Ch25P17-L3 Catagen-like & Sebaceous
Tricholemmoma

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R2353sebadenIFK800

F1Ch25 (R2353): The epidermis shows compact hyperkeratosis, acanthosis, mild follicular plugging, and focal, mild papillomatosis. In areas, the superficial unit of the epidermis shows intracellular edema. Focally, collections of keratinocytes, of superficial unit type, form compact whorls (squamous eddies). A dual population of squamous cells is represented in the epidermis. The papillary dermis is expanded; it is delicate with regularly spaced dilated vessels. At this level, the patterns are those of an inverted follicular keratosis; if the overall pattern were not so prominently columnar, the cell types and the focal arrangement of the cells might be cited as features of an “irritated seborrheic keratosis.”

R2353sebadenIFK820

F2Ch25: At a deeper level, the pattern of squamous eddies focally is a prominent feature. Some of the eddies have keratinized centrally; the keratinized debris is compactly aggregated. There are angulated and rounded defects in the population of keratinocytes among the scattered whorls. The defects are evidence of a cytolytic process that is common in the setting of inverted follicular keratosis and the follicular hamartomas of the butterfly area of the face. To the left, there are solid columns of keratinocytes. Two populations are represented. One population is composed of small squamous cells; they have basaloid characteristics; these cells qualify as germinative cells and extend to the dermal-epithelial interface. The other population is composed of large cells as seen in the superficial unit of the epidermis; focally, some of the cells show prominent intracellular edema (vacuolization of the cytoplasm).

R2353sebadenIFK830

F3Ch25: Two whorls and a portion of a third whorl are represented. One whorl shows a central area of keratinization; the surrounding cells contain keratohyalin granules. Of the three, the central whorl is the largest. Some of the keratinocytes in the neighboring epidermis show intracellular edema. Focally, there are rounded and angulated clefts. These clefts appear to have formed by the process of cytolysis; intracellular edema appears to be sequentially related to the cytolytic process. Keratinocytes near a defect, at the bottom of the field on the right, show evidence of dyskeratosis with increased cytoplasmic acidophilia. There are scattered wavy deposits of fibrinoid at the bottom of the field.

R2353sebadenIFK890

F4Ch25: Cytolysis in this area has progressed to partially disrupt the epithelial cells of one of the whorls in the central portion of the field. The compact keratinized debris that outlines small lumens is of a type that might be characterized sebaceous duct-like.

R2353sebadenIFK920

F5Ch25: In the evolution of the changes in the cytolytic portions, fibrous tissue,as seen in this field, tends to be inlaid in the defects. Follicular lesions showing this sequence of changes have been characterized as desmoplastic variants.This type of alteration was first characterized as sclerosing entrapment ( Reed, Letter to Editor, Am J Dermatopathol). In the progressive changes, some of the whorls appear to be entrapped in the fibrous tissue. As a result, the patterns might be misinterpreted as invasive growth, and the respective lesion then might be misdiagnosed as carcinoma.

R2353sebadenIFK910

F6Ch25: On the right, at the margin of the field, there is a large lytic defect. Just above the center of the field, there is a projection of fibrous tissue into the epithelial domain; there are also fibrin deposits in this area. At the bottom of the field, there are additional fibrin deposits at the epithelial-stromal interface. In the whorl near the bottom of the field, the patterns at the  epithelial-keratin interface resemble those of catagen-committed epithelium of the inconstant portion of a hair follicle. Two of the whorls showing keratinization, do so without the mediation of granular ayer. If emphasis is to be placed on the presence or absence of a granular layer, then the absence of such a quality in these two whorls qualifies the pattern as catagen-like.

R2353sebadenIFK990

F7Ch25: Sclerosing entrapment is a prominent feature. In areas, cords of entrapped cells do not show a definitive basal layer; such patterns might be mistaken for invasive growth.

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