Unruptured aneurysms affect about 3.2% of people worldwide. Ruptured aneurysms are less common, occurring in approximately 10 per 100,000 cases.

The above statistics come from the National Library of Medicine

The average age at which they happen is 50 years. While the female-to-male ratio at this age is 1:1, after age 50, the ratio approaches 2:1.

A brain aneurysm, or a cerebral aneurysm, is a thin place in an artery in the brain that bulges outward. It may burst or rupture, which spills blood into the surrounding tissues. When this happens, it can cause a stroke, brain injury, and death.

This article explains more about whether brain aneurysms are common, alongside detailing the causes, symptoms, diagnosis, treatment, outlook, and prevention.

Are brain aneurysms common?

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Unruptured aneurysms are more common than ruptured aneurysms. In the United States, about 6.7 million individuals have the unruptured type, and rupture happens in an estimated 30,000 annually. Hispanic and African American people have twice the risk.

Worldwide, the condition causes 500,000 deaths annually — half of which are people younger than 50 years.

Learn more about brain aneurysms.

Causes

A cause of brain aneurysms is constant pressure from blood flow. Brain aneurysms usually occur at the point where arteries branch, which are the weakest spots. Both inherited and noninherited risk factors may play a role.

Inherited risk factors

These include:

• arteriovenous malformations, which are tangles of veins and arteries in the brain that hinder blood flow
• genetic connective tissue disorders that weaken the walls of arteries
• history of an aneurysm in a closely related family member
• polycystic kidney disease, a condition where many cysts develop in the kidneys

Noninherited risk factors

Noninherited risk factors that increase over time include:

• cigarette smoking
• being over 40 years
• untreated high blood pressure
• drug misuse, particularly involving amphetamines or cocaine, which can raise blood pressure to very high levels

Less common risk factors include:

• brain tumor
• head trauma
• arterial wall infection

Additionally, certain factors can raise the risk of atherosclerosis — a condition where fatty deposits build up in the arteries. These include factors such as smoking and high cholesterol.

Symptoms

Most brain aneurysms do not cause symptoms until they become very large or rupture.

Symptoms from a large aneurysm

A large growing aneurysm may produce symptoms that stem from pressure on nearby nerves and tissues, such as:

• weakness
• pain behind and above the eye
• a dilated pupil
• numbness
• paralysis on one side of the face
• double vision or other vision changes

Symptoms from a ruptured aneurysm

If an aneurysm ruptures, a person can experience a sudden, severe headache. Other symptoms may include:

• stiff neck
• double vision
• nausea or vomiting
• sensitivity to light
• loss of consciousness
• seizures
• cardiac arrest, meaning the heart stops beating

Sometimes instead of rupturing, an aneurysm may leak a small quantity of blood. When this happens, it may cause a warning headache, which signals that a rupture may occur in the coming days or weeks.

Diagnosis

Most unruptured brain aneurysms escape notice until they rupture or medical imaging for another condition reveals them. If a person experiences a severe headache or other symptoms of a ruptured aneurysm, the following tests may help diagnose the condition:

• CT scan: Frequently the first test a doctor orders, this imaging uses X-rays to produce two-dimensional pictures of the brain and skull. In addition to a CT scan, a doctor may use CT angiography (CTA), which involves injecting a dye before the scan. A CTA can show an aneurysm’s shape, location, and size.
• MRI: An MRI uses a magnetic field and computer-generated radio waves to produce two or three-dimensional pictures of the brain. A form of this imaging called magnetic resonance angiography can also reveal an aneurysm’s shape, location, and size.
• Cerebral angiography: This finds blockages in an artery in the neck or brain and identifies weak spots in an artery. It can pinpoint the cause of bleeding in the brain and provide a detailed picture of an aneurysm.
• Cerebrospinal fluid analysis: This involves withdrawing a small amount of fluid, usually from the spine in the lower back region. It measures chemicals in the fluid surrounding the brain and spinal cord, which can help detect bleeding in the brain.

Treatment

The treatment depends on various factors, such as the size of the aneurysm.

Treatment of small aneurysms

Some very small brain aneurysms that do not link to rupture risk factors may not require treatment. Instead, doctors may monitor them with imaging.

Treatment for unruptured brain aneurysms may cause serious complications that a doctor weighs against the potential risk of rupture. However, co-occurring conditions that are risk factors necessitate aggressive treatment.

Treatment of problematic aneurysms

When an aneurysm is large or ruptures, treatment options may include the following:

• Surgery: Several surgeries can treat the condition but involve risks, such as damage to other blood vessels and stroke. One option is microvascular clipping, an open brain surgery that cuts off blood supply to the aneurysm. Depending on the characteristics of the aneurysm, this can be highly effective.
• Platinum coil embolization: This is less invasive than microvascular clipping surgery. It entails inserting a hollow plastic tube in an artery and threading it to the aneurysm, where coils of platinum wire release and reduce the blood flow.
• Flow diversion devices: This is a treatment option for large or complex aneurysms. The procedure involves the placement of small flexible mesh tubes called stents in an artery, which decreases blood flow to the aneurysm.

Other treatments

Treatment options for ruptured aneurysms include:

• a shunt to divert cerebrospinal fluid from the brain to elsewhere in the body
• calcium channel blockers, such as nimodipine (Nymalize), to lower the risk of stroke
• antiseizure drugs, such as phenytoin (Dilantin), to prevent seizures from a rupture
• rehabilitation therapy, which consists of physical, occupational, and speech therapy to regain lost function

Outlook

After a rupture of a cerebral aneurysm, the illness and death rate is very high. Evidence indicates that within the first 24 hours, nearly 25% of people die, and 50% die within 3 months. Factors that can influence outlook include:

• age
• presence of high blood pressure and other co-occurring conditions
• the extent of the bleeding from the rupture
• degree of vasospasms, which are contractions of arteries in the brain that limit blood flow
• neurological status

Prevention

According to a 2019 review, several factors may increase the risk of the formation and rupture of brain aneurysms. Therefore, addressing the factors can serve as preventive measures.

Following a diet rich in antioxidants may decrease the risk of a brain aneurysm. Antioxidant vitamins include:

• vitamin E
• vitamin C
• B vitamins
• carotenoids
• flavonoids
• omega-3 fatty acids

This means that the below foods and beverages should be key components of the diet:

• vegetables
• fruits
• whole grains
• nuts
• beans
• fish
• tea

The Dietary Approaches to Stop Hypertension (DASH) and the Mediterranean diet contain these dietary components.

Other means of prevention include:

• limiting caffeine consumption
• limiting alcohol consumption
• managing high blood pressure

Additionally, measures that can help prevent a rupture include quitting smoking and avoiding using cocaine and other stimulant drugs, if applicable.

Summary

In the U.S., about 6.7 million people have an unruptured brain aneurysm, and about 30,000 per year have the ruptured type.

Various factors such as genetics, smoking, and untreated high blood pressure can increase a person’s risk of the condition.

A very severe headache is a sign of a ruptured aneurysm. As this condition has a high death rate, someone experiencing such a headache should go to an emergency room immediately. Further symptoms of a large aneurysm may include numbness or paralysis on one side of the face.

A healthy, balanced diet rich in antioxidants, such as the Mediterranean diet, may help prevent the condition.