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Thread: Congenital Nevus picture - Pediatric Atlas

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    Default Congenital Nevus picture - Pediatric Atlas

    Pathophysiology
    The etiology of congenital melanocytic nevi remains unclear. The melanocytes of the skin originate in the neuroectoderm, although the specific cell type from which they derive remains unknown.One hypothesis is that 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 possible explanation for the presence of congenital melanocytic nevi is that an external insult results in a mutation that affects the morphogenesis of the embryonic neuroectoderm and migration of precursor cells to the skin.

    One study found that the MC1R (melanocortin-1-receptor) genotype, which corresponds to a red-haired genotype and a tendency to increased birthweight, was overrepresented in a cohort of congenital melanocytic nevi affected Northern European patients. How MC1R variants promote growth of congenital melanocytic nevi and thefetus itself is unknown as is the application of this finding to non-european and more darkly pigmented races.

    Congenital nevi have been stratified into 3 groups according to size. Small nevi are less than 1.5 cm in greatest diameter, medium nevi are 1.5-19.9 cm in greatest diameter, and large or giant nevi are greater than 20 cm in greatest diameter. Giant nevi are often surrounded by several smaller satellite nevi. An alternate definition is that a small congenital nevus is one for which primary closure is possible after excision.

    Congenital nevi may also be seen as a component of neurocutaneous melanosis, a rare congenital syndrome characterized by the presence of congenital melanocytic nevi and melanotic neoplasms of the central nervous system. Rokitansky first described neurocutaneous melanosis in 1861.The current diagnostic criteria for neurocutaneous melanosis are large (>20 cm) or multiple (>3) congenital nevi in association with meningeal melanosis or melanoma, no evidence of meningeal melanoma except in patients in whom cutaneous lesions are histologically benign, and no evidence of cutaneous melanoma except in patients in whom meningeal lesions are histologically benign.

    Neurocutaneous melanosis may result from an error in the morphogenesis of the neuroectoderm, which gives rise to the melanotic cells of both the skin and meninges. Clinically, patients may present with increased intracranial pressure due to hydrocephalus or a mass lesion. The prognosis of patients with symptomatic neurocutaneous melanosis is very poor, even in the absence of malignancy. In one review of 39 reported cases of symptomatic neurocutaneous melanosis, death occurred in more than half the patients within 3 years of the onset of neurological symptoms, and most deaths were in patients younger than 10 years.

    Mutations in NRAS in congenital melanocytic nevi can cause mitogen-activated protein kinase activation and may represent early events in melanoma development.
    Congenital Nevus picture Pediatric Atlas attachment.php?s=6e81aae9c977dafb1de178513b824871&attachmentid=1752&d=1441139569

    Oncogenic missense mutations in codon 61 of NRAS were found in affected neurological and cutaneous tissues in 12 of 15 patients with congenital melanocytic nevi with neurocutaneous melanosis, implying single postzygotic NRAS mutations were responsible.

    International
    Congenital nevi are present in 1-2% of newborn infants. One small study in Spain found a higher prevalence of congenital melanocytic nevi in preterm infants, females, and nonwhite infants, whereas maternal age, number of previous pregnancies, and birth weight did not appear to influence the prevalence.

    Mortality/Morbidity
    Congenital nevi, depending on size and location, may have a significant impact on cosmesis. Giant congenital nevi place individuals at an increased risk for the development of melanoma at the site of the nevus. For giant congenital melanocytic nevi, the risk of developing melanoma has been reported to be as high as 5-7% by age 60 years. One study suggests that the risk of melanoma may be greater in those with giant congenital melanocytic nevi with more satellite lesions or a larger diameter. Another suggests multiple satellite nevi alone or with associated posterior midline location of large congenital melanocytic nevi is linked with increased risk. Additionally, melanoma developing within giant congenital nevi may develop during childhood and occur deeper in the tissue where it is harder to detect clinically.

    While the general consensus regarding smaller nevi is that they pose a greater risk for the development of melanoma than normal skin, this risk has not been quantified. Also suggested is that melanoma developing within smaller congenital nevi usually occurs at puberty or later and develops more superficially in the skin, where it is easier to detect clinically.

    Physical
    Nevi may be located anywhere on the body. Classification as a congenital nevus depends in large part on an accurate history or photographs or medical reports from birth.

    Scalp nevi in children younger than 18 years old tend to have perifollicular hypopigmentation that creates the appearance of scalloped, irregular borders if occurring on the periphery, or variegation in pigmentation, if occurring within the nevi.

    Congenital melanocytic nevi affecting acral volar skin in children are larger, more asymmetrical, and commalike compared with their acquired counterpart

    Causes
    The etiology of congenital melanocytic nevi has not been elucidated. One possible cause is a mutation due to an external insult.An association between infantile hemangiomas and congenital melanocytic nevi has been suggested. Future investigation may yield more definitive causative factors.

    References:
    http://emedicine.medscape.com/articl...59-clinical#b5
    Congenital melanocytic naevi. DermNet NZ











    Last edited by Medical Photos; 09-01-2015 at 08:33 PM.

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