Core Dermatology Diagnoses / CategoriesNeoplastic Benign and Malignant

Nevus (including congenital melanocytic nevus)

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Publish date: Posted on
Last updated: May 25, 2022

Keywords #

nevus
melanocytic nevus
congential melanocytic nevus

Diagnosis #

The term “nevus” refers to a collection of cells; the type of nevus is determined by the cells involved (e.g. melanocytic nevus, epidermal nevus, sebaceous nevus)This paper will mainly discuss melanocytic nevi. Melanocytic neviare more common on sun-exposed skin, as ultraviolet light plays a major role in their induction.[1] Nevi can take on many forms (e.g pigmented vs non-pigmented) and have thus been subcategorized under many labels (melanocytic, spitz, halo, blue, etc.).[1]Melanocytic nevi are characteristically pigmented, and can either be congenital (present at birth or shortly after) or acquired.

Acquired nevi, including melanocytic nevi, are typically small (<6mm), asymptomatic, well-circumscribed macules, papules, or nodules.[1,3] They are symmetrical with uniform color(typical pigment network).[3] They have a typical pattern of maturation. Most are obtained in the first three decades of life.[3]They stabilize quickly in size and then slowly regress with age. Some may disappear entirely.[3]

Congenital melanocytic nevi (CMN) are present at birth or shortly after.[1] They are often flat and tan-to-brown in color, but may change over time and vary significantly in size and morphology.[1] About half of these lesions will develop significant overlying hair.[3]CMNs can be larger than acquired nevi.[1] Indeed, nevi greater than 1cm in length are more likely to be congenital, atypical, or melanoma.[1]There is a greater risk of malignant transformation in CMNs when compared with acquired melanocytic nevi, especially in large (>20cm) or giant CMN (> 50cm).[3]

Key Concepts #
  • Nevi, including congenital melanocytic nevus, are typically benign. However, some may become malignant.[4]
  • CMN have an increased risk of malignant transformation, especially in large (>20cm) or giant CMN (> 50cm), and should be monitored closely.[3]
  • Nevi should be screened for malignant transformation by monitoring their symmetry, borders, pattern of color (pigment network), diameter (>6mm), and evolution over time.[5]
  • Nevi greater than 1 cm in length are usually congenital, atypical, or melanoma.[1]
  • Individuals with > 50 nevi are at greater risk of developing melanoma, and should thus receive annual skin exams.[6]
  • Treatment of nevi is usually observation, though some may require biopsy or removal.[5]
Epidemiology #

Nevi are one of the most common benign tumors in humans. They are more common in Caucasian populations and less common in black and asian populations.[1]When they do occur in black and asian populations, they are more likely to be found on the palms and soles.[1]

Most acquired nevi appear in early childhood and reach a maximum number in the 3rd to 4th decade of life.[3] There is a subsequent decline in number as one ages.[3] Patients with greater than 50 nevi on their body are at increased risk of developing melanoma.[6]

Congenital melanocytic nevi (CMN) are present in 2-3% of all newborns.[3] There is a greater risk of malignant transformation in CMNs when compared acquired melanocytic nevi.[3] The incidence of this event is 1-2% overall.[3] While the incidence of melanoma in small CMN is low, it is much higher for large (>20cm) and giant CMN (> 50cm).[1,3]The estimated incidence is between 2% and 15%.[1,3]The majority of these melanomas develop in the first decade of life.[3]

Clinical Features #
  • Nevi generally appear as small(<6 mm), well circumscribed macules, papules, or nodules.[1,3,5]
  • Nevi can vary in color; they are commonly brown but may also be blue, black or pink to skin colored.[1,3,5]
  • Nevi may occur anywhere on the body. However, there is a predilection for sun-exposed-skin.[1]
  • Nevi are commonly asymptomatic, but may itch or cause cosmetic concern.[1]
  • Acquired nevi are almost always less than 1 cm in diameter.[1,3]
  • Congenital melanocytic nevi are usually less than 1 cm in diameter but can be greater than 1cm.[1,3]
  • Many congenital melanocytic nevi will develop significant overlying hair.[3]
Differential Diagnoses #
Diagnostic Workup #

No diagnostic workup is indicated for most nevi, as the diagnosis is clinical and they are typically benign.[3] Skin biopsy should be performed if there is suspicion of malignant change.[5] Greater than 50 nevi present on skin exam should prompt full body skin exams yearly, as these patients are at greater risk of developing melanoma.[6]

Treatment #

No treatment is indicated for common acquired nevi, as they are generally benign.[3] Malignant transformation may necessitate surgical removal.[5] Large (>20cm) or giant (>50cm) CMN may require frequent surveillance or staged excision given their increased risk of malignant transformation.[1,3]

References #
  1. Swanson DL. Nevi and Melanoma. In: Soutor C, Hordinsky MK, eds. Clinical Dermatology. McGraw-Hill Education; 2017. accessmedicine.mhmedical.com/content.aspx?aid=1177005832
  2. Melanocytic nevi and neoplasms. In: James WD, Elston D, Treat JR, Rosenbach MA, Neuhaus I, eds. Andrews’ Diseases of the Skin: Clinical Dermatology. 13th ed. Elsevier; 2019.
  3. Cuda JD, Moore RF, J. Busam K. Melanocytic Nevi. In: Kang S, Amagai M, Bruckner AL, et al., eds. Fitzpatrick’s Dermatology. 9th ed. McGraw-Hill Education; 2019. accessmedicine.mhmedical.com/content.aspx?aid=1161336104
  4. Bolognia J, Schaffer JV, Cerroni L. Dermatology. Fourth edition.. Philadelphia, Pa: Elsevier; 2018.
  5. Pigmented growths. In: Marks JG, Miller JJ. Lookingbill and Marks’ Principles of Dermatology. Sixth edition. Elsevier; 2019.
  6. Psaty EL, Scope A, Halpern AC, Marghoob AA. Defining the patient at high risk for melanoma. Int J Dermatol. 2010;49(4):362-376. doi:10.1111/j.1365-4632.2010.04381.x
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