Intracranial Abscess (Brain Abscess)

What an intracranial abscess is

When bacteria, or less often fungi or parasites, reach the brain, they first cause a patch of inflammation called cerebritis. Over 1 to 2 weeks, the body walls off the infection with a capsule, forming an abscess filled with pus. As it grows, it presses on surrounding brain and raises pressure inside the skull.

Types:

Causes and how infection reaches the brain

Spread from nearby infections (about half of cases)

• Sinusitis: especially frontal sinus infections in teenagers and young men; abscesses in the frontal lobe.
• Ear infections and mastoiditis: abscesses in the temporal lobe or cerebellum.
• Dental infections: frontal lobe abscesses.

Spread through the bloodstream

• Infective endocarditis (heart valve infection)
• lung abscesses, bronchiectasis and empyema
• congenital heart disease with right-to-left shunts, especially in children
• injected drug use

These often cause multiple abscesses.

Direct entry

• penetrating head injury or skull fracture
• brain or sinus surgery

Risk factors

• weakened immunity: HIV, organ transplant, chemotherapy, long-term steroids
• diabetes
• congenital heart disease
• untreated ear, sinus or tooth infections

People with weakened immunity are more likely to have abscesses from fungi (such as Aspergillus), Nocardia or the parasite Toxoplasma.

Symptoms

Symptoms often develop over days to 2 weeks:

• headache: the most common symptom, often severe, on one side, and not relieved by usual pain relievers
• fever: present in only about half of people, so its absence does not rule out an abscess
• changes in mental state: confusion, drowsiness, irritability
• focal neurological signs: weakness on one side, numbness, speech problems, vision changes, poor coordination
• seizures
• nausea and vomiting from raised brain pressure
• stiff neck if the abscess ruptures into the brain's fluid spaces

The classic triad of headache, fever and focal deficits is present in only about 1 in 5 patients.

Diagnosis

• MRI with contrast: the best test. It shows a ring-enhancing lesion and special sequences (diffusion-weighted imaging) help distinguish an abscess from a tumor.
• CT scan with contrast if MRI is not immediately available.
• Blood tests and blood cultures: to find the organism.
• Sampling the abscess: needle aspiration through a small hole in the skull, guided by imaging, provides pus for culture and relieves pressure.
• Searching for the source: sinus and dental imaging, echocardiogram for endocarditis, chest imaging, HIV testing.
• Lumbar puncture is usually avoided because of the risk of brain herniation with raised pressure.

Treatment

Antibiotics

Broad-spectrum intravenous antibiotics are started immediately after blood cultures and, where possible, an abscess sample. They are adjusted when the organism is known. Treatment typically lasts 6 to 8 weeks, guided by repeat imaging.

Surgery

• Stereotactic needle aspiration: drains the abscess through a small burr hole. Most abscesses larger than about 2.5 cm, or causing mass effect, are drained.
• Craniotomy and excision: removing the abscess, for multiloculated or fungal abscesses, subdural empyema, or those near the surface.
• Treating the source: sinus or ear surgery, dental extraction, heart valve surgery.

Supportive care

• medicines to prevent or treat seizures
• steroids in some cases to reduce severe brain swelling
• management of raised intracranial pressure
• rehabilitation for any deficits

Complications and outlook

With modern imaging, antibiotics and neurosurgery, death rates have fallen to about 10% or less. Outcome is worse when the person is deeply unconscious at diagnosis, when the abscess ruptures into the ventricles, or with fungal abscesses in immunocompromised people. Survivors may have:

• epilepsy (in roughly a third)
• weakness, speech or cognitive problems
• hydrocephalus

Prevention

• prompt treatment of ear, sinus and dental infections
• good dental hygiene
• antibiotic prophylaxis before dental procedures for people at high risk of endocarditis, as advised by a cardiologist
• safe injection practices and treatment of substance use

Frequently asked questions

What are the symptoms of a brain abscess?

The most common symptom is a worsening headache. Others include fever, confusion, drowsiness, seizures, nausea and vomiting, and weakness, numbness or speech problems on one side of the body. Fever is absent in about half of patients.

What causes an intracranial abscess?

Most come from infections that spread from the sinuses, middle ear or teeth, or travel through the blood from the heart valves or lungs. Head injuries and brain surgery can also introduce bacteria. Weakened immunity raises the risk.

How is a brain abscess treated?

Treatment involves several weeks of intravenous antibiotics, usually 6 to 8, plus surgical drainage or removal of the abscess in many cases. The source of infection, such as a sinus or dental infection, is also treated. Seizure medicines are often given.

Can you survive a brain abscess?

Yes. With prompt diagnosis, antibiotics and surgery, most people survive. Some have lasting effects such as seizures, weakness or memory problems. Outcomes are best when treatment starts before the person becomes severely drowsy or unconscious.

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

Hospital treatment usually lasts several weeks, followed by weeks to months of recovery and rehabilitation. Many people return to normal activities within a few months. Driving restrictions may apply if seizures have occurred.