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Subarachnoid hemorrhage

Last updated: October 25, 2021

Summarytoggle arrow icon

Subarachnoid hemorrhage (SAH) refers to bleeding into the subarachnoid space. While SAH is often caused by trauma, 5–10% of cases are nontraumatic or spontaneous, in which case they are often due to the rupture of an aneurysm involving the circle of Willis (aneurysmal SAH). Nontraumatic SAH typically manifests with sudden and severe headache, which may be accompanied by nausea, vomiting, signs of meningism, and/or acute loss of consciousness. The best initial diagnostic test is a head CT without contrast, in which acute subarachnoid bleeding can be seen as hyperdensities in the subarachnoid space. If a head CT is negative for SAH, this diagnosis can be ruled out in many patients. However, if clinical suspicion remains high, it may be necessary to perform a lumbar puncture or CT angiography. Once SAH is confirmed, angiography is always necessary in order to identify the source of bleeding (e.g., aneurysms or other vascular abnormalities) and plan definitive treatment. The management of traumatic and nontraumatic SAH consists mostly of neuroprotective measures (e.g., control of blood pressure) to prevent secondary brain injuries. In aneurysmal SAH, microsurgical clipping or endovascular coiling of the aneurysm is indicated to prevent potentially fatal rebleeding. Aneurysmal SAH has a high mortality rate as a result of complications such as rebleeding and delayed cerebral ischemia.

See also “Overview of stroke” and “Traumatic brain injury” for more information.


Epidemiological data refers to the US, unless otherwise specified.

There is no universally accepted grading scale for SAH, but the scales presented here are among the most commonly used and have some value in predicting the neurologic outcome (probability of death and expected level of disability). They have been created for the assessment of aneurysmal SAH and are usually not validated for the use in traumatic SAH. [10][11][12]

Clinical classification

Clinical severity should be graded at the time of presentation.

Hunt-Hess classification of aneurysmal SAH [12][13]
Grade Symptoms and level of consciousness Neurological exam
World Federation of Neurological Surgeons (WFNS) grading scale for SAH [14]
Grade GCS Motor deficit








May be present


May be present

Radiological classification

In addition to scales for clinical severity, the radiological appearance of SAH can also be graded. The most reliable tool is the modified Fisher scale, which is used to predict the incidence of delayed cerebral ischemia. [11]

Modified Fisher scale [11][15]
Grade Subarachnoid hemorrhage Intraventricular hemorrhage




2 Present


4 Present


The following information applies to the diagnostic workup of suspected SAH in patients without a history of trauma. See “Traumatic SAH” for information specific to trauma patients.

Approach [10][17][18][19]

Since a missed diagnosis of SAH can have devastating consequences, clinicians should maintain a high index of suspicion when deciding whether to pursue testing.

  • Common indications for testing
  • Best initial test: immediate head CT without contrast [18][20]
    • Confirmation of SAH: Obtain angiography to confirm source of bleeding and plan treatment.
    • Nondiagnostic CT in the first 6 hours in a neurologically intact patient: SAH is not likely; consider other differential diagnoses. [20]
    • Nondiagnostic head CT but persisting suspicion: Perform second-line diagnostic tests.
  • Second-line tests: lumbar puncture (LP) or CT angiography (CTA) [17][20]
    • Lumbar puncture
      • LP positive: Identify the source of bleeding with angiography (e.g., CTA, DSA) and plan intervention.
      • LP negative; : SAH can be ruled out in most cases. If suspicion remains high, obtain CTA.
    • CTA (alternative)
      • CTA positive: Consider if additional angiographic imaging is necessary (e.g., DSA, MRA) and plan intervention.
      • CTA negative: SAH can be ruled out; consider other diagnoses. If suspicion remains high (which is rare), consider additional imaging (e.g., DSA, MRA).
  • Additional studies: Obtain CBC, BMP, coagulation panel, and type and screen.

If patients are unstable or have signs of increased ICP, diagnostics should not delay stabilizing and neuroprotective measures.

The Ottawa SAH clinical decision rule [20][21]

The Ottawa SAH clinical decision rule can be used as a tool to exclude SAH in selected patients presenting to the emergency department with acute headache.

