Nevus flammeus
Early port-wine stains are usually flat and pink in appearance. As the child gets older, the color may deepen to a dark red or purplish color. They occur most often on the face but can appear anywhere on the body.
Your doctor can usually diagnose a port wine stain by looking at the skin.
In unusual cases, a skin biopsy may be needed. Depending on the location of the birthmark and other symptoms, your doctor may want to do an intraocular pressure test or x-ray of the skull.
Morelli JG. Vascular Disorders. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th Ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 649.