What Is Subarachnoid Haemorrhage?

A subarachnoid haemorrhage (SAH) is a bleed on the surface of the brain. It is a very serious condition and, if left untreated, can lead to permanent brain damage or can be fatal. Subarachnoid haemorrhages can happen at any age, but the average age of onset is in the mid-fifties.1


A subarachnoid haemorrhage (SAH) is bleeding into the subarachnoid space, which is the area between the brain and the membrane that surrounds it. The bleeding can occur either due to head trauma or due to a spontaneous rupture of a blood vessel in the brain. Subarachnoid haemorrhages are slightly more common in individuals assigned female at birth (AFAB) than in people assigned male at birth (AMAB)  and can occur at any age, with the average age of occurrence being between 50 and  60 years old. It is responsible for 5% of all strokes and is estimated to occur in 2 to 20 people per 100,000 per year.2 In around 80% of people, the bleeding arises from the rupture of an intracranial arterial aneurysm.2 One of the key risk factors for this illness is high blood pressure. The incidence has declined over the years, maybe in part due to alterations in lifestyle, such as smoking cessation as well as managing hypertension. 

Subarachnoid haemorrhage is the third most frequent type of stroke.1 Although clinical presentations can differ, the most characteristic symptom is a severe, unexpected headache called a 'thunderclap headache'. However, only 10% of people who go to accident and emergency complaining of a headache have a subarachnoid haemorrhage.4 Other symptoms may include loss of consciousness, neck stiffness, or vision abnormalities. A computed tomography (CT) scan or magnetic resonance imaging (MRI) of the head is usually used to make the diagnosis. SAH caused by blood vessel abnormalities can be diagnosed by cerebral angiography. The condition is best managed by a multidisciplinary team in specialised intensive care centres. 

Causes of subarachnoid haemorrhage

The most common cause of non-traumatic subarachnoid haemorrhage is a rupture of an intracranial aneurysm. An intracranial aneurysm is an abnormal bulge in a blood vessel supplying blood to the brain. According to the NHS, more than 80% of subarachnoid haemorrhages happen due to a ruptured brain aneurysm. Other causes of SAH can include a tangling of blood vessels, called an arteriovenous malformation (AVM) which is the result of incorrect development before birth. Risk factors include spontaneous rupture of blood vessels in the brain, uncontrolled high blood pressure and smoking.5

Signs and symptoms of subarachnoid haemorrhage

There are usually no warning signs, and the presentation can be non-specific,  but the most characteristic symptom is a thunderclap headache. A thunderclap headache is a very severe headache, which begins suddenly and develops within seconds to minutes but is most intense at the beginning.1 It is often described as the worst headache you have ever felt.6

Other signs and symptoms of subarachnoid haemorrhage potentially include:

  • Reduced consciousness or loss of consciousness
  • Neck pain or stiffness 
  • Nausea or vomiting
  • Sensitivity to light (photophobia)
  • Blurred or double vision
  • Seizures
  • Symptoms of stroke, such as slurred speech and weakness on one side of the body

Seizures are more common if bleeding from a ruptured aneurysm is the cause of the SAH. This bleeding may interfere with the brain's regular blood circulation, increasing the risk of a stroke, which happens when a portion of the brain does not get enough oxygen. Brain damage from strokes can be either temporary or permanent.

Management and treatment for subarachnoid haemorrhage

SAH is a neurological medical emergency.3 The first step in managing an SAH is stabilising the patient while monitoring blood pressure and respiratory rate. Once the diagnosis of an SAH is made, patients will most likely be admitted to an intensive care unit. Medication is provided to prevent immediate complications, and it may be necessary to do surgery to correct the cause of bleeding. The basis of medical therapy is intensive blood pressure reduction, which in some patients can improve outcomes by reducing the size of the haemorrhage. Whether there are long-term complications of the condition is determined by the size of the haemorrhage, the amount of swelling in the skull, and how quickly the bleeding is controlled. The treatment strategies include treating blood disorders, preventing hypertension, and, most importantly, treating aneurysms early with coil embolization or clipping to reduce the risk of rebleeding.7

