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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][3]


Epidemiological data refers to the US, unless otherwise specified.


Clinical features



Initial evaluation

  • Immediate noncontrast head CT
    • Best initial test
    • Sensitivity is almost 100% within the first 6 hours of hemorrhage [10]
    • 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).
  • Additional testing to consider

References: [12][10]


Medical therapy [13]

Surgical therapy [13]

  • 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
      • Platinum coils are placed into the aneurysm to induce thrombotic occlusion of the aneurysm.
      • Less invasive than clipping but higher risk of recurrent bleeding
      • Consider for poor surgical candidates
    • 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!


Acute management checklist


  • Vasospasm
    • Occurs in approx. 30% of patients with SAH [13]
    • 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 [13]
    • 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 [13]


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


  • Approx. 30% mortality rate in the U.S. within the first 30 days [13]
  • Survivors: increased rates of neurologic impairment (e.g., cognitive, mood changes, functional, epilepsy) and increased risk of recurrent SAH


  • 1. Lee et al. Comprehensive Assessment of Isolated Traumatic Subarachnoid Hemorrhage. JOURNAL OF NEUROTRAUMA. 2014: pp. 595–609. doi: 10.1089/neu.2013.3152.
  • 2. Daroff RB, et al. Bradley's Neurology in Clinical Practice. Elsevier.
  • 3. Feigin VL, Lawes CM, Bennett DA, Barker-Collo SL, Parag V. Worldwide stroke incidence and early case fatality reported in 56 population-based studies: a systematic review. The Lancet Neurology. 2009; 8(4): pp. 355–369. doi: 10.1016/s1474-4422(09)70025-0.
  • 4. Louis et al. Merritt's Neurology. Wolter Kluwers; 2015.
  • 5. Behari S, Bhaisora K, Godbole C, Phadke R. Traumatic aneurysms of the intracranial and cervical vessels: A review. Neurol India. 2016; 64(7): p. 14. doi: 10.4103/0028-3886.178032.
  • 6. Keedy A. An overview of intracranial aneurysms. McGill Journal of Medicine. 2006; 9(2): pp. 141–6. pmid: 18523626.
  • 7. Macdonald RL, Schweizer TA. Spontaneous subarachnoid haemorrhage. The Lancet. 2017; 389(10069): pp. 655–666. doi: 10.1016/s0140-6736(16)30668-7.
  • 8. Chalouhi N, Hoh BL, Hasan D. Review of Cerebral Aneurysm Formation, Growth, and Rupture. Stroke. 2013; 44(12): pp. 3613–3622. doi: 10.1161/strokeaha.113.002390.
  • 9. Etminan N, Rinkel GJ. Unruptured intracranial aneurysms: development, rupture and preventive management. Nature Reviews Neurology. 2016; 12(12): pp. 699–713. doi: 10.1038/nrneurol.2016.150.
  • 10. Singer RJ, Ogilvy CS, Rordorf G. Clinical manifestations and diagnosis of aneurysmal subarachnoid hemorrhage. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-aneurysmal-subarachnoid-hemorrhage. Last updated September 26, 2013. Accessed March 1, 2017.
  • 11. Muehlschlegel S. Subarachnoid Hemorrhage. CONTINUUM. 2018; 24(6): pp. 1623–1657. doi: 10.1212/con.0000000000000679.
  • 12. Becske T. Subarachnoid Hemorrhage. In: Subarachnoid Hemorrhage. New York, NY: WebMD. http://emedicine.medscape.com/article/1164341-overview#showall. Updated August 12, 2016. Accessed February 14, 2017.
  • 13. Connolly ES, Rabinstein AA, Carhuapoma JR, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/american Stroke Association. Stroke. 2012; 43(6): pp. 1711–1737. doi: 10.1161/STR.0b013e3182587839.
  • 14. Brunicardi F, Andersen D, Billiar T, et al. Schwartz's Principles of Surgery. McGraw-Hill Education; 2014.
  • 15. Singer RJ, Ogilvy CS, Rordorf G. Treatment of aneurysmal subarachnoid hemorrhage. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/treatment-of-aneurysmal-subarachnoid-hemorrhage?source=search_result&search=sah&selectedTitle=2~150#H9. Last updated October 7, 2014. Accessed February 14, 2017.
  • 16. Liebeskind DS. Intracranial Hemorrhage. In: Intracranial Hemorrhage. New York, NY: WebMD. http://emedicine.medscape.com/article/1163977-overview. Updated May 10, 2016. Accessed March 1, 2017.
  • 17. Singer RJ, Ogilvy CS, Rordorf G. Treatment of cerebral aneurysms. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/treatment-of-cerebral-aneurysms. Last updated October 18, 2013. Accessed March 1, 2017.
  • 18. Hemphill JC, Greenberg SM, Anderson CS et al. Guidelines for the Management of Spontaneous Intracerebral Hemorrhage. Stroke. 2015; 46(7). doi: 10.1161/STR.0000000000000069.
  • 19. Rordorf G, McDonald C, Kasner SE, Wilterdink JL. Spontaneous Intracerebral Hemorrhage: Treatment and Prognosis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/spontaneous-intracerebral-hemorrhage-treatment-and-prognosis. Last updated May 21, 2014. Accessed March 29, 2017.
