What is a Large/Giant Congenital Melanocytic Nevus?
What does CMN mean? Let's Break it Down.
LCMN: Large. Congenital. Melanocytic. Nevus.
Since nevi can be found on any part of the body, and grow as the body grows, the term large can be difficult to define. Doctors don’t all use the same definitions. Here are the most common ones - a doctor may use any of these in defining the size of a nevus.
A nevus may be described as large if:
- It would take more than one surgical excision to remove. Surgeons and others involved with the removal of nevi, sometimes use this definition.
- It covers more than 2% of the patient’s total body surface area, or is larger than the palm of the patient’s hand.
- It measures over 8” (20cm) at its largest point on a fully-grown adult. When applying this definition to a newborn or child, the nevus is large if it is expected to be this size by adulthood. For example, a 3” (7cm) lesion on the head or a 2” (5cm) lesion elsewhere, noted at birth, will grow to be at least 8” by adulthood. Therefore these would be considered large nevi at birth.
- It covers a large portion of a major anatomical site. Thus, nevi on the head, legs or arms may be categorized as large even if they do not meet the previous definitions.
The term giant is sometimes used when describing nevi. A giant nevus covers a very large part of the body, usually involves the torso, and is usually accompanied by a number of satellite nevi. Satellite nevi (or just satellites) are smaller melanocytic nevi. When a child is born with a giant nevus, it is common for satellite nevi to be present at birth. It is also common for satellite nevi to appear after birth. Sometimes during diagnosis, doctors may use a large number of satellites to support their diagnosis of a large or giant congenital melanocytic nevus (cmn). Sometimes a nevus can look like a large mole or a large birthmark.
Congenital simply means that it is present at birth. Sometimes people get confused about the difference between congenital and hereditary. Hereditary means you get if from your parents and/or pass it along to your kids. There is no evidence that congenital nevi are hereditary. We know of cases of identical twins, where one child has a large nevus and the other does not. We know of no cases where identical twins both have a large nevus. We know of no cases where a person with a giant nevus has either a parent or a child who also has one.
Melanocytic means that it is pigment-based. Melanin is the pigment found in human skin. Normally, melanin is distributed fairly evenly throughout the skin. Congenital melanocytic nevi (cmn), on the other hand, are made up of pigment-producing cells called nevomelanocytes. These cells are not evenly distributed. When many nevomelanocytes are clumped together, they can result in moles on the skin because of the higher concentration of melanin (pigment).
Nevus (also spelled naevus; plural nevi) in the broad sense, means birthmark and can be used to describe virtually any mole or birthmark.