Congenital melanocytic nevi

Abstracts

O nevo melanocitico congênito está presente em aproximadamente 1% dos recém nascidos. As lesões classificadas como pequenas e medias são relativamente comuns, ao passo que o nevo gigante, maior que 20 cm no maior diâmetro, é uma condição mais rara cuja a incidência esta estimada em 1 para cada 20 mil nascimentos. As lesões melanociticas congênitas pequenas e médias têm um risco de degeneração maligna baixo, raramente ocorrendo na infância. Por outro lado, estima-se um risco entre 5 a 12 % de um melanoma se desenvolver a partir ou relacionado com um nevo gigante, e de regra, metade dos casos ocorrem antes dos 3 anos de idade. Alem da possibilidade de degeneração maligna, o acometimento neurológico e as implicações psicológicas devido ao aspecto estético são dois aspectos importantes relacionados com as lesões gigantes, influindo também na decisão e na abordagem terapêutica.

melanoma; nevo pigmentado

CONTINUING MEDICAL EDUCATION

Congenital melanocytic nevi^*

Francisco Macedo Paschoal

Assistant professor of Dermatology, ABC college of Medicine, Masters degree in Dermatology, UNIFESP - EPM

^{Correspondence}

SUMMARY

Congenital melanocytic nevi is present in approximately 1% of new born. The lesions classified as small and medium are relatively common, while giant pigmented nevus, measuring over 20cm in the largest diameter, is a rarer condition, the incidence of which is estimated to be one in every 20 thousand births. The small and medium congenital melanocytic lesions present a low risk of malignant degeneration and this rarely occurs in childhood. On the other hand, there is a risk estimated between 5 to 12% of a melanoma growing from or being related to a giant nevus, furthermore in half of the cases this occurs before three years of age. Besides the possibility of malignant degeneration, the neurological involvement and psychological implications arising from aesthetic aspect are two important factors related to the giant lesions and also influence the therapeutic approach.

Key words: melanoma; nevus, pigmented.

INTRODUCTION

Congenital melanocytic nevi corresponds to the melanocytic nevus present at birth or that develops during infancy from preexistent nevoid cells.¹ Congenital nevus is present in approximately 1% of newborn. While the small and medium nevi are relatively common, the giant nevus, known as "bathing trunk" nevus in its most typical location is a rare condition, with an estimated incidence of one in every 20 thousand births (nevi measuring over 10cm).² In this situation they correspond to true cutaneous nevomelanocytic hamartomas. To classify a congenital nevus as giant is not sufficient to define what conduct should be chosen, since there are several other aspects that need to be taken into account.

DISCUSSION

Classically congenital melanocytic nevi presents the following microscopic characteristics:¹

- involvement of the two inferior thirds of the dermis, occasionally extending into the subcutaneous layers;

- individual nevoid cells distributed between the collagenous fibers;

- association with cutaneous appendixes, nerves and vessels located in the reticular dermis.

It is interesting that such involvement of the dermis is present in the neonatal period, as this fact contradicts the hypothesis of migration of nevoid cells during infancy. These deep cells do not modify themselves with age.³

Congenital melanocytic nevi can be classified in an arbitrary manner, according to its size in infancy: small (<1.5cm in diameter), medium (1.5 to 20cm in the largest diameter) and giant (> 20cm in diameter).^1,4 The most rational method, however, it is to establish the proportion of the cutaneous surface involved by the nevi, since it is considered that the risk of developing melanoma is directly proportional to the extension of the nevi.

It can be affirmed that the three main problems related with congenital melanocytic nevi and above all the giant pigmented nevus, are: the possibility of malignant transformation; neurological involvement; and implications related to aesthetic aspects. Of all these, the most worrying is undoubtedly the potential for becoming malignant.

Generally, small melanocytic nevus presents nevoid cells confined to the superior layers of the dermis, while giant melanocytic nevus presents the classic histological characteristics described above. In this manner, a melanoma that originates from the former frequently presents an epidermal origin. In compensation, more than two thirds of the melanomas originating from a giant nevus develop from the dermis. Its origin can be melanocytes localized at any level between the dermoepidermal junction and the meninges. This is so important because three fourths of the tumors related to giant nevus do not develop from cutaneous nevi, but from melanocytes located in the deep tissues and especially from the meninges.⁵ Twenty percent of patients with giant melanocytic pigmented nevus located in the upper back and cephalic segment present alterations in the electroencephalogram,⁴ as well as the occurrence of asymptomatic or oligosymptomatic meningeal melanosis. In this condition, the performing of a neurological exam is recommended and even a radiological study (magnetic resonance).⁴ Unfortunately, the current therapeutic possibilities for melanosis of the meninges are practically nonexistent.⁶

