W8L2 - Skin Histology

Question 1

Punch Biopsy

Answer 1

Punch Bx are performed to completely excise small lesions, sample large lesions, or evaluate an inflammatory process or a systemic disease
Punch Bx can be 2 to 8mm in diameter
Describe/record the type of specimen including;
- diameter, depth and colour.
- describe any lesions
- include size, type (macular, popular, vesicular, plaque), borders (well circumscribed, irregular), shape (verrucous, lobulated), distance from the closest margins
- ink all punch biopsies

Question 2

Verhoeff’s Van Gieson Stain

Answer 2

Used to distinguish:
- elastic fibres (black)
- collagen fibres (red)
- muscle/cytoplasm/RBC’s (yellow)
Verhoeff’s stain is an iron mordant haematoxylin and is acid fast and is not affected by the VG counterstain
Tissue is overstained with a complex of haematoxylin ferric chloride iodine
These components act as mordants to fix the Hx stain to the tissues by oxidising and converting Hx to haematein

Question 3

Epidermis Layers - Stratum Basale

Answer 3

Deepest layer of cuboidal cells anchored to the BM by hemidesmosomes
These are reserve cells or stem cells for the epidermis and undergo maturation
All cells in the stratum basale produce intermediate keratin filaments that increase in number as they move superficially

Question 4

Epidermis Layers - Stratum Spinosum

Answer 4

2nd layer which shrinks in H&E sections
The developed intercellular spaces between these cells appear to form numerous cytoplasmic extensions that project from their surfaces
These spines represent where the desmosomes are anchored to intermediate keratin filaments or tonofilaments, attached to neighbouring cells

Question 5

Epidermis Layers - Stratum Granulosum

Answer 5

3rd layer and contain cells with dense basophilic keratohyalin granules
3-5 layers of cells that are flat or polygonal in appearance
Cytoplasm of these cells contain membrane bound lamellar granules formed by lipid bilayers
Layers of lipid act as an impermeable layer to water
This layer stains dark with H&E

Question 6

Epidermis Layers - Stratum Lucidum

Answer 6

In thick skin only
Translucent
Clear zone that stains poorly
Very flat cells

Question 7

Epidermis Layers - Stratum Corneum

Answer 7

5th layer and most superficial layer
Nuclei and organelles have disappeared from these cells
Usually dead cells with soft keratin filaments
Keratinised superficial cells from this layer are continually shed or desquamated

Question 8

Melanocytes

Answer 8

Derived from neural crest cells
Located between the stratum basale and the stratum spinosum of the epidermis and synthesise the dark brown pigment melanin
- melanin is synthesised from the amino acid tyrosine by the melanocytes
- function of melanin is to protect the skin from the damaging effects of UV radiation
Have long irregular cytoplasmic extensions that branch into the epidermis

Question 9

Langerhans Cells

Answer 9

Found mainly in the stratum spinosum
They participate in immune responses
Langerhans cells recognise phagocytose, and process foreign antigens, and then present them to T lymphocytes for an immune response

Question 10

Merkels Cells

Answer 10

Found in the basal layer of the epidermis and are most abundant in the fingertips
Because these cells are closely associated with afferent (sensory) unmyelinated axons, it is believed that they function as mechanoreceptors to detect pressure

Question 11

Skin - Microanatomy

Answer 11

Rete pegs - downward extensions of the epidermis that divide the dermis into papillae
Papillary dermis - fine collagen and elastic containing the capillary loops of the vascular plexus
Reticular dermis - thick collagen with elastic bundles separated from above by the superficial vascular plexus and most of the adnexal structures are found here
Adnexal structures - hair follicles, sebaceous glands, eccrine and apocrine glands, arrector pili, nerves and BV’s
Subcutaneous - mature adipose tissue separated into lobules by fibrous septa

Question 12

Skin Samples in Histo

Answer 12

Skin is typically fixed in 10% NBF
Gross descriptions, size L x W x T, epidermis present?
Colour of tissue, hair, alterations to the epidermal surface including dimensions, distance to the nearest margin of discrete lesions
All surfaces except epidermis to be inked - not black

Question 13

Inking Gross Samples

Answer 13

Inking is performed in a way so that:
- orientation can be reconstructed, where microscopic lesions are detected close to or involves a specific margin, the location of the positive margin can be accurately conveyed to the surgeon to aid in a re-excision if necessary

Question 14

Some Terminology

Answer 14

Acantholysis - loss of attachments between keratinocytes
Acanthosis - thickening of the epidermis
Dyskeratosis - abnormal keratinisation
Epidermotropism - migration of malignant cells into epidermis
Hyperkeratosis - thickened stratum corneum
Hypergranulosis - increased number of cells in the granulosa, normal level of keratinisation for location e.g. palm
Parakeratosis - abnormally retained nuclei in stratum corneum

Question 15

Inflammatory Dermatoses

Answer 15

Lichen planus - a hypersensitivity reaction with lymphocytic infiltrates at the dermal/epidermal junction
Psoriasis - a proliferative skin disease characterised by persistent epidermal hyperplasia
Eczema - atrophic dermatitis
Cutaneous infections
- Molluscum contagiosum, verruca, HPV, plantar warts
- HSV
- Fungi dermatophytes
Cysts
Solar elastosis
Dermatitis - a clinical term used to describe a wide variety of inflammatory conditions with diverse causes

Question 16

Impetigo (‘School Sores’)

Answer 16

Results in an acute superficial pyoderma that heals without scarring
Typically occurs in pre school aged children as well as in immunocompromised adults/elderly
Starts as a small superficial pustules or vesicles on face and extremities that progress to honey-coloured crusted plaques with surround erythema
Often caused by staphylococcus aureus and streptococcus pyogenes
Spread by direct contact, especially in humid environments

Question 17

Pathological Basis of Dermatological Signs

Answer 17

Scaling - parakeratosis
Erythema - dilatation of skin vessels
Blisters - separation of layers of the epidermis from dermis
Bruising - leakage of blood into dermis
Pigmentation - endogenous pigment e.g. ochronosis, exogenous pigment e.g. tattoo
Plaques - inc in epidermal and dermal thickness with cells
Macules (skin discolouration) - dilated blood vessels, inflamm cells altered pigmentation
Papules (small, tender bump on skin) - inflamm cells, oedema, tumour
Nodules - epidermal tumours, adnexal tumours, dermal tumours, cysts
Rashes restricted to exposed areas - photosensitivity, contact eczema
Nail abnormalities - trauma to nail bed, psoriasis, fungi, tumour

Question 18

Epidermal Inflammatory Reactions

Answer 18

Accumulation of fluid beneath skin
Small lesions termed vesicles
Larger collections of fluid termed bullae
A collection consisting of neutrophils with some fluid, lying within or beneath the epidermis is called a pustule

Question 19

Acanthosis

Answer 19

Thickening of the epidermis
Usually due to increase in depth of stratum spinosum layer
Common feature in chronic inflammatory conditions
Marked by rete pegs which are expanded and elongated with prominent dermal papillae

Question 20

Psoriasis

Answer 20

Characterised by scaly lesions
Histologically, main feature is acanthosis with greatly elongated, narrow rete pegs
- can show expanded dermal papillae inbetween rete pegs in which dilated capillaries are prominent
- parakeratosis