Brain abscess

Background

Microbiology

• Direct spread (50%)
  • Nose/sinuses: Streptococcus (especially Streptococcus anginosus group), Haemophilus, Bacteroides, Fusobacterium
  • Teeth: Streptococcus, Bacteroides, Prevotella, Fusobacterium, Haemophilus
  • Ears: Enterobacteriaceae, Streptococcus, Pseudomonas aeruginosa, Bacteroides
• Hematogenous spread (25%)
  • Lungs: Streptococcus, Fusobacterium, Actinomyces
  • Urinary tract: Pseudomonas aeruginosa, Enterobacter
  • Endocarditis: Viridans group streptococci, Staphylococcus aureus
  • Congenital cardiac malformations (especially right-to-left shunts): Streptococcus
• Direct inoculation (10%)
  • Penetrating head trauma: Staphylococcus aureus, Enterobacter, Clostridium
  • Neurosurgery: Staphylococcus, Streptococcus, Pseudomonas aeruginosa, Enterobacter
• Cryptogenic (15%)
• Immunocompromised patient
  • HIV: Toxoplasma gondii, Nocardia, non-tuberculous mycobacteria, Listeria monocytogenes, Cryptococcus neoformans
  • Neutropenia: Gram-negative bacilli, Aspergillus, mucormycosis, Candida, Scedosporium
  • Transplantation: Aspergillus, Candida, mucormycosis, Scedosporium, Enterobacteriaceae, Nocardia, Toxoplasma gondii, and Mycobacterium tuberculosis
• Plus anaerobes, which are common
• Other organisms: Nocardia, 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

• Brain Abscesses. NEJM. 2015;371:447-456. doi: 10.1056/NEJMra1301635