From the practical point of view, due to the fact that almost all of the melanomas originating from small congenital nevi are epidermal and the incidence of degeneration is extremely low, the prophylactic removal of these nevi is not essential. According to current findings, clinical observation alone should be capable of detecting such a complication.⁷ If it is decided to remove this type of nevus, the procedure can safely be performed after puberty, since malignant transformation rarely occurs in prepubertal children.⁸

Nevertheless, due to the high risk of malignant transformation of giant melanocytic nevi, estimated to be between 5 and 20%, prophylactic excision is frequently recommended.⁶ Surgical techniques for removal and reconstruction include: progressive exeresis of the nevus (the most common option when the lesions are present in the extremities),⁹ reconstruction with tissular expansion (mainly in the nevi located in the cephalic segment and especially in the scalp)^9,10 and free graft. It should be underscored, however, that it is not rare for these procedures to be incomplete, thus necessitating multiple traumatic interventions for the patient and causing functional alterations and serious secondary deformities.¹¹

Half of the malignant tumors appear before three years of age and are usually fatal. Even so, the occurrence of melanoma in a general form (and not just related to congenital nevus) before puberty is rare, corresponding to 0.4% of the total cases.¹² Precocious diagnosis of a melanoma on a giant pigmented nevus is as a rule difficult and often impossible, due to the blackened coloration of both lesions. Other signs of malignant transformation, such as tumor development or ulceration, are tardive and usually accompanied by metastases. The difficulty should also be considered of accurately establishing the histopathological diagnosis of melanoma in childhood. Some histological criteria have been proposed and related to the possibility of malignancy:¹²

- epidermotropism of isolated cells in the periphery of the lesion;

- high number of mitoses and cytonuclear atypia;

- lack of maturation of the nevoid cells;

- presence of vascular invasion.

In the majority of cases, however, this diagnosis is more of a probability and can only be confirmed with certainty when associated to metastases. Studying tumor markers with anti-Ki67 antibodies can be a supplemental argument to guide the diagnosis of melanoma.⁷

Unfortunately it is frequently impossible to perform a complete excision because of the size of these nevi and also due to the fact that they present multiple satellite lesions. Even excision until the muscular fascia does not completely eliminate the risk of melanoma, because this cell is essentially neural and remains in the profound tissues and above all in the leptomeninges.¹ Unlike small congenital nevi, the risk of degeneration of a giant nevus is greater before 10 years of age. Therefore, for prophylactic purposes, it should be removed as early as possible. Exeresis of giant pigmented nevi is also indicated for aesthetic and psychological reasons.⁷ In fact, parents of children with a giant nevus are most concerned when it is located in a more exposed area of the body and also with the aesthetic aspect and its psychosocial impact, especially in girls. This problem in general assumes such importance that it can not be underestimated by the doctor. Despite the impossibility of surgical removal of many gigantic nevi, an improvement in the aesthetic aspect can be achieved, which contributes considerably to an improvement in the quality of life. These means are described below, however they must be considered in the light of doubts regarding their repercussions to the risk of a malignant transformation. The main methods used for improving the aesthetic aspect are: dermabrasion, curettage, chemical peeling with phenol and laser. All involve the removal of nevoid cells present in the dermoepidermal junction and in the superficial dermis. Those that advocate in favor of these methods argue that, besides the possibility of improving the aesthetic aspect, such removal of the most superficial pigmentation would facilitate the diagnosis of a melanoma that eventually developed in the profound dermis. It is recommended that such procedures are performed as soon as possible, during the first two weeks of life. Publications presenting the results with curettage,^13,14,15 dermabrasion16 and peeling with phenol¹⁷ (Baker's formula) have not reported the occurrence of malignant degeneration in the areas of treated skin. Nevertheless, these treatments are not without complications, principally hypertrophic scarring, repigmentation and a percentage of undesirable aesthetic results. However, there are studies in the literature attempting to relate the development of melanoma with these unorthodox methods of treatment,¹⁸ without counting the high risk of the procedure itself, mainly for neonates (hemorrhage, secondary infection, heart and renal toxicity due to the phenol, etc.). It is probable that the greatest hope for the treatment of giant nevi now lies in the laser. The literature contains descriptions of the use of several laser modalities, ranging from ablation, such as CO₂,^19,20 to methods other than ablation that produce selective photothermolysis of the melanin pigment, with secondary destruction of the nevoid cell, such as Q-switched ruby laser, Nd:YAG laser and Alexandrite laser.^21,22,23 In spite of the cosmetic improvement from its superficial whitening effect, data regarding the rate of recurrence, ability to mimic a melanoma and potential for malignant transformation point to the need for follow-up studies over long periods.^21,24,25,26

Possibly the best conduct when faced with an intermediate congenital melanocytic nevus is the performing of a small incisional or punch biopsy, with the purpose of determining the histological growth pattern of the nevus. In case this is the same as that of acquired nevus (a superficial variant of congenital nevus), the possibility of degeneration will be very low and when it occurs will be epidermal and probably detected in the clinical follow-up. However, if the histological pattern is one of a profound dermal tumor, this points to a significant risk, thus indicating excision of the lesion as precociously as possible.

