Ch29bP21bTricholemmal Basosquamous

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F1Ch29b:This tumor is multinodular with some variation in patterns from nodule to nodule. This field is representative of only a portion of the lesion; the section is badly faded. There is some basic resemblance to the follicular hamartomas of the butterfly area of the face. The larger component is attached to the epidermis by columns of squamous cells, one of which appears to be the infundibular portion of a follicle. To the left, blue arrows identify two small components, each of which has the columnar and vertical orientation of a lesion showing follicular differentiation. The pale areas in the large nodule are membranous deposits of hyalin. There are mild infiltrates of lymphoid cells.


F2Ch29b: Two additional nodular components are represented. The larger of the two nodules shows a central area of stromal pallor; cords of tumor cells are entrapped in this stroma.


F3Ch29b: This is another area of the multinodular tumor. The patterns are such that each of the tumor nodules appears to have a follicular orientation.


F4a&bCh29b: The tumorous component is composed of uniform pale cells. The overall pattern is compatible with a tumor that shows follicular differentiation and, in this field, the cytologic features, as well as the portion of follicle that is involved, suggest a pattern of follicular, tricholemmal differentiation.


F5Ch29b: The two columns that form an attachment to the epidermis might be compared to the infundibular portion of follicles. The nodular component is composed of pale cells; in areas, at the periphery of the nodule, on the left, basal cells form prominent palisades. Hyaline membranes are prominent in the nodule.


F6Ch29b: The basic pattern is somewhat reminiscent of those seen in zones of sclerosing entrapment, as seen in follicular hamartomas of the butterfly area of the face. The tumor cells have basosquamous qualities and are atypical. Nuclei are enlarged and have marginated chromatin; nucleoli are centrally placed. The nests and cords of cells are supported by loosely cellular fibro-myxoid tissue (a matrical quality not seen in sclerosing entrapment). Hyaline deposits, in membranous patterns, are a prominent feature. They resemble the deposits seen in the stroma of some basal cell carcinomas.


F7Ch29b: At the deep margin , two dilated ducts contain inspissated material (blue arrows) The epithelial lining is flatterned. A second (outer row) of cells shows degenerative changes; the patterns, with small ducts lined by a double layer of cells, are compatible with sweat duct differentiation. The ductal components may simply represent pre-existing sweat ducts that have been entrapped in the tumor. The possibility that the tumor is, itself, showing neoplastic sweat duct differentiation cannot be excluded; the patterns of differentiatin may be divergent. At the periphery, the stroma is that of a reactive stroma, as a common response to an infiltrating epithelial neoplasm of squamous cell type.


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