A brain abscess is a pus-filled swelling in the brain. It usually occurs when bacteria or fungi enter the brain tissue after an infection or severe head injury.

Although the risk of developing a brain abscess is extremely low in England, it is a life-threatening condition and should be diagnosed and treated as soon as possible.

The symptoms of a brain abscess may develop quickly or slowly but can include:

• headache – which is often severe, located in a single section of the head and cannot be relieved with painkillers
• changes in mental state – such as confusion or irritability
• problems with nerve function – such as muscle weakness, slurred speech or paralysis on one side of the body
• a high temperature
• seizures (fits)
• feeling sick
• being sick
• stiff neck
• changes in vision – such as blurring, greying of vision or double vision (due to the abscess putting pressure on the optic nerve)

Any symptoms that suggest a problem with the brain and nervous system should be treated as a medical emergency. These include:

• slurred speech
• muscle weakness or paralysis
• seizures occurring in a person with no previous history of seizures

If you or someone you know experiences any of these symptoms, phone 999 immediately and ask for an ambulance.

Any symptoms that suggest a worsening infection, such as a high temperature or being sick, should be reported to your GP immediately.

If your GP is not available, contact your local out-of-hours service or call NHS 111.

There are 3 main ways a brain abscess can develop. These are:

• an infection in another part of the skull – such as an ear infection, sinusitis or dental abscess, which can spread directly into the brain
• an infection in another part of the body – for example, the infection that causes pneumonia spreading into the brain via the blood
• trauma, such as a head injury – that cracks open the skull, allowing bacteria or fungi to enter the brain

However, in some cases, the source of the infection remains unknown.

Read more about the causes of a brain abscess.

If a brain abscess is suspected, an initial assessment will be made based on your symptoms, medical history and whether you've had a recent infection or a weakened immune system.

Blood tests can also be carried out to check for an infection.

If you're referred to hospital for further tests, you may have either:

• a CT scan – a series of X-rays are used to produce a detailed image of the inside of your body
• an MRI scan – which uses strong magnetic fields and radio waves to produce a detailed image of the inside of your body.

If an abscess is found, a procedure known as CT-guided aspiration may be used to remove a sample of pus for testing. This involves using a CT scan to guide a needle to the site of the abscess.

A brain abscess is regarded as a medical emergency. Swelling caused by the abscess can disrupt the blood and oxygen supply to the brain. There's also a risk of the abscess bursting (rupturing).

If left untreated, a brain abscess can cause permanent brain damage and could be fatal.

A brain abscess is usually treated using a combination of:

• medicines – either antibiotics or antifungals
• surgery – either draining the pus through a hole in the skull (simple aspiration) or opening the skull and removing the abscess entirely (craniotomy)

Treatment with antibiotics often begins before a diagnosis is confirmed, to reduce the risk of complications.

Read more about treating a brain abscess.

Complications of a brain abscess can include:

• a reoccurring abscess – seek immediate medical advice if you think there's even a small chance your abscess has reoccurred; this is more common in people with a weakened immune system or cyanotic heart disease
• brain damage – mild to moderate brain damage often improves with time but severe brain damage is likely to be permanent; brain damage is more of a risk if diagnosis and treatment are delayed
• epilepsy – where a person has repeated seizures (fits)
• meningitis – a life-threatening infection of the protective membranes around the brain, which requires urgent treatment; this is more common in children