Merck Manual

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Abscess of the Brain


John E. Greenlee

, MD, University of Utah Health

Reviewed/Revised Mar 2022 | Modified Sep 2022

A brain abscess is a pocket of pus in the brain.

  • An abscess may form in the brain when bacteria from an infection elsewhere in the head or in the bloodstream or from a wound enter the brain.

  • Headache, sleepiness, nausea, weakness on one side of the body, or seizures may result.

  • Imaging of the head is required.

  • Antibiotics are given, usually followed by drainage of the abscess with a needle or surgery to remove it.

Brain abscesses are fairly uncommon.

Fluid collects in the tissue around a brain abscess. As a result, the surrounding brain tissue swells, and pressure within the skull increases. The larger the abscess, the greater the swelling and the pressure. If the abscess leaks or breaks and pus enters the cerebrospinal fluid (which flows through the tissues that cover the brain and spinal cord), acute meningitis results.

Causes of a Brain Abscess

Brain abscesses can result from

  • An infection that spreads from somewhere else in the head (such as a tooth, the nose, or an ear)

  • An infection that spreads from another part of the body through the bloodstream to the brain

  • Bacteria that enter after a head wound that penetrates the brain, including incisions that are made during brain surgery

Sometimes the cause is unknown.

Many types of bacteria, including Streptococcus bacteria Streptococcal Infections Streptococcal infections are caused by any one of several species of Streptococcus. These gram-positive, sphere-shaped (coccal) bacteria (see figure ) cause many disorders, including... read more , Staphylococcus aureus Staphylococcus aureus Infections Staphylococcus aureus is the most dangerous of all of the many common staphylococcal bacteria. These gram-positive, sphere-shaped (coccal) bacteria (see figure ) often cause skin infections... read more <i >Staphylococcus aureus</i> Infections , and Bacteroides fragilis, can cause a brain abscess. The protozoa Toxoplasma gondii (which causes toxoplasmosis Toxoplasmosis Toxoplasmosis is infection caused by the protozoan parasite Toxoplasma gondii. Infection occurs when people unknowingly ingest toxoplasma cysts from cat feces or eat contaminated meat... read more ) and fungi, such as aspergilli Aspergillosis Aspergillosis is an infection, usually of the lungs, caused by the fungus Aspergillus. A ball of fungus fibers, blood clots, and white blood cells may form in the lungs or sinuses. People... read more , are common causes of brain abscesses in people who have a weakened immune system. The immune system may be weakened by disorders such as human immunodeficiency virus (HIV) infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more Human Immunodeficiency Virus (HIV) Infection , which leads to AIDS, or by drugs that suppress the immune system (immunosuppressants). Immunosuppressants Suppression of the Immune System Transplantation is the removal of living, functioning cells, tissues, or organs from the body and then their transfer back into the same body or into a different body. The most common type of... read more may be used to prevent rejection of a transplanted organ or to treat cancer or autoimmune disorders Autoimmune Disorders An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues. What triggers an autoimmune disorder is not known. Symptoms vary depending... read more .

Symptoms of a Brain Abscess

A brain abscess can cause many different symptoms, depending on its location, its size, and the extent of inflammation and swelling around the abscess.

A fever and chills may occur at first but then disappear.

People with a brain abscess may have a headache, feel nauseated, vomit, become unusually drowsy, and then lapse into coma (which often occurs when pressure within the brain continues to increase). Seizures may occur, one side of the body may become weak, or thinking may be impaired. Symptoms can develop over days or weeks. However, in some people, fever and chills are mild, do not occur until late in the infection, or do not occur at all.

Diagnosis of a Brain Abscess

  • Magnetic resonance imaging or computed tomography

  • Withdrawal and testing of a sample of pus from the abscess

If doctors suspect a brain abscess, magnetic resonance imaging (MRI) is done before and after gadolinium is injected intravenously. Gadolinium (an MRI contrast agent) makes abscesses easier to see on MRI scans. If MRI is unavailable, computed tomography (CT) can be done after a radiopaque contrast agent (which makes abscesses easier to see on CT scans) is injected intravenously. MRI has higher resolution and can show early abnormalities better than CT. However, additional tests may be needed to establish the diagnosis because a brain tumor or damage due to a stroke or multiple sclerosis can resemble a brain abscess.

To identify the causative organism and thus determine which drugs would be most effective, doctors withdraw a sample of pus from the abscess with a needle. It is examined under a microscope and sent to a laboratory to grow (culture) bacteria in the fluid so that they can be identified. MRI or CT is used to guide the needle into the abscess. For this procedure (called stereotactic needle aspiration), a frame is attached to the skull. The frame provides reference points that can be identified on the MRI or CT scan. Thus, after drilling a small hole through the skull, doctors can guide the needle precisely into the abscess.

However, doctors do not wait to get the result of culture to start treatment.

Treatment of a Brain Abscess

  • Antibiotics

  • Usually, drainage of the pus with a needle or surgery to remove the abscess

  • Sometimes drugs to reduce swelling and pressure

A brain abscess is fatal unless treated with antibiotics and possibly surgery. The most commonly used antibiotics are

  • Cephalosporins (such as cefotaxime or ceftriaxone)

  • Vancomycin (or nafcillin)

  • Metronidazole

These antibiotics may be used together until doctors determine which specific antibiotic is most effective against the organism causing the abscess. Antibiotics are usually given for 4 to 8 weeks, and MRI or CT is repeated every 2 weeks or more frequently to monitor the response to treatment.

For large abscesses and abscesses that become larger despite antibiotic treatment, a surgeon drains the abscess with a needle (using stereotactic techniques to guide placement of the needle) or does open surgery to remove the entire abscess.

Recovery may be quick or slow depending on

  • How successful surgery is

  • How many abscesses are present

  • How well the person’s immune system is functioning

If people with a weakened immune system have an abscess due to Toxoplasma gondii or a fungus, they may have to take antibiotics for the rest of their life.

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

Antiseizure drugs may be given to prevent seizures.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Ceftrisol Plus, Rocephin
FIRVANQ, Vancocin, Vancocin Powder, VANCOSOL
Flagyl, Flagyl ER, Flagyl RTU, LIKMEZ, MetroCream, MetroGel, MetroGel Vaginal, MetroLotion, Noritate, NUVESSA, Nydamax, Rosadan, Rozex, Vandazole, Vitazol
AK-Dex, Baycadron, Dalalone, Dalalone D.P, Dalalone L.A, Decadron, Decadron-LA, Dexabliss, Dexacort PH Turbinaire, Dexacort Respihaler, DexPak Jr TaperPak, DexPak TaperPak, Dextenza, DEXYCU, DoubleDex, Dxevo, Hemady, HiDex, Maxidex, Ocu-Dex , Ozurdex, ReadySharp Dexamethasone, Simplist Dexamethasone, Solurex, TaperDex, ZCORT, Zema-Pak, ZoDex, ZonaCort 11 Day, ZonaCort 7 Day
Aridol, BRONCHITOL, Osmitrol , Resectisol
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