Arteriovenous Malformations & Arteriovenous Fistulae
by Dr Panayiotopoulos, Consultant Vascular and General Surgeon Essex.

Arteriovenous Fistulae [AVF]

1. What is an arteriovenous fistula?

A fistula is an abnormal communication between an artery and a vein and in almost all cases they are acquired. The commonest cause is trauma [penetrating] or iatrogenic [following invasive medical tests or surgery] injury [90%]. However, they can also be caused by chronic inflammation, erosion through an aneurysmal wall into the adjacent vein or erosion between the two vessels in cases of cancer.

As the communication develops, a percentage of blood escapes the arterial circulation and takes immediately the route back to the heart through the vein [shortcut]. The end result is more blood volume returning to the heart [overloading it], which may lead to heart hypertrophy, less blood to be delivered to the muscles or organs from the artery [ischaemia] and blood to stagnate in the veins distally to the communication [risk of chronic venous hypertension].

In most cases the diagnosis is easy, as it follows a penetrating injury or an invasive procedure. The symptoms vary, depending on the extent of the escaping blood volume and the time that passed since the fistula developed. They become significant only in large and long-standing arteriovenous fistulae. [You should remember that an artificial fistula is made on the arms of people with non-functioning kidneys, when they are to be put on renal dialysis. The symptoms, therefore, are not so important for small or medium  fistulae and are well controlled in the majority of cases].

• There is a thrill over the area, as there is continuous blood flow through the communication. If one listens over the fistula. He may hear a machinery murmur, called after Nicoladoni-Branham.
• The limb distal to the communication may become cooler, with less strength and with a lower blood pressure.
• The heart rate may increase.
• The superficial veins will in due course become prominent.
• The limb may gradually become swollen, as there is difficulty in the venous return.

The definitive diagnosis is made with an ultrasound scan, or an arteriography [X-ray of the arteries, infusing dye into them].

When the diagnosis is established, treatment is essential and is usually surgical. The parts of the affected vessels may be excised and repaired, the fistula may be tied off and only rarely both the artery and the vein will have to be tied off above and below the communication. The procedure is done under general anaesthaesia.

A new technique has developed in the recent years, where a metallic cage covered by plastic material [Dacron] may be inserted through the artery [endovascular approach through the groin] and positioned just over the abnormal communication to exclude it from the circulation [Stent-graft insertion].

However, it cannot be used when there are other vessels branching off the artery, as it will exclude them from the circulation as well. This is the reason while surgery is the preferred treatment for limb AVFs.

Arteriovenous Malformations [AVMs]

The term malformation is quite broad and may be used to encompass a variety of conditions, including vascular growths [haemangiomas] to chronic post-traumatic communications and birth marks of the skin. The main difference from a fistula is that in malformations there is not a single but many points of communication between arteries and veins, and that quite often the vessels involved are abnormal in their structure.

These lesions are quite complex and many classifications have been proposed which probably cause more confusion. From the clinical point of view [and the angiographic appearance] they can be grouped as:

• Type 1, Predominantly arterial malformations

• Type 2, Lesions that affect tiny vessels, mostly capillaries

• Type 3, Predominantly venous malformations

5. What tests are required?

These should be undertaken only if the result is going to influence the decisions regarding the patient’s management.

• An ultrasound is the usually the first test done, as it is painless, and quite accurate.
• However, the x-ray of the arteries [arteriography] or veins [venogram] is the best diagnostic method.
• A CT-scan or MRI may be also required to assess the depth of the fistula and which tissues are involved.

6. What about treatment?

As arteriovenous malformations may cause disfigurement and discomfort, patients seek treatment. However, it should be understood that their management is best done in specialized centers, with vascular surgeons and interventional radiologists being present. Sometimes the input from plastic surgeons may also be essential.

In general, there are 4 treatment options:

·          Excision of the AVM en block into healthy surrounding tissues.

·          Skeletonisation [tying off all the branches] of the feeding artery by surgical exposure [rarely used].

·          Embolisation, which entails blocking of the feeding vessels near the origin of the lesion via an arteriography or insertion of coils, glu, sclerosants etc. into the venous component of the malformation to thrombose its venous part.

·          Laser or intense photo treatment may be useful in superficial skin lesion, as the cosmetic appearance may be significantly improved. However, the skin lesion may be just the tip of the iceberg, and the subcutaneous lesion may be more extensive that initially thought.

Embolisation and excisional surgery also have some limitations as the normal vessels and important tissues cannot be embolised or removed. Embolisation outside the nervous system or other vital organs is usually safe, but there are also some risks, including tissue breakdown and necrosis.

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Please note:
A written referral from a general practitioner is helpful but is not essentially required in order to make an appointment to see a consultant specialist.