Written by Ada’s Medical Knowledge Team
What is a subarachnoid hemorrhage?
Subarachnoid hemorrhage (SAH) is a type of stroke, or more specifically brain hemorrhage, in which there is bleeding on the surface of the brain. The bleeding occurs in a space between the layers of tissues that cover the brain, in an area called the subarachnoid space. SAH is a medical emergency and is life-threatening. People who survive an SAH may be left with disability.
An SAH occurs when a blood vessel bursts between the layers of tissues that surround the brain. This is normally due to a weakness of the vessel walls, which results in a balloon-like swelling known as an aneurysm. A hemorrhage occurs when the aneurysm ruptures, due to the pressure of blood as it is pumped through the brain.
The most common symptom is a sudden, very severe headache, often with nausea and vomiting and sometimes loss of consciousness. 1
The diagnosis is confirmed either by doing a CT scan or a lumbar puncture, which involves taking a sample of the fluid from around the spinal cord and testing it for the presence of blood.
Treatment depends upon the severity and may include emergency life-saving measures, surgical repair of the hemorrhaging area and medications to reduce the risk of complications.
The prognosis after a subarachnoid hemorrhage depends on the size and severity of the bleed.
Signs and symptoms
The most common symptom is a sudden, explosive headache called a thunderclap headache, which is often described as the worst headache ever or as if there had been a blow to the head. It may last only a few seconds or even a fraction of a second. 2
There is often a phase of intense headache for days or weeks before the bleed, which may often go unnoticed by doctors as an early warning sign of subarachnoid hemorrhage. If you or someone you know is experiencing a headache, try the Ada app for a free symptom assessment. While most people with sudden, severe headaches do not have subarachnoid hemorrhage, a sudden, severe headache should not be taken lightly and warrants medical attention immediately or as soon as possible.
Good to know: If a person experiences a sudden, severe headache, medical attention should be sought immediately, and the person affected should be transported to a hospital in the quickest possible way, e.g. in an ambulance. Subarachnoid hemorrhage is a life-threatening emergency.
Other symptoms may include: 3 4
- Nausea and vomiting
- A stiff neck
- Blurred or double vision
- Eyes which are sensitive to light
- Slurred speech
- Weakness on one side of the body
- Convulsions, i.e. uncontrollable shaking
- Loss of consciousness
What causes subarachnoid hemorrhage?
Subarachnoid bleeding is bleeding in the head that occurs in the subarachnoid space, the space between the layers of tissue that cover the brain. This can cause pressure on the brain and problems supplying the brain with blood.
It is commonly due to the rupture of a saccular aneurysm, also known as a berry aneurysm: a small, berry-like swelling that forms within the head due to a weak spot in an artery wall. Occasionally, there may be another cause for subarachnoid bleeding, such as in traumatic subarachnoid hemorrhage, when trauma to the head or neck, such as might be sustained in a car accident or a fall, may cause blood to leak into the subarachnoid space from nearby structures of the head. 2
Subarachnoid hemorrhage is not common. It tends to be more common in middle-aged adults, although it can affect people of any age.
Risk factors which most commonly contribute or lead to SAH include: 2 5
- High blood pressure
- High or excessive consumption of alcohol
- Cocaine use
Risk factors that lead to SAH less commonly, include: 2 6
- Head and neck trauma, when bleeding from injury to the brain or other nearby structures leaks into the subarachnoid space, which is known as traumatic subarachnoid hemorrhage
- Certain inherited conditions that weaken the blood vessels, such as autosomal dominant polycystic kidney disease (ADPKD), Marfan-Syndrome and Ehlers-Danlos syndrome.
- Vasculitis, when blood vessels inside the body, and therefore possibly also inside the brain become swollen and inflamed due to infection or to conditions affecting the immune system.
