Brain abscess

Page last reviewed: 13/07/2011

A brain abscess is a pus-filled swelling in the brain caused by an infection. It is rare and life threatening.

It happens when bacteria or fungi enter the brain tissue, usually after they have infected another part of the body.

Symptoms of a brain abscess vary depending on the part of the brain affected. Commonly reported symptoms include:

  • headache
  • fever
  • confusion
  • weakness or paralysis on one side of the body

A brain abscess can be extremely serious because the swelling can put pressure on delicate brain tissue and disrupt the blood and oxygen supply to the brain. There is also a risk that the abscess may burst (rupture). If left untreated, a brain abscess can cause permanent brain damage and can be fatal.

A brain abscess is a medical emergency and requires prompt treatment with antibiotics and surgery. The surgeon will usually open the skull and drain the pus from the abscess or remove the abscess entirely.

How common are brain abscesses?

Brain abscesses are extremely rare. It is estimated that only two to three people in every million will develop a brain abscess in any given year.

Brain abscesses can occur at any age, but most cases are reported in people aged 40 or younger. They are more common in men than women.


Because of advances in diagnostic and surgical techniques, the outlook for people with brain abscesses has improved dramatically.

Nowadays, deaths only occur in an estimated 10% of cases, and most people make a full recovery. However, without treatment, a brain abscess is nearly always fatal.

Page last reviewed: 13/07/2011

The symptoms of a brain abscess can develop quickly or slowly.

In around two-thirds of people, symptoms are present for two weeks or less before they worsen to such an extent that the person needs to be admitted to hospital.

Common symptoms include:

  • headache
  • 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
  • fever
  • seizures (fits)
  • nausea and vomiting
  • stiff neck
  • changes in vision, such as blurring, greying of vision or double vision (because of the abscess putting pressure on the optic nerve)

When to seek medical advice

Any symptoms that suggest a problem with the brain and nervous system, such as slurred speech, muscle weakness or paralysis, or seizures occurring in a person who had no previous history of seizures should be treated as a medical emergency. Phone 112 or 999 and ask for an ambulance.

Any symptoms that suggest a worsening infection, such as fever and vomiting, should be reported to your GP immediately. If your GP is not available, contact your local out-of-hours service .

Page last reviewed: 13/07/2011

An abscess is a pus-filled swelling caused by infection with either bacteria or fungi.

The abscess is created by your immune system as a defence mechanism. If the immune system realises that it is unable to defeat an infection, it will try to limit its spread. Your immune system will use healthy tissue to form a wall around the source of infection to stop the pus infecting other tissue.

The routes for brain infection

Infections of the brain are very rare because the body has a number of defences to protect this vital organ. One of these is the blood-brain barrier, which is a thick membrane that filters out impurities from blood before allowing it into your brain.

However, in some people, for reasons that are not always entirely clear, germs can get through these defences and infect the brain.

The three most common routes for germs to enter the brain are as follows:

  • Germs have already infected another part of the body, get into the bloodstream, bypass the blood-brain barrier and then infect the brain.
  • Germs have already infected one of the nearby cavities in the skull (such as the ears or nose) and go on to infect the brain.
  • Germs pass through the skull and enter the brain after the skull is damaged, for example after being hit by a blunt object or after a gunshot wound.

These are explained in more detail below.

In as many as one-third of cases, there is no apparent cause.

Germs invading the brain through the bloodstream

Infections that are spread through the blood are thought to be a major cause of brain abscesses.

People with a weakened immune system (who are immunocompromised) have a higher risk of developing a brain abscess from a blood-borne infection. This is because their immune system may not be capable of fighting off the initial infection.

Known risk factors include:

  • having a medical condition that weakens your immune system, such as HIV or AIDS
  • receiving medical treatment that is known to weaken the immune system, such as chemotherapy
  • having an organ transplant and taking immunosuppressants to prevent your body rejecting the new organ

The most commonly reported infections and health conditions that may cause a brain abscess are:

  • cyanotic heart disease, a congenital form of heart disease where the heart is unable to carry enough oxygen around the body (this lack of a regular oxygen supply makes the body more vulnerable to infection)
  • lung infections, such as pneumonia or bronchiectasis
  • skin infections
  • infections of the abdomen (tummy), such as peritonitis (an infection of the lining of the bowel)
  • pelvic infections such as infection of the lining of the bladder (cystitis)

Germs from another infection in the skull

In up to a quarter of cases, the brain abscess occurs as a complication of a nearby infection in the skull, such as:

  • a persistent middle ear infection (otitis media)
  • sinusitis (an infection of the sinuses, which are the air-filled cavities inside the cheekbones and forehead)
  • mastoiditis (an infection of the bone behind the eye)

This used to be a major cause of brain abscesses, but because of improved treatments for infections, a brain abscess is now a rare complication of these kinds of infection.

Germs invading the brain after a head injury

Direct trauma to the skull can also lead to a brain abscess.

The most commonly reported causes include:

  • skull fracture caused by penetrating injury
  • gunshot or shrapnel wound

In very rare cases, a brain abscess can develop as a complication of surgery.

Page last reviewed: 13/07/2011

An initial assessment will be made based on your physical symptoms and recent medical history, such as whether you have had a recent infection or have a weakened immune system.

