Lumbar Puncture (LP)
What is a lumbar puncture (LP)?
A lumbar puncture (an 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 peformed 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. For example, 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 examples, normal-pressure hydrocephalus and
benign intracranial hypertension).
How is the LP performed?
The patient is typically lying down sideways 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 needle is inserted in between the nearby bony
building blocks (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.
Next: What is normal CSF? »
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