Aneurysm

An aneurysm is a bulge in a blood vessel that is caused by a weakness in the blood vessel wall. As the blood passes through the weakened part of the vessel, the blood pressure causes it to bulge outwards like a balloon.

If the aneurysm grows too big, there is a danger that it will rupture (split) which can cause potentially fatal internal bleeding and organ damage.

Types of aneurysms

An aneurysm can develop anywhere in the body, but the two most common types of aneurysms are:

• an intracranial aneurysm (also known as a cerebral aneurysm) - which is an aneurysm that develops inside the brain, and
• an aortic aneurysm - which is an aneurysm that develops inside the aorta; the aorta is a large blood vessel that runs down the abdomen and transports blood away from the heart.

Ruptured aneurysms

A rupture in an intracranial aneurysm, or an aortic aneurysm, can have a potentially devastating effect on the body.

A ruptured intracranial aneurysm can lead to blood leaking out over the surface of the brain. This is known as a subarachnoid haemorrhage. The blood can cause brain damage and lead to a reduction in blood supply which, in turn, can cause further brain damage. Without emergency treatment, a subarachnoid haemorrhage will usually result in death.

A ruptured aortic aneurysm can cause massive internal bleeding. Without emergency treatment, a ruptured aortic aneurysm will result in death.

The risk of an aneurysm rupturing is small. It is estimated that there is a 0.05% - 0.5% risk that an intracranial aneurysm will rupture in any given year.

There is not enough evidence to estimate a similar risk figure for aortic aneurysms, although known risk factors for rupture include:

• if the aneurysm is larger than 5.5cm (0.8 inches), and/or
• if there is a family history of ruptured aneurysm.

How common are aneurysms?

In England, it is estimated that between 1-6% of the population has an intracranial aneurysm.

Aortic aneurysms usually develop in older people who are 65 years of age or over, and they are thought to be more common in men than women. It is estimated that between 1.3-8.9% of older men, and 1-2.2% of older women have an aortic aneurysm.

As unruptured aneurysms do not usually cause symptoms, it is difficult for researchers to produce a more accurate estimate.

Ruptured aneurysms are a small, but significant, cause of death in the UK. In the UK each year, an estimated 8,000 people die as a result of a ruptured aortic aneurysm, and an estimated 1,400 people die as a result of an intracranial aneurysm.

In many cases, the exact cause of an aneurysm is often unclear, but known risk factors include:

• smoking,
• high blood pressure (hypertension), and
• having a family history of aneurysms.

Preventative treatment and screening

Due to the potentially fatal risks associated with a ruptured aneurysm, preventative treatment is recommended if the risk of a rupture is considered to be above average.

Treatment usually involves clipping the aneurysm closed using a tiny metal clip, plugging the flow of blood with coils of metal wires, or removing a section of the blood vessel and replacing it with a piece of tubing, known as a graft.

In March 2009, the NHS launched a pilot screening service designed to check men who are 65 years of age or over, for aortic aneurysms. It is expected that the service will be introduced across of all of England by 2013. See the ‘diagnosis’ section for more information.

Outlook

In cases of ruptured aneurysms the outlook is poor.

An estimated 65-85% of people with a ruptured aortic aneurysm will die, and about half of all deaths occur before the person is taken to hospital.

An estimated 10% of people with a ruptured intracranial aneurysm will die before reaching hospital and a further 50% of people will die within one month.
Half of all people who survive an intracranial aneurysm will experience brain damage