Ch14aaP6aa Seborrheic Keratosis

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1. Histopathology of Inflammation

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F1Ch14aa (lesion of NSJ, continued): The basic features, as might be seen in a normal follicle, seem to be accentuated; they are further distinguished (in the manner of a dysplasia) by asymmetrical patterns. It is of interest that these distorted follicular units of NSJ usually do not show a convincing outer root sheath. Some of the abnormal bulbs are attached to a constant component by a slender strand of indifferent squamous cells.

The site of origin of the cells of the outer root sheath is uncertain, if reliance is placed solely on histologic observations. A notion that it, like the inner root sheath, is derived from specific cells of the bulb should, at least, be considered. In the normal development of a follicle, a trail of glycogen-rich cells is left behind to mark the trail of the descent of the bulb. In turn, the developing hair shaft must invade this column of clear cells. Perhaps, a column of specialized clear cells facilitates, in some manner, the development of a hair shaft. If an absence of an outer root sheath is truly a feature of the follicles of NSJ, then the alopecia of NSJ might be a consequence of such a developmental defect.


Seborrheic Keratosis

F2Ch14aa: This is the common and characterisitic pattern of seborrheic keratosis. Columns of squamous cells, mostly of germinative type, extend from the epidermis into the dermis; they branch, and the branches then become interconnected (confluent). Islands of stroma are present among the branches. Symmetrically rounded spaces in the epithelial component contain loosely laminated keratinized debris. Plump, pale squamous cells are stratified about the rounded defects. To the right, the section is somewhat tangential to the surface; elsewhere the deep margin of the epithelial component has a straight interface with the stroma; the interface is parallel to the surface of the skin. A thin zone of condensed stroma forms the interface with the reticular dermis.


F3Ch14aa: Two cell types are represented. The preponderant cells are small germinative cells; they are of a type that characterizes the cells of the basal unit of the epidermis. Plump, pale cells, that are stratified about the small keratin-filled cysts, form the second component; these cells are comparable to the cells of the superficial unit of the epidermis; they have the characteristics of cells that are committed to terminal differentiation. The basal layer is variably pigmented.


F4Ch14aa: The basic features of a seborrheic keratosis are represented. In the basal unit, near the basal layer, there are two whorls.


F5Ch14aa: The cells of the germinative component show mild to moderate cytologic atypia. In this field,the lesion qualifies as an atypical seborrheic keratosis. Intercellular spaces are widened, and there are small lytic defects. Pigmented, dendritic melanocytes are loosely sprinkled among the keratinocytes.


F6Ch14aa: Atypia is mild to moderate. Pigmented, dendritic melanocytes are irregularly sprinkled among the keratinocytes. Some of the defects appear to be the widened lacunae of the melanocytes. This lesion, as seen in F5 & F6, could be characterized as an atypical melanoacanthoma.


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