Brief Description – Lumbar puncture (also known as spinal tap) is a method of collecting cerebrospinal fluid (CSF) which is the fluid that surrounds the brain and spinal cord. CSF acts as a cushion, protecting the brain and spine from injury. The fluid is normally clear. It has the same consistency as water. The test is also used to measure pressure in the spinal fluid and the chemical consistency.
Why the Test is Performed
This test is done to measure pressures within the cerebrospinal fluid and to collect a sample of the fluid for further testing. CSF analysis can be used to diagnose certain neurologic disorders. These may include infections (such as meningitis, encephalitis) and brain or spinal cord damage. A spinal tap may also be done to establish the diagnosis of normal pressure hydrocephalus.
How the Test is Performed
- This is usually done in a hospital with sterilized equipment by a doctor.
- You will lie on your side with your knees pulled up toward the chest, and chin tuckeddownward.
- Sometimes the test is done sitting up, but bent forward.
- After the back is cleaned, the doctor will inject a local numbing medicine (anaesthetic) into the lower spine.
- A spinal needle will be inserted. Once the needle is in position, the CSF pressure is measured and a sample of 1 to 10 ml of CSF is collected.
- The needle is removed, the area is cleaned, and a bandage is placed over the needle site.
- You may be asked to remain lying down for a short time after the test.
- Occasionally, special x-rays are used to help guide the needle into position. This is called fluoroscopy. Lumbar puncture with fluid collection may also be part of other procedures such as an x-ray or CT scan after dye has been inserted into the CSF. In most cases, the procedure takes about 30 minutes. The actual pressure measurements and CSF collection only take a few minutes.How to Prepare For the Test
You will need to give the doctor your consent before the test. Individuals taking blood thinners, aspirin, clopidogrel, or other similar drugs to decrease the formation of blood clots should tell the
doctor so they can be prepared appropriately or even avoid the test altogether. The decision will rest on your doctor’s perception of your clinical picture. This test is also more dangerous for people with:
- A tumour in the back of the brain that is pressing down on the brain stem
- Blood clotting problems
- Low platelet count (thrombocytopenia)During the Test
It may be uncomfortable to stay in position for the test. Staying still is important because movement may lead to injury of the spinal cord. You may be told to straighten your position slightly after the needle is in place. This is to help measure the CFS pressure.
The anaesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted. Often, there is some brief pain when the needle goes through the tissue surrounding the spinal cord. This pain should stop in a few seconds.
After the Test
Afterward, you should plan to rest for several hours, even if you feel fine. This is to prevent fluid from leaking around the site of the puncture. You will do not need lie flat on your back the entire time.
You may have headaches after the test that can last a few hours or days. If headaches last more than a few days (especially when you sit, stand or walk) you might have a “CSF-leak”. You should talk to your physician if this occurs.
Risks of lumbar puncture include:
- Bleeding into the spinal canal or around the brain (subdural hematomas)
- Discomfort during the test
- Hypersensitivity (allergic) reaction to the anaesthetic
- Infection introduced by the needle going through the skin
- There is an increased risk of bleeding in people who take blood thinners.
- Brain herniation may occur if this test is done on a person with a mass in the brain (such as a tumour or abscess). This can result in brain damage or death. This test is not done if an exam or test reveals signs of a brain mass.
- Damage to the nerves in the spinal cord may occur, particularly if the person moves during the test.