Brain abscess
Introduction
What is a brain abcess?
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 as the swelling can put pressure on delicate brain tissue and disrupt the blood and oxygen supply to the brain. There is also the risk that the abscess can 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 in the United Kingdom. It is estimated that only 2-3 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 age forty or younger. Brain abscesses are more common in men than in women.
Outlook
Due to 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, with most people making a full recovery. However, without treatment, a brain abscess is nearly always fatal
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Symptoms
The symptoms of a brain abscess can develop quickly or slowly, depending on individual circumstances.
In around two-thirds of people, symptoms are present for two weeks or less, before they worsen to such an extent that hospital admission is required.
Common symptoms include:
- headache
- changes in mental state, such as confusion or irritability
- problems with nerve function, such as muscle weakness or paralysis on one side of the body, or slurred speech
- fever
- seizures (fits)
- nausea and vomiting
- stiff neck
- changes in vision, such as blurring, greying of vision, or double vision (this is due to the abscess placing 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 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 or NHS Direct Wales on 0845 46 47.
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Causes
Abscesses
Abscesses are pus-filled swellings caused by infection with either bacteria or fungi.
Abscesses are created by your immune system as a defence mechanism. If the immune system realises that it is unable to defeat an infection, it will then try to limit its spread. The 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 entirely clear, germs can breach these defences and infect the brain.
The three most common routes for germs to enter the brain are:
- 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 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 no apparent cause can be found.
Germs invading the brain through the bloodstream
Infections that are spread via the blood are thought to be a major cause of brain abscesses.
People with a weakened immune system (who are immunnocompromised) are at a higher risk of developing a brain abscess due to 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 had an organ transplant and taking immunosuppressants to prevent the 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 in which 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 an 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 fractures caused by penetrating injury
- gunshot or shrapnel wound
Very rarely, a brain abscess can develop as a complication of surgery.
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Diagnosis
An initial assessment will be made on the basis of your physical symptoms and recent medical history, such as if you have had a recent infection, or have a weakened immune system.
Blood tests
Blood tests are also 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.
Scans
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 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 what type of germ 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, as it can be dangerous to wait for the results.
If the test does reveal that the abscess is being cause by a fungus the treatment plan can be amended and antifungal medication can be given.
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Treatment
The treatment 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.
Medication
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.
Surgery
If the abscess is larger then 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 with 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 arising from 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.
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Recovery
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 brain 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 had brain surgery and hold a driving licence you are legally required to inform the Driving and Vehicle Licence Authority (DVLA). Due to the increased risk of you having an epileptic fit, the DVLA is likely to suspend your driving licence. The DVLA will only return your licence, once, your GP or surgeon confirms that it is safe for you to drive. For most people, this is likely to be 12 months after surgery with no seizures occurring.
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.
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Complications
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, where the diagnosis of a brain abscess was delayed and treatment did not begin quickly enough. Due to the ease with which brain abscesses can now be diagnosed with a CT or MRI scan, the risk of serious brain damage is now 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 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 topic on Meningitis.
- Return of the abscess.
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