• Clinical science

Subarachnoid hemorrhage


Subarachnoid hemorrhage (SAH) refers to traumatic as well as nontraumatic bleeding into the subarachnoid space. SAH most often results from head trauma. Nontraumatic SAH is responsible for 5–10% of all strokes and is most commonly caused by the rupture of an aneurysm involving the circle of Willis. SAH typically presents with severe headache, nausea, vomiting, and/or acute loss of consciousness. Acute bleeding in the subarachnoid space appears hyperdense on noncontrast CT scan, which is the initial recommended test in diagnosis. CT angiography and lumbar puncture may be necessary for further evaluation if the initial noncontrast head CT is unremarkable. Treatment consists of carefully lowering blood pressure and preventing cerebral vasospasm. Definitive management typically consists of clipping or coiling the bleeding aneurysm to prevent potentially fatal rebleeding. SAH has a high mortality rate as a result of complications such as rebleeding and secondary ischemic strokes due to vasospasm.

See also overview of stroke, ischemic stroke, and intracerebral hemorrhage for more information.



  • Traumatic
    • Head trauma is the most common cause of SAH.
    • 40–60% of patients with traumatic brain injury have subarachnoid bleeding. [1]
  • Nontraumatic
    • Ruptured cerebral aneurysm is the most common cause of nontraumatic SAH.
    • Peak incidence: approx. 50 years of age
    • > (3:2)
    • Nontraumatic SAH is responsible for 5–10% of all strokes. [2]


Epidemiological data refers to the US, unless otherwise specified.


References: [6][7][3][5]

Clinical features



Initial evaluation

  • Immediate noncontrast head CT
    • Best initial test
    • Sensitivity is almost 100% within the first 6 hours of hemorrhage [8]
    • Findings: shows blood in subarachnoid space (hyperdense)
  • Lumbar puncture (LP)
    • Best test if head CT is negative but suspicion for SAH remains high
    • Findings
      • ↑↑ RBC count: red discoloration
      • ↑ Protein (gamma globulin)
      • ↑ Or normal opening pressure
      • Xanthochromia: the yellowish discoloration of CSF is due to the presence of xanthematin, a yellow pigment derived from hematin that is released when RBCs break down
      • WBCs
      • Normal glucose

Subsequent evaluation

  • Angiography: if CT and lumbar puncture are negative but clinical suspicion for SAH is still high and/or to identify the source of ongoing bleeding (prior to intervention).
    • Digital subtraction angiography (DSA)
    • CT angiography (CTA)
  • Additional testing to consider

References: [3][8]


Medical therapy [9]

Surgical therapy [9]

  • Should be performed as early as possible to prevent rebleeding
  • Definitive treatment options for aneurysmal SAH
    • Surgical clipping
      • Following a craniotomy, the neck of an aneurysm is surgically occluded with the help of metal clips.
      • Treatment of choice but more invasive than coiling
    • Endovascular coiling
    • The decision on which procedure to perform should be made on an individualized basis.
  • If the patient has hydrocephalus: ventricular drain, serial LPs, or permanent ventriculoperitoneal shunt may become necessary.

Use of nitrates should be avoided, since they may raise ICP!



  • Vasospasm
    • Occurs in approx. 30% of patients with SAH [9]
    • Transcranial doppler ultrasound study can help identify vasospasm.
    • Pathophysiology
      • Impaired CSF reabsorption from the arachnoid villi → nonobstructive (communicating) hydrocephalus ↑ intracranial pressure → cerebral perfusion pressure → ischemia
      • Release of clotting factors and vasoactive substances → diffuse vasospasm of cerebral vessels ischemia
    • Can lead to ischemic stroke
    • Most common in patients with nontraumatic SAH due to a ruptured aneurysm
    • Usually occurs between 3–10 days after SAH
  • Recurrent bleeding
    • Occurs in 4–14% of patients with SAH in the first 24 hours [9]
    • Risk of rebleeding is highest in the first 2–12 hours after SAH
    • The cumulative risk of recurrent bleeding within the first six months is about 50%.
  • Hydrocephalus
  • Other complications [9]


We list the most important complications. The selection is not exhaustive.


  • Approx. 30% mortality rate in the U.S. within the first 30 days [9]
  • Survivors: increased rates of neurologic impairment (e.g., cognitive, mood changes, functional, epilepsy) and increased risk of recurrent SAH