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 later. These lesions typically grow in proportion to the growth of the child, meaning the lesions grow steadily throughout childhood. However, some VMs may appear to grow or become larger due to expansion of the existing abnormal vessels, which most commonly occurs around growth spurts, including puberty.

Vascular malformations do not go away over time. Even with surgical or medical treatment, VMs may not completely resolve since most cannot be entirely removed by surgery.