Lumbar Puncture or Spinal Tap

What Is It?

A lumbar puncture, also known as a spinal tap, is a medical procedure performed as part of the diagnosis, and sometimes treatment, of various diseases of the nervous system. Most notably, this procedure, usually performed at the bedside with just local anesthetic, is the gold standard test to confirm the presence of meningitis, an infection of the coverings of the brain.

The procedures is generally as follows. The patient is positioned in either a lateral (lying on their side) or sitting position and asked to flex their back and hips as far as they can. In other words, they bend their head forward towards their knees such as in the "fetal" position. This position helps to spread the bones of the spine apart in the back so that the spinal canal can be more easily accessed. The area of the lower back is sterilized and the skin near the midline is generally anesthetized with a local anesthetic. Then, at a level that will allow access to the spinal canal below the level of the bottom of the spinal cord (so as not to injure the spinal cord), a long spinal needle is inserted. This needle is inserted down between two spinal bones (vertebrae) so that it can pierce the dura mater, the thick covering that surrounds the brain and spinal cord.

This needle can then allow the sampling of cerebrospinal fluid (CSF), the fluid which surrounds the brain and spinal cord. Access to this fluid allows a number of tests including: measurement of fluid pressure and sampling of CSF to be cultured for the presence of bacteria, analyzed for the presence of cells (white blood cells, red blood cells, etc.), and for the presence of various chemicals that may be present (glucose, protein, antibodies, etc.).

There are other medical procedures which are similar to a lumbar puncture but are used for different reasons and may have slight differences in their actual technique. For example, if prolonged drainage of CSF is desired, a lumbar drain may be inserted in a similar way. This is a catheter which remains inside the spinal canal and comes out and can allow drainage of CSF over days. Epidural and spinal anesthesia, commonly used in childbirth in hospitals as well as with some surgical procedures, are also given in a similar fashion. However, in these cases, medications are being given into the area of the spine.

While this procedure is relatively simple and safe if performed by an experienced clinician, as with all procedures that are invasive in the body there is some risk. The risk for serious complications like paralysis are extremely low and generally not an issue, although the general public often assume that it is a significant risk. The most common negative effect of removing CSF is that it can cause a postural headache, a headache that is worse when upright. For this reason, most patients are advised to lay down following the procedure for a period of time. Other complications such as persistent drainage from the puncture site or infection are relatively rare and can usually be dealt with without any major consequences.


What Is It Used For?

There are a number of different pathologies of the nervous system which can affect the cerebrospinal fluid. In these cases, lumbar puncture to sample the CSF may be part of the diagnostic work-up for these diseases.

Most importantly, a spinal tap is the gold standard test used to diagnose meningitis and to distinguish the different types of meningitis (such as bacterial, viral, fungal, etc.). The CSF sampled in this case is cultured to look for any bacteria (normally there are no bacteria in the CSF) and to identify its type and sensitivities to antibiotics. Additionally, elevated levels of white blood cells in the CSF, the microscopic identification of bacteria, low levels of glucose and elevated levels of protein all help support the diagnosis of meningitis. Subtle differences of these and other factors can help confirm other causes of meningitis such as viruses, fungus and so on. Because bacterial meningitis can be an acute, life-threatening illness, a lumbar puncture is often done in an emergency setting to rule out or confirm this diagnosis.

There are other diseases which may use CSF sampling by a spinal tap to help make the diagnosis. However, in most of these cases it is not the only diagnostic test used and only helps to support the diagnosis and is not the one gold standard test. For example, changes in the CSF can be seen in multiple sclerosis, Guillain-Barre syndrome, normal pressure hydrocephalus, subarachnoid hemorrhage and others.

In some cases, the drainage of the CSF by lumbar puncture may be part of the treatment or a trial of treatment as well. For example, large volume taps of CSF or lumbar drainage may be used in the diagnosis and treatment of normal pressure hydrocephalus or pseudotumor cerebri.



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Important Note: This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.

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