Brain abscess: Symptoms, causes, diagnosis, treatment

A brain abscess is a collection of pus that develops in response to an infection or trauma. It remains a serious and potentially life-threatening condition.

In the past, a brain abscess was “invariably fatal,” but researchers writing in 2014 noted that progress in diagnosis and treatment have significantly increased the chances of survival.

The effects vary, depending on the size of the abscess and where it forms in the brain.

Between 1,500 and 2,500 cases occur each year in the United States. Brain abscesses are most likely to affect adult men aged under 30 years. Among children, they most commonly develop in those aged 4–7 years. Newborns are also at risk.

Vaccination programs have reduced the incidence of brain abscesses in young children.


The signs and symptoms of a brain abscess are as follows:

Headache is a common symptom
Headache is a common symptom of a brain abscess.

a headache (69–70 percent of cases)

a fever (45–53 percent)

seizures (25–35 percent)

nausea and vomiting (40 percent)

A seizure may be the first sign of an abscess. Nausea and vomiting tend to occur as pressure builds inside the brain.

Pain usually starts on the side of the abscess, and it may begin slowly or suddenly.

Changes in mental status occur in 65 percent of cases, and they may lead to:


drowsiness and lethargy


poor mental focus

poor responsiveness

slow thought processes

coma (possibly)

Neurologic difficulties affect 50–65 percent of people with brain abscesses. These issues often follow a headache, appearing within days or weeks, and they can include:

muscle weakness

weakness or paralysis on one side of the body

speech problems, such as slurred speech

poor coordination

Other symptoms may include:

a stiff neck, back, or shoulders

blurred, double, or graying vision

The symptoms of a brain abscess result from a combination of infection, brain tissue damage, and pressure on the brain, as the abscess grows to take up more space.

If the headache suddenly becomes worse, it may mean that the abscess has burst.

In two-thirds of cases, symptoms are present for as long as 2 weeks. On average, doctors diagnose the issue 8 days after symptoms start.

Brain abscess: What are the signs and symptoms?Brain abscess: What are the signs and symptoms?
It is important to recognize a brain abscess as early as possible, as it can be life-threatening without treatment. Find out more.
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How infection enters the brain

Brain infections are fairly uncommon for several reasons.

One reason involves the blood-brain barrier, a protective network of blood vessels and cells. It blocks certain components from the blood that flows to the brain, but it allows others to pass through.

Sometimes, an infection can get through the blood-brain barrier. This can happen when inflammation damages the barrier, leading to gaps.

The infection enters the brain through three main routes.

It may:

come through the blood from an infection in another part of the body

spread from a nearby site, such as the ear

result from a traumatic injury or surgery

Infection from another area of the body

If an infection occurs somewhere else in the body, the infectious organisms can travel through the bloodstream, bypass the blood-brain barrier, and enter and infect the brain.

Between 9 and 43 percent of abscesses result from pathogens that traveled from another part of the body.

Many bacterial brain abscesses stem from a lesion somewhere else in the body. It is crucial to find that primary lesion, or there may be a repeat infection in the future.

A person with a weakened immune system has a higher risk of developing a brain abscess from a bloodborne infection.

A person may have a weakened immune system if they:

have HIV

have AIDS

are infants under the age of 6 months

are receiving chemotherapy

are using long-term steroid medication

have had an organ transplant and take immunosuppressant drugs to prevent organ rejection

The most common infections known to cause brain abscesses are:

endocarditis, an infection of the heart valve

pneumonia, bronchiectasis, and other lung infections and conditions

abdominal infections, such as peritonitis, an inflammation of the inner wall of the abdomen and pelvis

cystitis, or inflammation of the bladder, and other pelvic infections

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