Congenital Melanocytic Nevus


Congenital Melanocytic Nevus, Congenital Melanocytic Nevi, Garment Nevi, Giant Congenital Nevi, Birthmark, Giant Hairy Nevi, Bathing Trunk Nevi, Congenital Nevus, Congenital Nevi

  • Epidemiology
  1. Prevalence: Up to 2% of newborns
  • Pathophysiology
  1. Neural crest Melanocytes and their precursors with disrupted migration
  • Signs
  1. Brown to black lesions that are typically flat (but can be elevated, and may thicken as children get older)
  2. Size can vary from a few millimeters to several centimeters to involving an entire region of the body
  3. Hair is variably present
  4. Typically with uniform pigmentation
  1. Variant of Congenital Nevi
    1. Hairless round to irregularly shaped brown nevus
    2. Larger nevus contains 1-3 mm dots of dark brown pigmentation (may be elevated)
    3. Diameter ranges from 1-20 cm
  2. Malignant transformation is uncommon but can occur
    1. Size of lesion directs management - follow the same protocols for Congenital Nevi based on size below
    2. Observe and biopsy or excise lesions if atypical
  • Lab
  • Histology
  1. Localized to the lower Dermis
  • Differential Diagnosis
  1. Small Congenital Nevi <1.5 cm (adult size) rarely progress to Melanoma
  2. Medium size lesions may develop Melanoma in up to 0.7% of cases
  3. Giant Congenital Nevi >20 cm (adult size) carry up to a 7% lifetime risk of Melanoma
    1. Half of Melanomas in Giant Congenital Nevi occur by age 3-5 years
  • Management
  1. Large Congenital Melanocytic Nevi (Giant Congenital Nevi)
    1. Criteria
      1. Garment Nevi or Giant Congenital Nevi: >14 cm in infants (>20 cm in adults)
      2. Large Congenital Nevi: >12 cm head or >7 cm elsewhere in infants (>20 cm adults)
    2. Precautions
      1. As noted above, Melanoma development in Giant Congenital Nevi occurs before age 3-5 years in 50% of cases
      2. Excise these lesions as infants or young children (before age 3-5 years)
      3. Observation may miss transformation due to depth of nevus
    3. Protocol
      1. Excise lesion as soon as possible (or currettage during the first 2 weeks of life)
      2. Close observation for recurrence (excision does not eliminate risk completely)
  2. Medium Congenital Melanocytic Nevi
    1. Criteria: 0.5 to 7 cm in infants (1.5 to 20 cm in adults)
    2. Protocol
      1. Close observation by dermatology
      2. Consider Punch Biopsy for risk stratification
        1. Deeper dermal lesions may elude early detection of malignant transformation despite observation
  3. Small Congenital Melanocytic Nevi
    1. Criteria: <0.5 cm in infants (<1.5 cm in adults)
    2. Low malignant potential (especially pre-Puberty)
    3. Protocol
      1. Close observation by primary provider
      2. If excised, it is safe to wait until after Puberty