Brain abscesses commonly occur when bacteria or fungi infect part of the brain. As a result, swelling and irritation (inflammation) develop. Infected brain cells, white blood cells, live and dead bacteria, or fungi collect in an area of the brain. Tissue forms around this area and creates a mass, or abscess.

The germs that cause a brain abscess can reach the brain through the blood. Or, they enter the brain directly, such as during brain surgery. In some cases, a brain abscess develops from an infection in the sinuses.

The source of the infection is often not found. However, the most common source is a lung infection. Less often, a heart infection is the cause.

The following raise your chance of developing a brain abscess: