Dermatology: Embryology Flashcards
What does the epidermis originate from?
Ectoderm - single layered epithelium
Ectoderm proliferates to form layer of surface epithelium called periderm
Periderm covers the developing epidermis until cornified cell layer is formed
Label this image
When does the epidermis stratify?
Then what happens?
At approximatey 8 weeks EGA
Cornification (‘dead’ keratinocytes held together by proteins & lipids) until about 19 weeks EGA
What occurs at 19 weeks EGA?
Keratinisation - skin becomes impermable
Prior to 19 weeks - fetal skin highly permeable & amniotic fluid volume mostly determined by fetal surface area
What is the vernix caseosa?
Greasy coat; protects skin from amniotic fluid in utero
When differentiation completes, periderm detatches from epidermis and remnants form the vernix caseosa
When does the skin acquire full barrier function?
A few weeks after birth
Epidermis is more similar to adult skin from around mid 3rd trimester
How do melanocytes develop?
Develop from ectoderm
Migrate from neural tube to epidermis
Active melanocytes are present throughout dermis during embryonic development and most migrate to the epidermis or undergo apoptosis by birth
Melanocytes are not fully functional until 2nd trimester
How does congenital dermal melanocytosis develop?
When melanocytes fail to reach epidermis and are trapped in dermis at time of birth
Slowly resolves spontaneously with time
What is cutaneous mosaicism?
2 or more genetically different populations of cells exist side by side in skin
Typical patterns: V shaped (upper spine), S shaped (abdomen), linear (arms/legs), spiral (scalp), vertical (midface)
What are Blaschko’s lines?
A manifestation of cutaneous mosaicism
A distribution pattern often followed by skin conditions that result from genetic abnormalities in the epidermis and/or its appendages.
The pattern represents migration pathways of epidermal cells during embryonic development
What are these 4 patterns of cutaneous mosaicism? (with examples)
A - narrow bands of Blaschko
- incontinentia pigmenti,
- epithelial naevi e.g. inflammatory linear verrucous epidermal naevus
- hypomelanosis of Ito
B - large bands of Blaschko
-McCune-Albright syndrome
C - chequerboard pattern
- Becker naevus
- vascular malformation (Port wine stain)
D - Phylloid pattern
- Mosaic trisomy 13
What is an epidermal naevus?
Defect in ectoderm –> overgrowth of epidermal keratinocytes
Presents at birth (50%) or in early infancy: localised, linear, warty, hyperpigmented plaque
2 types: linear (majority) and systematised
What is hypomelanosis of Ito?
Naevoid hypopigmentation - hypopigmented streaks that follow Blaschko’s lines
Part of rare neurogenetic cutaneous syndrome due to defect in NEMO gene.
Typically presents in newborn with blisters that also follow Blaschko’s lines. Blisters then resolve and reveal hyperkeratotic, warty plaques, followed by increasing pigmentation at 2-6 months
Hyperpigmented brown streaks later fade into atrophic hypopigmented streaks in later childhood.
What is a sebaceous naevus?
Genetic: overgrowth of entire skin component (epidermis, sebaceous glands, hair follicles, apocrine glands and connective tissue).
Typically brown/orange hairless patch on scalp which becomes warty during puberty. Small risk of tumour in later life. Surgery recommended late adolesence.
What is aplasia cutis?
TBC
How is infantile haemangioma managed?
Usually active non-intervention
Treatment should be considered for lesions which are large with potential for disfigurement, ulcerating, threatening vital function e.g. vision/hearing/breathing/feeding or high-output cardiac failure.
Steroids were mainstay but now oral propranolol (non-selective beta blocker) is treatment of choice for complicated lesions.
?inhibits angiogenesis + recruitment of endothelial progenitor cells
?induces apoptosis
Topical beta blocker eye drops applied directly also effective
