What is a Naevus

•  hamartomatous malformation of skin – benign proliferation of normal skin constituents

What is a melanocytic naevus

•   Benign proliferation of melanocytes or melanocytic naevus cells

What is the difference between naevus cell and melanocytes

• Naevus cells cluster as nests in lower epidermis and dermis; melanocytes are evenly dispersed in basal layer of epidermis

• Naevus cells do not have dendritic processes

How can malanocytic naevi be classified

• Location: Junctional, compound, dermal

• Congenital and acquired

• Atypical or banal

• Special variants and those of no special type.

What is the origin or melanocytes

· Originate in neural crest

· Migrate ® basal layer of epidermis by 3/12 in utero

· Failure of migration of dermal melanocytes leads to Mongolian spot and blue naevus

Function

· Produce melanin which is transferred to surrounding epithelial cells

— Protect from UV

Natural history of naevi

Junctional

• Proliferation of melanocytes @ dermal-epidermal junction forming a junctional naevus

• Flat pigmented macules.

• Pre pubertal, flat, hairless, well defined, normal skin markings present, low malignant potential

Compound

• Melanocytes drop into dermis so that naevus cells are present in D-E junction and dermis known as compound naevus

• Often appear raised and may be papillomatous

• Adolescents, dark brown, black, elevated, nodular, ± Hair, low malignant potential

Dermal

• When junctional activity ceases all that remains is the dermal naevus component.

• Often appear as flesh-colored often dome-shaped or pedunculated

• Adults, flat, raised, nodular, pedunculated, ± Pigment, ± Hair, very low malignant potential

• With progressive migration of naevus cells the lesions become more elevated and less pigmented.

• Common benign naevi appear after 6 months, increase in number during adolescence and peak in 30’s and decline thereafter.

What are the features of banal naevi

• No asymmetry with round or oval shape

• Border regular and sharply demarcated

• No colour variation

• Diameter <6mm

• No change with time

What is the treatment

• Vast majority remain benign throughout life.

• There is no vale to prophylactic removal for reducing risk of melanoma

What is an atypical melanocytic naevus

• Acquired melanocytic naevi that share some features of melanoma

• The colour is variegated, the borders are irregular or ill-defined, larger than banal naevi, but are generally stable and symptomatic.

• Atypical naevi increase the risk of melanoma the extent of which depends on total naevus burden, personal history, family history and sun exposure history

What are the special types of naevus

• Halo naevus, blue naevus and Spitz naevus

What is a Halo naevus

• Brown naevus surrounded by oval or round symmetric halo of depigmentation

• Depigmentation 2° immunological destruction of naevus cells by T cells

v Need to inform pathology of clinical appearance

Histo

· Compund or intradermal naevus

· Heavy lymphocytic infiltrate

• A biopsy is required when the central naevus has atypical or worrisome features.

What is a Spindle cell (Spitz) naevus

• Acquired proliferation of melanocytes with histological features which overlap with melanoma

· Predominantly children

· Raised lesion

· Often on face

· Reddish-brown

· Can be clinically confused with melanoma

Histo

· Variant of compound

— Junctional and dermal components

· Spindle shaped melanocytes in dermis

· Telangectasia with prominent vessels @ dermal-epidermal junction

· Mitotic figures common

· Lacks irregular or nodular invading edge of melanoma

What is a Blue naevus

· Dermived from a benign proliferation of dermal melanocytes

• Colour is due to preferential scattering or shorter wavelengths of light by dermal melanin

· Failure of complete migration in embryo

· Head, neck, upper limbs

· Malignant change very rare

Histo

· intradermal

· Wedge shaped with dendritic processes

— Apex points deep

· Spindle shaped melanocytes & deeply pigmented melanophages

What is a congenital naevus

• Melanocytic naevus present at birth or within the first few months of life

• They are proliferations of benign melanocytes that occur during embryogenesis

• Tend to penetrate deeper into the dermis and subcutaneous tissue than acquired naevi

How are congenital melanocytic naevi categorized

• Based on projected final size:

• Small <1.5cm

• Medium

• Large >20cm – called garment or bathing trunk naevi

What is the risk of melanoma

• For small and medium-sized less than 1% lifetime risk

• For large CMN the risk is 5% with 50% occurring in the first 5 years of life

What is neurocutaneous melanoisis

• Proliferation of melanocytes in CNS

• Associated with large CMN on scalp or posterior axial location.

What is the management

• For large CMN excision is recommended to reduce risk melanoma

• For smaller lesions excision may depend on ease of monitoring, cosmetic defect, colour location, parent’s anxiety.

Dysplastic naevus

v Greene et al 1985

· Naevi atypical clinically and histologically

· ­ Risk of developing melanoma

· Familial and non familial

· Overall 10- 20% Australian population have ³1 dysplastic naevus

Familial

· FH of dysplastic naevi or melanoma (B-K mole syndrome)

· 100% cumulative lifetime incidence of developing melanoma

· Autosomal dominant

· Chromosome 1p

v 5-10% of melanoma in patients with dysplastic naevi

Follow up

· Regular basis

· Excision of moles with ? atypical features

Sporadic

· 5% caucasian population

· Less risk of developing melanoma

— 6% lifetime risk