Ch39bP31B Catagen-likeTricholemmoma 
(sclerosing entrapment)

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F1Ch39b (K4455): The section from which this photomicrograph was made was faded (as is much of my material -to which I might add myself). The basic pattern is that of a variant of the follicular hamartomas of the butterfly area of the face. A localized lesion shows acanthosis, hyperkeratosis with focal parakeratosis, and papillomatosis. Vertically oriented, broad columns of squamous epithelium extend from the epidermis into an altered and widened papillary dermis (more appropriately, an expanded and altered stroma). At the deep extremity of the lesion (the larger lesion on the left), the epithelial component is confluent; the confluent epithelium forms an expansile interface with the compressed reticular dermis. Pallor is greatest in the confluent component; in large part, the pallor is contributed by a population of vacuolated (clear) cells of a type consistent with the characteristic phenotype of cells of the outer root sheath of an anagen follicle. Above the confluent portion, trabeculae of squamous epithelium are variable in width and irregular in distribution; they are irregularly spaced in an altered fibrous matrix. In areas, small islands of squamous epithelium are isolated in the fibrous matrix. If the reader has reached this site by first coursing through all the preceding chapters in numerical order, he will, even at this magnification (“Ackerman’s” pattern analysis) recognize the pattern as that of sclerosing entrapment as seen in the follicular hamartomas of the butterfly area of the face.

To the right, there is a second, apparently independent lesion. It is composed of cords and nests of stratified squamous epithelium. It is attached to the epidermis, and closely associated with two miniaturized follicles in the underlying dermis. Most of the nests show central areas of keratinization. Even at this magnification, palisaded basal cells are a prominent feature of the nests. The patterns are in keeping with a lesion showing follicular differentiation. The patterns are not diagnostic of trichoadenoma. In the search for expressions of differentiation, the location of the lesion in the upper portion of the dermis and phenotypic expressions might be interpreted as being in keeping with those found in the constant portion of a normal follicle; an interpretation that the lesion is a variant of a follicular hamartoma of the butterfly area of the face then would seem to be acceptable, especially in combination with the pattern of the separate lesion in the neighboring skin. Other features offer support for a somewhat different form of differetiation.

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F2Ch39b: At higher magnification, the larger lesion shows a preponderance of cells of the superficial unit type. Above the confluent portion, there is poor representation of both a basal layer and a basal reactive unit; this epithelial component might be characterized as being committed to terminal differentiation (death by a specialized form of keratinization). In this same component of the lesion, there are scattered dyskeratotic cells. There are scattered whorls showing central areas of keratinization - a neoplastic expression of an attempt to form a lumen. In the confluent portion, near the basement membrane zone, a basal unit, having a basal layer with prominent nuclear palisades, can be identified. The vacuolated cells are loosely and irregularly distributed; patterns of tricholemmal differentiation are represented. The stromal component within the confines of the epithelial component is fibrotic.

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F3Ch39b: The superficial component, showing a preponderance of terminally differentiating cells, is represented. To the right, at the bottom of the field, a whorl of cells shows an irregular zone of keratinization; the opinion might be offered that the patterns of keratinization identify the cells of the whorl as being committed to catagen phenomena; as such the whorl and the neighboring population of cells might be characterized as a catagen-committed population, of the type seen in catagen phase in the inconstant portion of a follicle. In keeping with this interpretation, there are focal areas showing intracellular edema with evidence of scattered individual cell dyskeratosis. There is a smaller focus of intracellular edema near the bottom of the field, on the left. Both foci are expansile and are apparently the central part of a whorl. See drawings of Chapter 13a F3, F4, and F5.

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F4Ch39b: To begin at the bottom, basal cells are columnar with prominent nuclear palisades. They have pale cytoplasm. A basal unit is represented; its boundary extends diagonally from the lower left to the upper right. The cells of the basal unit have pale cytoplasm; scattered cells have vacuolated cytoplasm. There is mild to moderate nuclear atypia in both epithelial units. The basement membrane is thin.

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F5Ch39b: The field that corresponds to this field can be identified in figure 1  (above). A defect in the basal unit, at the stromal-epithelial interface to the right, has been inlaid with fibrous tissue. In this manner, fibrous tissue gains access to the lytic defects as they develop in the basal and superficial units. Centrally, an island of cells of basal unit type is represented. Some of the cells are vacuolated. Atypia is accentuated in this area; it is moderate. Nucleoli are prominent. Scattered cells are vacuolated. In areas within this island, the cytologic features are more in keeping with those of cells of a superficial unit type. A more acceptable component of cells of superficial unit type is represented to the extreme left, particularly at the bottom of the field. There is one whorl. In addition, there are scattered individual dyskeratotic cells, both within, and outside, the whorl.

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F6Ch39b: Epithelium of the superficial unit type is represented to the right and along the bottom of the field; vacuolated cells and dyskeratotic cells are scattered about. There is mild atypia in this component. Fibrotic stroma protrudes into a defect,and presses upon the epithelium. An intact basal unit is not represented. The basal layer for the component of cells of superficial unit-like type, along the bottom of the field, is absent. Along the remainder of the stromal-epithelial interface, atypical cells of basal unit form the interface, but do so in the absence of basal unit. There cells abutting upon the stromal are immunologically vunerable. This basal unit shows mild to moderate atypia; one dyskeratotic cell shows an atypical mitotic figure. On the left, there are scattered dyskeratotic cells. The pattern at the stromal-epithelial interface is that of sclerosing entrapment.

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F7Ch39b: The epithelium in this field is all of superficial unit-like type. The cells are plump, polygonal, and acidophilic. There is mild nuclear atypia with variations in nuclear size and outline; the nucleoli are prominent. Whorls vary in size; in some areas, they are confluent. Individual cells and small clusters of cells show dyskeratosis. There are scattered small clusters of keratinized debris. To the right, there are scattered small clefts among keratinocytes. In the upper left corner, a portion of a lytic defect is represented. In this defect, dyskeratotic cells showing advanced patterns of keratinization, are loosely distributed.

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