About lumbar puncture

What is lumbar puncture?

A lumbar puncture (LP) is the insertion of a needle into the fluid within the spinal canal. It is termed a "lumbar puncture" because the needle goes into the lumbar portion (the "small") of the back.

Other names for a lumbar puncture (an LP) include spinal tap, spinal puncture, thecal puncture, and rachiocentesis.

Why is a lumbar puncture done?

An LP is most commonly performed to diagnose a disease, namely to obtain a sample of the fluid in the spinal canal (the cerebrospinal fluid) for examination.

An LP can also be done to treat diseases, as a way of administering antibiotics, cancer drugs, or anesthetic agents into the spinal canal. Spinal fluid is sometimes removed by LP for the purpose of decreasing spinal fluid pressure in patients with uncommon conditions (such as, for example, normal-pressure hydrocephalus and benign intracranial hypertension).

How is the LP performed?

The patient is typically lying down on their side for the procedure. Less often, the procedure is performed while the patient is sitting up. LPs in infants are often done upright.

After local anesthesia is injected into the small of the back (the lumbar area), a long needle is inserted in between the nearby bony building blocks of the spine (vertebrae) into the spinal canal. (The needle is usually placed between the 3rd and 4th lumbar vertebrae).

What is done next?

Spinal fluid pressure can then be measured and cerebrospinal fluid (CSF) removed for testing.

What is the cerebrospinal fluid (CSF)?

The CSF circulates around the brain and spinal cord (the central nervous system). This "water bath" acts as a support of buoyancy for the brain and spinal cord. The support of the CSF helps to protect the brain from injury.

The normal CSF contains various chemicals, such as protein and sugar (glucose), and few if any cells. The spinal fluid also has a normal pressure when first removed.

What are the risk factors for lumbar puncture?

A lumbar puncture is generally considered safe, but it can involve some risks. About 10% of people who get a lumbar puncture develop a headache afterward. A headache might come on within a few hours or a few days.

In a 2020 study of 117 people who had a lumbar puncture, 13 experienced a headache after the procedure. Those were more likely to be younger and have a lower volume of cerebrospinal fluid (CSF) in their body.

Other potential risks include tenderness or pain in your lower back and bleeding near the puncture site. You may experience some pain and numbness that shoots down your legs. In rare cases, people experience brain herniation, which is the movement of brain tissue from its normal position in your skull. This is uncommon.

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