I. General Principles

A. Inflammation vs Infection: 

Inflammation is not synonymous with infection. The body responds to an insult with inflammation; if an infectious agent is present, inflammation is accompanied by infection. The subject of this unit is the response of the nervous system to infectious agents.

B. Routes of Infection: 

Although the brain is well protected by coverings (meninges) and the blood brain barrier, these are not absolute barriers. Routes of infection include:

• Hematogenous Spread: blood-borne spread from a primary source of infection, often the lung
• Direct Implantation: infection as the result of trauma or surgery
• Local extension: infection from nearby site of suppura­tion
• Spread of viruses from PNS along nerves: A few viruses can spread along peripheral nerves to reach the central nervous system