Abscess, brain (CNS Infection)

Brain Abscess (CNS Infection)

Overview

A brain abscess is a focal, intracerebral infection that begins as localized encephalitis and evolves into a collection of pus surrounded by a capsule. It arises from direct spread (e.g., otitis media, sinusitis, dental infection), hematogenous spread (endocarditis, lung abscess), or post-trauma/surgery.

Common pathogens:

• Streptococcus species (esp. viridans group)

• Anaerobes (Bacteroides, Fusobacterium)

• Staphylococcus aureus (esp. after trauma/surgery)

• Gram-negative bacilli (in immunocompromised)

Symptoms: headache, fever, focal neurological deficits, seizures, altered mental status, signs of raised intracranial pressure.

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Treatment Options

1. Empiric Antimicrobial Therapy

(Initiate immediately, adjust based on cultures)

• Ceftriaxone: 2 g IV q12h
  PLUS

• Metronidazole: 500 mg IV q8h
  (covers anaerobes)

If trauma, neurosurgery, or suspected Staphylococcus aureus:

• Add Vancomycin: 15–20 mg/kg IV q8–12h (target trough 15–20 µg/mL).

If immunocompromised (risk of Nocardia):

• Add Trimethoprim–sulfamethoxazole (TMP-SMX): 5 mg/kg (TMP component) IV q6–8h.

Duration: Typically 6–8 weeks IV, followed by oral antibiotics if improving.

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2. Surgical Management

• Aspiration or excision if:

  • Abscess > 2.5 cm

  • Increased intracranial pressure

  • No response to medical therapy

  • Diagnostic uncertainty

• Stereotactic aspiration is often preferred to reduce morbidity.

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3. Adjunctive Therapy

• Corticosteroids (dexamethasone 4–8 mg IV q6h): only if significant cerebral edema or mass effect (otherwise may impair abscess encapsulation).

• Anticonvulsants (prophylaxis):

  • Levetiracetam 500–1000 mg PO/IV BID, especially in patients with seizures.

• Osmotic therapy (mannitol 0.25–1 g/kg IV bolus q6h PRN): if raised intracranial pressure.

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Supportive Care

• Admission to neurosurgical and infectious disease team.

• Serial imaging (CT or MRI) every 1–2 weeks to monitor resolution.

• Blood cultures, abscess aspirate cultures to guide therapy.

• Control of primary source (e.g., dental extraction, sinus drainage, ear surgery).

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Key Notes

• Lumbar puncture is contraindicated due to risk of brain herniation.

• Early recognition and aggressive therapy are essential to reduce mortality (10–20%).

• Prognosis depends on size, location, number of abscesses, and timing of intervention.

• HIV patients or immunocompromised require evaluation for toxoplasmosis, fungal, or nocardial abscesses.