There are different ways to get a sample of CSF. Lumbar puncture (spinal tap) is the most common method.
To have the test:
You will lie on your side with your knees pulled up toward the chest, and chin tucked downward. Sometimes the test is done sitting up, but bent forward.
After the back is cleaned, the health care provider will inject a local numbing medicine (anesthetic) into the lower spine.
A spinal needle will be inserted.
Once the needle is in position, the CSF pressure is measured and a sample of 1 to 10 ml of CSF is collected.
The needle is removed, the area is cleaned, and a bandage is placed over the needle site. You may be asked to remain lying down for a short time after the test.
Occasionally, special x-rays are used to help guide the needle into position. This is called fluoroscopy.
Lumbar puncture with fluid collection may also be part of other procedures such as an x-ray or CT scan after dye has been inserted into the CSF.
Rarely, other methods of CSF collection may be used.
Cisternal puncture uses a needle placed below the occipital bone (back of the skull). It can be dangerous because it is so close to the brain stem. It is always done with fluoroscopy.
Ventricular puncture may be recommended in people with possible brain herniation. This is a very rarely used method. It is most oftendone in the operating room. A hole is drilled in the skull, and a needle is inserted directly into one of brain's ventricles.
CSF may also be collected from a tube that's already placed in the fluid, such as a shunt or a ventricular drain.
How to Prepare for the Test
How the Test will Feel
It may be uncomfortable to stay in position for the test. Staying still is important because movement may lead to injury of the spinal cord.
You may be told to straighten your position slightly after the needle is in place. This is to help measure the CFS pressure.
The anesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted. Often, there is some brief pain when the needle goes through the tissue surrounding the spinal cord. This pain should stop in a few seconds.
In most cases, the procedure takes about 30 minutes. The actual pressure measurements and CSF collection only take a few minutes.
Why the Test is Performed
This test is done to measure pressures within the cerebrospinal fluid and to collect a sample of the fluid for further testing.
CSF analysis can be used to diagnose certain neurologic disorders. These may include infections (such as meningitis) and brain or spinal cord damage. A spinal tap may also be done to establish the diagnosis of normal pressure hydrocephalus.
Bleeding into the spinal canal or around the brain (subdural hematomas).
Discomfort during the test
Headache after the test that can last a few hours or days. If headaches last more than a few days (especially when you sit, stand or walk) you might have a “CSF-leak”. You should talk to your physician if this occurs.
Hypersensitivity (allergic) reaction to the anesthetic
Infection introduced by the needle going through the skin
There is an increased risk of bleeding in people who take blood thinners.
Brain herniation may occur if this test is done on a person with a mass in the brain (such as a tumor or abscess). This can result in brain damage or death. This test is not done if an exam or test reveals signs of a brain mass.
Damage to the nerves in the spinal cord may occur, particularly if the person moves during the test.
Cisternal puncture or ventricular puncture carries additional risks of brain or spinal cord damage and bleeding within the brain.
This test is more dangerous for people with:
A tumor in the back of the brain that is pressing down on the brain stem
Blood clotting problems
Low platelet count (thrombocytopenia)
Individuals taking blood thinners, aspirin, clopidogrel, or other similar drugs to decrease the formation of blood cloths.
Griggs RC, Jozefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 403.
Luc Jasmin, MD, PhD, FRCS (C), FACS, Department of Neurosurgery at Cedars-Sinai Medical Center, Los Angeles CA; Department of Surgery at Los Robles Hospital, Thousand Oaks CA; Department of Surgery at Ashland Community Hospital, Ashland OR; Department of Surgery at Cheyenne Regional Medical Center, Cheyenne WY; Department of Anatomy at UCSF, San Francisco CA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.