Vascular malformations are abnormal clusters of blood vessels that occur during fetal development. The exact cause of these malformations remains unknown.  Both males and females are equally affected by vascular anomalies.

Although these lesions are always present at birth, they may not be visible until weeks or even years after birth. These lesions will typically grow in proportion to the growth of the child, meaning they tend to grow steadily throughout life.

While they sometimes grow quite rapidly, their growth is usually gradual and steady during the first year of life. Without treatment, a vascular malformation will not diminish or disappear.