Benign Melanocytic Neoplasms

92

Benign Melanocytic Neoplasms

Benign Pigmented Cutaneous Lesions Other Than Melanocytic Nevi

• This group of lesions can further be divided into: (1) predominantly epidermal lesions (Table 92.1; Figs. 92.1–92.5); and (2) dermal melanocytoses (Table 92.2; Figs. 92.6 and 92.7).

Table 92.1

Benign pigmented lesions other than melanocytic nevi (predominantly epidermal lesions).

PUVA, psoralens plus ultraviolet A phototherapy.

Fig. 92.1 Oral melanotic macules (labial lentigines). Multiple hyperpigmented macules on the lower lip in a patient with Laugier–Hunziker syndrome. Additional lesions are present on the tongue. Peutz–Jeghers syndrome can have a similar clinical appearance.

Fig. 92.2 Anogenital melanotic macules (anogenital lentiginosis). Biopsy of the darker lesion (at 7 o’clock) showed no cellular atypia. Over a period of 10 years, several of the macules faded. Courtesy, Jean L. Bolognia, MD.

Fig. 92.3 Solar lentigines. Numerous light brown macules, some of which have an irregular border, on chronically sun-exposed skin. Courtesy, Raymond Barnhill, MD.

Fig. 92.4 Café-au-lait macule. Large tan patch in a geographic pattern on the lateral trunk. The patient did not have McCune–Albright syndrome.

Fig. 92.5 Becker’s nevus. Large patch of hyperpigmentation on the leg, which is medium brown in color. These lesions may be misdiagnosed as café-au-lait macules or congenital melanocytic nevi, especially when they do not occur on the upper trunk. Courtesy, Jean L. Bolognia, MD.

Fig. 92.6 Dermal melanocytosis (Mongolian spots) in a child with neurofibromatosis 1. Surrounding each café-au-lait macule, there is an absence of the characteristic blue discoloration.

Fig. 92.7 Nevus of Ota (oculodermal melanocytosis). Unilateral blue-gray discoloration of the face, which is either mottled or confluent. There is also involvement of the sclera.

• In the predominantly epidermal lesions, the tan to brown color can result from a variety of mechanisms – e.g. increased melanocyte activity (melanogenesis), increased melanin content in keratinocytes, and a mild increase in the number of melanocytes.

• In dermal melanocytoses, the skin is blue to blue-gray in color (ceruloderma) due to the presence of melanin-producing melanocytes in the mid to lower dermis and the resultant Tyndall phenomenon (the preferential scattering of shorter wavelengths of light by the dermal melanin).

Acquired Melanocytic Nevi (Moles)

• Benign proliferations of a type of melanocyte called a ‘nevus cell’.

• Nevus cells differ from ‘ordinary’ melanocytes, which typically reside as single units in the basal layer of the epidermis, in that they: (1) usually cluster as nests in the lower epidermis and/or dermis; and (2) do not have dendritic processes (except when found in a blue nevus).

• Both ‘ordinary’ melanocytes and nevus cells can produce melanin.

• Acquired melanocytic nevi can be categorized as common (banal) or atypical (dysplastic), and they are further named based on the histologic location of the collections of nevus cells (Fig. 92.8):

– Junctional melanocytic nevus: dermal-epidermal junction.

– Compound melanocytic nevus: dermal–epidermal junction plus dermis.

– Intradermal melanocytic nevus: dermis.

Fig. 92.8 Three common types of acquired melanocytic nevi. A Junctional, B compound, and C intradermal. The latter may also be pedunculated or papillomatous (see Chapter 1).

• Variants include halo, blue, Spitz, and ‘special site’ nevi (Fig. 92.9).

Fig. 92.9 Variants of acquired melanocytic nevi. A The three most common types of acquired melanocytic nevi. A1 Junctional nevus. Clinically, a brown macule with central hyperpigmentation. Dermoscopically, a uniform pigment network. A2 Compound nevus. Light to medium brown papule. A3 Intradermal nevus. A light tan, soft, raised papule. Dermoscopically, focal globular-like structures, whitish structureless areas, and fine comma vessels. B Clinically atypical acquired melanocytic nevi. B1 Multiple pigmented macules and papules of varying sizes on the back. B2 Close-up photo; the dermoscopy pattern is reticular-disorganized and can be seen with uncertain lesions. B3 ‘Fried egg’ appearance, with a central elevated soft papule and macular rim. C Blue nevi. C1 Common blue nevus. By dermoscopy, blue homogeneous color typically found in blue nevi. C2 Cellular blue nevus. A firm blue plaque is a common presentation. D Spitz nevi. D1 Classic Spitz nevus. Red dome-shaped papule on the ear of a child. D2 Reed nevus, typified dermoscopically by the classic starburst pattern (regular streaks at the periphery of a heavily pigmented and symmetric small macule). E Nevi of ‘special sites’ (e.g. scalp, acral, genital, milk-line). E1 Acral nevus. A brown macule on the sole of the foot. Dermoscopically, a lattice-like pattern is seen. F Other ‘specially named’ nevi. F1 Eclipse nevus. A tan center and thinner brown rim; note the stellate appearance of the brown rim. F2 Cockade or target nevus. Central lightly pigmented papule surrounded by a tan annulus then a brown ring. F3 One variant of combined melanocytic nevus. Dark brown to black papule within an otherwise uniformly pigmented light brown nevus. The differential diagnosis includes the possibility of a melanoma developing in a nevus. F4

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Apr 22, 2016 | Posted by admin in Dermatology | Comments Off

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