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INTRODUCTION

In this chapter, we review the spectrum of central nervous system (CNS) infections in a systematic manner: Definition, Symptoms (including both history and exam), Microbiology, Differential Diagnosis, Work-up/Diagnostics, Treatment/Management, and then Prognosis/Complications.

BRAIN ABSCESS

Brain abscesses commonly occur when bacteria or fungi infect part of the brain. As a result, swelling and irritation (inflammation) develop. Infected brain cells, white blood cells, live and dead bacteria or fungi collect in an area of the brain. Tissue forms around this area and creates a mass.

Symptoms:

  • The classic triad of symptoms for brain abscess is fever, headache, and focal neurological symptoms, but only a minority of patients develop all three.

  • A brain abscess usually presents as an acute to subacute mass lesion.

  • Symptoms of elevated intracranial pressure (ICP) include headache, nausea, and vomiting, which may worsen with the Valsalva maneuver or when the patient lies down.

  • Seizures occur and are often generalized with a focal onset, but this may not be easily apparent by history or observation.

Exam:

  • Focal neurological signs are often absent or may be extremely subtle.

  • Papilledema is frequently absent because the abscess evolves too rapidly for this sign to appear.

Differential diagnosis:

  • Staphylococcus aureus: Usually associated with a penetrating head wound, neurosurgical procedure, or bacterial endocarditis.

  • Streptococcus: Often arises from sinusitis or dental infections.

  • Gram-negative rods: Include Haemophilus, Pseudomonas, Escherichia coli, Enterobacter; often seen in neonates and the immunocompromised and with an associated meningitis.

  • Other: Aspergillus, Mucor: Usually due to direct extension from the sinuses in patients who are immunocompromised or suffer from diabetes and is often fatal.

Diagnosis:

  • Brain magnetic resonance imaging (MRI) with contrast is the test of choice: Demonstrates ring-enhancing lesion; head CT with contrast can be used if MRI is not available but is not as sensitive.

  • CSF exam is usually unhelpful, and LP may cause brain herniation and death; CSF exam is usually normal.

Treatment:

  • Broad antibiotic coverage should be initiated, usually with a third-generation cephalosporin and metronidazole.

  • In the setting of a neurosurgical procedure or head trauma, vancomycin should be used to cover Staphylococcus. Coverage can be narrowed when speciation and sensitivities are available. Total duration of therapy is 4 to 8 weeks.

  • Surgical aspiration or excision is often required.

  • Supportive care, including control of surrounding edema and elevated ICP and seizures, is essential.

Complications:

Early diagnosis and initiation of appropriate antibiotic therapy dramatically reduces mortality.

  • Acute complications include intraventricular rupture, which substantially worsens prognosis, hydrocephalus, and seizures.

image   WARDS TIP

Antibiotics may be started up to several hours before CSF is obtained without affecting culture results.

Prognosis:

  • Overall, 5% to 10% mortality rate.

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