The brain requires a large supply of blood due to its size and complexity (the brain uses a quarter of all the blood in the human body).
The supply of blood is delivered to the brain by four main blood vessels, which run up the neck and into the brain. These blood vessels divide into smaller and smaller vessels in the same way that a trunk of a tree divides into branches and twigs.
Most aneurysms develop at the points where the blood vessels divide and branch off because these are the sections where the vessel walls are weakest.
Risk factors for a brain aneurysm
In some cases, brain aneurysms are caused by pre-existing (present from birth) weaknesses in the blood vessels.
There are also a number of risk factors that can cause you to develop a brain aneurysm. These are discussed below.
Smoking
Smoking cigarettes is a major risk factor for developing a brain aneurysm. A study published in 2010 found that 8 out of 10 people who were diagnosed with a brain aneurysm were smokers or had smoked in the past.
The risk is particualry high in people with a family history of brain aneurysm (see below).
Exactly why this is the case in unclear. There may be harmful substances in tobacco smoke that could damage the walls of blood vessels.
High blood pressure
High blood pressure can place increased pressure on the walls of the blood vessels inside the brain.
You are more likely to develop high blood pressure if you:
- are overweight
- have a relative with high blood pressure
- are of African or Caribbean descent
- eat a lot of salt
- don't eat many fruit and vegetables
- don't do enough exercise
- drink a lot of coffee (or other caffeine-based drinks)
- drink a lot of alcohol
- are aged over 65
Read more about high blood pressure.
Family history
Family history can be a risk factor. Having a first-degree relative with a history of a brain aneurysm means that you're twice as likely to develop one than someone with no family history of the condition.
However, the increased risk is still small – only around 1 in 50 people with a family history of a ruptured brain aneurysm will go on to have a rupture themselves.
Cocaine
Cocaine abuse is another risk factor for brain aneurysms. Cocaine can inflame the walls of the blood vessels and raise your blood pressure. The combination of these two factors increases your risk of developing a brain aneurysm.
Autosomal dominant polycystic kidney disease
Autosomal dominant polycystic kidney disease (ADPKD) is a genetic condition that causes multiple cysts to develop on the kidneys. Cysts are small sacs that are filled with fluid.
Around 1 in every 1,000 people is born with ADPKD. Of these people, around 1 in 20 will develop an aneurysm in the brain.
Read more about autosomal dominant polycystic kidney disease.
