Trichogerminoma. Report of 14 cases.

We report 14 cases of trichogerminoma, a rare form of cutaneous adnexal neoplasm, derived from hair germ epithelium. The neoplasms occurred in 9 men and 5 women. Their ages ranged from 16 to 73 years (median 53 years). The tumors were slow growing, asymptomatic dermal or subcutaneous nodules, located on the head and neck (6), trunk (4), extremities (2) and hip (1), with no distinguishing clinical features. Histologically, trichogerminomas were characterized by sharply circumscribed, pseudoencapsulated dermal and subcutaneous nodules, ranging in size from 0.4 to 4.0 cm in diameter (mean 1.9 cm). The nodules were subdivided into lobules separated by variable amounts of stroma that demonstrated varying cellularity and mucin content. The lobules were composed of basaloid cells that formed densely packed, round nests or "cell balls" resembling hair bulbs. The basaloid cells demonstrated peripheral palisading, keratinization and differentiation towards various pilosebaceous structures. Retraction spaces, well developed hair follicles and hair shafts were not observed. These distinctive histologic features separated these neoplasms from other tumors of pilar origin and from basal cell carcinoma. The trichogerminomas behaved in a benign fashion with one exception. Complete excision of the lesions is the treatment of choice.