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 After the pressure of the CSF has been measured, a sample is withdrawn.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.

Why it is done?

A lumbar puncture is done to:

• Diagnose a disease, namely to obtain a sample of the fluid in the spinal canal (the cerebrospinal fluid) for examination.
• Inject a dye that is used to produce X-ray images of the spinal cord during a myelogram.
• Diagnose certain diseases of the brain and spinal cord, such as multiple sclerosis.
• Lumbar puncture is sometimes used as a treatment option, for example, as a way of putting antibiotics or cancer-fighting drugs into the body.

How to prepare?

• Tell your doctor if you have had bleeding problems.
• The patient must remain in the hospital for at least several hours after the test for observation.
• Tell your doctor if you are or might be pregnant.
• Tell your doctor ahead of time if you have ever had an allergic reaction to lidocaine or the numbing medicine used at the dentist’s office.

What are the risks of an lumbar puncture?

• Occasionally, a leak of cerebrospinal fluid may develop after a lumbar puncture.
• When spinal fluid is removed during an LP, the risks include headache, brain herniation, bleeding, and infection.
• Headaches occur less frequently when the patient remains lying flat 1-3 hours after the procedure.
• Damage to the spinal cord (particularly if the person moves during the test).
• People who have bleeding disorders and those who are taking a blood-thinning medication (such as warfarin or heparin) are at increased risk of continued internal bleeding after the procedure.