Lumbar Puncture is a technique for obtaining a sample of the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord. Another name for lumbar puncture is spinal tap. Laboratory examination of the CSF provides important diagnostic information about disorders such as stroke subarachnoid haemorrhage (bleeding onto the surface of the brain), multiple sclerosis, meningitis and encephalitis.
Lumbar puncture is performed in hospital. The patient lies on his or her side, legs bent at the knees and drawn up towards the abdomen, and with chin resting on chest so that the spine is stretched and the spaces between the vertebrae are widened. Local anaesthetic is injected into the skin and deeper tissues before a fine needle is inserted through the space between the third and fourth, or fourth and fifth, lumbar vertebrae into the space around the spinal cord, where the CSF circulates. After the pressure of the CSF has been measured, a sample is withdrawn. The procedure takes about 15 minutes, but the patient is then required to lie flat for several hours to help reduce the risk of headache. There is some discomfort during and after a lumbar puncture, and some people experience a severe headache for up to 24 hours afterwards.
Sometimes a lumbar puncture is done more than once. A lumbar puncture can be uncomfortable, and some people have difficulty staying curled up in a ball for more than a few minutes. The injection itself is only painful for a few seconds, and the area is usually numbed before the injection. In some circumstances, a lumbar puncture to withdraw a small amount of CSF for analysis may lead to serious complications. Serious complications such as nerve trauma, pressure effects are very rare. A lumbar puncture is done below where the spinal cord ends, so it is not possible to injure the spinal cord. Lumbar puncture should be performed only with extreme caution, and only if the benefits are thought to outweigh the risks, in certain conditions. It is generally easy to do for an experienced pediatrician. After the lumbar puncture has been completed, the needle is removed and a small dressing is put on. The entire procedure normally takes around 20 minutes, although this can vary depending on the reasons for why it is being done.
A lumbar puncture is done to: