trichoblastomas

Trichoblastoma is a rare benign skin adnexal neoplasm that shows differentiation toward hair follicle structures and is thought to originate from germinative cells of the hair follicle. It most commonly presents on the face and scalp of adults.

Clinically, trichoblastomas appear as small, firm, skin-colored or pigmented nodules or plaques. They typically grow slowly and are asymptomatic. Solitary lesions are most common, though multiple tumors can occur in certain familial syndromes such as Brooke-Spiegler syndrome.

Histologically, the tumor is usually well circumscribed and located in the dermis or extending into the subcutis. It consists of basaloid cell nests and cords with follicular differentiation, including primitive hair germ-like structures and abortive hair follicles set in a fibrous stroma. Desmoplastic variants show dense fibrous stroma. Mitoses are rare and there is little to no cytologic atypia. Unlike basal cell carcinoma, trichoblastoma typically lacks retraction artifacts and often has less prominent peripheral palisading.

Immunohistochemistry can aid in distinguishing trichoblastoma from basal cell carcinoma, as trichoblastoma generally does not show the strong Ber-EP4 positivity that is common in basal cell carcinoma and may express markers associated with follicular differentiation.

Management is by complete surgical excision. Recurrence is uncommon when margins are clear. Malignant transformation to trichoblastic carcinoma is rare but has been described. Differential diagnosis includes basal cell carcinoma and trichoepithelioma; clinical and histopathologic correlation is important. In familial contexts, multiple adnexal tumors can occur as part of Brooke-Spiegler syndrome.

See also: basal cell carcinoma, trichoepithelioma, Brooke-Spiegler syndrome.