Onychocytic matricoma

Definition

A rare, benign, nail tumor originating in the nail matrix characterized by localized pachyonychia and variable degrees of pigmentation: pigmented, melanocytic (common, longitudinal melanonychia that may simulate a foreign body) or hypopigmented. Histopathology demonstrates a purely epithelial tumor with endokeratinization in the deep portion and concentrically arranged nests of prekeratogenous and keratogenous cells.