Chapter 96

### Key Points

1. Ninety-eight percent of Caucasian children have at least 1 nevus by early childhood. In contrast, melanoma accounts for only 2% of all pediatric malignancies.

2. Physical features that may raise suspicion for malignant transformation include asymmetry, irregularity of the borders, variability in the color, and diameter greater than 5 mm (ABCD criteria).

3. A Spitz nevus in its typical form is a benign melanocytic lesion that is a diagnostic and management challenge for both pathologists and clinicians secondary to the histologic features it can potentially share with melanoma.

4. The nevus sebaceous of Jadassohn is a benign epidermal nevus most commonly encountered on the scalp and face with a reported incidence of basal cell carcinoma of 0.8%.

5. Giant congenital nevi carry a lifetime malignancy risk ranging from 2.8 to 8.5% and 60% of these malignancies occurred within the first decade of life.

6. Melanomas less than 1-mm thick should be excised with a 1-cm margin while for those greater than 1 mm in thickness, a 2-cm margin is acceptable.

7. Surgical treatment options for large pigmented lesions include serial excision, skin grafting, and tissue expansion.

### Introduction

The frequency of pigmented lesions in childhood as well as the rising incidence of melanoma in adults has raised awareness of screening for cutaneous malignancy. These concerns, however, are not completely justified in the pediatric population. Melanocytic nevi are highly prevalent amongst Caucasian children, with over 98% possessing at least 1 nevus by early childhood. In contrast, melanoma accounts for only 2% of all pediatric malignancies. Further, cutaneous melanoma prior to puberty is extremely rare with only a 0.3% to 0.4% incidence in the United States. Due to these factors and the cumulative risk of malignant transformation in adulthood, a working knowledge of the clinical spectrum of the most common pediatric pigmented lesions, their natural history, risk of malignant transformation, and treatment options is important to possess.

### Pathophysiology

A nevus is a benign skin lesion defined by its sharply circumscribed borders. The differential diagnosis of these pigmented lesions is based on the lesion's gross morphologic characteristics, the patient history, and microscopic examination. In general, a nevus' characteristics are derived from its cell line of origin and include melanocytic nevi (derived from melanocytes), epidermal nevi (derived from keratinocytes), connective tissue nevi (derived from fibroblasts and other connective tissue cellular elements), and vascular nevi (derived from vascular elements). With the exception of the nevus sebaceous of Jadassohn, an epidermal nevus, the focus of this chapter will be directed towards melanocytic nevi. Melanocytic nevi are composed of melanocytes whose embryologic origins are from the neural crest. The tan to black coloring of melanocytic nevi is the product of enzymatic reactions within the endoplasmic reticulum that convert tyrosine to melanin. This pigment is then packaged into melanosomes and in normal melanocytes, released from their dendritic processes to evenly color the skin.

Melanocytic nevi ...

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