Background
Microbiology
- Direct spread (50%)
- Nose/sinuses: Streptococcus species (especially Streptococcus anginosus group), Haemophilus species, Bacteroides species, Fusobacterium species
- Teeth: Streptococcus species, Bacteroides species, Prevotella species, Fusobacterium species, Haemophilus species
- Ears: Enterobacteriaceae, Streptococcus species, Pseudomonas aeruginosa, Bacteroides species
- Hematogenous spread (25%)
- Direct inoculation (10%)
- Cryptogenic (15%)
- Immunocompromised patient
- HIV: Toxoplasma gondii, Nocardia species, non-tuberculous mycobacteria, Listeria monocytogenes, Cryptococcus neoformans
- Neutropenia: Gram-negative bacilli, Aspergillus species, mucormycosis, Candida species, Scedosporium species
- Transplantation: Aspergillus species, Candida species, mucormycosis, Scedosporium species, Enterobacteriaceae, Nocardia species, Toxoplasma gondii, and Mycobacterium tuberculosis
- Plus anaerobes, which are common
- Other organisms: Nocardia species, Klebsiella pneumoniae (especially southeast Asia), Aspergillus, Taenia solium, and Toxoplasma gondii
Pathophysiology
- Either from contiguous spread from a head and neck infection, hematogenous spread from bacteremia or endocarditis, traumatic inoculation, or post-neurosurgery
- Typically starts as a small focus of infection in the brain parenchyma, followed by cerebritis and eventual capsule formation to give an abscess
- Microbiology (above) depends on mechanism of infection
Clinical Manifestations
- Often non-specific
- Headache is most common, then fever and focal neurological deficits
- May have seizures
- May have symptoms of increase ICP, such as comiting, blurry vision, drowiness, and confusion
Prognosis and Complications
- 10% mortality
- 50% seizures
- 20% significant cognitive impairment
Investigations
- MRI with gadolinium
- Typically demonstrates a ring-enhancing lesion with thin rim
- Temporal lobe and cerebellum suggests contiguous spread from chronic otitis or mastoiditis
- Frontal and temporal lobe suggests contiguous spread from frontal or ethmoid sinusitis
- Frontal lobe and cerebellum can be secondary to meningitis
- Frontal lobe scan be from dental infection or manipulation
- Multiple abscesses in a middle cerebral artery distribution suggests bacteremia
- Blood cultures positive in 15%
- Lumbar puncture usually contraindicated due to mass effect and risk of herniation
- Most important is aspiration of abscess for stain and culture, which is positive in 2/3 of cases
- Can do bacterial or fungal ribosomal PCR if cultures negative
Management
- Empiric therapy is directed at the likely organisms based on etiology (direct vs. hematogenous spread)
- For likely oral, ear, or sinus source, treated with ceftriaxone and metronidazole at CNS doses
- For likely hematogenous spread, treated with vancomycin
- For uncertain etiology, combination of ceftriaxone, metronidazole, and vancomycin
- For neurosurgical patients, vancomycin plus a broad-spectrum antipseudomonal antibiotic such as ceftazidime, cefepime, or meropenem
- Source control with neurosurgical aspiration
- Duration is typically 6 to 8 weeks of intravenous antibiotics following source control
- Monitor with serial MRI, though abnormalities may persist after successful treatment
- No role for routine use of steroids
Further Reading
