This article will help you read and understand your pathology report for dysplastic nevus of the skin.
by Allison Osmond, MD, FRCPC and Archan Kakadekar, MD
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 normally found in the bottom layer 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.
A mole is a growth on the skin made up of melanocytes. Another word for mole is nevus. Pathologists use the word nevi to describe more than one nevus. A mole that develops at birth or early in life is called a congenital nevus. A mole that develops later in life is called an acquired nevus.
A dysplastic nevus is a type of mole that develops later in life, usually in adulthood. A dysplastic nevus is a benign (non-cancerous) type of growth but some can turn into a type of cancer called melanoma over time.
Dysplastic nevi are usually seen in individuals of lighter skin complexion and are typically found on the abdomen, upper back and shoulders, scalp, breasts, and buttocks. The risk of developing melanoma is higher for people with more than one dysplastic nevus.
Most dysplastic nevi are flat, and they can show a variety of colours including black, brown, red, and blue. The border between the mole and the surrounding skin is uneven which can make it hard to tell where the mole ends, and the normal skin begins.
When examined without a microscope, a dysplastic nevus can look similar to a melanoma. For that reason, your doctor may suggest removing the growth so that it can be examined by a pathologist under the microscope.
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 mole in one piece along with a small amount of surrounding normal appearing skin.
When examined under the microscope, dysplastic nevi are made up of specialized cells called melanocytes. The melanocytes in a dysplastic nevus may be found in the epidermis, dermis, or both. The word junctional is used to describe a nevus where all of the melanocytes are found in the epidermis. In contrast, the word compound is used to describe a nevus where the melanocytes are found in both the epidermis and the dermis.
A dysplastic nevus shares many features with an ordinary or non-dysplastic nevus. Both are made up of melanocytes and both can be junctional or compound. However, there are specific microscopic features that make a dysplastic nevus different and more concerning. Pathologists divide these features into two categories: architectural and cytologic.
Architecture describe how the cells in the nevus connect together and how the tissue around the cells is responding to the growth. At least some of these architectural features will be found in order to make the diagnosis of dysplastic nevus:
Cytology describes the look of the individual nevus cells which includes the body of the cell and the genetic material inside. At least some of these cytologic features will be found in order to make the diagnosis of dysplastic nevus:
Both the architectural and cytologic features will be given a grade which is a way of describing the difference between the nevus and normal, healthy melanocytes. Most pathologists divide the grade into three levels – mild, moderate, and severe. Some pathology reports will use the term high grade instead of severe. The grade is important because the risk of developing cancer is greater if severe or high grade features are seen.
Sometimes dysplastic nevi are accompanied by a host response by the cells of your immune system. This can be mild, moderate, or brisk. Usually a brisk host response is often associated with a high grade dysplastic nevus.
Dysplastic nevi with mild or moderate features do not require additional treatment. Dysplastic nevi with high grade features are usually removed with a 5 millimeter rim of normal skin. The normal skin is called the margin and it helps to ensure that all of the abnormal nevus cells have been removed.