Ch39P31 Proliferating Pilar Tumor
(Catagen-like Tricholemmal Tumor)

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F1Ch39 (G7504): At its periphery, a proliferating pilar tumor presents a well-defined, expansile interface. The irregular interfaces, that develop within the confines of such a lesion as a consequence of individual cell dyskeratosis and sclerosing entrapment, generally do not distort the peripheral interface. On the other hand, a lesion that has developed into a destructive, invasive carcinoma will betray its nature at the periphery of the lesion. This type of invasion will be accompanied by cytologic atypia and mitotic activity. In the absence of patterns of destructive invasion at the periphery, cytologic atypia and mitotic activity is evidence of an atypical variant or a variant showing intraepithelial carcinoma, depending on the degree of atypia; such lesions should be thoroughly examined and sectioned. If destructive invasion at the periphery is not found , the atypical variants should be characterized as borderline lesions of uncertain malignant potential.


F2Ch39: Hyperplastic basal and superficial units are represented. In the superficial unit to the right, many of the cells show rounded perinuclear vacuoles; cytoplasmic vacuolization of this type most likely is evidence of intracellular edema; there are also scattered dyskeratotic cells. There is a thick hyalinized basement membrane (glassy membrane). The presence of such a membrane could be offered as evidence that the neighboring epithelium is basically of outer root sheath type. It seems proper to characterize these changes as being representative of          catagen-committed follicular phenomena; in this approach, features of anagen patterns would be eliminated from consideration.


F3Ch39: Hyperplastic basal and superficial units are represented. Perinuclear vacuoles and individual cell dyskeratosis are prominent features of the superficial unit. Some of the cells of the basal unit also show perinuclear vacuoles. In the basal unit, there are scattered dendritic cells that have a lacunar quality; these cells are not pigmented but their identity can not be established on this material.


F4Ch39: Basal and superficial unit components are hyperplastic. A keratotic focus is present on the left at the top of the field. The peg of stroma to the right of the center of the field shows a prominent hyalinized basement membrane.


F4Ch39: Cell detail is not well preserved. The section is faded; some of the pallor may be evidence of degenerative changes - over a broad interface, epithelium of superficial unit-like type abuts directly upon the fibrotic stroma. Keratinized debris is isolated in the fibrous tissue; this feature represents a late stage in the process of sclerosing entrapment. On the opposite surface of the broad island, a basal layer is preserved; the adjacent stroma is hyalinized - the patterns provide “chondroid” qualities.


F5Ch39: The epithelial component has been extensively disrupted by the process of cytolysis, followed by sclerosing entrapment. At this magnification, it might be difficult to exclude the possibility that the trabecular components are decalcified bone spicules (i.e., metaplastic ossification). The material has not been decalcified. An island of calcified, keratotic debris is present on the left at the bottom of the field. The stroma is densely sclerotic.


F6Ch39: An island of squamous epithelium of superficial unit type is represented. A basal unit is not represented. The cells of this island are committed to progressive keratinization and degeneration. Blue arrows identify the calcified, keratotic debris.


F7Ch39: A basal unit with a layer of basal cells is represented. The basement membrane is thickened and hyalinized (glassy membrane-like).


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