- Brain infection such as encephalitis or meningitis
Anyone displaying any signs of stroke should immediately be taken to a hospital emergency room for diagnosis, preferably by ambulance. Once there, a doctor will typically perform a physical examination and, if necessary, medical stabilization of the person. They will also obtain the person’s medical history, before a number of other tests and scans are done: 4 7 8
Brain scans are very often used to help confirm a diagnosis. A scan can also help to show the severity and location of the bleed and help detect additional problems it may be causing.
Brain scans should be carried out as quickly as possible after the person reaches the hospital, allowing for prompt and appropriate treatment to be received.
A CT scan of the head is, in general, the best method to detect bleeding. Additionally, it is quicker and more widely available than an MRI scan.
A magnetic resonance imaging (MRI) scan uses radio waves and a strong magnetic field to build a detailed image of the interior of the body.
A magnetic resonance angiogram (MRA) scan may be included with an MRI scan. This is a procedure that shows the blood vessels of the brain so doctors can identify the location of the bleeding, often without the need for injecting a contrast agent. If a contrast agent is used, it will involve an injection of dye into a vein using a peripheral intravenous line, usually placed in the veins of the arms or hands.
Digital subtraction angiography
Digital subtraction angiography (DSA) involves inserting a small, thin tube into a blood vessel in the leg and passing it up to the blood vessels in the brain. A contrast dye is injected through the catheter, and X-ray images are taken of the blood vessels. DSA has been considered the most accurate scan to visualize aneurysms, but also has its own limitations, so that many factors will influence whether this procedure is used by doctors in a given case.
The DSA procedure is normally carried out after a diagnosis of subarachnoid bleeding is made based on the CT scan and/or lumbar puncture results. It may also be performed if the CT and/or lumbar puncture tests are inconclusive. It may be repeated within 15 days after a subarachnoid hemorrhage, if an aneurysm is still suspected. 9
If the diagnosis is still uncertain after doing a CT scan, often a sample of fluid from an area below the spinal cord will be taken and investigated for blood. This procedure is known as a lumbar puncture or, colloquially, a spinal tap. 9
The brain and the spinal cord are surrounded by a clear liquid called cerebrospinal fluid (CSF). The cerebrospinal fluid will contain signs of blood if there has been an SAH.
A lumbar puncture involves taking a sample of the CSF by inserting a needle between two vertebrae – bones of the spine – at the lower end of the spine known as the lumbar region. A small amount of this fluid is drawn into a syringe and examined in a laboratory, where the presence of blood may be confirmed.
Good to know: A lumbar puncture is performed at a level of the lower back that contains a bunch of nerve fibers known as the cauda equina, which run below the spinal cord, so as to make sure there should not be a risk of accidental injury to the spinal cord.
A subarachnoid hemorrhage is a medical emergency and requires urgent medical attention and treatment.
The aim of treatment for subarachnoid hemorrhage is to stabilize the affected person, prevent further bleeding or rebleeding from the aneurysm, which may be at risk of rupturing once again, and prevent further brain injury. 2
Life-saving or supporting measures, such as help with breathing and blood pressure control, may be needed in the time directly following an SAH, especially if the bleed is big enough to cause a significant increase in the pressure inside the head.
Some medications are given to treat subarachnoid hemorrhage and its effects in the short-term. These may include: 1 10 11
- Nimodipine which can help prevent vasospasm, a possible complication of SAH (see vasospasm and improve blood supply to the brain, which can help improve the neurological outcome after an SAH from an aneurysm 12)
- Blood pressure medication to reduce the chances of rebleeding
- Pain relief, commonly opioids and acetaminophen, which not only reduce pain but also in turn reduce the chance of rebleeding, as pain leads to higher blood pressure, which can contribute to a higher chance of rebleeding
- Anticonvulsants to prevent seizures
- Antiemetics to stop the affected person feeling sick and vomiting
- Stool softeners, such as docusate and senna help to prevent rebleeding from increased blood pressure due to straining to pass a bowel movement
- If the person suffers from coughing, antitussives, such as codeine, may be given to suppress coughs, which can help prevent rebleeding.
Good to know: opioid antitussives, such as codeine or hydrocodone, are avoided in children aged 18 or under. This is because the risks, such as difficulty breathing and addiction, outweigh the benefits when used for cough with these people.
