This page has been written by the Lysholm Department of Neuroradiology at the National Hospital for Neurology and Neurosurgery (NHNN). Our aim is to provide you with information about flow-diverting stents and how they are used to treat cerebral (brain) aneurysms.
It is intended for use by patients (or their families and carers) in whom treatment with a flow-diverting stent has been proposed. It is not intended to replace discussion with your consultant.
If you have any questions about flow-diverting stents, or would like further information about cerebral aneurysms, please do not hesitate to contact a member of the team caring for you. They will be happy to answer any question you may have.
A flow-diverting stent (FDS) is a small tube, made of very fine wire mesh. These tubes act like a ‘patch’ within the blood vessel to stop the blood supply to the aneurysm and prevent any further bleeding (see Figure 1).
Older stents were made of wider mesh and were designed to hold fine metal coils within the aneurysm. The coils were used to pack the aneurysm rather than directly diverting blood flow away from the aneurysm.
Flow-diverting stents are similar, but are designed to disrupt the blood flow into the aneurysm, allowing it to clot off without the need for coils. We have been using flow-diverting stents at NHNN since early 2008.
The aim of flow-diverting stent treatment is to prevent blood from entering the aneurysm and therefore prevent the risk of it bursting. The stent covers the abnormality in the blood vessel (see above) and we believe it is likely to provide a more permanent cure of the aneurysm. Flow-diverting stents also allow us to successfully treat large, wide-necked or sausage-shaped (fusiform) aneurysms. These particular types of aneurysms have been difficult or impossible to treat with standard stents and coils in the past.
All treatments and procedures carry risks and we will talk to you about the risks of flow-diverting stents. Each case carries a different risk and we will try to estimate your personal risk in our discussions with you. The procedure will take place under a general anaesthetic. Your anaesthetist will discuss the risks of general anaesthesia with you. Risks associated with this procedure include:
Problems that may happen straightaway
During a flow-diverting stent treatment, a contrast agent will be injected into your arteries; this allows the Interventional Neuroradiologist (INR) to see the blood vessels and the aneurysm when an X-ray is taken. Contrast agents are considered safe drugs. However, as with all drugs, they have the potential to cause an allergic reaction. The department and team are well equipped to deal with reactions in the rare event of this happening.
Problems that may happen later
Headaches are quite common after aneurysm treatments, probably due to clotting inside the aneurysm as part of the healing process and may go on for some time. A mild painkiller, rest and drinking plenty of water will help. We will give you pain medication to help.
You may be at a higher risk of bleeding than normal. You will need to take tablets to make the blood thinner and less likely to clot in the days leading up to the procedure and for many months afterwards. These tablets can increase the risk of bleeding in other areas of the body and can irritate the stomach. It is important to tell your consultant if you have had a stomach ulcer in the past.
The contrast agent used during a flow-diverting stent treatment is iodine-based contrast and is excreted through the kidneys; this may affect kidney function. You will therefore have a blood test to test your kidney function beforehand to ensure it is safe for you to have contrast. The risk of you having contrast will be weighed against the benefit of having this treatment and is decided by the team referring you. For further information on the use of iodine-based contrast agents please see the information leaflet ‘Contrast Agents for X-ray, Fluoroscopy, CT and Angiography Examinations: An Information Guide’ or alternatively visit the trust website.
Problems that are rare, but serious
Flow-diverting stent treatments are difficult and complex procedures. Serious complications are unlikely, but are always present. Like all procedures involving the blood vessels of the brain, a flow-diverting stent treatment carries a risk of stroke which results from either a blockage of a blood vessel or from a haemorrhage. This can range from a minor problem which improves over time to a severe disability involving movement, balance, speech or vision or may even be a threat to life. On our current evidence, we would estimate that between three and seven people in one hundred will experience these problems.
Other Problems that occur
Haematoma, bruising or vessel damage around the puncture site may also occur. Usually, a stitch is placed in the femoral artery (in the groin) or radial artery (in the arm) after the tube has been removed. Often there is bruising and sometimes bleeding in the groin or arm. It is rarely serious but can go on for a few hours. Very occasionally, there is damage to the blood vessel requiring a further surgical operation.
Any problem is usually apparent during or immediately after the procedure, or during the next few days whilst you are still in the hospital.
Radiation Risk
The use of X-rays during any procedure results in a very small increase in the risk of developing cancer in the future. For the more complex cases, temporary hair loss and skin erythema (reddening) may occur a few weeks after the procedure. Our state-of-the-art imaging equipment and modern techniques help to ensure the radiation dose is kept as low as possible. In addition, your doctor will have made a judgement about your risk and benefit before agreeing to the procedure (including the risk to your health of not having the procedure).
Female 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 procedure may still go ahead but with additional precautions in place. To reduce the risk for early and unknown pregnancies, flow-diverting stent treatments are usually performed within the first ten days of the menstrual cycle when pregnancy is much less likely.
Our long experience with flow-diverting stents suggests delayed problems are very unusual. The Interventional Neuroradiologist performing the procedure will discuss all possible risks with you and give you the opportunity to ask questions.
Your case will have been discussed by a multidisciplinary of Neuroradiologists, Neurosurgeons and Neurologists. The treatment offered is based on the agreement of the team as to what is the best course of action. It is important that you fully understand the procedure, what it means for you and any alternative treatments available. You are under no obligation to follow the advice given. If you are unhappy about the treatment being offered, a full discussion with members of the team can be arranged. It is entirely reasonable to seek a second opinion if you still have concerns. Whatever decision you reach it will not affect the standard of care you receive. We will continue to offer you the best care possible, based on the best current evidence we have available.
