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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Neurology · Aneurysmal Subarachnoid Hemorrhage

Understanding Your Aneurysmal Subarachnoid Hemorrhage (aSAH)

At a Glance

An aneurysmal subarachnoid hemorrhage (aSAH) is a severe medical emergency caused by a ruptured brain aneurysm. Its hallmark symptom is a sudden "thunderclap" headache. Immediate treatment in a specialized neuro-intensive care unit is required to secure the aneurysm and prevent brain damage.

The moments following a diagnosis of aneurysmal subarachnoid hemorrhage (aSAH) can feel chaotic and overwhelming. It is completely normal to feel a sense of sudden panic; this is a serious medical event that happens without warning [1]. Understanding what is happening in the brain can help you and your family navigate the first critical hours and days of care.

What is an aSAH?

A subarachnoid hemorrhage is a type of stroke caused by bleeding into the subarachnoid space—the fluid-filled area that surrounds the brain [2]. In the case of an “acquired aneurysmal” hemorrhage, the cause is a brain aneurysm, which is a weak, bulging spot on the wall of an artery [3].

When the pressure inside that artery becomes too great, the aneurysm can burst, releasing blood directly into the space around the brain [4]. This blood causes immediate irritation to the brain’s protective layers (meninges) and can increase the pressure inside the skull [5].

The “Thunderclap” Warning

Most people who experience an aSAH describe a very specific symptom: the thunderclap headache [5].

  • Sudden Onset: It reaches its maximum intensity almost instantly, often within seconds [5].
  • Extreme Severity: It is frequently described as the “worst headache of my life” [1].
  • Additional Signs: The headache may be accompanied by nausea, vomiting, a stiff neck, or a brief loss of consciousness [5][6].

Why It Is a Medical Emergency

An aSAH is a rare but critical emergency, occurring in approximately 7 to 10 out of every 100,000 people globally each year [7]. Because it involves active bleeding near the brain, it requires immediate, highly specialized medical intervention for several reasons:

  1. Risk of Rebleeding: The most urgent priority is to “secure” the aneurysm (usually through surgery or a procedure called coiling) to prevent it from bleeding again [8].
  2. Hydrocephalus: The blood can block the normal flow of spinal fluid, leading to a dangerous buildup of pressure called hydrocephalus [9].
  3. Delayed Complications: In the days following the initial bleed, the brain’s blood vessels can narrow (vasospasm), which may reduce blood flow and cause a secondary injury known as delayed cerebral ischemia (DCI) [10][11].

The Importance of Specialized Care

Because of these complexities, patients with aSAH are best managed in specialized neuro-intensive care units (NICU) at high-volume hospitals [12][13]. These centers have multidisciplinary teams—including neurosurgeons, neurologists, and specialized nurses—who are experts in monitoring brain pressure and preventing the complications that can arise in the two weeks following the bleed [12][14].

While the situation is serious, medical advancements over the last 30 years have significantly improved the ability to treat aneurysms and manage the recovery process [15]. Standard treatments, such as the medication nimodipine, are used specifically to help protect the brain during this vulnerable window [16][17].

You can read more about what to expect next in The Roadmap to Diagnosis.

Common questions in this guide

What is a thunderclap headache?
A thunderclap headache is an extremely severe headache that reaches its maximum intensity within seconds. It is often described as the 'worst headache of my life' and is the most common warning sign of a ruptured brain aneurysm.
Why is an aneurysmal subarachnoid hemorrhage a medical emergency?
An aSAH involves active bleeding near the brain, which can quickly increase pressure inside the skull and damage brain tissue. It requires immediate treatment to stop the bleeding, prevent the aneurysm from rupturing again, and manage life-threatening complications.
What does it mean to 'secure' a brain aneurysm?
Securing an aneurysm means treating the weakened blood vessel so it cannot bleed again. This is typically done through a surgical procedure to place a metal clip across the base of the aneurysm, or a minimally invasive procedure to fill the aneurysm with tiny coils.
What is delayed cerebral ischemia (DCI)?
Delayed cerebral ischemia is a secondary brain injury that can happen days after the initial bleed. It occurs when blood vessels in the brain narrow (a condition called vasospasm), which reduces blood flow and deprives brain tissue of oxygen.
Why do patients with aSAH need a neuro-intensive care unit (NICU)?
Patients with aSAH are at high risk for severe complications in the two weeks following the bleed. A specialized NICU provides continuous monitoring by experts who can manage brain pressure, administer protective medications like nimodipine, and quickly intervene if the patient's condition changes.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is the current Hunt and Hess grade, and what does that mean for the next few days of care?
  2. 2.Has the aneurysm been definitively 'secured' with coiling or clipping, or is that still to come?
  3. 3.What specific signs of vasospasm or delayed cerebral ischemia (DCI) is the team watching for?
  4. 4.How is the pressure in the brain being monitored, and does the patient need a drain (EVD)?
  5. 5.What is the plan for using nimodipine to help prevent complications?
  6. 6.Is our care being managed in a dedicated neuro-intensive care unit (NICU)?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
  1. 1

    Subarachnoid hemorrhage mimicking myocardial infarction.

    Benninger F, Raphaeli G, Steiner I

    Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia 2015; (22(12)):1981-2.

