A weak, bulging blood vessel in the brain that can leak or rupture, causing a medical emergency.

Overview

• A brain aneurysm — also called a cerebral aneurysm or intracranial aneurysm — is a bulge or ballooning that forms at a weak spot in the wall of a blood vessel in the brain.
• Think of it like a thin balloon forming on a garden hose. The wall at that spot becomes weak and stretches outward over time.
• If a brain aneurysm leaks or bursts, it causes bleeding into and around the brain — a type of stroke called a subarachnoid haemorrhage (SAH). This is a life-threatening emergency.

How common are brain aneurysms?

• Approximately 30,000 Americans suffer a brain aneurysm rupture every year
• Most brain aneurysms never rupture and never cause any symptoms
• Brain aneurysms are more common in women than in men, particularly after menopause

Types of brain aneurysm

• Saccular (berry) aneurysm — the most common type; looks like a round berry hanging on a stem. Forms at branch points of arteries
• Fusiform aneurysm — the artery bulges on all sides, forming a sausage-like widening
• Mycotic aneurysm — caused by an infection that weakens the artery wall

Causes

What causes a brain aneurysm?

Blood flowing through blood vessels puts constant pressure on the vessel walls. Over time, this pressure can cause a weak spot to balloon outward and form an aneurysm.

• Wear and tear on artery walls over a lifetime — most aneurysms develop this way
• High blood pressure (hypertension) — the biggest controllable risk factor; constant high pressure weakens vessel walls
• Cigarette smoking — one of the two most significant risk factors; damages and inflames blood vessel walls
• Inherited weakness in blood vessel walls — some people are born with arterial walls more prone to aneurysm formation
• Severe head trauma or infection — can occasionally trigger aneurysm formation

Who is at higher risk?

• Smokers — smoking significantly increases both the risk of formation and rupture
• People with high blood pressure — especially if uncontrolled
• Women, particularly post-menopausal women
• People with a family history of brain aneurysms — having two or more first-degree relatives with an aneurysm raises risk
• People with certain inherited conditions: polycystic kidney disease, Ehlers-Danlos syndrome, Marfan syndrome, or fibromuscular dysplasia
• Adults aged 40 and over
• People with a previous brain aneurysm — they are at higher risk of developing another

Symptoms

Symptoms of an unruptured aneurysm

Most unruptured aneurysms cause no symptoms at all. They are often discovered by accident during a brain scan done for another reason.

• Occasionally, a large or growing aneurysm may press on nearby brain tissue or nerves, causing:
• Pain above or behind one eye
• A dilated (enlarged) pupil
• Double or blurred vision
• Numbness, weakness, or paralysis on one side of the face
• Headaches in some cases

Warning headache (Sentinel Bleed)

Sometimes, a small leak from the aneurysm — called a sentinel bleed — causes a sudden, unusual headache days or weeks before a major rupture.

• A sudden, severe headache that feels different from any you have had before
• This is an important warning sign — seek medical attention immediately, even if other symptoms are absent

Symptoms of a ruptured aneurysm — EMERGENCY

A ruptured brain aneurysm is a life-threatening emergency. The classic symptom is described as:

• 'The worst headache of my life' — a sudden, extremely severe headache that peaks within seconds
• Stiff neck
• Nausea and vomiting
• Sensitivity to light (photophobia)
• Blurred or double vision
• Drooping eyelid
• Loss of consciousness or sudden confusion
• Seizures

Call emergency services immediately. Every minute matters — prompt treatment dramatically improves survival and outcomes.

Diagnosis

If a brain aneurysm is suspected, whether ruptured or unruptured, urgent imaging is performed.

• CT scan (Computed Tomography) — the first test done in an emergency; quickly detects blood in or around the brain after a rupture
• CT Angiography (CTA) — a specialised CT using contrast dye to visualise the blood vessels and identify the aneurysm's size, shape, and location
• MRI and MR Angiography (MRA) — detailed imaging of the brain and blood vessels; used for unruptured aneurysms and monitoring
• Cerebral Angiogram (Digital Subtraction Angiography / DSA) — the gold-standard test; a catheter is inserted into a blood vessel and dye is injected to give the clearest possible image of the aneurysm. Used when the highest detail is needed to guide treatment
• Lumbar puncture (spinal tap) — if CT is normal but a ruptured aneurysm is still suspected; looks for blood in the cerebrospinal fluid

Treatment

Does every aneurysm need treatment?

Not always. The decision to treat an unruptured aneurysm depends on its size, location, shape, and the patient's age and overall health. Small, stable aneurysms in older patients are often monitored rather than treated immediately.

When a rupture occurs, urgent treatment is always required.

