ACQUIRED MELANOCYTIC NEVI
Acquired melanocytic nevocellular nevi are small (<1 cm), benign, well-circumscribed, pigmented lesions comprised of groups of melanocytes or melanocytic nevus cells.
They can be classified into three groups:
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Junctional nevi (cells grouped at the dermal–epidermal junction, above the basement membrane).
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Dermal nevi (cells grouped in the dermis).
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Compound nevi (combination of histologic features of junctional and dermal).
Clinical overlap exists among all three types.
INSIGHT
Only some 30% of melanomas arise from pre-existing nevi; thus prophylactically removing all the nevi on a person is neither warranted nor protective.
SYNONYMS Pigmented nevi, nevocellular nevus, moles.
AGE Nevi appear after 6 to 12 months of age, peak during the third decade, and then slowly disappear.
INCIDENCE Common. By age 25, most Caucasians will have 20 to 40 moles.
GENDER M = F.
RACE Caucasians have more total body nevi than darker skin types. Asians and blacks have more nevi on atypical locations (palms, soles, nail beds, and conjunctivae) than whites.
GENETICS Increased number of nevi tend to cluster in families. Increased clinically atypical nevi may be more prevalent in families with melanoma.
DURATION OF LESIONS Commonly called moles, lesions appear after the age of 6 to 12 months and reach a maximum number between ages 20 and 29. By age 60, many moles fade and/or disappear.
SKIN SYMPTOMS Nevocellular nevi are asymptomatic. If a mole is symptomatic, it should be evaluated and/or removed.
Melanocytic nevi need to be differentiated from seborrheic keratoses, dermatofibromas, neurofibromas, fibroepithelial polyps, basal cell carcinomas, and melanomas.
Indications for removal of acquired melanocytic nevi are the following:
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Asymmetry in shape. One-half is different from the other.
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Border. Irregular borders are present.
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Color. Color is or becomes variegated. Shades of gray, black, white are worrisome.
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Diameter. Greater than 6 mm (may be congenital mole, but should be evaluated).
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Evolution: If the lesion is growing rapidly, distinct from other nevi or a child’s overall growth pattern.
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Symptoms. Lesion begins to persistently itch, hurt, or bleed.
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Site. If the lesion is repeatedly traumatized in any given location (e.g., waistline, neck) or if the lesion is in a high-risk/difficult-to-monitor site such as the mucous membranes or anogenital area, it may warrant removal.
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 number of nevi increases the melanoma risk.
Melanocytic nevi, if treated, should always be excised for histologic diagnosis and for definitive treatment. Destruction by electrocautery, laser, or other means is not recommended.
TYPE Macule.
SIZE Less than 1 cm.
COLOR Uniform tan, brown, or dark brown.
SHAPE Round or oval with smooth regular borders (Fig. 7-1).
ARRANGEMENT Scattered discrete lesions.
DISTRIBUTION Random.
SITES OF PREDILECTION Trunk, upper extremities, face, lower extremities; may be located on palms, soles, and genitalia.
HISTOLOGY In junctional nevi, the cells and/or nest of nevus cells are located in the lower epidermis.
DERMOSCOPY Uniform pigment network thinning out toward the periphery of the lesion.
SYNONYM Intradermal nevus.
TYPE Elevated papule, nodule, polypoid, or papillomatous lesion.
COLOR Skin-colored, tan, or brown.
SHAPE Round, dome-shaped (Fig. 7-2).
DISTRIBUTION More common on the face and neck, but can occur on the trunk or extremities.
OTHER FEATURES Coarse hairs may be present within the lesion. Dermal nevi usually appear in late adolescence, 20s, and 30s.
Dermal nevi may be mistaken for other nevi such as junctional nevi, and on the face, from basal cell carcinoma.
HISTOLOGY Dermal nevi have nevus cells and/or nests in the dermis.
DERMOSCOPY Focal globules and white structure-less areas.
TYPE Macule or slightly elevated papule, or nodule (Fig. 7-3).
COLOR Tan, brown, or dark brown.
SHAPE Round.
DISTRIBUTION Any site.
OTHER FEATURES In late childhood, compound nevi can increase in darkness and become more elevated.
