A lumbar puncture is a procedure in which a needle is inserted into
the spinal canal to measure the pressure and obtain a sample of cerebrospinal
fluid (CSF), the colorless fluid that surrounds the brain and spinal cord. The
procedure may also be used to inject anesthetics, medicine, or a contrast dye
(for spinal X-rays) into the spinal fluid or to drain fluids that accumulate as
a result of certain medical conditions.
Fluid samples obtained from a lumbar puncture can be analyzed for
signs of infection (such as meningitis), inflammation, cancer, or bleeding in
the area around the brain or spinal cord.
A lumbar puncture is also sometimes called a spinal tap.