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For further information, see CMDT Part 33-31: Anaerobic Infections

Key Features

  • Common cause of brain abscess, subdural empyema, or septic CNS thrombophlebitis

  • The organisms reach CNS by direct extension from sinusitis, otitis, or mastoiditis or by hematogenous spread from chronic lung infections

Clinical Findings

  • Various neurologic deficits


  • MRI scan (most sensitive) or CT scan

  • Culture of infected tissue


  • Antimicrobial therapy is an important adjunct to surgical drainage

    • Ceftriaxone, 2 g every 12 hours intravenously, plus metronidazole, 500 mg every 8 hours intravenously

  • Duration of antibiotic therapy is 6–8 weeks but should be based on follow-up imaging

  • Some small multiple brain abscesses can be treated with antibiotics alone without surgical drainage

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