MSH: Usually a benign tumor, that commonly presents as a solitary blue nodule with spindled MELANOCYTES covered by smooth SKIN. Several variants have been identified, one variant being malignant. The blue color is caused by large, densely packed melanocytes deep in the DERMIS of the nevus. In CHILDREN, they usually occur on the BUTTOCKS and LUMBOSACRAL REGION and are referred to as cellular blue nevi. Malignant blue nevi are more commonly found on the SCALP.,NCI: An intradermal nevus characterized by the presence of benign pigmented dendritic spindle-shaped melanocytes. It most frequently occurs in the skin of the distal upper extremities, followed by the lower extremities, scalp, face, and buttocks. It usually presents as a single blue or blue-black papular lesion less than 1cm in diameter. Simple excision is usually curative.