Brain aneurysms

What are the symptoms of a brain aneurysm?

Symptoms depend heavily on whether the aneurysm is intact (unruptured) or has burst (ruptured).

Unruptured aneurysm

Most unruptured aneurysms cause no symptoms at all and are found only by chance, during a scan done for an unrelated reason. Occasionally, a large aneurysm presses on nearby nerves or brain tissue, causing:

• a headache, or pain above and behind one eye
• vision changes or double vision
• a drooping eyelid or an enlarged (dilated) pupil
• numbness, tingling or weakness, often on one side of the face.

See a doctor promptly if you notice these symptoms, even without a severe headache.

Ruptured aneurysm: a medical emergency

A ruptured brain aneurysm typically causes a sudden, extremely severe headache, often described as the worst headache of a person's life and unlike any previous headache; this is sometimes called a thunderclap headache. Call 999 immediately for a headache like this, or if you or someone you're with has any of the following:

• nausea or vomiting
• a stiff neck
• sensitivity to light
• blurred or double vision
• a seizure
• confusion or drowsiness
• a drooping eyelid or an enlarged pupil
• weakness or numbness
• loss of consciousness.

Do not have a family member or friend drive you to hospital in a private car; call an ambulance instead. This is a high-stress emergency where paramedics may need to begin lifesaving treatment on the way, and getting specialist care as fast as possible makes a real difference to the outcome.

Sometimes an aneurysm leaks a small amount of blood before a larger rupture, which can cause a milder 'warning' or sentinel headache, days to weeks beforehand. However, only a minority of people who go on to have a major rupture experience this warning sign, so its absence doesn't rule anything out; any sudden headache that's unusually severe or different from your normal pattern is worth urgent attention.

What causes a brain aneurysm and who's at risk?

A brain aneurysm develops when the wall of an artery in the brain becomes thin and weak, usually at a point where the artery branches. Some people are born with this weakness as a result of a defect in the artery wall; in others, it develops later in life.

You may be more likely to develop a brain aneurysm if you:

• are female (aneurysms are more common in women, and the risk may rise further after menopause)
• are aged between 30 and 60, though they can occur at any age
• have a parent, sibling or child with a history of brain aneurysm
• have an inherited condition affecting your connective tissue or blood vessels, such as Ehlers-Danlos syndrome, Marfan syndrome, polycystic kidney disease, or fibromuscular dysplasia
• have high blood pressure, high cholesterol or diabetes
• smoke, drink heavily, or use drugs such as cocaine or amphetamines
• have had a significant head injury, or an infection that has weakened an artery wall (leading to a rarer type called a mycotic aneurysm).

Not all aneurysms rupture, and several factors affect the risk of one doing so: growth over time is the single biggest warning sign, even in a small aneurysm, followed by a larger size, a previous rupture or warning leak, and location, since aneurysms on certain arteries towards the back or front of the brain carry a higher rupture risk than others.

A family history of rupture (rather than simply of aneurysms) also raises personal risk, as does age over 70.

In the moment, a sudden rupture is sometimes linked to a rise in blood pressure, such as from intense emotion or anger, or from straining to lift or push something heavy.

Are there different types of brain aneurysm?

There are 3 main types:

• Saccular (berry) aneurysm: The most common type, a rounded, blood-filled sac that bulges from a branching point or one side of an artery, resembling a berry on a stem – these vary from a few millimetres up to several centimetres across
• Fusiform aneurysm: A bulge affecting the whole width of the artery, rather than just one side
• Mycotic aneurysm: Caused by an infection that weakens the artery wall, more often affecting smaller vessels than those at the base of the skull.

Aneurysms are also sometimes described by size: small (under about 11mm, smaller than a large pea), large (11 to 25mm), or giant (over 25mm).

How is a brain aneurysm diagnosed?

