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NEVI

Congenital nevus, small or medium

Etiology and pathogenesis

As implied from their name, these are congenital and probably occur due to failure of nevus cells to migrate uniformly from the neural crest. Some would accept nevi that become apparent in the rst 2 months of life as also being congenital.

Clinical

A congenital pigmented plaque is characteristic (Figs 31.1 and 31.2). At birth, it may be a pale, tan macule or plaque that over time darkens, thickens, and sprouts hair (Fig.31.3). The congenital nevus (CN) usually grows in proportion to the patient's growth.

Figure 31.1 Small congenital nevus with a focus of pigment. A focus of pigment should raise suspicion. This lesion was benign.

Figure 31.2 Congenital nevus. Just as acquired nevi may elevate and lose color over the years, so may congenital nevi.

Figure 31.3 Trachyonychia. The nails are rough, lacking luster, and have been sandpapered.

Differential diagnosis

Occasionally CN in young children may resemble other congenital lesions, such as epidermal nevi.

    At a later age, nevus sebaceous (organoid nevus; Ch.23) of the scalp may be diagnosed as a CN (implying a melanocytic nevus). The warty morphology that applies in some acquired nevi may also suggest CN.

    The greatest issue, however, is not diagnosis of CN but exclusion of melanoma within a CN. Melanoma may, rarely, develop in a small CN, usually in adult life (Fig.31.4). Studies of the risk of melanoma in small- to medium-sized CN give widely varying results. Some confusing factors include the lack of exact distinction between a giant CN and a medium or small CN (Fig.31.5). Also, studies that rely on histologic criteria to establish the diagnosis of CN are greatly flawed, as some nevi that histologically have a congenital pattern may have been acquired early in life (so-called CN-like nevus). Obviously, the results of large prospective studies are preferred. One prospective study of 232 patients with CN covering 4% or less of the body surface area found no melanomas (median follow-up 25 years). This diagnostic dilemma may occur at any age but is particularly prominent in the second decade, when the natural history of CN is to become more elevated with a cobblestoned pattern, or to become more hairy, thereby creating alarm.

Figure 31.4 Melanoma arising in a congenital nevus. Small congenital nevi may, rarely, give rise to melanomas.

Figure 31.5 Medium-sized congenital nevus on the back.

Treatment

As already noted, the risk of melanoma is low. Therefore it is appropriate to wait until puberty to surgically remove these lesions. Furthermore, prophylactic removal of a small CN in a patient educated in the manifestations of malignant change and able to do periodic self-examination is not necessary. However, any unusual change or any new focus of pigment should be biopsied. Some are experimenting with the laser and, indeed, after four treatments the normal-mode ruby laser can remove most of the pigment, improve the texture, and reduce hair in both small and large CN.

PRACTICE POINTS

Congenital nevus, giant

Etiology and pathogenesis

There are no uniformly accepted criteria for when a CN is giant. However, one reasonable criterion is any CN that is either greater than 20cm in diameter or covers more than 5% of the body surface area of the patient. The risk of melanoma is signicant, and the best estimate puts the approximate lifetime risk of melanoma in a giant CN to be of the order of 5%.

Figure 31.6 Giant congenital nevus (CN). The approximate lifetime risk of melanoma in a giant CN is in the order of 5%.

Figure 31.7 (a,b) Giant congenital nevus. Sadly, this baby developed melanoma and died. (Courtesy of O. Dale Collins III, M.D., Ph.D.)

Figure 31.8 Recurrent pigmentation at site of surgically removed congenital nevus. Large congenital nevi are often hard to remove completely. Only partial removal may be attempted, or recurrence at the surgical site may occur, as shown here.

Clinical

An extensive, black, verrucous CN covering a large area of the body, commonly including the low back and thighs, is characteristic (Figs 31.6 and 31.7). Multiple smaller satellite lesions may be scattered over the rest of the skin, and mucous membrane nevi may occur. Benign nodules and plexiform overgrowths may develop. Extensive involvement of an extremity may reduce the extremity's growth or may be associated with congenital atrophy. Lesions overlying the spine may be associated with a tethered spinal cord.

Differential diagnosis

The diagnosis is rarely in doubt. The issue is the extent of investigation and intervention.

    The term neurocutaneous melanosis (NCM) describes the combination of melanocytes of the skin and central nervous system. It is associated most commonly with giant congenital melanocytic nevi, in particular those on the scalp or posterior axial location, and especially those that are accompanied by satellite nevi, and it may be a precursor of leptomeningeal melanoma. One study showed that more than 20 satellite nevi at age 3 years correlates with a vefold increased risk of NCM compared with in patients with less than 20 satellite nevi.

