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Benign Melanocytic Neoplasms and Melanoma


Acquired Melanocytic Nevi (Moles)

Description

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    Acquired melanocytic nevi are common benign skin tumors composed of melanocyte-derived nevus cells.

History

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    Acquired melanocytic nevi are more common in whites than Asians and Africans.

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    Numbers of acquired melanocytic nevi peak in early adolescence, slowly increase in number until age 30 years, and then regress in elderly people.

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    Genetic factors, as well as environmental influences, such as increased ultraviolet radiation (e.g., natural sunlight and tanning), determine the number of acquired melanocytic nevi.

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    Other factors, such as skin injury, immunosuppression, hormones, and medications, have been associated with increased numbers of acquired melanocytic nevi.

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    Skin disorders, such as lichen sclerosis and epidermolysis bullosa, may be associated with acquired melanocytic nevi.

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    Most acquired melanocytic nevi occur on sun-exposed areas, although Asians and Africans are more likely to develop nevi on acral sites (e.g., palms, soles, and nails) and the conjunctiva.

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    Most white adults have between 12 and 20 acquired melanocytic nevi.

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    Acquired melanocytic nevi are asymptomatic, although they may be irritated by clothing or external trauma.

Skin Findings

Junctional Nevi

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    Junctional nevi are brown to tan macules with preserved skin epidermal markings.

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    Acquired melanocytic nevi on the palms, soles, and genitalia are usually junctional nevi.

Fig. 18.1, Acquired melanocytic nevi distribution diagram.

Compound Nevi

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    Compound nevi are firm brown papules that may have a smooth or papillomatous surface.

Fig. 18.2, Developmental stages in the life history of common moles.

Fig. 18.3, Junctional nevi: flat, uniform hyperpigmented macules.

Fig. 18.4, Compound nevi: hyperpigmented papules.

Fig. 18.5, Intradermal nevi: skin-colored papules.

Intradermal Nevi

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    Intradermal nevi are skin-colored to tan papules with a smooth surface.

Nevus Spilus

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    Nevus spilus is a speckled tan to brown patch with sharply demarcated borders, similar to a café-au-lait macule.

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    There may be brown papules within the nevus spilus.

Fig. 18.6, Nevus spilus: light brown patch with dark brown macules. Nevus spilus rarely develops melanoma but is difficult to detect change because of the dark speckles.

Fig. 18.7, Nevus spilus with background café-au-lait macule containing small benign nevi. These lesions are benign and do not change appearance.

Fig. 18.8, Blue nevi. Dark blue due to pigment deeper in the dermis.

Fig. 18.9, Spitz nevus. They are considered benign, but if they are irregular in color or if they grow, they should be removed.

Blue Nevi

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    Blue nevi are solitary blue to black macules and papules, commonly found on the head and neck.

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    The dark color is attributed to heavily pigmented melanocytes in the deep dermis.

Spitz Nevus (Spindle and Epithelial Cell Nevus)

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    Spitz nevus is a pink to red-brown dome-shaped smooth papule.

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    Histologically, Spitz nevi may be difficult to differentiate from melanoma.

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    Spitz nevi are more common in children.

Halo Nevi

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    Acquired melanocytic nevi with a rim of depigmentation are called halo nevi .

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    An immune response to the melanocytes is responsible for the halo.

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    Vitiligo is associated with halo nevi.

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    Halo nevi occur primarily during adolescence.

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    Wood's lamp examination is helpful to evaluate for associated vitiligo.

Fig. 18.10, Halo nevi are associated with vitiligo. If the nevus is atypical, it should be biopsied.

Fig. 18.11, Recurrent nevi may look clinically and histologically like melanoma.

Recurrent Nevi

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    A recurrent nevus is an irregularly pigmented macule or papule associated with a scar from a previous procedure.

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    Recurrent melanocytic nevi appear similar to melanoma.

Laboratory

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    A skin biopsy should be performed on suspicious pigmented lesions.

Course and Prognosis

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    Acquired melanocytic nevi arise during childhood until about age 30 years and then slowly regress over a number of years.

Differential Diagnosis

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    Atypical (dysplastic) nevus

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    Melanoma

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    Hemangioma

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    Pyogenic granuloma

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    Juvenile xanthogranuloma

Treatment

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    Acquired melanocytic nevi do not require treatment.

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    Sun precautions (sunscreen and sun-protective clothing) prevent the occurrence of acquired melanocytic nevi.

