A lumbar puncture (also known as a spinal tap) is a procedure used to measure the pressure of the cerebrospinal fluid (CSF) in your spine and/or to take a sample of CSF. CSF surrounds your brain and spinal cord cushioning them and providing them with essential nutrients. It is important for your specialist to know the pressure in your brain as part of the assessment of hydrocephalus, normal pressure hydrocephalus (NPH) and Idiopathic Intracranial Hypertension (IIH). This can be at the time of diagnosis or to check for shunt malfunction. The pressure is taken from the spine as it closely relates to the pressure in your brain. In some cases where the pressure is high, some CSF can be taken away to reduce the pressure. This is a common treatment option for people with IIH if they do not have a shunt. Removing some CSF can also be used to help decide if a person with NPH is likely to find a shunt helpful.
A lumbar puncture can also be suggested to help check for infection such as meningitis or encephalitis. A pressure measurement may be done at the same time but a sample of the CSF will be sent for testing. It can also be used to help to rule out other conditions such as multiple sclerosis or to check for a bleed such as a sub-arachnoid haemorrhage.
You will usually be advised to take all your regular medication on the day. If you take any blood thinning medication such as aspirin, clopidogrel, warfarin, or apixaban, it is important to tell the doctor or nurse looking after you before the day of your lumbar puncture as you may be advised to stop taking your medication for a few days prior to the lumbar puncture.
You will likely have your blood tested to check if your blood clotting is ok. This may be on the day of the lumbar puncture or a few days before.
You may be advised to fast (not eat breakfast or drink anything other than water) on the day of your procedure.
You will be asked to lie on your side with your knees bent towards your chest. This opens up the spaces between your vertebrae in your spine allowing easier access to the spinal canal.
The doctor or nurse doing your procedure will press on your back to find the right place to put the needle. This is the area at the base of your spine below the end of the spinal cord to avoid damaging your spinal cord. The skin in this area will be cleaned thoroughly.
An injection of local anaesthetic will be given to the area to numb the skin. This will sting for a few seconds before the area becomes numb.
A needle will then be inserted slowly into the gap between the vertebrae into the space around your spinal cord. Once the needle is in the right place, the CSF will run down the needle and into a manometer. This is a tool used to measure the pressure. If no pressure measurement is needed, the fluid can be removed into a pot for testing or removal. The CSF can drip slowly so it may take a few minutes to get enough for testing or enough off to lower the pressure. A pressure reading may be taken again after the fluid has been removed.
Once the doctor or nurse has taken enough fluid or has measured the pressure, the needle will be removed. You will then have a dressing applied to the area and may be asked to lie down flat on your back for an hour or two. After this, your dressing will be checked and you will be able to get up from the bed. You may be able to go home immediately or may need to stay until the results of your fluid testing is back.
In some cases, depending on the testing needed, you may also have a blood test either immediately before or after the lumbar puncture. This is used to compare results between your blood and CSF. This will normally only be done if infection is suspected.
In some cases, it may be difficult to find the right area for the needle to be inserted into. This may be due to scarring, previous surgery or scoliosis which can make it harder to access the right space. If you are overweight or obese, it may be hard to feel the bones of the spine so the doctor or nurse might be unsure where to insert the needle. If you have a LP (lumbo-peritoneal) shunt, it is important to avoid damaging the tubing.
In these cases, you may be offered a lumbar puncture with X-ray guidance. Instead of the lumbar puncture being done on a hospital ward, you will be taken to an X-ray room. You will be asked to lie on your side, and multiple X-rays will be taken so that the doctor can see where the best place to put the needle is. They are also able to ‘see’ where the needle is at all times using X-ray. The pressure can be taken and CSF removed if needed.
Once the procedure is complete, you will be slid off the X-ray table onto a waiting trolley/bed to lie flat on and taken to a ward or day care unit for observation.
Headache
It is relatively common for people to have a headache after a lumbar puncture. This is more likely if you have had CSF removed to lower the pressure. This headache is generally worse when you sit up or stand up and is better on lying down. The headache may persist for a few hours to a few days. If it does not improve, contact your specialist team. It is important to stay well hydrated and you may be advised to take caffeine supplements for a short period of time.
CSF Leak
It is possible to have a leak of CSF from the needle site. This can be seen by having a wet dressing or swelling at the site without redness or pain. CSF is usually colourless and looks like water. You may develop a headache. You should speak to your specialist if this occurs. Most leaks settle on their own but in rare cases, you may need to return to hospital for further investigation.
Infection
There is a small chance of infection following a lumbar puncture even though your skin will be cleaned thoroughly and the procedure done with sterile equipment. The needle site may become red, swollen and hot to touch. If you suspect an infection, it is best to get an urgent review of the area.
Nerve damage
In rare cases, a nerve may be damaged during the procedure. This may be temporary or more permanent. The needle is inserted at the lowest point possible in the back to reduce this risk. Always tell your doctor or nurse if you feel pain, weakness or numbness at any point.
Seen in older adults, NPH is characterised by dementia, decreased mobility and urinary incontinence.
Most babies born with spina bifida have hydrocephalus. In addition to the lesion in the spinal cord, structural abnormalities in parts of the brain can develop before birth. This prevents proper drainage of the CSF which increases the pressure and can compress the brain further.
