Congenital nevi are benign melanocytic skin neoplasms already present at birth or arising during the first weeks (or months) of life. Congenital nevi are well known precursor lesions of melanoma, the reported risk of development of melanoma ranging from 5% to 10%, presumably depending on the size of the lesion.
Congenital nevi generally appear as flat or elevated light-brown to dark-brown lesions. The surface can be smooth, cribriform, papillated or verrucous. Numerous hairs are often present within a lesion, the nevus then being commonly called hairy nevus. A particular clinical dilemma is the so-called congenital pseudomelanoma, a type of congenital nevus characterized by several to numerous, roundish to oval, dark-brown or black pigmented areas within an otherwise stereotypical congenital nevus clinically simulating a melanoma within a pre-existing congenital nevus [Kerl et al. 1989]. Attempts have been made to classify congenital nevi according to size, e.g., less than 1.5 cm for small congenital nevi, more than 1.5 cm to 20 cm for intermediate congenital nevi, and 20 cm or more for large congenital nevi. Recently, Ackerman provided a new classification of congenital nevi subdividing them into blue nevi and non blue nevi. The latter, in turn are grouped into superficial and deep congenital melanocytic nevi, based on localization of melanocytes/nevus cells in the dermis, as judged by conventional microscopy. The stereotype of the superficial congenital melanocytic nevus is nevus spilus (congenital speckled lentiginous nevus) while that of the deep type is the so-called giant hairy nevus [Ackerman et al. 1994].
The dermoscopic assessment of congenital nevi is difficult, not only because in large congenital nevi the practical application of dermoscopy is somewhat burdensome, but also because their dermoscopic features are protean. The global features of congenital nevi are the cobblestone, globular or often the multicomponent pattern. As for local features, typical pigment network structures with slight variations on the theme may be found. Moreover, many variously sized dots and globules with different shades of brown and black are very often distributed more or less regularly throughout the lesion. Due to the many follicular openings in congenital nevi, localized multifocal hypopigmentation is commonly present, particularly around the pre-existing follicular ostia. Even more relevant dermoscopic findings are localized regular zones of hyperpigmentation corresponding to clusters of heavily pigmented melanocytes/nevus cells, a rather common histopathologic finding in congenital nevi. This particular dermoscopic finding can be clearly appreciated also clinically and represents the clinical and dermoscopic hallmark of congenital pseudomelanoma, as mentioned above. Further, congenital nevi of the verrucous type are characterized by peculiar dermoscopic features reminiscent of seborrheic keratosis, namely, comedo-like openings, irregular crypts and milia-like cysts as well as an opaque brown-yellowish coloration due to the pronounced orthohyperkeratosis. Small congenital melanocytic nevi are often clinically as well as dermoscopically similar to Clark nevi and can not be differentiated at all on the basis of clinical findings.