Skin-Melanocytic Tumors

Home Chapter Home Jobs Conferences Fellowships Books

Skin-Melanocytic Tumors

Nevi - general

Last major update: November 2008 - next update November 2009

Revised: 18 September 2009

Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.

Definition

=========================================================================

● Congenital or acquired benign melanocytic proliferation

Terminology

=========================================================================

● Nevus (singular) also spelled naevus

● Means birthmark in Latin

● Also called melanocytic, nevocellular or pigmented lesion

Epidemiology

=========================================================================

● Most common melanocytic tumor

● Usually clinically evident between ages 2-6 years

● Most whites have 20-30 nevi

● Can estimate total body count in 13-14 year olds by examining lateral arms (Am J Epidemiol 2007;166:472)

● Much less common in Asians and Afro-Caribbeans

Clinical

=========================================================================

● Nevi common on head, neck and trunk in Caucasians, on acral sites in Asians and Afro-Caribbeans

● Mostly occur in skin, but also mucosal membranes covered by squamous epithelium

● May be neoplastic since many are clonal

● Existence of freckles, lentigines (small, pigmented, flat or slightly raised spots with a clearly defined edge, but no nests of melanocytes) and melanocytic nevi increases chance of having melasma (BMC Dermatol 2008 Aug 5;8:3)

● Often accompanied by keratinous cysts, abscess, folliculitis

● Incidental microscopic aggregates of nevus cells occur in 1% of skin excisions (Am J Dermatopathol 2008;30:45); also occur in clusters in lymph node capsules (intracapsular nevus), particularly in axilla (see Lymph Nodes chapter of PathologyOutlines)

● Large numbers of nevi are risk factor for melanoma (Int J Cancer 2008 Sep 12 [Epub ahead of print])

● Increasing numbers of nevi are associated with neonatal phototherapy (Arch Dermatol 2006;142:1599), sun exposure on hot holidays (J Invest Dermatol 2005;124:56), number of nevi in parents (Cancer 2003;97:628), although this does not necessarily mean that these factors are risk factors for melanoma

Patterns associated with benign behavior

=========================================================================

● Small size, circumscription, symmetry

● Lentiginous hyperplasia (single cell melanocytic growth along dermoepidermal junction)

● Nested proliferation

● Uniform nests with regular distribution at the tips of the rete ridges

● Pagetoid proliferation (discohesive single cell growth throughout entire epidermis-seen in Spitz nevi and acral nevi, as well as melanoma)

● Melanocyte nuclei smaller than in adjacent keratinocytes

● Transdermal elimination of melanin pigment

Color

=========================================================================

● Due to Tyndall effect (scattering of light as it hits melanin granules, Wikipedia)

● Melanin in stratum corneum appears black, melanin in reticular dermis appears slate-gray or blue

● Nevi may regress due to lymphocytic infiltration (see Halo nevus)

Dermoscopy

=========================================================================

● Nevus type varies by skin type in whites (Arch Dermatol 2007;143:351)

Case reports

=========================================================================

● Melanocytic intranuclear inclusions due to molluscum contagiosum (J Cutan Pathol 2008;35:782)

● Nodal nevus cells associated with dermatopathic lymphadenopathy (Diagn Cytopathol 2004;31:180)

Treatment and prognosis

=========================================================================

● Biopsy any clinically atypical melanocytic lesions in adults, such as nevi causing chronic mechanical irritation, itching, bleeding, ulceration or oozing of serum, nevi with rapid growth, deepening pigmentation, pigmentation beyond outline of lesion, flat areas of depigmentation or erythema

● Pathologically confirmed banal nevi and mildly atypical nevi do not require additional treatment

● Nevi with moderate and severe atypia usually are excised with negative margins

● May recur with incomplete excision (shave biopsy), usually within 3 months

● Recurrent nevus may resemble melanoma due to irregular scarring, lentiginous melanocytic hyperplasia, basilar keratinocytic hyperpigmentation, nuclear enlargement and prominent nucleoli

Clinical description

=========================================================================

● Papule or macule, tan-brown, uniformly pigmented, small (0.6 cm or less)

● Often erosion or ulceration if adjacent to a hair follicle, with a granulomatous response or scale crust

Micro description

=========================================================================

Intraepidermal component:

● Junctional nests of melanocytes uniform in size, distributed at the tips of the rete ridges

Dermal component:

Type A cells

● In superficial dermis

● Pigmented epithelioid cells with well defined cell boundaries

● Abundant eosinophilic to amphophilic cytoplasm containing coarse melanin granules

● Uniform round/oval nuclei slightly smaller than that of adjacent keratinocytes

● Finely dispersed chromatin

● Delicate nuclear membrane

● No/small distinct eosinophilic nucleoli

Type B cells

● In intermediate dermis

● Cells more lymphoid than epithelioid

● Decreased cytoplasm with no melanin

● Smaller and slightly hyperchromatic nuclei with dispersed chromatin and no nucleoli

Type C cells

● In deep dermis

● Spindled, fibroblast-like or schwannian cells with oval nuclei and bland chromatin

● Single cell infiltration of superficial reticular collagen

Maturation

● Deeper portion of lesion has smaller cells with less pigment and less atypia

● Deep cells grow in smaller sized nests or single cells

● May resemble neural tissue

Traumatized nevi

● Features include parakeratosis (92%), dermal telangiectasias (61%), ulceration (51%), dermal inflammation (49%), melanin within stratum corneum (24%), dermal fibrosis (25%), pagetoid spread of melanocytes limited to the site of trauma (20%) or away from areas of trauma (8%) (Am J Dermatopathol 2007;29:134)

Micro images

=========================================================================

Clusters of nevus cells in neck node of patient with oral squamous cell carcinoma

Positive stains

=========================================================================

● MelanA in type A and B but not type C cells

● S100, HMB45 in the intraepidermal and superficial dermal component

Molecular / cytogenetics

=========================================================================

● BRAF mutations in 75% of congenital and acquired nevi (Am J Dermatopathol 2007;29:534), have clonal genetic changes (Hum Path 2002;33:191)

Videos

=========================================================================

● DermLectures.com, Recurrent nevi

End of Skin-Melanocytic Tumors > Nevi - general

This information is intended for physicians and related personnel, who understand that medical information is often imperfect, and must also be interpreted in the context of a patient's clinical data using reasonable medical judgment. This website should not be used as a substitute for the advice of a licensed physician.

All information on this website is protected by Copyright, (c) 2001-2009, PathologyOutlines.com, Inc. Information from third parties may also be protected by copyright. Please contact us at copyrightPathOut@gmail.com with any questions.