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Patient Story
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A small congenital nevus (Figure 144-1) was noted on this 6-month-old child by his new family physician during a routine exam. The parents acknowledged that it was present from birth and asked if it needed to be removed. They were reassured that nothing needs to be done about it and unless there were suspicious changes in the future it could remain there for the remainder of their child’s life.

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FIGURE 144-1

Small congenital nevus found on the foot of a 6-month-old child. The parents were counseled to not get it excised at this time. (Used with permission from Richard P. Usatine, MD.)

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Introduction
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Congenital melanocytic nevi (CMN) are benign pigmented lesions that have a wide variation in size and presentation and are composed of melanocytes, the pigment-forming cells in the skin.

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Synonyms
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  • Garment nevus, bathing trunk nevus (Figure 144-2), giant hairy nevus, giant pigmented nevus, pigmented hairy nevus, nevus pigmentosus, nevus pigmentosus et pilosus (pigmented nevus with hair).1

  • Tardive congenital nevus refers to a nevus with similar features to congenital nevi, but appears at age 1 to 3 years.

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FIGURE 144-2

Large bathing trunk nevus with multiple satellite nevi on this happy 2-year old boy. The mother has opted for no surgical intervention. (Used with permission from Richard P. Usatine, MD.)

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Epidemiology
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  • CMN develop in 1 to 6 percent of newborns and are present at birth or occasionally develop during the first year of life.1 In a recent case series in California (N = 594), 2.4 percent of the infants had CMN.2

  • In an Italian prevalence study of over 3000 children aged 12–17 years, congenital melanocytic nevi or congenital nevus-like nevi were found in 17.5 percent; most (92%) were small (<1.5 cm).3

  • Congenital nevi are also seen in neurocutaneous melanosis, a rare syndrome characterized by the presence of congenital melanocytic nevi and melanotic neoplasms of the central nervous system.

  • The development of melanoma within CMN (Figure 144-8) is believed to occur at a higher rate than in normal skin. Estimates range from 4 to 10 percent with smaller lesions having lowest risk.1

    • In a systematic review, 46 of 651 patients with CMN (0.7%) followed for 3.4 to 23.7 years developed melanomas, representing a 465-fold increased relative risk of developing melanoma during childhood and adolescence.4 The mean age at diagnosis of melanoma was 15.5 years (median 7 years).

    • Patients with giant CMN (larger than 20 cm; Figures 144-2 to 144-5) appear to be at highest risk where subsequent melanoma has been reported in 5 to 7 percent by age 60 years.5 In one study, ...

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