Nevus melanocytic (overview) D22.-

Benign, congenital or acquired melanocytic, brown to brown-black, more rarely reddish or skin-coloured, spotty, nodular, plaque or nodular melanocytic tumours, which mostly occur in plural, but also solitary form. Melanocytic nevi may be restricted to the epidermis (lentigo simplex, junctional melanocytic nevus), located in the epidermis and dermis (compound type of melanocytic nevus) or exclusively in the dermis (dermal melanocytic nevus). This clinical/histological typing describes a sequential developmental process that all melanocytic nevi go through in stages.

Classification of congenital and acquired melanocytic nevi according to histological and clinical criteria:

• Acquired melanocytic nevus:
  • lentigo simplex
  • Lentigo solaris (senilis)
  • Lentigo, reticular
  • Lentigo of the mucosa (melanosis of the mucosa)
  • Nevus melanocytic acral
  • Nevus melanocytic dysplastic (atypical)
  • Ordinary melanocytic nevus
    • Usual melanocytic nevus junctional type
    • Common melanocytic nevus compound type
    • Common melanocytic nevus dermal type
  • Nevus melanocytic halo-nevus
  • recurrent melanocytic nevus
  • Nevus Spitz
  • Naevus melanocytic deep infiltrating
  • Nevus melanocytic spindle cell nevus pigmented
  • Bladder cell nevus (balloon cell nevus)
  • Meyerson's melanocytic nevus.
• congenital melanocytic nevus:
  • Small congenital melanocytic nevus (< 4 cm)
  • Large congenital melanocytic nevus (> 4 cm)
  • Giant congenital melanocytic nevus (e.g. swimming trunks type)
  • melanosis neurocutanea
  • nevus spilus
• Dermal melanocytosis:
  • Mongolian spot
  • Nevus fuscocoeruleus ophthalmomaxillaris (Naevus Ota)
  • Naevus fuscocoeruleus deltoideoacromialis (Naevus Ito)
• Blue Nevus

It has been postulated that melanocytic nevi are derived from cells that migrate from the neural crest into the epidermis. Probably, melanocytes and "nevus cells" represent identical cell populations, so that the term "nevus cell" in connection with melanocytic nevi (alias nevus cell nevus) can be dispensed with.

On the whole integument, also on superficial mucous membranes possible.

Histologically 3 forms can be distinguished:

• Junction type (initial epidermal stage)
• Compound type (epidermo-dermal)
• Dermal type: Dermal melanocytic nevus.

Melanocytic nevi show intraepidermal and/or dermal accumulations of melanocytes. The melanocytes within the junctional zone have a round, oval or spindly appearance and lie in contiguous nests. In the superficial dermis, the cells generally have an epithelioid cell character with medium-sized, usually centrally located nuclei and a distinct cytoplasmic border. The degree of pigmentation varies, either finely granular or cloggy distributed over the cytoplasm. The nuclei show a uniform distribution of chromatin with a slightly clumped texture. Deeper in the dermis the melanocytes are arranged in strands. Often the cells show a reduced cytoplasm content. They resemble lymphocytes and are often arranged in linear strands but also diffusely. The skin appendages are covered by the dermal melanocytes, but always remain intact.

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7. Synnerstad I et al (2004) Fewer melanozcytic nevi found in children with active atopic dermatitis than in children without dermatitis. Arch Dermatol 140:1471-1475
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