A brain aneurysm, sometimes called a cerebral aneurysm, is a weak spot in a brain artery. The weak spot creates a balloon that fills with blood.

The walls of the artery are weaker near an aneurysm, which means that the aneurysm can break open, or rupture. A ruptured aneurysm is a life threatening condition that can cause serious brain injuries or stroke. However, not all aneurysms rupture.

People with an aneurysm may need ongoing monitoring to ensure that it is not growing. A doctor may need to remove a larger aneurysm.

In this article, we provide an overview of brain aneurysms, including the types, symptoms, causes, complications, and treatments.

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Around 3–5% of people in the United States experience a brain aneurysm during their lifetime.

According to the National Institute of Neurological Disorders and Stroke, brain aneurysms affect an estimated 3–5% of people in the United States during their lifetime. They are more common in females than in males and tend to affect adults between the ages of 30 and 60 years.

The Brain Aneurysm Foundation state that ruptured brain aneurysms account for just 3–5% of all new stroke cases. If an aneurysm does rupture, it is fatal in about 40% of cases, with 15% of people dying before they reach the hospital.

Doctors classify aneurysms according to the shape of the weak spot in the artery.

There are three main types of aneurysm:

  • Saccular aneurysms form a pocket on the outside of an artery. They are the most common type of cerebral aneurysm. Some people refer to them as berry aneurysms due to their appearance.
  • Fusiform aneurysms occur when the blood vessel expands on all sides. This type of aneurysm is more common after an injury to a blood vessel.
  • Mycotic aneurysms are those that form a sac around an artery. They happen when an infection from another area of the body gets into the bloodstream and spreads to the brain. Myocarditis, a type of heart infection, is a common culprit, but mycotic aneurysms are very rare.

The size of an aneurysm is a significant predictor of whether or not it will rupture:

  • Small aneurysms are less than 11 millimeters (mm) across — about the size of a large pencil eraser.
  • Large aneurysms are 11–25 mm in diameter — roughly the size of a dime.
  • Giant aneurysms are 25 mm or larger — more than the diameter of a quarter.

Some aneurysms grow over time, and a small number grow rapidly. Growth, especially rapid growth, increases the risk that the aneurysm will rupture.

Larger aneurysms are more likely than smaller ones to cause symptoms before they rupture, but most aneurysms do not cause any symptoms during this stage.

When people with an unruptured aneurysm do experience symptoms, they may include:

  • pain above or behind the eye that gets worse or does not go away with time
  • numbness
  • weakness
  • paralysis or twitching on one side of the face
  • vision changes, such as blurred or double vision
  • a dilated pupil in only one eye

Sometimes an aneurysm leaks before it ruptures. Doctors call this a sentinel rupture or sentinel bleed.

Sentinel ruptures sometimes cause sentinel headaches. A sudden, severe headache — especially one that does not fit a person’s usual headache pattern or that is worse than any other headache they have ever had — could be a sentinel headache.

Other symptoms of a sentinel rupture include:

  • nausea or vomiting
  • vision changes
  • confusion or changes in consciousness
  • a stiff neck
  • light sensitivity
  • fainting or seizures
  • cardiac arrest

Anyone who has symptoms of an aneurysm should seek immediate medical care. If a person has previously received a diagnosis of an unruptured aneurysm, it is essential that they make the emergency care team aware of this.

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A person may be at risk of a brain aneurysm if they have a family member who has experienced one.

Brain aneurysms are more common in females than in males and more likely to affect adults between 30 and 60 years old. In addition, genetic and lifestyle factors that weaken the walls of blood vessels greatly increase the risk of aneurysm.

Risk factors for brain aneurysms include:

  • genetic conditions that weaken blood vessels, including polycystic kidney disease, some connective tissue disorders, and arteriovenous malformations (AVM)
  • a close family member, such as a parent, child, or sibling, having an aneurysm
  • uncontrolled high blood pressure
  • drug use disorder, particularly that involving drugs that raise blood pressure, such as amphetamines and cocaine
  • using illicit drugs intravenously
  • smoking
  • a brain tumor
  • head injuries
  • infections in the arteries

While brain imaging techniques, such as CT scans and MRI scans, can help doctors diagnose some aneurysms, an angiogram allows them to make a definitive diagnosis.

