Introduction

A lumbar puncture is a medical procedure where a needle is inserted into the lower part of the spine to test for conditions affecting the brain, spinal cord or other parts of the nervous system.

During the procedure, pressure is measured and samples of cerebrospinal fluid (CSF) are taken from inside the spine. CSF is a clear, colourless fluid that surrounds and supports the brain and spinal cord. Analysis of CFS can often reveal a good deal about some conditions that affect the brain and spinal cord.

The fluid can be tested to help diagnose conditions, such as:

  • meningitis – an infection of the layers (membranes) surrounding 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

A lumbar puncture doesn't necessarily mean you have one of these conditions; it may be used to rule them out.

A lumbar puncture can also be used to treat some conditions, such as injecting antibiotics or chemotherapy medication into the CSF.

Read more about why lumbar punctures are used.

How is a lumbar puncture carried out?

Under local anaesthetic, a hollow needle is inserted into the base of the spine and into the spinal canal, which contains the spinal cord and the nerves coming from it.

The pressure within the spinal canal is usually measured and some CSF is removed either to reduce the pressure or for a sample to be sent for testing.

You will normally be lying on your side, with your legs pulled up and your chin tucked in, but sometimes the procedure is carried out while you’re seated and leaning forwards.

It usually takes around 30-45 minutes to complete.

It’s possible to get results on CSF samples within 48 hours, but specialised tests can take several weeks.

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 very low.

Serious side effects are generally uncommon, although many people experience headaches caused by CSF leaking out through the needle hole in the spine. This occurs internally, so you won’t see it.

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 painkillers 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.

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Why is it necessary?

A lumbar puncture is often used to diagnose certain conditions that affect the brain and spinal cord.

Meningitis

Meningitis is the inflammation of the membrane layers covering the brain and spinal cord. It can develop from a number of different causes, including infection by bacteria or viruses. Bacterial meningitis can be life-threatening.

A lumbar puncture is needed to diagnose meningitis and ensure appropriate treatment is started.

Subarachnoid haemorrhage

subarachnoid haemorrhage occurs when a blood vessel within or underneath the brain bursts (ruptures). It's usually diagnosed using a computerised tomography (CT) scan, but sometimes it may be necessary to perform a lumbar puncture to detect the presence of blood in the cerebrospinal fluid (CSF).

Guillain-Barré syndrome

Guillain-Barré syndrome is a rare condition that causes inflammation of nerves supplying the arms and the legs. A lumbar puncture is needed to check the protein level in the CSF, which is usually higher with this condition.

Providing treatment

A lumbar puncture can also be used to administer treatments by injecting medication into the CSF. Medications include:

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 give short-term relief of symptoms until a more permanent treatment can be provided.

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How is it performed?

Lumbar punctures are carried out in hospital. This may be after an emergency admission, or the procedure may be arranged in advance.

Preparation

Before a lumbar puncture, checks will be made to confirm the procedure is safe for you. Usually a computerised tomography (CT) scan or an magnetic resonance imaging (MRI) scan will have been carried out to make sure the lumbar puncture is needed and will not cause any harm. It will not be done if you have recently taken blood-thinning medication (anticoagulants) such as warfarin.

A doctor or nurse will explain why it’s needed and you’ll be asked to provide written consent for it. 

If it’s not possible for you to provide informed consent – for example, if you are unconscious or confused, the medical staff may decide to go ahead with the procedure, if it’s 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. As the lumbar puncture can take some time, you might want to use the toilet beforehand.

The procedure

In most cases, you’ll be asked to lie on one side and to curl up, with your knees up and your chin in, so your spine is curved. This helps to separate the bones in your spine, allowing the needle to be inserted more easily.

Sitting while bending forwards is an alternative position, although it’s not always suitable.

An antiseptic solution will be applied to the skin at the base of the spine. A local anaesthetic is then used to numb the area of the lumbar puncture site. If a child needs to have a lumbar puncture, medication may be given beforehand to help them relax and keep calm.

The doctor (or sometimes a specially trained nurse) will insert a special spinal needle between the bones at the base of the spine and into the spinal canal, penetrating the membrane containing 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 it will indicate to the doctor a need to adjust the needle’s direction.

Once the needle is in the correct position, the CSF will begin to drip out. Usually, the CSF pressure is then measured by attaching a length of plastic piping to the needle to see how far up the tube the fluid rises. This is called manometry. You may be asked to cough or strain while this is being done and the doctor may press gently on one side of your neck, to check that the CSF can pass freely between your head and spinal canal.

Following manometry, samples are usually collected in sterile containers. Only a small amount is normally needed for testing, but more may be removed if the doctor needs to reduce the pressure within the head.

Once the procedure is complete, the needle will be removed and a small plaster is applied. The whole procedure usually takes about 30-45 minutes, in most cases.

It normally takes your body less than two days to replace the fluid naturally.

After the procedure

Afterwards, you may be asked to lie flat for a period of time to reduce the chances of a post-lumbar puncture headache developing, although most headaches don’t develop for at least several hours and often not until the next day. You will normally have your pulse and blood pressure checked again.

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 be more comfortable and can treat any headaches with bed rest, drinking plenty of fluids and taking simple painkillers. The plaster can be removed the following day.

Returning to normal activities depends on how severe any post-lumbar puncture headache is and how long it lasts, but you should avoid driving or operating machinery for 24 hours. Once you can get up and about without experiencing troublesome headaches, you can return to normal activities, including work or school and driving. However, it’s best to avoid sports and strenuous activities for at least a week.

Getting the results

Your doctor or nurse who performs the lumbar puncture 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 – within a couple of hours, in an emergency.

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 days.

Can anything go wrong?

It's unusual for something to go seriously wrong during a lumbar puncture, but sometimes difficulties may occur. These can include:

  • The doctor may be unable to get the needle into the spinal canal. If this happens, it may be rearranged, using an X-ray to help guide the needle.
  • If a child is too upset or restless, the lumbar puncture may have to be postponed and perhaps performed under general anaesthetic.
  • The lumbar puncture may cause a small amount of bleeding into the spine. This is not dangerous, but if blood mixes with the spinal fluid sample it can affect the laboratory test results.
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Side effects

Lumbar punctures are generally very low-risk procedures. However, they sometimes cause short-lived side effects.

Back pain

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, but it can also be felt in the backs of your legs.

In most cases, the pain will ease after a few days and it can be treated with painkillers, such as paracetamol.

Headache

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, sometimes spreading 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 or cola, have helped to reduce the discomfort.

If post-lumbar puncture headaches persist, are particularly severe, or are accompanied by sickness and vomiting, contact the hospital that carried out the procedure.

Swelling and bruising

You may notice some bruising and minor swelling in your lower back. The swelling is caused by a small amount of fluid leaking and collecting under your skin. This is normally nothing to worry about and the swelling should go down naturally. However, seek medical advice if the swelling continues or gets worse.

Other risks

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 risks. 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, if the lumbar puncture site becomes painful and swollen, or if you notice blood or clear fluid around the site.

Rarer side effects include tingling and numbness in your legs, hearing loss and double vision.

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The information on this page has been adapted by NHS Wales from original content supplied by NHS Choices.
Last Updated: 22/04/2015 09:51:05