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Lumbar Puncture

Introduction

A lumbar puncture, also called a spinal tap, is a medical procedure that involves the insertion of a needle into the spinal canal to obtain a sample of cerebrospinal fluid (CSF) for laboratory examination or to inject medicine.

CSF is the fluid that surrounds the brain and spinal cord and carries out important functions, such as:

Cushions the brain and spinal cord, protecting them against injury
Provides nutrients and carries away waste products into the blood stream
Maintains a constant intracranial pressure

During a lumbar puncture, a needle is inserted into the spinal canal through the lower back or lumbar region to inject medication or obtain a sample of CSF. A sample of CSF may be collected to measure the pressure in the fluid. The sample is also studied for color and clarity, blood cell counts, substances such as protein and glucose, and for the growth of microorganisms, indicating the presence of infection.

Indications

Lumbar punctures are most commonly performed to test the cerebrospinal fluid to detect or rule out suspected diseases or conditions.

A lumbar puncture is done to:

Diagnose infection such as meningitis, inflammation, cancer, or bleeding in the area around the brain or spinal cord.
Diagnose diseases of the brain and spinal cord, such as multiple sclerosis (MS) or Guillain-Barré syndrome.
Assess and measure the pressure of the cerebrospinal fluid (CSF) in the space surrounding the spinal cord. Pressure above normal can cause problems.
Inject anesthetics or chemotherapeutic agents into the CSF to treat leukemia and other types of cancer of the central nervous system.
Insert dye in the CSF to act as a contrast for special X-ray tests enabling the spinal cord and fluid to appear clearer on the test.
Treat conditions such as intracranial hypertension where excess fluid is removed from around your brain to relieve elevated intracranial pressure.

Preparation

Preoperative preparation for a lumbar puncture may involve the following:

A thorough history and physical examination
Routine blood work and brain imaging
Refraining from blood thinners, aspirin, or NSAIDs
Informing your doctor of any allergies to medications, anesthesia, or latex
Refraining from solids or liquids at least 8 hours prior to surgery
Arranging for someone to drive you home following the procedure
Signing a consent form after the risks and benefits of the surgery have been explained

Procedure

The procedure usually takes about 45 minutes and includes the following steps:

You will typically be positioned on your side with your knees together and bent up towards the chest, so the spine is curved out.
The lumbar Puncture is performed in the spaces between the lumbar vertebrae located in the lower back, usually at the L3-L4 level.
The puncture site is cleaned with an antiseptic solution and numbed with a local anesthetic.
Then a long, thin needle is inserted into the lower spine between the two lumbar vertebrae.
The spinal canal is penetrated and a sample of your CSF is collected or medication is injected accordingly.
The needle is withdrawn, and the puncture site is covered with a bandage.

Results

The results of CSF analysis may take a few hours to a day or two. Abnormal findings may include a cloudy appearance, high protein levels, reduced glucose levels, and the presence of blood or organisms.