The common blue nevus of Jadassohn-Tieche most frequently presents as a solitary blue 1- to 10-mm dome-shaped papule on the dorsal hand or foot. It is characterized by greatly elongated wavy groups of spindled dermal melanocytes that are oriented parallel to the epidermis. Cellular blue nevi resemble common blue nevi clinically but are usually larger, ranging from 1 to 3 cm in diameter, and occur primarily on the buttocks or sacrum as a solitary blue nodule (summary by Knoell et al., 1998). [from
OMIM]