Ch18 Atyp FP vs Desmoplastic
Melanoma

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K1574fibpap110

F1Ch18 (K1574): There is liquefaction degeneration at the dermal-epidermal junction; a layer of “basal cells” is not represented. Some of the clefts contain proteinaceous material. Membranous hyaline deposits are spottily distributed  through-out the abnormal fibrous matrix. In the population of dendritic “fibroblasts,” there a mild degree of nuclear atypism with variations in nuclear size and staining. Vessels are ectatic.

K1574fibpap120

F2Ch18 (K1574): Rete patterns are partially preserved. There is mild melanocytic hyperplasia in the basal layer. Blue arrows identify ill-defined clefts at the    dermal-epidermal interface. The third arrow from the right points to a cleft containing 2 dendritic cells, each with an enlarged nucleus. One of these cells is associated with 2 lymphoid cells and a small dendritic cell that has the characteristics of a dendritic histiocyte. The underlying matrix contains smudgy, membranous hyaline deposits. Some of the hyalin is condensed about small vessels. There are two multinucleated giant cells; they can be easily dismissed as histiocytic giant cells but could represent “nevus-type” giant cells.

K1574fibpap130

F3Ch18 (K1574): Pale epithelioid cells and giant cells are present near the D-E interface. The epidermis abuts upon the altered dermis without an intact basal layer; the patterns have a “ cell-poor lichenoid” quality. The epidermis above the area of liquefaction degeneration has the qualities of an hyperplastic superficial unit. Acidophilic membranous deposits are prominent in the dermis. There is some degree of nuclear atypia. Vessels are ectatic.

K1574fibpap140

F4Ch18 (K1574): The lesion is cellular at the D-E interface. The cells are pale and epithelioid; there is mild nuclear atypia. Some of the nuclei contain prominent nucleoli. The cells form ill-defined fascicular patterns among coarse, membranous hyaline deposits. There is mild nuclear atypia. Vessels are ectatic.

K1574fibpap160

F5Ch18 (K1574): Some of the atypical cells are present in clefts at the     dermal-epidermal interface. There is mild nuclear atypia. The atypical cells form    ill-defined fascicles in the dermis. In one area, a coarse deposit of hyalin is present bordering a cleft at the dermal-epidermal interface. The pale epithelioid cells can be interpreted as histiocytes but immunoreactions to rule out a melanocytic lineage would be of interest. In any case, the lesion is atypical but has most of the features of a fibrous papule.

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