Tests for Brain, Spinal Cord, and Nerve Disorders :
Spinal Tap
Cerebrospinal fluid flows through a channel (the subarachnoid space) between the layers of tissue (meninges) that cover the brain and spinal cord. This fluid, which surrounds the brain and spinal cord, helps cushion them against sudden jarring and minor injury.
For a spinal tap (lumbar puncture), a sample of cerebrospinal fluid is withdrawn with a needle and sent to a laboratory for examination.
The cerebrospinal fluid is checked for evidence of infections, tumors, and bleeding in the brain and spinal cord. These disorders may change the content and appearance of the cerebrospinal fluid, which normally contains few red and white blood cells and is clear and colorless. For example, the following findings suggest certain disorders:
An increase in the number of white blood cells in the cerebrospinal fluid suggests an infection or inflammation of the brain and spinal cord.
Cloudy fluid, due to the presence of many white blood cells, suggests meningitis (infection and inflammation of the tissues covering the brain and spinal cord) or sometimes encephalitis (infection and inflammation of the brain).
High protein levels in the fluid may result from any injury of the brain, the spinal cord, or a spinal nerve root (the part of a spinal nerve next to the spinal cord).
Abnormal antibodies in the fluid suggest multiple sclerosis or an infection.
Low sugar (glucose) levels suggest meningitis or cancer.
Blood in the fluid may indicate a brain hemorrhage—for example, when a bulge in a weakened artery in the brain (aneurysm) bursts (ruptures).
An increase in the fluid’s pressure can result from many disorders, including brain tumors and meningitis.