To perform a cerebral angiogram, a doctor will insert a small, thin tube called a catheter into a blood vessel in the groin and direct it into the blood vessels of the brain under X-ray guidance. There, they will inject a dye that makes it easier to see the blood vessels and any unusual structures.

An angiogram can help the doctor assess the size and severity of the aneurysm, as well as its type. This information helps them make appropriate treatment recommendations.

Not all brain aneurysms require immediate treatment. If the aneurysm is small, a doctor may recommend monitoring it over time.

The best treatment option will depend on the following factors:

  • the person’s age
  • any neurological or medical conditions
  • whether the aneurysm has ruptured
  • the risk of the aneurysm rupturing
  • any family history of subarachnoid hemorrhage

A person with a family or personal history of aneurysm rupture may need treatment even if the aneurysm is small.

A doctor may recommend an endovascular procedure or surgery to treat the aneurysm.

Endovascular procedure

During an endovascular procedure, a surgeon inserts a catheter through the groin, then navigates to the aneurysm. Next, they pack the aneurysm with metal coils or a stent to redirect the blood flow. Doing this stops blood from flowing into the aneurysm, which prevents rupture.


Surgery for an aneurysm requires an operation on the brain, which will take place under general anesthesia. This procedure usually requires a person to spend several days in the hospital, and it may be necessary to shave the person’s head. During the operation, a surgeon clips the aneurysm to prevent blood from flowing into it.

Following this treatment, most aneurysms do not reoccur.

Risks of treatment

Both endovascular treatment and brain surgery come with risks, including:

  • heart or lung damage
  • stroke
  • surgical complications, such as infection
  • death
  • surgery failure that makes further treatment necessary

An unruptured aneurysm typically does not cause any complications. However, a ruptured aneurysm can cause serious, lasting health conditions, and it can be fatal.

Possible complications of a ruptured brain aneurysm include:

  • hemorrhagic stroke, a type of stroke that occurs as a result of bleeding in the brain
  • rebleeding, which happens when an aneurysm ruptures again
  • changes in the sodium level in the brain, which may cause permanent brain damage
  • vasospasm, a spasm that causes arteries to narrow, limiting blood flow to the brain and potentially causing serious brain damage or a stroke
  • seizures
  • hydrocephalus, which happens when cerebrospinal fluid accumulates in the brain, causing dangerous pressure that may damage this organ
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A healthful lifestyle may help reduce the risk of a brain aneurysm.

Some aneurysms are not preventable. However, a healthful lifestyle can support blood vessel health and reduce the risk of an aneurysm.

People can reduce their risk using the following strategies:

  • quitting smoking, if applicable
  • abstaining from using drugs that elevate blood pressure
  • avoiding or limiting medications that increase blood pressure, under the guidance of a doctor
  • adopting a healthful lifestyle that includes a balanced diet and regular exercise
  • talking to a healthcare professional about strategies to control blood pressure
  • seeking advice on further strategies to reduce aneurysm risk if a first degree relative (a parent, child, or sibling) has had an aneurysm

People who have unruptured aneurysms should talk to a doctor about how to minimize the risk of rupture. Ongoing monitoring can reduce this risk and guide a doctor’s treatment decisions.

An aneurysm is not a stroke, but it can cause one. When an aneurysm bursts, this deprives the brain of blood, potentially leading to a stroke.

The symptoms of a ruptured aneurysm and stroke are similar but not identical. While both cause neurological symptoms, such as dizziness or blurred vision, aneurysms also typically cause headaches.

Both conditions are serious medical emergencies that demand immediate treatment. Therefore, a person should see a doctor whether they have symptoms of an aneurysm, stroke, or both.

Learn more about the differences between aneurysms and stroke here.

Among people who survive an aneurysm rupture, about 25% die from complications within 6 months, and 66% have lasting neurological damage.

For this reason, it is important to identify and treat aneurysms as early as possible. Prompt medical care increases a person’s chances of survival.