Surgery might be needed to treat SAH. Surgery aims to treat the aneurysm that was responsible for the SAH, as well as any other aneurysms that may be present. The risk of rebleeding is high initially after an SAH, so these procedures are done as soon as possible, usually within 72 hours.
There are two main surgeries that may be given to treat a berry aneurysm and prevent it from bleeding again: coiling and clipping: 7 13 14
Some complications may require different surgical approaches earlier or later on, such as to lower the pressure inside the skull or to remove clotted blood.
Coiling – endovascular treatment
Coiling is usually done under general anesthesia, meaning the person treated is fully asleep, relaxed and doesn’t feel any pain. A flexible tube, known as a catheter, is inserted into an artery in the leg or groin and passed along the blood vessels in the body until it reaches the aneurysm in the brain.
The aneurysm is blocked from the inside by inserting small platinum coils into the aneurysm, once the catheter has reached its location . This prevents further bleeding by causing blood to clot around the coils, sealing off the weakened area.
Another surgical procedure known as clipping may instead be used to stop or prevent an aneurysm from bleeding or rebleeding. A clipping procedure is done under general anesthesia, too. It involves opening the skull in a procedure known as a craniotomy.
During clipping, a neurosurgeon places a tiny clip across the neck of the aneurysm to block the blood flow from entering the aneurysm.
Coiling versus clipping
The procedure chosen is often dependent on factors such as the location, size and shape of the aneurysm.
Coiling is often preferred because it aims to be minimally invasive, as it does not involve opening the skull and has a lower risk of short-term complications, such as seizures, than clipping. Coiling also tends to lead to a shorter hospital stay and a shorter recovery time, though these factors are generally more dependent on the rupture’s severity than the type of surgery used.
However, since coiling is a relatively new procedure, the long-term benefits over clipping are not entirely certain yet and are partially still being evaluated.
Depending on the affected person’s health status and medications, as well as the size and location of the aneurysm, among other factors, a doctor will recommend a treatment that best suits the individual’s situation and needs.
Triple H therapy
Triple H therapy, is sometimes used to prevent and treat vasospasm, a possible complication of SAH in which a blood vessel goes into spasm, causing the vessel to narrow and the blood supply to the area of the brain supplied by this vessel to become dangerously low (see vasospasm). Triple H therapy aims to improve blood flow and oxygen delivery in the brain. It does this by a combination of induced: 11]
- Hypertension, meaning high blood pressure
- Hypervolemia, meaning high fluid volume in the blood
- Hemodilution, meaning decreased concentration of solid particles in the blood resulting from a gain of fluid
In vasospasm, the diameter of cerebral vessels is reduced, increasing the resistance to blood flow. Increased arterial pressure is required to overcome this resistance. 15
Triple H therapy is only sometimes used, because its efficacy remains uncertain, and it may carry significant risks. 16
The time it takes to recover from a subarachnoid hemorrhage depends on its severity and if complications, such as re-bleeding, occur. Recovery commonly takes a minimum of three weeks. For many, it may be several months, and some symptoms may be permanent, despite intense rehabilitation efforts. Most people will need at least three months till they feel able to return to previous activity levels, such as hobbies and work, but this time frame may in many cases be substantially longer. Some affected people may not be able to return to their previous occupation. 17
Associated problems, such as loss of feelings in the limbs or problems understanding speech, are determined by the location of the hemorrhage. Such problems can ideally be successfully treated and may get better over time (see difficulties), but may also be permanent in some cases.
A number of complications can arise in the days and weeks after a person has experienced an SAH, either while they are still in hospital or once they are at home or in a rehabilitation facility. These complications are important to recognize and treat in a timely manner, as they can, in some cases, lead to serious health problems and may be life-threatening.
Some of the most common complications include: 1 17
Particularly in the few days after the SAH, the aneurysm is at risk of bleeding again. This is known as rebleeding.
