
Unruptured brain aneurysms: The DATA
Many small aneurysms carry a very low risk of rupture. However when a brain aneurysm ruptures it causes subarachnoid hemorrhage or bleeding on to the surface of the brain. This is often a life threatening or disabling condition. Therefore it is important to know the facts so you can make the best decision for yourself.
The FACTS
1. When an aneurysm ruptures there is a 50% chance that is can cause death or major disability
2. An aneurysm of any size carries some risk of bleeding, even if it is very small.
3. The average size of a ruptured brain aneurysm is 4-5mm.
4. There are many more people with small aneurysms than large ones. This is why the risk of a small aneurysm bursting is low.
5. The psychological impact of living with a brain aneurysm is not well studied but should play a role in your decision to have a brain aneurysm treated.
6. When the risk of repairing or treating a brain aneurysm is lower than the risk of a brain aneurysm bursting in your lifetime you should get your aneurysm fixed.
7. If your brain aneurysm has ruptured it needs to be repaired as soon as possible.
8. It is technically alot easier to repair a brain aneurysm before it has ruptured.
The DATA
ISUIA-2
The major trial published in 2003 that evaluated the risk of an unruptured trial in the USA was called the ISUIA -2 trial. It showed that for many aneurysms <7mm they are safe to watch with routine vascular imaging over time.
However there were some criticisms of the trial in that the research doctors were allowed to recommend treatment for patients with aneurysms they thought were more dangerous even smaller ones. This may have led the study to be biased towards a lower risk of bleeding than what actually is.
Key points:
1. Posterior Circulation aneurysms have a higher risk, including PCOM aneurysms
2. Many anterior circulation aneurysms <7mm are safe to watch if being followed closely with a neurovascular specialist
​

The DATA:
What other factors impact bleed risk?
A better study evaluating an entire population in Finland looked at the rupture risk of every single person who had a brain aneurysm in Finland.
They found that
1. Women had a higher rupture risk than men
2. Smokers had a higher risk of rupture than non-smokers
3. Again aneurysms >7mm had a higher risk of rupture
4. Still a small but real risk of aneurysms <7mm bleeding 0.9%-1.4% per year

A study from Japan showed that in addition to size that specific location also impacts the risk of an aneurysm bleeding and that for aneurysms in the ACOM or PCOM location carry a higher risk of bleeding than aneurysms at other locations in the anterior circulation.

