A brain abscess is usually caused by infection with either bacteria or fungi.

If the immune system is unable to kill an infection, it will try to limit its spread by using healthy tissue to form an abscess, to stop the pus infecting other tissue.

Infections of the brain are rare because the body has evolved 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 cases, germs can get through these defences and infect the brain.

Although the exact location of the original infection cannot always be identified, the most common sources are described below.

Infection in the skull

In up to half 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 (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.

Infection through the bloodstream

Infections spread through the blood are thought to account for around one in four cases of brain abscesses.

People with a weakened immune system 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.

You may have a weakened immune system if you:

• have a medical condition that weakens your immune system, such as HIV or AIDS
• receive medical treatment known to weaken the immune system, such as chemotherapy
• have an organ transplant and take immunosuppressant drugs 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 type of congenital heart disease (a heart defect present at birth) 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
• pulmonary arteriovenous fistula – a rare condition in which abnormal connections develop between blood vessels inside the lungs; this can allow bacteria to get into the blood and, eventually, the brain
• dental infections or treatment for tooth decay
• lung infections, such as pneumonia or bronchiectasis
• infections of the heart – such as endocarditis
• skin infections
• infections of the abdomen – such as peritonitis (an infection of the bowel lining)
• pelvic infections – such as infection of the bladder lining (cystitis)

Infection after a head injury

Direct trauma to the skull can also lead to a brain abscess and is thought responsible for 1 in 10 cases.

The most commonly reported causes include:

• skull fracture caused by penetrating injury to the head 
• gunshot or shrapnel wound

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

Complications of a brain abscess can include recurrence, brain damage, severe meningitis and epilepsy (seizures).

Reoccurring brain abscesses

If you have a previous history of having a brain abscess, there is a small chance of another abscess forming. This is especially the case if you have underlying risk factors, such as a weakened immune system or cyanotic heart disease.

You should be alert for symptoms that a brain abscess can cause, such as a persistent severe headache.

Seek immediate medical advice if you think there is even a small chance an abscess has reoccurred.

Brain damage

Brain damage can range from mild through moderate to severe.

Mild brain damage can result in:

• headaches 
• memory problems

Moderate brain damage can result in:

• changes in mood, such as feeling restless or agitated
• problems with tasks that require high-level thinking, such as planning and decision making
• difficulties with balance and coordination – the medical term for this is ataxia

Severe brain damage can result in:

• weakness in certain parts of the body
• coma or persistent vegetative state in the most serious of cases

Mild to moderate brain damage often improves with time. Severe brain damage is 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 now low.

Epilepsy

A common complication of brain abscesses is epilepsy – a condition that causes repeated fits or seizures. Epilepsy is a long-term condition and symptoms can usually be controlled using medication.

Read more about the treatment of epilepsy.

Meningitis

In some cases, especially those involving children, a brain abscess can develop into bacterial meningitis – a life-threatening infection of the protective membranes that surround the brain.

Symptoms of meningitis include:

• severe headache
• vomiting 
• high temperature (fever) of 38C (100.4F) or over
• stiff neck

Someone with bacterial meningitis will require urgent treatment in hospital, usually an intensive care unit (ICU).

Antibiotics will be used to treat the underlying infection. These will be given through a vein in the arm (intravenously).

At the same time, a person may also be given:

• oxygen
• intravenous fluids – through a vein
• steroids or other medication to help reduce the swelling (inflammation) around the brain

Read more about the treatment of meningitis.  

If a brain abscess is suspected, the diagnosis can be confirmed using a brain scan.

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

Blood tests can also 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 you are referred to hospital for further tests, you may have either:

• a computerised tomography (CT) scan – which involves a series of X-rays to produce a detailed image of the inside of your body
• a magnetic resonance imaging (MRI) scan – which uses strong magnetic fields and radio waves to produce a detailed image of the inside of your body.

A CT scan can often detect the presence of the abscess and any associated swelling inside the brain.

A MRI scan can provide a more detailed image than a CT scan, so is sometimes used if the results of the CT scan are inconclusive. 