  • Inclusion criteria (all of the following need to be fulfilled):
    • Age > 15 years
    • Neurologically intact and alert (GCS 15)
    • New, nontraumatic, severe headache, reaching maximum intensity in < 1 hour
  • Risk features
  • Interpretation [21]
    • Presence of 0 risk features: SAH ruled out
    • Presence of ≥ 1 risk feature: SAH cannot be ruled out

Head CT without contrast [11][17][22]

If there is a high index of suspicion for SAH, a negative head CT does not exclude the diagnosis and second-line tests are necessary. [17]

Second-line tests

Lumbar puncture (LP) [20][26][27]

Concerns for elevated ICP (e.g., on physical examination or CT scan) or coagulopathy are relative contraindications for lumbar puncture.

CT angiography (CTA) [10][17][18]

  • Widely available and minimally invasive
  • High sensitivity and specificity for aneurysms larger than 3–4 mm.
  • Can provide enough information to plan aneurysm repair. [11][29]
  • Findings [30]
    • Visualization of aneurysms (accumulation of contrast)
    • May detect extravasation of contrast in the case of active bleeding
    • May detect vascular abnormalities (e.g., AVM)

Additional studies [11][17][29][31]

The initial management of all patients with spontaneous SAH is similar, but further management depends on the underlying etiology. While aneurysmal hemorrhage can be treated with endovascular coiling or microsurgical clipping, there are few specific definite treatment options for nonaneurysmal SAH.

Initial management [11][17][19]

Primary measures should be initiated urgently in the ED. The goal is to stabilize the patient and prevent early rebleeding and secondary brain injury.

Rebleeding is a life-threatening complication that occurs most commonly in the first 6 hours after SAH. Start measures to prevent rebleeding immediately. [11][17]

Do not use nitrates for blood pressure management, since they may raise ICP. [19]

Aneurysmal SAH [17][32]

All aneurysmal SAHs require definitive endovascular or microsurgical aneurysm repair as early as possible. Patients should be admitted to critical care for further management to prevent and treat secondary brain injury and systemic complications.

Intracranial aneurysm repair [17]

Intracranial aneurysm repair [10][17][33]
Endovascular coiling Microsurgical clipping
  • Minimally invasive
  • Higher risk of incomplete obliteration and recurrent bleeding
  • More invasive
  • Higher rate of complete aneurysm occlusion
  • Lower risk of recurrent bleeding
  • Insertion of a catheter under fluoroscopic guidance
  • Placement of metal coils in the aneurysm lumen to interrupt blood flow and induce thrombotic occlusion

Further management [32]

Nonaneurysmal SAH

Depending on the etiology, some specific measures may help improve the outcome.

Typically, patients present with a clear history of trauma, and the diagnosis of SAH is then made based on imaging. For the initial management of trauma patients and the initial management of traumatic brain injury (TBI), see also the respective articles.



There is no specific surgical or interventional treatment for traumatic SAH. Management is mostly supportive, with the goal of preventing secondary brain injury. If there are associated lesions, surgical intervention may be required.

  • Mild TBI with isolated SAH [37][38][39][40]
    • Typically, no surgical intervention is required and outcomes are good.
    • Consider neurosurgical and critical care consult if red flags for mTBI are present.
    • Repeat neuroimaging in the case of clinical deterioration or based on individual evaluation.
    • See the article on “Mild TBI” for additional information.
  • Moderate or severe TBI with SAH [41]
  • SAH with other pathologic radiographic findings [39]
    • Regardless of the initial GCS, these patients are at a higher risk of deterioration.
    • Admit the patient to a critical care unit.
    • Surgical intervention (e.g., hematoma evacuation) may be required.
    • See also “Treatment” in “SDH,” “EDH,” and “ICH.”


