The histologic spectrum of pigmented spindle cell nevus: a review of 120 cases with emphasis on atypical variants.

The histopathologic features of 120 cases of pigmented spindled nevus (PSCN) from the years 1973 through 1988 were reviewed from a consultative practice heavily weighted with difficult nevomelanocytic lesions. The patients' mean age was 25.2 years, and females outnumbered males (68 versus 52). Extremity lesions made up 69.6% of the total, with the thigh the most common site. The lesions were categorized into one of four variants of PSCN, based on the presence or absence of various architectural and cytologic parameters and involvement of the reticular dermis. Thirteen cases (10.8%) were designated typical PSCN, and were characterized by fascicles of uniform pigmented spindle cells without cellular atypia and limited to the epidermis or papillary dermis. Ninety-five cases (79.2%) were classified as atypical PSCN (PSCN with architectural and/or cytologic atypia). Some of the latter also demonstrated substantial numbers of epithelioid cells, thus exhibiting some overlap with Spitz nevus. Eight cases showed striking features of dysplastic nevus. Ten cases had fascicles of pigmented spindle cells involving the reticular dermis ("plexiform" PSCN). Two cases were designated as combined PSCN because of the presence of banal nevus cells in addition to the spindle cell component. Clinical follow-up of a small group of patients has not suggested, to date, any aggressive behavior. Knowledge of PSCN and its atypical variants is important for discrimination from malignant melanoma.