What Is A Giant Congenital Melanocytic Naevus?

A Giant Congenital Melanocytic Naevus is a rare skin change traditionally seen in young infants. This article will go through the causes, diagnosis, treatment, and complications of the condition.


Melanocytic Naevus, otherwise known as a mole, is a common skin lesion caused by the increased production of melanocytes in a particular area. A giant congenital melanocytic naevus (CMN) is a large mole that is present at birth. There are varied definitions for what exactly counts as a “giant mole”, but one definition is a mole that is above 20 cm in diameter in adults.1 Often, giant congenital melanocytic naevi are accompanied by smaller lesions across the surface of the skin.2 These are known as satellite lesions and occur in 78% of Giant Congenital Melanocytic Naevi cases.2 Smaller skin moles are considered to be common in young babies, but giant moles are rare. The estimated incidence of large or giant CMNs is between 1 in 20,000 newborns and 1 in 500,000 newborns.

How do they develop?

It is believed that moles develop whilst an individual is in the womb. Research states that this occurs due to genetic abnormalities causing an over-production of a type of cell called a melanocyte.1 Melanocytes produce a chemical called melanin, which is a skin pigment. This gives moles their darkened appearance.

How do giant CMNs differ from small CMNs?

CMNs that are small or medium-sized tend to be oval-shaped with clear borders. They will be the same colour throughout (most commonly brown) and be smooth. On the other hand, giant and large CMNs have different pigmentations throughout and a rough texture. Larger lesions may also have ulcers present within the structure.1 Larger CMNs can be unsightly to look at, and this can have a psychological impact on the affected individual. Over time, all types of moles may evolve. These can lead to colour changes, texture changes, and more. 

How are giant congenital melanocytic naevi diagnosed?

Giant CMNs are mostly diagnosed during a clinical examination. Measurements of the naevi are taken and looked at to see whether it fits the criteria for a giant CMN. If there is any doubt about whether the skin lesion is a giant mole, an instrument called a dermatoscope can be used to examine the lesion more closely.1 When using a dermatoscope, structures that differentiate a giant congenital lesion from a simpler mole can be seen.1 In addition to this, a skin biopsy can be used to diagnose any unusual lesions.1 This is where a small sample is taken from the lesion and is sent to the lab for closer inspection. Biopsy of the affected skin area can also be useful to ensure that the mole does not have a sinister cause, such as skin cancer.1

MRI scans with contrast are recommended for individuals with multiple congenital melanocytic naevi or those with more than 10 satellite naevi. This is because these individuals are more likely to have neurological complications.3

What skin lesions are similar to congenital melanocytic naevi?

Skin lesions that could be mistaken for CMN include:1

  1. Cafe au lait spots
  2. Lentigo
  3. Mongolian Spots
  4. Other types of moles

What are the complications of a giant congenital melanocytic naevus?

Complications are more common in larger congenital melanocytic naevi. Examples of complications include itching, ulceration, and systemic symptoms affecting other areas of the body.1


Occasionally, a giant congenital melanocytic naevus can lead to the development of a type of skin cancer called melanoma. When melanomas arise in smaller CMN, the risk is lower. However, in giant congenital melanocytic naevi, the risk is a lot higher.2 Studies have found that the reported survival over 5 years for 35 patients with melanoma was 34.3%, implying that the majority of such patients tended to pass away within 5 years.2

Neurocutaneous melanosis

Neurocutaneous Melanosis (NCM) is one of the more serious complications. This is a disorder that leads to the presence of congenital melanocytic naevi on the skin and tumours in the central nervous system. The tumours often consist of melanocytes, the same cells that can result in  Giant CMN.1 This can cause symptoms such as seizures, epilepsy, movement issues, sensory issues, and behavioural changes.4 There is also a rise in intracranial pressure,4 which leads to symptoms such as papilloedema, headache, and vomiting. This complication is usually diagnosed using MRI scans and specialist treatment is often needed.1

If a patient has symptoms such as nighttime bedwetting, tiptoeing etc. they should undergo an urgent evaluation by the neurologists and undergo specialist imaging.5 Patients who have NCM without any symptoms should be followed up by a neurologist at least once a year.5

What are the treatment options for giant congenital melanocytic Naevi?