Repair of the aneurysm should be done as soon as possible, generally within 72 hours, to avoid rebleeding, as it can lead to permanent disability or may be life threatening.
Vasospasm is a common complication of an SAH. If it occurs, it is usually between the fourth and fourteenth day after the initial SAH.
Vasospasm is when a blood vessel goes into spasm, causing the vessel to narrow, and the blood supply to certain brain areas become dangerously low. The brain relies on a constant supply of blood to provide it with oxygen and nutrients. When the supply of blood becomes blocked, brain cells can quickly begin to stop working. If the blockage lasts for more than a couple of minutes, these cells can start disintegrating, leading to serious damage to the brain. Depending on the location and supply area of the affected vessel, the damage can range from mildly debilitating to severe or life-threatening.
Common symptoms of vasospasm include:
- Stroke-like symptoms, such as weakness down one side of the body or speech problems
Treatments are available to prevent and treat vasospasm, such as nimodipine and triple H therapy. Read more about the treatment of subarachnoid hemorrhage »
Subarachnoid hemorrhage can lead to a buildup of fluid inside the skull, as it commonly disrupts the production and drainage of cerebrospinal fluid (CSF). A buildup of fluid inside the skull, known as hydrocephalus, increases pressure on the brain tissue, which can lead to brain damage if not treated quickly enough.
Hydrocephalus may be treated with an external ventricular drain, which allows the temporary drainage of cerebrospinal fluid (CSF) from the ventricles of the brain, relieving raised intracranial pressure.
Seizures may develop after an SAH, usually starting within the first year after the hemorrhage. Symptoms of seizures usually last up to a few minutes per bout.
Common symptoms of seizures include: 18
- Loss of consciousness
- Muscle twitching and jerking
- Becoming stiff
Medications are available to treat and prevent seizures as much as possible, and some doctors may prescribe or recommend anti-seizure medication, even if a seizure is yet to occur.
Read more about Generalized Seizure ».
Difficulties after subarachnoid hemorrhage
A person’s physical abilities can often be restricted immediately after a subarachnoid hemorrhage. The extent to which the person is affected varies, including such problems as recurrent headaches and prolonged feelings of drowsiness and fatigue. 19 Some people experience a feeling of numbness or weakness in parts of their body and, rarely, even a complete loss of power. Other reported difficulties include difficulty swallowing and a loss of balance. This can sometimes lead to additional problems, including: 4 8
- Deep vein thrombosis, dangerous blood clots which are more likely to form if the person is not moving around for long periods
- Unhealthy nutrition, because of difficulty swallowing or chewing
- Aspiration pneumonia, a type of pneumonia caused by food or drinks being accidentally inhaled into the lungs
- Falls and other accidents related to a sudden loss of balance and/or physical weakness
Physical rehabilitation will usually begin in the hospital to improve muscular function and is often continued in an inpatient or outpatient rehabilitation center after hospital discharge .
Cognitive dysfunction is when a person experiences problems with one or more brain functions, especially those related to their thinking abilities. It affects at least half of the people who have experienced an SAH, to some degree. 20
Some common thinking problems include: 21
Memory problems, such as problems remembering names or faces, or making and keeping new memories.
Difficulty concentrating for longer periods of time, often on previously straightforward tasks, such as making a cup of tea, and being easily distracted.
Difficulty solving more complex tasks. This is due to increased tiredness, difficulty concentrating and other complex effects of the bleeding. Some examples include:
- Tasks at work that require more thinking than routine behaviour
- Repairing broken objects in a logical order
- Solving crossword puzzles
Cognitive difficulties can improve with time and treatment. An occupational therapist may be able to help overcome difficulties by setting therapeutic activities to practise, helping to find new ways of doing things or suggesting equipment that could help. 22
Some people may find that their speech becomes slurred or slowed, or that they have difficulty finding the right words to express themselves. This usually improves gradually. A language therapist may be able to advise on management of speech difficulties.
After SAH, many people experience emotional problems, feel fearful of living with future complications or illness recurrence and may feel a loss of confidence in everyday tasks or social activities.
