Immunohistologic patterns of congenital nevocellular nevi.

To establish sensitive histologic criteria for small congenital nevi (SCN), we examined 29 biopsy specimens of SCN from patients younger than age 1 year by serial sectioning and S100 immunoperoxidase staining. The depth of papillary and reticular dermal infiltration was variable; only the results of six biopsy specimens contained nevomelanocytes in the lower third of reticular dermis. However, all cases had focal nevomelanocytic involvement of adnexa at the midreticular dermis or below (26 of 29 cases in eccrine and 15 of 29 in pilosebaceous structures). Follow-up specimens in ten patients were obtained (mean interval, 10.25 years), and no difference in histologic pattern or cytology was observed. There were variable size increases in the surface area of SCN, ranging from no increase to a maximal ninefold increase.