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 indicate the type of germ 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 the abscess is caused by a fungus, the treatment plan can be changed and antifungal medication given.

Read more information about treating a brain abscess.

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

A brain abscess usually occurs when bacteria or fungi enter the brain tissue.

Symptoms of a brain abscess include:

• headache – which is often severe and cannot be relieved by taking painkillers
• changes in mental state, such as appearing very confused
• weakness or paralysis on one side of the body
• a high temperature (fever) of or above 38C (100.4F)
• seizures (fits) 

What causes a brain abscess?

There are three main ways that 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 severe 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.

Treating a brain abscess

A brain abscess is regarded as a medical emergency. This is because the swelling caused by the abscess can 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.

If you suspect that you or someone you know may have a brain abscess, call 999 for an ambulance.

A brain abscess is usually treated using a combination of antibiotics (or in some cases, antifungals) and surgery. The surgeon will usually open the skull and drain the pus from the abscess, or remove the abscess entirely.

The sooner the condition is diagnosed and treated, the lower the chance a person has of developing long-term complications.

Read more about treating a brain abscess.

Complications

Any damage to brain tissue can result in long-term complications, such as:

• brain damage – ranging from mild to severe
• epilepsy – where a person has repeated seizures (fits)

Read more about the complications of a brain abscess.

Who is affected

Brain abscesses tend to only be a significant problem in parts of the world where access to antibiotics is limited.

In England, brain abscesses are extremely rare. Most neurosurgeons (surgeons who specialise in the brain and nervous system) would only expect to treat around one to four cases per 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, though the reason for this is unclear.

Outlook

Because of advances in diagnostic and surgical techniques, the outlook for people with brain abscesses has improved dramatically. Around 70% of people will make a full recovery.

However, in around 10% of cases, a brain abscess may be fatal.

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 escalate to the point where the person needs to be admitted to hospital.

Common symptoms include:

• headache – the headache 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 (fever) of or above 38C (100.4F) 
• seizures (fits)
• nausea and vomiting
• stiff neck
• changes in vision – such as blurring, greying of vision or double vision (due to 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 should be treated as a medical emergency. These include:

• slurred speech
• muscle weakness or paralysis
• seizures occurring in a person who had 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 fever and vomiting, should be reported to your GP immediately. If your GP is not available, contact your local out-of-hours service or call NHS 111.

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 treatment in hospital until your condition is stable.

Medication

Surgery will be avoided if thought 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 (an infection of the protective membranes that surround the brain) 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.

Surgery

If the abscess is larger than 2cm, it is usually necessary to drain the pus out of the abscess.

There are two surgical techniques for treating a brain abscess:

• simple aspiration
• craniotomy

Simple aspiration involves using a CT scan to locate the abscess, then drilling a small hole known as a “burr hole” into the skull. The pus is then drained through the hole and the hole sealed.

A simple aspiration takes around one hour to complete.

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

Craniotomy

A craniotomy may be recommended if an abscess does not respond to aspiration or reoccurs at a later date.

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. The operation usually takes around three 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 described below: 

• Swelling and bruising around your face, which is common after a craniotomy. This will lessen after the operation.
• Headaches. These are common after a craniotomy and may last 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 heals, 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 cut (incision) in your skull can become infected, although this is uncommon. You are usually given antibiotics around the time of your operation to prevent infection.

Recovering from surgery

Once your brain abscess has been treated, you will probably stay in hospital for several weeks so your body can be supported while you recover.

You will also receive a number of CT scans, to make sure the brain abscess has been completely removed.

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

After 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.

Advice for drivers

If you’ve had brain surgery and you hold a driving licence, you are legally required to inform the Driving and Vehicle Licensing Agency (DVLA).

It’s likely that the DVLA will suspend your driving licence due to your increased risk of having an epileptic fit. Your licence will only be returned once your GP or surgeon confirms that it’s safe for you to drive.

For most people, this is likely to be 12 months after surgery with no seizures occurring.