Incidental microscopic foci of nevic aggregates in skin

Microscopic foci of nevic aggregates have been described in normal lymph nodes, where they may pose diagnostic challenges to pathologists. In the course of our practice, we have observed a similar phenomenon in cutaneous tissue. For this reason, we performed a retrospective study of cutaneous excisions over a 1-year period to better characterize this observation. We reviewed 2482 pathology reports of cutaneous excisions, of which 0.8% were associated with such microscopic foci of incidental nevic aggregates. Incidental nevic aggregates were typically dermal in nature and found commonly in excisions from the head and neck region. They were clinically unapparent, with a maximum mean horizontal and vertical diameter of 0.86 mm (0.3-1.5 mm) by 0.46 mm (0.1-1.3 mm). The nevic aggregates were separate and located in normal skin, away from any associated tumors or scar tissue. Although their etiology remains unknown, we hypothesize a derivation from dermal melanocytes, in keeping with the Hochsteigerung theory of nevogenesis. The purpose of this study is to draw attention to the existence of incidental cutaneous nevic aggregates, thereby alerting pathologists and dermatopathologists to their potential as a diagnostic pitfall, especially in the setting of concurrent primary cutaneous malignant melanoma or melanoma in situ.