Brain Abscess: Definition, Symptoms, Causes, Diagnosis, Treatment and Overview

It is a collection of pus that develops in response to infection or trauma.

It is a serious and life-threatening condition.

In the past, a brain abscess was “invariably fatal,” but researchers writing in 2014 noted that progress in diagnosis and treatment has 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 more likely to affect adult men under the age of 30.

Among children, they most commonly develop in those ages 4 to 7. Newborns are also at risk.

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

Symptoms of a brain abscess

The signs and symptoms of a brain abscess include the following:

  • Headache is a common symptom of a brain abscess.
  • Fever (45–53 percent)
  • Seizures (25-35 percent)
  • Nausea and vomiting (40 percent)

A seizure can be the first sign of an abscess. Nausea and vomiting tend to occur as pressure increases within the brain.

The pain usually begins on the side of the abscess and can start slowly or suddenly.

Changes in mental state occur in 65 percent of cases, and can lead to:

  • Confusion.
  • Drowsiness and lethargy
  • Irritability.
  • Poor mental focus.
  • Poor responsiveness.
  • Slow thought processes.
  • Eat (possibly).

Neurological difficulties affect 50–65 percent of people with brain abscesses. These problems often follow a headache, which appears over days or weeks, and can include:

  • Muscular weakness.
  • Weakness or paralysis on one side of the body.
  • Speech problems, such as difficulty speaking.
  • Poor coordination.

Other symptoms can include:

  • Stiff neck, back, or shoulders
  • Blurred, double, or gray vision.

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

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

In two-thirds of cases, symptoms are present for up to 2 weeks. On average, doctors diagnose the problem 8 days after symptoms begin.

Causes of a brain abscess

A brain abscess is more likely to be the result of a bacterial or fungal infection somewhere in the brain. Parasites can also cause an abscess.

When bacteria, fungi, or parasites infect part of the brain, inflammation and swelling occur. In these cases, the abscess will consist of infected brain cells, active and dead white blood cells, and the organisms causing the problem.

As cells accumulate, a wall or membrane develops around the abscess. This helps isolate the infection and prevents it from spreading to healthy tissues.

If the abscess becomes inflamed, it increases pressure on the surrounding brain tissue .

The skull is not flexible, and it cannot expand. The pressure from the abscess can block blood vessels, preventing oxygen from reaching the brain, causing damage or destruction of delicate brain tissue.

How does infection enter the brain?

Brain infections are quite rare for a number of reasons.

One reason is the blood-brain barrier, a protective network of blood vessels and cells. It blocks certain components of the blood that flow to the brain, but allows others to pass through them.

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

The infection enters the brain through three main routes.


  • Passing through the blood of an infection in another part of the body.
  • Spread from a nearby site, such as the ear.
  • Result of traumatic injury or surgery.
  • Infection from another area of ​​the body.

If an infection occurs elsewhere in the body, 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 are due to pathogens that traveled from another part of the body. Many bacterial abscesses in the brain stem from injury to another part of the body.

Finding that primary lesion is crucial, 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 due to a blood-borne infection.

A person can have a weakened immune system if:

  • You have HIV.
  • Have AIDS.
  • They are babies under 6 months.
  • They are receiving chemotherapy.
  • They are using long-term steroid medications.
  • You have received an organ transplant and are taking immunosuppressive medications 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.
  • Direct contagion.

A middle ear infection can lead to a brain abscess.

An untreated infection in the middle ear can lead to a brain abscess.

An infection can spread from a nearby area, and this accounts for between 14 and 58 percent of brain abscesses.

If an infection starts inside the skull, for example in the nose or ear, it can spread to the brain.

Infections that can trigger a brain abscess include:

  • Otitis media, or a middle ear infection.
  • Sinusitis.
  • Mastoiditis, an infection of the bone behind the ear.

The location of the abscess may depend on the site and type of original infection.

direct trauma

A brain abscess can be the result of trauma, such as neurological surgery or a penetrating brain injury.

An abscess can be the result of:

  • A blow to the head that causes a compound skull fracture, in which bone fragments are inserted into the brain.
  • The presence of a foreign body, such as a bullet, if someone does not remove it.
  • A complication of surgery, in rare cases.

Diagnosis of a brain abscess

To diagnose a brain abscess, the doctor will evaluate the signs and symptoms and review the patient’s recent travel and medical histories.

They will need to know if the individual:

  • You have recently had an infection.
  • You have a weakened immune system.

Symptoms can be similar to other diseases and conditions, so it can take time to confirm a diagnosis. Diagnosis will be easier if the doctor can identify exactly when the symptoms started and how they progressed.

The tests may include:

  • A blood test to check for high levels of white blood cells, which may indicate an infection.
  • Imaging scans, such as an MRI or CT scan, in which an abscess will show up as one or more dots.
  • A CT-guided aspiration, a type of needle biopsy, which involves taking a sample of pus for analysis.

The number of deaths from brain abscesses has decreased in recent decades, due to the increasingly routine use of CT and MRI for screening.

Treatment of a brain abscess

Treatment generally involves surgery and medication.

The chance of recovering from a brain abscess is much higher now.

Recent developments in medicine and technology mean that the chance of recovering from a brain abscess is much higher now than in the past.

Generally, if a doctor suspects a brain abscess, they will immediately prescribe broad-spectrum antibiotics, as an abscess can be life-threatening.

If tests show that an infection is viral rather than bacterial, the doctor will alter the treatment accordingly.

The effectiveness of the treatment will depend on:

  • The size of the abscess.
  • How many abscesses are there.
  • The cause of the abscess.
  • The general state of health of the person.

If the abscess is less than 1 inch wide, the person will likely only receive intravenous antibiotics, antifungals, or antiviral medications.

However, a doctor may need to drain a smaller abscess to determine which antibiotics will be the best.

If an abscess is more than 1 inch wide, the doctor will need to aspirate, drain, or trim it.

If there are multiple abscesses, cutting them may be too risky. The surgeon will recommend aspiration.

The person will also need treatment for any primary infection, for example in the lungs, abdomen, or nose.


A person may need surgery if:

  • The pressure in the brain keeps increasing.
  • The abscess does not respond to medication.
  • There is gas in the abscess.
  • There is a risk that the abscess will rupture.
  • A craniotomy is a procedure in which the surgeon makes an opening in the skull.

The steps are the following:

  • The surgeon will shave a small area of ​​the scalp.
  • A small piece of bone is removed to access the brain.
  • They can remove the abscess or drain the pus, possibly with the help of a CT scan.
  • They replace the bone and stitch the skin.


A short course of high-dose corticosteroids can help if there is an increase in intracranial pressure and a risk of complications, such as meningitis.

However, doctors do not prescribe corticosteroids as a routine measure.

A doctor can prescribe anticonvulsants to prevent seizures, and a person who has had a brain abscess may need to take anticonvulsants for up to 5 years.


Studies show that 5 to 32 percent of brain abscesses are fatal.

Among those that survive, there may be long-lasting effects, depending on the extent of any damage. A brain abscess can lead to long-term neurological problems, involving problems with physical function, personality changes, and seizures.

It is important to recognize the possible symptoms of a brain abscess and seek help immediately if they occur. The sooner a person receives treatment, the more likely it is to be effective and the better the chances of survival.

The outlook also depends on the characteristics of the abscess. Multiple abscesses and any location deep in the brain are more difficult to treat.

The doctor will monitor a person during recovery, as an abscess can recur. This may involve undergoing a weekly CT scan for at least 2 weeks.

Also, an abscess can return after months or years, so long-term follow-up is essential.