Practice Essentials
Blue nevi are melanotic dermal lesions that can be present at birth or develop later on in life. Once a blue nevus appears, it tends to remain unchanged throughout life. The clinically noted blue color is due to the depth of melanin in the epidermis and the Tyndall effect. The Tyndall effect is the preferential absorption of long wavelengths of light by melanin and the scattering of shorter wavelengths, representing the blue end of the spectrum, by collagen bundles. It is currently unclear whether there is a genetic component associated with blue nevus.
There are two clinically recognized variants of blue nevus: the common blue nevus and the cellular blue nevus. The common blue nevus is a flat to slightly elevated, smooth-surfaced macule, papule, or plaque that is gray-blue to bluish black in color. Lesions are usually solitary and found on the skin in the head and neck, the sacral region, and the dorsal aspects of the hands and feet. Less commonly, they occur in the oral mucosa, vagina, prostate, and conjunctiva. [1] Rarely, blue nevi have been found in the nasal cavity and sinuses. [2] Very rarely, they are found in the spinal cord. [1]
The cellular blue nevus was first described as a variant of melanoma. Later, it was classified as a variant of blue nevus. Controversy still exists over the precise distinction of atypical cellular blue nevus from melanoma. [3] The cellular blue nevus is less common than, but often clinically similar to, the common blue nevus. These lesions tend to be large, usually measuring 1-3 cm in diameter. They are elevated, smooth-surfaced papules or plaques that are gray-blue to bluish black in color. Histologically, they are characterized by a cellular appearance and subcutaneous infiltration. [4] Lesions are usually solitary and found on the buttocks, the sacral region, and occasionally on the dorsal aspects of the hands and feet.
In addition to the common blue nevus and the cellular blue nevus, other variants include the following [5] :
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Combined blue nevus
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Sclerosing (desmoplastic) blue nevus
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Amelanotic blue nevus
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Epitheliod blue nevus
Pathophysiology
Although definitive experimental evidence is lacking, blue nevi are believed to represent dermal arrest in embryonal migration of neural crest melanocytes that fail to reach the epidermis. Collections of melanocytes can be found in fetal dermis, but they involute during later gestation. The clinically noted blue color is due to the depth of melanin in the epidermis and the Tyndall effect. The Tyndall effect is the preferential absorption of long wavelengths of light by melanin and the scattering of shorter wavelengths, representing the blue end of the spectrum, by collagen bundles.
Because of the variation of blue nevi in different populations, a genetic predisposition has been suggested. However, familial cases of blue nevi are exceedingly rare. Common blue nevi show fewer BRAF mutations compared with congenital and acquired nevi, [6] but they show somatic mutations in the heterotrimeric G protein α-subunit, GNAQ, in up to 83% of cases. [7, 8]
Etiology
See Pathophysiology. Although blue nevi are most frequently seen on the skin, they have also been reported in the oral cavity, subungually, [9] in lymph nodes, and in organs such as the brain, pulmonary tract, and prostate.
Epidemiology
Frequency
The international incidence of blue nevi varies with the population examined.
Sex
Blue nevi are more common in women than in men, with a 3:2 reported predominance. [10]
Age
Blue nevi may develop at any age but are usually noticed in the second decade of life or later.
Prognosis
The prognosis of blue nevi is excellent. Most cases remain entirely benign. Blue nevi usually persist unchanged throughout life and are asymptomatic. Rare cases of malignant melanoma have been reported arising in association with cellular blue nevi. [11]
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Common blue nevus on the scalp.
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Common blue nevus on the hand.
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Common blue nevus. Numerous elongated dendritic melanocytes with a subepidermal grenz zone. Courtesy of Rose Elenitsas, MD.
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Cellular blue nevus. Deep proliferation of dendritic melanocytes, broader at the surface than the base, with islands of paler cells with larger nuclei. Courtesy of Rose Elenitsas, MD.