Treatment

If possible, the entire lesion should be removed. Completing all surgery by age 3 years has been recommended. The use of tissue expanders is a signicant surgical advance: it is impressive how these can expand a small area of normal skin (e.g. over one scapula) through a series of procedures to cover nearly the entire back. When surgery is not possible, curettage or shaving early in life has been advocated for large CN, but these are incomplete procedures, and recurrence of some pigment over time is anticipated (Fig. 31.8).

    Any nodularity should be biopsied and reviewed by a dermatopathologist, as benign clonal proliferations can mimic melanoma and are frequent. Patients may be seen every 3 months during the rst year and every 6 months thereafter. Since such patients are at risk for extracutaneous melanoma, it would seem advisable for all such patients to undergo lifelong, periodic examinations, including a general history and physical examination, complete skin examination, and thorough neurologic examination.

    For patients with giant CN of the posterior axis, and particularly in those with many satellite nevi, magnetic resonance imaging (MRI) of the central nervous system is indicated to exclude detectable NCM.

Practice point

Spitz nevus

Etiology and pathogenesis

The Spitz nevus is a fairly common nevus that has its onset most commonly in childhood. In fact, approximately three-quarters of patients are younger than 15 years. This melanocytic proliferation is benign; however, the histologic appearance may at times be difcult to distinguish from melanoma. Indeed, there are a few cases where the most experienced dermatopathologist has called a lesion a benign Spitz nevus but the lesion went on to metastasize. Histologically atypical or borderline spitzoid melanocytic tumors are histopathologically challenging in differentiation from melanoma. A high rate of BRAF gene mutations in malignant melanomas (66%) and nevi (82%) has been reported, but a recent study found none in 20 Spitz nevi. It may be that genetic analysis will prove to be a helpful diagnostic tool in the future.

Clinical

The most common appearance is that of a pigmented, dome-shaped nevus; followed by a flesh-colored, dome-shaped papule; followed by a flat, pigmented papule (Figs 31.9 – 31.12). The head and neck are the most common sites in patients between 0 and 10 years of age. For teenagers and adults, the torso and legs are the most common sites. Over half of tumors are 4–6mm in diameter. Diascopy (compressing the vascularity out of the lesion with a clear glass slide or plastic strip) can demonstrate visible brown pigment within the red nodule (see Fig.2.22).

Differential diagnosis

The differential depends on the clinical appearance and age of the patient. Spitz nevi with a prominent vascular component and little pigment may resemble angiomas of various types, including pyogenic granuloma. Occasionally, a red nodule that erupts quickly may initially be felt to represent an insect bite or an inflamed cyst.

    In the older age group, and on the limbs, Spitz nevi tend to be darker, and the differential is usually between a benign acquired nevus versus melanoma.

Figure 31.9 Spitz nevus. This is the classic appearance: a round, red, nondescript papule on a child.

Figure 31.10 This red nodule arising in a compound nevus in a 10-year-old boy caused some concern but had the typical histology of a Spitz nevus.

Figure 31.11 Agminated Spitz nevus. Spitz nevi may rarely erupt in an aggregated fashion in childhood.

Figure 31.12 Giant congenital nevus (CN). The approximate lifetime risk of melanoma in a giant CN is in the order of 5%.

Treatment

Ideally, all Spitz nevi should be completely excised. Sentinel lymph node biopsy and wider excision should be considered in cases where the lesion may indeed represent a thick melanoma.

    However, this is not always acceptable on the face of a young child, in whom the risk of melanoma is very low and in whom the lesion may become less prominent in time; in such cases, observation is appropriate.

Nevus spilus

The term nevus spilus comes from the Greek word spilos , meaning spot. The lesion is not present at birth, but instead seems to appear during the early years of childhood. It may occur anywhere but is commonly found on the trunk and extremities. Most are small, but some may be large, often segmental in appearance. These lesions are often called speckled lentiginous nevi. A hyperpigmented patch speckled with darker macules or papules is typical (Figs 31.13 – 31.15). For some lesions, the background skin is not hyperpigmented. Very rarely, malignant change may occur. A biopsy should be obtained if the diagnosis is in question.

Figure 31.13 (a,b) Nevus spilus. The nevus spilus appears as multiple, grouped, speckled, pigmented macules. The background is usually slightly hyperpigmented compared with the surrounding skin.

Figure 31.14 Large, segmental nevus spilus. This large variant is often called a speckled lentiginous nevus. (Courtesy of Michael O. Murphy, M.D.)

