Nevus depigmentosus (achromicus). These are localized areas of hypopigmentation that are usually present at birth. The lesions may be irregular in size and shape and occasionally follow a linear or segmental pattern. Electron microscopic study of these areas suggests that melanosomes are not being transferred from melanocytes into surrounding keratinocytes. There are no associated abnormalities.
http://www.rxlist.com/collection-of-images/nevus_depigmentosus_achromicus_picture/pictures.htm
