(tricholemmoma, benign) A benign hair follicle neoplasm in the outer hair sheath and infundibulum, characterized by central cells showing highly eosinophilic amorphous keratin.

A benign neoplasm arising from the outer hair sheath and infundibulum. It occurs in the head and neck, usually on the face. It usually presents as an exophytic wart-like lesion or a dome-shaped lesion with a smooth surface. Morphologically, it is characterized by the proliferation of cuboidal cells with clear or eosinophilic cytoplasm in the dermis with connection to the epidermis/hair follicle. There is peripheral cellular palisading, and the lesion is surrounded by a hyaline band.

A benign tumor originating from the outer root sheath of the hair follicle.

In 1962, Headington and French first described trichilemmoma as a benign neoplasm with differentiation toward pilosebaceous follicular epithelium, or outer root sheath. Though benign in nature, the significance of trichilemmoma resides in the association with Cowden disease (ie, multiple hamartoma syndrome) and the need to differentiate...