Ch34bP31b Pilomatrixoma

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F1Ch34b: This is a representative field from a pilomatrixoma; germinative epithelium is represented in variable patterns. To the right, the cells mostly are small with round nuclei, prominent nucleoli, and scanty cytoplasm; they qualify as a variant of matrical cells. Along the interface with keratinized debris, a single row of flattened cells separate the small round cells from the keratinized debris. Perhaps, this row of cells corresponds to the “cuticle” of the inner root sheath of a normal follicle. To the left of the population of small, round cells, there is a cluster of uniform cells that have pale, amphophilic cytoplasm and nuclei of intermediate size; nucleoli are prominent but uniform; a match for this population of cells can be identified in a normal anagen hair bulb. Above the blue arrows, polygonal acidophilic cells have numerous, uniformly small, brightly acidophilic granules in their cytoplasm; the granules are small, and uniform in size; the cytologic features are not those of the cells of Huxley’s layer. The acidophilic cells seem to stream from left to right. Red arrows identify a whorl of mature squamous cells in what is otherwise a population of germinative cells.


F2Ch34b: At higher magnification, the acidophilic, polygonal cells are converted to ghost cells without an intermediate granular layer. There is some evidence of focal parakeratosis. The cells seem to stream form left to right. This pattern may be indicative of an abortive expression of the formation of a hair shaft.


F3Ch34b: In this expanse of germinative epithelium, a whorl of mature, keratinizing squamous cells is something of a surprise; there is a granular layer with keratohyaline granules. The pattern of a keratinized whorl would suggest an attempt to form a lumen. There are scattered mitotic figures.


F4Ch34b: An island of germinative cells of pale acidophilic type has undergone extensive lysis. Irregular clusters and rows of germinative cells are scattered about in an empty space. There are scattered aggregates of dyskeratotic material. Histiocytes, some of which are multi-nucleated, are present at the periphery of the zone of cytolysis. Cytolysis is a prominent feature of the reaction in these lesions. Some of the changes might be characterized as having, in addition to    anagen-like qualities, features in common with early catagen patterns.

Some examples of pilomatrixoma present as cysts.


F5Ch34b: In this field, the germinative epithelium of a pilomatrixoma surrounds a nubbing of cellular stroma (blue arrows); The configuration of the combined stroma and epithelium produces a pattern that resembles a portion of a hair bulb. Above the basal layer (the single row of cells that abuts upon the stroma), dark cells form two or three layers. The cells of the next layer also form two or three layers; the cells vary in size and have pale or clear cytoplasm; many of these cells contain trichohyaline granules. The adjacent area is occupied by keratinized debris, proteinaceous fluid, and a loose infiltrate of inflammatory cells. The population of pale cells, many of which contain trichohyaline granules, resembles that of Huxley’s layer.


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