Cerebrospinal fluid (CSF) collection is a test to look at the fluid that surrounds the brain and spinal cord.
CSF acts as a cushion, protecting the brain and spine from injury. The fluid is normally clear. The test is also used to measure pressure in the spinal fluid.
There are different ways to get a sample of CSF. Lumbar puncture, commonly called a spinal tap, is the most common method. The test is usually done like this:
The patient lies on his or her side, with knees pulled up toward the chest, and chin tucked downward. Sometimes the test is done with the person 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 is inserted, usually into the lower back area.
Once the needle is properly positioned, CSF pressure is measured and a sample is collected.
The needle is removed, the area is cleaned, and a bandage is placed over the needle site. The person is often asked to lie down for a short time after the test.
Occasionally, special x-rays are used to help guide the needle into the proper position. This is called fluoroscopy.
Lumbar puncture with fluid collection may also be part of other procedures, particularly a myelogram (x-ray or CT scan after dye has been inserted into the CSF).
Alternative methods of CSF collection are rarely used, but may be necessary if the person has a back deformity or an infection.
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 is even more rare, but may be recommended in people with possible brain herniation. This test is usually done 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. These sorts of tubes are usually placed in the intensive care unit.