Nevus, or as it is often called in common language, mole, is a benign neoplasm that can affect any of the cell types that populate the skin surface or epidermis. Examples of types of nevi include epidermal nevi and connective tissue nevi. In addition there are nevi that affect the skin melanocytes. This type of nevi is very common and will be the topic of this article.
Melanocytes are types of cells that populate the epidermal layer of the skin. They are so called due to their role in producing and secreting the pigment melanin. This pigment is responsible for imparting the skin its characteristic brown color. The difference between light skin and dark skin lies in the amount of the pigment melanin in the skin. Dark skin has more concentration of this pigment.
Melanocytic nevi are derived from melanocytes. Therefore, they are usually colored from brown to blue and black. Some of the melanocytic nevi have the potential to become malignant. There are two types of nevi that can become malignant. These are: congenital melanocytic nevi and atypical nevi, or as it is often called, dysplastic nevi.
Atypical nevi, like their counterpart the congenital nevi, have a tendency to become malignant. I will discuss, in addition to these, two other types of nevi that do not have the potential to become malignant such as the rare condition Becker nevus. Congenital nevi are so called because they are present on the body from the moment of birth or shortly after that.
It is estimated that 1% of the population has congenital mealnocytic nevi. Congenital melanocytic nevi are usually large in size and range in color from light brown to black. They also become hairy often. Their main effect is disfigurement. They carry a relatively high risk of developing malignancy. The risk of developing malignancy in this type of mole is estimated at 5%.
The other type of nevi that has potential for developing malignancy is the atypical nevus or the dysplastic nevus. They differ than the normal non-malignant mole in their type of pigmentation. In addition, there is nonuniformity in shape of these moles. Other than these two types of moles and which carry the potential for malignancy I will discuss some other types and which do not carry the risk for developing malignancy.
Junctional nevi are nevi cells that are located at the border between the epidermis and the dermis. They are usually colored. Their color range from light brown to dark brown. Their shape is uniformly oval or round and is usually symmetrical. Compound nevi are nevi cells that are located in or have moved toward the dermal layer. They have a variable degree of pigmentation. Thie color is usually uniform like the junctional nevi. They may occur at any part of the skin.
Dermal nevi are cells of nevi that populate the dermal layer of the skin. They are dome shaped and can be skin colored or pigmented. Their structure can be mistaken for nodular melanoma which is also dome shaped and pigmented. Spitz nevus is also similar to nodular melanoma and to dermal nevus with red to brown color. It is rounded nodular that is usually present on the face of small children.
They grow rapidly in their initial stage. They resemble nodular melanoma if pigmented in particular. Halo nevi are characterized by a nevus that is surrounded by white background of depigmentation that surrounds the nevus. The white spot is probabley an autoimmune reaction against the melanocytic cells of the skin neighboring the nevus.