Segmentation of a continuum

figure1new41128 This is basically the same diagram as that represented as Fig. 1 in the contribution on desmoplastic melanoma. The interdeterminate stage of dysplasia (grade 0) is represented. There are 4 determinate grades of dysplasia along the plane with the highest grade abutting upon the cone at the extremity of the plane. The cone extends into the domain of grade 2 dysplasias ; this relationship give recognition to vertical growth patterns in thin lesions in which the degree of dysplasia is only moderate. The cone has two boundaries early on. The first is at 1 mm in vertical dimension (diameter of the cone) and the second is at 1,5 mm in vertical dimensions. The domain to the left of the 1mm. boundary is a borderland in which the high grade dysplasias and the thin “melanomas” are properly characterized as borderline lesions (representatives of borderline melanocytic neoplasias of indeterminate malignant potential). The domain of the cone between the 1 mm boundary and the 1.5 mm boundary is an intermediate zone (intermediate melanocytic neoplasia of indeterminate malignant potential). Lesions of the domain beyond 1.5 mm might be characterized as real melanomas. To the right, level Iv invasion is represented as an independent dimension.

whither1part2fig2opt1029Fig. 2

This is basically a modification of Fig. 1 giving recognition to the indeterminate (grade 0) dysplasias and in addition, emphasizing the dominance of typical vertical growth patterns in the category of real melanomas beyond 1.5 mm in vertical dimensions. The indeterminate dysplasias ar characterized by minimal atypia in lentiginous and junctional patterns and by minimal markers for host immune response (lymphoid infiltrates and lamellar fibrosis). These minimally deviant lesions are not sufficient in themselves to be cited as a marker for the dysplastic nevus syndrome. On the other hand, these lesions are commonly encountered in the setting of other lesions which clearly have the characteristics of significant dysplasias, as encountered in the dysplastic nevus syndrome. Level III lesions in typical vertical growth tend to be expansile nodules confined to the native soil of the skin (the adventitial dermis). All the white, gray, and black domains above the red boundary are stroma (prepared soil). Variant vertical growth patterns will be encountered mostly in the borderline and intermediate categories (the domains of the cone). The spindle cell melanomas are an exception to this general characterization. The red boundary along the lower margin of the domains in white, grays, and black defines the interface between the soil and of native melanocytes (the epidermis and the adventitial dermis) and the unprepared strata of the reticular dermis. For neoplastic melanocytes, extensions beyond the red boundary is evidence of the acquisition of new properties. It signifies a transition from communal cells as members of the community at level III (pattern III) to migrant cells which extend to at least level IV (pattern IV). The migrants do not respect boundaries and readily invade not only the reticular dermis but also vessels. melanoma in situ is not specified as a separate lesion; it is embraced in the categories of the high grade dysplasias (grade III and IV dysplasias). The collection of dots beyond the red boundary are symbolic of individual tumor cells and clusters of such cells. The likelihood that such cells will be encountered beyond the red boundary is relative to the degree of dysplasia or to the presence of a vertical growth component. The more advanced ( the higher the degree of neoplastic progression) the neoplasm, the greater the likelihood that a portion of the lesion will have advanced beyond the red boundary to level IV. It should be noted that spindle cell melanomas, such as acral and actinic variants (lesions with prominent lentiginous components), are an exception and may be found commonly at level IV even for the borderline and intermediate domains (i.e., thin lesions). Also level IV invasion should not be equated with the documentation of vertical growth. Cells, particularly in the low grade dysplasias, may be found at level IV but may not be arranged in patterns that would satisfy the criteria for vertical growth.

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