A lumbar puncture is a medical procedure where a needle is inserted into the lower part of the spine, in order to look for evidence of conditions affecting the brain, spinal cord or other parts of the nervous system.
During the procedure, pressure measurements are recorded and samples of fluid are taken, from inside the spine. The fluid is known as cerebrospinal fluid (CSF) and it can be tested to help diagnose various conditions, such as:
- meningitis - an infection of the layers (membranes) that surround the brain and spinal cord
- subarachnoid haemorrhage - a type of stroke, caused by bleeding in and around the brain
- Guillain-Barré syndrome - a rare condition that causes inflammation of the nerves in the arms and legs.
However, if you are advised to have a lumbar puncture, it doesn't necessarily mean you have one of these conditions or any other serious disorder. Instead, the procedure may be used to exclude such conditions.
Read more about why lumbar punctures are used.
How is a lumbar puncture carried out?
A hollow needle is inserted into the base of the spine, under local anaesthetic. The needle passes into the spinal canal, which is the channel running down the spine that contains the spinal cord and the nerves that come off it.
The pressure within the spinal canal is usually measured, after which some of the cerebrospinal fluid (CSF) is removed. The fluid is removed either to reduce the pressure or so that a sample can be sent to the laboratory for testing.
In most cases the lumbar puncture is carried out while you are lying on your side, with your legs pulled up and your chin tucked in. Alternatively, the procedure may be carried out while you are seated and leaning forwards.
A lumbar puncture usually takes around 30-45 minutes to complete.
It is often possible to get results of laboratory tests on CSF samples within 48 hours but it can take several weeks for results of more specialised tests to become available.
Read more about how a lumbar puncture is performed.
Are there any risks?
A lumbar puncture is generally safe and the risk of serious complications is low.
Serious side effects are uncommon, although many people experience headaches caused by CSF leaking out through the hole in the spine made by the needle. You won’t see this leakage because it occurs internally, not through the skin.
The headaches are typically worse when in the upright position and can usually be relieved by lying down. Drinking plenty of fluids and taking simple pain killers will also help. It can take up to a week for the hole to heal and the fluid to stop leaking.
Read more about the possible side effects of a lumbar puncture.
How it is performed
Lumbar punctures are often carried out after somebody is admitted to hospital in an emergency, but they are also often arranged in advance and carried out on a day-case basis.
Before having a lumbar puncture, checks will be carried out to make sure the procedure is safe for you. Usually a CT or MRI scan will have been carried out to ensure that the lumbar puncture is needed and will not cause any harm. It will not be carried out if you have recently taken blood-thinning medication (anticoagulants), such as warfarin.
A doctor or a specially trained nurse will explain why the lumbar puncture is required. You will then be asked to provide written consent for it to be carried out.
If it is not possible for you to provide informed consent - for example, if you are unconsciousness or confused, the medical staff may decide to go ahead with the procedure, if it is in your best interests. This will normally be discussed with close relatives, but the final decision is made by medical staff.
You will usually change into a hospital gown before the procedure.
In most cases, you will be asked to lie on one side. You will be asked to curl up, with your knees pulled up and your chin tucked in, so that your spine is curved. This will help separate the bones in your spine, allowing the needle to be inserted more easily.
Sitting while bending forwards is an alternative position, which is often used when spinal anaesthetic is administered. However, this position is not always suitable.
An antiseptic solution will be applied to the skin at the base of the spine. A local anaesthetic is then be used to numb the area of skin where the lumbar puncture needle will be inserted. There is usually little in the way of discomfort beyond an initial sting when the anaesthetic is injected. This is followed by a sensation of pressure when the anaesthetic is injected a little deeper.
If a child needs to have a lumbar puncture then medication may be given beforehand, to help them relax and keep them calm.
The doctor will insert a special spinal needle in between the bones at the base of the spine. The needle is passed into the spinal canal, penetrating the layer that contains the cerebrospinal fluid (CSF).
Occasionally you may feel a sudden, sharp sensation in one of your legs if the needle tip touches one of the nerves within the spinal canal. This is only a brief pain and will indicate to the doctor that direction of the needle insertion needs to be adjusted.
Once the needle is in the correct position, the CSF will begin to drip out. Usually the CSF pressure is then measured. To do this, the doctor will attach a length of plastic piping to the needle and note how far up the tube the CSF rises. This is called manometry. You may be asked to cough or strain down while this is being done and the doctor may also press gently on one side of your neck to check that the CSF can pass freely between the head and the spinal canal.
