Brain abscess

Definition

A brain abscess is a mass of immune cells, pus, and other material that can occur when the brain is infected by bacteria or fungus.

Alternative Names

Causes

Brain abscesses commonly occur when bacteria or fungi infect part of the brain. Inflammation develops in response. Infected brain cells, white blood cells, and live and dead microorganisms collect in a limited area of the brain. This area becomes enclosed by a membrane that forms around it 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 in response to the inflammation, and the mass may put pressure on delicate brain tissue. Infected material can block the blood vessels of the brain, further damaging tissues by causing cell death and swelling of additional cells. Multiple abcesses are uncommon except in immunocompromised patients.

Infectious agents gain access to the brain in several ways. The most common way is through infected blood. Ear and sinus infections may also spread directly to the brain because of their close proximity.

Symptoms may develop gradually or suddenly. There may be little or no sign of general infection throughout the body. Early symptoms are usually headache, muscle weakness, visual changes, difficulty with balance or coordination, or seizures.

People at higher risk include those with congenital heart diseases, such as Tetralogy of Fallot, and people with congenital blood vessel abnormalities of the lungs, such as Osler-Weber-Rendu disease. These disorders carry a high risk of infection of the heart or lungs, which can then spread to the brain. People with HIV infection or other conditions that compromise the immune system are also at higher risk.