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| AVM on left |
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AVMs of the brain (or arteriovenous malformations) are congenital (but usually not inherited) lesions that are composed of a tangle of abnormal arteries and veins joined together without the presence of the smallest blood vessels of the brain (ie. capillaries). Within the tangle of blood vessels there is little, if any, functioning brain. They can occur anywhere in the brain or spinal cord. It is unusual for their to be more than one AVM. |
| How do AVMs cause trouble? |
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Within the AVM, blood rushes from the artery-type vessel to the vein-type vessel without being slowed down by the very small vessels normally separating artery from vein (fig 1 and 2). Blood rushing more quickly than normal is like a road with more traffic than planned. The surface develops wear-and tear and may ultimately break. This is the cause of bleeding into the brain. Half of all patients present with bleeding (or hemorrhage). Of the remainder, seizures (or epilepsy), headache and loss of function are ways in which AVMs can declare themselves. |
| What are the consequence of AVM bleeding? |
| When an AVM bleeds into the brain there is approximately a 50% chance that either death or a permanent loss of some brain function will occur. |
| How likely is it that an AVM will bleed? |
| The risk varies from person to person and also with each person over time. On average, the risk of bleeding over the 10 years from diagnosis is 30%. But if signs of wear-and-tear are present (such as aneurysms) this risk might be greater than 50%. Over 30 years from diagnosis the risk of bleeding averages 66% but may be as high as 90% (if wear-and-tear changes are present). |
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