HISTOLOGY In compound nevi, nevus cells and/or nests are seen in both the epidermis and dermis.
DERMOSCOPY Globular ovoid pattern sometimes in a cobblestone pattern, structureless brown or hypopigmented areas with reticulated periphery, or mixed pattern.
CONGENITAL NEVOMELANOCYTIC NEVUS
Congenital melanocytic nevi (CMN) are pigmented lesions of the skin usually present at birth. CMN may be of any size from very small to very large. CMN are benign neoplasms comprising cells called nevomelanocytes, which are derived from melanoblasts.
SYNONYMS Giant pigmented nevus, congenital nevomelanocytic nevus, garment nevus, bathing-trunk nevus, and giant hairy nevus.
AGE Present at birth (congenital). Rarely, a CMN becomes visible after birth (“tardive”), usually within the first 3 to 12 months of life.
GENDER M = F.
RACE All races.
INCIDENCE Small CMN: 0.5% to 2.5% of the population. Large/giant CMN: 0.005% of the population.
ETIOLOGY Likely multifactorial. Rare familial cases have been reported.
CMN are derived from neural crest-derived melanoblasts embryologically migrating to form the nevus after 10 weeks in utero but before the sixth month of gestation. It is unclear what causes these melanoblasts to migrate differently from other melanoblasts when forming nevi in the skin. CMN have shown an increase in mutations in the gene NRAS, suggesting a possible contributor to their etiology.
Congenital nevi are present at or soon after birth. They begin as pale brown to tan macules, which become darker and more elevated during adolescence. Most of them are benign and grow proportionately with the child and are asymptomatic for life. As the child grows older, the lesions develop coarse terminal hairs and may become more verrucous in appearance.
TYPE Well-circumscribed macules, slightly raised papules or plaques with or without coarse terminal hairs.
BORDERS Sharply demarcated, regular contours.
SURFACE May or may not have altered skin surface (“pebbly,” mammillated, rugose, cerebriform, bulbous, tuberous, or lobular).
COLOR Light or dark brown. May exhibit a “halo” phenomenon with a peripheral rim of depigmentation over time.
SIZE Small CMN: <1.5 cm; medium CMN: 1.5 to 20 cm (Fig. 7-4); large/giant CMN: >20 cm. CMN >9 cm on the scalp or >6 cm on the trunk in newborns qualify as large/giant CMN based on an expected adult size of >20 cm.
SHAPE Oval or round, symmetric. Large/giant plaques may have a geographic appearance.
DISTRIBUTION Isolated, discrete lesions on any site.
Without a good birth history, small CMN are often confused with common acquired nevomelanocytic nevi. A CMN can also be confused with a dysplastic nevus, Mongolian spot, nevus of Ota, congenital blue nevus, nevus spilus, Becker’s nevus, neurofibroma, smooth muscle hamartoma, pigmented epidermal nevus, or café au lait macule (CALM).
HISTOPATHOLOGY In congenital nevi, the nevomelanocytes occur as well-ordered clusters in the epidermis, and in the dermis as sheets, nests, or cords. Unlike the common acquired nevomelanocytic nevus, the nevomelanocytes in CMN tend to occur in the skin appendages (eccrine ducts, hair follicles, and sebaceous glands), in nerve fascicles and/or arrectores pilorum muscles, blood vessels (especially veins), and lymphatic vessels, and extend into the lower two-thirds of the reticular dermis and deeper.
DERMOSCOPY Reticular, globular, reticular-globular, diffuse brown or multicomponent pigment pattern.
By definition CMN appear at birth but varieties of CMN may arise during infancy (so-called tardive CMN). The lifetime risk for development of melanoma in small or medium CMN is low. Patients with large/giant CMN have been estimated to have a lifetime risk of 4.5% to 6.3% for developing melanoma within the CMN, though estimates vary widely both below and above this range.
Neurocutaneous melanosis is a rare condition associated with large/giant CMNs, or multiple >3 cm smaller CMNs. Histologically, melanosis may be seen at the base of the brain, ventral surfaces of the pons, medulla, upper cervical, or lumbosacral spinal cord. It may be asymptomatic, or cause seizures, focal neurologic deficits or obstructive hydrocephalus. The latter symptomatic form carries a worse prognosis.
