S13C12P10LichenoidMelanocytic


S13C12P10-1: For occasional examples of melanocytic dysplasia, the host immune response is so well-developed that the primary nature of the process, as a neoplasm, is obscured. This is such an example. There are dense band-like infiltrates of lymphoid cells in a widened papillary dermis. Focally, the infiltrates hug the epidermis to produce lichenoid patterns (i.e., liquefaction degeneration at the dermal-epidermal interface). The effects of the lichenoid reaction have reduced the number of atypical melanocytes at the dermal-epidermal interface (the melanocytes being the target cells of the aggressive lymphocytes); the patterns could easily be dismissed as those of a reactive process.



S13C12P10-2: The rounded defect in this field could be mistaken for a spongiotic vesicle. A blue arrow identifies a single, atypical cell in the epidermal defect. Centrally, blue arrows identify a cluster of atypical cells forming a nest which bulges into the papillary dermis. To the right, a blue arrow identifies a somewhat different atypical cell. This pale, epithelioid cell shows features which suggest that the lymphoid infiltrate is a manifestation of halo nevus-like phenomena; large, pale, epithelioid melanocytic cells are common in the dermal component of melanocytic lesions showing halo nevus-like phenomena.

S13C12P10-3: In this area of the same lesion as S13C12P10-1&2, the small, dark cells, forming rounded nests in the epidermis, might - with “pattern analysis” - be mistaken for clusters of inflammatory cells. They are interpreted as melanocytes, but it is of interest that the nests are above the basal layer of the epidermis; one nest appears to be on its way to the surface. This distribution of the nests, in the absence of more typical patterns at the dermal-epidermal interface, and in combination with what appears to be halo nevus-like phenomena, is not a representative pattern of a common, premalignant melanocytic dysplasia.

S13C12P10-4: At higher magnification, the small, dark cells are closely clustered; they have dense chromatin patterns. Melanin deposits are present in the cytoplasm of many of the cells. The neighboring basal unit of the epidermis shows spongiosis with infiltrates of lymphocytes and histiocytes. Cytologic features of the type seen in these epidermal nests may be seen in the setting of some examples of lentigo maligna and lentigo maligna melanoma.

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