A spinal tap or lumbar puncture is a routine medical procedure used for collecting samples of cerebrospinal fluid. It is an important diagnostic tool and generally considered safe, though it does have some risks. Because some people have a difficult time getting into the position required for a lumbar puncture, doctors also employ alternative methods when needed.
During a spinal tap, the patient lays on their side with their chin, hips, and knees pulled into their chest to open the spaces between the vertebra as much as possible. Once they are positioned, the doctor applies a local anesthetic to the patient's lower spine. When the area is numb, the doctor inserts a thin, hollow needle between two lower vertebrae to access the cerebrospinal fluid (CSF), which surrounds the brain and spinal cord.
When the doctor gets the needle into the right place, they determine the pressure of the cerebrospinal fluid then withdraw a small amount for a sample. The procedure takes about 45 minutes, and recovery is pretty straightforward.
Doctors use the samples of cerebrospinal fluid (CSF) obtained from lumbar punctures for diagnosing inflammatory or cancerous conditions and infections involving the central nervous system.
These conditions include meningitis, brain cancer, bleeding between the brain and the tissues covering it, and spinal cord inflammation. Doctors may also use spinal taps to investigate symptoms like headaches when they have unknown causes, and to evaluate diseases that attack the covering of nerve fibers, like multiple sclerosis.
In addition to obtaining a CSF sample, doctors can also use a lumbar puncture to inject medicine directly into the spinal column, such as anesthetics before spinal surgery, or chemotherapy drugs. In some cases, x-rays and other scans require contrast dye to get an accurate view, and doctors can inject the dye with this procedure, as well.
Once the doctor obtains a CSF sample through a spinal tap it goes to the lab for analysis. Normal CSF is colorless. If the fluid is pink, cloudy, or yellow, it may indicate bleeding, whereas green CSF could mean an infection is present.
Samples are also checked for white blood cells, bacteria, viruses, and sugar, as these things can also indicate an infection.
Spinal taps or lumbar punctures are common, but because they involve the brain and spinal cord, watching for complications is important. Some people experience numbness in their lower back or legs during or after a spinal tap, and because the needle penetrates the skin, there is a risk of infection.
If too much fluid is drawn from the lumbar puncture or if it leaks after the procedure, the person may get a severe headache. This headache usually starts several hours or days after the procedure and resolves when the person lies down.
Immediately after a lumbar puncture or spinal tap, the person is instructed to lay flat to help reduce the chances of developing a headache. Log-rolling from side to side is fine, but the person cannot sit up right away.
Drinking plenty of fluids helps replace the CSF removed during the procedure. Patients who are sent home after the procedure must take it easy for the rest of the day and call the doctor if they notice numbness and tingling in the legs, have difficulting urinating, develop a persistent headache, or see any drainage or blood from the injection site.
People who should not have a lumbar puncture include those with trauma to the spine, skin infections near the insertion site, and increased risk of bleeding, whether from low platelets, a bleeding disorder, or blood thinner taken in the previous 24 hours.
When a doctor suspects increased intracranial pressure or elevated pressure around the brain, they will order a CT scan before the lumbar puncture to determine the cause.
One safe alternative to a lumbar puncture is a lateral cervical puncture. This procedure is similar to a lumbar puncture. as the doctor inserts a long thin needle between the vertebrate to collect a CSF sample, but the needle goes between the cervical vertebrae at the top of the spine rather than the lower lumbar vertebrae. One study shows that the fluid samples collected in this way were comparable to fluid obtained from a traditional lumbar puncture. This procedure can be a better option for people with an infection near or affecting the lumbar spine or people who cannot get into the proper position for a lumbar puncture.
Fluoroscopy is an imaging technique that uses continuous x-rays to create a moving image, almost like an x-ray movie. A fluroscopy-guided lumbar puncture uses this imaging to guide the physician during the procedure.
A doctor may choose this modified lumbar puncture procedure if there were previous unsuccessful attempts at a standard lumbar puncture or if the patient has a condition that makes a normal spinal tap difficult, like prior spinal surgery or obesity. This technique improves success rates and may lower the chance of traumatic lumbar punctures, which occur when the procedure causes bleeding into the CSF.
Another alternative to a traditional lumbar puncture uses ultrasound guidance.
Fluoroscopy-guided procedures are not ideal for everyone, particularly pregnant women who are concerned about radiation. Ultrasound creates an image using soundwaves, eliminating that risk. One study showed that ultrasound guidance successfully reduced the number of insertion attempts and failed procedures, making it a viable option that is likely to become more prevalent in the future.
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