F1Ch17 (R4564): This is a variation in pattern of the same lesion as represented in Ch16. The surface configuration remains the same; the lesion appears to sit upon the skin. To the right and to a lesser degree to the left, the squamous cell patterns, as seen in the pictorials of Ch16, are preserved. To the right, the squamous cell patterns are sufficiently preserved to qualify as “seborrheic keratosis-like,” or as “inverted follicular keratosis-like.” Centrally, irregular columns of basal cells are loosely spaced in a fibrous matrix. The matrix is condensed (more brightly acidophilic) about some of the nests of basal cells. Some of the larger columns show central cavities. Some of the nests are irregularly pigmented, and pigmented debris has collected in some of the cavities. The lesion has seized the fibrous stroma; the interface between the stroma and the underlying dermis is sharply defined. There is no area in which a column of basal cells is in continuity with the epidermis or the squamous cell component of the tumor.
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