Small (<1.5 cm) and medium (1.5–20 cm) benign-appearing congenital nevi can be safely monitored clinically. Their risk of malignant transformation is too low to warrant removal, thus patients should be instructed about signs of malignant transformation and regular skin examinations should suffice:
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Changes in shape. One-half is different from the other.
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Irregular or fuzzy borders. Irregular borders are present.
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Color variegation. Shades of gray, black, white are worrisome.
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Symptoms. Lesion begins to persistently itch, hurt, or bleed.
Large/giant CMN (>20 cm) are clinically difficult to manage since the risk of malignant transformation is present at birth, plus they are logistically more difficult to remove. It is important to follow these lesions clinically with measurements and/or photographs. Complete surgical removal of the lesion is difficult and often requires multiple-staged surgeries with tissue expansion, skin grafting, and/or artificial skin replacement.
An MRI to screen for neurocutaneous melanosis should be considered in neonates with large posterior axial lesions or multiple satellite nevi. Asymptomatic neurocutaneous melanosis can be monitored with repeat scans. Symptomatic neurocutaneous melanosis carries such a poor prognosis that surgical removal of the large CMN is typically not pursued.
Dermabrasion, laser removal, cryosurgery, electrocautery, or curettage of congenital nevi of any size is currently not recommended.
ATYPICAL “DYSPLASTIC” MELANOCYTIC NEVUS
Atypical “dysplastic nevi” are acquired nevi with a clinically atypical appearance: asymmetry, irregular borders, and/or color variation. Histologically, they may exhibit architecturally or cytologically atypical cells, the significance of which is controversial.
SYNONYMS Clark’s nevus, B-K mole.
AGE May appear at any age.
GENDER M = F.
RACE White = black.
INCIDENCE Estimated 5% of the population.
ETIOLOGY Familial tendency.
GENETICS Autosomal dominant.
Genetic loci (especially CDKN2A located at 9p21) have been implicated in familial cases of dysplastic nevi/melanoma. Immunosuppression is also associated with an increased risk of dysplastic nevi.
Dysplastic nevi typically appear later in childhood (puberty) than benign nevi. They most frequently involve the trunk and show a predilection for covered areas of the body (scalp, breasts in females, and bathing trunk in males), and are more numerous in sun-exposed areas.
SKIN SYMPTOMS Typically asymptomatic. Itching or bleeding may be indicators of malignant change.
TYPE Macules, papules, or poorly circumscribed nodules.
SIZE 6 to 15 mm.
COLOR Asymmetrically brown, tan, pink, or variegated (Fig. 7-5).
SHAPE Round to oval with irregular or angulated borders.
DISTRIBUTION Back > chest > extremities. Predilection for covered areas (scalp, breasts in females, and bathing trunk in males).
Dysplastic nevi can be confused with acquired nevomelanocytic nevi, small congenital nevi, melanoma, Spitz nevi, seborrheic keratoses, solar lentigines, and other pigmented lesions.
Dermatopathology The histologic criteria for a dysplastic nevus include the following:
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Architectural disorder with asymmetry of the lesion.
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Intraepidermal melanocytes in a single file or in nests beyond the dermal component.
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Lentiginous hyperplasia with elongation of the rete ridges (may be “bridging”).
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± Fibrotic changes around the rete ridges.
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± Vascular changes.
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± Inflammation.
Clinically, it seems atypical nevi are an intermediate on the continuum between normal common nevi and melanoma. The majority of atypical nevi are clinically stable and not inevitable precursors to melanoma. A rare few do progress to melanoma, especially in patients with numerous atypical nevi or a family history of melanoma. Thus these patients should self-check for changes in their moles and routinely have their skin checked by a physician.
Patients with atypical nevi should have regular skin examinations with excision and histologic evaluation of any changing or worrisome lesions. These patients should also be educated and instructed on worrisome signs in moles:
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Asymmetry in shape. One-half is different from the other.
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Border. Irregular borders are present.
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Color. Color is or becomes variegated. Shades of gray, black, white are worrisome.
