Melanocytic nevus typically begins as a flat, dark, junctional nevus. These junctional nevi expand to be 3-4 mm across. They typically stop growing laterally at that point and begin to become raised, the compound nevus.
The nevus continues to become more elevated, losing melanocytes over time.
The soft, pale, polypoidal lesion is called a dermal nevus.
Most dermal nevi eventually drop off the skin in old age.
Two types of nevi, the dysplastic nevus and the Spitz nevus, don't seem to disappear with time.
Dysplastic nevi continue to expand as flat "junctional" nevi with increasing irregularity of color and edge. Dysplastic nevi can evolve into malignant melanomas.
Spitz nevi are a special nevus variant, showing a highly atypical histology that pathologists may confuse with malignant melanoma. Spitz nevi are usually red-brown papules or nodules on the face of children, although dark-brown-black lesions have been described, as well as lesions occurring well into middle age.
There are four indications for removing nevi:
- suspicion of melanoma
- high risk of evolution to melanoma
- chronic irritation annoying to the patient
- for cosmetic reasons.
It is good practice to submit all excised nevi for histologic examination.