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Meningoencephalitis: Bacterial
T1 post contrast MRI study in axial view. The leptomeninges enhance post gadolinium contrast injection.
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Meningoencephalitis: Bacterial

Bacterial
Overview
  • Acute, purulent meningitis (the most dangerous).
    • On gross brain inspection, this classically causes opacity of the leptomeninges.
    • On microscopic inspection, we see neutrophilic infiltration.
  • Abscess/empyema (often iatrogenic).
    • See: Brain Abscess
    • On gross inspection, we see central, liquefactive necrosis and granulation tissue.
    • On microscopic inspection, we see reactive astrocytes surrounding a fibrous capsule.
  • Chronic meningitis (which often acts like fungal meningitis).
Normal CSF
  • < 10 cells, 70% of which are lymphocytes
  • Glucose is 60% of that of the serum glucose
  • Protein is from 15 to 45
  • CSF pressure is usually 70 to 180 mmH2O.
Bacterial:
  • Cell counts are typically > 1,000, the majority of cells are usually polymorphonuclear cells (PMNs)
  • Glucose is low
  • Protein is elevated
  • Intracranial pressure is elevated from CSF obstruction
  • Group B. strep and E. Coli are notable causes of neonatal meningitis.
    • Group B strep is more common, whereas E. coli is more fatal.
  • Listeria is most often found in those older than 50 who are immunocompromised.
  • Meningococcal meningitis (from Neisseria meningitidis) occurs most often in teens and young adults.
  • Pneumococcal meningitis from Streptococcus pneuomniae is the most common cause of bacterial meningitis across all ages.
    • Waterhouse-Friderichsen syndrome can occur in meningococcal and pneumococcal meningitis, wherein patients present with septicemia, cutaneous petechiae and purpura, and adrenal gland hemorrhagic infarcts.
Abscess/empyema
  • Typically polymicrobial (eg, staphylococcus aureus and streptococcus).
    • Direct implantation (most commonly from surgery)
    • Hematogenous causes, notably, are: tooth extraction, immunosuppression, bronchiectasis, endocarditis, and congenital heart disease.
    • Local extension occurs most commonly from mastoiditis and sinusitis.
Chronic meningitis
  • Mycobacteria, most notably: tuberculosis (TB).
    • Causes a basilar meningitis, which manifests with hydrocephalus (swelling of the ventricles from CSF obstruction).
    • Commonly causes tuberculomas (mass lesions) and typically occurs in immunosuppressed individuals.
  • Spirochete causes: Neurosyphilis and Lyme disease
    • Neurosyphilis also causes a basilar meningitis and causes gummas. It manifests with obliterative endarteritis (often presenting with sensori-neuronal hearing loss).
    • Lyme disease is a rare cause of meningitis. Indicate that it is one of the few causes of bilateral facial palsies. It is caused by the Ixodes tick.
  • Rickettsia rickettsi
    • Causes Rocky mountain spotted fever, which notably manifests with a non-itchy red rash that starts on the wrists and ankles.