What is Congenital Nevus?

Congenital melanocytic nevi (CMN) are common skin marks found at birth. They are made up of melanocytes, which are cells that create pigment, and they have unique physical and microscopic characteristics. Unlike melanocytic nevi that develop later in life, CMNs behave differently.

CMNs hold significant medical interest because of their potential to develop into skin cancer, known as malignant melanoma, and their occasional association with the brain and nervous system (a condition known as neurocutaneous melanosis). The probability of these complications depends largely on the size of the CMN.

This article will cover the causes, signs, diagnosis, and treatment options for CMN.

What Causes Congenital Nevus?

Congenital melanocytic nevi, a type of skin condition present at birth, develops due to changes in certain genes while a fetus is still in the womb. Changes mainly occur in the NRAS and BRAF genes. These genes are important contributors to the so-called MAPK pathway, which is involved in cell growth and division. These mutations result in an irregular pattern (mosaic) of skin and sometimes other tissues.

Risk Factors and Frequency for Congenital Nevus

Congenital melanocytic nevi, a type of birthmark, has an occurrence rate that can differ according to the study, it ranges from 0.2% to 6%. Interestingly, the rate is lower when the diagnosis is confirmed with a microscope (which is known as being ‘histologically confirmed’). On the other hand, when the diagnosis is made based on signs and symptoms (referred to as ‘clinical diagnostic criteria’), the occurrence rate seems to be higher.

Giant congenital nevi, which are larger types of these birthmarks, are rather rare. These are found in about 0.005% of the population.

Signs and Symptoms of Congenital Nevus

Congenital melanocytic nevi are types of skin lesions that can be seen at birth or within the first few years of a child’s life. When they appear during the first two to three years, they are often called tardive congenital nevi. They can be classified into four types based on size: small (less than 1.5 cm), medium (1.5 to 20 cm), large (20 to 40 cm), and giant (more than 40 cm). This is important because the size of these lesions is one of the main factors that increase the risk of developing skin cancer (melanoma) or having neurological difficulties.

At birth, these nevi often look like colored spots or slightly raised bumps which can be sometimes mistaken for café-au-lait spots. As time goes on, they usually darken in color and often develop a clear border. They can also become raised or verrucous, showing a variety of colors, including light brown to black. They may also have excess hair growing from them and often show areas of lighter skin around the hair follicles. These birthmarks usually grow as the child grows, covering the same amount of skin in adulthood as in childhood.

PN, or nodules, can also be found within these nevi. They can be present at birth or develop during childhood. They are generally round or oval bumps having a well-defined border and usually appear less pigmented than the surrounding skin. Occasionally, itching and inflammation can occur.

Giant nevi often have a garment-like appearance, for example, looking like a bathing trunk or coat sleeve. They may show smaller lesions, called satellite lesions, which resemble small or medium congenital melanocytic nevi. Another associated condition is Neurocutaneous melanosis, where these nevi are associated with excessive growth of melanocytes in the nervous system. People with larger nevi and satellite lesions are particularly at risk. While some may not have any symptoms, others may experience seizures, cranial nerve problems, or signs and symptoms of increased pressure within the skull. Patients showing symptoms often have a serious prognosis.

Testing for Congenital Nevus

Dermoscopy is an essential tool for doctors when checking skin conditions. It’s cost-effective, quick, and doesn’t hurt the patient. Moreover, it can greatly help doctors distinguish between different types of skin lesions and recognize early signs of harmful changes. Patterns doctors often encounter include globular, cobblestone, and reticular patterns.

Helpful features for diagnosing CMN, a type of skin mark, can include haloed and target globules, blotches, and areas of lightened skin around hair follicles.

On hands and feet, CMN often combines a parallel furrow pattern (similar to another type of skin mark) with dots on the skin ridges, presenting what looks like a “peas-in-a-pod” appearance.

If a doctor thinks a skin mark could be a type of skin cancer known as melanoma, they must perform a biopsy as soon as possible. This is where a small piece of the affected skin is removed and examined under a microscope.

Patients with large or giant CMN, especially when additional smaller marks are present, need to be checked quickly (within the first 4 to 6 months of life) with an MRI scan. This scan can check for potential involvement of the nervous system. MRI scans can find melanocytic deposits, which show up as bright areas on T1-weighted images and dark areas on T2-weighted images. The most commonly affected part of the brain is the temporal lobe, specifically the amygdala. Also, the thin tissue covering the brain and spinal cord is frequently affected.

Treatment Options for Congenital Nevus

The decision to remove birthmarks, specifically congenital melanocytic nevi, depends on several factors. Key considerations include the potential risk of melanoma, a type of skin cancer, and any cosmetic or psychological impact linked to the appearance of the nevus or nevi.

