Chapter 8: Lumps and Bumps
Melanocytic Lesions: Acquired Melanocytic Nevi
What is it?
Melanocytic nevi are most commonly referred to as moles. The number of moles in any patient is related to their skin type, age, genetics, and sun exposure. Acquired nevi first appear in early childhood, increase in size and number into the third or fourth decade, and then slowly decrease in number with age. In childhood, fair skin colour, sun exposure and sunburns are associated with a higher number of moles. The biggest concern about moles from patients and their parents is the risk of melanoma and some are of cosmetic concern. The vast majority of nevi are benign. but acquired nevi may be a marker of an increased risk and very rarely a mole can be a precursor lesion to a melanoma.
What does it look like?
Acquired melanocytic nevi are classified by the location of the nevus cells in the skin. This classification system mirrors the natural history of a nevus from a junctional nevus early in life which develops into a compound nevi and then an intradermal nevus in later adulthood.
Junctional nevi: light to dark brown, hairless macules measuring 1mm-1cm diameter.
Compound nevi: skin-coloured to brown papules with smooth or rough surface – may have coarse hairs.
Intradermal nevi: soft, dome-shaped papules varying from skin coloured to brown – may also contain hairs.
How is it treated?
Acquired melanocytic nevi should be observed routinely by the child or parent for any new or concerning features. Any nevi with sudden unusual growth or bleeding, should be referred to dermatology for evaluation.
Special considerations:
- Nevi on the palms, soles and genitalia tend to retain a flat, junctional appearance throughout life.
- Scalp nevi are often larger than other acquired nevi, present at the part-line, and may have a fried egg or eclipse pattern
- Halo nevi are common in children and young adults. They appear as a central (usually pigmented) melanocytic nevus with a peripheral halo between 1-5mm of hypo- or de-pigmented skin. Patients with halo nevi have an increased incidence of vitiligo.
- Blue nevi can be congenital or acquired. There are two subtypes – common and cellular blue nevi. They appear as blue-grey/black smooth papules or plaques with uniform color. They should be monitored for change, but are generally benign.
- Atypical or dysplastic nevi often appear in puberty, are somewhat larger than other acquired nevi, and have some pigment variability. Having multiple atypical nevi is thought to suggest elevated risk of developing melanoma.
- Familial atypical multiple mole-melanoma (FAMMM) syndrome is an autosomal dominant genetic syndrome characterized by multiple atypical nevi and an increased risk of melanoma and pancreatic cancer. Children with a family history of FAMMM syndrome should be seen regularly for a full cutaneous exam.
- Spitz nevi are a subtype of melanocytic nevi that occur primarily in children. On histology they share features of malignant melanoma but are a benign process. They appear as a solitary smooth, red-brown or dark brown to black dome-shaped papule. Occasionally a child will have multiple lesions, referred to as agminated spitz nevi. Because of their histologic similarity to melanoma, the diagnosis may be difficult or the lesion concerning. If Spitz nevi are not excised, they should be monitored.
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