Definition of Brain abscess:

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

Causes, incidence, and risk factors:

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