Question about the AVM walls

Are the walls of the AVM already weak due to the genetic malformation or are they weakened only due to the high pressure's of no capillary system? Or both?

My vascular neurosurgeon explained to me that the weakness of an AVM is due to larger blood vessels feeding directly into much smaller ones without the usual gradual decrease in size. Usually large blood vessels get smaller and smaller and smaller, then the small vessels feed into equally small ones, which gradually get larger and larger. When you have large vessels connected directly to very small ones, you have in increased chance of a rupture.

So it's closer to the option of no capillaries, although the real problem is that there are capillaries on one side and not the other.

Thank you for that answer!