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.
A brain abscess can result from
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.
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).
All patients receive antibiotics for ≥ 4 to 8 wk. Initial empiric antibiotics include cefotaxime 2 g IV q 4 h or ceftriaxone 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, metronidazole 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, vancomycin 1 g q 12 h is used (with cefotaxime or ceftriaxone) until sensitivity to nafcillin (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 (dexamethasone 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 November 2012 by John E. Greenlee, MD
Content last modified December 2012