Melanocytic nevus

Mother's mark, nevus cell naevus, naevus naevocellularis, nevocyte naevus.

Congenital or acquired, melanocytic skin change. It is a hamartoma.

• More common in Caucasians than in Asians
• Rarely occurring or barely visible in Africans due to pigmentation

Dermal melanocytosis

• Naevus bleu
• Mongolian spot
• Naevus Ota (head, also called nevus fuscocoeruleus ophtalmomaxillaris)
• Naevus Ito (shoulders, "inferior", also called nevus fuscocoeruleus deltoideoacromialis

Congenital nevi

• Small congenital nevus cell nevi (< 3cm)
• Large congenital nevus cell naevi (> 3cm) --> from 3 cm or from 20 satellites or both, extended work-up including MRI should be performed.
• Large-area nevus cell naevus (whole body segment covered similar to garment) --> in any case extended work-up
• Melanosis neurocutanea
• Naevus spilus

Acquired nevi

• Lentigines
  • Lentigo simples
  • Lentigo senilis (solares), transition to seborrhoeic keratosis
  • Lentigo reticularis
  • Lentigo of the mucosa
• Melanocytic nevi
  • Junctional type
  • Compound type
  • Dermal type
  • Halo nevus
  • Recurrent nevus
  • Pointed nevus
  • Deep infiltrating nevus
  • Spindle cell nevus
  • Meyerson--nevus

The aetiopathogenesis is not completely clear. It is assumed that it is a matter of cells migrating from the neural crest into the epidermis.

• Sharply demarcated, facultative brownish/blackish papules and plaques
• Multiple different types

Geographical position on the body:

• Varies by type, certain types of melanocytosis for example have clear predilection sites associated with the diagnosis

Vertical position:

• Epidermis: junctional melanocytic naevus
• Epidermis & dermis: compound type of melanocytic naevus
• Dermis: dermal melanocytic naevus

Degeneration to malignant melanoma.

• Patients with >100 benign moles on the body have an 11x higher risk for malignant melanoma. This is a stronger risk factor than UV exposure in the history (this only increases the risk by 2.5x)
• All individuals have these benign melanocyte tumours
• There are new moles up to about 30 years of age, a spurt is seen between 20-30 years of age. After that, the moles decrease in number. 
• If in doubt, biopsy a raised pigmented change, do not wait if melanoma is suspected.
• 3 months interval may be too short to detect changes clinically. Therefore, better biopsy or wait 6 months, in case of doubt biopsy
• In the acral area, a biopsy is often delayed because patients want to be protected from the pain of the biopsy. This leads to a delayed diagnosis of acral melanomas
• Even by good dermatologists, about 10-20 moles are biopsied to detect a single melanoma. The aim is not to miss a melanoma - unfortunately they may not be clinically detectable

1. Barnhill RL, Mihm MC, Magro CM. Plexiform spindle cell naevus: a distinctive variant of plexiform melanocytic naevus. Histopathology 1991;18:243-7.
2. Mackie RM, Doherty VR. The desmoplastic melanocytic naevus: a distinct histological entity. Histopathology 1992;20:207-11.