CT myelogram: why it is done, what happens and what to expect afterwards

In a myelogram, a contrast agent, which Newcastle Hospitals describes as an X-ray dye, is injected into the spine so that several sections of the spine can be studied at one time. The leaflet explains that a special dye is injected through a needle in order to coat the spinal cord and nerve roots.

A CT myelogram adds a CT scan after the injection. Royal Berkshire explains that CT uses X-rays and a computer to create detailed images of the inside of your body, and that this examination is a diagnostic X-ray examination to look at your spine and spinal cord in order to investigate any previous diagnosis. CT slices through the spine in thin layers, which Royal Berkshire likens to slices in a loaf of bread.

A CT myelogram is a test used when MRI is not possible or not suitable. Royal Berkshire says you will have been referred for a CT myelogram if you are unable to have an MRI scan due to claustrophobia or because it is contraindicated, which it illustrates with an implanted electronic device such as a pacemaker.

Newcastle explains the underlying purpose: a myelogram is used to determine the cause of pain or numbness in the back, neck, arms or legs. Your specialist will explain which question the test is meant to answer, for example whether a nerve is being squeezed and where.

Both trusts ask you to tell the department about certain things before the day. These checks reduce risk, so do raise them early.

• Blood-thinning medicines. Newcastle asks you to ring the department if you take medication to thin your blood, and Royal Berkshire asks you to contact the X-ray nurses to check whether medicine such as warfarin should be stopped. Do not stop it on your own.

• Diabetes. Newcastle asks you to call if you are diabetic or take metformin.

• Allergies. Newcastle asks you to call if you think you may be allergic to X-ray dye, and Royal Berkshire says to notify the radiology department if you know you are allergic to iodine.

• Pregnancy. Newcastle asks you to call if there is a possibility you may be pregnant.

• Food and other medicines. Royal Berkshire says you may eat and drink normally and continue other medicines, apart from blood thinners. Newcastle says most medicines should be taken as normal and recommends a light breakfast or lunch. Bring medicines and inhalers with you.

• Someone to take you home. Both leaflets say you should have someone to take you home. Newcastle says you will not be able to drive home and must not drive for 12 hours after discharge.

Before the test a doctor explains the procedure and its risks and asks for your written consent, according to Newcastle. You are given an X-ray gown. You lie on the X-ray table and the radiologist cleans your back and injects a local anaesthetic to numb the area. A small spinal needle is placed into the membrane surrounding the spinal cord, and contrast is injected through it. The needle is then removed and a small dressing is applied. Royal Berkshire says local anaesthetic should mean you experience a pushing sensation rather than pain.

Several X-ray images may be taken, and you need to remain still. In the Newcastle pathway you are then transferred to the neuroradiology CT scanner for further images while lying on your back. At Royal Berkshire you return to the day bed for approximately one hour after the injection before being taken to the CT scanner, where you may be asked to roll over a couple of times to help disperse the contrast. The scan normally takes place with you lying on your stomach, or on your back if that is not possible, and takes only a few seconds.

Because a needle is placed in the spinal canal, there are specific risks. Royal Berkshire lists bleeding as a possibility, which is why a blood test checks how well your blood is clotting beforehand, and infection as extremely rare, since the procedure is performed under strict sterile conditions. The CT scanner uses ionising radiation, and the leaflet says the dose is kept as low as practically possible.

Newcastle says a common side effect of a myelogram is headache, so you are advised to drink plenty of fluids once the test is finished. Nausea and sickness are not common but can occur. Most side effects resolve within a few hours. If you continue to feel unwell, contact your GP or the neuroradiology department. You are advised to sit upright and avoid bending forward for a few hours, and the contrast, a colourless liquid, leaves the body when you next pass urine. Royal Berkshire adds that you may have some discomfort in your back after the procedure.

Newcastle says the images are examined by the radiologist once the test is finished and a report is sent to the specialist who referred you, who then arranges for you to receive the results.