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Acquired melanocytic nevocellular nevi are small (<1.0 cm),
benign, well-circumscribed, pigmented lesions comprised groups of
melanocytes or melanocytic nevus cells.
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They can be classified into three groups:
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- 1. Junctional nevi (cells grouped at the dermal–epidermal
junction, above basement membrane).
- 2. Dermal nevi (cells grouped in the dermis).
- 3. Compound nevi (combination of histologic features of junctional
and dermal).
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But there is clinical overlap among all three types.
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Only some 30% of melanomas arise from preexisting nevi;
thus prophylactically removing all the nevi on a person is neither
warranted nor protective.
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Synonym Pigmented nevi, nevocellular
nevus.
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Age Nevi appear after 6 to 12 months
of age, peak during the third decade, and then slowly disappear.
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Incidence Common, by age 25, most
Caucasians will have 20 to 40 moles.
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Race Caucasians have more total
body nevi than darker skin types. But Asians and blacks have more nevi
on atypical locations (palms, soles, nail beds, and conjunctivae)
than whites.
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Genetics Increased number of nevi
tend to cluster in families. Increased clinically atypical nevi
may be more prevalent in families with melanoma.
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Duration of Lesions Commonly called
moles, lesions appear after age 6 to 12 months and reach a maximum
number between ages 20 and 29. By age 60, most moles fade and/or
disappear.
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Skin Symptoms Nevocellular nevi
are asymptomatic. If a mole is symptomatic, it should be evaluated
and/or removed.
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Differential
Diagnosis
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Melanocytic nevi need to be differentiated from seborrheic keratoses,
dermatofibromas, neurofibromas, fibroepithelial polyps, basal cell
carcinomas, and melanomas.
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Indications for removal of acquired melanocytic nevi are:
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1. Asymmetry in shape. One-half
is different from the other.
2. Border. Irregular borders are
present.
3. Color. Color is or becomes variegated.
Shades of gray, black, white are worrisome.
4. Diameter. Greater than 6 mm (may
be congenital mole, but should be evaluated).
5. Symptoms. Lesion begins to persistently
itch, hurt, or bleed.
6. Site. If lesion is repeatedly
traumatized in any given location (e.g., waistline, neck) or if
lesion is in a high-risk/difficult-to-monitor site such
as the mucous membranes or anogenital area, it may warrant removal.
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These criteria are based on anatomic sites at risk for change
of acquired nevi to malignant melanoma or on changes in individual
lesions (color, border) that indicate the development of a focus of
cells with dysplasia, the precursor of malignant melanoma. Dysplastic
nevi are usually >6 mm, and darker,
with a variegation of color (tan, brown), and irregular borders.
Approximately one-third of melanomas are associated with precursor
nevi, and an increased ...