A lumbar puncture, also known as a spinal tap, is most often performed as a diagnostic procedure, but may also be performed as a means to administer anesthetic or chemotherapy medications. When a lumbar puncture is performed for diagnostic purposes, a small amount of cerebrospinal fluid (CSF), the fluid that surrounds and protects the brain and spinal cord, is withdrawn from the lower portion of the spine for analysis. Analysis of CSF can help detect the presence or absence of several serious diseases. These diseases include: meningitis, encephalitis, multiple sclerosis, Guillain-Barre syndrome and certain cancers.
The Lumbar Puncture Procedure
A lumbar puncture procedure may be performed in the doctor's office, an outpatient surgical setting or a hospital. The patient is usually positioned lying on the side with the knees drawn up, or occasionally, sitting in a chair and leaning forward. After an anesthetic is applied, the surgeon inserts a needle between two of the patient's lumbar (lower) vertebrae in order to extract CSF for examination.
During the procedure, a manometer, a device used to measure the internal pressure of the CSF, is attached to the needle and the patient may be asked to straighten slightly so that the most accurate pressure reading may be obtained. Some patients may experience minor discomfort during the procedure which usually takes under an hour. Once it has been completed, the targeted area is cleaned and covered with a bandage.
Recovery from Lumbar Puncture
Patients are advised to lie flat for a period of time after the procedure and to avoid any strenuous activity for at least 24 hours. There may be some temporary after effects of the puncture, including a bloody discharge from the site, tenderness or pain in the lower back that may extend into the back of the legs, and a painful spinal headache. For the third of all patients who experience the post-lumbar puncture headache, it can be very troublesome, but normally there is no residual damage of any kind.
Risks of Lumbar Puncture
While a lumbar puncture is a common procedure and considered very safe, like all invasive procedures, it is at times associated with complications. In rare instances, a headache following the lumbar puncture does not resolve, signaling a CSF leak that must be treated. A small percentage of patients experience an allergic reaction to the anesthesia or an infection after a lumbar puncture. While excessive bleeding rarely occurs, it is more common in patients who take blood thinning medication so it is essential that patients inform their physicians if this is the case. Another rare complication of lumbar puncture is brainstem herniation due to increased intracranial pressure. This may occur when a tumor is present.
Results of Lumbar Puncture
After the CSF has been removed, it is sent to a laboratory for a comprehensive analysis in order to accurately diagnose the patient's condition. Lab technicians analyze the fluid for:
- General appearance
- White blood cell levels
- Protein levels
- Glucose levels
- Bacteria and fungi
- Cancer cells
Normally, CSF is clear. When the fluid is cloudy or has color, it may be an indication of infection, bleeding, blockage or an excessive level of protein. Pressure readings of CSF can also indicate a problem if such readings are too high or too low, since an elevated pressure may indicate excessive intracranial pressure and diminished pressure may be a sign that the patient has a tumor, is in shock, or is experiencing a serious diabetic complication.