In this section
Blood in normal arteries is at high pressure. This pressure forces the blood cells through tiny capillaries before collecting into veins. Therefore blood in normal veins is at low pressure. In an AVM, there are multiple direct connections between the arteries and veins. This results in high speed blood flow into the veins and much higher pressure in the veins than normal. Because of the direct flow, the surrounding capillaries have a greatly reduced flow and there is a lack of nourishment of the surrounding skin and other tissues.
We do not know what causes AVMs. We believe that like other vascular malformations they might be caused by ‘somatic mutations’, which are errors of DNA copying during development, but such mutations have not yet been found. The majority of AVMs occur by random chance but a small number of AVMs run in families. In many of these families, the affected family members develop small red patches that appear to be small capillary malformations on the skin.
Small AVMs usually do not cause too much of a problem. If the skin breaks down over them, they can bleed alarmingly (control the bleeding by applying pressure and go to a hospital). AVMs tend to enlarge over time, but this enlargement is unpredictable and can take many years, so treatment is generally not urgent. AVMs often enlarge at puberty and can enlarge during pregnancy. Larger AVMs can be disfiguring and painful, and can erode surrounding tissues.
Children who have an AVM which is not in the
brain, and who do not have a family member who also has an AVM, almost never
have another AVM elsewhere including in the brain. In these children there is little risk of
stroke and normally no need to scan the brain for AVMs
AVMs are among the most challenging vascular anomalies to treat. The two most commonly used treatments are surgery and interventional radiology. For both treatments, it is essential that the treatment is performed by someone with experience in treating AVMs. Recurrence after treatment is common. Both surgery and interventional radiology must target the ‘nidus’ (core) of the AVM. Sometimes a combination of treatments is required.
If the AVM cannot be cured, then a strategy of ‘embolizing’ the feeding vessels is sometimes used to slow down the flow into the AVM. This is only a temporary solution because new vessels soon grow back, so it is only used as one component of the treatment or a last resort if all options for cure have been considered by an expert team. Use of embolization when it is not part of a comprehensive treatment strategy can make later treatment more difficult.