Nevus is a non-specific term for a pigmented skin lesion. Nevi occur when there is a benign or dysplastic proliferation of melanocytes. Melanocytes are melanin-producing dendritic cells found within the epidermis and dermis. Nevi are further classified as congenital, acquired, or dysplastic. Congenital and acquired nevi are generally benign with low malignant potential. Dysplastic nevi are associated with a 3 to 20-fold risk of transforming into melanoma.

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Nevus NCI

Image: Nevus NCI by National Cancer Institute. License: Public Domain


Classification: Nevi 

Classification    Type Description
Acquired Acquired melanocytic nevi
  • Described later (see following section)
Atypical or dysplastic nevi
  • Described later (see following section)
Congenital 

(at birth or shortly after birth)

Congenital melanocytic nevi
  • Benign neoplasm of melanocytes
  • Occurs in 1-3% of newborn infants
  • Black/tan lesions
    • May occur in any cutaneous location
    • +/- irregular border
    • +/- ↑ hair growth 
  • Have malignant potential 
    • Risk of melanoma development is associated with size of nevus
Congenital dermal melanocytosis
  • Benign neoplasm of melanocytes
  • Also called “Mongolian spots”
  • Blue-grey patches with indefinite borders
    • Sacral/buttock area
  • More common in Asian and African Americans
Nevi of Ito 
  • Benign neoplasm of melanocytes
    • Preferentially affects areas innervated by the posterior supraclavicular nerves
      • Often shoulder and the upper chest
  • More common in Asian and African Americans
Nevi of Ota
  • Benign neoplasm of melanocytes
    • Preferentially affects areas innervated by the 1st and 2nd division of the trigeminal nerve
      • Often affecting the sclera 
    • Usually more mottled appearance 
  • More common in Asian and African Americans
  • Have malignant potential
    • Requires yearly ophthalmologic examinations

Video

Nevus (Moles) in Children by Brian Alverson, MD

Congenital melanocytic nevus

Image: Congenital melanocytic nevus. Brown papule on the nose, which developed shortly after birth. The brownish exophytic lesion is well circumscribed. By M. Sand, D. Sand, C. Thrandorf, V. Paech, P. Altmeyer, and F. G. Bechara. License: CC BY 2.0

Nevus of Ito

Image: Nevus of Ito: Blue-grayish macule with stained aspect. By Anais Brasileiros de Dermatologia. License: CC BY 4.0

Nevus of Ota

Image: Nevus of Ota: As seen, often affects the sclera. By Brian Boxer Wachler. License: CC BY-SA 4.0

Acquired Melanocytic Nevi

Etiology:

  • Benign neoplasms of melanocytes that arise later in life (after 6 months of age)
  • Melanocytes: melanin-producing cells in the basal layer of the epidermis

Risk factors: 

  • Family history
  • Fair complexion 
  • Sun exposure 

Pathophysiology:

  • Three types of acquired melanocytic nevi as a progression
  • Junctional nevus → compound nevus → intradermal nevus
  • Begins as a group of melanocytes at the dermo-epidermal junction (junctional nevus)
  • Grows and extends into the dermis (compound nevus)
  • Eventually, the junctional component is lost resulting in an intradermal nevus.
  • As the cells migrate deeper, they become smaller and produce less melanin (cellular senescence).

Diagnostics:

  • Based on clinical appearance

Management:

  • Most acquired nevi remain benign
  • However, having a large number of acquired nevi increases risk for melanoma.
Acquired melanocytic nevi overview
Types Description Presentation
Junctional nevi

(See image 1a and 1b.)

  • Melanocytes are found at the dermo-epidermal junction 
    • Large cells and produce melanin  
  • Most common mole in children
  • Well-demarcated, brownish macules that are minimally raised
  • Uniformly pigmented 
    • Tan to brown/black
  • Usually ≤ 5 mm
Compound nevi 

(See image 1c and 1d.)

  • Melanocytes are found at the dermo-epidermal junction and intradermally  
    • Smaller cells and produce less melanin  
  • Pigmented papules
  • Smooth, dome-shaped
    • Similar to junctional nevi but with elevation and lighter color
Intradermal nevi

(See image 1e.) 

