A brain abscess is a collection of immune cells, pus, and other material in the brain, usually from a bacterial or fungal infection.

Brain abscesses commonly occur when bacteria or fungi infect part of the brain. Swelling and irritation (inflammation) develops in response. Infected brain cells, white blood cells, and live and dead bacteria and fungi collect in an area of the brain. A membrane forms around this area and creates a mass.

While this immune response can protect the brain by isolating the infection, it can also do more harm than good. The brain swells. Because the skull cannot expand, the mass may put pressure on delicate brain tissue. Infected material can block the blood vessels of the brain.

The bacteria or fungi that cause a brain abscess commonly reach the brain through the blood. The source of the infection is often not found. However, the most common source is a lung infection. Bacteria or fungi may also travel from a nearby infected area (for example, an ear infection) or be introduced into the body during an injury (such as a gun or knife wound) or surgery.

In children with heart disease or a birth defect, such as those born with Tetralogy of Fallot, infections are more able to reach the brain from the intestines, teeth, or other body areas.

The following raise your risk of a brain abscess:

• A weakened immune system (such as in AIDS patients)
• Chronic disease, such as cancer or Osler-Weber-Rendu syndrome
• Drugs that suppress the immune system (corticosteroids or chemotherapy)
• Right-to-left heart shunts

Symptoms may develop slowly, over a period of 2 weeks, or they may develop suddenly. They may include:

• Aching of neck, shoulders, or back
• Changes in mental status
  • Confusion
  • Decreasing responsiveness
  • Drowsiness
  • Eventual coma
  • Inattention
  • Irritability
  • Slow thought processes
• Decreased movement
• Decreased sensation
• Decreased speech (aphasia)
• Fever and chills
• Headache
• Language difficulties
• Loss of coordination
• Loss of muscle function
• Seizures
• Stiff neck, shoulders, or back
• Vision changes
• Vomiting
• Weakness

A brain and nervous system (neurological) exam will usually show increased intracranial pressure and problems with brain function.

Tests to diagnose a brain abscess may include:

• Blood cultures
• Chest x-ray
• Complete blood count (CBC)
• Cranial CT scan
• Electroencephalogram (EEG)
• MRI of head
• Testing for the presence of antibodies to organisms (including toxoplasma and Tinea solium)

A needle biopsy is usually performed to identify the cause of the infection.

A brain abscess is a medical emergency. Pressure inside the skull may become high enough to be life-threatening. You will need to stay in the hospital until the condition is stable. Some people may need life support.

Medication, not surgery, is recommended if you have:

• Several abscesses (rare)
• A small abscess (less than 2 cm)
• An abscess deep in the brain
• An abscess and meningitis
• Shunts in the brain for hydrocephalus (in some cases the shunt may need to be removed temporarily or replaced)
• A disease that makes surgery dangerous

You will get antibiotics. Antibiotics that work against a number of different bacteria (broad spectrum antibiotics) are most commonly used. You may be prescribed several different types of antibiotics to make sure treatment works.

Anti-fungal medications may also be prescribed if the infection is likely caused by a fungus.

Immediate treatment may be needed if an abscess is injuring brain tissue by pressing on it, or there is a large abscess with a large amount of swelling around that it is raising pressure in the brain.

Surgery is needed if :

• Pressure in the brain continues or gets worse
• The brain abscess does not get smaller after medication
• The brain abscess contains gas (produced by some types of bacteria)
• The brain abscess might break open (rupture)

Surgery consists of opening the skull, exposing the brain, and draining the abscess. Laboratory tests are often done to examine the fluid. This can help identify what is causing the infection, so that more appropriate antibiotics or anti-fungal drugs can be prescribed.

The surgical procedure used depends on the size and depth of the abscess. The entire abscess may be removed (excised) if it is near the surface and enclosed in a sac.

Needle aspiration guided by CT or MRI scan may be needed for a deep abscess. During this procedure, medications may be injected directly into the mass.

Certain diuretics and steroids may also be used to reduce swelling of the brain.

If untreated, a brain abscess is almost always deadly. With treatment, the death rate is about 10-30%. The earlier treatment is received, the better.

Some patients may have long-term neurological problems after surgery.

• Epilepsy
• Meningitis that is severe and life threatening
• Permanent loss of vision, speech, movement
• Return (recurrence) of infection

Go to a hospital emergency room or call the local emergency number (such as 911) if you have symptoms of a brain abscess.

You can reduce the risk of developing a brain abscess by treating any disorders that can cause them. Have a follow-up examination after infections are treated.

Some people, including those with certain heart disorders, may receive antibiotics before dental or urological procedures to help reduce the risk.

Nath A. Brain abscess and parameningeal infections. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 438.