Dysplastic nevus (skin)

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What is a dysplastic nevus?

A dysplastic nevus is a non-cancerous type of growth made up of specialized cells called melanocytes. Although it is considered non-cancerous, some can turn into a type of cancer called melanoma over time. 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.

Dysplastic nevi (more than one nevus are called 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. Most dysplastic nevi develop later in life, usually in adulthood. The risk of developing melanoma is higher for people with more than one dysplastic nevus.

The skin

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 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

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.

What does a dysplastic nevus look like when examined without a microscope?

Most dysplastic nevi are flat, and they can show a variety of colours including black, brown, red, and blue. The border between the dysplastic nevus and the surrounding skin is uneven which can make it hard to tell where the nevus 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.

How do pathologists make the diagnosis of dysplastic nevus?

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, 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.

How is a dysplastic nevus different from an ordinary (non-dysplastic) nevus?

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.

Architectural features

Architecture describes 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:

• Irregular nests – The melanocytes in a nevus are usually found in small round groups called nests. In a dysplastic nevus, the nests often have an irregular shape (they are less round) and they may be larger than the nests seen in an ordinary nevus.
• Bridging or fusing of nests – In an ordinary nevus, the nests of melanocytes do not touch. However, the nests in a dysplastic nevus may grow in a way where they start to touch or even join. Pathologists describe this as bridging or fusing of the nests.
• Lentiginous growth – Lentiginous is a word pathologists use to describe melanocytes spreading side by side as single cells along the bottom of the epidermis. A lentiginous pattern of growth is not normally seen in an ordinary nevus.
• Shouldering – The melanocytes in the epidermis of an ordinary nevus do not normally extend beyond the melanocytes deeper in the dermis. However, in a dysplastic nevus, the melanocytes may grow beyond the cells in the dermis creating the appearance of a shoulder at the top of the nevus.
• Dermal lamellar fibroplasia – This is a change that happens in the dermis immediately below the nevus. In a dysplastic nevus, the stroma becomes darker and more wavy than normal. Pathologists describe this as lamellar fibroplasia and it is an abnormal finding.

Cytologic features

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:

• Size of the nucleus – The nucleus is the part of the cell that holds the genetic material (DNA). The melanocytes in a dysplastic nevus may have nuclei that are larger than normal melanocytes.
• Nucleoli – Nucleoli are small round balls of genetic material inside the nucleus. The melanocytes in a dysplastic nevus may have easy-to-see nucleoli. Pathologists describe these nucleoli as prominent because they can be seen even at low magnification.
• Mitotic figures – Cells divide to create new cells. A cell that is in the process of dividing to create a new cell is called a mitotic figure. Mitotic figures are not usually seen in ordinary (non-dysplastic) nevi. In contrast, dysplastic nevi may have one or more mitotic figures.
• Atypia – Atypia is word pathologists use to describe a cell that looks different from the normal, healthy cells in that location. Atypia in a nevus is a sign of abnormal growth and is more often seen in a dysplastic nevus. Atypia in a nevus can mean that the melanocytes were larger, darker, or had an irregularly shaped nucleus compared to normal melanocytes.

Grade

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.

What happens next? ​

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.

by Allison Osmond MD FRCPC and Archan Kakadekar MD (updated July 2, 2021)