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Blue Nevi: Pathophysiology, Mortality/Morbidity/Statistics

Also known as blue moles, blue nevi are blue-black moles that are commonly found in people of Asian descent. They are usually benign even if they are present for many years. A collection of the body's pigment-producing cells cause a formation known as melanocytes. However, to rule out a type of melanoma or cancer it is important to have any new formation of these blue-black lesions.

Background

Currently there are two variants of the blue nevus that are clinically recognized. The first of these variants is the common blue nevus and the other is called by the name cellular blue nevus. The common blue nevus was first described in 1906 by Tieche, a student of Jadassohn. The nevus has a flat surface or a surface that is slightly elevated and shows itself as a macule, papule or plaque. The pigmentation can vary between gray-blue to a bluish-black color. The lesions usually appear on the head, pelvic region and the upper surfaces of both the hands and the feet as a single lesion.

At first the cellular blue nevus was thought to be a variant of melanoma, but it was later classified as a variant of the blue nevus. However, there is still controversy over whether or not the uncharacteristic cellular blue nevus is melanoma. Although the cellular blue nevus is an uncommon lesion, it has characteristics in a clinical sense that are similar to the common blue nevus. The lesions are large, measuring one to three cm in diameter.

Pathophysiology

It is believed that blue nevi represent "dermal arrest in embryonal migration of neural crest melanocytes that fail to reach the epidermis". Although this belief isn't supported by any definitive experimental evidence. Accumulations of melanocytes are found in the fetal dermis but they coil or roll in the later stages of a woman's pregnancy.

It has been suggested that there may be a genetic predisposition since there are varied incidences of blue nevi found throughout the different populations, but among the documented cases, hereditary ones are rare.

The causes of the blue color come from the amount of melanin that is present in the epidermis combined with the Tyndal effect. The melanin absorbing favored long wavelengths of light along with the shorter wavelengths being scattered is what comprises the Tyndal effect. In turn, this represents the blue end of the spectrum in collagen bundles. Chromosomal changes are not commonly associated with blue nevi including B-RAF mutations than congenital and acquired nevi.

Blue nevi are found most frequently in the United States in those that are of Asian descent where the frequency is about three to five percent in adults based on calculated estimates. It is found approximately one to two percent of the white adult population and is hardly ever seen in blacks. Blue nevi rarely appear during birth, in infants and during the toddler stages of life where less than one case per one thousand is seen in the population. The frequency of blue nevi on an international level varies according to the population examined.

Mortality/Morbidity/Statistics

Blue nevi remain benign in most cases no matter how long individuals have symptoms. There have been infrequent cases that are identified as malignant melanoma but they are usually linked to cellular blue nevi rather than the common blue nevi. Women are more likely to be diagnosed with blue nevi than men. While it may develop at any age, most cases are identified in individuals in their twenties or later.

History

Through life the blue nevus tend to stay the same, although sometimes they may flatten and the color may fade. Through the lesion these changes will evenly distribute. Malignant cellular blue nevi may become enlarged and occasionally ulcerate. After a skin trauma including but not limited to sunburn and other similar trauma, blue nevi have been identified.

Physical

Blue nevi are best described as slowly developing from a macule to a papule as a smooth-surfaced, dome-shaped lesion. The common blue nevi tend to measure less than one cm, but are usually larger than one cm. Most commonly they are found on the skin, but in rare cases blue nevi have been found in the vagina, the spermatic cord, the uterine cervix, the lymph node, the prostate, the oral mucosa and the bronchus.

Histologic Findings

Between the common blue nevi and the cellular blue nevi there is a histologic continuum. There is a "vaguely nodular collection of poorly melanized spindled melacytes and deeply pigmented dentritic melanocytes within thickened collagen bundle" in common blue nevus. Scattered melanophages are noted in most cases, but no mitoses are present.

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