Pathology of pigmented lesions Flashcards
What does the MC1R gene code for?
Melanocortin 1 receptor proteins
What is the function of MC1R proteins?
Turns phaeomelanin into eumelanin and thus determines the balance of pigment in the skin and hair
What colour does eumelanin colour hair?
Anything but red
What colour does phaeomelanin colour hair?
Red
What is caused by 1 defective MC1R gene?
Freckling
What is caused by 2 defective copies of the MC1R gene?
Red hair
Freckling
What is the medical name for freckles?
Ephilides
What are freckles?
Patchy clumps of melanin pigmentation, usually brought on by UV exposure and genetics (MC1R)
What are other names for actinic lentigines?
Solar lentigines
Age spots
Liver spots
What are the most common places to get actinic lentigines?
Face
Forearms
Dorsal hands
What are actinic lentigines?
Groups of increased melanin and basal melanocytes, related to sun exposure (Melanin overproduction)
What condition is shown?
Actinic lentigines
What is the medical term for a mole?
Naevus
What are some types of melanocytic naevi?
Congenital
Dysplastic
Spitz
Blue
Halo
What are the 3 stages of acquired naevus development?
Junctional naves - Childhood
Compound naves - Adolescence
Intradermal naves - Adulthood
What are the features of a junctional naevus?
- Melanocytes proliferate at the basal layer forming clusters of cells at the dermo-epidermal junction
- Tends to be flat or slightly elevated with smooth surface and uniform pigmentation
What are the features of a compound naevus?
- Junctional clusters of melanocytes as well as groups of melanocytes moving down into the dermis
- Lesions are slightly elevated or dome shaped and are often pigmented
- Hairs may project from the surface
What are the features of an intradermal naevus?
- All junctional activity is ceased, with all melanocyte clusters forming in the dermis
- Usually dome shaped, verrucous (Warty), pedunculated or sessile, often flesh-coloured, occasionally hairy and may display surface telangiectasia
How is the size of a congenital naevus classified?
- Small <2cm diameter
- Medium >2cm but <20cm diameter
- > 20cm Giant-garment type lesions
What is a risk of large congenital naevi?
10-15% increased risk of melanoma
What causes the formation of simple naevi in infancy?
There is usually a breakdown of malenocyte:keratinocyte ration at a number of cutaneous sites, which is thought to be immune related
How many naevi does the average person have?
20-30
What are the surface features of dysplastic naevi?
> 6mm diameter
Variegated pigment
Asymmetrical border
What are the 2 types of dysplastic naevi?
Sporadic
Familial
How does sporadic dysplastic naevi present?
Sporadic dysplasic naevi usually affect one to several naevi and slightly increase risk of malignant melanoma
How does familial dysplastic naevi present?
Familial dysplastic naevi have a high penetrance in families and cause many atypical naevi, increasing lifetime risk of melanoma up to 100%
How will dysplastic naevi show on histology?
- Architectural atypia
- Cellular atypia
- Fibrosis
- Inflammation
Unlike in melanoma, the epidermis is not usually effected, however, severe dysplasia may be difficult to distinguish from melanoma in-situ
Describe the features of halo naevi
Halo naevi have a peripheral halo of depigmentation. They show inflammatory regression and are overrun by lymphocytes
Describe the features of blue naevi
Blue naevi are entirely dermal and consist of pigment rich dendritic spindle cells. The cellular variant may have mitoses and mimic melanoma
These look blue due to the light scattering effect
Describe the features of Spitz naevi
Spitz naevi usually occur in those under 20 and consist of large spindle and/or epithelioid cells with pink colouration due to prominent vasculature
They may closely mimic melanoma, but most are entirely benign
What condition is shown?
Halo naevus
What condition is shown?
Blue naevus
What condition is shown?
Spitz naevus