Figure 31.15 Atypical nevus arising in a nevus spilus. Rarely, a nevus spilus may develop melanoma. Therefore any portion that stands out from the rest should be biopsied. The unusually large lesion here was identi?ed as an atypical melanocytic proliferation.

Figure 31.16 Normal mole on the upper chest of a child. Note the light brown color and oval shape. There is nothing worrisome about this mole.

    Patients should monitor the lesion for any change and seek prompt medical attention if such occurs. Excision of small lesions may be done. Wholesale removal of all such nevi is not warranted. The Q-switched ruby or alexandrite laser has been reported effective.

Acquired melanocytic nevus

Etiology and pathogenesis

The acquired melanocytic nevus is what the layperson calls a mole. Nearly everyone has several, and their incidence increases during childhood and adolescence. A typical acquired nevus often follows the following‘life cycle'. Early on in childhood and adolescence, it is flat and black (junctional nevus). During its middle years, the nevus raises up and loses some color (combined nevus). Late in life, the melanocytic nevus loses all color and becomes a flesh-colored papule (intradermal nevus). By the ninth decade of life, most nevi have disappeared. The tendency to have multiple nevi is increased by sun exposure and by a familial predisposition.

Clinical

Most acquired melanocytic nevi are less than 1.5cm in diameter (Fig.31.16). Their color ranges from light tan, to brown, to dark black. Most are round to oval, with a regular smooth border. Some exhibit variation in their coloring, but usually the color is symmetric and uniformly arranged, typically in rings spreading out from the center, with the edges being the lightest. In such nevi, the center may be raised and the periphery flat.

    The typical junctional nevus is small, flat, and black. The compound nevus is raised and brown. The intradermal nevus, so common on the face of older adults, is a flesh-colored papulonodule (Fig.31.17). Occasionally, pigment may spare the skin immediately adjacent to a hair follicle (Fig. 31.18). Multiple hairs may be found to emanate from nevi. Some nevi develop a warty appearance (Fig. 31.19).

Differential diagnosis

A huge range of lesions may resemble benign acquired nevi. The most important, either because they have close resemblance or because they are common, are listed in Table 31.1.

Treatment

The vast majority of nevi require no intervention. It is only when a pigmented lesion causes diagnostic concern that it should be removed; in most cases, a nevus that actually represents a melanoma has developed two of the ABCD criteria (see later). It must be emphasized that any nevus that is clinically atypical should be removed in its entirety for examination (see later).

Figure 31.17 ‘Old’ nevus. After many decades, a nevus tends to lose color and elevate. The end stage is a raised, soft, flesh-colored papule. Histologic examination would show an intradermal nevus.

Figure 31.18 Nevi with hair. Benign nevi very commonly contain multiple hairs. If the patient desires removal, standard excision, as opposed to shave excision, is needed to remove the roots of the hair.

Figure 31.19 Warty nevus. Many nevi, especially those in or near the scalp, develop a warty appearance.

Figure 31.20 Intradermal nevus. This intradermal nevus is entirely benign in appearance. If desired, shave biopsy would give an excellent cosmetic result.

Figure 31.21 Intradermal nevus in the scalp. These raised, fleshy nevi are common in the scalp. They interfere with combing, and often patients want them removed. A shave excision is very effective here.

    Those intradermal nevi that are of cosmetic concern, for example those on the face, may be treated adequately by shave excision with or without light electrocautery, or with a non-staining chemical hemostatic such as aluminum chloride solution (Figs 31.20 and 31.21). This approach gives excellent cosmetic results. Some pigment may remain or even develop in flesh-colored nevi (see under Recurrent nevus ). However, the sites of hairy nevi treated in this manner may regrow hair (approximately 25% of the time in one study).

PRACTICE POINTS

Halo nevus

Etiology and pathogenesis

Occasionally, the body's immune system attacks a nevus and removes it over the course of many years. During this process, a halo of pigment from the surrounding skin is lost as well. Vitiligo is associated in a small percentage of cases.

Clinical

A circular or oval depigmented macule with a central pigmented or pink nevus, either solitary or (commonly) multiple, usually on the trunk of a child, is characteristic (Figs 31.22 – 31.26).

Differential diagnosis

Rarely, haloes may also occur around melanoma, basal cell carcinoma, café au lait macules, Mongolian spots, or CN. The central pigmented lesion of any halo nevus should be evaluated by the ABCD criteria (without regard to the halo) and biopsied if indicated. However, all these other halo phenomena are usually solitary. Halo eczema (Meyerson nevus, later) may be confused, and even the most obvious halo nevi are sometimes referred from non-dermatologists as presumed melanoma.