Surgical clipping

• A neurosurgeon opens the skull and places a tiny metal clip at the base (neck) of the aneurysm to cut off its blood supply
• This permanently seals the aneurysm and prevents re-bleeding
• Requires open brain surgery under general anaesthesia

Endovascular coil embolisation (Coiling)

• A minimally invasive procedure — a thin tube (catheter) is passed through a blood vessel in the leg up to the brain
• Tiny platinum coils are placed inside the aneurysm to fill it and block blood flow, causing the aneurysm to clot off and seal
• No need to open the skull — recovery is generally faster than clipping
• Your neurovascular team will advise which procedure is most appropriate based on the aneurysm's characteristics

Watchful waiting (Observation)

• Small, unruptured aneurysms that are at low risk of rupture may be monitored with regular MRI or CT angiography
• Lifestyle measures — controlling blood pressure and stopping smoking — are essential during monitoring

Medicines used after rupture

• Nimodipine (calcium channel blocker) — given routinely after rupture to reduce the risk of vasospasm-related stroke
• Blood pressure medicines — to maintain safe blood pressure and reduce re-bleeding risk
• Pain relief — for severe headache
• Anti-seizure medicines — if seizures occur
• A surgical shunt may be placed to drain cerebrospinal fluid if hydrocephalus develops

Complications

Complications after a ruptured aneurysm

After a rupture, several serious complications can develop — often in the days following the initial bleed:

• Re-bleeding — the greatest risk in the first 24 hours if the aneurysm is not treated urgently
• Vasospasm — blood irritates the arteries causing them to contract and narrow, reducing blood flow to the brain. Occurs in up to 50–90% of cases after rupture and can cause stroke and brain damage. Usually occurs 3–14 days after the bleed
• Hydrocephalus — blood blocks the normal flow of cerebrospinal fluid, causing it to build up and raise pressure in the brain. May require a shunt to drain the fluid
• Hyponatraemia (low blood sodium) — a metabolic complication that can worsen brain swelling
• Seizures — may occur after rupture or as a late complication
• Delayed cerebral ischaemia (DCI) — one of the leading causes of death and disability after rupture; related to but more complex than vasospasm

Prognosis after rupture

The outcome after a ruptured aneurysm varies widely depending on age, general health, and how quickly treatment is received.

• About 25% of individuals do not survive the first 24 hours after rupture
• Another 25% may die from complications within 6 months
• Many survivors experience lasting neurological effects — but with rehabilitation, significant recovery is possible
• Early treatment at a specialist neurovascular centre gives the best chance of a good outcome

Recovery

What to expect after treatment

Recovery after a ruptured aneurysm is a long process and varies greatly between individuals. Recovery from an unruptured aneurysm treated electively is usually faster.

• Physical deficits — weakness, balance problems, or difficulty walking may require physiotherapy
• Cognitive challenges — difficulty with memory, concentration, organisation, and decision-making are common after rupture
• Speech and language difficulties — a speech-language pathologist can help
• Fatigue — one of the most common and persistent complaints after brain aneurysm; the brain uses enormous energy to recover
• Depression and anxiety — very common; influenced by the aneurysm event, physical changes, and life disruption. Seek support early
• Subtle changes — family members may notice personality or behavioural changes before the patient does

Rehabilitation

• Physical, occupational, and speech therapy can aid recovery significantly — even for subtle deficits
• A neuropsychologist can assess and help manage cognitive difficulties
• Rehabilitation may be inpatient at first, then continued on an outpatient basis for months

Lifestyle and long-term care

• Stop smoking — the single most important lifestyle change for anyone with an aneurysm, diagnosed or undiagnosed
• Control blood pressure — take medicines as prescribed, monitor at home, reduce salt and stress
• Avoid stimulants — excessive caffeine, cocaine, and other stimulant substances can suddenly raise blood pressure
• Exercise moderately — avoid extreme exertion or heavy lifting if you have an unruptured aneurysm; discuss safe activity levels with your doctor
• Eat a heart-healthy diet — low in salt and saturated fat, rich in vegetables, whole grains, and lean protein
• Limit alcohol intake
• Attend all scheduled imaging appointments to monitor the aneurysm or check for new ones
• Report any new or unusual headache immediately — especially a sudden severe one
• Family members of patients with brain aneurysms may consider screening — especially those with two or more affected first-degree relatives
• Join a support group — connecting with other survivors can significantly help emotional recovery

When to contact a doctor?

Call emergency services immediately if you experience

• The sudden worst headache of your life, even without other symptoms
• Sudden vision changes, drooping eyelid, or a dilated pupil
• Sudden facial weakness or numbness
• Sudden loss of consciousness or extreme confusion
• Neck stiffness with severe headache
• Seizures

Do not wait to see if it gets better. A ruptured brain aneurysm is always a medical emergency.

See your doctor soon if

• You have a new or unusual headache pattern that is different from your usual headaches
• You have been told you have an unruptured aneurysm and notice any new neurological symptoms
• You have a strong family history of brain aneurysms and have not been screened

Myths & Facts

Frequently Asked Questions