This lesion on the face of a 56-year-old man is a typical example of a trichilemmoma. These lesions are almost exclusively found on the face. Multiple lesions can be seen in Cowden disease, but this was a solitary, likely idiopathic form. The characteristic changes include the clear cell change with overlying hyperkeratosis and a peripheral thick eosinophilic basement membrane. The differential diagnosis would include an inverted follicular keratosis or a type of pilar acanthoma.
Histologic sections of skin show a solitary well-circumscribed nodular lesion continuous with the overlying epidermis. The lesion is vaguely exophytic, consisting of large nodules of clear cells, most evident in the deeper portions of the lesion. Hyperkeratosis overlies an invagination, associated with squamous metaplasia.