Brain abscess

Definition

A brain abscess is a mass of immune cells, pus, and other material that can occur when the brain is infected by bacteria or fungus.

Causes, incidence, and risk factors

Brain abscesses commonly occur when bacteria or fungi infect part of the brain. Inflammation develops in response. Infected brain cells, white blood cells, and live and dead microorganisms collect in a limited area of the brain. This area becomes enclosed by a membrane that forms around it and creates a mass.

While this immune response can protect the brain by isolating the infection, it can also do more harm than good. The brain swells in response to the inflammation, and the mass may put pressure on delicate brain tissue.

Infected material can block the blood vessels of the brain, further damaging tissues by causing cell death and swelling of additional cells. Multiple abscesses are uncommon except in immunocompromised patients.

The bacteria or fungi can reach the brain through the blood, by traveling from a neighboring infected area, or by direct contamination from an injury or surgery. Most commonly, the infectious organism reaches the brain via the bloodstream. The source of the infectious organism is often not found. When identified, the most common source is a lung infection.

In children with congenital heart disease or defect, such as those born with Tetralogy of Fallot, infections are more able to reach the brain from other sources (such as the intestines or teeth). Also, individuals with Osler-Weber-Rendu syndrome and similar conditions are prone to developing brain abscesses.

A brain abscess can develop by direct extension from an adjacent infected area. For example, infections of the middle ear and mastoid sinuses can spread to the brain.

A brain abscess can develop following a penetrating trauma through the skull, such as a gun or knife wound. This risk of infection is higher if fragments and dead tissue are left behind, and if antibiotic therapy is not started immediately. Surgery, especially when the air sinuses were opened or a foreign body was left in the brain (intracranial pressure monitor, stimulating electrode), can result in an infection.

Symptoms may develop gradually or suddenly. There may be little or no sign of general infection throughout the body. Early symptoms are usually headache, muscle weakness, visual changes, difficulty with balance or coordination, or seizures.

People at higher risk of developing a brain abscess include those with right-to-left heart shunts, a chronic debilitating illness like cancer, who are immunocompromised (such as AIDS patients) and those taking immunosuppressants (corticosteroids).

Symptoms

• Headache
• Stiff neck, shoulders, or back
• Aching of neck, shoulders, or back
• Vomiting
• Changes in mental status
  • Drowsiness
  • Confusion
  • Inattention
  • Irritability
  • Slow thought processes
  • Decreasing responsiveness
  • Eventual coma
• Seizures
• Fever and chills
• Localized loss of nerve functions (focal neurologic deficits)
  • Vision changes
  • Muscle function/feeling loss
  • Decreased sensation
  • Decreased movement
  • Weakness
  • Decreased speech (aphasia)
  • Other language difficulties
  • Loss of coordination

Note: Symptoms may develop gradually, over a period of 2 weeks, or they may develop suddenly. Once symptoms occur, they progressively worsen.

Signs and tests

A neurologic examination will usually reveal increased intracranial pressure and problems with brain function causing confusion or other problems. The problems will relate to the area of the brain where the abscess is located. The physician will look for the possible source of the infection.

• CBC may indicate infection or inflammation.
• Blood cultures should be done but usually do not help identify the infecting organism.
• Chest X-ray will reveal lung infections (one of the more common sources of infection).
• EEG may be abnormal if seizures or focal neurologic deficits are present.
• Cranial CT scan or MRI of head shows the abscess and its exact location.

Treatment

Cerebral abscess is a medical emergency. Intracranial pressure may become high enough to cause death. Hospitalization is required until the condition is stabilized.

Life support may be required in some cases.

Medication, not surgery, is advised for multiple abscesses, a small abscess (less than 2 cm), an abscess deep within the brain, an abscess accompanied by meningitis, the presence of shunts in the brain (for hydrocephalus), or an underlying disease that makes surgery dangerous (debilitating disease). A needle biopsy is usually performed to identify the infecting organism.

Antimicrobials are given, initially through a vein, then by mouth. Antibiotics that work against a number of different bacteria (broad spectrum antibiotics) are the most common antimicrobial prescribed. It is not uncommon for multiple antibiotic medications to be used to ensure effective treatment. Antifungal medications may also be prescribed if fungal infection is likely.

An abscess that is injuring brain tissue by pressing on it or a large abscess with a high degree of swelling around it can raise intracranial pressure to the point where immediate treatment is needed.

Surgery is required if there is persistent or progressive increase in intracranial pressure, if the mass does not reduce after use of antimicrobial medications, or if the mass contains gas (produced by some types of bacteria). Surgery may also be needed if there are signs of impending rupture of the abscess into the fluid-containing system of the brain (the ventricles).

Surgery consists of opening and draining the abscess and is usually accompanied by cultures of the fluid. This allows antimicrobial treatment to be adjusted to the specific microorganism causing the infection. The specific surgical procedure depends on the size and depth of the mass. The entire mass may be removed (excised) if it is near the surface and completely encapsulated (surrounded by a membrane).

Needle aspiration guided by CT scan or MRI scan may be needed for a deep abscess. This may also include injecting antimicrobials directly into the mass.

Osmotic diuretics and steroids may also be used to reduce swelling of the brain.

Expectations (prognosis)

If untreated, the disorder is almost always fatal. The outcome is usually improved with the use of CT and MRI scans for accurate diagnosis and by the administration of broad-spectrum antimicrobials.

The death rate is around 10% with treatment. Neurologic changes may be chronic or may resolve over time. Seizures or neurologic losses (inability to move, speak, see) may occur after surgery.

Complications

• Meningitis, severe and life threatening
• Epilepsy
• Permanent neurologic losses (vision, speech, movement)
• Recurrence of infection

Calling your health care provider

Go to the emergency room or call the local emergency number (such as 911) if symptoms suggestive of brain abscess occur. Cerebral abscess is a medical emergency!

Prevention

The risk of developing a cerebral abscess may be reduced by treating any disorders that can cause them. Such treatment should include a follow-up examination after infections are treated.

Preventive antibiotics given for people with congenital or rheumatic heart disorders prior to dental or urologic procedures may reduce the risk.

Illustrations

Amebic brain abscess

Page Content:

Abscess - brain; Cerebral abscess; CNS abscess ; cerebral abscess