42 Melanocytic Nevi
Summary
Melanocytic nevi are common in children. The primary indication for removal is to improve a deformity. Giant nevi are associated with a low risk of malignant degeneration. Generally, serial excision is preferred to skin grafting or tissue expansion when feasible.
42.1 Introduction
Melanocytic nevi are one of the most common pediatric cutaneous conditions; lesions can be present at birth or acquired. Congenital nevi affect 1% of the population and form when nevomelanocytes become ectopically located during migration from the neural crest to the epidermis. Congenital melanocytic nevi can cause a deformity and psychosocial morbidity. Patients and families frequently are anxious about malignant degeneration, but the risk of transformation to melanoma often has been overestimated. This chapter will focus on evidence-based management of congenital melanocytic nevi.
42.2 Diagnosis
Melanocytic nevi are diagnosed by history and physical examination. Age of onset (congenital or acquired), asymmetry, border irregularity, color, size, and symptoms should be elicited. In contrast to acquired nevi, histopathology of congenital lesions exhibits nevomelanocytes in the lower two-thirds of the dermis and subcutis involving sebaceous glands, hair follicles, vessels, and nerves. Congenital melanocytic nevi can be classified based on their diameter or percent total body surface area (TBSA). Although a consensus definition does not exist, lesions usually are categorized as small (<1.5 cm), medium (1.5–10 cm), large (11–20 cm), and giant (>20 cm or >2% TBSA). We favor the definition of giant nevi greater than 2% TBSA because it is easy to assess clinically by determining if the lesion is twice the area of the infant’s hand (1% TBSA). Giant congenital melanocytic nevi are rare (1/20,000 births) but problematic.
Imaging is unnecessary to diagnose congenital melanocytic nevi. However, patients with giant lesions are at risk for melanocytes involving the leptomeninges. Neurocutaneous melanosis can cause developmental delay, hydrocephalus, and seizures. Children with lesions located in the midline head or trunk and those with multiple satellite nevi are at greatest risk for neurocutaneous melanosis. Magnetic resonance imaging of the central nervous system is performed during infancy to rule out neurocutaneous melanosis in patients with giant pigmented nevi.
Biopsy of a congenital melanocytic nevus is indicated to exclude melanoma if there is a change in appearance, ulceration, bleeding, or enlargement. Additional criteria include the “ABCDs”: Asymmetric shape, Borders are irregular, multiple Colors are present, and the Diameter is greater than 6 mm. Malignant degeneration is very rare (0.03% lifetime risk) for small nevi. The rate of melanoma for giant lesions historically has been overestimated (up to 12%). However, recent studies suggest that malignant degeneration is approximately 3%. The incidence of melanoma is greatest within the first 3 years of life, followed by another peak during adolescence. Nevi at highest risk for malignancy are those located on the trunk and lesions covering an extensive area. Melanoma has an approximately equal chance of occurring in the main nevus, a satellite lesion, or in the central nervous system.
42.3 Nonoperative Management
Congenital melanocytic nevi can be observed and do not mandate intervention. Nonexcisional treatments (e.g., curettage, dermabrasion, hydroquinone, laser) may be used to improve the appearance of the nevi. These nonextirpative methods are reserved for lesions in aesthetically sensitive areas where resection would cause greater disfigurement than the nevus. However, the cancer risk is not eliminated and fibrosis may complicate later histopathology.
42.4 Operative Management
Indications for removing congenital melanocytic nevi are (1) concern for malignancy, (2) lesions causing psychosocial morbidity, or (3) to reduce the risk of malignant transformation for giant congenital nevi.
42.4.1 Timing of Resection
Concern for melanoma requires immediate excision of the suspicious area. Removal of a lesion that is likely to cause psychosocial morbidity can be delayed until 3 to 4 years of age when self-esteem and long-term memory develop. Extirpation of nevi on the scalp during infancy is advantageous because the tissue is particularly lax during this period. Lower extremity lesions should be removed in infancy while the patient is nonambulatory to reduce the risk of suture line dehiscence.
Because the peak incidence of malignant conversion for giant lesions is greatest within the first 3 years of life, prophylactic resection to decrease the occurrence of melanoma is most effective if completed before this time. We begin excision at 6 months of age when we are trying to completely remove a giant nevus to reduce the likelihood of malignant conversion. We avoid elective procedures prior to 6 months of age because the risk of anesthesia is higher.
42.4.2 Small and Medium Congenital Melanocytic Nevi
Small and medium-sized lesions are resected to aesthetically improve a deformity or if the clinical appearance becomes worrisome for malignancy. These nevi usually can be removed lenticularly and closed linearly in one stage. Circular excision and purse-string closure may be performed for small, round nevi on the face to minimize the length of the scar; lenticular excision of a round lesion results in a scar two to three times its diameter (Fig. 42‑1). Approximately 50% of patients are satisfied with the circular cicatrix, which can appear as an acne or chicken pox scar. One-half of patients undergo a second stage to convert the circular scar into a line that is approximately the same length as the diameter of the original lesion. Lesions located in difficult locations can result in more challenging reconstructive problems (e.g., nose, eyebrow; Fig. 42‑2, Fig. 42‑3, Fig. 42‑4, Fig. 42‑5). Raised dermal nevi that are located in unfavorable locations (particularly the nose) can be improved by shave excision to the papillary dermis (Fig. 42‑6). The patient’s appearance and contour will be improved without a scar, but the individual likely will require repeat shave excision in the future if the nevus re-enlarges.
Small/medium melanocytic nevi on the face being removed for “cosmetic” reasons should have minimal gross margins (0–1 mm) to ensure the most favorable scar. If no atypical cells are present, then positive margins require no further treatment, although there is a low risk (~1%) of minor re-pigmentation along the scar, which can be resected secondarily. If histopathology shows cellular atypia then re-excision to negative margins is required. Small/medium nevi located in nonaesthetically important areas or those at risk for atypia can be extirpated with 1- to 2-mm margins.
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