Congenital nevi
They are melanocytic nevi whose presence is determined in utero. In contrast, acquired melanocytic nevi form after birth and their development appears to be dependent on environmental factors. However, the distinction between congenital and acquired nevi has become more nebulous in recent years. Although most CMN are present at birth, some may not become clinically apparent for months or even years after birth. These tardive CMN are not visible at birth due to either the lack of visible pigment or because the growing nidus of the nevus is imperceptible due to its small size. As the tardive CMN grows and/or develops pigment, it eventually becomes apparent on the skin. Although the appearance of nevi after birth are often deemed to be acquired nevi (Changchien et al., 2007), tardive CMN are actually congenitally derived. Melanocytic nevi possessing clinical features consistent with CMN, but in which clinical history is lacking to conclusively verify their presence since early life, are termed congenital nevus-like nevi (CNLN). Although it is possible that some CNLN are acquired nevi, most are probably tardive CMN. Between 1% and 6% of the population have a CMN or a CNLN (Happle, 2009). The most widely used classifi cation of CMN divides lesions into categories based on size: small (<1.5 cm); medium (1.5–19.9 cm); large (≥20 cm); and giant (≥50 cm) (Kovalyshyn et al., 2009). While melanoma may develop in association with any CMN, irrespective of size, the risk of developing melanoma appears proportional to the size of the CMN. Patients with CMN can develop cutaneous or extracutaneous melanoma (Kovalyshyn et al., 2009). The location and age at onset of melanoma differs between small to medium and large CMN. Melanomas developing in smaller CMN tend to appear after puberty and are more likely to originate at the dermoepidermal junction (DEJ) and at the peripheral edge of the CMN. Thus, dermoscopy is an ideal instrument to evaluate smaller CMN for melanoma since it can easily help the clinician observe morphologic changes at the DEJ that may be indicative of melanoma. In contrast, melanomas occurring in large CMN develop earlier in life and frequently have their origin below the DEJ. Thus, dermoscopy has a limited role in evaluating large CMN, especially those that are thick and rugous, since it cannot adequately visualize morphologic changes that may be indicative of melanoma developing below the papillary dermis. One type of CMN requires special mention here. A nevus spilus or speckled lentiginous nevus is a CMN that consists of a lentiginous patch of skin that is studded with nevi. There are two variants of a nevus spilus. Nevus spilus maculosus consists of dark macular speckles on a light brown background (Marghoob, 2002). The speckles, all of approximately the same size, have a reticular or homogenous appearance under dermoscopy. In contrast, nevus spilus papulosis consists of variously sized dark macules and papules unevenly distributed on a light brown background (Marghoob, 2002). With dermoscopy these macules and papules can be reticular, homogenous, globular, or can manifest a combined pattern. Although melanoma can develop in any nevus spilus, the risk is highest in larger speckled lentiginous nevi of the maculosa variant. The current management options for CMN include close clinical followup with or without baseline photographs and/or prophylactic surgical excision, when feasible (Marghoob et al., 2007). Most physicians, however, are electing to follow CMN, especially those that have a homogenous clinical appearance and are small to medium in size, by periodic followup examinations. Dermoscopy has improved our ability to clinically monitor CMN, especially the smaller ones. Knowledge of the dermoscopic features and patterns common to CMN can aid physicians in following these lesions and recognizing aberrancy that may be suggestive of melanoma. In other words, if a signifi cant change occurs or the dermoscopic pattern does not conform to the known CMN patterns, then a biopsy or an excision may be warranted. Needless to say, many physicians fi nd baseline photographs and dermoscopy to be very helpful in the followup monitoring of CMN (Nehal et al., 2002a; Nehal et al., 2002b). Ideally, the photographs of CMN should include overview clinical images and dermoscopic images (Nehal et al., 2002b). The dermoscopic images should capture the representative architecture and border of the CMN (Braun et al., 2001). In addition, supplemental dermoscopic images should be obtained of any areas within the CMN that are of “special interest” (Braun et al., 2001). dermoscopic evaluation of cmn Most small and medium CMN are fairly homogenous, both clinically and dermoscopically. Large CMN, on the other hand, are often heterogenous, displaying multiple islands of color and irregular topography. Under dermoscopy, multiple patterns can be seen within the same lesion, but each “island” within the large CMN tends to be fairly homogenous in its appearance. Previously, authors have documented dermoscopic features and patterns common to CMN of all sizes, including the presence of reticular network, globules that may form a cobblestone pattern, and diffuse homogenous pigmentation (Seidenari & Pellacani, 2002; Seidenari et al., 2003; Braun et al., 2001; Wang et al., 2000a; Wang et al., 2000b; Soyer et al., 2001b). Other features associated with CMN include terminal hairs, perifollicular hypo- or hyperpigmentation, and milia-like cysts. This chapter reviews the dermoscopic features of CMN. For a lesion to be categorized as a CMN, it must meet the following criteria:
- Any melanocytic nevus that was documented to be present since birth, or;
- Any CNLN in which the history is reliable that it was present since early life and the clinical examination or histology is consistent with a CMN (Kenet et al., 1993). dermoscopic features of cmn Dermoscopic evaluation of a CMN begins by observing dermoscopic structures.
