Deep penetrating (plexiform spindle cell) nevus. A frequent participant in combined nevus.

This report describes 41 patients with lesions similar to those previously termed "deep penetrating" or "plexiform spindle cell" nevus (DPN). DPN occurs primarily during the first four decades, is somewhat more common in females, and has a predilection for the face, trunk, and proximal extremities. It is usually less than 1 cm in diameter and often shows variegation in color, including shades of brown, blue, and black, that create clinical concern regarding malignant melanoma. None of the present tumors nor those from the literature recurred following excision. Microscopically, DPN usually has a wedge shape, invariably involves reticular dermis, and may penetrate subcutis. Involvement of neurovascular structures and adnexae and spread between fibers of the reticular dermis create a fascicular-plexiform architecture. The melanocytes are fusiform or epithelioid, lightly to moderately pigmented, and exhibit mild to focally prominent nuclear atypia. Sparse to abundant melanophages are characteristic. Mitotic figures are few and present in only a small minority of lesions. The present study of a consecutive series also indicates that DPN is a frequent participant in combined nevus, as it was associated with ordinary nevus in two-thirds of the lesions.