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Information ⬇

[Section Outline]

A focal, suppurative infection within the brain parenchyma, typically surrounded by a vascularized capsule. The term cerebritis is used to describe a nonencapsulated brain abscess. Predisposing conditions include otitis media and mastoiditis, paranasal sinusitis, pyogenic infections in the chest or other body sites, head trauma, neurosurgical procedures, and dental infections. Many brain abscesses occur in immunocompromised hosts and are caused less often by bacteria than by fungi and parasites including Toxoplasma gondii, Aspergillus spp., Nocardia spp., Candida spp., and Cryptococcus neoformans. In Latin America, the most common cause of brain abscess is Taenia solium (neurocysticercosis). In India and the Far East, mycobacterial infection (tuberculoma) remains a major cause of focal CNS mass lesions.

Clinical Features !!navigator!!

Brain abscess typically presents as an expanding intracranial mass lesion, rather than as an infectious process. The classic triad of headache, fever, and a focal neurologic deficit is present in <50% of cases.

Diagnosis !!navigator!!

MRI is superior to CT for demonstrating abscesses in the early (cerebritis) stages and also for abscesses in the posterior fossa. A mature brain abscess appears on CT as a focal area of hypodensity surrounded by ring enhancement. The CT and MRI appearance, particularly of the capsule, may be altered by treatment with glucocorticoids. The distinction between a brain abscess and other focal lesions such as tumors may be facilitated with diffusion-weighted imaging (DWI) sequences in which brain abscesses typically show increased signal due to restricted diffusion.

Microbiologic diagnosis best determined by Gram's stain and culture of abscess material obtained by stereotactic needle aspiration. Up to 10% of pts will also have positive blood cultures. CSF analysis contributes nothing to diagnosis or therapy, and LP increases the risk of herniation.

TREATMENT

Brain Abscess

  • Optimal therapy involves a combination of high-dose parenteral antibiotics and neurosurgical drainage.
  • Empirical therapy of community-acquired brain abscess in an immunocompetent pt typically includes a third- or fourth-generation cephalosporin (e.g., cefotaxime, ceftriaxone, or cefepime) and metronidazole (see Table 194-2 Antibiotics Used in Empirical Therapy of Bacterial Meningitis and Focal Central Nervous System Infectionsa for antibiotic dosages).
  • In pts with penetrating head trauma or recent neurosurgical procedures, treatment should include ceftazidime to enhance coverage of Pseudomonas spp. and vancomycin for coverage of resistant staphylococci. Meropenem plus vancomycin also provides good coverage in this setting.
  • Aspiration and drainage essential in most cases. Empirical antibiotic coverage is modified based on the results of Gram's stain and culture of the abscess contents.
  • Medical therapy alone is reserved for pts whose abscesses are neurosurgically inaccessible and for pts with small (<2-3 cm) or nonencapsulated abscesses (cerebritis).
  • All pts should receive a minimum of 6-8 weeks of parenteral antibiotic therapy.
  • Pts should receive prophylactic anticonvulsant therapy.
  • Glucocorticoids should not be given routinely.
  • Serial MRI or CT scans should be obtained on a monthly or twice-monthly basis to document resolution of the abscess.

Prognosis !!navigator!!

In modern series, the mortality is typically <15%. Significant sequelae including seizures, persisting weakness, aphasia, or mental impairment occur in ≥20% of survivors.

Outline ⬆

Section 14. Neurology