Hi and welcome!
If you will look at http://birthmark.org/pdf/VBF%20Pamphlet.pdf
and scroll down to the section on AVM's, you will find some information. Usually the treatment is a mixture of embolization and surgery. Can you feel your blood pressure in the mass above your knee?
You might have a better response if you start a new post under the AMV section of the forum ... more adults dealing with birthmarks there. Let me know if you'd like to and I can move it for you.