In small and medium size birthmarks, the chance of developing melanoma is extremely low, so ongoing monitoring may not be necessary for these cases.

However, it is advisable to maintain regular check-ups for those with large or numerous nevi. A process called ‘mole mapping’ can help track changes in each nevus using photography and a technique called dermoscopy. Surgery to remove these nevi can be considered if there are cancer-related concerns or if it can improve the person’s appearance and wellbeing.

For birthmarks that are removed solely for cosmetic reasons, techniques like dermabrasion, laser treatments, and curettage might be used. But note that these methods do not completely erase the nevi and do not reduce melanoma risk. Plus, there are chances that the birthmark can reappear.

Patients with a condition called neurocutaneous melanosis, where nevi are found on the skin and the brain or spinal cord, should be evaluated by a pediatric neurologist. They may benefit from surgery or chemotherapy, and other treatments like anticonvulsants or dexamethasone may be needed to alleviate symptoms.

Birthmarks that are dark in color (also known as congenital melanocytic nevi) can look a lot like skin abnormalities that develop over time (acquired atypical nevi) or even skin cancer (melanoma). When doctors have a difficult time telling them apart, they opt to take a small sample of the skin (biopsy) to make sure it isn’t the latter. The preferred method is to remove the entire area (excisional). Besides these, other conditions that might be considered are smooth muscle hamartomas (noncancerous skin growths), Becker melanosis (a type of brown skin mark), and plexiform neurofibromas (tumors on nerve tissue).

Surgical Treatment of Congenital Nevus

Smaller birthmarks, known as congenital melanocytic nevi, can be removed by simple surgery. However, removal of larger birthmarks may entail more complicated surgical methods including staged removal over multiple sessions, usage of a surgical balloon to progressively stretch the nearby skin, or transplantation of skin patches or sections.

What to expect with Congenital Nevus

The future health of these patients is mainly dependent on the chances of developing cancer and having neurocutaneous involvement.

Often, the threat of developing skin cancer or melanoma in patients with birthmarks known as congenital melanocytic nevi has been overstimated. Small to medium single congenital melanocytic nevi usually have great outcome with a lifetime risk of only around 1% of developing skin cancer, and it’s exceedingly rare before teenagers. However, those with large or giant birthmarks have a roughly 5% risk, which grows larger as the birthmark does. In these cases, skin cancers are seen more during childhood. Notably, these particular patients are still more at risk for developing skin cancer than the general population, even if the birthmark is fully removed. This is perhaps because skin cancers can come from skin cells anywhere in the body and not just on the birthmark itself. If there are abnormalities in the brain identified by MRI, their risk for developing skin cancer increases. If the skin cancer starts in the brain, it has nearly a 100% mortality rate.

Another condition that has a large impact on life quality and death rates is neurocutaneous melanosis. The chances of developing this disease in patients with large and giant congenital melanocytic nevi are estimated to be between 10% to 33%. Like with skin cancers, it’s tied heavily to the size of the birthmark and its spread. The outlook becomes much more severe when there are signs and symptoms related to the nervous system.

Possible Complications When Diagnosed with Congenital Nevus

Some patients may experience itching and eczema, skin conditions characterized by inflammation and itchiness, at the point of the skin lesion. These symptoms can often be relieved with treatments like topical steroids, which are creams or ointments applied to the skin.

Having congenital melanocytic nevi, a type of birthmark, can lead to psychological problems due to changes in appearance. These can include depression, anxiety, and self-isolation. It can be helpful to discuss treatments focused on improving the appearance of the birthmark with healthcare professionals. If necessary, psychological support can be sought to help cope with these issues.

Melanomas, or skin cancers, that develop from these birthmarks are often very aggressive. They typically form in the deeper layers of skin and can appear as raised spots or nodules, sometimes with a broken skin surface. These cancers can be hard to spot early in their growth because of their location. They may also appear in the central nervous system or other organs. Swelling of the lymph nodes due to cancer spread is often evident when the cancer is diagnosed.

Neurological problems related to the melanoma can show up in different ways:
Some may not cause any symptoms and can only be seen on a brain imaging scan (MRI).
Others may cause developmental delays, seizures, or mental health symptoms.
In some cases, increased pressure inside the skull may occur, leading to symptoms like irritability, lethargy, an increase in head size, and nerve problems.

Unfortunately, individuals with these symptoms often have a poor outlook, and they typically pass away at a very young age.

Preventing Congenital Nevus

Patients should be guided to regularly check themselves for any changes in their skin lesions, and to talk to their doctors if they notice any differences. For people with small or medium-sized skin spots, it’s important for them to understand that these are not harmful, to prevent unnecessary worry or stress.

Also, before undergoing any procedures meant to improve their appearance, it’s crucial that they have a realistic understanding of the expected outcomes. This way, they are better prepared for the process and final results.