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congenital melanocytic nevus
May be premalignant lesions, especially giant melanocytic nevi.
Etiology:
1) developmental defect in neural crest-derived melanoblasts
2) defect problably occurs after 10 weeks in utero, but before 6th uterine month
Epidemiology:
1) present at birth
2) some lesions may become visible after birth "fading in" as a large lesion over a period of weeks (tardive)
3) equal prevalence in males & females
4) all races
5) 1% of white newborns - most < 3 cm in diameter
Clinical manifestations:
1) present at birth
2) isolated lesions, may be found on any skin surface
3) variably sized, may cover entire body parts
4) medium-dark brown, variegated color across lesion
5) generally round or oval with regular or irregular borders
6) generally a plaque with rough or lobulated surface, increasingly so with time
7) coarse hair growth
8) may involve leptomeninges if large lesion occurs on head
a) seizures
b) focal neurologic deficits
c) obstructive hydrocephalus
Differential diagnosis:
1) common acquired melanocytic nevus
2) dysplastic melanocytic nevus
3) congenital blue nevus
4) nevus spilus
5) Becker's nevus
6) pigmented epidermal nevus
7) cafe-au-lait macules
Complications:
1) large or giant congenital melanocytic nevus
a) risk of melanoma is 6.3%
b) diagnosis generally made between 3-5 years of age
c) prognosis is poor
2) small lesions - lifetime risk of melanoma is 1-5%
Management:
1) small nevi not known to be present at birth should be assumed to be acquired & managed according to appearance
2) atypical appearing lesions should be surgically excised
3) small congenital melanocytic nevi should be removed before age 12
4) large nevi > 1.5 cm
a) periodic follow-up for life
b) prophylactic surgical excision
1] excision with full-thickness skin graft as indicated
2] swing flaps, tissue expanders for large lesions
5) giant lesions
a) risk of developing melanoma is significant before age 3-5
b) lesion should be excised as soon as possible
c) techiniques using patients own skin grown in tissue culture
d) tissue expanders
General
melanocytic nevus (mole)
References
- Saunders Manual of Medical Practice, Rakel (ed), WB Saunders,
Philadelphia, 1996, pg 960-61
- Color Atlas and Synopsis of Clinical Dermatology, Common
and Serious Diseases, 3rd ed, Fitzpatrick et al, McGraw Hill, NY,
1997, pg 187-91