There are several options available for the treatment of aneurysms. However, the location, size and shape of the aneurysm can dictate which treatment is the safest. It is likely that these other treatments will be considered as higher risk than the treatment offered. Your Consultant or a senior member of their team will talk through all options with you. Alternative treatments for cerebral aneurysms include:
Conservative treatment
On occasion, treatment consists of clinical follow-up and Magnetic Resonance Imaging (MRI) or Computerised Tomography (CT) scans. This is done in conjunction with blood pressure control and advising on any appropriate lifestyle changes (such as giving up smoking). This option carries a risk of the aneurysm bleeding or causing other problems in the future.
Surgical treatment
Some aneurysms can be treated surgically by placing a metal clip across the neck of the aneurysm (narrow part of the aneurysm), this is called ‘clipping’. This procedure is performed under a general anaesthetic and involves opening the skull to reach the aneurysm.
Other radiological techniques
More commonly, aneurysms are treated by passing a catheter (fine tube) through the blood vessels and ‘packing’ the aneurysm from the inside with very fine metal coils (coiling). This is more likely to result in a recurrence of the aneurysm requiring further treatment(s).
You will be given a course of anti-platelet medication for six days prior to your flow-diverting stent treatment. This course will involve taking oral aspirin and prasugrel, which are used to thin the blood, these are given to reduce the likelihood of your blood clotting and potentially causing a stroke, during or shortly after the procedure. The neurovascular clinical nurse specialists will contact you before your treatment to advise on these medications. You should take all your other medications as normal, unless advised otherwise.
You will be asked to arrive at the hospital the day before or on the morning of your procedure. If you are arriving the morning of your procedure, you will be asked to arrive at 8am to the ward specified by the admission officer in contact with you. Your procedure may take place at any time during the day due to emergency cases, but we will endeavour to keep you informed and perform your procedure as early in the day as possible.
The procedure is performed by specialist doctors called Interventional Neuroradiologist (INR). The INR will see you on the ward to explain the procedure and any associated risks. Please feel free to ask any questions at this time.
The procedure is performed under a general anaesthetic (this means you will be unconscious or ‘asleep’ throughout). Your anaesthetist will talk to you about the anaesthetic, pain relief and what you can expect when having a general anaesthetic both in clinic before the procedure and again briefly on the ward the day of your procedure. You will need to fast for six hours before your procedure. Your anaesthetist will confirm with you a specific time you must stop eating and drinking. You should still take all of your medications at the normal times throughout this period with a sip of water.
A member of staff, usually the nurse caring for you, will accompany you to the radiology department.
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.
You will be given a general anaesthetic in the anaesthetic room prior to transfer to the angiography suite. The procedure is performed by an INR in the angiography suite (operating theatre) located in the radiology department. It usually takes between one and three hours. A dedicated team of radiologists, radiographers, anaesthetists and nurses will be in the angiography suite. They will be monitoring you closely throughout the procedure.
Once the procedure has commenced, the INR uses X-ray guidance to place a thin, flexible plastic tube (catheter) into the femoral (in the groin) or radial (in the arm) artery. The catheter passes through the main artery in the body called the aorta and finally into an artery supplying the brain.
A second smaller catheter is inserted inside the first. The second catheter goes past the ‘neck’ of the aneurysm to the normal blood vessel on the far side. The collapsed stent is pushed to the tip through the smaller catheter. The smaller catheter is then pulled back to allow the stent to expand in the vessel across the neck of the aneurysm. This usually immediately reduces the amount of blood getting into the aneurysm. Sometimes it is necessary to place two or more stents inside one another to get the best result.
Once the INR is satisfied with the result, the catheters are removed and the blood vessel in the groin or arm is sealed with a small plug like device or stitch.
After the procedure you will spend some time in the high dependency unit (HDU) before being transferred back to your ward. This unit provides a high level of monitoring.
You can expect to remain in hospital for a minimum of four to five days after the procedure, until you are walking around and feeling back to normal. You should plan to take some time off work, at least a week or two and you should arrange to have someone to stay with when you first return home. Everyone is different and people recover from these procedures at different rates.
It is common to experience headaches in the days or weeks following the procedure. This is related to the aneurysm shrinking. You will be given pain killing drugs to help.
If this headache becomes severe or you experience nausea, vomiting, drowsiness or severe stiffness in your neck go immediately to your nearest Accident and Emergency Department (A & E, Casualty) where a CT scan will be performed.
For any non-urgent questions or concerns you may have following your procedure, please contact the Neurovascular Nurse Specialists.
The Brain & Spine Foundation UK
Telephone: 0808 808 1000
UCLH cannot accept responsibility for information provided by other organisations.
- Lylyk, P, et al, Curative Endovascular Reconstruction of Cerebral Aneurysms with the Pipeline Embolization Device: the Buenos Aires Experience; Neurosurgery: April 2009 -Volume 64 - Issue 4 - p 632-643.
Lysholm Department of Neuroradiology, National Hospital of Neurology and Neurosurgery, Queen Square, London, WC1N 3BG
Direct line: 020 344 83444
Switchboard: 0845 155 5000
Extension: 83444/ 83446
Fax: 020 344 84723
Email: uclh.
Website: www.
Neurovascular Clinical Nurse Specialists, National Hospital for Neurology and Neurosurgery, Queen Square, London, WC1N 3BG
Direct line: 020 344 83523
Switchboard: 0845 155 5000
Extension: 83523
Email: uclh.
Website: www.
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: 25 April 2025
Review due: 01 April 2027