Cerebral Aneurysm (Brain Aneurysm)

How brain aneurysms form

Arteries at the base of the brain (the circle of Willis) divide into branches. At these forks, blood flow puts stress on the wall. Where the muscle layer is weak, the wall can balloon outward, often forming a small, round "berry" (saccular) aneurysm on a stalk. Less common types are fusiform (a spindle-shaped widening) and mycotic aneurysms, caused by infection.

Most aneurysms develop over a lifetime and are found in adults aged 30 to 60.

Risk factors

• Smoking: the most important modifiable risk factor for both formation and rupture
• High blood pressure
• Family history: two or more first-degree relatives with aneurysms
• Autosomal dominant polycystic kidney disease
• Connective tissue disorders: Ehlers-Danlos syndrome type IV, Marfan syndrome
• Female sex, especially after menopause
• Heavy alcohol use and stimulant drugs (cocaine, amphetamines)
• Coarctation of the aorta, arteriovenous malformations and previous aneurysm

Symptoms

Unruptured aneurysms

Most cause no symptoms. A large aneurysm can press on nerves or brain tissue, causing:

• pain above or behind one eye
• a dilated pupil
• double vision or a drooping eyelid (third nerve palsy)
• numbness or weakness of one side of the face
• vision changes

Ruptured aneurysm

Rupture causes a subarachnoid hemorrhage, bleeding into the space around the brain:

• sudden, extremely severe headache, often described as a thunderclap
• nausea and vomiting
• stiff neck
• sensitivity to light
• blurred or double vision
• seizure
• confusion, drowsiness or loss of consciousness
• sometimes cardiac arrest

About a quarter to a third of people with a ruptured aneurysm do not survive, and many survivors have lasting disabilities. Rapid treatment improves outcomes.

Warning leaks

Some people have a sudden, unusual headache days or weeks before a major rupture, from a small leak. Any thunderclap headache needs immediate assessment, even if it gets better.

Diagnosis

• CT scan of the head: the first test for suspected rupture; most sensitive within 6 hours.
• Lumbar puncture: if the CT is normal but suspicion remains, to look for blood breakdown products in spinal fluid.
• CT angiography (CTA) or MR angiography (MRA): show the aneurysm's size, shape and location.
• Catheter angiography (DSA): the most detailed test, often done when planning treatment.

Treatment

Ruptured aneurysm

Treatment happens in a neurosurgical center:

• securing the aneurysm quickly to prevent rebleeding, which is most likely in the first hours to days
• endovascular coiling: a catheter is threaded from the groin or wrist to the brain, and soft platinum coils fill the aneurysm so it clots off
• surgical clipping: an opening in the skull lets the surgeon place a small metal clip across the aneurysm's neck
• nimodipine tablets to reduce brain injury from vasospasm (narrowing of brain arteries), which peaks 4 to 14 days after the bleed
• treatment of hydrocephalus (fluid build-up), seizures and low sodium
• intensive care monitoring

Unruptured aneurysm

The decision to treat weighs the risk of rupture against the risks of treatment. Factors include:

• size: small aneurysms under about 7 mm have a low annual rupture risk; larger ones higher
• location: posterior circulation and communicating arteries carry higher risk
• shape: irregular shape or a "daughter sac"
• growth on follow-up scans
• age, health, family history and previous bleeding

Options:

• observation with repeat MRA or CTA scans
• lifestyle changes: stop smoking, control blood pressure, limit alcohol, avoid stimulant drugs
• coiling, flow-diverting stents or clipping for higher-risk aneurysms

Screening

Routine screening is not recommended for the general population. It may be offered to people with two or more first-degree relatives with aneurysms, or with polycystic kidney disease and a family history of aneurysm, usually with MRA.

Outlook

Most people with small unruptured aneurysms live normal lives without rupture. After rupture, outcomes depend on the severity of the bleed, age and how quickly treatment starts. Recovery can take months and often involves rehabilitation for memory, mood, fatigue and physical function.

Frequently asked questions

What are the warning signs of a brain aneurysm?

An unruptured aneurysm usually has no symptoms, but large ones can cause pain behind an eye, a drooping eyelid, double vision or a dilated pupil. Rupture causes a sudden, explosive headache, vomiting, stiff neck, light sensitivity, seizures or collapse. Call 911 immediately.

What causes a brain aneurysm?

Aneurysms form where an artery wall is weak, usually at branch points. Smoking and high blood pressure are the biggest risk factors. Family history, polycystic kidney disease, connective tissue disorders, female sex and drug use also raise the risk.

Can you live a normal life with a brain aneurysm?

Yes. Most unruptured aneurysms are small and never rupture. People are usually advised to stop smoking, control blood pressure and have follow-up scans. Higher-risk aneurysms can be treated with coiling or clipping to prevent rupture.

What is the survival rate of a ruptured brain aneurysm?

Roughly a quarter to a third of people die from a ruptured aneurysm, some before reaching hospital, and many survivors have some lasting effects. Fast emergency treatment, securing the aneurysm and specialist intensive care improve the chances of survival and recovery.

Is a brain aneurysm the same as a stroke?

Not exactly. A ruptured brain aneurysm causes a hemorrhagic stroke, specifically a subarachnoid hemorrhage. Most strokes are ischemic, caused by blocked arteries. An unruptured aneurysm is not a stroke.