A brain abscess is a collection of pus that occurs in the brain because of an infection. In the past, a brain abscess was “invariably fatal,” but progress in diagnosis and treatment have greatly increased the odds of survival.
However, it remains a serious and potentially life-threatening condition.
The effects of a brain abscess vary, depending on the size of the abscess and where it occurs in the brain.
Men appear to be more susceptible than women. In studies, the average age of onset has ranged from 24 years to 57 years of age.
The BMJ Best Practice states that prevalence is higher among men aged under 30 years. In children, it is more likely to appear between the ages of 4 and 7 years. Neonates are also at risk.
In 2010, the Cleveland Clinic put the number of cases of brain abscess in the United States at between 1,500 and 2,000, of which some 25 percent were children.
A dull headache is a common symptom of a brain abscess.
The hallmark signs of a brain abscess are headache, fever, and neurologic difficulties. Over 75 percent of people have a “dull, achy headache,” according to the Harvard Medical School.
Changes in mental status may lead to:
- Poor mental focus
- Poor responsiveness
- Slow thought processes
Other symptoms may include:
- Muscle weakness
- Weakness or paralysis on one side of the body
- Speech problems, such as slurred speech
- Poor coordination
- Nausea and/or vomiting
- Fever and chills
- Stiff neck, back or shoulders
- Blurred, double, or graying vision.
Symptoms are caused by a combination of infection, brain tissue damage, and pressure on the brain, as the abscess grown and takes up more space.
A brain abscess is most likely to result from a bacterial or fungal infection in some part of the brain. Parasites may also cause an abscess.
When the 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 causative organisms.
As these accumulate, a wall or membrane develops around the abscess. This helps to isolate the infection and to stop it from spreading to healthy tissue.
If the volume of the abscess swells, it places increasing pressure outward on brain tissue. The skull is not flexible, and it does not expand. The pressure caused by the abscess can block blood vessels to the brain. As a result, oxygen cannot reach the brain, and delicate brain tissue is damaged or destroyed.
How infection enters the brain
Brain infections are fairly uncommon for several reasons. One reason is the blood-brain barrier. This is a protective network of blood vessels and cells that blocks certain components from blood as it flows to the brain, and permits others.
Sometimes, an infection can get through the blood-brain barrier and infect the brain. This can happen when inflammation compromises the integrity of the blood brain barrier and causes gaps to open.
The infection enters the brain from three main routes. It may be carried in the blood from an infection in another part of the body, spread from a nearby site, such as an ear infection, or result from trauma.
Infection from another place in the body
The bloodstream carries infectious organisms. This route accounts for about 25 percent of abscesses.
If an infection occurs somewhere else in the body, it can travel through the bloodstream, bypass the blood-brain barrier, and enter and infect the brain.
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.
People with a weakened immune system have a higher risk of developing a brain abscess caused by a blood-borne infection.
Examples include people with HIV/AIDS, infants under the age of 6 months, patients receiving chemotherapy, individuals on long-term steroid use, and organ transplant recipients who take immunosuppressant drugs to prevent organ rejection.
The most common infections known to cause a brain abscess 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 accounts for between 50 percent of brain abscesses.
Infection starts inside the skull, for example in the nose or the ear, and it spreads into the brain.
Examples include otitis media or middle ear infections, sinusitis, or mastoiditis, an infection of the bone behind the ear.
The location of the abscess may depend on the site and type of the original infection.
Trauma accounts for a small percentage of brain abscesses.
A blow to the head can cause a compound skull fracture, in which fragments of bone are pushed into the brain, causing a brain abscess. A foreign body, such as a bullet, which is left in place may also be a source of infection.
Rarely, a brain abscess may be a complication of surgery.
People with a weakened immune system are more prone to brain abscesses stemming from fungi and parasites.
To diagnose a brain abscess, the doctor will evaluate any signs and symptoms and look at the patient’s recent medical and travel history.
Technological improvements have reduced the number of fatalities from brain abscesses.
It is important to know whether the individual has had an infection recently, or has a weakened immune system.
Symptoms may be similar to those of other illnesses and conditions, so diagnosis may be delayed.
Diagnosis is easier if the doctor can pinpoint exactly when symptoms started and how they progressed.
Tests may include:
- A blood test to check for high levels of white blood cells, which indicates infection
- A chest x-ray to determine whether there is a lung infection
- Imaging scans, such as an MRI or a CT scan, in which an abscess will show up as one or more spots
- A CT-guided aspiration, a type of needle biopsy in which a sample of pus is taken for analysis. This can help to pinpoint the cause of the abscess, and how to treat it.
Fatalities from a brain abscess have fallen dramatically in the last few decades due to routine use of CT scans in detection and follow up.
If a brain abscess is suspected, a physician will normally prescribe antibiotics immediately, because an abscess can be life-threatening. If the infection turns out to be viral rather than bacterial, treatment can be altered accordingly.
However, effective treatment will depend on the size of the abscess, how many masses there are, the cause of the abscess, and the patient’s general state of health.
If the abscess is less than an inch across, the patient will probably only receive intravenous administration of an antibiotic, antifungal or antiviral medication.
An abscess that is over an inch across will need to be aspirated, or drained, or cut out.
If there are several abscesses, it may be considered too risky to cut them out. The surgeon will recommend aspiration.
Any primary infection, for example in the lung, abdomen, or nose, will be treated with medication.
Surgery may be needed if pressure in the brain continues to build, if the abscess does not respond to medication, if there is gas in the abscess, or if there is a risk that it might rupture, or burst.
A craniotomy is a procedure in which the surgeon makes an opening in the skull.
First, the surgeon shaves a small area of scalp hair. Then, they remove a small piece of bone, to gain access to the brain.
The abscess can then be drained of pus or removed, possibly with the aid of a CT scan.
After this, the bone is replaced and the skin is stitched.
A short course of high-dose corticosteroids may help if there is increased intracranial pressure.
Anticonvulsants are often used to prevent seizures.
Many people survive a brain abscess, but there may be long-term neurological problems, such as body function issues, personality changes, and seizures.
Between 5 percent and 32 percent of brain abscesses will be fatal, but the sooner treatment is given, the higher the chances of effective treatment and survival.
If an abscess is deeper in the brain, or if there are multiple abscesses, it is harder to treat.
Patients should be monitored, as an abscess can occasionally recur.