Three-dimensional melanin distribution of acral melanocytic nevi is reflected in dermoscopy features: analysis of the parallel pattern.

BACKGROUND: Acral melanocytic nevi have parallel patterns on dermoscopy; however, it is not understood why pigment distributions exhibit such patterns. AIM: To clarify the reason why melanin distributions in acral melanocytic nevi exhibit a parallel pattern on dermoscopy.
METHODS: A serial sectioning perpendicular to the skin markings was performed, and each section was stained with modified Fontana-Masson staining to pick out melanin granules. These sections were then reconstructed to three-dimensional images by an image processing software, and these three-dimensional images were analyzed.
RESULTS: Melanin columns in the cornified layer were mainly seen in the dermoscopic images of acral melanocytic nevi. In the parallel-furrow pattern melanin columns were arranged vertically, and in the fibrillar pattern they were arranged in a slanting fashion.
CONCLUSION: Melanin columns in the cornified layer, not melanin in the basal layer, mainly contribute to the dermoscopic pattern of acral melanocytic nevi.