Brain Aneurysm

What a brain aneurysm is

Arteries at the base of the brain form a ring called the circle of Willis. Where arteries branch, the wall is naturally under more stress. Over time, a weak spot can balloon outward. Most brain aneurysms are saccular or "berry" aneurysms: round pouches on a short neck. Less common are fusiform aneurysms, where a section of artery widens all around.

Aneurysms are described by size: small (under 7 mm), large, and giant (over 25 mm). Larger aneurysms, those that are growing, and those in certain locations (such as the back of the circle of Willis) have a higher risk of rupture.

Symptoms

Unruptured aneurysms

Most cause no symptoms and are found by chance on scans done for other reasons. A larger aneurysm can press on nerves or brain tissue, causing:

• Pain above or behind one eye
• A dilated pupil
• Double vision or a drooping eyelid (pressure on the third cranial nerve)
• Numbness or weakness of one side of the face

Warning (sentinel) headaches

Some people have a sudden, unusually severe headache days or weeks before a major rupture, caused by a small leak. It can be mistaken for a migraine. Any sudden severe headache should be assessed.

Ruptured aneurysm

A rupture causes a subarachnoid hemorrhage:

• Sudden severe headache, reaching full intensity within seconds to a minute
• Nausea and vomiting
• Stiff neck
• Sensitivity to light
• Blurred or double vision
• Confusion, drowsiness, seizure
• Loss of consciousness or sudden death

Causes and risk factors

Aneurysms develop from a combination of inherited weakness and damage to the artery wall over time.

• Smoking: the most important modifiable risk factor for both forming and rupturing.
• High blood pressure: see hypertension.
• Female sex: aneurysms are more common in women, especially after 50.
• Family history: two or more first-degree relatives with aneurysms.
• Genetic and connective tissue conditions: polycystic kidney disease, Ehlers-Danlos syndrome (vascular type), Marfan syndrome, and coarctation of the aorta.
• Heavy alcohol use and stimulant drugs such as cocaine and amphetamines, which cause sudden spikes in blood pressure.
• Previous aneurysm.
• Rarely, infections (mycotic aneurysms) and head injury.

Diagnosis

Suspected rupture

• Non-contrast CT scan of the head: detects most bleeds, especially within the first 6 hours.
• Lumbar puncture: if the CT is normal but suspicion remains, a spinal fluid sample can show blood breakdown products.
• CT angiography (CTA): shows the aneurysm's location, size and shape.
• Catheter angiography: the most detailed test, often done before treatment.

Unruptured aneurysms

Usually found on MRI, MR angiography or CT angiography. Specialists assess size, shape, location and growth over time with repeat scans.

Treatment

Ruptured aneurysm

This is a neurosurgical emergency, treated in a specialized center:

• Securing the aneurysm as soon as possible, ideally within 24 hours, to prevent rebleeding: - Endovascular coiling: a catheter is passed from the groin or wrist to the aneurysm, and soft platinum coils are packed inside to seal it. - Surgical clipping: through an opening in the skull, a metal clip is placed across the aneurysm's neck.
• Nimodipine, a medicine that reduces the risk of delayed brain injury from narrowed arteries (vasospasm).
• Intensive care to manage blood pressure, fluid in the brain (hydrocephalus), seizures and other complications.

Unruptured aneurysm

Options are weighed against the aneurysm's rupture risk and the risks of treatment:

• Observation with repeat imaging for small, low-risk aneurysms, plus stopping smoking and controlling blood pressure.
• Endovascular treatment: coiling, flow-diverting stents that redirect blood past the aneurysm, or intrasaccular devices.
• Surgical clipping.

Complications of rupture

• Rebleeding, most likely in the first hours to days
• Vasospasm and delayed cerebral ischemia, usually 3 to 14 days after the bleed
• Hydrocephalus (fluid buildup), sometimes needing a drain or shunt
• Seizures
• Low sodium levels
• Long-term problems with memory, concentration, mood and fatigue

Outlook

Unruptured small aneurysms have a low annual risk of rupture, and many people live normal lives with monitoring. A rupture is serious: a significant proportion of people die, some before reaching the hospital, and many survivors have lasting effects. Fast treatment in a specialist center improves the chance of a good recovery. Rehabilitation helps with physical, cognitive and emotional recovery.

Prevention

• Stop smoking. This is the most important step.
• Control blood pressure.
• Limit alcohol and avoid stimulant drugs.
• Screening with MRA may be offered to people with two or more affected first-degree relatives or with polycystic kidney disease.

Frequently asked questions

What are the warning signs of a brain aneurysm?

Most unruptured aneurysms have no symptoms. Warning signs can include pain behind one eye, a dilated pupil, double vision, a drooping eyelid or a sudden, unusually severe headache from a small leak. A ruptured aneurysm causes a sudden, explosive headache with vomiting and stiff neck and needs emergency care.

What does a ruptured brain aneurysm feel like?

People typically describe a sudden, severe headache, often the worst of their life, that reaches full intensity within seconds to a minute. It may come with nausea, vomiting, a stiff neck, sensitivity to light, confusion, seizure or loss of consciousness. Call 911 or your local emergency number immediately.

What causes brain aneurysms?

Aneurysms form where artery walls are weak, usually at branch points. Smoking, high blood pressure, family history, female sex and conditions such as polycystic kidney disease and some connective tissue disorders increase the risk. Heavy alcohol and stimulant drug use also contribute.

Can you live a normal life with an unruptured brain aneurysm?

Yes, many people do. Most small unruptured aneurysms never rupture. Specialists recommend monitoring with periodic scans, stopping smoking and controlling blood pressure. Treatment may be advised for larger, growing or higher-risk aneurysms.

What is the survival rate of a ruptured brain aneurysm?

A ruptured aneurysm is life-threatening. Roughly half of people die, including some who never reach the hospital, and many survivors have some long-term disability. Rapid treatment in a specialized center improves outcomes, and many people recover well with rehabilitation.