These problems may include: 17 23
- Low, depressed mood and mood swings
- Clinical depression
- Crying or laughing easily, sometimes with no apparent reason or in socially inappropriate situations
- The feeling that the person’s personality has changed
- Developing generalized anxiety disorder
- Developing post traumatic stress disorder
- Denial about the consequences of the SAH
Emotional difficulties generally improve with time and treatment, and there are various treatments available to help, including:
- Talking therapies, such as psychotherapy
- Medications, such as antidepressants
- Support groups to speak to others who have had similar experiences
Q: Subarachnoid hemorrhage vs subdural hematoma – what is the difference?
A: A subdural hematoma is another condition where blood collects on the surface of the brain in a layer of tissue between the arachnoid space and the dura, a tough layer covering the inside of the skull. The two conditions have similar symptoms and may both cause brain damage. It is usually caused by a head injury, whereas a subarachnoid hemorrhage is usually caused by a weakness in the blood vessel walls.
Both a subarachnoid hemorrhage and a subdural hematoma very often cause a headache as their primary symptom. The subdural hematoma headache is a headache that often comes on more slowly and may be severe from the beginning or increase in severity over time, whereas the subarachnoid hemorrhage headache is known as a thunderclap headache, very sudden in onset and severe from the beginning. 24 There may also be a phase of intense headache for days or weeks before a subarachnoid hemorrhage as an early warning sign of subarachnoid hemorrhage, which may often go unnoticed .
Q: What is a hemorrhage?
A: Hemorrhage is another word for bleeding, the loss of blood from a ruptured blood vessel. It can happen inside the body or on the outside of the body. A person may bleed when they get a cut or other wound. They may also bleed due to an injury to internal organs. Sometimes, bleeding can be a sign of an underlying condition. In other cases, bleeding can cause further complications, for instance if too much blood is lost, or if the hemorrhaging occurs in parts of the body where it will cause a problem, e.g. due to bleeding into a small, closed space like the skull, such as in the case of subarachnoid hemorrhage.
Q: Subarachnoid hemorrhage vs intracerebral hemorrhage – what is the difference?
A: Both intracerebral hemorrhage, sometimes also referred to as a cerebral hemorrhage, and subarachnoid hemorrhage are types of hemorrhagic stroke, where a blood vessel ruptures or bursts in or around the brain. An intracerebral hemorrhage is when a blood vessel within the brain tissue or the brain ventricles ruptures, whereas a subarachnoid hemorrhage is bleeding between the layers of tissue that surround the brain. Intracerebral hemorrhages are about twice as common as subarachnoid hemorrhages.
Read more about Hemorrhagic Stroke »
Q: Aneurysm vs stroke – what is the difference?
A: An aneurysm is a bulge in a blood vessel wall that is caused by a weak spot. It has the potential to rupture. Such a rupture in a vessel running on the surface of the brain can cause a subarachnoid hemorrhage, which is a type of stroke. Not all aneurysms cause stroke, and not all strokes are caused by an aneurysm.
Q: I am experiencing the worst headache of my life. Am I having a stroke?
A: While most people with sudden, severe headaches do not have subarachnoid hemorrhage, a sudden, severe headache should not be taken lightly and warrants medical attention immediately or as soon as possible. The most common symptom of a type of stroke known as a subarachnoid hemorrhage is a sudden, explosive headache called a thunderclap headache, which is often described as the worst headache ever or as if there had been a blow to the head. It may last only a few seconds or even a fraction of a second.
Good to know: SAH is a life-threatening emergency. If suspected, medical attention should be sought immediately, and the person affected should be transported to a hospital in the quickest possible way, e.g. in an ambulance.
Other names sometimes used for subarachnoid hemorrhage
- Bleeding on the brain
- Subarachnoid haemorrhage (British English)
- Aneurysmal subarachnoid hemorrhage
- Rupture of an intracranial aneurysm
- Ruptured cerebral aneurysm
- Ruptured intracranial aneurysm
- Brain bleed
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