About nevus and nevi
A nevus (pl. nevi), or mole, is a benign growth comprised of aggregates of pigment producing cells. They vary greatly in appearance, size, pigmentation, and surface characteristics. However, each individual nevus is uniform in border, color, and texture, distinguishing it from a malignant melanoma. There are three types of nevi: junctional, compound and intradermal.
Junctional. A junctional nevus is macular (flat). The nevus cells are limited to the lower layers of the epidermis.
Compound. A compound nevus is papular (it can be felt). Nevus cells are found in both the epidermis and dermis.
Intradermal. The intrademral nevus is also papular (it can be felt). The nevus cells, as implied by the name, are restricted to the dermis.
Nevi can be either congenital (present at birth) or acquired, with most appearing between the ages of 6 months and 35 years of age. Large congenital nevi (>20 cm diameter) can transform into malignant melanoma and removal is often recommended; Small congenital nevi are not at risk of transformation and can be left in place, though this remains controversial.
The dysplastic nevus, also known as an atypical mole, is dealt with under its own heading.
With what can a nevus be confused?
It is critical to distinguish a benign nevus from malignant melanoma. The key feature that distinguishes a nevus as compared to a malignant melanoma is regularity of color, border, and surface texture. A junctional nevus can be confused with other macular pigmented macules, such as a freckle or lentigo. A compound or intradermal nevus can be confused with other papular growths, such as a seborrheic keratosis or dermatofibroma or, when flesh colored, a basal cell carcinoma, skin tag (acrochordon), or neurofibroma.
How is a nevus diagnosed?
A nevus may be diagnosed clinically by your dermatologist. If there is any doubt as to the diagnosis, a biopsy will be performed to rule out malignant melanoma.
How is a nevus treated?
Other than for cosmetic reasons, removal of nevi (except certain congenital nevi) is not required. A nevus that bleeds, itches, or has recently changed in color, size or texture, should be removed with an excisional biopsy with 2-3 mm margins. Removal of a non-worrisome nevus for cosmetic reasons can be accomplished by shave biopsy. Excision of large congenital nevi is technically challenging; therefore, these lesions are sometimes followed clinically with excision only of newly developing nodules within the nevus.
What is the prognosis for a nevus?
The risk of developing malignant melanoma is increased in individuals with a large number of nevi. Some nevi resolve on their own, most likely due to an immune-mediated reaction. The development of a depigmented “halo” around the nevus often precedes its dissapearance.
How is a nevus prevented?
There is no way to prevent nevus formation. Large congential nevi should be excised to prevent transformation to malignant melanoma, as should suspicious nevi that have changed in color, size or texture, or that bleed or itch.