A junctional nevus is a non-cancerous type of growth made up of melanocytes. Junctional nevi are usually seen in individuals of lighter skin complexion and can be found anywhere on the body. Most junctional nevi are called acquired because they develop in children or young adults. A nevus that develops shortly after birth is called a congenital nevus. Another name for this type of growth is a mole. Mole is a common term used to describe any kind of growth made up of melanocytes.
Your skin is the largest organ in your body. It is made up of three layers: epidermis, dermis, and subcutaneous fat. The surface and the part you can see when you look at your skin is called the epidermis. The cells that make up the epidermis include squamous cells, basal cells, melanocytes, Merkel cells, and cells of the immune system. The squamous cells in the epidermis produce a material called keratin which makes the skin waterproof and strong and protects us from toxins and injuries.
The dermis is directly below the epidermis. The dermis is separated from the epidermis by a thin layer of tissue called the basement membrane. The dermis contains blood vessels and nerves. Below the dermis is a layer of fat called subcutaneous adipose tissue.
Melanocytes are specialized cells that are normally found at the very bottom of the epidermis. They are responsible for producing a dark pigment called melanin that helps protect our skin from the sun’s ultraviolet light. The amount of melanin in a person’s skin determines their skin colour – people with light skin produce little melanin and people with darker skin produce more melanin.
Most junctional nevi are flat and round to oval in shape. The border between the nevus and the surrounding normal skin is usually well defined and easy to see. Without a microscope, these growths can look pink, brown, black, or blue with most only showing a single colour.
This diagnosis can only be made after a tissue sample is removed and examined under the microscope by a pathologist. This usually involves removing the entire nevus in one piece along with a small amount of surrounding normal-appearing skin.
When examined under the microscope, junctional nevi are made up of large round melanocytes. The melanocytes in a junctional nevus are found in the epidermis either in small groups called nests or spread out as single cells near the bottom of the epidermis.
Over time, the melanocytes in a junctional nevus will spread down towards the dermis. When the melanocytes are found in both the epidermis and the dermis, the growth is called a compound nevus. When the melanocytes are found only in the dermis, the growth is called a dermal (or intradermal) nevus.