Nevus melanocytic congenitalD22.-

Prenatally developed, benign melanocytic tumour of the skin and, if necessary, the adjacent mucous membrane of different size, colour and localisation.

In about 1% of all newborns; no gender dominance; in mixed white/non-white collectives no preference of skin colour could be detected.

In large congenital melanocytic nevi as well as in neurocutaneous melanosis, postzygotic mutations in codon 61 of the NRAS have been found. The significance of the BRAF mutations detected in individual cases is still unclear.

Small and medium congenital melanocytic nevi were distributed in larger groups as follows: trunk: 27%; head and neck: 23%.

Large and giant-type melanocytic nevi are distributed preferentially over the head/neck, buttocks and trunk.

Congential melanocytic nevi (CMN) have a broad clinical spectrum. Their size ranges from a few millimeters to "giant" nevi with a diameter > 20 cm. The surface of the BMN can be smooth or rough, hairless or hairy (naevus pigmentosus et pilosus). BMN may be present at birth or trten in appearance 1-2 years later (tardive forms). They may be more discretely brown at birth and darken with age (not a sign of malignancy). Others develop deep dark or black spots during life (note: these should be excised). Other BMN remain rather discrete throughout life, even with large areal extension.

From the size extension, 3 categories can be divided (n. Krengel S. et al. 2012):

• Small KMN: <1.5 cm
• Medium sized KMN (intermediate type): 1,5-20cm
• Large KMN (giant type): 20-40cm
• Giant KMN >40cm
• Specificity: Swimsuit type melanocytic naevus (see naevus, melanocytic, congenital, swimsuit type)
• Specificity: Melanocytic nevus with involvement of the meninges, brain and/or spinal cord(melanosis neurocutanea)

S.u. Nevus, melanocytic.

In lymph node examinations from the lymphatic outflow region of large congenital melanocytic nevi, nests of melanocytic cells can be found in a high percentage (Bowen AR et al. 2015) without this finding being interpreted as an indication of malignancy.

Soft tissue growths: Large congenital melanocytic nevi may develop bulging benign soft tissue proliferations over the course of life, e.g. lipomatous excess formation has been found where the lipomatous tissue was interspersed with melanocytic cells (HMB45 and S100 positive) (Agarwal A et al. 2019; Belysheva TS et al. 2019)

Malignancy: In about 5% of patients with melanocytic giant nevi malignant degenerations are found either within the nevus or extracutaneously.

> 50% of all observed malignancies occur within the first 5 years of life. In a larger study (n=976 patients) of patients with congenital melanocytic giant nevi who developed invasive malignant melanoma, "thick" melanomas with lymph node and distant metastasis were observed more frequently.

Also, an unusually aggressive melanoma growth was observed in a giant congenital melanocytic nevus (De la Rosa Carrillo D et al.2018).

Neurocutaneous melanosis: The classical prognostic criteria for this are:

• Presence of a large KMN (>20cm in adulthood) or
• multiple (>3) smaller KMN in connection with the
• Presence of meningeal melanosis or meningeal melanoma
• Safe differentiation from a meningeal metastasized cutaneous melanoma or a cutaneously metastasized, primarily meningeal melanoma.

In medium-sized melanocytic nevi, a multi-stage strip-like excision under general anesthesia is recommended, depending on the location and extent of the nevi (Hong SN et al. 2019).

In large giant anevi which may cover several body parts, dermabrasion should be performed in the first weeks of life. Even if melanocytes in the middle and deep dermis are not included, the risk of melanoma can demonstrably be significantly reduced by this surgical procedure.

Instead of dermabrasion, an ablative laser (e.g. Erbium-YAG laser) can also be used for this surgical procedure (only by appropriately experienced colleagues). The final results are apparently comparable.

Note: If the described procedures are not possible, a regular half-yearly clinical check-up (if necessary photo documentation) and excision of suspicious areas should be performed.

With very large melanocytic nevi (>40cm = nevus giganteus) the lifelong, absolute melanoma risk is >10%. In this case a significant proportion of developing melanomas appear as deep nodular proliferations.

The rare clinical picture of melanosis neurocutanea has to be separated by differential diagnosis. This is of eminent clinical importance, since this syndrome has a high malignancy rate and further neurological complications (e.g. hydrocephalus internus).

1. Agarwal A et al (2019) Giant congenital melanocytic nevus associated with lipoma in an Indian man. BMJ Case Rep 12. pii: e228688.

2. Belysheva TS et al (2019) Melanoma arising in a Giant congenital melanocytic nevus: two case reports. Diagn Pathol. 14:21.

3. Bowen AR et al (2015) Benign melanocytic lymph node deposits in the setting of giant congenital melanocytic nevi: the large congenital nodal nevus. J Cutan Pathol 42: 832-839.

4. Carrera J et al (2014) Surgical treatment of giant congenital melanocytic nevi: a change of aim. Cir Pediatr 27:36-42

5. Fernandes NC et al (2009) Clinical study of the congenital melanocytic naevi in the child and adolescent. On Bras Dermatol 84:129-135
6. Kinsler VA (2013) Multiple congenital melanocytic nevi and neurocutaneous melanosis are caused by postzygotic mutations in codon 61 of NRAS. J Invest Dermatol 133: 2229-2236
7. Krengel S (2012) News about congenital melanocytic nevi. dermatologist 63: 82-88
8. Krengel S et al.(2013) New recommendations for the categorization of cutaneous features of congenital melanocytic
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9. of Houten AH et al (2010) Proliferative nodules in a giant congenital melanocytic nevus-case report and review of the literature. J Cutan catholic 37:764-776

10. Wang L et al(2013) Congenital melanocytic nevus with features of hybrid schwannoma/perineurioma. J Cutan pathogen 40:497-502.