Congenital Melanocytic Nevus Defined as benign nevomelanocytic proliferations present at birth



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Congenital Melanocytic Nevus


  • Defined as benign nevomelanocytic proliferations present at birth.

  • Rarely, melanocytic nevi with features indistinguishable clinically and histologically from typical congenital melanocytic nevi appear in children between 1 month and 2 years of age. This subset is termed nevus tardive


Classification
Small <1.5cm

Intermediate 1.5-19cm

Large >20cm >2%BSA or 1%SA of Head
Clinical appearance


  • Generally, congenital melanocytic nevi are round to oval in shape and have a regular, smooth, and well-demarcated border.

  • After the first 6 months, the lesions grow proportionally to the particular area of the body involved

  • Clinical appearance may change with age.

  • In neonates, the moles may be light in color and relatively hairless, with a flat or raised surface. As the child grows, the nevi may become progressively darker, with a uniform brown to dark brown or black color and may acquire long, coarse, darkly pigmented hairs.

  • May exhibit a papular, rugose, pebbly, verrucous, or even cerebriform surfaces

  • Satellite smaller melanocytic nevi may also be present,

  • “Kissing nevus,” or divided nevus of the eyelid, is an interesting clinical variant of congenital melanocytic nevi. It occurs on adjacent parts of the upper and lower eyelids and appears contiguous, as a single lesion, when the eyelids are closed. This finding implies that congenital melanocytic nevi develop between the 9th and 20th week of gestation, when the eyelids are fused


Histology

  1. nevomelanocytes splaying or extending between the collagen bundles of the reticular dermis as single cells, “Indian” files, or cords of cells

  2. nevus cells in lower 2/3rd dermis

  3. extension of nevomelanocytes around and within hair follicles, sebaceous glands, eccrine apparatus, vessel walls, and nerves

  4. perivascular and perifollicular distribution of nevomelanocytes simulating an inflammatory reaction such as figurate erythema

  5. arrector pili that may be enlarged, distorted, and infiltrated by nevomelanocytes.

Atypical features of congenital nevi include



  1. dysplasia of intraepidermal nevomelanocytes

  2. pagetoid spread of nevomelanocytes - pagetoid intraepidermal growth pattern in benign melanocytic nevi is confined to the area of nested intraepidermal proliferation, in contrast to melanoma in which the pagetoid growth is observed as lateral spread beyond the nested proliferation

  3. proliferative dermal nodules.


Distinctive “Indian file” array of nevomelanocytes.


During the first 6 months of life, some nevi can appear to ‘‘grow’’ significantly as tardive pigment becomes more visible.

Some satellite nevi may become visible for the first time over the first 2 to 3 years (tardive CM)


Associations

  • scoliosis, spina bifida, clubfoot, cranial bone hypertrophy


Neurocutaneous melanosis

  • First described by Rokitansky

  • presence of giant (2/3rd) or multiple(1/3rd) melanocytic nevi associated with benign or malignant melanotic tumors of the central nervous system.

  • posterior axial location, especially when associated with "satellite" melanocytic nevi at greatest risk

  • Called leptomeningeal melanocytosis with CMS melanoma

  • Leptomeningeal melanoma present in upto 62% of the cases, but even in the absence of melanoma, symptomatic neurocutaneous melanosis has an extremely poor prognosis.

  • Patients with large or multiple congenital melanocytic nevi in axial locations (head, neck, or posterior midline) or multiple satellite lesions seem to have an increased risk of leptomeningeal melanocytosis.

  • Most case are sporadic, and no gender or racial predilection is evident.

  • Melanocytes of both skin and leptomeninges are thought to be derived from multiple potential precursor cells of the neural crest, NCM is postulated to represent a congenital error in embryonic neuroectoderm morphogenesis.

  • CSF shows increased protein, decreased sugar, and a normal cell count.. May show melanin-filled cells

Criteria for the diagnosis of neurocutaneous melanosis:

      1. The presence of large or multiple congenital melanocytic nevi (one of which is at least 20 cm in diameter) with benign (melanosis) or malignant (melanoma) central nervous system (CNS) tumors.

