Vascular malformations are benign (non-cancerous) lesions that are present at birth, but may not become visible for weeks or months after birth. Unlike hemangiomas, vascular malformations do not have a growth cycle and then regress but instead continue to grow slowly throughout life.
Most vascular malformations are sporadic (occurring by chance), though some are inherited in a family as an autosomal dominant trait. Autosomal dominant means that one gene is necessary to express the condition, and the gene is passed from parent to child with a 50/50 risk for each pregnancy. Males and females are equally affected and there is great variability in expression of the gene. In other words, a parent may unknowingly have had a hemangioma because it faded, but your child is more severely affected. The family may not come to the attention of a geneticist until the birth of the child with a more severe condition.