Excerpt from Blue Nevi

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Background

Two clinically recognized variants of blue nevus exist: the common blue nevus and the cellular blue nevus.

Tièche, a student of Jadassohn, first described the common blue nevus in 1906. Earlier authors described similar lesions as chromatophoroma and melanofibroma. 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 head and the neck, the sacral region, and the dorsal aspects of the hands and feet.

The cellular blue nevus was first described as a variant of melanoma. Later, it was classified as a variant of blue nevus. Controversy still arises over the precise distinction of atypical cellular blue nevus from melanoma. The cellular blue nevus is a less common lesion but often clinically similar to the common blue nevus. These lesions tend to be large, usually measuring 1-3 cm in diameter. Lesions are elevated, smooth-surfaced papules or plaques that are gray-blue to bluish black in color. Lesions are usually solitary and found on the buttocks, the sacral region, and occasionally on the dorsal aspects of the hands and the feet.

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.

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.

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.

Common and cellular blue nevi are not associated with chromosomal aberrations, and they show fewer B-RAF mutations compared with congenital and acquired nevi.

Frequency

United States

Blue nevi are most frequently noted in Asian populations, where the prevalence is estimated to be 3-5% in adults. They are found in 1-2% of white adults and are rarely found in blacks. Blue nevi are uncommon at birth or in the first few years of life, with an estimated prevalence of less than 1 case per 1000 population.

International

The international incidence of blue nevi varies with the population examined.

Mortality/Morbidity

• 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.

Sex

Blue nevi are twice as common in women than in men.

Age

Blue nevi may develop at any age but are usually noticed in the second decade of life or later.

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