The blue skin mole is a benign neoplasm, also called blue nevus or Jadassohn-Tièche nevus, appears clinically as a dark-blue or blue-black smooth nevus formed by melanin-heavily pigmented spindle cells in the middle and lower two-thirds of the dermis. Clinically, the blue nevus appears as a slate blue or bluish black, sharply circumscribed, flat or slightly elevated nodule, occurring on any area of the body. It originates from mesodermal cells. The common blue nevus is always benign. Cellular blue nevus is larger, especially on buttocks and can degenerate into malignant melanoma.
Blue skin moles are present in fewer than 1 in 3000 newborns, in about 1 in 1000 during the first 5 years of life, and in 1 to 2 percent of white school children, and 0.5 to 4 percent of healthy white adults. They are said to be uncommon in darkly pigmented persons. The vast majority of blue skin moles are single, small, deep-blue macules or papules about 1 to 2 mm in diameter.
Common blue skin moles are usually acquired, singular, asymptomatic blue, blue-gray, or blue-black papules, usually less than 10 mm in diameter. The blue-gray color of blue skin moles is an optical effect of dermal melanin viewed through the overlying skin. The longer wavelengths of visible light penetrate the deep dermis and are absorbed by black dermal melanin, but the shorter (blue) wavelengths do not penetrate deeply enough to be absorbed by melanin and are thus reflected back to the observer's eye, giving a blue-gray cast to the deeply situated melanin. Common blue skin moles occur anywhere, but about half the reported cases present on the dorsa of hands and feet. The common blue nevus occasionally may have a target-like appearance, with a blue-gray central nodule, a flesh-colored or hypopigmented surrounding area, and a blue-black rim. The target blue nevus occurs mostly on the hands and feet but also on the back and perianal area. Common blue skin moles occasionally may have satellite lesions that may be mistaken for melanoma metastasis.
Cellular blue skin moles are blue-gray or blue-brown nodules or plaques 1 to 3 cm in diameter, occasionally larger. Their surface is usually smooth but may be irregular. About half the cases are located on the buttocks or sacrum. Malignant blue nevus may develop in contiguity with a cellular blue nevus or de novo. Malignant blue nevus presents as an expanding dermal nodule with or without ulceration.
A common blue nevus that is stable for many years in an adult usually requires no therapy. Sudden appearance of a blue nodule, expansion of a preexisting blue nodule, a congenital blue nodule, or a relatively large blue nodule or plaque greater than 10 mm in diameter demands histopathologic examination. Excision should include subcutaneous fat to ensure complete removal of deep dermal melanocytes, which are frequently present in the subcutaneous tissue of cellular blue nevus. Cellular blue nevus should be evaluated for excision because of its malignant potential.