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1. Histopathology of Inflammation

2. Minimal Deviation Melanoma, etc.

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F1Ch27 (G5357): This is a classic configuration for a tricholemmoma; the vertical dimension is equal to, or greater than, the horizontal dimensions. There is prominent papillomatosis with hyperkeratosis. If we accept the crevices between the epithelial papillae as the equivalent of the ostia of hair follicles, there is a confluence of the epithelial components just beneath the papillae. There is a broad columnar extension that forms the terminus of the lesion. The pallor of the squamous epithelium, in part, is evidence that the section has faded; in addition, pallor is contributed by cytoplasmic vacuolization of many of the cells. There is a striking hyperplasia of sebaceous glands beneath the hair sheath component. It is difficult to dismiss an association between the sebaceous glands and the hair sheath component.

F2Ch27: The deep extremity of the lesion is represented. Palisaded basal cells of a type associated with the outer root sheath are a prominent feature. Many of the cells above the basal layer have clear cytoplasm.

F3Ch27: The cytoplasmic vacuoles are similar to those seen in the outer root sheath of hair follicles. There are numerous whorls of squamous cells; some of the cells forming the whorls also have vacuolated cytoplasm. Nuclei and nucleoli are small and uniform.

F4Ch27: Most of the vacuoles are eccentric, and displace the nucleus of the affected cells; cell membranes are prominent.

F5Ch27: Squamous eddies are common to both tricholemmoma and inverted follicular keratosis; they mark areas with the potential to develop into a keratin-filled lumen. In this lesion, the cells generally deviate from those of classic tricholemmoma; they are too acidophilic with “heavy” cell walls. They seem to relate to patterns of the inconstant portion of a follicle; they may be committed to terminal differentiation (a process that recapitulates catagen phenomena) but regressive changes are not a feature at this stage.

Atypism, as a variable feature of tricholemmomas, is discussed in chapters 40c & 40d.