Section 9: Benign Neoplasms and Hyperplasias

DISORDERS OF MELANOCYTES

ACQUIRED MELANOCYTIC NEVI ICD-10: D22.L10

• Melanocytic nevi commonly called moles, are very common, acquired pigmented macules, papules, or nodules.

• Composed of groups of melanocytic nevus cells located in the epidermis and dermis.

• They are benign tumors arising as nevus cell clusters at the dermal–epidermal junction (junctional melanocytic nevi), in combination with the papillary dermis (compound melanocytic nevi), or exclusively in the dermis (dermal melanocytic nevi).

EPIDEMIOLOGY AND ETIOLOGY

One of the most common acquired new growths in Caucasians (most adults have about 20 nevi), though patients with the lightest skin and red hair tend to have fewer nevi. Also less common in persons with more pigmented skin.

RACE Blacks and Asians have more nevi on the palms, soles, and nail beds.

HEREDITY Common acquired melanocytic nevi can occur in family clusters.

SUN EXPOSURE A likely factor in the induction of nevi on the exposed areas, especially when intermittent and intense.

SIGNIFICANCE Risk of melanoma is related to the number of acquired melanocytic nevi.

CLINICAL MANIFESTATION

DURATION AND EVOLUTION OF LESIONS Melanocytic nevi appear in early childhood and reach a maximum in young adulthood even though some lesions arise in adulthood. Later on, there is a gradual involution and fibrosis of lesions, but most disappear after the age of 60. In contrast, dysplastic nevi continue to appear throughout life and are believed not to involute (see Section 12).

SKIN SYMPTOMS Melanocytic nevi are asymptomatic. However, these nevi grow, and growth can be accompanied by itching. Itching per se is not a sign of malignancy, but if a lesion persistently itches or is tender, it should be followed carefully or biopsied, since persistent pruritus may be an early indication of malignant change.

CLASSIFICATION

Melanocytic are multiple (Fig. 9-1A) and can be classified according to the histologic level of the nevus cell clusters (Fig. 9-1B).

1. Junctional melanocytic nevi: These arise at the dermal–epidermal junction, on the epidermal side of the basement membrane (Figs. 9-1B and 9-2).

2. Compound melanocytic nevi: Nevus cells invade the papillary dermis, and nevus cell nests are now found both intraepidermally and dermally (Figs. 9-1B and 9-3).

3. Dermal melanocytic nevi: These represent the last stage of the evolution of melanocytic nevi. “Dropping off” into the dermis is now completed, and the nevus grows or remains intradermal (Figs. 9-1B and 9-4). With progressive age, there will be gradual fibrosis (Fig. 9-4C).