Dermal nevus

by Allison Osmond MD FRCPC and Archan Kakadekar MD
March 9, 2023

What is a dermal nevus?

A dermal nevus is a non-cancerous type of skin tumour made up of specialized cells called melanocytes. The tumour is called ‘dermal’ because the melanocytes are only found in a layer of skin called the dermis. Dermal nevi (more than one nevus are called nevi) are usually seen in individuals of lighter skin complexion and can be found anywhere on the body. 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.

skin normal no adenexa

What causes a dermal nevus?

A dermal nevus is caused by a combination of prolonged exposure to UV light (typically the sun) and genetic susceptibility.

Is a dermal nevus a type of cancer?

No. A dermal nevus is a non-cancerous growth.

Can a dermal nevus turn into melanoma over time?

About one-third of all melanomas (a type of skin cancer made up of melanocytes) are believed to arise from previously non-cancerous melanocytic nevi. However, because dermal nevi are so common, the actual risk of a dermal nevus turning into melanoma over time is very low.

What is the difference between a congenital nevus and an acquired nevus?

A dermal nevus that develops shortly after birth is called a congenital nevus. A dermal nevus that develops later in life (as a child or an adult) is called an acquired nevus.

How does a dermal nevus form?

Most dermal nevi develop from junctional and compound nevi. In a junctional nevus, the melanocytes are only found in the epidermis. Over time, the melanocytes in a junctional nevus spread down towards the dermis forming a compound nevus. Eventually, all of the melanocytes move into the dermis creating a dermal nevus.

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

A dermal nevus can be flat or raised. The surface of the nevus is usually smooth and may contain hair. Most dermal nevi are light in colour and the colour may be lost slowly over time. The border between the nevus and the surrounding normal skin is usually well-defined and easy to see although it may be more difficult to see if the colour of the nevus is similar to the surrounding skin.

How is this diagnosis made?

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, dermal nevi are made up of melanocytes. The melanocytes in a dermal nevus are found only in a layer of skin called the dermis. The melanocytes form groups called nests although single cells may also be seen. The melanocytes near the top of the dermis are usually large and round while those near the bottom are often smaller and thinner. This change in size and shape is called maturation and is a normal finding in a dermal nevus.

Dermal nevus
Dermal nevus. Small round groups of melanocytes can be seen in the dermis at the bottom of the image.
A+ A A-