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A brain abscess is an intracerebral collection of pus. Symptoms may include headache, lethargy, fever, and focal neurologic deficits. Diagnosis is by contrast-enhanced MRI or CT and sometimes culture. Treatment is with antibiotics and usually surgical drainage.

An abscess forms when an area of cerebral inflammation becomes necrotic and encapsulated by glial cells and fibroblasts. Edema around the abscess may increase intracranial pressure.

Etiology

A brain abscess can result from

• Direct extension of cranial infections (eg, osteomyelitis, mastoiditis, sinusitis, subdural empyema)
• Penetrating head wounds (including neurosurgical procedures)
• Hematogenous spread (eg, in bacterial endocarditis, congenital heart disease with right-to-left shunt, or IV drug abuse)
• Unknown causes

The bacteria involved are usually anaerobic and sometimes mixed, often including anaerobic streptococci or Bacteroides. Staphylococci are common after cranial trauma, neurosurgery, or endocarditis. Enterobacteriaceae are common with ear infections. Fungi (eg, Aspergillus) and protozoa (eg, Toxoplasma gondii, particularly in HIV-infected patients) can cause abscesses.

Symptoms and Signs

Symptoms result from increased intracranial pressure and mass effect. Headache, nausea, vomiting, lethargy, seizures, personality changes, papilledema, and focal neurologic deficits develop over days to weeks. Fever, chills, and leukocytosis may develop before the infection is encapsulated, but they may be absent or subside over time.

Diagnosis

• MRI
• Sometimes CT-guided aspiration

When symptoms suggest an abscess, contrast-enhanced MRI or CT is done. An abscess appears as an edematous mass with ring enhancement, which may be difficult to distinguish from a tumor or occasionally infarction; CT-guided aspiration, culture, surgical excision, or a combination may be necessary. Lumbar puncture is not done because it may precipitate transtentorial herniation and because CSF findings are nonspecific (see Table 1: Approach to the Neurologic Patient: Cerebrospinal Fluid Abnormalities in Various Disorders).

Brain Abscess (CT Without Contrast)

Brain Abscess (CT With Contrast)

Treatment

• Antibiotics (initially cefotaximeSome Trade Names
  CLAFORAN
  Click for Drug Monograph
  or ceftriaxoneSome Trade Names
  ROCEPHIN
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  , then as guided by culture and susceptibility testing)
• Usually surgical drainage
• Sometimes corticosteroids, anticonvulsants, or both

All patients receive antibiotics for ≥ 4 to 8 wk. Initial empiric antibiotics include cefotaximeSome Trade Names
CLAFORAN
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2 g IV q 4 h or ceftriaxoneSome Trade Names
ROCEPHIN
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2 g IV q 12 h; both are effective against streptococci, Enterobacteriaceae, and most anaerobes but not against Bacteroides fragilis, which requires metronidazoleSome Trade Names
FLAGYL
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15 mg/kg (loading dose), then 7.5 mg/kg IV q 6 h. If Staphylococcus aureus is suspected, vancomycinSome Trade Names
VANCOCIN
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1 g q 12 h is used until sensitivity to nafcillinSome Trade Names
UNIPEN
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(2 g q 4 h) is determined. Response to antibiotics is best monitored by serial CT or MRI.

Drainage, stereotactic or open, provides optimal therapy and is necessary for most abscesses that are solitary and surgically accessible, particularly those > 2 cm in diameter.

Patients with increased intracranial pressure may benefit from a short course of high-dose corticosteroids (dexamethasoneSome Trade Names
DECADRON
DEXASONE
HEXADROL
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10 mg IV once, then 4 mg IV q 6 h for 3 or 4 days). Anticonvulsants are sometimes recommended to prevent seizures.

Last full review/revision December 2009 by Michael Jacewicz, MD

Content last modified December 2009