Acute bacterial meningitis is rapidly developing inflammation of the subarachnoid space (located within the layers of tissue covering the brain and spinal cord) that is caused by bacteria.
- Older children and adults develop a stiff neck, usually with a fever and headache.
- Infants and young children may have a high or low body temperature, be irritable or drowsy, or not eat well.
- Antibiotics are effective if given promptly.
- Usually, a spinal tap is done but typically after treatment is started.
- Vaccines can prevent some forms of meningitis.
The subarachnoid space is located between the middle layer (arachnoid mater) and the thin inner layer (pia mater) of tissues (called meninges) that cover the brain and spinal cord (see Biology of the Nervous System: Viewing the BrainFigures). This space contains the cerebrospinal fluid, which flows through the meninges, fills internal spaces within the brain, and helps cushion the brain and spinal cord.
When bacteria invade the subarachnoid space, the immune system eventually reacts to the invaders, and immune cells gather to defend the body against them. The result is inflammation. Severe inflammation can spread to blood vessels within the brain, sometimes causing clots to form. A stroke can result. Inflammation can also cause widespread damage to brain tissue, causing swelling (edema) and small areas of bleeding. If swelling is severe, it can increase pressure within the skull (intracranial pressure), causing parts of the brain to shift. If these parts are pressed through one of the small natural openings in the tissues that separate the brain into compartments, a life-threatening disorder called brain herniation results.
Bacterial meningitis is most common among infants, children, adolescents, and people over 55. Small epidemics of one particularly dangerous type of meningitis, called meningococcal meningitis, may occur among people living in close quarters, as occurs in military barracks and college dormitories.
Meningitis may also be caused by viruses, fungi, protozoa, cancer cells, certain drugs (which trigger an allergic reaction), and irritating substances (including air and chemicals).
By Michael Jacewicz, MD
The above information thankfully comes from the merck.com at the following link.
