Congenital vascular malformations (CVM) occur in about 1% of all
births and can vary from simple, flat birthmarks to complex,
3-dimensional structures deep within the body. They can be made up of
arteries, veins, lymph vessels, or a combination of these. They are
usually present at birth, but are unlikely to be passed on from parent
to child or for there to be more than one in any given person.