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INTRODUCTION

Many cutaneous biopsies are performed to evaluate a lesion’s malignant potential. Fortunately, most of these tumors are benign. The distinction is important, however, since significant surgical procedures may be needed for some tumors but are inappropriate for others. Further, some of these lesions may indicate underlying conditions that require additional evaluation and treatment. For these, as well as other reasons, it is imperative that dermatopathologists seek to accurately classify those epidermal tumors that they are called on to evaluate.

EPIDERMAL NEVI AND RELATED PROCESSES

Epidermal naevus

Epidermal nevi are proliferations of the epithelium that may be associated with different syndromes. Most tumors are isolated lesions that are present at birth or arise within the first few years of life. Others are associated with what is termed the “epidermal nevus syndrome.” These patients demonstrate defects of the central nervous system (epilepsy, mental retardation), skeletal system (bone anomalies, cysts and deformities), eyes (colobomas, cataracts, choristomas), and oral cavity (absent or malformed teeth).1 A neurocutaneous syndrome consisting of epilepsy and psychomotor retardation with papular epidermal nevi (PENS syndrome) has recently been described. Reportedly, the basal-layer cells exhibit palisaded nuclei imparting a “skyline” type appearance.2 The most impressive variant is termed “nevus unius lateris”; in this subtype, the epidermal nevi are arranged in a whorled fashion on the trunk and/or extremities in the pattern of Blaschko lines. Greater and more systematized involvement is termed “ichthyosis hystrix.” The term “epidermal nevus syndrome” has been applied solely to 5 conditions: Schimmelpenning syndrome, nevus comedonicus syndrome, pigmented hair epidermal nevus syndrome (Becker nevus syndrome), Proteus syndrome, and CHILD syndrome.3 A sixth syndrome, phacomatosis pigmentokeratotica has been described as well.4 Chromosomal breakpoints, indicating genetic mosaicism, have been found on some cell lines in affected patients.5 Patients with the epidermal nevus syndrome and hypophosphatemic rickets and papillary transitional cell bladder carcinoma have been reported.6,7

Clinical Features

Epidermal nevi present as papules, nodules, and patches of verrucous epidermal hyperkeratosis. They may be isolated, linear, zosteriform, or whorled.8 Most lesions are different shades of brown but may also be gray, black, or flesh colored. Comedo-like plugs and filiform hyperkeratosis have also been described.9 Inflammation or irritation are usually confined to traumatized epidermal nevi. Most lesions are asymptomatic, but mild pruritus may occur. A form of epidermal nevus with clinical and pathologic features of acanthosis nigricans has been reported (Table 26-1).10

Table 26-1Epidermal Nevus

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