Treatment options are mostly surgical. The gold standard treatment is to replace the skin and its full thickness. Replacement skin is usually taken from other areas of the body or expanding nearby skin to cover the surgical site. If the naevi is too big to be replaced, then surveillance is used. This is simply monitoring the lesion to ensure that none of the complications listed above develop. Psychological treatment is also recommended for all patients, along with physical treatment plans.


What are the risk factors for developing giant congenital melanocytic naevi/ who is more likely to get it?

According to studies, there is a slightly higher risk of getting Giant Congenital Melanocytic Naevi if the patient is assigned female at birth. Research has shown that the ratios for GCMN in female patients range from 1.17:1 to 1.46:1.2

Are giant congenital melanocytic naevi sinister/dangerous?

Giant Congenital Melanocytic Naevi are not dangerous individually. However, they can cause issues with self-image and self-esteem. They also can have dangerous complications such as melanoma and neurocutaneous melanosis.1 For more details on these conditions, please read the relevant section of this article.

Can giant congenital melanocytic naevi change over time?

It has been noted that GCMNs can change over time. They can change in colour, becoming darker or lighter. They can also sprout increased levels of hair, have a more irregular texture, and occasionally decrease in size spontaneously. Certain trends have been noted over time. Generally, it is believed that GCMNs tend to become thicker over time. Some research has also found that GCMNs become darker during a patient's teenage years, then become lighter and tend to produce nodules.2

Can the risk of melanoma (skin cancer) be reduced if the GCMN is removed early in life?

Research has found that 50% of melanomas in such patients often occur at a different site than the initial lesion.2 Therefore, it cannot be said with certainty that the removal of the naevus would protect against melanoma.

Can non-surgical methods be used to remove a GCMN?

There are other treatment options, such as laser treatment, chemical peels, and dermabrasion. However, these are believed to only remove the uppermost layer of the mole. As a result, these procedures are generally used to make the lesion look better instead of removing it entirely.2

What are the treatment options for complications linked to GCMN?

Some studies have shown that radiotherapy can be used in late-stage melanomas. Chemotherapy has been used to treat complications such as neurocutaneous melanosis, but this has had limited success.1


A giant congenital melanocytic naevus is an inherited large mole. It can develop whilst a fetus is in the womb. It is often due to an overproduction of melanocytes and usually covers a large area of the patient's body. Giant congenital melanocytic naevi can lead to complications such as melanoma and neurocutaneous melanosis. Patients should be regularly monitored for any signs of complications. Giant Congenital Melanocytic Naevi can be a cause for low self-esteem. As a result, it is recommended that all patients receive psychological support. 


  1. Macneal P, Patel BC. Congenital melanocytic nevi. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Aug 24]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK563168/
  2. Viana ACL, Gontijo B, Bittencourt FV. Giant congenital melanocytic nevus. An Bras Dermatol [Internet]. 2013 [cited 2023 Aug 24];88(6):863–78. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3900335/
  3. Jahnke MN, O’Haver J, Gupta D, Hawryluk EB, Finelt N, Kruse L, et al. Care of congenital melanocytic nevi in newborns and infants: review and management recommendations. Pediatrics [Internet]. 2021 Dec 1 [cited 2023 Aug 24];148(6):e2021051536. Available from: https://publications.aap.org/pediatrics/article/148/6/e2021051536/183438/Care-of-Congenital-Melanocytic-Nevi-in-Newborns
  4. Ruggieri M, Polizzi A, Catanzaro S, Bianco ML, Praticò AD, Di Rocco C. Neurocutaneous melanocytosis (Melanosis). Childs Nerv Syst. 2020 Oct;36(10):2571–96. Available from: 10.1007/s00381-020-04770-9
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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