RESUMEN
Though trichogenic tumors were classified as trichoblastoma, trichoblastic fibroma, trichogenic trichoblastoma and trichogenic myxoma by Headington(1970), their true classification depends upon the epithelial and mesodermal component as well as evidence of their induction. Because of the rarity of hair germ cell tumors their classification is still controversial. In this report, we describe a case of trichogerminoma which is not included in the above classification. The trichogerminoma was first described by Sau et al. in 1992 and characterized by its morphologic pattern of germinal centers and lymphoid follicle-like structures in the nests of trichoblasts. Herein we reporte a tumor which arose on the skin on the back of a 51-year-old man and presented as a sharply circumscribed mass(4.5x2.0x1.5 cm) involving both the dermal and subcutaneous tissues without any epidermal connection. The tumor had many germinal center-like structures in the basaloid trichoblasts. Lobular cell nests were separated by variable amounts of stroma, but no horn cyst were noted. The germinal center-like cells showed early differentiation of hairs, resembling early hair bulbs. Trichogerminoma is considered to be a type of tumor located between trichoblastoma and trichoblastic fibroma.