A lumbar puncture, or spinal tap, is a procedure in which a needle is inserted into the lower part of the spinal column to remove a sample of cerebrospinal fluid. The fluid surrounds and protects the brain and spinal cord.
A lumbar puncture is performed to collect and test the cerebrospinal fluid for diseases, infections and conditions that affect the central nervous system, including:
- Cancer (e.g., brain cancer, spinal cancer, leukemia)
- Bleeding around the brain or spinal cord
- Inflammation of the brain, spinal cord or bone marrow
- Multiple sclerosis
- Reye syndrome
- Guillain-Barré syndrome
- Headaches of unknown cause
Lumbar punctures may also be used to measure the pressure of the cerebrospinal fluid. Additionally, they may be performed to inject medications into the spinal cord. Spinal anesthesia, contrast dye for an X-ray exam or chemotherapy drugs are medications that can be given via a lumbar puncture.
For the procedure, the patient’s back is cleaned with an antibacterial solution. A doctor then administers a local anesthetic to numb the area. Next, the doctor inserts a hollow, thin needle into the lower back in the space between two vertebrae. The patient must stay completely still while the needle is inserted. He or she may feel some pressure. The cerebrospinal fluid is then removed through the needle. About a tablespoon of fluid is collected and sent to a lab for testing. Any medication the patient is to receive via the lumbar puncture is administered after the fluid is collected.
A lumbar puncture takes approximately 30 minutes to perform.