      2. The absence of malignant melanoma in any organ (including skin) other than the CNS.


Histology

        • accumulation of melanotic cells in the arachnoid and pia mater

        • Parenchymal melanin deposits probably represent melanocytes in the perivascular spaces.



Clinical

Hydrocephalus – usually secondary to meningeal thickening,

Seizures

Mass lesions

Cranial nerve palsies

Mental retardation

Spinal cord compression
Investigations

MRI – T1 shortening characteristic

CSF cytology
Prognosis


  • death occurred in more than half the patients within 3 years of the onset of neurological symptoms, most <10 years old


Outcome

2 main concerns

  1. Risk of melanoma

  2. Stigma of visible lesion and how it will affect psychosocial development


Risk of melanoma

    • In general, risk is related to nevomelanocytic load

    • In several case series, no melanoma noted in small and intermediate lesions

    • Approximately 50% of the malignancies that develop in large CMN do so in the first 3 years of life, and 70% by puberty (<10yr old)

    • Giant melanoma – 2 prospective studies

      1. Ruiz-Maldonado (1992): Three of 80 patients (3.8%) developed cutaneous melanoma during an average follow-up period of 4.7 years

      2. Marghoob (1996): Ninety-two patients were followed up prospectively for an average of 5.4 years. Melanoma developed in 3 patients (3.3%) in extracutaneous sites.

      3. Watt (PRS 2004) – review of 8 studies. Observed incidence of melanoma was 2600 times higher than would be expected.

  • majority of melanomas that arise in association with large or giant congenital melanocytic nevi originate in the dermis. They are usually composed of epithelioid cells, spindle cells, or small round cells.

  • Melanomas arising in small congenital melanocytic nevi usually originate in the epidermis

  • To date, no case of melanoma has been reported arising in a satellite nevus


Treatment

Rationale for early treatment



  1. greatest risk of melanoma during early years

  2. elasticity and healing capacity of the skin in the early years

  3. more tolerant to surgery /tissue expansion

  4. psychological benefit

Treatment options



    1. observation

    2. dermabrasion

    3. curettage

    4. chemical peel

    5. Q-switched ruby laser

    6. staged excision and reconstruction

Dermabrasion and curettage



      • remove the more concentrated population of nevus cells near the lesion’s surface.

      • Theory is that the nevus cell migrate deeper with age

      • can be effective in reducing the overall nevus ‘‘cell load’’ but cannot fully remove the nevus, because of the well-known depth of nevus cells in CMN

      • may result in significant lightening of the color of the lesion, it is quite common to see later ‘‘bleed-through’’ of the deeper nevus, with gradual darkening and reappearance of the lesion.

      • lightening of pigmented giant congenital nevi using these techniques may make it more difficult to monitor the resultant lesion for signs of malignant transformation, because alteration in pigmentation of the lesion can no longer be followed reliably.

      • no longitudinal studies documenting decreased rates of malignant transformation after laser or dermabrasion treatment.


Reconstruction

  • there is no evidence in the existing literature that the excision of large congenital melanocytic nevi decreases the prevalence of melanoma.


Serial excision

  • undertaken if lesion can be removed in 3-4 excisions. Otherwise tissue expand.


SSG

  • SSG or full thickness grafts(preferred)

    • FTSG donor sites – postauricular, supraclavicular, buttock, groin, medial arm, abdomen

    • May be expanded to increase donor area

    • Use of Integra at recipient site may improve scar


Tissue expansion (Bruce Baeur)

  • Advantage - large flaps of color-, thickness-, and texture-matched skin while simultaneously minimizing donor-site defects.

  • optimized to ensure that the landmarks of the forehead aesthetic unit will be disturbed as little as possible.

  • Particular emphasis is placed on brow symmetry, temporal hairline position and hair direction, and scar orientation.


Scalp

  • Treatment starts as early as 6 months, with some cranial molding expected by the time the expanders are removed

  • No instance of long-term cranial deformity has been noted (remodeling usually occurs over 3 to 4 months).

  • Rectangular expanders with remote ports, placed subgaleal (250-500ml size)

  • Usually 2 expanders used

  • Expanded weekly, 2nd stage in 10 weeks





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