Pilomatricomal horn: a new superficial variant of pilomatricoma.

We describe a pilomatricomal horn on the right arm of a 39-year-old man. Although initially the tumor was clinically thought to be a verruca vulgaris, the microscopic features were similar to those found in classic pilomatricoma, except for the epidermal location and the presence of a cutaneous horn. Light microscopy showed replacement of the epidermis by basaloid cells, with masses of cornified material containing shadow cells that formed a cutaneous horn. Whereas classic pilomatricoma is confined to the deep reticular dermis or subcutis, the present case represents a unique heretofore unreported epidermal variant of pilomatricoma that pathologists should be aware of to differentiate it from malignant epidermal tumors.