TRICHILEMMOMA
Follicular outer root sheath differentiation is seen in the hyperplastic epithelium that constitutes this lesion. The acanthotic epithelium is connected to the surface in a broadly based fashion in several places, and the surface may be verrucous. Peripheral palisading is present to varying degrees, and this can lead to a false diagnosis of basal cell carcinoma with follicular differentiation. The basement membrane around the hyperplastic epithelium is thickened and may be visible in H&E stained sections. There is clear cell differentiation in some trichilemmomas, and the clear cells contain increased glycogen. Most examples are solitary, but multiple trichilemmomas are seen in Cowden's syndrome.
 
 
Scan power view of the lesion. The surface of this one is slightly verrucous. Viral etiology has been postulated by a minority of observers and has not been proven.
Low power view of above. Palisading of the cells around the periphery of the bulbous, acanthotic epithelium is apparent at this magnification.
High power view of above. Peripheral palisading, a thickened basement membrane, and minimal clear cell differentiation are seen.

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