Nevus melanocytic (overview) D22.-

Benign, congenital or acquired, melanocyte-derived, brown to brown-black, less commonly reddish or skin-colored, patchy, nodular, plaque-like, or nodular melanocytic nevi that are usually plural but may also be solitary.

Melanocytic nevi may be confined to the epidermis(lentigo simplex, junctional melanocytic nevus), localized in the epidermis and dermis (compound type of melanocytic nevus), or localized exclusively in the dermis (dermal melanocytic nevus). This clinical/histologic typing denotes a sequential developmental process that all melanocytic nevi undergo 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 originate from cells migrating from the neural crest into the epidermis. It is likely that melanocytes and "nevus cells" represent identical cell populations, so that the term "nevus cell" can be dispensed with in connection with melanocytic nevi (aka nevus cell nevus).

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

Histologically, 3 variants can be distinguished:

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

Melanocytic nevi show intraepidermal and/or dermal accumulations of melanocytes. Melanocytes within the junctional zone have a round, oval, or spindle-shaped appearance and are located in contiguous nests. In the superficial dermis, the cells generally have an epithelioid cellular character with medium-sized, usually centrally located nuclei, and a distinct cytoplasmic rim. The degree of pigmentation is variable, either finely granular but also scollic across the cytoplasm. The nuclei show a uniform chromatin distribution with a slightly clumped texture. Deeper in the dermis, melanocytes lie in strands. Often, the cells show decreased cytoplasmic content. They then resemble lymphocytes and are often arranged in linear strands but also diffusely. The skin appendages are sheathed by the dermal melanocytes, but always remain intact.

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