Regarding dermatoscopy, this technique has a limited role in the approach to giant congenital melanocytic nevi. Observation of the lesion using the dermatoscope is considerably limited due to the great amount of melanin pigment present in these nevi. In addition, the malignant nodules develop at a depth which is not accessible to dermatoscopes.²⁷ In small and intermediate congenital nevi, the greater the superficial component (junctional and papillary dermis) and the whiter the lesion, better is the possibility of clinical and dermatoscopic follow-up with the objective of detecting changes that may or may not to be related to a malignant degeneration of the lesion.²⁷

CONCLUSION

It can be affirmed that the therapeutic approach for congenital melanocytic nevi, and especially giant pigmented nevi, represents one of the greatest scientific challenges to be overcome in the future. The creation of organizations for patients, families and friends moved by the problem can be useful in the sense of offering support to those with such lesions and to provide better understanding of the disease for both patients and family, in addition to stimulating further research into the condition.⁴

REFERENCES

Received in October, 30^th of 2002.

Approved by the Editorial Council and accepted for publication in November, 8^th of 2002.

Questions and Answers to Questions

Assinale a alternativa correta:

1. O nevo melanocítico congênito gigante:

a) Está presente em aproximadamente em 1% dos recém- nascidos

b) É relativamente comum conhecido também como nevo em "calção de banho"

c) Corresponde a verdadeiros hamartomas cutâneos de nevomelanocítos

d) É uma condição rara com incidência estimada e 1 para cada 200 mil nascimentos

e) Desenvolve-se a partir do nascimento

2. O envolvimento da derme no nevo melanocítico congênito gigante:

a) Geralmente se estende aos 2/3 inferiores, ocasional- mente acometendo o subcutâneo

b) Apresenta padrão histológico semelhante ao observa- do no nevo melanocítico adquirido

c) Ocorre após a migração das células névicas localiza das na junção dermo-epidérmica

d) Caracteristicamente os ninhos de células névicas estão distribuídos entre as fibras colágenas

e) Não apresenta associação com os apêndices cutâneos

3. O nevo melanocítico pequeno apresenta de regra a seguinte característica microscópica:

a) Associação com apêndices cutâneos, nervos e vasos

b) Ocasionalmente se estende até o subcutâneo

c) Células névicas individuais distribuídas entre as fibras colágenas

d) Células névicas confinadas as camadas superiores da derme

e) Acometimento dos 2/3 inferiores da derme

4. O estudo radiológico do Sistema Nervoso Central está indicado em qual circunstancia:

a) Em todos os nevos melanocíticos congênitos

b) Em todos os nevos melanocíticos congênitos gigantes

c) Nos nevos gigantes localizados no dorso superior e no segmento cefálico

d) Quando associado a manifestações neurológicas

e) Quando associado a alterações eletroencefalográficas

5. A degeneração maligna no nevo gigante:

a) Geralmente ocorre a partir de células névicas localizadas na junção dermo-epidérmica

b) Raramente desenvolve a partir de células névicas localizadas na derme

c) Apresenta um risco estimado entre 5 a 20%

d) Raramente ocorre em pré-puberes

e) De regra o diagnóstico precoce é fácil de se proceder

6. Possivelmente a melhor conduta frente ao nevo melanocítico congênito intermediário é:

a) A exérese sistemática e precoce

b) Proceder inicialmente uma biopsia incisional

c) Seguimento clínico até a puberdade

d) Caso o padrão histológico seja igual ao de um nevo melanocítico adquirido proceder a exérese o mais precoce possível

e) Seguimento clínico e dermatoscópico

7. A dermatoscopia na abordagem dos nevos melanocíticos congênitos:

a) Apresenta um grande valor, sobretudo no seguimento dos nevos gigantes

b) Método sensível em detectar o processo de degenera- ção ocorrendo nos nódulos profundos

c) Quanto mais profundo for o componente névico mais fácil é a visualização das estruturas pigmentadas como o auxílio do dermatoscópio

d) A grande quantidade de pigmento melânico presente nos nevos gigantes facilita a visualização dermatoscópica

e) Apresenta um papel limitado no nevo gigante

Assinale a alternativa incorreta:

