A brain abscess is most likely caused by a bacterial or fungal infection in the brain. An abscess can also be caused by parasites.
Inflammation and swelling occur when bacteria, fungi, or parasites infect a part of the brain. The abscess in these cases will be made up of infected brain cells, active and dead white blood cells, and the organisms that are causing the problem.
As the cells multiply, a wall or membrane forms around the abscess. This aids in the isolation of the infection and prevents it from spreading to healthy tissue. When an abscess swells, it puts pressure on the surrounding brain tissue.
The skull is rigid and unable to expand. The abscess pressure can block blood vessels, preventing oxygen from reaching the brain and causing damage or destruction of delicate brain tissue.
For a variety of reasons, brain infections are relatively uncommon. One reason is the blood-brain barrier, a network of blood vessels and cells that protects the brain.
Certain components of the blood that flows to the brain are blocked, but others pass through. An infection can sometimes cross the blood-brain barrier.
This can occur when inflammation damages the barrier, causing gaps to form.
The infection enters the brain via three main pathways.
- come through the blood from another part of the body’s infection
- spread from a nearby location, for example, the ear
- come as a result of a traumatic injury or surgical procedure
If an infection occurs elsewhere in the body, infectious organisms can enter the bloodstream, cross the blood-brain barrier, and infect the brain.
Pathogens that have traveled from another part of the body cause 9 to 43% of abscesses. Many bacterial brain abscesses are caused by a lesion elsewhere in the body.
It is critical to locate the primary lesion, or else the infection may reoccur. A person with a weakened immune system is more likely to develop a brain abscess as a result of a bloodborne infection.
The following are the most common infections known to cause brain abscesses:
- Endocarditis, a heart valve infection
- Bronchiectasis, pneumonia, and other lung infections and conditions
- Peritonitis, an inflammation of the inner wall of the abdomen and pelvis, a type of abdominal infection.
- cystitis, or bladder inflammation, and other pelvic infections
An infection can spread from a nearby area, accounting for 14-58% of brain abscesses. If an infection begins inside the skull, such as in the nose or ear, it has the potential to spread to the brain. The following infections can cause a brain abscess:
- otitis media, also known as a middle ear infection
- mastoiditis, a bone infection behind the ear.
Trauma, such as neurological surgery or a penetrating brain injury, can cause a brain abscess. An abscess can develop as a result of:
- a blow to the head that results in a compound skull fracture with bone fragments pushed into the brain
- presence of a foreign body, such as a bullet, if it is not removed
- in rare cases, a surgical complication