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This information has been written by the Lysholm Department of Neuroradiology at The National Hospital for Neurology and Neurosurgery (NHNN). The aim of this page is to provide information about CT cisternograms. It is intended for use by patients (or their families or carers) who have been referred to our service for this procedure. It is not intended to replace discussion with your consultant.

If you have any questions about CT cisternograms a member of the Neuroradiology team will be happy to answer them for you.

A CT cisternogram is an examination which provides detailed information about the fluid spaces around your brain. Cerebrospinal fluid (CSF) normally flows through the various cisterns and ventricles (subarachnoid space), which is the space that surrounds your brain and spinal cord.

An iodine-based contrast agent (sometimes called a dye) is injected through a spinal needle, into the fluid space at the base of the spine, below the level of the spinal cord. This dye tracks around the system of fluid spaces of the spine and brain, showing these areas up on CT brain imaging. The information obtained can help to make a diagnosis or to plan your further treatment.

A CT scanner is a type of X-ray machine that produces highly detailed cross-sectional images of the inside of the body. The patient travels slowly through the centre of the scanner on a moving bed whilst the X-rays are being taken. The X-ray signals are then processed by a computer to form an image.

A CT cisternogram can show any problems with the way CSF circulates through your system and identify any CSF leaks, which could be causing your symptoms.

This type of examination is sometimes also used for patients unable to have an MRI scan, for example some patients who have pacemakers. In other patients CT cisternogram is used in addition to an MRI scan as it provides different information.

All treatments and procedures have risks and we will talk to you individually about the risks of CT cisternogram and the use of X- rays.

Problems that may happen straight away

  • Some stinging may occur when the local anaesthetic is being injected; however, this is only temporary.
  • There may be some short-lived pain when the lumbar puncture needle is being positioned.
  • You may feel some discomfort when the contrast is injected, for example a heavy, dragging feeling in your legs or a tingling into the buttocks.
  • On a very rare occasion allergic reaction to the contrast agent may occur. Please let us know if you are sensitive to iodine or if you have had any previous problems with contrast agents.
  • Contrast can cause headaches, and in very rare occasions a seizure.
  • The lumbar puncture performed to introduce contrast can cause a CSF leak.

Problems that may happen later

  • Some people experience backache or a headache immediately after or within a day or so of the cisternogram. This is common and can be relieved by simple painkillers such as paracetamol. Drinking plenty of fluids reduces the risk of headache and will also help to relieve it.

Problems that are rare, but serious

Whilst serious complications remain very unlikely, they may include:

  • nerve root damage
  • bleeding into the spinal cord
  • meningitis
  • infection
  • CSF leak or haemorrhage
  • radiation effects
  • seizure.

Radiation Risk

Like all X-ray machines, a CT scanner produces X-rays which can potentially be harmful and may cause some cancers to develop in the future. Modern CT equipment and techniques are designed to keep the -ray exposure as low as possible whilst producing some exceptionally clear images of your body. In addition, your doctor will have made a judgement about your risk and benefit before agreeing to the scan (including the risk to your health of not having the scan). The dose of radiation for each procedure can be compared to the amount of background radiation that you will receive just by living in the UK. The amount you receive will depend on the type of scan you are having. For example, a CT scan of the head will be the same as receiving an additional six months of natural background radiation.

Patients of child bearing capacity between the ages of 12 and 55 years are required by law to be asked about possible pregnancy when undergoing examinations involving x-ray. Patients who either are, or think they may be pregnant must inform the Neuroradiology Department as soon as possible. In some urgent cases the scan may still go ahead but with additional precautions in place. To reduce the risk for early and unknown pregnancies, CT cisternograms are usually performed within the first ten days of the menstrual cycle when pregnancy is much less likely.

The Radiologist will discuss all possible risks with you and give you the opportunity to ask questions.

The decision whether or not to have this diagnostic examination is entirely yours. To decline the procedure will not affect your personal care. However, it may mean that your consultant cannot be as certain or specific about any future treatment or procedures and it may affect some clinical decision making.

Your referring consultant will discuss alternative investigations with you, including their risks and benefits. These may include CT scan without contrast or MRI.

