Anatomical patterns of presentation of congenital melanocytic nevi.

Abstract

Background: Congenital melanocytic nevi (CMN) appear at birth and are caused by a proliferation of benign melanocytes in the dermis, epidermis, or both. Melanocytes are pigment-producing cells with a strongly polarized dendritic morphology that reaches the skin by the migration of neural crest cells from the neuroectoderm. They protect the skin against ultraviolet radiation by providing melanin from their cellular cytoplasm to neighbouring keratinocytes. Melanocytes may have a mutation resulting in a lack of dendrites, leading to melanin existing in the cytoplasm, which causes these nevi. Some areas of the skin rely on specific spinal nerves for their sensory distribution, called dermatomes. This study aimed to investigate the correlation between CMN distribution and a pre-existent dermatomal pattern. Due to the dermatomes on the body being different from that of the face, two subsets were conducted. The first subset investigated the correlation between the CMN on the overall body and its association with body dermatomes. Hence, this study also analyses the distribution of CMN and its association with facial dermatomes. Methods: Clinical photographs of CMN (> 1.5 cm) obtained from the database of Inkosi Albert Luthuli Central Hospital were analysed. A total of 31 patients with CMN were collected. Results: Subset 1: The results for CMN distribution over the body revealed a higher preference for T10 (58.1%), T11 (54.8 %), and T12 (51.6 %) dermatomes. Furthermore, facial dermatomes V1 and V2 (54.8 %), C5 in the cervical region (32.3 %), and L1 in the lumbar (41.9 %) were notably affected. Varied CMN patterns were observed in the head and neck region, emphasizing the complexity of the nevi distribution. Subset 2: Only 19 patients met the inclusion criteria in this subset. The zygomaticofacial, zygomaticotemporal, and supraorbital nerve areas of distribution emerged as the most affected, while the transverse cervical and mental nerve areas of distribution were the least affected. Conclusion: This study provides evidence of a correlation between CMN distribution and dermatomes of the body/face and enhances our understanding of CMN presentation, shedding light on the potential for CMN to follow a dermatomal distribution, with CMN often mostly found in the trunk region around T10, T11, and T12. In the face, V1 and V2 dermatomes were found to be mostly affected, with subbranches of V2 (zygomaticofacial and zygomaticotemporal) as the most affected branches. The findings contribute to broader knowledge and invite future investigations into the complex nature of CMN distribution across body regions.