Giant trichoblastoma on the scalp.

We describe a case of giant trichoblastoma that had been present for many years on the scalp of a 69-year-old man. The specimen was examined histopathologically, immunohistochemically, and ultrastructurally. Histopathologic examination showed that neoplastic cells were arranged in different patterns from area to area, including rippled, adenoid, and palisading patterns. In some areas of the neoplasm, foci of sebaceous differentiation were also present. The ultrastructural characteristics of neoplastic cells support the notion that trichoblastomas are neoplasms composed mostly of follicular germinative cells.