What Is A Brain Aneurysm? And What Are The Causes, Symptoms, and Treatment?

The brain is a complex vital organ of the central nervous system that requires a constant supply of blood for oxygen. So what happens when parts of the brain are missing and the blood supply is interrupted?

Amazingly, the blood "finds a different route to get around" the brain, explained Emilia Clarke, the Game of Thrones star who has survived two life-threatening brain aneurysms, including a subarachnoid hemorrhage (a stroke caused by bleeding inside the brain).

In an interview with the BBC's Sunday Morning program on July 17, Clarke revealed "quite a bit" of her brain is gone due to the stroke and "basically, as soon as any part of your brain doesn't get blood for a second, it's gone. And so the blood finds a different route to get around, but then whatever bit it's missing is therefore gone.

"The amount of my brain that is no longer usable—it's remarkable that I am able to speak, sometimes articulately, and live my life completely normally with absolutely no repercussions," she added.

About 30,000 people in the U.S. experience a brain aneurysm rupture each year, while approximately 6.5 million (1 in 50 people) in the country have an unruptured brain aneurysm, according to the Brain Aneurysm Foundation.

Anyone at any age, including children, can experience a brain aneurysm. However, they're most prevalent among those aged between 30 and 60 and are more common in women than in men, the NINDS says.

Below we take a closer look at the causes, symptoms and risks of brain aneurysms.

Emilia Clarke at 2020 BAFTA.
Emilia Clarke at the 2020 BAFTA (The British Academy Film Awards) ceremony in London, England in the U.K. Mike Marsland/WireImage via Getty Images

What Is Brain Aneurysm?

A brain aneurysm (also known as a cerebral or intracranial aneurysm) is an abnormal bulge or ballooning in the wall of an artery in the brain.

Most brain aneurysms form in the major arteries along the base of the skull, but they can occur anywhere in the brain, explains the National Institute of Neurological Disorders and Stroke (NINDS).

Some brain aneurysms, especially ones that are small, don't cause any issues. However, some can put pressure on the nerves or brain tissue and can also burst or rupture, leading to a hemorrhage (the spilling of blood into the surrounding tissue), the institute says.

There are several types of brain aneurysms but the most common is berry aneurysm, which can vary in size from a few millimeters to over a centimeter. Giant berry aneurysms, which are bigger than 2.5 centimeters, are more common in adults, according to MedlinePlus, a website of the National Library of Medicine.

What Causes a Brain Aneurysm?

A brain aneurysm is caused by the thinning or weakening of a wall of a brain artery, which causes a portion of the blood vessel to bulge or balloon out.

An aneurysm may be present from birth (congenital) or develop later in life and the risk of an aneurysm rupturing depends on the size, location, and growth of the aneurysm.

Below are some risk factors for the development of brain aneurysms:

  • Polycystic kidney disease (the formation of a cyst in the kidneys)
  • Coarctation of the aorta (a narrowing of the aorta, which carries blood from the heart to blood vessels for the rest of the body)
  • Endocarditis (an inflammation of the inside lining of the heart chambers and heart valves)
  • Drug use, especially cocaine or amphetamines, raise blood pressure to dangerous levels, warns the NINDS.
  • A family history of brain aneurysms (also a risk factor for an aneurysm rupture)
  • High blood pressure (also a risk factor for an aneurysm rupture)
  • Smoking (also a risk factor for an aneurysm rupture)

Can Brain Aneurysms Be Fatal?

A ruptured aneurysm can be fatal or lead to serious health conditions, including hemorrhagic stroke, brain damage or a coma.

According to the Brain Aneurysm Foundation, around 50 percent of ruptured brain aneurysms cases are fatal, while around 66 percent of those who survive suffer "some permanent neurological deficit."

The foundation says about 15 percent of patients with a ruptured aneurysm die before arrival at the hospital and most deaths are due to "rapid and massive brain injury from the initial bleeding."

About 25 percent of those who have a ruptured aneurysm don't survive the first 24 hours, while another 25 percent die from complications within six months, says the NINDS.

Brain Aneurysm Symptoms

Most brain aneurysms do not present symptoms until they become very large or rupture, while small, unchanging aneurysms will typically not show any symptoms.

Below are some symptoms of aneurysms, as outlined by the NINDS.

Unruptured aneurysm

A large aneurysm that's growing may put pressure on the tissues and nerves and produce the following symptoms:

  • Pain above and behind the eye
  • Numbness
  • Weakness
  • Paralysis on one side of the face
  • A dilated pupil in the eye
  • Changes to vision or have double vision

Ruptured aneurysm

When an aneurysm bursts, the patient will always have a sudden, extremely severe headache (one that feels "the worst headache of one's life") and may also have the following symptoms:

  • Double vision
  • Nausea
  • Vomiting
  • A stiff neck
  • Sensitivity to light
  • Seizures
  • A loss of consciousness (brief or prolonged)
  • Cardiac arrest

Leaking aneurysm

Sometimes an aneurysm can cause a small amount of blood to leak into the brain (known as a sentinel bleed). Sentinel headaches may result from a small leak that occurs days or weeks before a significant aneurysm rupture. Only a minority of people have a sentinel headache before a rupture.

Those who feel a sudden, severe headache, especially combined with any other symptoms, should seek immediate medical attention, advises the NINDS.

How Are Brain Aneurysms Treated?

Treatments for brain aneurysms vary depending on the size, location and shape of the aneurysm and whether it is infected or has burst.

The patient's age, medical condition, family history of aneurysms and subarachnoid hemorrhage also play a role in the treatment they receive.

Below are some treatment options for brain aneurysms, as outlined by the Brain Aneurysm Foundation:

  • Clipping: a surgery that places a metal clip across the base of the aneurysm to prevent blood from entering it.
  • Endovascular therapy: The placing of coils, stents or a flow diversion device within the blood vessel)
  • No treatment: Observing the aneurysm, with control of risk factors and possible repeat imaging.

For more information, see the websites of the National Institute of Neurological Disorders and Stroke and the Brain Aneurysm Foundation.

An MRI/MRA brain scan image.
An MRI (magnetic resonance imaging)/MRA (magnetic resonance angiography) scan of a brain artery. iStock/Getty Images Plus