Brain aneurysm: What you need to know

Published by Health Professional

on Monday, March 27th 2023

Trending Health Topics

An aneurysm is a bulge in a blood vessel caused by a weakness in the blood vessel wall, usually where it branches.

As blood passes through the weakened blood vessel, the blood pressure causes a small area to bulge outwards like a balloon.

Aneurysms can develop in any blood vessel in the body, but the 2 most common places are:

  • the artery that transports blood away from the heart to the rest of the body (the abdominal aorta)
  • the brain

This topic is about brain aneurysms.

About brain aneurysms

The medical term for an aneurysm that develops inside the brain is an intracranial or cerebral aneurysm.

Most brain aneurysms only cause noticeable symptoms if they burst (rupture).

This leads to an extremely serious condition known as a subarachnoid hemorrhage, where bleeding caused by the ruptured aneurysm can cause extensive brain damage and symptoms.

Symptoms of a burst brain aneurysm include:

  • a sudden agonizing headache – it’s been described as a “thunderclap headache”, similar to a sudden hit on the head, resulting in a blinding pain unlike anything experienced before
  • a stiff neck
  • sickness and vomiting
  • pain on looking at light

A ruptured brain aneurysm is a medical emergency.

If you think someone has had a brain hemorrhage, call 911 immediately and ask for an ambulance.

How brain aneurysms are treated

If a brain aneurysm is detected before it ruptures, treatment may be recommended to prevent it from rupturing in the future.

Most aneurysms do not rupture, so treatment is only carried out if the risk of a rupture is particularly high.

Factors that affect whether treatment is recommended include age, size, and position of the aneurysm, family medical history, and other health conditions.

If treatment is recommended, this usually involves either filling the aneurysm with tiny metal coils (coiling) or an open operation to seal it shut with a tiny metal clip (surgical clipping).

The same techniques used to prevent ruptures are also used to treat brain aneurysms that have already ruptured.

If your risk of a rupture is low, you’ll have regular check-ups to monitor your aneurysm.

You may also be given medicine to reduce your blood pressure and advice about reducing your chances of a rupture, such as stopping smoking if you smoke.

Why brain aneurysms develop

What causes the wall of affected blood vessels to weaken is still unclear, although risk factors have been identified.

These include: 

  • smoking
  • high blood pressure
  • a family history of brain aneurysms

In some cases, an aneurysm may develop because there is a weakness in the walls of the blood vessels at birth.

Who’s affected

It’s difficult to estimate how many people are affected by brain aneurysms because they usually cause no symptoms and pass undetected.

Some experts believe it could be as high as 1 in 20 people, while others think it is much lower at around 1 in 100 people.

The number of aneurysms that actually rupture is much smaller. Only 1 in 15,000 people have a ruptured brain aneurysm yearly.

Brain aneurysms can develop in anyone at any age but are more common in people over the age of 40.

Women tend to be affected more commonly than men.

Preventing brain aneurysms

The best way to prevent getting an aneurysm, or reduce the risk of an aneurysm growing bigger and possibly rupturing, is to avoid activities that could damage your blood vessels.

Things to avoid include:

  • smoking
  • eating a high-fat diet
  • not controlling high blood pressure
  • being overweight or obese

Symptoms of an unruptured brain aneurysm

A brain aneurysm rarely causes any symptoms unless it bursts (ruptures).

Unruptured brain aneurysms occasionally cause symptoms if they’re particularly large or press against tissues or nerves inside the brain.

Symptoms of an unruptured brain aneurysm can include:

  • visual disturbances, such as loss of vision or double vision
  • pain above or around your eye
  • numbness or weakness on 1 side of your face
  • difficulty speaking
  • headaches
  • loss of balance
  • difficulty concentrating or problems with short-term memory

You should see a GP as soon as possible if you experience symptoms of an unruptured brain aneurysm.

