What is a Congenital Melanocytic Nevus (CMN)?

A CMN is a pigmented lesion of the skin present at birth or within the first few months of life.  They are proliferations of benign melanocytes that arise during development.  They are present in 1% of white newborns and the majority of these are <3 cm in diameter.  Large or giant CMN occur in approximately 1 of 20,000 births.

What are the physical characteristics of a CMN?

They usually distort the skin surface to some degree becoming plaque like with or without coarse dark brown or black terminal hair growth.  The boarders often are geographic and irregular.   Large lesions may be wormy or soft in quality.  They can be light to dark brown in color.  They vary in size from small to giant.  

What is the treatment?

Many are surgically removed for aesthetics, but larger ones are excised for prevention of cancer.   The risk of melanoma developing within a CMN seems to correlate with the size of the nevus.  For patients with large CMN, risk of developing melanoma is approximately 5% over a lifetime.