A brain abscess is a pus-filled swelling in the brain caused by an infection. It is a rare and life-threatening condition that must receive urgent medical attention 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 not treated, 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.
Brain abscesses are extremely rare in the UK. It is estimated that only 2-3 people in every million will develop a brain abscess in any given year. In England, most neurosurgeons (surgeons who specialise in the brain and nervous system) would only expect to treat around 1 to 4 cases per year. They can occur at any age, but most cases are reported in people age 40 or younger. They are more common in men and boys than in women or girls.
Infections of the brain are rare because the body has a number of defences to protect this vital organ. These include the blood-brain barrier, a thick membrane that filters out impurities from blood before allowing it into your brain. However, in some cases germs can get through the defences and infect the brain.
What are the symptoms of a brain abscess?
- Headache, which is often severe and cannot be relieved by taking painkillers
- Changes in mental state - for example appearing very confused
- Weakness 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 (from the abscess putting pressure on the optic nerve)
In around two-thirds of people with a brain abscess, symptoms are present for 2 weeks or less before they reach the point where the person needs to be admitted to hospital.
What causes a brain abscess?
A brain abscess usually occurs when bacteria or fungi enter the brain tissue. This can be caused by:
- An infection in another part of the skull, such as a 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 via the blood into the brain. These types of infection are believed to account for around 1 in 4 cases of brain abscesses. People with a weakened immune system (the body’s defence system) have a higher risk of developing a brain abscess from infections carried by the blood because their immune system may not be capable of fighting off the initial infection. You may have a weakened immune system if you have HIV or AIDS, are receiving chemotherapy, or take immunosuppressant medication.
- Trauma, such as a severe head injury, that cracks open the skull, allowing bacteria or fungi to enter the brain. Direct trauma to the skull is thought to be responsible for 1 in 10 cases of brain abscess.