Pigment network
A reticular network consists of a honeycomb-like grid of brown-black pigment in which the pigmented lines correspond to rete ridges, and the open holes or spaces correspond to the suprapapillary plate overlying the dermal papillae (Soyer et al., 1989; Kenet et al., 1993; Soyer et al., 2001a). The reticular network, as seen in CMN, is characterized by its:
- Quality, which can be fi ne and/or thick
- Distribution, in which the network can be present homogenously throughout the lesion or present focally (patchy), or may be present only at the periphery;
- Specific type, thick linear network fragments that resemble hyphal elements (i.e., resemblance to the tubular branching of fungal hyphae)
Globules
Globules consist of sharply circumscribed, round-to-oval aggregates that are usually brown in color; however, they can also appear with a black or blue color. Globules correspond to nests of melanin-containing nevomelanocytes within the dermis. Globules in CMN are characterized by their:
- Quality, which can be small and/or large;
- Distribution, in which the globules can be present diffusely throughout the lesion in a sparse or dense distribution, or clustered centrally and surrounded by reticulation;
- Specific type, in which the globules form a cobblestonelike arrangement or form target-like structures.
Target-like structures consist of the presence of globules within the “holes” of the network. Target network with globules corresponds to the presence of nevomelanocytic nests in the dermal papillae (Changchien et al., 2007). Diffuse homogenous background pigmentation is due to the diffuse distribution of melanin in the epidermis and dermis (Kenet et al., 1993). Often these CMN appear structureless, in that one cannot see any discernible dermoscopic structures (i.e., network or globules), but on occasion a few scattered reticular network fragments and/or globules may be visible focally within the lesion. other dermoscopic features seen in cmn
Other structures:
Other structures frequently observed in CMN viewed with dermoscopy include the following:
- Milia-like cysts
- Hypertrichosis
- Blood vessels
- Perifollicular pigment changes.
Milia-like cysts are white to yellow, rounded, often hazy structures that correlate histologically with intraepidermal keratin cysts/pseudocysts (Soyer et al., 1989). They derive their name from their resemblance to the small seeds or millets of various grain grasses. They may be observed scattered throughout a CMN (Changchien et al., 2007). It is important to stress that although the presence of milia-like cysts is one of the dermoscopic hallmarks of seborrheic keratosis, they can also be seen in melanocytic neoplasms, including CMN, papillomatous dermal nevi and, rarely, in melanomas (Braun et al., 2002; Argenziano et al., 2003). Thus, if the lesion is deemed to be a nonmelanocytic growth then the presence of multiple milia-like cysts favors the diagnosis of seborrheic keratosis; however, if the lesion is a melanocytic tumor then the presence of multiple milialike cysts favors a diagnosis of CMN. With that being said, it is important to remember that in a melanocytic tumor the presence of milia-like cysts, in and of themselves, are not diagnostic of a CMN since they can also be seen in melanoma. Hypertrichosis is characteristic of CMN and is often accompanied by perifollicular hyperpigmentation or hypopigmentationIn addition, the presence of blood vessels of varying morphologies is commonly observed in CMN. Occasionally, the blood vessels can be seen within the hole of the network and correspond to vessels in the dermal papillae. When a network surrounds these vessels they create a target structure called “target network with blood vessels.” dermoscopic patterns After identifying the local dermoscopic features commonly seen in CMN, it becomes apparent that these nevi often exhibit specifi c dermoscopic patterns. In CMN, these global patterns are generally appearing symmetric and organized. The four primary global patterns that emerge are
- Reticular (reticular throughout or patchy reticular throughout);
- Globular;
- Reticuloglobular with globules in the center and network at the periphery;
- Diffuse brown pigmentation (with or without network fragments and/or presence of a few sparse globules).
Some CMNs are either primarily reticular or primarily globular. Others exhibit peripheral reticulation in conjunction with central globules, and are designated reticuloglobular. As noted earlier, CMN that primarily have diffuse brown pigmentation are often structureless, but some may contain fragments of reticulation and/or globules. Approximately 7% of CMN will manifest a multicomponent pattern. If the structures in a multicomponent nevus are distributed asymmetrically then differentiating these CMN from melanoma may be challenging. In addition, thick mamillated CMN are often difficult to evaluate using dermoscopy. These lesions often have ridges, comedo-like openings, and many blood vessels. This pattern can sometimes mimic a seborrheic keratosis. Although any of the above-mentioned dermoscopic patterns could be present in CMN at any anatomical location, CMN on the torso are more frequently globular and CMN on the lower extremities are more frequently reticular (Changchien et al., 2007). conclusion Dermoscopy can be enormously valuable in the diagnosis and followup of CMN (Braun et al., 2005; Lodha et al., 2003). This noninvasive in vivo technique allows the clinician to examine morphologic structures within the epidermis, DEJ, and superficial dermis. Since most melanomas arising in association with smaller CMN develop along the DEJ, dermoscopy is an ideal instrument to help in the evaluation, screening, and monitoring of these nevi. Dermoscopy may also assist in evaluating, screening, and monitoring of fl at large CMN. However, due to the limitation of how deep into the skin dermoscopy allows the observer to see, this tool is not ideal for evaluating large rougouse CMN, because melanomas developing in such lesions are often located below the papillary dermis. Although dermoscopy can assist in evaluating the superficial component of these thicker CMN, other techniques, such as palpation, ultrasound, or other imaging modalities, may need to be used to evaluate the deeper nevus component. The classification system proposed in this chapter should provide the foundation for the recognition of CMN. Those CMN that do not conform to the known patterns described above should be viewed with caution. One such example is provided in Figure 7a.30. Within one section of this asymmetric melanocytic lesion one can see the classic cobblestone globular pattern of a CMN. This part of the lesion also reveals milia-like cysts, hypertrichosis, and multiple blood vessels—all structures commonly seen in CMN. However, another portion of the same lesion has features that are not seen in CMN and are, in fact, features commonly seen in melanoma. This lesion was excised and revealed a melanoma arising in association with a CMN.
