BRAIN ABSCESS – Causes and Risk Factors, Pathophysiology, Clinical Manifestations, Diagnostic Evaluations and Management 

BRAIN ABSCESS – Causes and Risk Factors, Pathophysiology, Clinical Manifestations, Diagnostic Evaluations and Management

A brain abscess is a bacterial brain infection. Also called a cerebral abscess, these infections are destructive lesions within the substance of the brain itself. An abscess is a general term for a walled off area of infection which includes the surrounding ring of tissue containing a liquefied center filled with bacteria, white blood cells and fluid. This purulent fluid is also known as puss. In the brain, an abscess can occur if bacteria are introduced into the brain. First leading to cerebritis, a local area of inflamed, infected brain tissue, as the infection grows it destroys brain tissue, leading to liquefaction and the formation of the pus-filled abscess.

CAUSES AND RISK FACTORS

The brain is usually sterile, without bacteria in or around it. But there are a number of things that can introduce bacteria into the brain which can lead to a brain abscess.

• Ear infection
• Dental abscess
  
• Infection of paranasal sinuses
  
• Infection of the mastoid air cells of the temporal bone
  
• Lung, heart, kidney infectious diseases
  
• Penetrating injury or surgery
  

The following raise your risk of a brain abscess:

• A weakened immune system (such as in AIDS patients)
• Chronic disease, such as cancer or Osler-Weber-Rendu syndrome
  
• Drugs that suppress the immune system (corticosteroids or chemotherapy)
  
• Right-to-left heart shunts, usually the result of congenital heart disease
  

Common bacteria involved in brain abscesses include streptococcal and staphylococcal bacteria. Fungi such as candida (which causes thrush) can also cause brain infections if they get into the brain or bloodstream. Although some of these micro-organisms, such as candida, are relatively commonly found in the body, it is rare for them to get into the blood and cause an abscess.

PATHOPHYSIOLOGY

Brain abscess is a serious disorder that occurs when micro-organisms such as bacteria or fungi get into the brain, causing inflammation. The bacteria or fungi, along with infected brain cells and pus, mass together in one area of the brain. They are joined by white blood cells that have been trying to fight the infection. The body’s immune system responds by creating a membrane around this infected portion of the brain

The swelling inside the brain can put pressure on delicate brain tissue and the mass of pus itself can block blood vessels that are supplying essential blood to parts of the brain. If prolonged, this can cause brain damage, because the oxygen supply to these tissues has been disrupted. It is therefore important to treat abscesses as early as possible

Most brain abscesses occur when infection spreads to the brain from elsewhere in the body, mostly from nearby areas such as the ears. They can also be carried in the blood from further away areas of the body. Sometimes they are caused by head injuries or surgery.

 

CLINICAL MANIFESTATIONS

Symptoms may develop slowly, over a period of 2 weeks, or they may develop suddenly. The effects of a brain abscess depend on its position and whether the brain has been squashed and damaged. Symptoms may be rapid or develop slowly over a period of weeks

Headache is usually the first symptoms of brain abscess. This result from raised pressure inside the skull, as the abscess presses on the brain. Abscesses in the lower rear brain (the cerebellum) tend to cause loss of balance, a staggering walk, and neck stiffness. If the abscess is in the frontal lobes of the brain, it may cause loss of memory and reduced attention span, and dysphasia (speech disorders). Abscesses in the temporal lobes at the sides of the brain usually cause partial loss of vision

OTHER SYMPTOMS OF BRAIN ABSCESS

Drowsiness, paralysis, weakness, confusion, loss of sensation, fever and chills, seizures (fits), loss of coordination, vomiting, irritability, decreased movement, loss of muscle function, coma, language difficulties, stiff neck

DIAGNOSTIC EVALUATIONS

In a patient that presents with symptoms suggestive of abscess, a general neurological evaluation generally includes some form of imaging study, such as CT scan and/or MRI scan who contrast, to visualize the abscess. Contrast agents enhance the surrounding ring of the abscess and make the diagnosis fairly straightforward, although some tumors and other infections can mimic a bacterial abscess. Definitive diagnosis usually involves drainage of the abscess, allowing collection of the purulent fluid to be examined microscopically and to be cultured to identify the causative organisms

Other tests

• Blood cultures
  
• Chest and skull X-ray
  
• Complete blood count (CBC)
  
• Electroencephalogram (EEG)
  
• Needle biopsy
  
• Lumbar puncture
  
• Testing for the presence of antibodies to organisms such as Toxoplasma gondii and Taenia solium
  

 

MANAGEMENT

A brain abscess is a medical emergency. Pressure inside the skull may become high enough to be life threatening. Patient will need to stay in the hospital until the condition is stable. Some people may need life support. Medication is the first line of treatment if the abscess is relatively small, there are multiple abscesses, it is deep within the brain, it is accompanied by meningitis, or surgery would be dangerous due to an underlying condition.

A very large dosage of antibiotic medication is injected directly into a vein. Unless a specific bacteria has been identified as the cause, broad spectrum antibodies will be given, such as penicillin, or metronidazole. Alternatively, patient may be treated with several different types of specific antibiotics, and if fungal infection is suspected then antifungal medications will also be given. Intravenous treatment with antibiotics should continue for 3-6 weeks, then another 3 weeks of oral treatment should follow, with close monitoring for the disappearance of any sign of infection. Additional treatment of the source of infection (sinusitis, mastoiditis, endocarditis, etc.) may be indicated.

In some cases, corticosteroid drugs such as dexamethasone are used to ease the swelling and reduce pressure inside the skull, but this is not fully proven to be beneficial, because steroid use can slow the rate at which antibiotic treatments work.

SURGICAL MANAGEMENT

Most brain abscesses require surgical drainage. The abscess is opened surgically and the infectious material is removed and washed out thoroughly. Surgical drainage of the abscess is indicated to accelerate healing and relieve increased intracranial pressure. The surgical procedure used depends on the size and depth of the abscess. The entire abscess may be removed (excised) if it is near the surface and enclosed in a sac.

Needle aspiration guided by CT or MRI scan may be needed for a deep abscess. During this procedure, medications may be injected directly into the mass.