Subarachnoid Hemorrhage

Subarachnoid Hemorrhage is a topic covered in the 5-Minute Emergency Consult.

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  • Bleeding into the subarachnoid space and CSF:
    • Spontaneous:
      • Most often results from cerebral aneurysm rupture
      • Aneurysms that occur are more likely to rupture (>25 mm).
    • Traumatic:
      • Represents severe head injury


  • Incidence is 6–16 per 100,000 individuals.
  • Affects 21,000 in US annually
  • Associated mortality in 30–50% of patients
  • Uncommon prior to 3rd decade; incidence peaks in 6th decade

Risk Factors

  • Previous ruptured aneurysm who have other aneurysms
  • Family history
  • Hypertension
  • Smoking
  • Alcohol abuse
  • Sympathomimetic drugs:
    • Cocaine, methamphetamine, and ecstasy (MDMA) use
  • Gender (female:male 1.6:1)

  • 3–7-fold increased risk with 1st-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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