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Arteriovenous Malformations

Overview I Diagnosis I Treatment I Frequently Asked Questions 

Overview 

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Arteriovenous Malformations

Arteriovenous malformations are fast-flow vascular malformations with an abnormal connection between the arteries and veins, called a ‘nidus’.  Many abnormal connections can be present in arteriovenous malformations.  They are the most dangerous of all the vascular anomalies.  Many are present at birth, however some only become evident later around the time of puberty.  Often they are evident in the second or third decade of life and persist throughout life.  Early in life, they are sometimes misdiagnosed as hemangiomas or capillary malformations.  Arteriovenous malformations can involve the skin (when there is a red colour to the skin) and deeper tissues including muscle and bone.  They may be localized or extensive within an affected body part.  


Arteriovenous malformation in the hand. Photo shows typically enlarged veins draining blood from the arteriovenous malformation.

There is a high blood flow through arteriovenous malformations.  The affected body part can be warm to touch with pulsatile blood vessels and prominent veins due to the increased blood flow from the arteries into the veins.  An increased growth of the tissue can occur, which results in enlargement of the affected body part, such as in an arm or a leg.  In the majority of patients, puberty and trauma can increase the growth of an arteriovenous malformation.  Over years, an arteriovenous malformation can progress through a series of stages.  With growth of the arteriovenous malformation, increased blood flow through the malformation can reduce blood flow to the normal body tissues in the vicinity of the arteriovenous malformation.  This can cause pain and result in a loss of tissue such as a skin ulcer (a break in the skin) which heals very slowly.  In a few patients with advanced disease, the heart may be affected.  


Arteriovenous malformation in the hand particularly affecting the little finger. The AVM increased in size over time (Fig. A is 4 years earlier than Fig. B).

Arteriovenous malformations are most common in the head and neck, although they can occur in an arm, leg, and the remainder of the body including internal organs within the abdomen.  

Rarely, arteriovenous malformations may occur in complex combined vascular malformations.  

Arteriovenous Fistulae

Arteriovenous fistulae are abnormal connections between arteries and veins, resulting in high blood flow from arteries into veins.  Although this is similar to an arteriovenous malformation, there is no nidus.  Arteriovenous fistulae can be seen in Parkes-Weber Syndrome.  In this syndrome, which can affect an arm or a leg, there is fast blood flow from arteries into veins which results in overgrowth of the arm or leg and prominent veins.  There is an associated red skin colour and lymphedema (swelling of tissue with fluid as a result of reduced lymphatic flow).  A worsening of the condition can result in pain in the affected body part and some patients may develop heart failure.  Parkes-Weber Syndrome is sometimes misdiagnosed as Klippel-Trenaunay Syndrome (KTS), however, in KTS there is no fast blood flow from arteries into veins, and the affected arm or leg therefore is not warm to touch.  

Diagnosis

Patients with an arteriovenous malformation can often be diagnosed from history and physical examination.  When a patient with an arteriovenous malformation requires full evaluation and treatment, an MRI scan is done to evaluate the extent of the arteriovenous malformation.  A catheter angiogram (a radiological procedure where a temporary tube called a catheter is placed into an artery and a dye is injected which allows the arteries and veins to be visible on x-ray) is done when a patient requires treatment for their arteriovenous malformation.  This provides the most precise information on evaluating the abnormalities within an arteriovenous malformation.


Catheter angiogram of arteriovenous malformation in the arm and hand. Radiological dye is injected through the catheter (arrow in A) showing enlargement of the arteries in the arm and abnormal connections between arteries and veins (arrow in C). Large veins draining blood from the arteriovenous malformation are seen (arrow in D).

Treatment

There are several treatment options to consider.  Some children with very early disease require no specific treatment as they may have no problems related to their arteriovenous malformation.  Treatment is often extremely difficult and no single treatment can provide a cure.  Treatments are not without risk.  Generally, treatment is considered when patients show progression of their arteriovenous malformation, leading to problems such as pain, skin ulcers, bleeding, or heart complications.  

