Unruptured brain aneurysm
In the largest international study, aneurysms of less than seven millimetres in the anterior circulation, in people who had never had a haemorrhage, carried a five-year rupture risk of zero per cent. Having an aneurysm is not the same as needing an operation.
Almost everyone who reads this page arrived the same way: an MRI for headaches, for dizziness, for a routine check, and there in the report was the word aneurysm. Between that moment and the appointment with the neurosurgeon come days or weeks, and those are some of the worst days a person can spend.
So let us start with what helps most in getting through them: around three in every hundred adults have a brain aneurysm and do not know it. The overwhelming majority live their whole lives with it and nothing ever happens.
What it actually is
An aneurysm is a bulge in the wall of an artery in the brain, almost always at a branching point, where the blood strikes. It looks like a small pouch forming at a spot where the wall is weaker. Most measure a few millimetres.
It is not a tumour. It does not grow by invading anything. It does not consume the body. And — this matters — an aneurysm that has not ruptured causes no symptoms. If you have headaches and a small aneurysm was found, the likeliest explanation is that the two have nothing to do with each other. It is an incidental finding, and these are becoming more common for the simple reason that more MRI scans are being done.
What is serious is rupture, because it produces a subarachnoid haemorrhage. The entire medical conversation turns on a single question: how likely is this aneurysm, in this person, to rupture, and how does that compare with the risk of treating it.
The numbers worth having
From the landmark international study of unruptured aneurysms, which followed 4,060 patients, these are the cumulative five-year rupture rates in people who had never had a haemorrhage:
| Size | Anterior circulation | Posterior circulation |
|---|---|---|
| less than 7 mm | 0% | 2.5% |
| 7 to 12 mm | 2.6% | 14.5% |
| 13 to 24 mm | 14.5% | 18.4% |
| 25 mm or more | 40% | 50% |
Two readings of that table, both of them important.
The first: size and location change the risk dramatically. A five-millimetre aneurysm in the middle cerebral artery is nothing like a fifteen-millimetre one in the posterior circulation. When somebody gives you a risk figure, ask whether it belongs to your aneurysm or is a general average.
The second, which the authors themselves underline: in many of these cases, the risk of repair equals or exceeds the risk of the natural course. Treatment is not free. Both surgery and the endovascular procedure carry their own rate of complications, and when the annual risk of rupture is very low, intervening can worsen the balance instead of improving it.
A few more numbers, to give a sense of scale:
- Prevalence of aneurysm in the adult population: 3.2 per cent.
- Incidence of subarachnoid haemorrhage worldwide: 7.9 per 100,000 people per year.
- A family history of aneurysm or haemorrhage in a first-degree relative: multiplies the risk by 3.4. Polycystic kidney disease: by 6.9.
Putting those first two figures side by side is the most reassuring exercise there is on this subject: there are a great many aneurysms and very few haemorrhages. The arithmetic itself says that the vast majority never rupture.
When not to wait
These symptoms mean calling the emergency services immediately. They are not something to raise at tomorrow's appointment:
- The worst headache of your life, reaching its peak within seconds. People describe it as a blow, an explosion, something unlike any pain they have had before.
- A sudden headache along with a stiff neck, vomiting, intolerance of light or loss of consciousness.
- Sudden double vision, a drooping eyelid or one pupil larger than the other.
- Weakness, difficulty speaking or confusion coming on abruptly.
That thunderclap headache is how a haemorrhage presents itself, and it is a neurosurgical emergency. If in doubt, go to the emergency department.
What you will hear that is not true
"Every aneurysm has to be operated on." No. Many are monitored. The decision weighs size, location, shape, age, family history, blood pressure, smoking and whether it grew between two scans. A small anterior circulation aneurysm in an older person is often watched, and that is the right course.
"It is a time bomb." This is the most widespread metaphor and the most damaging. A time bomb goes off by definition; an aneurysm, almost always, does not. Three per cent prevalence against eight haemorrhages per hundred thousand people per year does not describe a bomb: it describes something very common that rarely comes to anything.
