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.
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.
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
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.
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.
Post Procedure Care
After care instructions following a lumbar puncture may involve the following:
- Drink plenty of fluids to rehydrate after the procedure
- Take pain medicines as directed to relieve headache and back pain
- Do not operate machinery or drive for at least a day
- Refrain from strenuous activities or sports for at least a week
- Contact your doctor if headaches or other symptoms persist
Risks and Complications
Some of the risks and complications of a lumbar puncture include:
- Bleeding at the puncture site
- Back pain or discomfort
- Injury to nerves or blood vessels
- Numbness and tingling