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III. Meningitis (Leptomeningitis)

C. Pathological changes:

1. Acute pyogenic meningitis (usually bacterial):

  • Purulent exudate in subarachnoid space and along vessels, includes neutrophils and bacteria; the severity of the exudate varies with the organism
  • Inflammatory infiltrate in walls of arteries and veins (vasculitis);   in severe cases ischemia may result from subsequent thrombosis
  • Cellular infiltration of cranial nerves and spinal roots
  • Edema may occur in brain tissue

2. Acute aseptic (viral) meningitis:  lymphocyte infiltrate;  mild

Dense exudate in the subarachnoid space surrounds vessels and would cause communicating hydrocephalus.