Lumbar puncture is indicated in a number of conditions. It is indispensable in the diagnosis of disease of the central nervous system (brain and spinal cord) and is also used in the treatment of meningitis and allied conditions.
Lumbar puncture is always performed by a doctor. It is the same procedure as is used to induce local anesthesia from about the waist level down. Lumbar puncture is the insertion of a needle between two backbone segments (vertebrae) into the spinal canal. The spinal canal is a passage extending from the inside of the skull down through the backbone (vertebral column). The spinal cord is a continuation of nerve tissue off the base of the brain, from which nerves take their origins. The inside of the skull and the spinal canal are lined with membranes called meninges. The spinal canal contains fluid which bathes the brain and the spinal cord within their bony shells. This is called spinal fluid.
In diseases of brain, spinal cord, and meninges, changes take place in the spinal fluid which are detectable by laboratory tests of the fluid. The spinal cord terminates about 2 inches above the waist level, but the canal continues down the entire length of the backbone. There is therefore a rather large segment of the spinal canal from which a sample of spinal fluid may be obtained without the least danger to the spinal cord. The false notion that the spinal cord is occasionally injured by lumbar puncture needles is without foundation; complications from the procedure are nil.
The most distressing part of the procedure for the patient is the awkward position he must assume, but this is just a matter of minutes. The back must be arched to spread the vertebrae apart. The patient is either lying on one side with back arched or is sitting up with the back bowed out. The doctor works behind the patient. The procedure is by sterile technique. The skin is cleansed with antiseptics, and the site for injection of the needle is located by feeling of the bony landmarks. Into the site is injected a small amount of anesthetic, which renders the area insensible to pain. The anesthetic injection is the only pain the patient will feel, and this is no more than that of a “hypo” injection elsewhere on the body. One minor prick is all the pain that is felt. You will feel the doctor touching you around the area, but there will be no pain from the needle passing into the spinal canal. There must be no movement from the patient. When the needle is correctly in place, the doctor will then measure the spinal fluid pressure by means of an instrument designed for this purpose, and he will take a specimen of the spinal fluid for analysis or he will inject a medication—whichever is the purpose of the lumbar puncture. The procedure is relatively simple for the patient and not associated with marked discomfort. You will know ahead of time when you are going to have a lumbar puncture. Do not become apprehensive about it, for there is little reason for alarm.