Dermal Nevi
Melissa Shive
Stephanie Martin
Gary P. Lask
BACKGROUND
Acquired melanocytic nevi are most frequently classified into 3 categories based upon their location in the skin: junctional, compound, or intradermal. Of these 3 types, intradermal nevi, also commonly referred to as dermal nevi, exist deepest in the skin in the papillary and reticular dermis.1 They are very common, present in about 25% of people.2 Age, race, anatomic location, and genetic factors are thought to affect the presence and appearance of nevi.3,4 Generally speaking, the number of acquired melanocytic nevi starts to increase in childhood, peaks by the third decade, and then starts to decrease thereafter.2,5,6
PRESENTATION
Patients present with a history of a recently acquired mole or growth that is often pigmented. The age of the patient may range from childhood to adulthood.
DIAGNOSIS
Clinical Diagnosis
Dermal nevi are papules or nodules typically <1 cm that are either smooth and dome shaped or exophytic and papillomatous and/or may be accompanied by a surrounding brown patch. They may be flesh colored, lightly pigmented, or tan-to-brown. In older patients, the nevus may be soft and compressible and resemble an acrochordon.
Histopathology
Dermal nevi demonstrate nests of nevomelanocytes confined to the dermis. Occasionally, they may have focal junctional melanocytic hyperplasia, which may appear slightly atypical, with small nucleoli and nuclear enlargement.
The appearance of dermal nevi can also change with age, some of them undergoing a process of neurotization in which spindle-shaped melanocytes become arranged
in cords or fascicles resembling neural structures in the dermis.3,7,8 Nevi in older people are also more likely to have fatty infiltration, mucin deposition, and fibrosis.9
in cords or fascicles resembling neural structures in the dermis.3,7,8 Nevi in older people are also more likely to have fatty infiltration, mucin deposition, and fibrosis.9
Subtypes
As classified by Andrade and Kopf in 1990,10,11 intradermal nevi can be further subdivided into Unna nevi, Miescher nevi, compound nevi, and blue nevi (Table 12.2.1).
Unna Nevus
Unna’s nevi are characteristically exophytic and papillomatous. They represent roughly 2.5% of all nevi and are typically located on the neck, trunk, and extremities.5,12 While dermal nevi increase in frequency with age, Unna nevi peak in the eighth decade.5 The mean age of patients who have intradermal nevi excised is 31 for an Unna nevus.12
Clinical Diagnosis. Unna nevi (Figure 12.2.1A) can be recognized by their soft, fleshy, exophytic, often cerebriform, papillomatous, and potentially pedunculated appearance. They are found predominantly on the neck, trunk, and limbs and can sometimes be clinically confused with fibroepithelial polyps/papillomas or acrochordons because of their fleshy, exophytic appearance. Upon close inspection, milia-like cysts and comedo-like openings may be observed on the surface of the nevus (Figure 12.2.2). Diagnosis of Unna nevi is usually based on clinical appearance.
TABLE 12.2.1 Comparison of Types of Dermal Nevi | ||||||||||||||||||||||||||||||
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Dermoscopic Findings. On dermoscopy, one can appreciate cerebriform, papillary structures sometimes studded with comedone-like openings and milia-like cysts (Figure 12.2.3). The nevi can appear skin-colored to light brown and often lack definitive pigment networks.13 If pigment networks are seen, these nevi can demonstrate homogeneous, globular, and reticular pigment patterns. When these nevi lack pigment, the vascular structures may be the most prominent findings. Comma vessels are common, although dotted vessels are also seen.13
Histopathology. Unna nevi can be classified into 4 histological types: papillomatous, horizontal, semispherical, and verrucous. Papillomatous nevi are primarily exophytic with a dominant vertical axis. Horizontal nevi occur when the horizontal axis is greater than the vertical axis. Semispherical nevi are
defined when the vertical and horizontal axes are comparable, and the verrucous type consists of any combination of 3 previously discussed types.12 The surface of these nevi can be either smooth or coarsely papillated.14 Melanocytes are located primarily in the dermis, although junctional nests may exist. Melanocytes should mature and change from epithelioid to more lymphocyte-like as they descend deeper into the dermis. They can also become thinner, elongated, and schwannian in the deep dermis as well. There may be an accompanying terminal hair and/or large sebaceous glands.14
defined when the vertical and horizontal axes are comparable, and the verrucous type consists of any combination of 3 previously discussed types.12 The surface of these nevi can be either smooth or coarsely papillated.14 Melanocytes are located primarily in the dermis, although junctional nests may exist. Melanocytes should mature and change from epithelioid to more lymphocyte-like as they descend deeper into the dermis. They can also become thinner, elongated, and schwannian in the deep dermis as well. There may be an accompanying terminal hair and/or large sebaceous glands.14
 FIGURE 12.2.1 Unna nevus before (A) and after (B) shave removal. Note the papillomatous and sometimes pedunculated appearance of the nevus. These nevi can range in color from skin-colored to light brown to dark brown. When shave removal is performed carefully and flush with the surrounding skin, the area will often heal without dyspigmentation or scarring. (Photos courtesy of Macrene Alexiades, MD, PhD.) |
 FIGURE 12.2.2 A close-up photograph of an Unna nevus. Note the presence of milia-like cysts and comedo-like openings on the surface of the nevus. |
 FIGURE 12.2.3 Dermoscopic photo of a Miescher nevus. A slight golden brown halo appears at the base of the nevus, which can help distinguish a Miescher nevus from a basal cell carcinoma. The arrowheads point to comma-shaped vessels, which are somewhat curved and branching vessels that can be commonly seen in both Unna and Miescher nevi. |
Miescher Nevus
Miescher nevi have smooth, dome-shaped surfaces and melanocytes that extend into the reticular dermis in a wedge-shaped pattern. They are most commonly found on the face and represent about 6% of all nevi.5,12,15 While both Unna and Miescher nevi increase in frequency with age, Miescher nevi peak in frequency in the sixth decade.5 The mean age of patients who have intradermal nevi excised is 41 years for a Miescher nevus.12
Clinical Diagnosis. Miescher nevi are named after Guido Miescher who conducted a study of 100 melanocytic nevi in 1935 and classified them into 3 different types based on location. These nevi are characteristically dome shaped or have semispherical appearance and are typically diagnosed clinically (Figures 12.2.4 and 12.2.5).16 They are most frequently located on the face, although they can also rarely be located on acral surfaces.17 A study looked at the frequency of different types of nevi in 400 patients at an outpatient clinic and found that Miescher nevi represented about 6% of all nevi, and 46% of Miescher nevi were found in the head and neck region. The differential diagnosis for Miescher nevi include basal cell carcinomas, neurofibromas, and fibrous papules.12,16
Dermoscopic Findings. On dermoscopy, Miescher nevi lack the cerebriform appearance of Unna nevi though may still have comedo-like openings and milia-like cysts.13 Dermal nevi typically lack a true pigment network, but there may be a pseudonetwork pattern surrounding facial follicular structures. Like Unna nevi, Miescher nevi may have comma-shaped, dotted, and occasional hairpin vessels (Figure 12.2.3).13,18 The vascular structures of a Miescher nevus can sometimes be difficult to distinguish from the arborizing telangiectasias of a basal cell carcinoma, but Miescher nevi may additionally have a golden brown halo, comedo-like openings, and milia-like cysts that can help with diagnosis.17,18
Histopathology. Miescher nevi typically have an elevated, smooth epidermal surface, often with pseudovascular spaces, multinucleated floret cells, and several pilosebaceous follicles. Melanocytes are typically intradermal with a wedge-shaped base and vertical silhouette. There may be follicular structures present.14
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