Trichogerminoma.

A case of distinctive benign follicular neoplasm previously reported under the designation of trichogerminoma is described. A 45-year-old man presented with an asymptomatic nodule on the scalp since 3 years. Histologically, the lesion corresponded to a well-organized, symmetrical dermal nodule made up of basophilic lobules included in a fibrocytic stroma. The lesion had the characteristics of hair germ tumors; however, most lobules depicted a distinctive pattern of rounded nests of concentrically arranged clear cells. Small follicle bulb-like basophilic structures, foci of sebaceous differentiation, and areas of infundibulocystic, isthmic, and outer sheath keratinization were also seen. This neoplasm and the other tumors with hair germ differentiation such as trichoblastoma and panfolliculoma seem to represent the same spectrum of hair follicle neoplasms only distinguishable by their degree of differentiation.