Brain abscess: How it happens, risk factors, and causes

The most common cause of a brain abscess, also known as a cerebral abscess, is an infection. Bacteria, fungi, or a parasite can infect a part of the brain, causing swelling.

Infected brain cells, white blood cells, live and dead fungi, bacteria, and parasites all accumulate in a brain abscess. A membrane forms around the area, and this creates a mass.

As the swelling grows, it puts increasing pressure on brain tissue. Since the skull is not flexible and does not expand, the swelling can create pressure on the surrounding brain. This can lead to the destruction of delicate brain tissue.

A number of factors and conditions can lead to a brain abscess.

Fast facts on the cause of a brain abscess:

Here are some key points about the cause of a brain abscess. More detail is in the main article.

A brain abscess can result from an infection around the head or face or elsewhere in the body, or as a result of a traumatic blow or puncture wound.

The infection may be a bacterial, viral, or parasitic.

Congenital heart disease, meningitis, and some chronic infections increase the risk in children.

People with a weakened immune system have a higher chance of developing an abscess.

Often, the cause remains unclear, but identifying it increases the chance of effective treatment.

How does infection enter the brain?

Pinpointing the cause of a brain abscess will lead to more effective treatment.
Pinpointing the cause of a brain abscess will lead to more effective treatment.

A brain abscess can occur as a result of direct infection, or when infection spreads from another part of the body.

The infection enters the brain from three main routes.

Blood-borne infections

The bloodstream carries blood-borne infections from another part of the body. This accounts for between 15 and 30 percent of cases.

Normally, the blood-brain barrier stops infection from entering the brain, but sometimes an infection can cross the barrier and infect the brain. Exactly how or why this happens remains unclear.

If an infection from another part of the body travels through the bloodstream to the central nervous system (CNS) or somehow bypasses the blood-brain barrier, and reaches the brain, it can cause an infection and an abscess.

When a bacterial brain abscesses comes from a lesion somewhere else in the body, the bacteria are normally Streptococci.

The most common sources of blood-borne infections that cause a brain abscess are:

Cyanotic heart disease, where a heart defect that is present from birth results in low blood oxygen levels.

Pneumonia and other lung infections and conditions.

Bronchiectasis, a permanent widening, or dilatation, of the the bronchi, large air tubes which begin at the bottom of the trachea and branch into the lungs. This can result in recurrent respiratory infections, as well as other serious illnesses.

Peritonitis, or inflammation of the tissue layer of cells lining the inner wall of the abdomen and pelvis and other abdominal infections.

Cystitis, an inflammation of the bladder, and and other infections located in the pelvis.

Bacterial endocarditis, an infection of the heart tissues.

Other reported causes of brain abscess include liver abscess, tongue piercing, and gastrointestinal conditions and procedures.

When treating the abscess, it is important to know where the original infection came from. Treating the first infection site can prevent another brain abscess from arising.

Direct contagion

Direct contagion happens when an infection starts in the skull, perhaps in the nose or ear, and spreads into the central nervous system, and from there into the brain.

Examples include:

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