Blood tests 

Blood tests will be carried out to check for the presence of infection. A high level of white blood cells in your blood indicates the presence of a serious infection.


If a brain abscess is suspected, the diagnosis can be confirmed using a CT (computerised tomography) scan or MRI (magnetic resonance imaging) scan. The high-definition images produced by these scans are able to detect the presence of an abscess.

For more information, see the Health A-Z topics on CT scans and MRI scans.

CT-guided aspiration

If an abscess is found, neurosurgeons (doctors who specialise in the treatment of the nervous system and brain) can use a CT scan to guide a needle to the site of the abscess and remove a sample of pus for further testing. This is known as CT-guided aspiration. The sample of pus should be able to indicate the type of germ that is causing the abscess.

Treatment with broad-spectrum antibiotics will usually begin as soon as possible, even before a CT-guided aspiration is carried out, because it can be dangerous to wait for the results.

Broad-spectrum antibiotics can be used against a wide range of bacteria. They will be used before a specific diagnosis is made because there is a high chance they will be effective if the infection is caused by bacteria.

If the test reveals that the abscess is being caused by a fungus, the treatment plan can be changed and antifungal medication can be given.

Page last reviewed: 13/07/2011

Treatment for a brain abscess will depend on the size and number of brain abscesses present. A brain abscess is a medical emergency, so you will need to have treatment in hospital and will stay there until your condition is stable.


Surgery will be avoided if it is thought to be too risky or if an abscess is small and could be treated by medication alone.

Medication is recommended over surgery if you have:

  • several abscesses
  • a small abscess (less than 2cm)
  • an abscess deep inside the brain
  • meningitis as well as an abscess
  • hydrocephalus (a build-up of fluid on the brain)

You will normally be given antibiotics or antifungal medication through a drip (directly into a vein). Doctors will aim to treat the abscess and the original infection that caused it.


If the abscess is larger than 2cm, it is usually necessary to drain the pus out of the abscess (open aspiration) or cut the abscess out of the brain tissue (excision).

Open aspiration and excisions are usually carried out using a surgical procedure known as a craniotomy.

During a craniotomy, the surgeon will shave a small section of your hair and then remove a small piece of your skull bone (a bone flap) to gain access to your brain.

The abscess will then be drained of pus or totally removed. A CT-guided localisation system may be used during the operation, which allows the surgeon to more accurately locate the exact position of the abscess.

Once the abscess has been treated, the bone is replaced and held in position with small metal screws to prevent movement and encourage better healing. The operation usually takes between four and six hours, which includes recovery from the general anaesthetic (where you are put to sleep).

Complications of a craniotomy

As with all surgery, a craniotomy carries risks, but serious complications are uncommon.

Possible complications of a craniotomy are:

  • Swelling and bruising around your face, which is common after a craniotomy. This will die down after the operation.
  • Headaches. These are common after a craniotomy and may last for several months, but should eventually settle down.
  • A blood clot in the brain (further surgery may be required to remove it).
  • Stiff jaw. During a craniotomy, the surgeon may need to make a small cut to a muscle that helps with chewing. The muscle does heal, but can become stiff for a few months, causing your jaw to feel stiff. Exercising the muscle by regularly chewing sugar-free gum should help relieve the stiffness.
  • Movement of the bone flap. The bone flap in your skull may feel like it moves and you may experience a clicking sensation. This can feel strange, but it is normal and not dangerous. It will stop as the skull heals.

The site of the incision (cut) in your skull can become infected, although this is uncommon. You are usually given antibiotics around the time of your operation to prevent infection.

Page last reviewed: 13/07/2011

Once your brain abscess has been treated, you will probably need to stay in hospital for several weeks so the functions of your body can be supported while you recover from the effects of the abscess. You will also receive a number of CT scans, to make sure that the brain abscess has been completely removed.

Most people will then need a further 6 to 12 weeks of rest at home before they are fit enough to return to work or full-time education.

If you have a brain abscess, it could affect your ability to drive. It is important that you inform your doctor and the Road Safety Authority (RSA) about a medical condition that could have an impact on your driving ability.

After having treatment for a brain abscess, avoid any contact sport where there is a risk of injury to the skull, such as boxing, rugby or football.

Page last reviewed: 13/07/2011

Possible complications of a brain abscess include:

  • Brain damage. This can range from mild impairment, such as slightly slurred speech, to serious impairment such as permanent disability. Mild impairments may improve with time, but serious impairments are more likely to be permanent. Brain damage is more of a risk when the diagnosis of a brain abscess was delayed and treatment did not begin quickly enough. Brain abscesses can now be diagnosed very easily with a CT or MRI scan, so the risk of serious brain damage is very low.
  • Epilepsy. A small number of people go on to develop epilepsy, a condition that causes repeated fits or seizures. Epilepsy is a long-term condition and symptoms can usually be controlled using medication. For more information, see the Health A-Z topic on Epilepsy.
  • Meningitis. In some cases, especially those involving children, a brain abscess can develop into meningitis, a life-threatening infection of the protective membranes that surround the brain. For more information, see the Health A-Z topic on Meningitis.
  • Return of the abscess.

Content provided by NHS Choices and adapted for Ireland by the Health A-Z.

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