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

  • Approx. 30% mortality rate in the U.S. within the first 30 days [17]
  • 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 : p.595-609. doi: 10.1089/neu.2013.3152 . | Open in Read by QxMD
  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): p.355-369. doi: 10.1016/s1474-4422(09)70025-0 . | Open in Read by QxMD
  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 . | Open in Read by QxMD
  6. Keedy A. An overview of intracranial aneurysms.. McGill Journal of Medicine. 2006; 9 (2): p.141-6.
  7. Macdonald RL, Schweizer TA. Spontaneous subarachnoid haemorrhage. The Lancet. 2017; 389 (10069): p.655-666. doi: 10.1016/s0140-6736(16)30668-7 . | Open in Read by QxMD
  8. Chalouhi N, Hoh BL, Hasan D. Review of Cerebral Aneurysm Formation, Growth, and Rupture. Stroke. 2013; 44 (12): p.3613-3622. doi: 10.1161/strokeaha.113.002390 . | Open in Read by QxMD
  9. Etminan N, Rinkel GJ. Unruptured intracranial aneurysms: development, rupture and preventive management. Nature Reviews Neurology. 2016; 12 (12): p.699-713. doi: 10.1038/nrneurol.2016.150 . | Open in Read by QxMD
  10. Lawton MT, Vates GE. Subarachnoid Hemorrhage. N Engl J Med. 2017; 377 (3): p.257-266. doi: 10.1056/nejmcp1605827 . | Open in Read by QxMD
  11. Muehlschlegel S. Subarachnoid Hemorrhage. CONTINUUM. 2018; 24 (6): p.1623-1657. doi: 10.1212/con.0000000000000679 . | Open in Read by QxMD
  12. Rosen DS, Macdonald RL. Subarachnoid Hemorrhage Grading Scales: A Systematic Review. Neurocrit Care. 2005; 2 (2): p.110-118. doi: 10.1385/ncc:2:2:110 . | Open in Read by QxMD
  13. Hunt WE, Hess RM. Surgical Risk as Related to Time of Intervention in the Repair of Intracranial Aneurysms. J Neurosurg. 1968; 28 (1): p.14-20. doi: 10.3171/jns.1968.28.1.0014 . | Open in Read by QxMD
  14. [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 . | Open in Read by QxMD
  15. Frontera JA, Claassen J, Schmidt JM, et al. Prediction of Symptomatic Vasospasmafter Subarachnoid Hemorrhage: The Modified Fisher Scale. Neurosurgery. 2006; 59 (1): p.21-27. doi: 10.1227/01.neu.0000218821.34014.1b . | Open in Read by QxMD
  16. Singer RJ, Ogilvy CS, Rordorf G. Clinical manifestations and diagnosis of aneurysmal subarachnoid hemorrhage. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: September 26, 2013. Accessed: March 1, 2017.
  17. 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): p.1711-1737. doi: 10.1161/STR.0b013e3182587839 . | Open in Read by QxMD
  18. Singer RJ, Ogilvy CS, Rordorf G. Treatment of aneurysmal subarachnoid hemorrhage. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: October 7, 2014. Accessed: February 14, 2017.
  19. Marcolini E, Hine J. Approach to the Diagnosis and Management of Subarachnoid Hemorrhage. Western Journal of Emergency Medicine. 2019; 20 (2): p.203-211. doi: 10.5811/westjem.2019.1.37352 . | Open in Read by QxMD
  20. 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): p.211-240. doi: 10.1007/s12028-011-9605-9 . | Open in Read by QxMD
  21. Grasso G, Alafaci C, Macdonald Rl. Management of aneurysmal subarachnoid hemorrhage: State of the art and future perspectives. Surg Neurol Int. 2017; 8 (1): p.11. doi: 10.4103/2152-7806.198738 . | Open in Read by QxMD
  22. Ahmadian A, Mizzi A, Banasiak M, et al. Cardiac manifestations of subarachnoid hemorrhage.. Heart, lung and vessels. 2013; 5 (3): p.168-78.
  23. Zhang L, Zhang B, Qi S. Impact of echocardiographic wall motion abnormality and cardiac biomarker elevation on outcome after subarachnoid hemorrhage: a meta-analysis. Neurosurg Rev. 2018; 43 (1): p.59-68. doi: 10.1007/s10143-018-0985-6 . | Open in Read by QxMD
  24. Al-Mufti F, Stein A, Damodara N, et al. Decision-Making for Patients With Cerebral Arteriovenous Malformations. Cardiol Rev. 2020; 29 (1): p.10-14. doi: 10.1097/crd.0000000000000342 . | Open in Read by QxMD
  25. Derdeyn CP, Zipfel GJ, Albuquerque FC, et al. Management of Brain Arteriovenous Malformations: A Scientific Statement for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke. 2017; 48 (8). doi: 10.1161/str.0000000000000134 . | Open in Read by QxMD
