Brain Abscess

Key Features

Essentials of Diagnosis

• Symptoms and signs of expanding intracranial mass

• There may be signs of a primary infection or of congenital heart disease

• Fever may be absent

General Considerations

• Presents as an intracranial space-occupying lesion

• May occur as a sequela of ear or sinus infection, a complication of infection elsewhere in the body, or an infection introduced intracranially by trauma or surgical procedures

• Most common infective organisms

  • Streptococci

  • Staphylococci

  • Anaerobes

• Mixed infections also occur

Clinical Findings

Symptoms and Signs

• Early symptoms

  • Headache

  • Drowsiness

  • Inattention

  • Confusion

  • Seizures

• Later signs

  • Increasing intracranial pressure

  • Focal neurologic deficits

• There may be little or no systemic evidence of infection

Differential Diagnosis

• Other rapidly expanding intracranial space-occupying lesions

Diagnosis

Laboratory Tests

• Examination of the cerebrospinal fluid does not help in diagnosis and lumbar puncture may precipitate herniation

• Peripheral leukocytosis sometimes present

Imaging Studies

• CT scan of the head characteristically shows an area of contrast enhancement surrounding a low-density core (similar to metastatic neoplasms)

• MRI permits earlier recognition of focal cerebritis or abscess

Diagnostic Procedures

• Stereotactic needle aspiration may enable a specific etiologic organism to be identified

Treatment

Medications

• Intravenous antibiotics, combined with surgical drainage (aspiration or excision) if necessary to reduce the mass effect, or to establish the diagnosis

• Broad-spectrum antibiotics are used if the infecting organism is unknown (Table 30–5)

• Initial empiric antibiotic regimens typically include

  • Ceftriaxone, 2 g intravenously every 12 hours

  • Metronidazole, 15 mg/kg intravenous loading dose, followed by 7.5 mg/kg intravenously every 6 hours

  • Vancomycin, 1 g intravenously every 12 hours

• Antimicrobial treatment is usually continued parenterally for 6–8 weeks and is followed by oral treatment for certain infections, such as nocardiosis, actinomycosis, fungal infections, and tuberculosis

• Dexamethasone (4–25 mg orally four times daily, depending on severity, followed by tapering of dose, depending on response) may reduce any associated edema; intravenous mannitol is sometimes required