A case of trichogerminoma.

Trichogerminoma is a rare neoplasm which was first described in 1992 and there is still controversy over its inclusion into the spectrum of trichoblastoma. A 79-year-old woman presented with a 5-year history of an asymptomatic nodule on the left posterior neck. Histologically, the lesion revealed a well-demarcated deep dermal nodule surrounded by a pseudocapsule. The tumor was composed of lobules with basophilic cells and some of the lobules displayed a distinctive pattern of densely packed 'cell balls' with peripheral condensation. Immunohistochemically, the tumor cells showed zonal CK5/6 immunoactivity in contrast with the negatively stained 'cell balls'. These characteristics were compatible with the diagnosis of trichogerminoma. We report here on a rare case of a hair germ tumor called trichogerminoma.