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. 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 in chronic 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 at presentation or subside over time.

Diagnosis

• Contrast-enhanced MRI or, if unavailable, contrast-enhanced CT

When symptoms suggest an abscess, contrast-enhanced MRI or, if unavailable, contrast-enhanced CT is done. A fully developed 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. Culture results help direct antibiotic therapy. 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
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  or ceftriaxoneSome Trade Names
  ROCEPHIN
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  , plus metronidazoleSome Trade Names
  FLAGYL
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  for Bacteroides sp or vancomycinSome Trade Names
  VANCOCIN
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  for Staphylococcus aureus based on suspicion, then as guided by culture and susceptibility testing)
• Usually CT-guided stereotactic aspiration or surgical drainage
• Sometimes corticosteroids, anticonvulsants, or both

All patients receive antibiotics for ≥ 4 to 8 wk. Initial empiric antibiotics include cefotaximeSome Trade Names
CLAFORAN
Click for Drug Monograph
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. If clinicians at all suspect Bacteroides sp, metronidazoleSome Trade Names
FLAGYL
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15 mg/kg (loading dose) followed by 7.5 mg/kg IV q 6 h is also required. If S. aureus is at all suspected, vancomycinSome Trade Names
VANCOCIN
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1 g q 12 h is used (with cefotaximeSome Trade Names
CLAFORAN
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or ceftriaxoneSome Trade Names
ROCEPHIN
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) 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 MRI or CT.

Drainage (CT-guided stereotactic or open) provides optimal therapy and is necessary for most abscesses that are solitary and surgically accessible, particularly those > 2 cm in diameter. If abscesses are < 2 cm in diameter, antibiotics alone may be tried, but abscesses must then be monitored with serial MRI or CT; if abscesses enlarge after being treated with antibiotics, surgical drainage is indicated.

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.

Key Points

• Brain abscess can result from direct extension (eg, of mastoiditis, osteomyelitis, sinusitis, or subdural empyema), penetrating wounds (including neurosurgery), or hematogenous spread.
• Headache, nausea, vomiting, lethargy, seizures, personality changes, papilledema, and focal neurologic deficits develop over days to weeks; fever may be absent at presentation.
• Do contrast-enhanced MRI or, if unavailable, contrast-enhanced CT.
• Treat all brain abscesses with antibiotics (usually initially with ceftriaxoneSome Trade Names
  ROCEPHIN
  Click for Drug Monograph
  or cefotaximeSome Trade Names
  CLAFORAN
  Click for Drug Monograph
  plus metronidazoleSome Trade Names
  FLAGYL
  Click for Drug Monograph
  if clinicians at all suspect Bacteroides sp or vancomycinSome Trade Names
  VANCOCIN
  Click for Drug Monograph
  if they suspect S. aureus ), typically followed by CT-guided stereotactic aspiration or surgical drainage.
• If abscesses are < 2 cm in diameter, they may be treated with antibiotics alone but must then be monitored periodically with MRI or CT; if abscesses enlarge after being treated with antibiotics, surgical drainage is indicated.

Last full review/revision November 2012 by John E. Greenlee, MD

Content last modified December 2012