Doctors use a thin needle for removing the fluid sample. Its actual length depends on the patient’s build and how many layers must be penetrated. The needle used is hollow and contains what is known as a stylet, an even thinner needle that acts like a plug. Once the needle is inserted, the stylet is removed so the CFS can enter the collection tubes.
After changing into a hospital gown, the patient will be asked to lie on his or her side, knees pulled toward the chest and chin tucked down. This will get the spinal column close to the surface. Sometimes the test is done with the patient sitting up but bent forward.
After the back area is sterilized, a local anesthetic will be injected into the lower spine. Once that takes hold, a spinal needle will be inserted. X-rays are sometimes used for guidance in a process called a fluoroscopy, which uses dye for guidance. About one to 10 millimeters of CFS are usually collected.
Once that is accomplished, the needle will be taken out, the back area re-cleaned, and a bandage put over the needle insertion spot. The patient will usually rest for a short period after the procedure.
OTHER PROCEDURES
Another spinal fluid collection procedure is called a cisternal puncture. In this procedure, a needle is positioned below the occipital bone (the back of the skull). This procedure is always done with a fluoroscopy because of its proximity to the brain stem.
In patients with a brain herniation, a procedure called a ventricular puncture may be used, but it is done rarely and requires an operating room procedure. In this process, a hole is drilled in the skull and the collection needle is inserted directly into a brain ventricle. The CSF may be collected from a tube there.