Delineation of the various shapes and patterns of nevi.

It has been proposed that all nevi reflect mosaicism, and this concept has been corroborated at the molecular level in a number of nevi. If the concept of mosaicism holds true, one would expect that the various types of nevi should be characterized by intrinsic shapes or patterns. A photographic review of 1,188 recognizable images of a list of nevi of the skin was undertaken in order to delineate a classification of the various shapes and patterns of nevi. We disclosed three distinct shapes and two so far undescribed archetypical patterns, in addition to the well-known Blaschko-linear, flag-like and extensive garment-like patterns, to which all lesions could be allocated. The newly delineated shapes are called round or oval shape; patches with indented borders; and teardrop or triangular shape. The newly proposed archetypical configurations are the agminated pattern and the diffuse patchy pattern. Other mosaic patterns, such as the phylloid pattern or the lateralization pattern, were not observed in any of the images reviewed. We conclude that the various types of nevi can be assigned to specific shapes or patterns. Admittedly, however, a given nevus may manifest itself in several different shapes, whereas its archetypical pattern tends to be the same. This 'archetypical' pattern can be taken as the perfect or ideal model of a given type of nevus, whereas the newly described shapes are subordinated to the archetypical patterns and are best considered to be 'nonarchetypical'. Our work gives more consistency to the idea that nevi reflect mosaicism, because they display repetitive shapes and patterns.