AVMs are defects of the circulatory system that can arise during embryonic or foetal development or can be acquired, as described, at any stage after birth.
In the normal situation, blood vessels called ‘arteries’ carry oxygenated blood away from the heart to all tissues and organs of the body. Inside each organ or tissue these arteries divide into smaller microscopic vessels called capillaries. It is at this level that oxygen is transferred from the blood to the tissues. Deoxygenated blood is then carried away from the tissues and back to the heart and lungs via blood vessels called ‘veins’
In a normal situation blood in arteries is under high pressure and blood in veins is under low pressure. The pressure reduction occurs as the blood passes through the capillary network in the tissues and organs.
An AVM is an abnormal connection (or usually multiple small connections) between an artery and vein. The point of abnormal connection between the artery and vein is referred to as the “nidus”. In this situation blood bypasses the capillary network within the organs and tissues and the normal pressure down regulation does not occur.
This depends largely on the site of the AVM and symptoms can vary significantly. The majority of AVMs however can be asymptomatic until a complication occurs. The most common and potentially life-threatening complication of AVMs is bleeding. Symptoms are often non-specific and can be caused by a wide range of other medical conditions.
AVMs in the brain may present with headaches, seizures or weakness of one or more parts of the body, or may only become apparent after a bleed (ie: burst / rupture).
AVMs in the lungs are typically asymptomatic although shortness of breath on exertion and the coughing up of blood (haemoptysis) can occur.
AVMs in the gastrointestinal tract typically present with bleeding and abdominal pain. The bleeding may be minimal and manifests itself as black stools or even anaemia (low blood count).
AVMs in the soft tissues (for example on the face, trunk, arms or legs) may typically be cosmetic, seen as a swelling or asymmetry that may or may not be painful. On the trunk and limbs these are often lumps that can be painful under certain circumstances and can over a period of time be seen to grow. Occasionally these AVMs can be disfiguring. Most soft tissue lumps are often thought to be tumours and sent for a biopsy before the diagnosis of an AVM is made.
AVMs may also show rapid growth in size over a relatively short time period or swelling may develop in the months following localised trauma if this is the cause. They can be classified related to their symptoms using the Schobinger classification, which can help plan the timing of treatment / intervention.
If AVMs are left untreated they may progress with growth, bleeding and eventually heart failure due to the rapid transit of blood through the AVM bypassing the rest of the body and returning rapidly to the heart. This leads to the hearts inability to cope with the increased blood flow and may lead to shortness of breath or chest pain and light-headedness.
At present very little can be done to prevent the development of an AVM. However, their progression and complications can be prevented if tailored treatment is appropriately offered. Life-threatening situations can be prevented from arising and stop the AVM getting larger.
Your doctor will have a suspicion or a good indication that you have an AVM on the basis of the history you provide and on physical examination or in some circumstance your family history. Your doctor will refer you to a specialist.
The diagnosis is typically clinical and imaging the lesion is key to understand the size and nature of the lesion. Imaging can also help decide when and how to treat these lesions. Ideally AVMs should be managed by a ‘multi-disciplinary’ team of doctors, nurses and specialists with a specific interest and experience in diagnosing and treating this condition.
Ultrasound: This is a test that uses sound waves to detect abnormalities and is particularly good at showing flow of blood as it a dynamic and non-invasive investigation. This test will help to determine the flow characteristics of the lesion but will not give a detailed anatomical picture of the problem.
CT scan: This a non-invasive X-ray test that allows the radiologist to see the body in slices on a computer screen. An injection of special ‘dye’ called ‘contrast’ is used at the same time to highlight blood vessels and this is sometimes called a CT Angiogram. These images can then be manipulated on a computer and give a detailed 3-D picture of the AVM and allow management planning.
MRIscan: This is similar to a CT scan but uses magnetic fields instead of radiation. Often MRI gives more detailed anatomical information especially in the brain.
Figure: MRA demonstrating abnormality around the left elbow consistent with a high flow AVM.
Angiography: This is a more invasive investigation that involves the introduction of a small, narrow plastic tube into the blood vessels called a catheter. This is usually carried out using local anaesthetic. The catheter is placed typically in the artery in the groin called the femoral artery. A picture of the blood vessels can be obtained by injecting dye (contrast) through the catheter using an X ray machine. This gives detailed information to the nature and anatomy of the blood vessels making up the AVM. This test is not always necessary nowadays as CT and MRI scanning offers similar accuracy. Angiography is usually carried out at the same time as treatment or occasionally if CT or MRI findings are indeterminate.