    PMID: 26183304
  2. 2

    Are We Barking Up the Wrong Vessels? Cerebral Microcirculation After Subarachnoid Hemorrhage.

    Terpolilli NA, Brem C, Bühler D, Plesnila N

    Stroke 2015; (46(10)):3014-9 doi:10.1161/STROKEAHA.115.006353.

    PMID: 26152299
  3. 3

    Analysis of biochemical laboratory values to determine etiology and prognosis in patients with subarachnoid hemorrhage: a clinical study.

    Ogden M, Bakar B, Karagedik MI, et al.

    Neurological research 2019; (41(2)):156-167 doi:10.1080/01616412.2018.1545414.

    PMID: 30417744
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    The role of imaging in the management of non-traumatic subarachnoid hemorrhage: a practical review.

    Khatri GD, Sarikaya B, Cross NM, Medverd JR

    Emergency radiology 2021; (28(4)):797-808 doi:10.1007/s10140-021-01900-x.

    PMID: 33580850
  5. 5

    Toothache as a Warning Sign of Subarachnoid Hemorrhage Postmortem Findings.

    Xingang Q, Wang X, Meichen P, et al.

    The Journal of craniofacial surgery 2019; (30(5)):e418-e420 doi:10.1097/SCS.0000000000005399.

    PMID: 31299799
  6. 6

    [Diagnostic criteria for prolonged and chronic disturbances of consciousness after aneurysmal subarachnoid hemorrhages].

    Sergeenko EV, Belousova OB, Pilipenko YV

    Zhurnal voprosy neirokhirurgii imeni N. N. Burdenko 2024; (88(4)):117-121 doi:10.17116/neiro202488041117.

    PMID: 39169590
  7. 7

    Inflammation and Anti-Inflammatory Targets after Aneurysmal Subarachnoid Hemorrhage.

    Muhammad S, Hänggi D

    International journal of molecular sciences 2021; (22(14)) doi:10.3390/ijms22147355.

    PMID: 34298971
  8. 8

    Perioperative Management of Aneurysmal Subarachnoid Hemorrhage.

    Sharma D

    Anesthesiology 2020; (133(6)):1283-1305 doi:10.1097/ALN.0000000000003558.

    PMID: 32986813
  9. 9

    Monocyte Count on Admission Is Predictive of Shunt-Dependent Hydrocephalus After Aneurysmal Subarachnoid Hemorrhage.

    Cuoco JA, Guilliams EL, Klein BJ, et al.

    Frontiers in surgery 2022; (9()):879050 doi:10.3389/fsurg.2022.879050.

    PMID: 35574528
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    Radiographic Evaluation and Clinical Management of Cerebral Vasospasm.

    Amuluru K, Shah KJ, Payner TD, et al.

    Neuroimaging clinics of North America 2025; (35(3)):383-395 doi:10.1016/j.nic.2025.04.006.

    PMID: 40634006
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    Association of nosocomial infections with delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage.

    Foreman PM, Chua M, Harrigan MR, et al.

    Journal of neurosurgery 2016; (125(6)):1383-1389 doi:10.3171/2015.10.JNS151959.

    PMID: 26871202
  12. 12

    Acute Multidisciplinary Management of Aneurysmal Subarachnoid Hemorrhage (aSAH).

    Ran KR, Wang AC, Nair SK, et al.

    Balkan medical journal 2023; (40(2)):74-81 doi:10.4274/balkanmedj.galenos.2023.2023-1-100.

    PMID: 36883719
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    Subarachnoid Hemorrhage.

    Lawton MT, Vates GE

    The New England journal of medicine 2017; (377(3)):257-266 doi:10.1056/NEJMcp1605827.

    PMID: 28723321
  14. 14

    Construction and verification of risk predicting models to evaluate the possibility of hydrocephalus following aneurysmal subarachnoid hemorrhage.

    Hao G, Shi Z, Huan Y, et al.

    Journal of stroke and cerebrovascular diseases : the official journal of National Stroke Association 2024; (33(2)):107535 doi:10.1016/j.jstrokecerebrovasdis.2023.107535.

    PMID: 38134551
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    Time Trends in Outcomes After Aneurysmal Subarachnoid Hemorrhage Over the Past 30 Years.

    La Pira B, Singh TD, Rabinstein AA, Lanzino G

    Mayo Clinic proceedings 2018; (93(12)):1786-1793 doi:10.1016/j.mayocp.2018.06.027.

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    An overview of pharmacotherapy for cerebral vasospasm and delayed cerebral ischemia after subarachnoid hemorrhage.

    Maruhashi T, Higashi Y

    Expert opinion on pharmacotherapy 2021; (22(12)):1601-1614 doi:10.1080/14656566.2021.1912013.

    PMID: 33823726
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    Pharmacological Prevention of Delayed Cerebral Ischemia in Aneurysmal Subarachnoid Hemorrhage.

    Caylor MM, Macdonald RL

    Neurocritical care 2024; (40(1)):159-169 doi:10.1007/s12028-023-01847-6.

    PMID: 37740138

This page provides an educational overview of aneurysmal subarachnoid hemorrhage (aSAH). It does not replace professional medical advice; always consult your neuro-critical care team for specific diagnostic and treatment decisions.

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