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Aneurysms of the cerebral vasculature are relatively common. A recent systematic review collecting data from many countries reported a prevalence of 0.4% and 3.6% in retrospective and prospective autopsy studies, respectively, and 3.7% and 6.0% in retrospective and prospective angiographic studies, respectively (1). The angiographic studies likely overestimate the true prevalence due to a selection bias, whereas the retrospective autopsy studies likely underestimate the true prevalence due to an inability to review the original material. Eighty-five percent of saccular aneurysms of the cerebral vasculature occur in the circle of Willis (2). Multiple aneurysms are seen in 30% of patients. Most are small and asymptomatic, but each year, approximately 30,000 people in the United States suffer a rupture, peaking in the sixth decade (3). When an intracranial aneurysm ruptures, it may bleed into the brain parenchyma resulting in a parenchymal hemorrhage, or more often, it will bleed into the subarachnoid space, resulting in a subarachnoid hemorrhage (SAH). A SAH is a catastrophic event with a mortality rate of 25% to 50%. Permanent disability occurs in nearly 50% of the survivors, thus, only approximately one-third of patients who suffer a SAH have a positive outcome.


You need emergency care if you suddenly get an intensely painful headache, lose consciousness, or have any of these other symptoms of an aneurysm rupture:

Intense headache that comes on suddenly

Loss of consciousness

Nausea and vomiting


Loss of balance in things like walking and normal coordination

Stiff neck

Dilated pupils

Sensitivity to light

Sudden blurred or double vision

Drooping eyelid

Confusion or trouble with mental awareness


Although brain aneurysms usually don’t show symptoms, they can press on the brain and nerves as they get bigger.

Unruptured brain aneurysm symptoms

See a doctor at once if you’re having a new headache or pain above or behind your eye. Call 911.  Other symptoms of an unruptured aneurysm are:

Dilated pupils

Blurred or double vision

Drooping eyelid

A hard time speaking

Weakness and numbness in one side of your face

A sudden and intense headache can also be a sign you have a leaking aneurysm (sentinel bleed). This can be a warning sign you’ll soon have a full rupture.


 aneurysms usually develop as people age, becoming more common after 40. It’s also possible to have a blood vessel defect at birth.

Women tend to have higher rates of aneurysms than men.

Aneurysms tend to form at the fork of blood vessels, places where they branch off, because those sections tend to be weaker. They are most commonly found at the base of the brain.

What Causes Brain Aneurysms to Rupture?

If your brain aneurysm ruptures or leaks and causes a hemorrhagic stroke, you’ll need medical treatment right away. This is rare but can be life-threatening.

Your doctor usually won’t know why your brain aneurysm ruptured. But experts know a few reasons that could heighten your risk of bleeding:

High blood pressure. This is the most common factor that leads to a ruptured brain aneurysm.

Heavy lifting or straining. Your brain aneurysm may rupture because of pressure from lifting or straining.

Strong emotions. If you’re very upset or angry, this can raise your blood pressure and lead to a ruptured aneurysm.

Medications. Blood thinners including warfarin (Coumadin, Jantoven) and other medicines or prescription drugs, such as diet pills like ephedrine and amphetamines, can cause an aneurysm to bleed

Risk factors

There are many risk factors for the development of intracranial aneurysms, both inherited and acquired. Females are more prone to aneurysm rupture, with SAH 1.6 times more common in women. The prevalence of aneurysms is increased in certain genetic diseases; the classic example is autosomal dominant polycystic kidney disease (ADPKD), but other diseases such as Ehlers-Danlos syndrome, neurofibromatosis, and a1-antitrypsin deficiency also demonstrate a link. In ADPKD, 10% to 15% of patients develop intracranial aneurysms. Marfan's Syndrome was once thought to be linked to intracranial aneurysm formation, but recent evidence suggests that this may not be true. Aneurysms also run in families in the absence of an identified genetic disorder, with a prevalence of 7% to 20% in first or second degree relatives of patients who have suffered a SAH . The acquired risk factors are listed.

Acquired risk factors for intracranial aneurysms (4).

Increasing age



Alcohol abuse

Estrogen deficiency


Carotid artery stenosis

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When a brain aneurysm ruptures, the bleeding usually lasts only a few seconds. However, the blood can cause direct damage to surrounding cells, and the bleeding can damage or kill other cells. It also increases pressure inside the skull.

If the pressure becomes too high, it may disrupt the blood and oxygen supply to the brain and loss of consciousness or even death may occur.

Complications that can develop after the rupture of an aneurysm include:

Re-bleeding. An aneurysm that has ruptured or leaked is at risk of bleeding again. Re-bleeding can cause further damage to brain cells.

Narrowed blood vessels in the brain. After a brain aneurysm ruptures, blood vessels in the brain may contract and narrow (vasospasm). This condition can cause an ischemic stroke, in which there's limited blood flow to brain cells, causing additional cell damage and loss.

A buildup of fluid within the brain (hydrocephalus). Most often, a ruptured brain aneurysm occurs in the space between the brain and the thin tissues covering the brain. The blood can block the movement of fluid that surrounds the brain and spinal cord. As a result, an excess of fluid puts pressure on the brain and can damage tissues.

Change in sodium level. Bleeding in the brain can disrupt the balance of sodium in the blood. This may occur from damage to the hypothalamus, an area near the base of the brain. A drop in blood sodium levels can lead to swelling of brain cells and permanent damage.


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


If you smoke, stopping can significantly reduce your risk of developing a brain aneurysm.

If you decide to stop smoking, your GP can refer you to an NHS stop smoking service, which provides dedicated help and advice about the best ways to give up smoking.

You can also call the NHS Smokefree national helpline on 0300 123 1044. The specially trained helpline staff can offer you free expert advice and encouragement.

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

See stop smoking treatments and NHS stop smoking services for more information.

High blood pressure

Having 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 regularly drink more than 14 units a week

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 taking 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 it's important these drinks aren't your only source of fluid


Don't smoke or use tobacco products. Quit smoking or chewing tobacco and avoid secondhand smoke. ...

Eat a healthy diet. Focus on eating a variety of fruits and vegetables, whole grains, poultry, fish, and low-fat dairy products. ...

Keep your blood pressure and cholesterol under control. ...

Get regular exercise.