AVMs are very complicated. It is important that treatment and follow up is carried out and supervised by a multi-disciplinary team with an interest in vascular malformations. The management of these conditions requires input from the whole team.
Most AVMs do not require immediate treatment and often surveillance is all that is required (Schobinger type 1). Even those that are growing (Schobinger type 2) can be actively monitored. The decision to treat AVMs depends on a number of factors including presenting features, site, size and symptoms. An AVM that presents with acute bleeding may require emergency treatment but often an elective approach with multidisciplinary input is best for the patient.
The most important factor is that each AVM is addressed on an individual basis taking into account the above factors and most importantly detailed discussion with the patient.
AVMs have historically been difficult entities to manage. Surgery has been the mainstay for decades with a number of different techniques employed. Recent advances in the understanding of AVMs and the technological developments within Interventional Radiology successful minimal invasive treatments are preferred. Surgery still has a role in specialist centres in collaboration with the Interventional Radiologists available.
Treatment options range from endovascular therapy to surgery to radiation treatment. Endovascular therapy is the treatment of AVMs using catheters and needles placed in the blood vessels under x-ray control to allow the permanent blockage of the abnormal communications. This can be achieved by a number of techniques, which are known as embolisation. These techniques are carried out by Interventional Radiologists and are usually the safer option compared to surgery.
This is defined as the intentional occlusion of the blood vessels that make up the AVM. This is carried out in conjunction with an angiogram (see earlier). Depending on the embolisation agent and access technique used by the Interventional Radiologists a general anaesthetic may be required.
Embolisation of these lesions typically involves one of two techniques:
- Percutaneous direct stick and direct instillation of embolic material into the nidus of the AVM.
- Endovascular transcatheterembolisation. This is very similar to the angiogram you will have had but often involves using more specialised catheters and guidewires. The embolic material is then delivered via the catheter. An arterial or venous approach can be used.
There are a number of embolic materials used. The interventional radiologist will discuss these with you. They range from liquids (sodium tetradecylsulphate STD, alcohol, histoacryl glue and Onyx™), metal springs (coils) or metal plugs that block the blood vessels in this region.
Treatment can be curative, but more often is palliative, in that it is to reduce potentially life threatening complications and down grade the AVM. Simple AVMs maybe treatment successfully in a single session but the majority require more than one treatment session is required over a period of time.
Surgical resection of AVMs can be appropriate is some cases but is fraught with danger as these lesions can bleed significantly at surgery. Surgery can also be quite disfiguring and even lead to functional impairment. AVMs can often recur after surgery.
That’s not to say there is no place for surgery in the management of AVMs. Often surgery and embolisation are complimentary where the lesion is first de-vascularised (blood supply reduced) by embolisation and then surgery performed to remove the residual AVM with limited blood loss at the time of the operation.
Radiosurgery utilises a focal beam of radiation, directing it towards the AVM. This beam destroys the walls of the blood vessels making up the AVM and the lesion gradually shrinks. This type of treatment is only currently used in AVMs in the brain and is not widely available in the UK.
As with all medical treatments complications can arise. In AVM treatment complications can be broken down into those related to the angiographic procedure and those related to the embolisation or surgical procedure itself.
The angiographic complications are covered in a separate section on the website, but in summary include a very small risk of bleeding and bruising at the puncture site and infection along with a small risk of damaging the blood vessels as the catheter is advanced.
Complications related to the embolisation procedure are related to the delivery of the embolic agent and its local and systemic effects. Pain is often encountered following the procedure but this is usually short-lived and may last a few days. This can be controlled with pain-killers of different strengths depending on the degree of pain. Swelling is sometimes experienced at the site of treatment and is related to the local inflammatory process caused by blocking the blood vessels and sometimes by the embolic agent itself. Occasionally nausea can be encountered but this is well controlled with anti-sickness medication.
One of the main risks of AVM embolisation is ‘non-target’ embolisation. This is when the embolic agent passes in to the wrong blood vessels at the time of delivery with or without causing problems in this blood vessel. Even if some material passes into the wrong vessel there is an even smaller chance that it may cause problems. This risk varies in each individual patient and depends on a number of factors but is generally less than 5%. However this risk will rise with the complexity of the AVM.
The risks will be discussed with you prior to any procedure but are generally low as embolisation is proven as a safe and effective method of treating AVMs worldwide.