A lumbar puncture is sometimes called a spinal tap because it removes a small amount of the fluid that bathes the brain and spinal cord. This fluid, called cerebrospinal (sir-REEB-bro-SPY-nool) fluid or CSF then is examined by a specialist to diagnose or rule out certain illnesses and conditions.
A lumbar puncture might also be done to measure the amount of pressure in the spinal canal, to place medicine in the CSF and to remove some excess fluid in babies who have a condition called hydrocephalus (hi-dro-SEF-a-lus).
First, the doctor will numb the skin at the base of the spine where the needle will go using either a cream or a shot. The numbing is done so that when the test begins, your child will feel a little pressure, but not sharp pain. Then a small special needle will be used to remove the fluid. The doctor inserts the needle near the base of the spine but the needle does not enter the spinal cord or nerves.