A brain abscess, also known as a cerebral abscess or CNS abscess, is an abscess within the brain tissue caused by inflammation and collection of immune cells and infected material originating from local or remote infection sources.
A brain abscess is a rare, life-threatening infection of the brain. Local sources may include ear infections, a dental abscess, infection of the paranasal sinuses, or epidural abscess, while remote sources may include infections in the lung, heart or kidney.
A brain abscess may also be the result of a head trauma or surgical procedure.
In children cerebral abscesses are usually linked to congenital heart disease.
How is a brain abscess caused?
When the bacteria, fungi or parasite infect part of the brain, inflammation (swelling) occurs. Infected brain cells, immune cells (white blood cells), live and dead organisms (fungi, bacteria, parasites) accumulate, a membrane forms around the area, creating a mass.
Our immune system creates the membrane to isolate the infection; however, sometimes our defense mechanism does more harm than good.
If the mass (abscess) swells it places increasing pressure on brain tissue. The skull is not flexible; it does not expand. The mass can block blood vessels to the brain, resulting in the possible destruction of delicate brain tissue.
Put simply:
- Our immune system realizes it cannot overcome the infection.
- It tries to curb its spread by forming a wall (membrane) around the source of infection, creating an abscess.
- It does this (create an abscess) in order to stop the pus from infecting healthy tissue.
- As the abscess grows it places pressure in delicate brain tissue, and sometimes blocks the supply of oxygen-rich-blood to that part of the brain.
- Delicate brain tissue can become damaged or destroyed.
Sometimes an infection can get through the blood-brain barrier and infect the brain. Experts are not entirely sure why this happens. The infection enters the brain from three main routes:
The bloodstream (blood borne infections) – account for about 25% of cases. 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 come from a primary lesion somewhere else in the body. Locating that primary lesion is crucial, otherwise there is an increased risk of a relapse.
People with 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 six months
- Patients receiving chemotherapy
- Individuals on long-term steroid use
- Organ transplant recipients who take immunosuppressant drugs to prevent organ rejection.
The most common blood-borne infections known to cause a brain abscess are:
- Cyanotic heart disease – a heart defect, present at birth (congenital), that results in low blood oxygen levels.
- Pneumonia, bronchiectasis and other lung infections and conditions. Bronchiectasis is the permanent widening (dilatation) of the large air tubes which begin at the bottom of the trachea and branch into the lungs (bronchi) – it can result in recurrent respiratory infections, as well as other serious illnesses.
- Peritonitis – inflammation of the tissue layer of cells lining the inner wall of the abdomen and pelvis (peritoneum); and other abdominal infections.
- Cystitis – inflammation of the bladder; and other infections located in the pelvis
Direct contagion – account for between 45% and 50% of brain abscesses. The infection starts off inside the skull, perhaps in the nose or ear and spreads into the brain. Examples include otitis media (middle ear infection), sinusitis, or mastoiditis (infection of the bone behind the eye). The National Health Service (NHS), UK, stresses that the risk of a brain abscess developing as a result of direct contagion is about 1 in 10,000 (tiny risk).
Direct trauma – account for about 10% of brain abscesses. A head trauma, in which a compound skull fracture may push fragments of bone into the brain, can also cause a brain abscess. In such cases identifying the cause is relatively easy. A bullet or some other foreign body which is left in place may also be a source of infection. In extremely rare cases a brain abscess may be a complication of surgery.
The location of the abscess may help the doctor identify where the primary lesion is (where the original infection is):
- Middle-ear infection may result in lesions in the middle and posterior cranial fossae
- Congenital heart disease with right-to-left shunts may result in abscesses in the distribution of the middle cerebral artery
- Frontal and ethmoid sinus infections often result in abscesses in the subdural sinuses
The most common signs and symptoms include:
- Headache
- Changes in mental status, which may include:
– Confusion
– Drowsiness
– Irritability
– Poor mental focus
– Poor responsiveness
– Slow thought processes - Muscle weakness
- Hemiparesis – weakness, paralysis on one side of the body
- Aphasia – poor speech, for example slurred speech
- Coordination becomes poorer
- Nausea and/or vomiting
- Fever, chills
- Fits (seizures)
- Stiff neck, back or shoulders
- Blurred, double or graying vision if the abscess presses on the optic nerve
The signs and symptoms are caused by a combination of increased intracranial pressure as the abscess occupies more space, infection and focal neurologic brain tissue damage.
Treatment for a brain abscess, also called a cerebral abscess, depends on several factors, including how big it is, how many there are, what caused it, and the patient’s general state of health.
Source: Medical News, 04-16-2010
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