Arteriovenous Malformations

What are arteriovenous malformations?

Arteriovenous malformations (AVMs) are abnormal connections of blood vessels that can occur during the development of the foetus (congenital) or may be acquired (e.g. after trauma).

Genetic mutations have been identified that can lead to AVM formation, including mutations in genes called KRAS, MAP2K1 and others involved in blood vessel development. Most AVMs occur sporadically without a family history, though some are associated with genetic conditions.

In a normal situation, high pressure blood vessels called arteries carry oxygen and nutrient-rich blood from the heart to all organs of the body.

Inside each organ, the arteries divide into smaller blood vessels called capillaries, where oxygen and nutrients are delivered to the tissues of the organ. Blood then returns to larger low-pressure vessels called veins to the heart, and the cycle repeats.

In an AVM, there are abnormal connections between arteries and veins, without intervening capillaries, resulting in abnormal blood pressure within these abnormal connections.

What symptoms do AVMs present with?

Symptoms of AVMs vary depending on their locations, i.e. which organ is involved. AVMs on the skin or soft tissues typically appear as a swelling with pulsations (usually in sync with the heartbeat). If the overlying skin is thin, there may be a reddish or purplish discolouration. Their size may grow over time, potentially causing pain, skin thinning, ulceration or bleeding.

AVM of the internal organs may present differently, for example:

• Brain AVMs: headaches, seizures, symptoms of stroke
• Lung AVMs: breathlessness, coughing up blood
• Gastrointestinal AVMs: abdominal pain, bleeding

Brain arteriovenous malformation

What complications can AVMs cause?

Most AVMs are asymptomatic initially but may indolently grow overtime. The skin over an AVM may breakdown (ulcerate) and cause severe pain, and significant, sometimes life-threatening bleeding.

When an AVM is large, it can cause heart failure, a serious condition where the heart is unable to cope with the increased demands of the AVM due to haemodynamic issues, resulting in breathlessness, chest pain or light-headedness.

Rarely, AVMs may be part of a vascular malformation syndrome, for example Parkes-Weber syndrome, where an affected limb may become larger or longer than the normal limb.

Ulcerated arteriovenous malformation

How are arteriovenous malformations diagnosed?

AVM are diagnosed with a combination of clinical history, physical examination and tests including ultrasound, magnetic resonance imaging (MRI), angiography and less commonly, computed tomography (CT) and tissue biopsies.

Ultrasound:

• Commonly used as a first line imaging test as it is non-invasive,
  non-painful, with no radiation. 
• May be available at the clinic or at the hospital’s imaging centre.
• A probe is placed on the area of interest with some gel.
• Duration: 5 to 30 minutes depending on complexity of the AVM; requires some cooperation from a child.

MRI:

• High-resolution, advanced imaging allowing the visualisation of the AVM and its surrounding organs/structures without radiation.
• Duration: 30 to 60 minutes or longer (rare). The patient needs to remain completely still for the entire duration, which may be challenging for infants and young children. In such cases, general anaesthesia (GA) may be required, administered by our team of paediatric anaesthetists.

Angiography:

• Typically performed along with the intention to administer treatment to the AVM.
• A small catheter (tube) is placed into a blood vessel, typically at the groin (femoral artery) to act as a conduit to the AVM. A detailed map of the blood vessels and AVM is acquired using injections of dye (contrast material) under X-ray.

How are AVMs treated?

The complex nature of AVMs requires a dedicated multi-disciplinary team management, which typically include dermatologists, haematologists, surgeons (vascular, plastics, orthopaedics) and radiologists performing image guided therapies (interventional radiologists).

The decision of when and how to treat an AVM depends on the location, stage of the disease and what complications of the AVM needs addressing. Treatment options are wide, ranging from medications to endovascular therapy, surgery and radiation therapy. A combination of treatment options may be offered in some cases.

Endovascular therapy, performed by interventional radiologists, utilises angiography to access the AVM abnormal vessels to permanently block them internally using a combination of embolic agents (e.g. histoacryl glue, alcohol, EVOH-based agents) and metallic coils. In large AVMs, several sessions may be needed. This may be performed in combination with surgery for cases where excision of the AVM is required.

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