You may be asked to attend pre assessment clinic before your admission, this is so we can take blood tests and ensure you are prepared for the procedure.

You will be admitted to hospital on the morning of the procedure. A member of the nursing staff on the ward will complete an admission checklist with you and give you an identity bracelet to wear whilst you are in hospital. You will be offered a hospital gown or you can bring your own loose, comfortable clothing if you prefer. All jewellery and hair clips should be removed.

We will ask you about all of the medicines you are taking especially anticoagulants such as warfarin or heparin, or antiplatelet agents such as aspirin, clopidogrel or dipyridamole. These medicines may need to be stopped before your procedure. The clinical team organising your admission will advise you of this in advance. Please do not stop taking any medicines unless you have been specifically advised to do so. The staff will also need to know about any previous reactions you have had to iodine-based contrast agent or any allergies you may have, including iodine.

On the day of the procedure, you can eat and drink normally and take all of your usual medications, except for those mentioned above. It is advisable to be well hydrated prior to this test.

We want to involve you in all the decisions about your care and treatment. If you decide to go ahead with treatment, by law we must ask for your consent and will ask you to sign a consent form. This confirms that you agree to have the procedure and understand what it involves. Staff will explain all the risks, benefits and alternatives before they ask you to sign a consent form. If you are unsure about any aspect of your proposed treatment, please don’t hesitate to speak with a senior member of staff again.

The nurse caring for you will escort you from the ward to the angio suite within the Neuroradiology department for your test.

A Radiologist (radiology doctor) will explain what will happen and answer any additional questions you may have. We will ask you to lie on the examination table either on your front or on your side. The Radiologist will clean the skin and a local anaesthetic will be is injected to numb the area of skin. A fine needle is inserted into the fluid-filled space below the spinal cord. X-rays are taken to help position the needle correctly. During this part of the procedure a small amount of cerebrospinal fluid may be drained off and sent to the laboratory for analysis. Once the needle is in the correct position the iodine-based contrast agent is injected slowly. The needle is then removed.

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You will be transferred onto a trolley and taken to the CT scanner, within the same department where very detailed images can be obtained. We may tilt the trolley so your head is lower than your body and legs; this helps encourage the contrast to flow to the basal cisterns and fill these CSF spaces.

The Radiologist will ask you to lie on the CT table and we will try to make you as comfortable as possible. Throughout the scan it is very important to lie still to ensure the best possible images are obtained. This scan usually only takes a few minutes. Sometimes we will recall you for a second scan after a delay.

After the procedure you will be taken back to the ward. On the ward you must remain in bed for two to three hours with your head slightly raised. Drinking plenty of fluids is advised.

You will not normally be required to stay overnight unless further delayed imaging is required, or other investigations have been arranged for you during your admission. You can resume normal day-to-day activities after discharge.

The Radiologist who performed the procedure will write a report to your referring doctor. They will discuss the test results with you at your next consultation.

If you experience any of the following you should contact your GP or go to the nearest Accident and Emergency Department straight away:

  • severe headache which is not relieved by over the counter medicine or which lasts longer than 24 hours
  • drowsiness
  • fever
  • new symptoms such as weakness or numbness in your limbs
  • difficulty passing urine or moving your bowels
  • dizziness
  • discharge of blood or fluid from the injection site in your back.

NHS Direct is a useful source of health information.

The CSF Leak Association also has helpful information and online support for patients:

UCLH cannot accept responsibility for information provided by other organisations.

Lysholm Department of Neuroradiology

National Hospital of Neurology and Neurosurgery

Queen Square




Direct line: 020 344 83444

Switchboard: 0845 155 5000 / 020 3456 7890

Extension: 83444 / 83440

Fax: 020 344 84723


The Lysholm Department of Neuroradiology reception is located in Chandler wing, on the lower ground floor of the National Hospital for Neurology & Neurosurgery, Queen Square.

Please turn left when you exit the chandler wing lifts on the lower ground floor to find our main departmental reception.

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Page last updated: 28 May 2024

Review due: 01 May 2026