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What is a lumbar puncture (spinal tap)?
A lumbar puncture (LP) is a test that looks at the fluid surrounding the brain. That fluid is called cerebrospinal fluid (CSF). A special needle is used to get this fluid.
The LP is also called a spinal tap.
Why does an LP need to be performed?
A lumbar puncture is done for several reasons. One is to provide important medical information so proper treatment can be given. For example, an LP can test for a brain infection in a baby with a fever. Meningitis is a brain infection that occurs in both children and adults. The only way for a physician to accurately diagnose meningitis is by obtaining a small sample of CSF by a LP. An LP might also tell you if the fluid pressure is too high. This can be seen in people who have too much CSF and can be treated with surgery. In some cases, certain brain cancers can be found with an LP.
Although an LP is usually done to diagnose a problem, it can also be done as therapy to decrease fluid pressure.
How is a lumbar puncture done?
First, an area on the lower back is numbed using medicine. Then a very thin needle is put through the skin and into the back. The patient is usually awake when this is done, and it is usually not painful. Crying babies need to be held tightly during this procedure. Once the needle is in place, the fluid pressure can be measured. Some CSF is removed and the needle is taken out. That fluid is sent to the lab for testing.
Sometimes, a CT scan of the brain is done before the LP.
In some hospitals, an x-ray machine may be used during the LP to guide the needle.
How long does the procedure take?
The process usually takes less than an hour. It may take a few hours for the lab to process the results, so you may have to wait a while. You will go home the same day if there are no major problems.
What are the risks?
The procedure is considered low risk, so major problems are rare. Bleeding and infection are possible at the needle site. You may see some swelling and bruising. Damage to nerves or other organs is uncommon. You may develop a headache as a side effect of lumbar puncture. To reduce the risk of developing a headache, most physicians will request that the patient lie flat for a period of time after the procedure. Very rarely, a severe headache will require what is called a blood patch to help resolve the pain. A blood patch is a procedure in which a small amount of the patient's own blood is injected around the area in the lower back where the spinal fluid was obtained. Other risks, including death, are very rare and should not happen.
Although it may not sound like a fun thing to go through, a lumbar puncture could reveal important information that could save your life.
This article was reviewed and updated June 2007.
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