The term dermal nevus encompasses two clinical, dermoscopic and histopathologic rather distinctive variants of benign melanocytic nevi, namely, Unna nevus (papillomatous dermal nevus) and Miescher nevus (dermal nevus of the face).

Clinical features

Clinically, Unna nevus is a soft polypoid or sessile, usually papillomatous lesion frequently located on the trunk, arms, and neck. The clinical features of Miescher nevus are rather firm, brownish to nearly skin-colored, dome-shaped papules that occur mostly on the face [Unna 1885, Miescher 1956, Magana-Garcia and Ackerman 1990]. 

The clinical features of these two common types of benign melanocytic nevi are often quite straightforward, allowing clinical diagnosis at a glance. Thus in many instances dermoscopic examination is superfluous. Nevertheless, the dermoscopic features of Unna and Miescher nevi are rather distinctive and are described here below.

Dermoscopic features

Dermoscopically, Unna nevi reveal a globular pattern composed of numerous light- to dark-brown, round to oval globules distributed regularly throughout the lesion, or a cobblestone pattern consisting of larger, somewhat angulated globular structures. In addition, Unna nevi in some instances display densely packed exophytic papillary structures, which are commonly separated by irregular, black comedo-like openings also known as irregular crypts. These exophytic papillary structures correspond to an exaggeration of the papillomatous surface of an Unna nevus. 

In contrast to Unna nevi, the surface of Miescher nevi is clinically as well as dermoscopically smooth and, as a rule, does not reveal these exophytic papilliary structures. Miescher nevi are dermoscopically characterized by a so-called pseudonetwork with round, equally sized meshes corresponding to pre-existing follicular openings. Sometimes, milia-like cysts and comedo-like openings are also detected dermoscopically. When appearing as skin-colored nodules Miescher nevi reveal numerous comma-like vessels [Kreusch 1996] especially at the periphery, which allow the distinction from nodular basal cell carcinoma to be made with confidence. The latter ones can be observed clinically by experienced clinicians and represent a subtle clue for differentiation between dermal nevi and nodular basal-cell carcinoma on the face.