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Diameter. Greater than 6 mm (may be congenital mole, but should be evaluated).
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Evolution: If the lesion is growing rapidly, distinct from other nevi or a child’s overall growth pattern.
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Symptoms. Lesion begins to persistently itch, hurt, or bleed. If a skin lesion is constantly 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.
It may be harder for patients to follow these general guidelines given the atypical presentation of their dysplastic nevi at baseline, thus routine skin examinations (± photos) with a physician are recommended. Physicians will be looking for lesions that “stand out” or differ from the patient’s other baseline nevi. It is not recommended to remove all clinically atypical nevi; rather, close follow-up and removal of changing or worrisome nevi is indicated. Additionally, first-degree relatives of patients with melanoma or atypical nevi should have regular skin checks, and counseling regarding sun avoidance and protection.
BLUE NEVUS
A blue nevus is an acquired, benign, small, dark blue to blue–black, sharply defined papule or nodule of melanin-producing dermal melanocytes.
SYNONYMS Blue neuronevus, dermal melanocytoma, common blue nevus, blue nevus of Jadassohn–Tieche.
AGE May appear at any age; up to 25% are present at birth.
GENDER F > M, 2:1.
RARE VARIANTS Cellular blue nevus, combined blue nevus–nevomelanocytic nevus, plaque-type blue nevi.
A blue nevus arises from ectopic dermal melanocytes. It is thought that melanocytes migrate away from the dermis during the second half of embryogenesis, and that blue nevi represent arrested embryonal migration of the melanocytes. They appear blue because of the Tyndall’s phenomenon refracting light from the deeper location of the nevus cells. Mutations in the gene GNAQ, encoding a membrane G-protein with GTPase activity, have been found in a majority of blue nevi.
Blue nevi are benign growths that appear during childhood and adolescence, remain stable in size, and persist for life. In contrast, cellular blue nevi are generally >1 cm in size and have a low but distinct danger of malignant transformation. Rarely, multiple blue nevi have been associated with the Carney complex, with findings including lentigines, and both cutaneous and internal myxomas.
TYPE Macule or dome-shaped papule.
SIZE 2 to 10 mm.
COLOR Blue, blue–gray, blue–black (Fig. 7-6). Occasionally has target-like pattern of pigmentation.
SHAPE Usually round to oval.
DISTRIBUTION Dorsa of the hands and feet (50%), scalp or the face (34%), or buttocks (6%).
The diagnosis of a blue nevus is usually made on clinical findings. Although worrisome in color, blue nevi can be diagnosed by their normal skin markings. The diagnosis can be confirmed by excision and histologic examination. The differential diagnosis includes a radiation tattoo, traumatic tattoo (e.g., pencil lead tip), dermatofibroma, glomus tumor, primary or metastatic melanoma, venous lake, angiokeratoma, sclerosing hemangioma, apocrine hidrocystoma, and a pigmented spindle cell (Spitz) nevus.
HISTOLOGY Skin biopsy reveals spindle-shaped melanocytes grouped in bundles in the middle and lower third of the dermis.
DERMOSCOPY Homogenous blue–gray or blue–black pigmentation.
Common blue nevi appear and persist throughout life. They may flatten and fade in color over time. Malignant degeneration is rare.
Common blue nevi smaller than 10 mm in diameter and stable for many years usually do not need excision. Those larger than 10 mm are more likely to be the cellular blue nevus variant, which does have a low risk of malignant degeneration, and for which surgical removal is recommended. The sudden appearance or change of an apparent blue nevus also warrants surgical excision.
HALO NEVUS
A halo nevus is a nevus (usually compound or dermal nevus) that becomes surrounded by a halo of depigmentation. The nevus then typically undergoes spontaneous involution and regression followed by repigmentation of the depigmented area.
SYNONYMS Sutton’s nevus, leukoderma acquisitum centrifugum, perinevoid vitiligo.
AGE Typically in patients <20 years. Age range: first through fifth decades.
GENDER M = F.
INCIDENCE <1% of patients under age 20 years.
FAMILY HISTORY Halo nevi occur in siblings and in persons with a family history of vitiligo.

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