  • 20. Frontera JA, Lewin III JJ, Rabinstein AA, et al. Guideline for Reversal of Antithrombotics in Intracranial Hemorrhage. Neurocrit Care. 2015; 24(1): pp. 6–46. doi: 10.1007/s12028-015-0222-x.
  • 21. Velat GJ, Kimball MM, Mocco JD, Hoh BL. Vasospasm After Aneurysmal Subarachnoid Hemorrhage: Review of Randomized Controlled Trials and Meta-Analyses in the Literature. World Neurosurgery. 2011; 76(5): pp. 446–454. doi: 10.1016/j.wneu.2011.02.030.
  • 22. Tichter AM, Malhi J. Does Magnesium Therapy in Aneurysmal Subarachnoid Hemorrhage Affect Clinical Outcome?. Ann Emerg Med. 2017; 69(2): pp. 208–209. doi: 10.1016/j.annemergmed.2016.05.027.
  • 23. Zazulia A, Diringer M. Aneurysmal Subarachnoid Hemorrhage: Strategies for Preventing Vasospasm in the Intensive Care Unit. Semin Respir Crit Care Med. 2017; 38(06): pp. 760–767. doi: 10.1055/s-0037-1607990.
  • 24. Kirkpatrick PJ, Turner CL, Smith C, Hutchinson PJ, Murray GD. Simvastatin in aneurysmal subarachnoid haemorrhage (STASH): a multicentre randomised phase 3 trial. The Lancet Neurology. 2014; 13(7): pp. 666–675. doi: 10.1016/s1474-4422(14)70084-5.
  • 25. Ortega-Gutierrez S, et al. Effectiveness and Safety of Nicardipine and Labetalol Infusion for Blood Pressure Management in Patients with Intracerebral and Subarachnoid Hemorrhage. Neurocrit Care. 2012; 18(1): pp. 13–19. doi: 10.1007/s12028-012-9782-1.
  • 26. Diringer MN, Bleck TP, Claude Hemphill J, et al. Critical Care Management of Patients Following Aneurysmal Subarachnoid Hemorrhage: Recommendations from the Neurocritical Care Society’s Multidisciplinary Consensus Conference. Neurocrit Care. 2011; 15(2): pp. 211–240. doi: 10.1007/s12028-011-9605-9.
  • Singer RJ, Ogilvy CS, Rordorf G. Aneurysmal subarachnoid hemorrhage: Epidemiology, risk factors, and pathogenesis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-epidemiology-risk-factors-and-pathogenesis. Last updated September 26, 2013. Accessed March 1, 2017.
  • Perry JJ, Alyahya B, Sivilotti MLA, et al. Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort study. BMJ. 2015; 350(feb18 8): pp. h568–h568. doi: 10.1136/bmj.h568.
  • Marcolini E, Hine J. Approach to the Diagnosis and Management of Subarachnoid Hemorrhage. Western Journal of Emergency Medicine. 2019; 20(2): pp. 203–211. doi: 10.5811/westjem.2019.1.37352.
  • Mensing LA, Vergouwen MDI, Laban KG, et al. Perimesencephalic Hemorrhage. Stroke. 2018; 49(6): pp. 1363–1370. doi: 10.1161/strokeaha.117.019843.
  • Hunt WE, Hess RM. Surgical Risk as Related to Time of Intervention in the Repair of Intracranial Aneurysms. J Neurosurg. 1968; 28(1): pp. 14–20. doi: 10.3171/jns.1968.28.1.0014.
  • Meurer WJ, Walsh B, Vilke GM, Coyne CJ. Clinical Guidelines for the Emergency Department Evaluation of Subarachnoid Hemorrhage. J Emerg Med. 2016; 50(4): pp. 696–701. doi: 10.1016/j.jemermed.2015.07.048.
  • Westerlaan HE, van Dijk JM, Jansen-van der Weide MC, et al. Intracranial aneurysms in patients with subarachnoid hemorrhage: CT angiography as a primary examination tool for diagnosis--systematic review and meta-analysis. Radiology. 2011; 258(1): pp. 134–45. doi: 10.1148/radiol.10092373.
  • Lawton MT, Vates GE. Subarachnoid Hemorrhage. N Engl J Med. 2017; 377(3): pp. 257–266. doi: 10.1056/nejmcp1605827.
  • Li H, Pan R, Wang H, et al. Clipping Versus Coiling for Ruptured Intracranial Aneurysms. Stroke. 2013; 44(1): pp. 29–37. doi: 10.1161/strokeaha.112.663559.
  • [No authors listed]. Report of World Federation of Neurological Surgeons Committee on a Universal Subarachnoid Hemorrhage Grading Scale. J Neurosurg. 1988; 68(6). doi: 10.3171/jns.1988.68.6.0985.
  • Singer RJ, Ogilvy CS, Rordorf G. Unruptured intracranial aneurysms. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/unruptured-intracranial-aneurysms. Last updated September 26, 2013. Accessed February 7, 2017.
  • Muralidharan R. External ventricular drains: Management and complications. Surgical Neurology International. 2015; 6(7): p. 271. doi: 10.4103/2152-7806.157620.
  • Gigante P, Hwang BY, Appelboom G, Kellner CP, Kellner MA, Connolly ES. External ventricular drainage following aneurysmal subarachnoid haemorrhage. Br J Neurosurg. 2010; 24(6): pp. 625–632. doi: 10.3109/02688697.2010.505989.
  • Bederson JB, Connolly ES, Batjer HH, et al. Guidelines for the Management of Aneurysmal Subarachnoid Hemorrhage. Stroke. 2009; 40(3): pp. 994–1025. doi: 10.1161/strokeaha.108.191395.
  • Bisnaire D, Robinson L. Accuracy of levelling intraventricular collection drainage systems. J Neurosci Nurs. 1997; 29(4): pp. 261–8. doi: 10.1097/01376517-199708000-00008.
last updated 09/21/2020
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