  26. Mensing LA, Vergouwen MDI, Laban KG, et al. Perimesencephalic Hemorrhage. Stroke. 2018; 49 (6): p.1363-1370. doi: 10.1161/strokeaha.117.019843 . | Open in Read by QxMD
  27. Meurer WJ, Walsh B, Vilke GM, Coyne CJ. Clinical Guidelines for the Emergency Department Evaluation of Subarachnoid Hemorrhage. J Emerg Med. 2016; 50 (4): p.696-701. doi: 10.1016/j.jemermed.2015.07.048 . | Open in Read by QxMD
  28. Godwin SA, Cherkas DS, Panagos PD, et al. Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting to the Emergency Department With Acute Headache. Ann Emerg Med. 2019; 74 (4): p.e41-e74. doi: 10.1016/j.annemergmed.2019.07.009 . | Open in Read by QxMD
  29. Perry JJ, Stiell IG, Sivilotti ML, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013; 310 (12): p.1248-55. doi: 10.1001/jama.2013.278018 . | Open in Read by QxMD
  30. Heit JJ, Iv M, Wintermark M. Imaging of Intracranial Hemorrhage.. Journal of stroke. 2017; 19 (1): p.11-27. doi: 10.5853/jos.2016.00563 . | Open in Read by QxMD
  31. Barreau X, Marnat G, Gariel F, Dousset V. Intracranial arteriovenous malformations. Diagn Interv Imaging. 2014; 95 (12): p.1175-1186. doi: 10.1016/j.diii.2014.10.004 . | Open in Read by QxMD
  32. Seehusen, et al. Cerebrospinal Fluid Analysis. American Family Physician. 2003 .
  33. Long D, Koyfman A, Long B. The Thunderclap Headache: Approach and Management in the Emergency Department. J Emerg Med. 2019; 56 (6): p.633-641. doi: 10.1016/j.jemermed.2019.01.026 . | Open in Read by QxMD
  34. Czuczman AD, Thomas LE, Boulanger AB, et al. Interpreting Red Blood Cells in Lumbar Puncture: Distinguishing True Subarachnoid Hemorrhage From Traumatic Tap. Acad Emerg Med. 2013; 20 (3): p.247-256. doi: 10.1111/acem.12095 . | Open in Read by QxMD
  35. Maher M, Schweizer TA, Macdonald RL. Treatment of Spontaneous Subarachnoid Hemorrhage. Stroke. 2020; 51 (4): p.1326-1332. doi: 10.1161/strokeaha.119.025997 . | Open in Read by QxMD
  36. Kobata H, Sugie A, Yoritsune E, Miyata T, Toho T. Intracranial extravasation of contrast medium during diagnostic CT angiography in the initial evaluation of subarachnoid hemorrhage: report of 16 cases and review of the literature. SpringerPlus. 2013; 2 (1). doi: 10.1186/2193-1801-2-413 . | Open in Read by QxMD
  37. Mitchell P, Wilkinson ID, Hoggard N, et al. Detection of subarachnoid haemorrhage with magnetic resonance imaging. J Neurol Neurosurg Psychiatry. 2001; 70 (2): p.205-11. doi: 10.1136/jnnp.70.2.205 . | Open in Read by QxMD
  38. Cooper SW, Bethea KB, Skrobut TJ, et al. Management of traumatic subarachnoid hemorrhage by the trauma service: is repeat CT scanning and routine neurosurgical consultation necessary?. Trauma Surg Acute Care Open. 2019; 4 (1): p.e000313. doi: 10.1136/tsaco-2019-000313 . | Open in Read by QxMD
  39. Quigley MR, Chew BG, Swartz CE, Wilberger JE. The clinical significance of isolated traumatic subarachnoid hemorrhage. J Trauma Acute Care Surg. 2013; 74 (2): p.581-584. doi: 10.1097/ta.0b013e31827d6088 . | Open in Read by QxMD
  40. Witiw CD, Byrne JP, Nassiri F, Badhiwala JH, Nathens AB, da Costa LB. Isolated Traumatic Subarachnoid Hemorrhage. Crit Care Med. 2018; 46 (3): p.430-436. doi: 10.1097/ccm.0000000000002931 . | Open in Read by QxMD
  41. Phelan HA, Richter AA, Scott WW, et al. Does Isolated Traumatic Subarachnoid Hemorrhage Merit a Lower Intensity Level of Observation Than Other Traumatic Brain Injury?. J Neurotrauma. 2014; 31 (20): p.1733-1736. doi: 10.1089/neu.2014.3377 . | Open in Read by QxMD
  42. Armin SS, Colohan ART, Zhang JH. Traumatic subarachnoid hemorrhage: our current understanding and its evolution over the past half century. Neurol Res. 2006; 28 (4): p.445-452. doi: 10.1179/016164106x115053 . | Open in Read by QxMD
  43. 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): p.134-45. doi: 10.1148/radiol.10092373 . | Open in Read by QxMD
  44. Perry JJ, Alyahya B, Sivilotti MLA, et al. Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort study. BMJ. 2015; 350 (feb18 8): p.h568-h568. doi: 10.1136/bmj.h568 . | Open in Read by QxMD