Skin-melanocytic tumor
Nevi
General

Author: Christopher Hale, M.D. (see Authors page)

Revised: 30 January 2017, last major update December 2014

Copyright: (c) 2003-2017, PathologyOutlines.com, Inc.

PubMed Search: melanocytic nevi [title] skin
Cite this page: General. PathologyOutlines.com website. http://pathologyoutlines.com/topic/skintumormelanocyticnevigeneral.html. Accessed February 22nd, 2017.
Definition / General
  • Congenital or acquired benign melanocytic proliferation
  • Dermoscopy: nevus type varies by skin type in whites (Arch Dermatol 2007;143:351)
  • 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)
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; much less common in Asians and Afro-Caribbeans
  • Can estimate total body count in 13 - 14 year olds by examining lateral arms (Am J Epidemiol 2007;166:472)
  • Two theories of nevogenesis: "Abtrofung" vs. "Hochsteigerung" (Arch Dermatol 2007;143:284)
Patterns associated with benign behavior
  • Small size, circumscription and symmetry
  • Nested proliferation with nests regularly distributed at tips of the rete ridges
  • Melanocyte nuclei smaller than in adjacent keratinocytes
  • Uniform cellular density throughout same level of lesion
  • Melanocytes decrease in size towards base of lesion ("maturation")
  • Coalescent eosinophilic globules (Kamino bodies) are associated with Spitz nevi
  • Absence of mitotic activity (particularly at base of lesion), although rare mitoses may be seen in benign nevi (J Cutan Pathol 2007;34:713, Am J Dermatopathol 2010;32:643)
  • Lack of necrosis and cytologic atypia
Clinical Features
  • 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;8:3)
  • Often accompanied by keratinous cysts, abscess or 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)
  • Large numbers of nevi are risk factor for melanoma (Int J Cancer 2009;124:420)
  • 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) and number of nevi in parents (Cancer 2003;97:628), although this does not necessarily mean that these factors are risk factors for melanoma
Prognostic Factors
  • May recur with incomplete excision (shave biopsy), usually within 3 months
  • Recurrent nevus ("persistent nevus") may resemble melanoma ("pseudo-melanoma") due to irregular scarring, lentiginous melanocytic hyperplasia, basilar keratinocytic hyperpigmentation, nuclear enlargement and prominent nucleoli (J Cutan Pathol 2011;38:503)
Case Reports
Treatment
  • 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
Gross Description
  • Papule or macule, tan-brown, uniformly pigmented and 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 morphology:
    • 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 morphology:
  • 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 morphology:
  • 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
  • Terminal differentiation recapitulates some aspects of Schwann cell development (Am J Pathol 1999;155:549)

    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

Images hosted on other servers:
Missing Image

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 Description