Congenital melanocytic naevi

Abstract

Congenital melanocytic naevi, consisting of clusters of naevo-melanocytes, develop in utero. Although many congenital naevi are visible at birth, some may not become evident until later in life. The timing of naevo-melanocyte proliferation, senescence and melanogenesis may all contribute towards determining when a naevus will become clinically manifest on the skin. Besides the fact that congenital melanocytic naevi may be aesthetically displeasing, resulting in a multitude of psychosocial issues, they also increase the risk for developing cutaneous melanoma, leptomeningeal melanoma, neurocutaneous melanocytosis, malformations of the brain and, rarely, other tumours such as rhabdomyosarcoma and liposarcoma. Whereas the risk of developing malignancy in association with congenital naevi is dependent, to some extent, on the size of the naevus, the risk of developing neurocutaneous melanocytosis correlates best with the number of satellite naevi. Management of patients with congenital melanocytic naevi requires individualization, taking into account the naevus size and location, and the risk of developing cutaneous melanoma or neurocutaneous melanocytosis. When contemplating treatment options, it is important to set realistic expectations and to address the possible aesthetic and functional outcomes, while at the same time addressing the risk for developing cutaneous and/or extracutaneous melanoma.

Expression of the embryonic morphogen Nodal in cutaneous melanocytic lesions

“…It has been hypothesized that the pathogenesis of congenital nevi may be linked to dysregulation of melanocyte migration, proliferation, or differentiation. 18,19 Although other members of the TGF-b family have been shown to influence melanocyte development/differentiation, [20][21][22] a role for Nodal in this process has not been reported. The high expression of Nodal in congenital nevi suggests that Nodal signaling may have as-yet undescribed roles in melanocyte specification, proliferation, migration, and/or differentiation.…”

Nevo melanocítico congénito gigante

“…No se conoce la incidencia exacta de la MNC, pero es más frecuente cuando existen NMC grandes o gigantes, situados en planos corporales posteriores de la cabeza, cuello, vertebrales y paravertebrales y/o numerosos NMC pequeños. En diversos estudios, la prevalencia de MNC en pacientes con NMC grandes oscila entre el 4,8 y el 30% para la forma asintomática y entre el 4,5 y el 11% la sintomática 9 . Desgraciadamente, los diversos intentos de tratamiento de la MNC sintomática no han conseguido modificar sensiblemente su pronóstico y el desenlace suele ser fatal a los pocos años de su diagnóstico 3 .…”

“…Su indicación es absoluta para eliminar un tumor maligno desarrollado en el NMC y relativa cuando se pretende reducir el riesgo de malignización de las lesiones y/o mejorar sus consecuencias estéticas, sopesando entonces el riesgo/beneficio 9 . Para los nevos pequeños y de aspecto benigno, que son los más frecuentes, se considera adecuada la observación sin cirugía, siempre que su ubicación permita vigilar su evolución.…”

“…En los NMC gigantes, como el de nuestra paciente, además de que los riesgos quirúrgicos pueden ser considerables, conviene recordar que, aunque la cirugía disminuya la lesión, es imposible eliminar todas las células névicas y, por lo tanto, el riesgo de melanoma y de MNC 3,9 .…”

Congenital Melanocytic Nevus

“…Among patients with giant melanocytic nevus, about 5-7% may develop melanoma, also associated neurocutaneous melanocytosis, CMN malformation and in rare instances rhabdomyosarcoma and liposarcoma may occur and would need close follow up [6]. The risk for melanocytic nevus, in small, medium and large have not been defined, and therefore prophylactic removal is not recommended unless for cosmetic reasons.…”