Subarachnoid Hemorrhage



  • Bleeding into the subarachnoid space and CSF:
    • Spontaneous:
      • Results from ruptured cerebral artery aneurysm in up to 80% of cases
      • Aneurysms that are >25 mm are more likely to rupture
    • Traumatic:
      • Represents severe head injury


  • Incidence is 6–16 per 100,000 individuals
  • Affects 21,000 in the U.S. annually
  • Associated mortality in 30–50% of patients with 1 in 4 dying within 1 d
  • Uncommon prior to third decade of life; incidence peaks in sixth decade

Risk Factors

  • Aneurysms ≥7 mm have greater risk for rupture
  • After adjustment for size and location, aneurysm aspect ratio >1.3 and irregular shape also significantly associated with rupture
  • Family history
  • Hypertension
  • Smoking
  • Alcohol abuse
  • Sympathomimetic drugs:
    • Cocaine, methamphetamine, and ecstasy (MDMA)
  • Gender (female:male 1.6:1)

  • Three- to sevenfold increased risk in first-degree relatives with subarachnoid hemorrhage (SAH)
  • Strongest genetic association represents only 2% of SAH patients:
    • Autosomal dominant polycystic kidney disease, Ehlers–Danlos type IV, familial intracranial aneurysms

Pediatric Considerations
  • Most often due to arteriovenous malformation in children
  • Although rare in children, SAH is a leading cause of pediatric stroke


  • “Congenital,” saccular, or berry aneurysm rupture (80–90%):
    • Occur at bifurcations of major arteries
    • Incidence increases with age
    • Aneurysms may be multiple in 20–30%
  • Nonaneurysmal perimesencephalic hemorrhage (10%)
  • Remaining 5% of causes include:
    • Mycotic (septic) aneurysm due to syphilis or endocarditis
    • Arteriovenous malformations
    • Vertebral or carotid artery dissection
    • Intracranial neoplasm
    • Pituitary apoplexy
  • Severe closed head injury

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