Brain Abscess

How a brain abscess forms

Germs infect a small area of the brain, causing local inflammation (cerebritis). Over 1 to 2 weeks the body walls it off with a capsule, forming an abscess. As it grows, it acts like a mass, pressing on the surrounding brain and raising pressure inside the skull. Swelling (edema) around it adds to the pressure.

Causes and risk factors

Spread from nearby infection

• Sinusitis: frontal sinus infection can spread to the frontal lobe.
• Middle ear infection and mastoiditis: can spread to the temporal lobe or cerebellum.
• Dental abscess and dental procedures.

Spread through the bloodstream

• Endocarditis (infected heart valves), lung abscesses and bronchiectasis.
• Congenital heart disease with a right-to-left shunt, which lets germs bypass the lungs' filter.
• Hereditary hemorrhagic telangiectasia with lung blood vessel malformations.
• Bloodstream spread often causes several abscesses.

Direct entry

• penetrating head injury or skull fracture
• brain surgery or neurosurgical devices

Weakened immune system

People with HIV, organ transplants, chemotherapy or long-term steroids can develop abscesses from unusual germs, such as toxoplasmosis, Nocardia, Aspergillus or tuberculosis.

In up to a quarter of cases, no source is found.

Symptoms

Symptoms usually develop over days to two weeks:

• Headache: the most common symptom, often on one side, steadily worsening and poorly relieved by painkillers
• Fever: present in only about half, so its absence does not rule out an abscess
• Focal neurological signs: weakness on one side, speech difficulty, vision loss, poor balance
• Seizures
• Confusion, drowsiness, personality change
• Nausea and vomiting from raised pressure
• Stiff neck if the abscess leaks into the spinal fluid

The classic trio of headache, fever and a focal neurological deficit is present in only a minority of patients.

Diagnosis

• MRI with contrast: the best test. It shows a ring-enhancing lesion, and diffusion-weighted imaging helps distinguish an abscess from a brain tumor.
• CT scan with contrast: faster, used in emergencies.
• Blood tests and blood cultures.
• Aspiration of pus: a neurosurgeon draws out pus through a small hole in the skull, both for treatment and to identify the germ.
• Search for the source: sinus and dental imaging, echocardiogram, chest imaging.
• Lumbar puncture is usually avoided because raised pressure makes it risky.

Treatment

Antibiotics

Broad-spectrum intravenous antibiotics that reach the brain are started as soon as samples are taken, then tailored to the germ. Treatment typically lasts 6 to 8 weeks, sometimes partly as oral antibiotics after the first weeks.

Surgery

• Stereotactic needle aspiration: drains pus through a small burr hole, guided by imaging. Used for most abscesses larger than about 2.5 cm.
• Open surgery (craniotomy): for large, multi-chambered abscesses, those caused by fungi, or near the brain's ventricles, or when aspiration fails.
• Small abscesses or multiple deep ones may be treated with antibiotics alone, with close scan monitoring.

Other treatment

• Anti-seizure medicines.
• Steroids for severe brain swelling, used short term.
• Treating the source: sinus surgery, dental extraction, heart valve treatment.

Complications

• abscess rupture into the ventricles, which carries a high risk of death
• brain herniation from raised pressure
• meningitis
• epilepsy, which develops in a significant minority of survivors
• lasting weakness, speech or memory problems

Outlook

Survival has improved greatly with MRI and modern antibiotics, and most patients now survive. Outcomes are best when treated before consciousness is impaired. Many survivors return to normal life, though some have lasting seizures or neurological problems and need rehabilitation. Follow-up scans confirm the abscess has resolved. For a closely related overview, see intracranial abscess.

Prevention

• Treat sinus, ear and dental infections promptly and completely.
• People with certain heart conditions may need antibiotics before some dental procedures, as advised by their cardiologist.
• Good care of chronic conditions that weaken immunity.

Frequently asked questions

What are the first signs of a brain abscess?

The earliest and most common sign is a headache that gets steadily worse over days. Fever, nausea, confusion, weakness on one side, speech or vision problems, and seizures may follow. Many people do not have a fever, so a worsening headache with neurological symptoms always needs urgent assessment.

What causes a brain abscess?

Most are caused by bacteria spreading from a nearby infection in the sinuses, ears or teeth, or traveling through the blood from infections such as endocarditis. Head injuries and brain surgery are other causes. People with weakened immune systems can develop fungal or parasitic abscesses.

Can a brain abscess be cured?

Yes. Most brain abscesses are cured with several weeks of antibiotics, usually combined with drainage. Early treatment improves the chances of full recovery. Some people are left with seizures or other neurological effects.

How long does it take to recover from a brain abscess?

Antibiotic treatment usually lasts 6 to 8 weeks, and the abscess shrinks gradually on follow-up scans. Many people return to normal activities within a few months, while those with neurological effects may need longer rehabilitation.

Is a brain abscess contagious?

No. The abscess itself does not spread between people. However, the germs that caused the original sinus, ear or dental infection may be passed on in the usual ways, without causing brain abscesses in others.