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What does LCMN Mean?

Let's Break it Down.

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.


GThe 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.

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) nevus on the head or a 2” (5cm) nevus 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.

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. 

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 or naevi) in the broad sense, means birthmark and can be used to describe virtually any mole or birthmark. On this website, when you see the word "nevus", it generally refers to LCMN. 

Trunk Nevus
Trunk Nevus
Foot Nevus
Hand Nevus

Medical Challenges Associated with Large CMN

One of the primary medical challenges presented to people with large nevi is lack of accurate information provided by many professionals.

Because it is a relatively rare condition, most doctors have never had experience with large congenital melanocytic nevi (LCMN). Misinformation is often more common than not, and many new parents are given an incorrect and often frightening prognosis, or simply not given information at all. Nevus Outreach was formed to help provide accurate information about LCMN.

How do I know if I have NCM?

If you have a large nevus or multiple congenital nevi, and you have any of these neurological symptoms listed, ask your doctor to screen you for NCM. NCM can be detected on an MRI if it is done correctly. 

Here is a paper about MRI scans for NCM.

More Than Skin Deep

Because it is primarily a skin disease, it is common for people, including some doctors and insurance companies, to think of LCMN as only an appearance challenge. However, there can be more to it than that. Here are some other things that can happen with LCMN.

Malignant Melanoma

The life-time risk of a person with LCMN developing a melanoma is between 2-5%.

Between 2-5% of individuals with LCMN will develop a melanoma within the nevus or in the central nervous system. It remains impossible to predict which person with a LCMN will develop a melanoma but some insights are emerging. Individuals with very large LCMN, with thick and nodular LCMN, and those with many satellite nevi appear to be at higher risk as compared to those individuals with smaller LCMN that are flat and homogeneous brown in color.

Neurocutaneous Melanocytosis (NCM)

(This used to be called neurocutaneous melanosis, but we’re talking about the same thing).

People with large nevi, and also people who don’t have a large nevus but who were born with numerous smaller congenital nevi, can have melanocytes (nevus cells) in their central nervous systems (their brains and/or spinal cords). These cells produce melanin. Melanin does not particularly belong in your brain, and it can cause complications when present.

It is estimated that 93% of people who have a large nevus or multiple congenital nevi do not have NCM. More than half (60%) of the remaining 7% who do have NCM, don’t have complications from it, even though the melanin is present in their brain or spinal cord. The few who do have complications usually have a relatively good long term prognosis. Many of those with complications have seizures caused by NCM but no other symptoms. If the seizures can be controlled, the patient can lead a relatvely normal life.

Occasionally, a person with NCM may have complications so severe that their prognosis is not so good. About 1% of people with a giant nevus cannot survive these complications. These other symptoms include hydrocephalus, unconsciousness, vomiting, and certain reflex and eyesight issues.

What can be done about NCM?

There is no treatment for NCM itself. 

There is no treatment for NCM itself. There are various things that can be done for various symptoms. In some cases, removing melanin deposits from the brain appears to be able to stop seizures permanently, but this depends on where the melanin is located. Some parts of the brain are inoperable. A person with symptomatic NCM should be under the care of a neurologist.

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