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Congenital Nevi and Malignant Melanoma - Submitted on: Friday May, 05, 2000
Contributed by:Zeina Tannous, MD, N/A
Congenital nevi are benign nevomelanocytic proliferations present at birth.

Small congenital nevi are defined as those less than 1.5 cm in their largest diameter, medium-sized congenital nevi as those 1.5 to 19.9 cm, and large or giant congenital nevi as those greater or equal to 20 cm.
1% of the newborns have a biopsy-proven nevomelanocytic nevus. However, giant congenital nevi are rare with an incidence of approximately 1 in 20,000 births.

Clinically, congenital nevi are round to oval in shape with regular, smooth, and well-demarcated border. Their clinical appearances may change with age. As the child grows, the nevi become progressively darker with uniform brown to dark brown or black color and they acquire long, coarse, darkly pigmented hairs.

Occasionally, they may show considerable variation in pigment color within the background color, irregular border, and sometimes nodule formation.

Such changes should be always evaluated for any malignant transformation.

The lifetime risk of melanoma for patients with giant congenital nevi ranges from 5% to 10%. The risk is greatest between the ages of 5 and 10 years.

The issue of malignant transformation of small congenital nevi is very controversial. Currently, there exists no consensus regarding their increased risk of developing melanoma or their management. However, many authors believe that small congenital nevi may be precursors for at least some cases of cutaneous melanoma.

Congenital nevi are benign nevomelanocytic proliferations present at birth.

Clinical Features:

(Click on an image for a larger view)
Figure 1. Superficial spreading melanoma (right) in association with a congenital nevus (left).
Figure 2. Lymphatic invasion by highly atypical melanoma cells.
Figure 3. The associated nevus has features of congenital onset with characteristic extension of nevus cells into the deep reticular dermis and subcutaneous fat.
Figure 4. The distinctive wrapping of the congenital nevus cells around the sebaceous lobules.
The majority of melanomas arising in association with large or giant congenital nevi originate in the dermis. They are usually composed of epithelioid cells, spindle cells, or small round cells.
On the other hand, melanomas arising in small congenital nevi usually originate in the epidermis. These melanomas often resemble the conventional superficial spreading or nodular melanomas.

Figures 1-4 show an example of superficial spreading melanoma arising in a small congenital nevus.

More than one half of melanomas associated with giant congenital nevi develop during the first decade of life leading some authors to recommend prophylactic excision of giant congenital as early as possible.
However, surgical removal cannot eliminate the risk completely due to the deep infiltration of nevus cells to the underlying muscle or the lining of the central nervous system in some cases.

Prepubertal risk of malignant melanoma in association with small congenital nevi is very low. A reasonable approach is to excise small congenital nevi after the age of 10 years. Another option is lifelong observation.

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