Ch41aP33a Catagen-like Tricholemmoma
(sclerosing entrapment)

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F1Ch41a (R695): This is a portion of a larger lesion. In this area, follicle-like patterns are well developed. Columns of squamous cells are vertically oriented. At the periphery, some of the columns fold inward; they are confluent with neighbors. Whorls of cells, some containing prominent keratohyaline granules, mark patterns that anticipate the formation of a lumen. Near the deep extremities of the columns, whorls are numerous. Bordering the whorls, some of the keratinocytes have perinuclear vacuoles. Centrally, the widest column, at its extremity, shows small zones of cytolysis. The last column to the right shows an empty, rounded defect. In the same area, at the extremity of the area of confluence, stroma distorts the contour of the epithelial component; a basal layer cannot be identified in this area. The papillary dermis is widened, and contains a mild infiltrate of inflammatory cells.


F2Ch41a: Whorls are numerous. Many of the cells among the whorls are vacuolated squamous cells.


F3Ch41a: In other areas, the lesion is somewhat polypoid and expansile; patterns are complex. Whorls are numerous; empty clefts and rounded defects are interspersed among the whorls. A basal unit is not a prominent feature; such a component is most evident on the right, near the epidermis. In areas, whorls are small and numerous; in these areas, the associated clefts are small and numerous. It would appear that, as the lytic process proceeds, the whorls become smaller and more numerous. This would explain the complexity of patterns in the area in which thin cords and nests project from the epithelial component into the central core of fibrous tissue.


F4Ch41a: The invasive, new formed fibrous tissue has entrapped clusters of squamous cells, mostly represented in the pattern of small whorls. At the periphery of some of the whorls, near the more intact epithelium on the right, the cells show evidence of dyskeratosis; they will keratinize and disappear; in the act, the size of each of the affected whorls will be correspondingly reduced. Atypia is not a prominent feature of any of the epithelial components in this field. The young fibrous tissue is lightly stained and loosely cellular. Near the top of the field, the lytic defects are little altered; scattered , individual fibrocytes have found their way along the adjacent epithelial walls.


F5CH41a: Basal and superficial units are represented. Whorls are prominent in the superficial unit; many of the cells of the superficial unit, particularly those of the whorls, are vacuolated. Near the extremity of the column on the left, there are lytic defects.


F6Ch41a: To the right, prominent clefts have formed among clustered whorls. To the left of the clefts, two larger whorls have keratinized centrally. Some of the cells of the whorls contain keratohyaline granules. There are occasional dyskeratotic cells. Along the interface between keratinized debris and epithelium of the more superior of the two whorls, the patterns are reminiscent of that seen in a catagen phase, and in a pilomatrixoma.


F7Ch41a: The process of cytolysis is active on the right among the small whorls. To the left, the lytic process has produced well developed empty clefts.


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