Following manometry, samples of CSF are usually collected in sterile containers. In most cases only a small volume is needed for laboratory testing but a larger volume may be removed if the doctor wishes to reduce the pressure within the head.
Once the procedure is complete, the needle will be removed and a small plaster will be put on the skin. The whole procedure usually takes about 30-45 minutes in most cases.
After the procedure
After having a lumbar puncture, you may be asked to lie flat for a period of time, on the basis that this may reduce the likelihood of a post-lumbar puncture headache developing, although many headaches don’t develop for at least several hours and often not until the following day.
Most people undergoing non-emergency lumbar puncture on a day-case basis will be allowed to return home as soon as possible, where they can treat any headache with bed rest, fluids and simple pain killers. The skin plaster can be removed the following day.
When you can return to normal activities depends on how severe any post-lumbar puncture headache is and how long it lasts. Once you can get up and about without experiencing troublesome headache, then you can return to normal activities including work or school and driving. However, as a precaution it is usually best to avoid sports and strenuous activities for at least a week.
Getting the results
Your doctor can tell you the results of pressure measurements straight away, and explain what they mean. The results of some laboratory tests, such as looking for signs of inflammation or checking for evidence of bleeding into the head, are available quite quickly - in the case of a medical emergency, within a couple of hours.
Other tests, such as identifying bacteria causing meningitis, are more complex and may take at least 48 hours to complete. More specialised tests may take several weeks before the results become available.
Lumbar punctures are generally very low-risk procedures. However they sometimes cause short-lived side effects.
Some people experience some lower back pain after a lumbar puncture. This is usually felt in and around the area where the needle was inserted. In most cases the pain will ease after a few days and it can be treated with painkillers, such as paracetamol, if necessary.
A headache is a common side effect of a lumbar puncture, usually developing within 24 to 48 hours of the procedure. Most people describe a dull or throbbing pain at the front of their head and this can sometimes spread to the neck and shoulders. The pain is usually worse while standing or sitting up and is usually relieved by lying down.
The headache can usually be treated with simple painkillers such as paracetamol. Some people have also reported that drinks containing caffeine, such as coffee, tea and or cola, have helped reduce the discomfort.
If post-lumbar puncture headaches persist, are particularly severe, or are accompanied by sickness and vomiting, the hospital that carried out the procedure should be contacted.
There is a small risk of a lumbar puncture leading to bleeding inside the head, although this is very rare. In most cases, the benefits of the lumbar puncture far outweigh this risk. The likelihood of a lumbar puncture causing an infection in the spine is also very small.
However, you should seek medical advice if you develop a temperature or sensitivity to bright lights, or if the lumbar puncture site becomes painful and swollen.
Why it is necessary
A lumbar puncture is often used to diagnose certain conditions that affect the brain and spinal cord.
Some of these conditions are described below.
Meningitis is the inflammation of the membrane layers that cover the brain and spinal cord. It can develop from a number of different causes, including infection by bacteria or viruses. Bacterial meningitis can be serious and even life-threatening.
A lumbar puncture is needed to diagnose the condition and ensure appropriate treatment is started.
A subarachnoid haemorrhage occurs when a blood vessel, within or underneath the brain, bursts (ruptures). The condition is usually diagnosed using a computerised tomography (CT) scan but in some instances it may be necessary to perform a lumbar puncture as well, to detect the presence of blood in the cerebrospinal fluid (CSF).
A diagnosis is important because there is a risk of further haemorrhages. Treatment is available to prevent this.
Guillain-Barré syndrome is a rare condition which causes inflammation of the nerves that supply the arms and the legs. A lumbar puncture is needed to check the protein level in the CSF, which is usually higher than normal in people with this condition.
As well as being used to diagnose conditions, a lumbar puncture is sometimes used to administer treatments, by injecting medication into the cerebrospinal fluid. Such medications include antibiotics to treat bacterial meningitis and chemotherapy medicines to manage certain types of cancer affecting the central nervous system.
A lumbar puncture can also be used to relieve a pressure build-up within the skull (known as raised intracranial pressure) by removing some CSF. This can provide short-term relief of symptoms, until a more permanent treatment for the underlying problem can be provided.