Although most aneurysms will not rupture, it’s important to get them checked in case treatment is necessary.

Ruptured brain aneurysm

Symptoms of a ruptured brain aneurysm usually begin with a sudden agonizing headache.

It’s been likened to being hit on the head, resulting in a blinding pain unlike anything experienced before.

Other symptoms of a ruptured brain aneurysm also tend to come on suddenly and may include the following:

  • feeling or being sick
  • a stiff neck or neck pain
  • sensitivity to light
  • blurred or double vision
  • sudden confusion
  • loss of consciousness
  • fits (seizures)
  • weakness on 1 side of the body or in any limbs

Medical emergency

A ruptured brain aneurysm is a medical emergency. Call 999 immediately and ask for an ambulance if someone’s experiencing symptoms of a ruptured brain aneurysm.

Brain aneurysms are caused by a weakness in the walls of blood vessels in the brain. There are several reasons why this may happen, although an exact cause isn’t always clear.

The brain requires a large supply of blood delivered via the main blood vessels that run up the neck and into the brain.

These blood vessels divide into smaller and smaller vessels in the same way the trunk of a tree divides into branches and twigs.

Most aneurysms develop at the points where the blood vessels divide and branch off, as these areas are often weaker.

Increased risk

There are a number of things that can increase your risk of developing a brain aneurysm. These are discussed here.


Smoking tobacco can significantly increase your risk of developing a brain aneurysm.

Studies show the majority of people diagnosed with a brain aneurysm smoke or have done so in the past.

The risk is particularly high in people with a family history of a brain aneurysm.

Exactly why smoking increases the risk of brain aneurysms is unclear. It may be that the harmful substances in tobacco smoke damage the walls of your blood vessels.

High blood pressure

High blood pressure can place increased pressure on the walls of the blood vessels inside the brain, potentially increasing your chances of developing an aneurysm.

You’re more likely to develop high blood pressure if you:

  • are overweight
  • have a relative with high blood pressure
  • are of Black African or African Caribbean descent
  • eat a lot of salt
  • don’t eat enough fruit and vegetables
  • don’t do enough exercise
  • drink a lot of coffee or other caffeine-based drinks
  • drink a lot of alcohol
  • are aged over 65

Family history

Having a first-degree relative, such as a parent, brother, or sister, with a history of a brain aneurysm may make you more likely to develop one than someone with no family history of the condition. But this is very rare.


Your risk of developing a brain aneurysm increases as you get older, with most cases diagnosed in people over the age of 40.

This may be because the walls of the blood vessels are weakened over time by the constant pressure of blood flowing through them.

Your sex

Women are more likely to develop a brain aneurysm than men. This may be because levels of a hormone called estrogen lower significantly after menopause. Oestrogen is thought to help maintain the elasticity of the blood vessels.

Pre-existing weakness in the blood vessels

Weaknesses in the blood vessels present from birth sometimes cause brain aneurysms.

Severe head injury

A brain aneurysm can develop after a severe head injury if the blood vessels in the brain are damaged, although this is very rare.

Cocaine abuse

Cocaine abuse is considered to be another risk factor for brain aneurysms. Cocaine can inflame the walls of the blood vessels and raise your blood pressure. The combination of these factors increases your risk of developing a brain aneurysm.

Autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic condition that causes multiple cysts to develop in the kidneys. Cysts are small sacs filled with fluid.

Brain aneurysms can be more common in people with ADPKD due to high blood pressure affecting the weakened blood vessel walls.

Body tissue disorders

Your risk of developing a brain aneurysm can be higher if you have a condition that affects your body tissues, such as Ehlers-Danlos syndrome or Marfan syndrome.

This is because these conditions can sometimes cause weaknesses in the walls of your blood vessels.

Coarctation of the aorta

People with coarctation of the aorta may also have a small increased risk of developing a brain aneurysm.

