Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 89. Infections of the Brain and Spinal Cord

Topics: Introduction | Acute Bacterial Meningitis | Chronic Meningitis | Viral Infections | Brain Abscess | Subdural Empyema | Parasitic Infections

Introduction

The brain and spinal cord are remarkably resistant to infection, but when they become infected, the consequences are usually very serious. Infections may be caused by bacteria, viruses, fungi, or, occasionally, protozoa or parasites. Another group of brain disorders that resemble infections, called spongiform encephalopathies, are caused by prions, which are abnormal tiny protein particles (see Section 6, Chapter 90).

Infections usually cause inflammation. For example, meningitis, an inflammation of the layers of tissue covering the brain and spinal cord (meninges), is usually caused by a bacterial or viral infection. However, meningitis may be caused by other conditions, for example, by an allergic reaction to certain drugs or to a radiopaque dye injected into the spinal canal as part of a diagnostic procedure (myelography (see Section 6, Chapter 77)). Encephalitis, an inflammation of the brain, is usually caused by a viral infection, but it may be caused by an autoimmune reaction, in which the body attacks its own tissues (see Section 16, Chapter 186).

Infections may affect a large area, or they may be localized as a collection of pus (abscess). An abscess, which resembles a boil, can form anywhere in the body, including the brain. Fungi (such as Aspergillus), protozoa (such as Toxoplasma gondii), and parasites (such as Cysticercus) may produce a localized brain infection similar to an abscess.

Bacteria and other infectious organisms can reach the meninges and other areas of the brain in several ways. They can be carried by the blood, enter the brain from the outside (for example, as the result of an injury or surgery), or spread from nearby infected structures, such as the sinuses or middle ear.