Treatment options usually include radiological catheter embolization and surgical resection.  A catheter embolization is a radiological procedure performed in Image Guided Therapy where a temporary tube called a catheter is placed into an artery as in an angiogram, through which a substance is injected to block the abnormal connection between the arteries and veins.  As there are often multiple abnormal connections, the procedures may take several hours and multiple catheter embolizations are required.  Blockage of the abnormal connections can also sometimes be performed by directly passing a needle through the skin into the nidus and injecting a blocking substance through the needle.  It is important that a catheter embolization or a direct needle injection closes the nidus and not the main artery that supplies blood to the arteriovenous malformation.  Sometimes, combined embolization and surgery is needed.  To date, there is no effective medical drug therapy for most patients with arteriovenous malformations.  

Frequently Asked Questions

Can an arteriovenous malformation be cured?

There are very few cures when treating an arteriovenous malformation.  At best, most arteriovenous malformations can be controlled by treatments.  In order to achieve a cure, catheter embolization followed by extensive surgery is required.  Often, surgery is difficult due to the extensive nature of the arteriovenous malformation.

Why aren’t all arteriovenous malformations surgically removed?

Small arteriovenous malformations may be suitable for surgery.  However, surgery may not prevent further extension or recurrence of the arteriovenous malformation.  

Are there treatments and procedures which can worsen an arteriovenous malformation?

Yes, there are certain treatments and procedures which can cause an arteriovenous malformation to worsen.  These include surgical and radiological procedures when an artery supplying the malformation is closed and not the nidus.  Laser therapy, which may be used to treat the red skin colour, can worsen an arteriovenous malformation.  

How many radiological treatment sessions are needed to treat an arteriovenous malformation?

Usually, many treatments under general anesthesia are required.  This is to ensure that good closure of the malformation is achieved and that symptoms such as pain are relieved.  Treatments need to be at frequent intervals to prevent re-opening of the malformation.  The number of treatments is determined by the improvement in symptoms.  

What do compression garments do?

Compression garments may help in some patients in providing external support to the affected arm or leg.  They may help reduce pain.  

How will I know the compression garments are working?

To see the benefits of wearing a compression garment, the garment must be worn consistently and daily for a few months.  It maybe advisable to gradually build up the length of time the garment is worn, in order to ensure tolerance of the garment.  If you have concerns regarding the fit of the garment, please contact the physiotherapist and the garment fitter within two weeks of receiving the garment.  

I find the cost of continuously purchasing compression garments very expensive.  What should I do?

A compression garment is a medical device and your doctor at SickKids will provide you with a prescription for this.  Your insurance company may cover part of the cost of your compression garment and will likely require that a prescription be provided to them.  The physiotherapists at the Vascular Anomalies Clinic can provide you with more information about compression garments and other options that may be available for subsidizing their cost.  

Why does an arteriovenous malformation cause pain?

As there is fast blood flow from arteries into veins through the nidus, there is reduced blood flow into the tissues through the normal capillary blood vessels.  These normal tissues have a reduced supply of oxygen and nutrients which can result in pain.  

What should I do if I notice that an arm or leg length difference is becoming more apparent?

This will be assessed during your yearly clinic visit.  It is very important that you attend the Vascular Anomalies Clinic every year to measure your leg lengths and to be followed-up.  

Should I be participating in regular activities such as gym classes and sports?

Generally, yes, you will benefit from being as active as possible.  Extreme sports (for example, bungee jumping and sky diving) should always be avoided.  In certain cases, it may be recommended to avoid high impact activities (for example, football, wrestling, skateboarding) if there is advanced bone involvement with the arteriovenous malformation.  The clinic physiotherapist can offer advice regarding activity risks and appropriate protective equipment.  

Is this considered a disability?  (Do I qualify for disability benefits or services?)

An arteriovenous malformation may or may not be considered a disability.  This is evaluated on an individual basis.  

What can I do to deal with my arteriovenous malformation at school?

If your arteriovenous malformation affects your ability to write or use a keyboard or move between classes in the allotted time, it is encouraged that you speak to someone at your school about this. A school may make arrangements to accommodate you and may require a medical note.  

After the age of 18, where are patients with arteriovenous malformations treated?

When you reach 18 years of age, the clinic will arrange transfer of care to an adult clinic in Toronto.