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    Pigmented nevi that are irritated may be removed, although irritation does not induce malignant transformation.

Pearls

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    Acquired melanocytic nevi on skin areas with limited sun exposure and newly acquired nevi after age 30 years should be regarded as suspicious.

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    Spitz nevi in adults should be closely evaluated for melanoma because both are similar histologically.

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    Adults with halo nevi should have a full skin examination to look for an occult melanoma.

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    A new “junctional melanocytic nevus” in an adult is suspicious for early melanoma.

Fig. 18.12, A dermal nevus with horn pearls on the surface. It is stuck onto the surface and has the consistency of a seborrheic keratosis.

Fig. 18.13, A dome-shaped smooth-surfaced papule. This common presentation for a dermal nevus occurs on the face and trunk. Patients are often more concerned with elevated lesions than with flat, dark lesions.

Fig. 18.14, Speckled lentiginous nevi are common benign hairless brown lesions, dotted with darker brown to black specks.

Fig. 18.15, A common presentation for a dermal nevus on the face. The dome-shaped papule has telangiectasias on the surface and resembles a basal cell carcinoma. The lesion has remained stable for years.

Fig. 18.16, This is a common presentation for scalp nevi. There is no pigment, and the surface is lobulated.

Fig. 18.17, A dermal nevus with no pigment. Patients commonly think that all moles are pigmented. This smooth white papule had remained unchanged for years.

Fig. 18.18, This dermal nevus has the consistency of a wrinkled sack. Biopsy showed an abundance of connective tissue and very few nevus cells.

Atypical Melanocytic Nevus (Dysplastic Nevus)

Description

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    An atypical melanocytic nevus is a benign melanocytic nevus with abnormal clinical and histologic features.

History

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    Approximately 10% of the U.S. population has atypical melanocytic nevi.

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    Patients with multiple atypical nevi are at increased risk for melanoma, especially if there is a family history of atypical nevi and melanoma (also known as the familial atypical mole and melanoma syndrome).

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    Atypical melanocytic nevi may arise at any age and continue up until the sixth decade of life.

Fig. 18.19, Atypical mole syndrome distribution diagram.

Fig. 18.20, Melanocytic nevi: junction nevus. The lesion is slightly raised, dark, and uniform.

Fig. 18.21, Melanocytic nevi: compound nevus. The surface is covered with uniform brown-black dots.

Fig. 18.22, Melanocytic nevi: dermal nevus. The nevus is skin-colored colored with surface vessels and resembles basal cell carcinoma.

Fig. 18.23, Melanocytic nevi: dermal nevus. The nevus is dome shaped.

Fig. 18.24, Melanocytic nevi: dermal nevus. The nevus is skin-colored and dome shaped.

Fig. 18.25, Melanocytic nevi: dermal nevus. The nevus has a warty (verrucous) surface.

Fig. 18.26, Melanocytic nevi: dermal nevus. The nevus is polypoid.

Skin Findings

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    Atypical melanocytic nevi show asymmetry, border irregularity, color variation, and larger size (between 6 and 15 mm in diameter).

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    Atypical melanocytic nevi can appear anywhere in the skin but occur most commonly on the trunk and upper extremities.

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    Patients with familial atypical mole and melanoma syndrome have atypical melanocytic nevi in sun-protected areas, such as the scalp, groin, buttocks, genitalia, breasts (in women), and the palms and soles.

Fig. 18.27, Melanocytic nevi: dermal nevus. The nevus is pedunculated with a soft, flabby, wrinkled surface.

Nonskin Findings

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    Many atypical melanocytic nevi may indicate an increased risk for ocular melanoma.

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    Eruptive atypical melanocytic nevi have been described in patients with immunosuppression, chronic myelocytic leukemia, and HIV.

Laboratory

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    Histologic evaluation of an atypical melanocytic nevus is difficult and should be performed by a dermatopathologist.

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    Patients with eruptive atypical melanocytic nevi should be evaluated for HIV and leukemia.

Fig. 18.28, Atypical nevi. A, Macular brown pigmentation with uniform dots. B, Brown pigmentation with a complex pattern. C, Clinical differentiation from melanoma is difficult. D, Uniform, brown homogeneous pigmentation. E, “Fried-egg lesion.” The papular component is dark and uniformly pigmented. F, “Fried-egg lesion.” The macular and papular components are uniformly pigmented.

Fig. 18.29, Atypical nevi have variations in pigmentation with both papular and macular components. Differentiating them from melanoma can be difficult.

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