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Brain Aneurysm

What is a brain aneurysm?

A brain aneurysm, also called a cerebral aneurysm, is a weak spot along a blood vessel in the brain that bulges outward. Often described as balloon-like in appearance, these malformations may burst and bleed into the brain (hemorrhage, or hemorrhagic stroke). This can potentially cause life-threatening complications.

Even if a brain aneurysm does not burst, it can cause other problems by putting pressure on nerves or brain tissue. Most cerebral aneurysms occur along a ring of interconnected arteries at the base of the brain known as the circle of Willis.

brain aneurysm illusrated on the basilar artery
This illustration shows a brain aneurysm on the basilar artery. The aneurysm is the balloon-like structure slightly to the right of center. Aneurysms often occur where a single artery splits in two, as is illustrated here.

Brain Aneurysm Symptoms

Cerebral aneurysms usually do not cause symptoms until they either become very large or burst. Most are found when they rupture and bleed into the space between the skull and the brain. This is a serious condition called subarachnoid hemorrhage, or hemorrhagic stroke.

Symptoms of a brain aneurysm pressing on nearby tissue and nerves may include:

  • Pain above and behind the eye
  • Numbness, weakness, or paralysis on one side of the face
  • Dilated pupils
  • Vision changes

Symptoms of a ruptured aneurysm may include:

  • Sudden, severe headache
  • Double vision
  • Drooping eyelid
  • Nausea
  • Vomiting
  • Stiff neck
  • Sensitivity to light
  • Loss of consciousness, including coma
  • Seizures

Subarachnoid hemorrhage can cause serious complications, including:

  • Hydrocephalus is an abnormal buildup of cerebrospinal fluid in the skull that puts pressure on brain tissue.
  • Vasospasm is a narrowing of blood vessels. It reduces the amount of blood flow to the brain and can cause stroke or tissue damage.

If you are experiencing these symptoms, contact a medical professional.

Brain Aneurysm Treatments

Not all aneurysms rupture. Small lesions may be watched for growth and symptom onset. When deciding whether or not to treat an unruptured brain aneurysm, your doctor will consider many factors. These include the type, size, and location of the aneurysm; your health, age, and medical history; and the risks associated with treatment.

There are three kinds of treatments for brain aneurysms:

  • Aneurysm clipping
  • Occlusion and bypass
  • Endovascular embolization

Aneurysm Clipping

Aneurysm clipping, also called microvascular clipping, is a surgical procedure that involves cutting off blood flow to the brain aneurysm. Your neurosurgeon will open up part of your skull and place a clip on the neck of the aneurysm to halt its blood supply.

This illustration shows a brain aneurysm that has been treated with aneurysm clipping. A small clip or series of clips is placed across the neck of the aneurysm, cutting it off from blood circulation and nearly eliminating the risk that it will bleed.

Bypass and Occlusion

Occlusion is a procedure where your neurosurgeon clamps off the entire artery leading to the brain aneurysm. This surgery is often performed when an aneurysm has damaged an artery. It may be accompanied by a bypass, in which a small blood vessel is surgically grafted to the artery. This reroutes blood flow away from the damaged section of the vessel.

Illustration showing bypass surgery.

Endovascular Embolization

Endovascular embolization is a minimally-invasive treatment where a catheter is inserted into a major artery in the wrist or groin and threaded through the blood vessels to the site of the brain aneurysm. Coils are passed through the catheter and then released into the aneurysm.

The coils then fill the aneurysm, preventing blood from flowing through it and causing it to clot. This decreases the chances of rupture. Alternatively, an aneurysm can be treated by placing a special stent called a flow diverting stent across the base of an aneurysm. This leads to clotting and shrinkage of the aneurysm, eventually blocking it off from the main artery.

brain aneurysm treated with stents and endovascular coils
An aneurysm that has been treated with a combination of endovascular stenting and coiling.

Additional Information

Types of Brain Aneurysms

There are different types of cerebral aneurysms:

  • Saccular is the most common type. It develops along weak spots in the wall of an artery.
  • Dissecting is a type of aneurysm that forms from tears to the innermost layers of a blood vessel. It follows a traumatic injury or plaque formation.
  • Mycotic is a type of brain aneurysm that is caused by a bacterial infection in the wall of an artery.
  • Pseudoaneurysm is the dilatation of an artery that forms when the artery is injured by abrupt, severe trauma.

How common are brain aneurysms?

About five percent of the population has at least one cerebral aneurysm. One-third of those people have more than one. Each year, these lesions rupture in 10 to 20 per 100,000 people.

Who gets brain aneurysms?

Brain aneurysms can occur in anyone at any age, but they are more common in adults than in children and slightly more common in women than in men. They also occur more often in people with certain genetic diseases and blood vessel disorders.

Other causes of aneurysms include:

  • Head trauma
  • Tumors
  • High blood pressure
  • Infection
  • Atherosclerosis and other diseases of the vascular system
  • Cigarette smoking
  • Drug abuse

How are brain aneurysms diagnosed?

Most cerebral aneurysms go unnoticed until they rupture or are found by imaging tests done for other reasons.

The following tests may be used to diagnose an aneurysm:

  • Angiography
  • CT scan
  • MRI scan
  • Lumbar puncture (spinal tap)
ct angiogram showing a basilar bifurcation brain aneurysm
A CT angiogram showing a brain aneurysm at the bifurcation of the basilar artery.
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About five percent of the population has at least one cerebral aneurysm.
Medically Reviewed by Michael T. Lawton, MD and Andrew Ducruet, MD on January 26, 2021