Coarctation of the aorta is the term used to describe a narrowing of the main artery in the body (the aorta), which is present from birth (congenital). It is a common type of congenital heart disease.

A brain aneurysm is usually diagnosed using angiography. Angiography is a type of X-ray used to check blood vessels.

This involves inserting a needle, usually in the groin, through which a narrow tube called a catheter can be guided into one of your blood vessels.

Local anesthetic is used where the needle is inserted so you won’t feel any pain.

Using a series of X-rays displayed on a monitor, the catheter is guided into the blood vessels in the neck that supply the brain with blood.

Once in place, a special dye is injected into the brain’s arteries through the catheter.

This dye casts a shadow on an X-ray, so the outline of the blood vessels can be seen, and an aneurysm can be recognized if one is present.

Occasionally, angiography may be done using scans instead of X-rays. These scans are called magnetic resonance angiography or CT angiography.

Magnetic resonance angiography (an MRI scan) is usually used to look for aneurysms in the brain that haven’t ruptured. This type of scan uses strong magnetic fields and radio waves to produce detailed images of your brain.

CT angiography is usually preferred if it’s thought the aneurysm has ruptured and there’s bleeding on the brain (subarachnoid hemorrhage).

This type of scan takes a series of X-rays, which are then assembled by a computer into a detailed 3D image.

Sometimes, a ruptured aneurysm is not picked up by a CT scan. If a CT scan is negative, but your symptoms strongly suggest you have a ruptured aneurysm, a test called a lumbar puncture will usually be carried out.

A lumbar puncture is a procedure where a needle is inserted into the lower part of the spine to remove a sample of the fluid (cerebrospinal fluid) that surrounds and supports the brain and spinal cord. This fluid can be analyzed for signs of bleeding.


There’s no routine screening program for brain aneurysms, and it’s unlikely that one will be introduced in the future.

Screening is only recommended for people with a significant risk of a brain aneurysm that could rupture at some point in the future.

This would usually only apply to you if you had 2 or more first-degree relatives (father, mother, sister, or brother) who experienced a subarachnoid hemorrhage.

If this applies to you, contact your GP. They can refer you to a specialist clinic for further assessment if needed.

Discovering you have an aneurysm unsuitable for surgical treatment can cause worry and distress, even though the risk of it rupturing is small. Some people have reported regret at getting screened.

There are no right or wrong answers, but you must discuss the potential implications of screening with the staff at the clinic.

Screening may also be recommended if you have a condition that increases your chances of developing a brain aneurysm, such as autosomal dominant polycystic kidney disease.

Brain aneurysms can be treated using surgery if they have burst (ruptured) or there’s a risk that they will burst.

Preventative surgery is usually only recommended if there’s a high risk of a rupture.

This is because surgery risks potentially serious complications, such as brain damage or stroke.

Assessing your risk

If you’re diagnosed with an unruptured brain aneurysm, a risk assessment will be conducted to assess whether surgery is necessary.

The assessment process is usually based on the following factors:

  • your age – research has found the risks associated with surgery in older adults often outweigh the potential benefits (extending natural lifespan)
  • the size of the aneurysm – aneurysms larger than 7mm often require surgical treatment
  • the location of the aneurysm – brain aneurysms located on larger blood vessels have a higher risk of rupture
  • other health conditions – you may have an existing health condition that increases the risks of surgery

After these factors have been considered, your surgical team should be able to tell you whether the benefits of surgery outweigh the potential risks in your case.

Active observation

If the risk of rupture is considered low, a policy of active observation is normally recommended.

This means you won’t receive immediate surgery but will be given regular check-ups to monitor your aneurysm carefully.

You may also be given medication to lower your blood pressure.

Your doctor will discuss lifestyle changes that can help lower the risk of a rupture, such as losing weight and eating less saturated fat.

Surgery and procedures

If preventative treatment is recommended, the main techniques used are neurosurgical clipping and endovascular coiling.