8. Classifica-se nevo melanocítico congênito conforme a medida do tamanho na infância em:

a) Pequeno (< 1,5 cm)

b) Médio (1,5 a 20 cm)

c) Intermediário (10 a 20 cm)

d) Gigante (> 20 cm)

e) NDA

9. Os principais problemas relacionados com o nevo melanocítico congênito gigante são:

a) Dificuldade na abordagem terapêutica

b) Possibilidade de transformação maligna

c) Implicações relacionadas com o aspecto estético

d) Acometimento neurológico

e) Traumatismos e infecções recorrentes

10. O nevo melanocítico congênito pequeno:

a) Apresenta um risco baixo de degeneração maligna

b) Geralmente os melanomas oriundos dos mesmos são epidérmicos

c) A transformação maligna raramente ocorre em pré- puberes

d) A excisão após a puberdade seria um ato seguro

e) A observação clínica raramente diagnóstica a degener ação maligna em fases precoces

11. O melanoma relacionado com o nevo congênito gigante:

a) 3/4 não se desenvolvem a partir dos nevos cutâneos

b) É exclusivamente cutâneo

c) Metade se manifesta antes dos 3 anos de idade

d) Os sinais de transformação maligna são tardios e geralmente acompanhados de metástases

e) Desenvolve-se com freqüência de melanócitos localizados nos tecidos profundos

12. Os critérios histológicos relacionados com a possibilidade de malignidade de um nevo gigante são:

a) Epidermotropismo de células isoladas na periferia da lesão

b) Número elevado de mitoses

c) Número elevado de atípias citonucleares

d) Maturação de células névicas

e) Presença de invasão vascular

13. A abordagem terapêutica do nevo gigante:

a) visa à excisão profilática do nevo

b) elimina completamente o risco de desenvolvimento do melanoma

c) A exérese deverá ser o mais precoce possível

d) Deve considerar as razões estéticas e psicológicas

e) na maioria das vezes os procedimentos cirúrgicos são incompletos

14. Os principais métodos empregados para a melhoria do aspecto estético do nevo gigante com exceção da exérese cirúrgica tradicional são:

a) Dermoabrasão

b) Curetagem

c) Peeling químico com fenol

d) Laser

e) Radioterapia

15. Os métodos terapêuticos empregados para melhoria do aspecto estético dos nevos gigantes:

a) Estão diretamente relacionados com um aumento do risco de degeneração maligna.

b) Recomenda-se a sua realização o mais precoce possível.

c) As principais complicações são a cicatriz hipertrófica e a repigmentação.

d) São procedimentos de alto risco, principalmente quando realizados em neonatos.

e) Demandam estudos clínicos de seguimento a longo prazo

16. O uso do Laser no tratamento dos nevos congênitos:

a) Produzem um efeito clareador superficial e profundo

b) Há citações de uso de Laser ablativos e não ablativo

c) Os métodos não ablativos produzem uma fototermólise seletiva do pigmento melânico

d) Os métodos não ablativos produzem destruição secundária da célula névica

e) Ainda faltam dados quanto à taxa de recidiva e o potencial de indução de transformação maligna

17. A melanose das meninges:

a) corresponde a uma das principais causas de degener ação maligna associada com o nevo gigante

b) pode ser assintomática ou paucissintomática

c) O estudo radiológico está sempre indicado visto as boas possibilidades terapêuticas desta condição

d) Pode estar presente principalmente no nevo gigante localizado no segmento cefálico e dorso superior

e) Corresponde ao principal foco de melanocíticos extra cutâneos

18. Os nevo melanocítico congênito pequeno:

a) Apresenta o mesmo padrão histológico que os nevo gigante

b) Sua medida na infância é inferior ou igual a 1,5 cm no maior eixo

c) A dermatoscopia apresenta-se útil principalmente quanto mais clara e superficial for à lesão

d) A transformação maligna raramente ocorre antes da adolescência

e) a incidência de degeneração maligna é extremamente baixa

19. A classificação do nevo melanocítico congênito pode ser feita de acordo com:

a) o seu tamanho na infância

b) o seu padrão histológico

c) a proporção da superfície cutânea acometida pelo nevo

d) o acometimento extracutâneo

e) NDA

20. O envolvimento da derme no nevo congênito:

a) está presente desde o período neonatal.

b) confinado as camadas superiores no nevo pequeno.

c) corresponde a origem de mais de 2/3 dos melanomas oriundos dos nevos gigantes.

d) é a causa principal de recidiva após tratamento por métodos terapêuticos não convencional.

e) apresenta padrão histológico indistinguível do nevo melanocítico adquirido

Gabarito

Genética Molecular das Epidermólises Bolhosas

2002; 77(5): 519-532

1.a 11.d 2.b 12.a 3.a 13.d 4.d 14.e 5.c 15.c 6.b 16.d 7.c 17.d 8.a 18.a 9.d 19.e 10.c 20.c

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*

Work done at the Dermatology Service of the ABC College of Medicine.

Publication Dates

• Publication in this collection
  03 Nov 2005
• Date of issue
  Dec 2002

History

• Accepted
  08 Nov 2002
• Received
  30 Oct 2002