What is Congenital Melanocytic Nevi (Giant Hairy Nevi)?
A congenital melanocytic nevus (CMN) is a type of benign skin lesion that mainly consists of nevomelanocytes, which are cells related to skin color. These skin spots are present at birth or appear within the first few weeks. Sometimes, these are also known as giant hairy nevi because they often come with excessive hair growth.
CMNs are mainly sorted by their size into small, medium, and large or giant. This is predicted based on the expected adult size of the largest diameter of the lesion. Small CMNs are expected to be less than 1.5cm in diameter, medium ones are between 1.5cm to 19.9cm, and large or giant ones are over 20cm.
The prediction of their adult size is determined by where they are located on the body. Those on the head are expected to grow 1.7 times their size, on the lower limb 3.3 times, and on the upper limb and torso 2.8 times. Size is an important factor in categorizing because larger spots tend to have a higher risk of becoming cancerous, can affect appearance, are harder to remove surgically, and tend to have associated symptoms more often.
What Causes Congenital Melanocytic Nevi (Giant Hairy Nevi)?
Congenital Melanocytic Nevi (CMNs) occur during development in the womb between the 5th and 24th week. These are birthmarks that arise due to certain genetic irregularities, leading to an excessive growth of melanocytes. Melanocytes are the skin cells responsible for producing the pigment melanin, and their precursors, called melonoblasts, start to move from the neural crest to the outer layer of the skin between the 8th and 10th weeks of pregnancy.
A common mutation named N-Ras is often seen in CMNs. This mutation is believed to cause an unnaturally high growth of melanocyte lineage cells, resulting in the formation of CMNs.
Moreover, this condition may also be linked to the dysfunction of a protein called hepatocyte growth factor. This substance plays a role in guiding the movement and growth of melanocytes. Although there is some evidence showing a familial link, most CMNs are thought to be caused by spontaneous mutations that occur randomly.
Risk Factors and Frequency for Congenital Melanocytic Nevi (Giant Hairy Nevi)
Congenital Melanocytic Nevi (CMNs), commonly known as birthmarks, can vary in size. While small CMNs are fairly common, larger ones are rare. The likelihood of a newborn having a small CMN is roughly 1 in 100, medium CMNs 1 in 1000, and large or giant CMNs happen rarely – between 1 in 20,000 to 1 in 500,000 newborns. These birthmarks are slightly more common in females than males, with the ratio being approximately 3 to 2.
- Small CMNs are fairly common and found in about 1 in 100 newborns.
- Medium CMNs have an occurrence rate of 1 in 1000 newborns.
- Large or giant CMNs are rare, affecting 1 in 20,000 to 1 in 500,000 newborns.
- CMNs are slightly more likely to appear in females than males, with a ratio of roughly 3 to 2.
Signs and Symptoms of Congenital Melanocytic Nevi (Giant Hairy Nevi)
Congenital Melanocytic Nevi, or CMNs, are usually noticed at or shortly after birth. These skin lesions can vary widely in appearance and size. Smaller ones typically appear round or ovoid, with a smooth surface and a consistent brown color. Larger CMNs can have rough or uneven surface textures, irregular borders, and varied pigmentations. They frequently have additional smaller nevi, called satellite nevi, nearby.
- Small CMNs: Well-defined, round or ovoid, smooth surface, uniform brown color
- Large CMNs: Irregular border, different pigmentations, rough or nodular surface, often have satellite nevi
As time passes, CMNs can change. Their color may darken or lighten, nodules (small lumps) can form, and they may start to grow hair. Though usually harmless, larger lesions may cause dry skin, itching, skin erosion, or even ulceration. They also may affect the psychiatric wellbeing of both the child and their parents due to their appearance.
A specific type of nevus, known as the “divided nevus”, consists of two nevi that may occur on locations such as the penis, fingers, or eyelids. They are also named “kissing nevi”. They start as a single lesion and divide when, for example, the eyelids separate in the fetal development stage. Despite being typically present at birth, they can also appear later in life. These nevi can cause excess tear production, changes in eyelid position, or poor vision.
Testing for Congenital Melanocytic Nevi (Giant Hairy Nevi)
Congenital melanocytic nevi (CMNs), commonly known as birthmarks, are usually identified based on how they look. However, if a doctor isn’t sure of the diagnosis, they could use dermatoscopy – which is a method of examining the skin under a special light, or a biopsy – which involves taking a small sample of the skin for further testing.
Typically, dermatoscopy shows a pattern of pigmentation that looks like tiny globules. However, it can also show no specific pattern, or patterns that look like a net or a mix of these.
A biopsy involves removing a small piece of the tissue for detailed examination under a microscope. This can help ensure that the birthmark isn’t actually a skin cancer or another serious disease.
Treatment Options for Congenital Melanocytic Nevi (Giant Hairy Nevi)
Treatment for these skin conditions can be divided into two main categories: surgical and non-surgical. Surgical treatments includes techniques such as tangential excision (removing only the uppermost layer of the skin), curettage (scraping the skin), and more complex procedures like en bloc or serial excision and direct closure (removing a lesion in one piece), and tissue reconstruction that uses techniques like tissue expansion, skin graft, or a flap of skin.
