Lumbar Puncture, also known as Spinal Tap is a medical procedure that makes use of a needle to draw out a sample of cerebrospinal fluid (a fluid that surrounds the brain and spinal cord to protect them from injury) from the spinal column to examine and help diagnose several disorders and infections related to the central nervous system. The procedure is termed ‘lumbar puncture’ because the needle is used to puncture in the lumbar portion of the back through tissues to enter the spinal canal. This extensive procedure also goes by other names in the medical world such as thecal puncture, spinal puncture, and rachiocentesis.

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Lumbar puncture (spinal tap)

Uses Of Lumbar Puncture

A Lumbar Puncture procedure may be performed due to several reasons including:

  • Collecting cerebrospinal fluid for laboratory analysis
  • Measuring the pressure of the CSF around the brain and spinal cord
  • Looking for infections such as meningitis or encephalitis which might be the cause of epileptic seizures
  • Injecting spinal anesthetics, chemotherapy drugs or other medications
  • Injecting dye for myelography or radioactive substances for cisternography into the cerebrospinal fluid to make diagnostic images of the fluid's flow

The CSF chiefly comprises of glucose (sugar), proteins, and other substances found in the blood. A detailed essay of the fluid will show the number and types of white blood cells, the level of glucose, the types and levels of proteins, and the presence of bacteria, fungi, or abnormal cells. The information obtained by studying the cerebrospinal fluid is primarily used for the diagnosis and management of the following:

  • Chronic bacterial, fungal and viral infections, including meningitis, encephalitis and syphilis
  • Certain inflammatory conditions of the nervous system, such as multiple sclerosis, Guillain-Barre syndrome and headaches of unknown origin
  • Bleeding around the brain (i.e., subarachnoid hemorrhage)
  • Certain cancerous conditions involving the brain or spinal cord

Also Read: Spinal Cord Tumour: Causes, Symptoms And Treatment

Preparation For A Lumbar Puncture Procedure

Before undergoing the process, the treating doctor, nurse or other health care professional basically does a thorough physical exam, acknowledges your medical history, and conducts blood tests to check for bleeding or clotting disorders. The doctor may also recommend for a CT-scan or MRI-scan to rule out any abnormal swelling in and around the brain. The patient going for the procedure is asked to maintain a normal eating schedule and advised to talk clearly about any allergies due to latex or medications. The patient should also ask the doctor for specific guidelines about discontinuing alcohol use, aspirin products, and blood-thinning drugs before the procedure. Since, it is advised not to drive immediately after the procedure, the patient must also ensure proper transportation arrangements.

Procedure

Before starting the procedure, the patient is first asked to change into a hospital gown. The person is then asked to lie on the side with the knees drawn as close to the chest as possible or to sit and lean forward on a stable surface. After cleaning the back with an antiseptic soap or iodine and covered with a sterile sheet. Next, a local anesthetic is injected into the area on the back to numb the puncture site. This might cause a slight burning sensation. Then a thin, hollow needle is inserted in the lower back between two lumbar vertebrae. This may sometimes cause a feeling of pressure. The spinal canal is then penetrated and the fluid is collected or medication is injected. After drawing the fluid, the needle is removed and the area is covered with a small bandage. The entire process takes about 45 minutes. For a short duration after the procedure, the medical professional might monitor you for a headache, dizziness, or other side effects.

Risks

Though the procedure is generally considered safe, it does pose certain risks:

  • Around 10% to 20% of people develop a post-lumbar spinal headache (one that worsens when sitting or standing) due to a leak of fluid into nearby tissues.
  • Some people may feel back discomfort or pain radiating down the legs
  • There might be some bleeding at the puncture site
  • Some people might have brainstem herniation

After the procedure, the doctor mainly suggests the patient to take adequate rest, avoid strenuous activities, drink enough water and to take pain-relieving medications to help subdue a headache or back pain.

Results

After collection of the sample, it is then sent to a laboratory for analysis. The fluid is examined for a number of things like general appearance, presence of protein, white blood cells, microorganisms, cancer cells and sugar.

The normal values of the CSF examination are as follows:

  • Protein (15-60 mg/dl)
  • Glucose (50-80 mg/dl)
  • Cell count (0-5 mononuclear cells)
  • Initial pressure (70-180 mm)

The normal values are generally altered in case of a diseased condition or infection.  A specialized doctor or a health care professional chiefly reviews and interprets the test results with the patient. Depending upon the test result, further blood tests and radiological tests are conducted.