Most unruptured brain aneurysms are found unexpectedly, during a brain scan carried out for an unrelated reason. If a rupture is suspected because of symptoms, doctors will arrange urgent tests, which may include:

• A CT scan: This is usually the first test used to check for bleeding, sometimes combined with an injected contrast dye (CT angiogram) to show the aneurysm's size, shape and location in more detail
• An MRI scan: This can similarly be combined with a dye-free angiogram (MRA) to produce detailed images of the brain's arteries
• Cerebral angiography: This is a more invasive test in which a thin tube (catheter) is passed from an artery in the groin or wrist up to the brain, with a contrast dye injected to show the arteries clearly on X-ray – this gives the most detailed picture of an aneurysm's exact size, shape and location
• Cerebrospinal fluid analysis: This is where a sample of the fluid surrounding the brain and spinal cord is taken via a lower back needle (a lumbar puncture, or spinal tap), to help confirm whether bleeding has occurred – this test cannot detect an aneurysm that hasn't bled.

If you have two or more close relatives (a parent, sibling or child) with a history of brain aneurysm, your doctor may recommend a screening scan, such as an MRA, even without any symptoms.

How is a brain aneurysm treated?

Treatment depends on whether the aneurysm has ruptured, and, for unruptured aneurysms, its size, location, growth and your personal risk factors.

Unruptured aneurysms

A small aneurysm that isn't causing symptoms and has no other concerning features may simply be monitored with regular scans over time, alongside managing risk factors such as blood pressure and smoking.

If the aneurysm is larger, growing, or carries other risk factors, you and your specialist will weigh up the risks and benefits of treating it against the risk of leaving it be. This decision takes into account your age, general health, the aneurysm's size, shape and location, and your family history.

Treatment procedures

• Microvascular clipping: This is open brain surgery in which a neurosurgeon places a tiny metal clip across the base of the aneurysm to stop blood flowing into it – a fully clipped aneurysm usually doesn't return
• Endovascular coiling: This is a less invasive procedure using a catheter threaded from the groin or wrist to the brain, through which soft platinum coils are released into the aneurysm to encourage clotting and seal it off – sometimes a small stent is used alongside the coil, and the procedure occasionally needs repeating in future
• Flow diversion: This involves a mesh stent placed across the affected section of artery, redirecting blood flow away from the aneurysm so that it gradually seals and shrinks – often used for larger or harder-to-treat aneurysms
• Intrasaccular devices (such as the WEB device): A small mesh device is placed inside the aneurysm itself, working in a similar way to coiling
• Bypass surgery: For large or complex aneurysms, a blood vessel taken from elsewhere in the body creates a new route for blood flow around the aneurysm.

Treating a ruptured aneurysm

A ruptured aneurysm needs emergency treatment, usually including admission to an intensive care unit, to repair the aneurysm using one of the procedures above and to manage complications. Additional treatments may include:

• medicines to help prevent seizures
• calcium channel blocker medicines, which can reduce the risk of a stroke caused by the brain's arteries narrowing in the days after a bleed (vasospasm)
• a shunt, which is a tube used to drain a build-up of fluid around the brain (hydrocephalus), if this develops.

Close monitoring continues for around 2 weeks after a rupture, since a complication called delayed cerebral ischaemia, causing further neurological damage, can develop between about 3 and 14 days afterwards. Physical, speech and occupational therapy often follow, to help regain function and adapt to any lasting effects.

When should you see a doctor?

Call 999 immediately for a sudden, extremely severe headache unlike any you've had before, particularly alongside nausea or vomiting, a stiff neck, light sensitivity, vision changes, a seizure, confusion, drowsiness, loss of consciousness, a drooping eyelid, an enlarged pupil, or new weakness or numbness.

Don't drive yourself or be driven to hospital privately – call an ambulance so treatment can start as soon as possible.

See a doctor promptly, even without a severe headache, if you notice a drooping eyelid, an enlarged pupil, double vision, pain above or behind one eye, or new weakness or numbness, since a large unruptured aneurysm pressing on nearby structures can cause these symptoms.

It's also worth mentioning a sudden, significant change in your usual headache pattern to your doctor, even on its own.