"An aneurysm is the same as a stroke." No. An unruptured aneurysm is a silent malformation of an artery. A stroke is an event.
"Straining or getting stressed will burst it." This belief does enormous harm: people who stop working, stop training, stop having sex, stop flying. Unless your doctor has told you otherwise for a specific reason, ordinary life can carry on. What does have solid evidence behind it is keeping blood pressure under control and giving up smoking: those are the two modifiable factors that weigh most.
"If my mother had one, I have one." Family history multiplies the risk by 3.4, on a baseline of 3.2 per cent. It raises the probability; it does not turn it into a certainty. In some families, where two or more first-degree relatives are affected, screening the relatives is indeed recommended; it is worth asking about.
What will happen at the appointment
The aneurysm will be measured precisely, and its exact position and shape established. An aneurysm with a daughter sac or an irregular outline is more concerning than a round one of the same size. A CT angiogram or a catheter angiogram may be requested to see it better.
You will be asked about blood pressure, about smoking and about family history. All three change what is recommended.
And out of that comes one of three things: monitoring with a scan in six or twelve months, endovascular treatment, or surgical treatment. The first is very common, and it is not an elegant way of doing nothing: in many cases it is the course with the best balance.
Questions worth writing down before you go
- How big is it exactly, and where is it?
- What is the annual rupture risk of my aneurysm, not the average?
- What is the risk of the treatment you are proposing, at this centre and with this team?
- If we monitor it, how often and with which scan?
- What would change the plan: growth, symptoms, what exactly?
- Do my relatives need to be screened?
- How much of my ordinary life can I carry on with?
The questions people ask most
Can you live with an unruptured brain aneurysm?
Yes, and it is what most people who have one do: around 3 per cent of adults, almost all of them without knowing. Many aneurysms are monitored for years without being treated, and that is an active medical decision, not an omission.
When is a brain aneurysm dangerous?
The risk rises with size, with a posterior circulation location, with an irregular shape, with growth between two scans and with a previous haemorrhage. Aneurysms of less than seven millimetres in the anterior circulation, with no previous haemorrhage, had a five-year rupture risk of 0 per cent in the landmark international study.
Does an unruptured aneurysm cause symptoms?
As a rule, no. That is why they are found by chance. The exception is large aneurysms, which can press on neighbouring structures and cause double vision or a drooping eyelid. If a small one was found while your headaches were being investigated, the headache most likely has another cause.
When does a brain aneurysm need surgery?
When the estimated risk of rupture clearly exceeds the risk of treatment. That depends on the aneurysm, on the person and also on the team who will be treating it. It is a decision made with specific numbers, and you have every right to be told them.
Can I exercise, fly or have sex with a brain aneurysm?
Generally yes. Blanket restriction of activity is not supported by evidence and carries a high cost in quality of life. What is worth doing, with firm evidence behind it, is keeping blood pressure under control and giving up smoking. If your doctor advises a specific restriction, ask what it is based on.
Is a brain aneurysm hereditary?
There is a family component: having a first-degree relative with an aneurysm or with a subarachnoid haemorrhage multiplies the risk by 3.4. Autosomal dominant polycystic kidney disease multiplies it by 6.9. When two or more first-degree relatives are affected, screening the rest of the family is usually recommended.
Which scan detects a brain aneurysm?
MR angiography and CT angiography detect it well and require no catheter. Catheter angiography remains the study with the highest definition and is used when treatment has to be planned or when some doubt remains.
Is an aneurysm the same as a stroke?
No. An aneurysm is a bulge in the wall of an artery; as long as it does not rupture, it does nothing. A stroke is an acute event, from a blockage or from bleeding. A ruptured aneurysm does cause a particular kind of haemorrhagic stroke, subarachnoid haemorrhage, but while it remains intact there is no stroke under way.