I don't know if this is relevant or not but the symptoms of avm can be similar to the symptoms of venous angiomas. Some people here (me included) have venous angiomas in addition to other venous malformations. They are also considered a congenital defect. Interestingly, they can be common and are not generally treated unless they cause symptoms -- but they *are* a recognized congenital venous malformation that can cause symptoms and, when they do cause symptoms, merit serious consideration and treatment. (That reminds me a bit of some of the CCSVI statements.)
They are part of the whole drainage system.
There's a lot of info out there. Here is just one quick link.
I saw a venous expert who said mine was definitely playing a major role in some of most challenging symptoms and recommended a brain procedure that, to me, sounded worse than the symptoms.