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  • Direct extension from a local infection: ear infection, dental abscess, infection of paranasal sinuses or mastoid air cells, epidural abscess
  • Direct inoculation: head trauma or surgical procedures
  • Remote or hematogenous spread: bacteremia, endocarditis, and congenital heart disease

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  • Bacterial: often polymicrobial; gram-negative and gram-positive: Staphylococcus, Streptococci, Bacteroides, Prevotella, Fusobacterium, Enterobacteriaceae, Pseudomonas species, and anaerobes. Less common: Haemophillus influenzae, Streptococcus pneumoniae, and Neisseria meningitides; Nocardia in immunosuppressed hosts
  • Mycobacterial (M tuberculosis, Mycobacterium avium intracellulare)
  • Protozoan (Toxoplasma gondii, Entamoeba histolytica, Trypanosoma cruzi, Schistosoma, Paragonimus)
  • Helminths (Taenia solium)
  • Fungal: mainly immunocompromised patients (Aspergillus, Candida, Cryptococcus, Mucorales, Coccidioides, Histoplasma capsulatum, Blastomyces dermatitidis)
  • Secondary to underlying tumors/malignancy

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  • Alterations in mental status: anywhere along a continuum from confusion/inattention to coma
  • Fever/chills
  • Stiff neck
  • Symptoms of increased intracranial pressure: headache, vomiting, visual disturbances
  • Seizures
  • Decreased motor skills or sensation perception
  • Language difficulty

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  • Blood cultures
  • CT and MRI of brain: Diffusion-weighted imaging (DWI) is helpful to distinguish abscess versus necrotic tumor (sensitivity and specificity over 90%)
  • Antibody testing (Toxoplasma gondii and Taenia solium if epidemiology consistent with diagnosis)
  • CXR: look for images suggesting septic emboli
  • EEG
  • Needle sampling (CT-guided, stereotactic) of collection for causative agent if feasible

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  • Identification of causative organisms(s) is paramount to successful therapy. Initial therapy should be commenced with broad-spectrum antibiotics that cross blood–brain and blood–CSF barriers; choice of surgical procedure needs to be tailored to and specific for each patient
    • Empiric antibiotics:
      • Dental origin: amoxicillin + ornidazole (or metronidazole)
      • Ear, mastoid, unclear origin: cefotaxime + ornidazole (or metronidazole)
      • Immunocompromised: imipenem + trimethoprim/sulfamethoxazole
  • Surgical options:
    • Twist drill craniotomy
    • Therapeutic burr-hole drainage
    • CT-guided stereotactic procedure: for most superficial and large abscesses; allows drainage and identification of causative pathogen
    • Craniotomy (rare)
  • Combination approach:
    • Surgical aspiration or removal of all abscesses larger than 2.5 cm in diameter
    • 6 weeks or longer course of intravenous antibiotics
    • Weekly CT or MRI
    • Cure rate of more than 90% serial imaging until radiographic resolution
    • Any enlargement or failure to resolve should lead to further surgical aspiration or excision
  • Medical approach favored in clinical situations of:
    • Multiple abscesses
    • Small abscess (less than 2 cm)
    • Toxoplasma: very amenable to medical therapy alone
    • Tuberculous abscesses often can be managed medically
    • Abscess anatomically very deep: difficult to access and may be harmful to attempt surgical approach
  • Target treatment to culture data; removal of the primary focus paramount; treat for at least 6 weeks
  • Antiepileptics—in high-risk patients—initiated immediately and continued for at least 1 year
  • Outcome
    • Mortality is 50% to 90% and morbidity is even higher if severe neurologic impairment is evident at the time of presentation (or with extremely rapid onset of illness), even with immediate medical treatment
    • Pneumococcal abscess has the highest mortality among bacterial etiologies (20–30% in adults, 10% in children) and morbidity (15%)
    • Viral meningitis (without encephalitis) mortality rate is less than 1%
    • Prognosis worse for patients at extremes of age, with significant comorbidities and immunosuppression

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