(dysplasias and vertical growth, cont.)
Patterns of dysplasia, variant vertical growth, and typical vertical growth are represented at three respective levels with the upper diagram representative of an evolving dysplasia. In the dysplasias, junctional nests are irregular in distribution. Some of the nests are outlined on the dermal side by laminated fibrous tissue. Scattered nests have dropped into the papillary dermis. The process is independent of degrees of atypia. The basic patterns have application to the interpretation of the atypical variant “nevi.” In the middle diagram, progression is represented. Markers for the patterns of the dysplasia (precursor) are preserved but, in addition, in an area to the right of the center of the field, a progressive focus is represented in the dermis; the nidi for the delivery of the nests of cells into the dermis in this area are the junctional nests in the epidermis over the dermal focus. The gradient would be from the epidermis into the dermis and the type of growth might be characterized as accretive; new nests are near the epidermis and the older nests are near the interface between the papillary dermis and the reticular dermis; the dermal patterns are stratified by age (and generally by degree of atypia with the most advanced degree of atypia in the component that is cytologically the most atypical - the component nearest the dermal-epidermal interface. The newest generation is the most atypical). In accretive growth, the nests of cells are delivered into the dermis from nidi at the dermal-epidermal interface; if the same nidi in the epidermis are the source of several generations of nests of cells, the stratified nests may form regularly spaced columns, In any case, the dermal patterns of accretive growth are characterized by loosely, but regularly, spaced nests in the papillary dermis. Such patterns qualify as variant vertical growth. To the left of the center of the field, the variability of the phenomena of melanocytic dysplasia is manifested. There has been focal regression with loss of lentiginous and junctional patterns focally in the epidermis. In the bottom diagram, new phenomena have modified the histologic patterns and new designations to characterize the changes are required. To the right of the center of the field, the cells of what was formerly a variant vertical growth component in the dermis have become independent of nidi at the dermal-epidermal interface. The cells of some of the dermal nests have acquired the capacity to modify stroma and to induce a complementary blood supply. The nests of cell in the dermis can multiply independently of the phenomena at the dermal-epidermal interface. In contrast to variant vertical growth, stratification is not a significant feature and one nest is cytologically similar to all its neighbors. The nests are closely aggregated and, in toto, often form an expansile nodule. Typical vertical growth persists as the basic pattern for as long as the vertical growth component is confined to a widened papillary dermis. Such a lesion may obtain considerable size in typical vertical growth by compressing the underlying reticular dermis. Once the tumor cells violate the boundary between the papillary and the reticular dermis, the patterns are no longer purely those of typical vertical growth; they qualify as diffuse, variant vertical growth and the cells are universal migrants: they no longer respect anatomic boundaries and the risk of metastasis is great. The concept of typical vertical growth is basic to a definition of variant or minimal deviation melanoma.