Spinal Tap (Lumbar Puncture)

Why It Is Done

A spinal tap is done to:

• Find a cause for symptoms possibly caused by an infection (such as meningitis), inflammation, cancer, or bleeding in the area around the brain or spinal cord (such as subarachnoid hemorrhage).
• Diagnose certain diseases of the brain and spinal cord, such as multiple sclerosis or Guillain-Barré syndrome.
• Measure the pressure of cerebrospinal fluid (CSF) in the space surrounding the spinal cord. If the pressure is high, it may be causing certain symptoms.

A spinal tap may also be done to:

• Put anesthetics or medicines into the CSF. Medicines may be injected to treat leukemia and other types of cancer of the central nervous system.
• Put a dye in the CSF that makes the spinal cord and fluid clearer on X-ray pictures (myelogram). This may be done to see if a disc or a cancer is bulging into the spinal canal.

In rare cases, a spinal tap may be used to lower the pressure in the brain caused by too much CSF.

How To Prepare

• Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
• If you take aspirin or some other blood thinner, ask your doctor if you should stop taking it before your test. Make sure that you understand exactly what your doctor wants you to do. These medicines increase the risk of bleeding.
• You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

How It Is Done

A spinal tap may be done in your doctor's office, in an emergency room, or at your bedside in the hospital. It may also be done in the radiology department if fluoroscopy is used.

You will empty your bladder before the procedure.

The doctor also may look into your eyes using a special lighted scope (ophthalmoscope) to see if the pressure is high. If the pressure is high, you may need other tests before the spinal tap.

You will lie on a bed on your side with your knees pulled up toward your chest. Or you may sit on the edge of a chair or bed and lean forward over a table with your head and chest bent toward your knees. These positions help widen the spaces between the bones of the lower spine so that the needle can be inserted more easily. If fluoroscopy is used, you will lie on your stomach so the fluoroscopy machine can take pictures of your spine during the procedure.

Your doctor marks your lower back (lumbar area) with a pen where the puncture will occur. The area is cleaned with a special soap and draped with sterile towels. A numbing medicine (local anesthetic) is put in the skin.

Then a long, thin needle is put in the spinal canal. When the needle is in place, the solid central core of the needle (stylet) is removed. If the needle is in the right spot in the spinal canal, a small amount of cerebrospinal fluid (CSF) will drip from the end of the needle. If not, the stylet will be put back in and the needle will be moved in a little farther or at a different angle to get to the fluid. Your doctor may need to move to another area of your spine if it is hard to get to the spinal fluid.

When the needle is in the spinal canal, a device called a manometer is hooked to the needle to measure the pressure of the CSF. You may be asked to straighten your legs while you are lying down. Your doctor takes the pressure reading, called the opening pressure, and checks whether the fluid is clear, cloudy, or bloody. Several small samples of fluid are collected and sent to the lab for study.

A final pressure reading, called the closing pressure, may be taken after the fluid samples are done. The needle is taken out and the puncture site is cleaned and bandaged.

Following a spinal tap, you may be told to lie flat in bed or with your head slightly raised for 1 to 4 hours. Since your brain makes new CSF all the time and replaces it 2 or 3 times a day, the small amount of fluid that is removed will be quickly replaced.

How long the test takes

The entire procedure takes about 30 minutes.

How It Feels

Some people find it uncomfortable to lie curled up on their side. The soap may feel cold on your back. You will probably feel a brief pinch or sting when the numbing medicine is given. You may feel a brief pain when the spinal needle is inserted or repositioned.

During the procedure, the needle may touch one of your spinal nerves and cause a tingling feeling, like a light electrical shock, running down one of your legs.

Risks

A spinal tap is generally a safe procedure. In some cases, a leak of cerebrospinal fluid (CSF) may develop after a spinal tap. Symptoms of this problem are a headache that does not go away after 1 to 2 days. A CSF leak can be treated with a blood "patch," in which the person's own blood is injected into the area where the leak is occurring in order to seal the leak.

Some people develop a headache after having a spinal tap. Of those who do get headaches, only about half report that they are severe. These headaches may last up to 48 hours and then go away on their own. Drinking extra fluids, taking pain medicine, and lying down for several hours after the procedure may help the headache be less severe.

A few people who have a spinal tap have a minor nerve injury. This heals on its own with time. Serious nerve injury is very rare. There is also a small chance of infection of the CSF (meningitis), bleeding inside the spinal canal, or damage to the cartilage between the vertebrae. Your doctor will talk with you about these risks.

People who have bleeding problems and those who are taking blood-thinning medicine (such as warfarin or heparin) have a higher chance of bleeding after the procedure. A spinal tap may not be done unless it is needed for a life-threatening illness.

A spinal tap may cause serious problems for people who have high pressure in the brain caused by a tumor, a pocket of infection in the brain (abscess), or major bleeding inside the brain. Your doctor will check your nervous system, spinal cord and brain before doing a spinal tap. In some cases, a CT scan or an MRI scan may be done before the spinal tap to know that it is safe to do the puncture.

Results

Many different tests can be done on the fluid (cerebrospinal fluid, or CSF) collected during a spinal tap. Some results will be ready right away, some will take a few hours after the procedure, and others will take several weeks.

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

Values may include CSF pressure, protein, glucose, and cell counts.

Your doctor may order other special tests on the CSF fluid depending on your symptoms and past health.