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This page provides information about endovascular treatments of AVMs undertaken in the NHNN angiography suite.

If you have any questions about endovascular AVM treatment, please do not hesitate to contact a member of the team caring for you or of the neuroradiology team. They will be happy to answer any question you may have.

Normally a fine network of microscopic capillaries connects arteries and veins in all tissues including the brain. Capillaries assist in slowing down blood flow between arteries and veins.

An AVM is a tangle of feeding arteries and draining veins that have abnormal connections bypassing capillaries. The high-pressure blood flowing from arteries directly into thinner-walled veins gives AVMs a high risk of haemorrhage or bleeding. This abnormal blood flow is called a shunt.

AVMs vary between a few millimetres to several centimetres in size, and can occur anywhere in the brain or spinal cord. It is not known what causes AVMs to form in the brain, they most commonly present in early adult life with seizures or bleeding. An AVM in the brain carries approximately 3% chance of bleeding per year, considerably higher than this in some cases and following a previous bleed. A bleed results in a haemorrhagic stroke which is almost always a severe event and sometimes catastrophic.

You may have been referred for endovascular treatment as you previously suffered an intracranial haemorrhage or have experienced common symptoms of AVMs such as seizures, headaches or neurological deficit. Some patients have asymptomatic lesions that have been identified on imaging or investigations as ‘incidental findings.’

There are three main types of treatment for an AVM:

  • Endovascular treatment (also known as embolisation)
  • Stereotactic radiosurgery (also known as gamma knife treatment)
  • Surgical excision

These treatments will be discussed in further detail throughout this page.

Endovascular treatments or embolisations are carried out to protect the AVM from bleeding. In an embolisation, special glue-like liquid is injected into the AVM in order to cut off blood supply and cause the AVM to shrink over time.

An embolisation is normally performed to treat the AVM completely. If the AVM is particularly large or complex, an embolisation may be completed prior to further surgical excision (removal) or gamma knife treatment of the lesion, in order to reduce blood flow to the AVM and ensure further treatment is safer.

All treatments and procedures have risks and we will talk to you about the risks of having an AVM embolisation. No two AVMs are the same: The risks of embolisation vary from one AVM to the next according to the size, position and configuration of the vessels.

Sometimes it is not possible to embolise an AVM safely. The procedure will need to take place under a general anaesthetic; the anaesthetist will discuss the risks of general anaesthesia with you.

Problems that may happen straight away

During an AVM embolisation, a contrast agent will be injected into your arteries; this allows the Interventional Neuroradiologist (INR) to see the blood vessels and the AVM when an X-ray is taken. Contrast agents are 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

The contrast agent used during an AVM embolization is iodine based contrast and is excreted through the kidneys, this may affect your kidney function. You will 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 an embolisation. 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’.

Problems that are rare, but serious

AVM embolisations are difficult and complex procedures: serious complications are unlikely, but are always present. Like all procedures involving the blood vessels of the brain, an AVM embolisation 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. The percentage level of this risk can only really be discussed on a case by case basis and depends on the size, position and configuration of the AVM itself.

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 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 ensure the radiation dose is 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).

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, AVM embolisations are usually performed within the first ten days of the menstrual cycle when pregnancy is much less likely. The interventional neuroradiologist performing the procedure will discuss all possible risks with you and give you the opportunity to ask questions.

If we think you will benefit from embolisation of your AVM we will offer you this procedure, the final decision whether or not to have this procedure is entirely yours. To decline the procedure will not affect your personal care. However, it may mean that your doctor cannot be as certain or specific about any future treatment or procedures and it may affect some clinical decision making.

Certain patients with multiple risk factors or who have very complex AVMs for which treatments would be considered high risk, may have conservative management of their AVM instead. This would involve interval imaging and clinical assessment to monitor the progression of the lesion; however this would not reduce the risk of an AVM bleeding. Some patients may be able to take medication to reduce symptoms they experience from their AVM.

As mentioned previously AVMs can be treated by multiple methods:

Gamma Knife Treatment

This involves a high dose of radiation directed specifically at the nidus or nest of tangles within the AVM. This causes the AVM to shrink over time which usually takes about 3-4 years to fully cure; this can vary between patients and the size of the lesion. Gamma knife tends to be selected for treatment of smaller AVMs.

Surgical excision

This involves a craniotomy, or creating an opening in the skull to allow the neurosurgeon to surgically remove the AVM. The feeding arteries and draining veins that remain in the brain are then clipped off. Surgery is a well-established and effective treatment and can provide immediate protection from AVM rupture or haemorrhage. This might not be an option for AVMs deep within the brain. As with AVM embolisations, the alternatives carry their own specific risks and your neurosurgeon will discuss these in detail with you. If you are unsure about the treatment you are due to receive do not hesitate to speak with your referring doctor.

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 surgical reception unit (SRU) or 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 neuroradiologists (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, 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, unless advised otherwise. You will be asked to change into a hospital gown and disposable underwear. A member of staff, usually the nurse caring for you, will accompany you to the neuroradiology department.

It is important that you are involved 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.

The AVM embolisation is performed while you are under general anaesthetic. The anaesthetic team will put you to sleep in the anaesthetic room prior to transfer to the angiography suite. The procedure is performed by the INR in the angiography suite (operating theatre) located in the neuroradiology department. It usually takes between one and three hours.

A dedicated team of radiologists, radiographers, anaesthetists and nurses will be in the angiography suite to monitor you closely throughout the procedure. Once the procedure has commenced, the INR will use local anaesthetic to numb your groin or arm before placing a thin, flexible, plastic tube (catheter) into the femoral artery in the groin or radial artery in the arm. The catheter passes through the main artery in the body called the aorta and finally into the arteries in your brain.

Before the embolisation begins the INR will inject the cerebral arteries to confirm the best approach into the AVM nidus, a contrast agent will be injected which will allow the blood vessels and the AVM to be seen when an X-ray is taken. When an accessible feeding artery is identified the catheter is placed into this feeding artery.

Following this a second microcatheter is inserted inside the first. This microcatheter is placed directly into the nidus of the AVM. Embolic material (glue like material) is then injected to seal off and obliterate the AVM nidus. Occasionally small metal coils or permanent balloons will be used too. This embolic material creates an artificial blood clot or blockage to stop blood flowing into the AVM. Further x-rays will be taken to ensure the AVM has been obliterated as much possible. 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 stitch.

After the procedure you will spend some time in the recovery unit or high dependency unit (HDU) before being transferred back to your ward. These units provide a high level of monitoring. You will be on bed rest for at least a few hours following the procedure to ensure the entry site of the catheter in your groin or arm begins to heal and that you are neurologically stable.

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. You will be given pain killing drugs to help. You may also experience some pain or bruising at your groin or arm, depending where the catheter was placed, this should reduce over a few days.

For any non-urgent questions or concerns you may have following your procedure, please contact the neurovascular clinical nurse specialists.

The Brain & Spine Foundation UK
0808 808 1000

UCLH cannot accept responsibility for information provided by other organisations.

Lysholm Department of Neuroradiology
National Hospital of Neurology and Neurosurgery
Queen Square, London

Direct line: 020 3448 3444
Switchboard: 0845 155 5000
Extension: 83444/ 83446
Fax: 020 344 84723

Neurovascular Clinical Nurse Specialists
National Hospital for Neurology and Neurosurgery
Queen Square, London

Direct line: 020 3448 3523
Switchboard: 0845 155 5000
Extension: 83523

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.

Page last updated: 15 May 2024

Review due: 30 September 2024