Trichilemmoma

Excerpt

Trichilemmomas are benign adnexal tumors originating from the hair follicles and were first described by Headington and French in 1962. Trichilemmomas are classified within the spectrum of benign follicular tumors, which encompass a diverse group of uncommon neoplasms originating from various locations within the hair follicle. Trichilemmomas originate from the outer root sheath of the hair follicular unit. Other similar growths originating from this locus include dilated pore of Winer, pilar sheath acanthoma, and pilar cyst, each delineating a unique facet of follicular pathogenesis.

Trichilemmomas often present as asymptomatic, solitary, or multiple verrucous papules, primarily surfacing on the face or neck. When solitary, these lesions can often be clinically misdiagnosed due to their resemblance to other skin conditions, such as verruca vulgaris, verrucous papilloma, basal cell carcinoma, or squamous cell carcinoma, thereby posing diagnostic challenges. However, when a patient presents with numerous trichilemmomas, clinicians should evaluate potential associations with genetic syndromes, notably Cowden syndrome. Trichilemmomas may also be associated with other benign neoplasms such as nevus sebaceous and syringocystadenoma papilliferum.

Histopathologically, trichilemmomas exhibit a lobular proliferation extending from the epidermis, characterized by pale-to-clear cells exhibiting peripheral palisading, enveloped by a thickened eosinophilic basement membrane. This is often accompanied by overlying hyperkeratosis and variable papillomatosis. In addition, a desmoplastic variant of trichilemmoma may be present, characterized by infiltrating basaloid cells amidst a thick, sclerotic stroma.