  • Melanocytes are found intradermally 
    • Small cells and produce little to no melanin  
  • Most common mole in adults
  • Skin-colored to tan
  • Similar to compound nevi
    • Dome-shaped or papillomatous
    • +/- terminal hair 
    • +/- fibrotic texture 
    • +/- speckled, brown pigmentation
Non-Melanoma

Image: Natural history of acquired melanocytic nevi. Ordinary nevi begin as uniformly tan or brown macules, 1 to 2 mm in diameter (a), expand to a larger macule (b), progress to a pigmented papule that may be minimally (c) or obviously (d) elevated above the surface of the skin, and terminate as a pink or flesh-colored papule (e). These lesions are junctional (a,b), compound (c,d), and dermal (e) nevi, respectively. Note their smooth borders and clear demarcation from the surrounding skin. By Unknown author. License: Public Domain

Dysplastic or Atypical Nevi

Epidemiology:

  • Prevalence in white populations: 2–10%

Etiology:

  • Benign neoplasms of melanocytes
  • Often appear during puberty
  • Share some of the clinical features of melanomas
  • Asymmetry
  • Color variegation
  • Irregular borders
  • Diameter > 5mm
    • Associated with an increased risk of melanoma
    • 3 to 20-fold higher risk
Cancer

Image: Classical example of an atypical nevus with asymmetry, color irregularity and a diameter of more than 5 mm. By W. Bergman. License: CC BY-SA 3.0

Dysplastic Nevi

Image: Dysplastic Nevi. This large (7 by 11 mm) macular lesion displays an irregular, scalloped border, which is indistinct in some areas. In addition to hues of tan and brown, several pink areas (arrows) are present. The presence of pink colors in the macular portion of a melanocytic nevus is quite distinctive for dysplastic nevi. By National Cancer Institute. License: Public Domain

Risk factors:

  • Fair complexion 
  • Sun exposure 
  • Family/personal history of melanoma 
  • Familial atypical multiple mole and melanoma (FAMMM) syndrome

Pathophysiology: 

  • Development is primarily due to genetics.
  • Associated with activating NRAS or BRAF gene mutations

Diagnosis:

  • Usually made on a clinical basis, but dermoscopy or biopsy may be done to rule out melanoma
  • Distinctive clinical features based on “ABCDE criteria”
    • Asymmetry
    • Border
    • Color
    • Diameter
    • Evolution

Clinical presentation of Dysplastic or Atypical Nevi

(Should be tested against the ABCDE criteria)

Morphology 
  • Prominent macular component often with a papular center
Asymmetry (A) and Border (B)
  • Asymmetric shape
  • Irregular margin with indistinct border
Color (C)
  • Variegated color
Diameter (D)
  • Often larger than melanocytic nevi
    • ≥ 5 mm 
Evolution (E)
  • Generally remain stable
Location 
  • Most common location:
    • Trunk and extremities

Management and follow up:

  • Annual skin examinations
  • Encourage use of broad-spectrum sunscreen
  • Excision of suspicious lesions
  • Routine ophthalmologic examinations

Video

Benign Nevus and Dysplastic Nevus by Carlo Raj, MD

Differential Diagnosis

Seborrheic keratosis

  • Commonly occurs in the elderly
  • Benign squamous proliferation of immature keratinocytes
  • Well-demarcated, waxy, stuck-on appearance

Basal cell carcinoma: 

  • Malignant proliferation of basal cells in the epidermis
  • Pearly, nodular skin lesions with telangiectasias and slow growth

Melanoma

  • Malignant transformation of melanocytes 
  • Clinical features that differ from atypical or dysplastic nevi
    • Shades of blue-gray
    • “Ugly duckling sign:” distinct nevi differing from nevi pattern
    • Newly developed pigmented lesion in >40 years old
  • Histopathology: atypical melanocytes in the dermis

Dermatofibroma

  • Mesenchymal growth of the skin where skin fibroblasts are the major constituents
  • Firm, indurated, mobile nodule measuring 0.5-1 cm in size
  • “Buttonhole” sign
    • Upon lateral compression, a dimple-like depression occurs in the overlying skin

Café-au-lait macule

  • Flat, pigmented skin lesions
  • No clinical value but may be associated with type 1 neurofibromatosis and McCune-Albright syndrome
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