Brain Abscess

Brain Abscess

Introduction to Brain Abscesses
- Brain abscesses are focal infections of the central nervous system, accounting for 8% of intracranial space-occupying lesions.
- More common in men aged 30-50, with a mortality rate of up to 53%.
- Incidence: 0.3-1.3 cases per 100,000 people per year in developed countries.

Causes of Brain Abscesses
- Common pathogens: Staphylococcus aureus, Streptococcus viridans, and anaerobic microorganisms (40% of cases).
- Enteric gram-negative bacilli found in 33% of cases.
- Fungal infections account for 1% of brain abscesses, increasing due to immunosuppressants and broad-spectrum antibiotics.
- Nocardia spp. infections are rare (less than 1%) and can cause single or widespread CNS lesions.

Pathophysiology of Brain Abscesses
- Three main mechanisms:
1. Inoculation of skin microorganisms (e.g., head trauma, neurosurgery).
2. Spread from nearby areas (e.g., mastoiditis, otitis media, sinusitis).
3. Hematogenous spread from distant sites (e.g., bacterial endocarditis, lung abscess).
- Blood-brain barrier damage increases susceptibility to infection.
- Brain abscess development occurs in four stages: early cerebritis, late cerebritis, early capsule formation, and late capsule formation.

Microscopic Features of Brain Abscesses
- Five key areas under the microscope:
1. Necrotic center: Core filled with dead tissue.
2. Inflammatory cell area: White blood cells fighting infection.
3. Capsule: Fibrous layer containing the infection.
4. Neovascularization area: New blood vessels supplying nutrients.
5. Astrogliosis and perilesional edema: Swelling and scarring around the abscess.

Symptoms and Diagnosis
- Common symptoms: Headache (69%), fever (53%), focal neurological deficits (48%), impaired consciousness (48%), nausea/vomiting (47%), papilledema (35%), meningeal signs (32%), seizures (25%).
- Diagnosis involves clinical history, physical exam, neuroimaging, and laboratory studies.
- Lumbar puncture is risky due to potential brain herniation; neuroimaging must precede it.

Diagnostic Imaging
- Contrast-enhanced head CT: Hypodense nucleus with a thin contrast-enhancing ring and perilesional edema (85% of cases).
- Contrast-enhanced brain MRI: Preferred for high sensitivity and specificity; detects early cerebritis, ventricular spread, and satellite lesions.
- Diffusion-weighted imaging (DWI): Differentiates pus (hyperintense) from tumor necrosis (hypointense).
- Magnetic resonance spectroscopy (MRS): Detects amino acids from bacterial metabolism.

Treatment Overview
- Treatment involves a combination of surgery and antibiotics.
- Non-surgical candidates: Patients with small abscesses (less than 1.5 cm), lesions in critical brain areas, or concurrent infections (e.g., meningitis).
- Empirical antibiotic therapy should start immediately and continue for 6-8 weeks.

Antibiotic Therapy
- Empirical broad-spectrum antibiotics are adjusted based on microbiological results.
- Immunosuppressed patients: Third-generation cephalosporins (e.g., ceftriaxone, cefotaxime).
- Suspected Pseudomonas: Fourth-generation cephalosporins (e.g., cefepime) with metronidazole or vancomycin.
- Fungal infections: Voriconazole; Toxoplasma gondii: Voriconazole with pyrimethamine and sulfadiazine.

Surgical Treatment
- Open surgery: For lesions greater than 2.5 cm, midline shift greater than 5 mm, or proximity to ventricles.
- Stereotactic aspiration: Minimally invasive, allows microbiological studies, and is increasingly used.
- Complete surgical removal: For superficial abscesses, fungal infections, or failed prior treatments.
- Repeat surgery may be needed for inadequate drainage, immunosuppression, or insufficient antibiotic therapy.

Follow-Up and Monitoring
- Weekly CT scans to monitor progress, adjusted based on clinical status.
- High serum C-reactive protein post-treatment may indicate treatment failure.
- Close follow-up is essential to detect complications and ensure recovery.

Conclusion
- Brain abscesses are serious and require prompt diagnosis and treatment.
- Treatment typically involves a combination of surgery and antibiotics, tailored to the patient’s condition.
- Regular follow-up is crucial to monitor improvement and identify complications.