Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 89. Infections of the Brain and Spinal Cord

Topics: Introduction | Acute Bacterial Meningitis | Chronic Meningitis | Viral Infections | Brain Abscess | Subdural Empyema | Parasitic Infections

Brain Abscess

A brain abscess is a localized collection of pus in the brain.

Brain abscesses are fairly uncommon. They can result from the spread of an infection somewhere else in the head (such as in a tooth, in the nose, or in an ear), from a head wound that penetrates the brain, or from an infection in another part of the body that spreads through the bloodstream. Many types of bacteria, including Staphylococcus aureus and Bacteroides fragilis, can cause a brain abscess. Toxoplasma gondii (see Section 17, Chapter 196), a protozoan, is a common cause of brain abscess in people who have AIDS.

A brain abscess causes the surrounding brain tissue to swell and causes pressure to increase within the skull. The larger the abscess, the greater the swelling and the pressure.

Symptoms and Diagnosis

A brain abscess can cause many different symptoms, depending on its location, its size, and the extent of inflammation and swelling around the abscess. Symptoms include headache, nausea, vomiting, sleepiness, seizures, personality changes, and other signs of brain dysfunction. These symptoms can develop over days or weeks. A fever and chills may occur at first but then disappear as the body fights off the infection.

The best procedure for diagnosing a suspected brain abscess is computed tomography (CT) or magnetic resonance imaging (MRI). CT or MRI readily shows the abnormality. However, a brain tumor or damage from a stroke can resemble an abscess, and additional procedures may be needed to establish the diagnosis. A specialized form of MRI called MRI spectroscopy enables doctors to distinguish between the dead debris inside an abscess and the multiplying cells inside a tumor.

Sometimes a biopsy of brain tissue (in which a tissue sample is removed for examination under a microscope) is necessary. The biopsy may be performed using CT to guide the placement of the needle. In this procedure (called a stereotactic biopsy), a metal imaging frame is attached to the person's skull. Attached to the frame are a series of rods that appear as dots on the CT scan. The frame and rods act as reference points for the placement of a biopsy needle. Also, a sample of the pus may be removed for examination under a microscope and for culture.

Treatment

A brain abscess may be fatal unless treated with antibiotics and possibly surgery. Those most commonly used are penicillin, metronidazole, nafcillin, and cephalosporins, such as ceftizoxime. An antibiotic is usually given for 4 to 6 weeks, and CT or MRI is repeated every 2 weeks to monitor the response to treatment. If the abscess does not shrink, a surgeon may have to drain the abscess with a needle (using stereotactic techniques to guide placement of the needle) or perform open surgery to remove the entire abscess. Recovery may be quick or slow depending on how successful surgery is, how many abscesses are present, and how well the person's immune system is functioning. People who have an abscess due to Toxoplasma gondii and an impaired immune system must take antibiotics for the rest of their life.

Doctors treat the swelling and increased pressure within the skull due to a brain abscess aggressively, because these effects can permanently damage the brain. Corticosteroids, such as dexamethasone, and other drugs that reduce swelling and pressure (such as mannitol) may be used.