Congenital skin moles are defined as benign nevomelanocytic proliferations that are present at birth. Occasionally, skin moles that are clinically and histologically indistinguishable from congenital skin moles that develop in children during the first 2 years of life. This type is referred to as congenital nevus tardive and can be treated similar to a congenital skin mole.
Congenital skin moles are present in approximately 1% of newborn infants and are important for three reasons. First, they can be cosmetically disfiguring, depending on the size and location. Second, congenital skin moles, particularly large ones, are at an increased risk of developing melanoma. Third, and most importantly, melanoma that develops in large congenital skin moles most often occurs deep within the dermis where it is not easily detectable on clinical examination until at an advanced stage.
The cause of congenital skin moles is uncertain. The melanocytes of the skin originate in the neuroectoderm, although the specific cell type from which they are derived is unknown. One theory of the origin of melanocytes in the skin considers that the pluripotential nerve sheath precursor cells migrate from the neural crest to the skin along paraspinal ganglia and peripheral nerve sheaths, and differentiate into melanocytes upon reaching the skin.
One explanation for the development of a congenital skin mole is that some type of external insult results in a mutation that disrupts the normal morphogenesis of the embryonic neuroectoderm and migration of precursor cells to the skin.
Based on the observation of divided congenital skin moles found on adjacent parts of the upper and lower eyelids, it has been concluded that they develop between the 9th and 20th week of fetal development, as this is the period during which the eyelids are fused.
Congenital skin moles have been classified into three groups. The most common method of classification is based on the size of the lesion during infancy. Small congenital skin moles are defined as those lesions less than 1.5 cm at the greatest diameter, medium congenital skin moles as those between 1.5 and 20 cm, and large or giant congenital skin moles as those with a diameter of 20 cm or greater. Large congenital skin moles may have smaller surrounding satellite skin moles . Congenital skin moles have also been classified based on the ease of surgical removal. Small congenital skin moles can usually be removed with simple excision. Medium congenital skin moles, depending on size, may require skin grafts or flaps for closure. In cases where large congenital skin moles can be removed, they often require staged excisions using tissue expanders and skin grafts. Other classifications take into account the percentage of body surface area covered by a lesion based on anatomic location.
Distinguishing congenital from acquired skin moles on the basis of histology is not always possible. However, a set of distinctive histological features may help differentiate between the two. Congenital skin moles classically display the following elements: (1) the presence of nevus cells within the deeper two-thirds of the dermis with possible extension into the subcutaneous tissue, (2) involvement of nevus cells around and within neurovascular structures and deep dermal appendages including hair follicles, arrector pili muscles, sebaceous glands, nerves, and walls of blood vessels, (3) infiltration or splaying of nevus cells between collagen bundles of the reticular dermis either as single cells or cords of cells, and (4) a perifollicular and perivascular distribution of nevus cells simulating an inflammatory reaction. Although these features are not pathognomonic for congenital skin moles , they are most consistently observed in large congenital skin moles. Small and medium congenital skin moles may show all, some, or none of these features and may be histologically indistinguishable from acquired skin moles. In contrast to congenital skin moles, acquired skin moles are usually composed of nevomelanocytes that do not involve the appendages and are limited to the papillary and upper reticular dermis. Large congential skin moles may demonstrate a number of patterns including intradermal or compound mole. The nevus cells of congenital skin moles are also typically positive for the markers S-100, Melan-A, and HMB-45. In the absence of a clear history, the aforementioned features can be useful in establishing the likelihood that a skin mole is a congenital rather than an acquired one.
Treatment of congenital skin moles is guided by two factors: risk of cancerous change and cosmetic impact. Many treatment options have been used in an attempt to reduce the rate of melanoma and/or improve the cosmetic appearance of patients with congenital skin moles. Different treatment strategies have included careful monitoring, serial photography, surgical excision, dermabrasion, curettage, and laser treatment.
Many factors must be taken into consideration when managing these lesions, including the perceived risk of melanoma, size and location of the lesion, cosmetic impact, proximity to vital structures, psychosocial effects, risks of invasive intervention, and likely cosmetic outcome. An open discussion with patients and/or family members, including treatment options, realistic outcome expectations, and the relative scarcity of evidence-based data is essential.
Although the great majority of patients with congenital skin moles of any size will never develop melanoma, the presence of large congenital skin moles clearly places an individual at increased risk of cancerous change.
Because melanoma develops at an early age in large congenital skin moles and often originates deep to the epidermis where it cannot easily be detected on clinical examination, watchful waiting is not the recommended approach. Surgical excision of these lesions at an early age remains the mainstay of treatment for those seeking prophylactic therapy. One study, which examined the physical and psychosocial effects of large congenital skin moles and their surgical removal, suggests 6 to 9 months as an optimal age for surgical excision. Unfortunately, surgical excision down to fascia does not entirely eliminate the risk of melanoma as it is not possible to ensure the removal of all nevus cells, some of which may be found deep to the fascia within muscle and nerve. Additionally, excisions of very large congenital skin moles that pose the greatest risk of melanoma, are often very difficult or impossible, and frequently produce unacceptable cosmesis. There is also a lack of published evidence to quantify the reduction of melanoma risk following prophylactic surgery.
Patients with small congenital skin moles appear to be at an increased lifetime risk of melanoma, although not to the same extent as patients with large congenital skin moles. Given the current evidence, watchful waiting with regular
follow-up, dermatoscopic and photographic evaluation, and monitoring by parents is an appropriate treatment strategy for most of these lesions. Unlike the case of large congenital skin moles, careful clinical observation will detect cancerous changes in these lesions because melanomas arising in small congenital skin moles are almost always epidermal in origin.
When prophylactic removal is desired, it can generally be delayed until just prior to puberty because melanoma in these lesions develops almost exclusively during adulthood.
Treatment of medium congenital skin moles is the most difficult of the three classes of congenital skin moles. While they do not appear to present the same melanoma risk as large congenital skin moles, an accurate risk assessment has not been established. There is also insufficient data to suggest that one treatment strategy is superior.
Some have suggested taking a biopsy of these lesions prior to excision. If histologic patterns are similar to those of acquired skin moles, then the lesions could be managed similarly to the case of small congenital skin moles. If patterns of deep dermal growth are observed, as in large congenital skin moles, the risk of clinically undetectable melanoma presumably would be higher and warrant prophylactic excision as early as possible.
Because the risk of prepubertal melanoma in these lesions is small, others have suggested excision of these lesions in the pubertal years when the risks of anesthesia are lower than during childhood.
Labels: Congenital moles