Medical management

Nimodipine – Nimodipine is given to patients with a confirmed subarachnoid haemorrhage. Secondary cerebral ischaemia is one of the most significant consequences of an SAH. This happens when the brain's blood flow is gravely compromised, interfering with its usual circulation and harming the brain. Nimodipine is prescribed to lessen the likelihood of this occurring. Other types of medicine are often also required for symptom control, including:

  • Pain control – pain relief is usually needed to relieve the severe headache. Pain relief options include morphine or co-codamol (a combination of codeine and paracetamol)
  • Antiemetics – to prevent nausea and vomiting, e.g., promethazine 
  • Anticonvulsants – to prevent seizures, e.g., phenytoin2

Surgical management

The method of aneurysm management decided upon, depends on the person's clinical condition, the characteristics of the aneurysm, and the amount and location of the subarachnoid bleed. Possible surgical treatment options include two procedures called endovascular coiling and neurosurgical clipping. NICE Guidelines recommend that, if surgical treatment is planned, it is carried out as early as possible to prevent the risk of rebleeding. The 24-hour window following the onset of symptoms is when rebleeding risk is at its peak.2

Endovascular coiling – a tiny tube known as a catheter is inserted into the body through an artery in the leg. The tube is then directed into the aneurysm through the network of arteries in the body. The aneurysm is then injected with tiny platinum coils that are inserted via the tube. Blood cannot enter the aneurysm once it is clogged with coils. By being cut off from the main artery by this block, the aneurysm is prevented from expanding or rupturing again.

Neurosurgical clipping – a cut is made in the scalp and a craniotomy is performed –a small flap of bone from the skull is removed to give the surgeon access to the brain. A little metal clip is wrapped around the base of the aneurysm to clamp it shut.  The bone flap is then replaced, and the scalp is stitched back together. The clip will permanently seal the aneurysm and stop it from enlarging or rupturing as the blood vessel lining along the clip's placement is caused to mend over time.

Doctors consider the following factors when evaluating the options for surgical management of an aneurysm: 

  • Size and location of the aneurysm
  • The lifetime risk of the aneurysm rupturing
  • The anticipated risks of each treatment option
  •  Patient comorbidities 
  •  Patient preferences

Patients considered unsuitable for surgical management are treated conservatively and followed up accordingly.

Diagnosis of subarachnoid haemorrhage

Neuroimaging plays a crucial part in the diagnosis and follow-up of a patient with suspected subarachnoid haemorrhage.3 Generally, a CT scan is obtained immediately to check for signs of bleeding around the brain. If done within a 6-hour timeframe, a head CT will detect over 99% of cases of SAH. However, as time moves on, MRI is thought to be more sensitive than a head CT.4

A lumbar puncture may be performed after a head CT scan to look for blood in the cerebrospinal fluid. If aneurysms are the underlying cause of spontaneous SAH, they can be diagnosed by angiography

CT scan – the first-line diagnostic test for a suspected subarachnoid haemorrhage is a non-contrast CT head scan. This imaging examination can detect brain haemorrhage. While a CT scan is a highly effective diagnostic tool, it might not be able to detect small amounts of blood. 

MRI – This imaging test can also be used to detect bleeding in the brain. A dye can be injected into a blood vessel to help observe the arteries and veins in greater detail and to highlight blood flow. In the rare instances where the signs of SAH do not appear on a CT scan, this technique may reveal indications of a subarachnoid haemorrhage.

Cerebral angiography – a long, thin tube known as a catheter is inserted into an artery and threaded into your brain blood vessels during cerebral angiography. Through the tube, a dye is then introduced into the arteries in order to make them visible on X-ray imaging. 

Lumbar puncture – the bleeding may not be visible on the initial imaging in some aneurysmal subarachnoid haemorrhages, in which case a doctor may advise performing a lumbar puncture. A needle is introduced into the lower back to remove a small amount of the cerebrospinal fluid, which is the fluid that surrounds the brain and spinal cord. If blood is seen in the fluid, it is a strong indicator of the presence of an SAH. NICE guidelines recommend allowing at least 12 hours after the start of symptoms before doing a lumbar puncture.2


How can I prevent subarachnoid haemorrhage?

