Infections of the Central Nervous System
A variety of bacteria, viruses, fungi and parasites may infect the brain and surrounding tissues. This figure depicts a case of severe pneumococcal meningitis, a bacterial infection.
The most common route of infection is through the blood circulation (hematogenous). The other two common routes are through a contiguous infection, such as an infection of the cranial sinuses, and direct invasion, such as infection that results from penetrating traumatic brain injury (e. g. gunshot wounds). Some compromise of the blood-brain barrier is usually required for infection. The most common manifestations of infection are meningitis and brain abscess.
The pattern of infection is strongly related to the anatomy of the skull and spinal column. For example, once an infection invades the meninges, it follows the course of the coverings across the brain surface. The rigidity of the skull and spinal canal also prevents the swelling of inflamed tissue; this results in cerebral infarction and other injury in addition to the direct injury from the infection. The blood-brain barrier also inhibits the free movement of antibodies and antibiotic medication.