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In figures cat3Pa1-5, c7t3P1-3, c10t3P1 & 2, c11t3P1, and c12t3P3, lentiginous and junctional patterns, with varying degrees of dysplasia (cytologic and histologic atypia), are represented. The degrees of dysplasia range from moderately severe to severe. In all examples, rete ridges are elongated. In all examples, there is hyperplasia of the superficial unit of the epidermis. The patterns in the epidermis differ from those of classic SSM. Lentiginous hyperplasia is more consistently a prominent feature of lesions of ALM. The cells tend to have a more prominent dendritic quality, and in their upward migrations, the cells lie within defects, providing a lacunar quality to the resulting patterns. The lacunar changes become more prominent in the higher grades of dysplasia. In areas in which cells form clusters in the epidermis, the defects take on the qualities of cavities; they often are not symmetrically rounded.
In figures cbt3Pb 2-5, patterns of vertical growth are represented.
In figures c11t3P2-6, c12t3P3, and c14t3P1, uniform, atypical cells form rounded nests in a fibrous matrix. The patterns resemble those of variant vertical growth, as might be seen in some examples of SSM; the rounded nests tend to be uniform in size and loosely, but regularly, spaced in the fibrous matrix. Inflammation often is not a prominent feature. There is a tendency for the cells to show a uniform degree of atypia. The patterns have a minimal deviation quality; a lesion showing only this pattern in vertical growth qualifies as a nevoid variant of ALM. This pattern may be seen as a regional variation in a large lesion in which other, more significant, patterns of vertical growth are represented. This nevoid pattern of vertical growth might be characterized as a minimal deviation pattern.
In figures c7t3P6, c8t3P2, c13t3P8, and c14t3P2, broad fascicles of atypical cells are interconnected, but loosely spaced, in a fibrous matrix. Often, inflammation is not a prominent feature. The degree of atypia is variable. In some examples, atypia is moderate; such lesions qualify as minimal deviation variants. In other examples, the degree of atypia is moderately severe. In a few examples, the atypia is severe, and there is nuclear pleomorphism. The fibrous matrix is not simply an expanded papillary dermis; it appears to represent an alteration of the collagenous matrix of the reticular dermis. Although this pattern may be associated with a pushing margin, close examination usually will reveal areas in which thin fascicles of neoplastic cells extend into the pre-existing reticular dermis among collagen bundles. This pattern qualifies as intermediate in type.
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