Treatment

A sunscreen to prevent the white areas burning, and reassurance by explanation of the process, are all that is required.

Figure 31.22 The classic halo nevus. A fading pigmented papule surrounded by a white halo in a child is classic.

Figure 31.23 Halo nevus. The central nevus has nearly disappeared. The process of complete removal of the central nevus takes some time (e.g. 5 years).

Figure 31.24 Halo nevus without nevus. After several years, the immune system removes the nevus, leaving the halo without the nevus. Over time, the normal skin color will return.

Figure 31.25 Halo nevus. Note the oval white spot in the center. A nevus used to be at its center, but the body’s immune attack has removed it. Also note the pink sunburn that resulted from the skin’s lack of protective pigment, and the second halo nevus, which is less obvious due to lying in the paler skin under the clothing strap.

Figure 31.26 Halo congenital nevus. Even congenital nevi may develop haloes.

Figure 31.27 Small blue nevus on the back of the hand. The blue nevus commonly occurs on the back of the hand.

Blue nevus

Etiology and pathogenesis

The blue nevus represents a dermal collection of pigment-producing melanocytes. It typically extends deeply, especially around hair follicles.

Clinical

A solitary blue macule or small papule on the dorsum of the hand or foot is characteristic of a blue nevus (Fig. 31.27). It also may occur on the scalp, feet, or buttock area, where dermal melanocytes are often still present at birth (Figs 31.28 and 31.29). A nodular type may occur, especially on the buttocks. Occasional patients with innumerable or eruptive blue nevi have been reported.

    The color is typically a shade of blue (e.g. blue, blue-black, and steel blue). Occasionally, a blue nevus will be targetoid (gray-black or blue-black center surrounded by a flesh-colored area that merges with an outer macular rim of blue-black). Moderately commonly, blue nevi have a more yellowish color, but the diagnosis may be suspected from the rmness of the lesion and the site (this type is often acral).

Figure 31.28 Nodular blue nevus on the dorsum of the foot.

Figure 31.29 Macular blue nevus. This congenital blue patch was a blue nevus on biopsy. Almost any pigmented oral lesion must be biopsied to exclude melanoma.

Figure 31.30 Combined nevus. Histologically, combined nevus has features both of a standard nevus and a blue nevus. Note the unusual color that results from this combination.

Figure 31.31 Nevus en cocarde. This targetoid nevus is common on the scalps of children. It is benign. The term en cocarde means rosette-like.

Figure 31.32 Desmoplastic nevus. This flesh-colored papule histologically showed benign nevomelanocytic cells in desmoplastic stroma.

Differential diagnosis

See Table 31.1. Malignant blue nevus is extremely rare.

Treatment

Simple excision may be done if necessary. Shave excision will fail, as the pigment lies deep.

Miscellaneous nevi

Some other specic types of nevus require brief discussion.

PRACTICE POINTS

Figure 31.33 Meyerson nevus. The Meyerson nevus, an eczematous halo about a nevus, is much less common than the halo nevus.

Figure 31.34 Becker nevus. A large, unilateral, pigmented patch, with hair, on the arm, shoulder, or chest of a teenage boy is characteristic of a Becker nevus.

Figure 31.35 Becker nevus. Note the large hyperpigmented patch with associated hypertrichosis.

Becker nevus

Etiology and pathogenesis

This is an epidermal (not melanocytic) developmental abnormality that usually presents in adolescence and is most common in males.

Clinical

An acquired, unilateral, pigmented patch with irregular borders on the trunk of an adolescent is characteristic of a Becker nevus (Figs 31.34 and 31.35). Hypertrichosis may develop later, and familial cases have occurred. Breast hypoplasia may be associated in lesions overlying a woman's breast, and fat atrophy at other sites such as the thigh has been reported. Although the condition occurs mainly in males, associated lipoatrophy is more common in women (or at least is more likely to present in women, due to involvement of the breast area). Ipsilateral hypoplasia of the shoulder girdle and an ipsilateral absence of the pectoralis major muscle have also been seen, as well as ipsilateral skeletal defects (rare). Skin conditions reported to occur restricted to the area of a Becker nevus include acne and granuloma annulare.

Differential diagnosis

Lentiginous melanocytic lesions may be considered but do not have the irregular geographic border of a Becker nevus, nor do they develop hair growth. The hairiness of a lesion may suggest a CN if a history is not obtained.

Treatment

No treatment is effective. The important issue is that this is not a form of melanocytic nevus and does not have malignant potential; the lesion is usually of cosmetic concern only, but reassurance that it will not turn cancerous can be very important to the patient and often avoids unrealistic requests for excision.

PRACTICE POINTS

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.