A capillary malformation (commonly referred to as a port-wine stain), is a flat, sharply defined vascular stain of the skin. It may cover a large surface area or it may be scattered and appear as little islands of color. It can be anywhere on the body and in more than one place on the body (illustration 1), but is most commonly seen in the head / neck region (illustration 2).

The exact cause of this lesion is not known, but it is thought that it arises because of abnormal formation of the tiny blood vessels of the skin early in the life of the embryo, after the larger blood vessels are in place.

The occurrence of capillary malformations is unrelated to drugs or medications that may have been taken during pregnancy or to environmental exposures that may have occurred at that time.

Although the number of blood vessels in a capillary malformation is normal, the diameter of the affected vessels is much larger than that in normal vessels; this enlargement results in increased blood flow. Because the vessels are close to the surface, this increased flow gives the skin its pink to purple appearance.

As your child grows, the affected blood vessels will continue to enlarge and thicken, causing the color of the lesion to darken. Over time, the clusters of tiny, dilated venules (small vessels that collect blood from the capillary junctions and join to form veins) give a lumpy appearance to the skin. The period of time over which this progression occurs varies greatly from person to person, and may even be delayed until ages 40, 50, or 60.

Capillary malformations on the forehead and upper eyelid can be associated with lesions of the brain and eye (Sturge-Weber syndrome).

Capillary malformations in the skin over the spine can be associated with Cobb syndrome, which involves the spine and/or meninges (tissue covering the spinal cord). Capillary malformations in this area can also be associated with other abnormalities of the spine, and should be investigated with an ultrasound or MRI. 

Capillary malformations located in the middle of the face (forehead, nose, upper lip) can be associated with vascular abnormalities of the brain, and should also be investigated.

A group of capillary vascular lesions seen primarily in newborn is often confused with capillary malformations. When these birthmarks appear on the forehead, eyelids, nose or upper lip, they are commonly called "angel kisses." When located on the back of the neck, they are commonly called "stork bites." These lesions usually fade by 1 year of age and do not require treatment.