What is a lumbar puncture (spinal tap)?

A lumbar puncture is a procedure performed on the lower back in which a needle is inserted into the spinal column in order to extract cerebrospinal fluid, explains Johns Hopkins Medicine. Medication and dyes for diagnostic imaging may be injected during spinal taps as well.

A lumbar puncture is a sterile procedure in which a doctor uses a local anesthetic to numb the injection site, states Johns Hopkins Medicine. The cerebrospinal fluid drips out of the hollow needle that is inserted into the spinal column and into test tubes to be examined. If the doctor is injecting medication into the spinal canal, it is delivered through the same needle that collects the cerebrospinal fluid.