Unna's and Miescher's nevi: two different types of intradermal nevus: hypothesis concerning their histogenesis.

In 1991, we tentatively introduced the classification of Ackerman and Magana-García for acquired melanocytic nevi in our laboratory. We soon realized that every acquired intradermal melanocytic nevus might be easily classified into either Unna's or Miescher's patterns and that this classification had both clinical implications and significant histological differences. The decisive discriminative feature between Unna's and Miescher's nevi is that Unna's nevus is an almost purely adventitial lesion confined to expanded papillary dermis and, many times, to the perifollicular dermis too.