Nodular desmoplastic variant of trichoblastoma.

A case of an unusual, previously unreported, nodular desmoplastic variant of trichoblastoma (hair germ neoplasm) in the scalp of a 65-year-old woman is reported. Four discrete nodules were present in close proximity at presentation. Another nodule developed in the same vicinity 3 1/2 years after excision, and there was no further recurrence 2 1/2 years later. The tumors were located in the dermis, made up of cords of primitive hair germ-like structures radiating down from discrete hyalinized nodules located in the superficial dermis. There were small foci of keratinization or mucoid change within the epithelial islands. Toward the deep portion of the tumor, the epithelial cells became spindly and grew in a more dispersed pattern, within a desmoplastic stroma. There was also infiltration of the epineurium of the cutaneous nerves and arector pili muscle. This uncommon benign neoplasm of hair germ merits wider recognition; in particular, this desmoplastic variant may mimic invasive carcinoma, morphea-type basal cell carcinoma, desmoplastic trichoepithelioma, and desmoplastic trichilemmoma. Distinguishing this variant from the former two possibilities is particularly important in order to avoid unduly aggressive treatment.