Harvey's Garden

Routes of invasion for intracranial infection

2 min read

  • Hematogenous Spread (Arterial)
    • Mechanism: Bacteria travel via arterial circulation, often lodging at the gray-white matter junction (poorly vascularized transition zone) to form brain abscesses.
    • Sources & Pathogens:
      • Infective Endocarditis: Staphylococcus aureus (most common for abscess), Viridans streptococci.
      • Pulmonary Infections (Lung Abscess/Empyema): Streptococcus pneumoniae, Klebsiella pneumoniae.
      • Immunocompromised (HIV/AIDS): Toxoplasma gondii (ring-enhancing lesions), Cryptococcus neoformans.
  • Direct Extension (Contiguous Spread)
    • Mechanism: Infection erodes through bone or spreads via emissary veins from adjacent structures.
    • Sources & Pathogens:
      • Otitis Media / Mastoiditis: Causes temporal lobe or cerebellar abscess.
        • Pathogens: Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas (chronic otitis).
      • Paranasal Sinusitis (Frontal/Ethmoid): Causes frontal lobe abscess.
        • Pathogens: Streptococcus spp., Anaerobes (Bacteroides), Staphylococcus aureus.
        • Diabetic Ketoacidosis (DKA): Rhizopus/Mucor (invades vessel walls).
      • Dental Infections:
        • Pathogens: Anaerobes (e.g., Fusobacterium, Prevotella), Viridans streptococci.
  • Retrograde Venous Spread
    • Mechanism: Valveless veins in the “Danger Triangle” of the face allow retrograde flow into the Cavernous Sinus.
    • Source: Skin infections of the nose/upper lip.
    • Pathogen: Staphylococcus aureus (Methicillin-resistant or sensitive).
  • Trauma and Neurosurgery (Direct Implantation)
    • Mechanism: Breach of the dura via penetrating injury or surgical instruments.
    • Sources & Pathogens:
      • Penetrating Trauma/Surgery: Staphylococcus aureus (Skin flora), Staphylococcus epidermidis.
      • CSF Shunts/Drains: Staphylococcus epidermidis (Biofilm former), Staphylococcus aureus.
      • Basilar Skull Fracture (CSF Rhinorrhea/Otorrhea): Streptococcus pneumoniae (Recurrent meningitis).
  • Peripheral Nerve Axonal Transport (Neurotropic)
    • Mechanism: Pathogen enters peripheral nerve endings and travels retrograde to the CNS.
    • Pathogens:
      • Rabies: Retrograde via dynein motors along axons.
      • HSV-1: Latent in trigeminal ganglia → Reactivation → Temporal lobe encephalitis.
      • Naegleria fowleri: Penetrates olfactory mucosa (cribriform plate) after swimming in warm freshwater → Primary Amebic Meningoencephalitis (PAM).

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