Catagen-like Atyp Tricholemmoma

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F1Ch45: This epithelial neoplasm, of squamous cell type, is expansile. Grossly, the diameter of the lesion was greater than 1 cm. It extends to the deep margin of the biopsy; anatomic landmarks are not represented to a degree that depth of invasion can be evaluated but it would appear that the lesion extends through the dermis. The lesion shows the complex patterns emphasized in the diagnosis of follicular hamartomas of the butterfly area of the face; the size of the lesion is a distinctive trait; for lesions of this type that measure greater than 1 cm. in diameter, the lesion should be characterized as a giant variant. Giant variants are not confined to the butterfly area of the face; they may be encountered on the trunk, buttocks, extremities, and scalp. Some examples may measure 3 or more centimeters in diameter.

Having reached tier 4 of this Section, and then having moved along this tier to its end, I would hope that the reader can look at the patterns in F1, and identify the features of sclerosing entrapment, as represented in scattered foci. In the past, I have classified this lesion as atypical giant inverted follicular keratosis; by the criteria offered herein, the lesion would qualify as an atypical giant catagen-like tricholemmoma.


F2Ch45: Broad cords and columns of squamous cells are supported by a delicate, vascularized fibrous matrix. Two cells types comprise the columns and cords; a small cell population has basaloid or germinitative qualities (as manifested in the basal unit of stratified squamous epithelium), and a large, pale cell population has the qualities of a superficial unit (a population committed to terminal differentiation). The small cell population forms a background for the whorls of large cells. The small cell component presents an epithelial interface with stroma (with the exception of the the areas of sclerosing entrapment, as seen in the area that is outlined by blue arrows. On the other hand, the large cell population has a role in the formation of      keratin-filled lumina. The process of cytolysis that initiates the process of sclerosing entrapment generally seems to begin in the component of small cells. The epithelial remnants that eventually become entrapped in the inlay of fibrous tissue mostly represent the large cell component. This epithelium is ill-suited to survive in a fibrous matrix; it lacks the protection offered by a basal layer and, by its nature, is committed to terminal differentiation. It is, however, a paradox that this type of epithelium - destined to evolve into keratinized debris - seldom evokes a significant giant cell reaction.


F3Ch45: A dual population of cell types is represented. Whorls, one of which is keratinizing centrally, are a prominent feature. Near the top of the field on the right, there are lytic defects with scattered dyskeratotic cells. Just below the center of the field, in a small cell component, most of the cells have vacuolated cytoplasm; there are, in addition, scattered dyskeratotic cells. In this portion of the field, the patterns are in keeping with changes seen in the outer root sheath of an anagen follicle. This is a relatively minute component of the overall patterns; how does this tiny component influence the selection of a designation? If both the major and minor components are accepted as evidence of tricholemmal differentiation, then the dilemma becomes relatively unimportant.


F4Ch45: This is the classic epithelial pattern as a result of catagen-like phenomena. The changes have progressed beyond the initial pattern of empty defects among cords and nests of squamous cells; the changes have progressed to a stage in which migratory fibroblasts have inlaid young fibro-myxoid tissue in the defects. The entrapped nests and cords lack a basal layer (and a basement membrane).


F5Ch45: The features include whorls (one of which is keratinizing), dyskeratosis, a cytolytic cleft, and a few vacuolated cells. There are a few small deposits of melanin. Atypia is moderate, and each nucleolus is prominent.


F6Ch45: The pattern in this field is evidence of recent cytolysis and dyskeratosis. Only whorls remain; fibrous tissue has not been inlaid in the defects among the whorls.


F7Ch45: Among the keratinized cells and lamellae, a structure, that resembles a small hair shaft (blue arrows), has been cut in cross section. To the right, a portion of a cystic component is represented.


F8Ch45: Atypia is moderate; nucleoli are prominent. There are scattered mitotic figures. The cells among the whorls are loosely spaced.


F9Ch45: To the right, some of the cells show perinuclear vacuoles; there are scattered dyskeratotic cells. The large whorl shows a central area of keratinization; bordering the keratin-filled lumen, some of the cells contain a few keratinohyaline granules; at this interface, individual cells bulge into the closely aggregated, keratinized debris. The patterns of keratinization are not those of classic infundibular type. To the left, the small cell, germinative epithelium abuts upon the stroma.


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