Stroma

Biology

Stromal cell

Fibroma

Nuclear atypia

Medicine

Immunohistochemistry

Atypia

Pleomorphism (cytology)

Pathology

Journal of Cutaneous Pathology

Onychomatricoma is a rare tumor that appears to originate from cells of the nail matrix. Three cases of onychomatricoma that met Perrin et al.'s 1 histologic criteria of onychomatricoma are described. However, using a single term to classify all three tumors ignores the apparent microscopic differences that exist among them. To demonstrate better the spectrum of so‐called onychomatricoma and properly acknowledge the noticeable disparity among our cases, a series of terms is proposed. This terminology is based on the histologic spectrum of epithelial–stromal ratio of stromal cellularity and of extent nuclear pleomorphism. Use of such criteria has a precedent in the classification of follicular and odontogenic fibroepithelial neoplasms. This new nomenclature includes ‘unguioblastoma’ for tumors with a predominant epithelial component and ‘unguioblastic fibroma’ for tumors where a cellular stroma is more prominent and characteristic. The term ‘atypical unguioblastic fibroma’ is used to describe a third rare neoplasm, in which the cellular stroma shows nuclear pleomorphism and atypia with an increase of mitotic activity.

Unguioblastoma and unguioblastic fibroma – an expanded spectrum of onychomatricoma