hrs due to rebleeding
• risk factors
  • smoking, hormonal oral contraception, alcohol, hypertension, stimulants
  • genetic predisposition – family history of a ruptured aneurysm increases risk 3-7 times
    

Etiology

• there are three distinct SAH patterns; for each pattern, specific etiologies, treatment, and prognostic implications were described
  • suprasellar cisterns with peripheral extension
  • perimesencephalic SAH (pmSAH)
  • convexial SAH (cSAH)

Traumatic SAH

Spontaneous (non-traumatic) SAH

Prognosis

• prognosis depends on the severity of the initial insult and our ability to prevent complications, specifically rebleeding (by early detecting and treating the source)
• overall mortality up to 50%
  • 10-15% of patients die before arriving at the hospital
  • another 10-12% die within 24 h
  • rebleeding or brainstem dysfunction due to a massive intraventricular hemorrhage or decompensated intracranial hypertension are the usual causes of death
• 1/3-1/2 of the survivors have significant functional deficits (motor and/or cognitive)
  • cognitive deficits are present in numerous patients considered to have a good outcome
  • SAH patients commonly experience deficits in memory, executive function, and language; these symptoms are accompanied by depression, anxiety, fatigue, and sleep disturbances