The best strategy to avoid a subarachnoid haemorrhage (SAH) is to address the risk factors for a head injury or a brain aneurysm. The most effective steps that can be taken to reduce these risks are:

  • Safety precautions and equipment to prevent head injury, such as helmets
  • Control of high blood pressure through lifestyle changes and medication
  • Stopping smoking 
  • Reducing or stopping the consumption of alcohol
  • Exercising regularly without excessive lifting of weights because heavy exertion or straining can cause an aneurysm to rupture

How common is subarachnoid haemorrhage

According to NICE, subarachnoid haemorrhage is estimated to occur in 2 to 20 people per 100,000 per year. [2] 

Who are at risk of subarachnoid haemorrhages?

The presence of an unruptured aneurysm in the brain or anywhere else in the body, as well as a history of a ruptured aneurysm in the brain, increases the likelihood of developing a SAH. Uncontrolled high blood pressure, smoking, and excessive alcohol consumption are all also considered three of the main risk factors for SAH.    

When should I see a doctor?

A subarachnoid haemorrhage may cause sudden, severe headaches called 'thunder-clap headaches'. As this is a serious and life-threatening event, it requires urgent emergency treatment and urgent hospitalisation. Seek medical care immediately at a hospital accident and emergency department if experiencing signs of a thunderclap headache, especially if accompanied by other symptoms of SAH such as neck pain or stiffness, loss of consciousness, photophobia or vomiting.


A subarachnoid haemorrhage is bleeding into the fluid-filled subarachnoid space around the brain and spinal cord that typically results from head trauma or a blood vessel rupture. The main symptom is a sudden and severe ‘thunderclap’ headache, although it may also cause nausea, vomiting, dizziness, fainting, or seizures. Rapid advancements in endovascular and surgical therapies are expected to result in improved outcomes in patients with SAH. Since a subarachnoid haemorrhage is a very serious condition that can be fatal, it is essential to get the right emergency care as soon as possible. Diagnosis is primarily made with a CT scan of the head. SAH can be treated either medically or surgically, depending on the location and size of the bleed as well as the patient’s condition. Surgical interventions can include either coiling or clipping the blood vessel to stop the bleeding.


  1. Claassen J, Park S. Spontaneous subarachnoid haemorrhage. The Lancet [Internet]. 2022 Sep 10 [cited2023Jun5];400(10355):846–62.Available from: https://www.sciencedirect.com/science/article/pii/S0140673622009382
  2. Overview | Subarachnoid haemorrhage caused by a ruptured aneurysm: diagnosis and management | Guidance | NICE [Internet]. 2022 [cited 2023 Jun 6]. Available from: https://www.nice.org.uk/guidance/ng228
  3. Mazzoleni V, Padovani A, Morotti A. Emergency management of intracerebral hemorrhage. Journal of Critical Care [Internet]. 2023 Apr 1 [cited 2023 Jun 6];74:154232. Available from: https://www.sciencedirect.com/science/article/pii/S0883944122002611
  4. Kairys N, M Das J, Garg M. Acute subarachnoid hemorrhage. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jun 14]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK518975/
  5. Steiner T, Juvela S, Unterberg A, Jung C, Forsting M, Rinkel G. European stroke organization guidelines for the management of intracranial aneurysms and subarachnoid haemorrhage. Cerebrovasc Dis [Internet]. 2013 [cited 2023 Jun 6];35(2):93–112. Available from: https://www.karger.com/Article/FullText/346087
  6. Ziu E, Khan Suheb MZ, Mesfin FB. Subarachnoid hemorrhage. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jun 13]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK441958/
  7. Toth G, Cerejo R. Intracranial aneurysms: Review of current science and management. Vasc Med. 2018 Jun;23(3):276–88. Available from:https://pubmed.ncbi.nlm.nih.gov/29848228/
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Afsheen Hidayat

M.B.B.S, MSc in Clinical Microbiology

Afsheen possesses a strong background in both the medical and scientific disciplines and is a highly educated health researcher. She is a medical expert who is eager to pursue a career in clinical research and medical writing because she believes that it is crucial to improve patient outcomes and provide better medical care. After working as a clinician in Dubai, she came to realise that her goal was to use her extensive research skills to raise the standard of healthcare. She obtained an MSc in Clinical Microbiology from Queen Mary University of London to advance her research career, and she is currently working as a medical writer.

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