What is a brain aneurysm?

A brain aneurysm is a bulge in a blood vessel caused by a weakness in a blood vessel wall in the brain combined with the pressure of the circulating blood. The higher the blood pressure, the greater the risk of a weakened vessel bursting

Blood vessels most commonly burst or leak into the subarachnoid space surrounding the brain and spinal cord, causing a brain injury called a subarachnoid haemorrhage

What are the symptoms of a brain aneurysm?

It is rare for an aneurysm to be detected before it starts to leak. The initial symptom is usually a sudden, intense headache that lasts for more than an hour, often at the back of the head. Most people will describe it as the worst headache they have ever experienced.

A correct diagnosis is made easier if the headache is followed by other symptoms, such as

• Vomiting
• A stiff neck
• Collapse
• Loss of consciousness
• Blurred vision
• Inability to bear bright light (photophobia)

However, these symptoms generally occur only with a fairly major leak. A CT scan, and sometimes a lumbar puncture, are usually performed to confirm the diagnosis.

In about 50% of cases, there is a small 'warning' leak before the serious rupture occurs. This results in a very bad headache but very few other symptoms, and it is these cases that are most often missed. It is particularly important that a correct diagnosis is made at this stage because subsequent bleeds are usually more severe and frequently result in death or severe disability

If a brain aneurysm is detected at an early stage, before a major leak occurs, it can often be successfully treated by neurosurgery with the application of clips to the affected vessel.

What are the causes and risks?

Usually, the bleed occurs during physical effort - such as coughing or during physical activities - when the pressure of blood in the brain is temporarily raised, but it can happen at any time

Smokers and people with high blood pressure are most at risk of a subarachnoid haemorrhage. It is most common in older people, but can occur in young people with an inherited aneurysm

How is a brain aneurysm diagnosed?

A brain scan will usually be carried out when a brain aneurysm is suspected. This is usually in the form of either:

• A magnetic resonance imaging (MRI) scan - This provides detailed images of the brain using strong magnetic fields and radio waves
• A computerised tomography (CT) scan - This uses a number of X-rays that are assembled in 3D

A lumbar puncture may also be performed should the CT scan prove negative but a ruptured aneurysm is strongly suggested by the symptoms.