Lumbar puncture (spinal tap) is performed in your lower back, in the lumbar region. During lumbar puncture, a needle is inserted between two lumbar bones (vertebrae) to remove a sample of cerebrospinal fluid ; the fluid that surrounds your brain and spinal cord to protect them from injury.A lumbar puncture can help diagnose serious infections, such as meningitis; other disorders of the central nervous system, such as Guillain-Barre syndrome and multiple sclerosis; or cancers of the brain or spinal cord. Sometimes doctors use lumbar puncture to inject anesthetic medications or chemotherapy drugs into the cerebrospinal fluid.