On the other hand, non-surgical treatments encompass methods such as dermal abrasion (a skin resurfacing technique), chemical peels, cryotherapy (freezing), electrosurgery (using electric currents), and ablative lasers. These strategies are typically used to lighten the skin and enhance its cosmetic appearance without fully eliminating pigmented cells.
Historically, treatment for these conditions had two main objectives: to enhance the appearance of the skin and reduce the risk of skin cancer. However, whether or not surgical removal actually lowers cancer risk is a topic of ongoing debate. Those in favor of surgery argue that the chances of a serious form of skin cancer called melanoma are lower in patients who’ve had surgery compared to those who were only observed. Critics of surgery cite the relatively low incidence of melanoma as well as the risks related to surgery. They also point out that surgery does not reduce the risk of melanoma appearing outside the skin (extracutaneous melanoma), which accounts for a significant portion of new melanoma cases in this patient group. Therefore, many centers won’t offer surgical removal solely for reducing cancer risk but will monitor the condition unless aesthetic concerns or functional issues necessitate surgery. Further studies are needed to provide more insight into this issue.
What else can Congenital Melanocytic Nevi (Giant Hairy Nevi) be?
- Skin moles acquired over time
- Born with blue moles
- Flat brown spots (Lentigo)
- Bluish-grey birthmarks (Mongolian spots)
- Speckled birthmark (Nevus spilus)
- Large brown birthmark (Becker nevus)
- ‘Coffee with milk’ spots (Café-au-lait spots)
- Pigmented birthmark on the outer layer of the skin (Pigmented epidermal nevus)
What to expect with Congenital Melanocytic Nevi (Giant Hairy Nevi)
Small and medium congenital melanocytic nevi (CMNs), which are birthmarks or moles present at birth, generally pose less risk for becoming cancerous or causing neurocutaneous melanosis, a skin and nervous system condition. These patients usually have a good survival outlook. Conversely, when melanoma, a type of skin cancer, develops in large or giant CMN, it often results in a poor survival outlook. In a study of 35 patients with giant CMN who developed melanoma, the 5-year survival rate was only 34.3%. This may be due to the cancer’s deep skin origins, making it harder to detect early. Furthermore, this deep origin may cause faster lymphatic and metastatic spread, a process where the cancer spreads to other parts of the body. A study indicated that 24% of melanomas in patients with giant CMN had already spread at the time of diagnosis.
As for patients with symptomatic neurocutaneous melanosis, they too have an unfavorable outlook. A study reported that 50% of these patients passed away within three years of the symptoms appearing, and no fully effective treatments have been discovered yet.
Possible Complications When Diagnosed with Congenital Melanocytic Nevi (Giant Hairy Nevi)
Complications are more frequent in patients with large Congenital Melanocytic Nevi (CMNs). These can involve simple skin irritation to dangerous malignant melanoma transformation. Symptoms can vary from skin irritation, such as sores and itching, to potentially affecting the structure and function of certain body parts. Large lesions impact the way the body looks and functions, which can result in a psychological burden on both the child and the parents. More serious complications can include the growth of malignant melanomas and neurocutaneous melanosis, conditions associated with a high risk of developing cancer.
Malignant melanomas can develop in any patient with Congenital Melanocytic Nevi (CMNs), but the chances are much higher in patients with larger lesions that are >20cm in size, or in those with multiple CMNs. These can occur on the skin or in other parts of the body, including the brain, deep within the abdomen, or the lining of the digestive tract. The reported risk varies by the size of the CMNs. Patients with small to medium-sized CMNs have a risk of 0 to 4.9%, while the risk for those with larger CMNs ranges from 1.25 to 10.00%. As a result, those with larger CMNs need regular checkups for signs of skin and other types of cancer.
Meningeal melanocytosis, an abnormal growth of pigment-making cells in the central nervous system, can occur in those with giant or multiple CMNs. Another closely related condition is neurocutaneous melanosis, which is characterised by the abnormal growth of these cells but does not necessarily transform into cancer. Estimates suggest that 5%-10% of patients with large CMNs may have neurocutaneous melanosis, but most probably do not show any symptoms. The exact occurrence of this condition is still unknown. However, the growth of these pigment-making cells or bleeding may cause symptoms similar to high pressure on the brain – like seizures, nerve palsies, or water on the brain. These conditions are diagnosed using MRI scans, and are managed with a combination of medicines and surgery by a team of health care providers.
Preventing Congenital Melanocytic Nevi (Giant Hairy Nevi)
It’s crucial for healthcare professionals to know what Congenital Melanocytic Nevi (CMNs) look like so they can identify these skin lesions at birth or shortly after. Proper identification is key in ensuring the correct diagnosis is made and there is an appropriate referral to a skin specialist. Patients who have larger CMNs are at a higher risk of serious complications. Therefore, they need long-term monitoring for potential signs of skin cancers and malignancy in other parts of the body.