Both techniques help prevent ruptures by stopping the blood from flowing into the aneurysm.

Neurosurgical clipping

Neurosurgical clipping is performed under general anesthetic, so you’ll be asleep throughout the operation.

A cut is made in your scalp, or sometimes just above your eyebrow, and a small flap of bone is removed so the surgeon can access your brain.

When the aneurysm is located, the neurosurgeon will seal it shut using a tiny metal clip that stays permanently clamped on the aneurysm. After the bone flap has been replaced, the scalp is stitched together.

Over time, the blood vessel lining will heal along the line where the clip is placed, permanently sealing the aneurysm and preventing it from growing or rupturing.

Clipping the artery that the aneurysm is formed on, as opposed to clipping the aneurysm itself, is rarely necessary. This is usually only carried out if the aneurysm is particularly large or complex.

When this is necessary, it’s often combined with a procedure called a bypass. This is where the blood flow is diverted around the clamped area using a blood vessel removed from another place in the body, usually the leg.

Endovascular coiling

Endovascular coiling is also usually carried out under general anesthetic.

The procedure involves inserting a thin tube called a catheter into an artery in your leg or groin.

The tube is guided through the network of blood vessels, up into your head, and finally into the aneurysm.

Tiny platinum coils are then passed through the tube into the aneurysm.

Once the aneurysm is full of coils, blood cannot enter it. This means the aneurysm is sealed off from the main artery, which prevents it from growing or rupturing.

Coiling versus clipping

Whether clipping or coiling is used often depends on the aneurysm’s size, location, and shape.

Talk to your healthcare team about your treatment options. If it’s possible to have either procedure, discuss the risks and benefits of both procedures.

Coiling has generally been shown to have a lower risk of complications, such as seizures, than clipping in the short term.

The long-term risks of further bleeding are low with both of these techniques.


Emergency treatment

Suppose you require emergency treatment because of a ruptured brain aneurysm. In that case, you’ll initially be given nimodipine medication to reduce the risk of the blood supply to the brain becoming severely disrupted (cerebral ischemia).

Either coiling or clipping can then be used to repair the ruptured brain aneurysm. The technique used will usually be determined by the expertise and experience of the surgeons available.

You can’t always prevent brain aneurysms, but you can lower your risk by not smoking and by reducing high blood pressure.


Stopping smoking can significantly reduce your risk of developing a brain aneurysm.

If you decide to stop smoking, your doctor can refer you to a stop-smoking service, which provides dedicated help and advice about the best ways to quit smoking.

If you’re committed to quitting smoking but don’t want to be referred to a stop-smoking service, your doctor should be able to prescribe medical treatment to help with any withdrawal symptoms you may have after quitting.

High blood pressure

High blood pressure can also significantly increase your chance of developing a brain aneurysm.

You can help reduce high blood pressure by:

  • eating a healthy diet – in particular, cutting down on salt and eating plenty of fruit and vegetables
  • moderating your alcohol intake – men and women are advised not to drink more than 14 units a week regularly
  • maintaining a healthy weight – even losing just a few pounds will make a big difference to your blood pressure and overall health
  • exercising regularly – being active and doing regular exercise lowers blood pressure by keeping your heart and blood vessels in good condition
  • cutting down on caffeine – it’s fine to drink tea, coffee, and other caffeine-rich drinks as part of a balanced diet, but these drinks mustn’t be your only source of fluid

In conclusion

Brain aneurysms are serious medical conditions that can lead to life-threatening complications. It’s important to understand the symptoms, risk factors, and treatment options available to individuals who may be at risk. 

By maintaining a healthy lifestyle, regularly visiting a healthcare provider, and understanding the warning signs of a potential aneurysm, individuals can take steps to minimize their risk and improve their chances of successful treatment in the event of a diagnosis. 

With early detection and prompt medical attention, individuals with brain aneurysms can receive the care they need to lead fulfilling, healthy lives.