Part twos - skin Flashcards
What is necrostising fasciitis
A necrotising soft tissue infection of the deeper tissues that results in progressive destruction of the muscle fascia and overlying subcutaneous fat.
Muscle tissue is frequently spared because of its generous blood supply.
Infection typically spreads along the muscle fascia due to its relatively poor blood supply.
Initially the overlying tissue can appear unaffected. It is this feature that makes necrotizing fasciitis difficult to diagnose without surgical intervention.
What is Fournier’s gangrene?
Necrotising soft tissue infection of the perineum
Initially described in men only but does no include women.
Risk factors for necrotising soft tissue infections
DIabetes Immunocompromise - HIV Obesity PVD CRF Alcohol and IVD abuse Trauma - surgery, bites IDUC Chicken pox, vesicles GIT perforation 0 rare Abscess
Pathophysiology of necrotising soft tissue infection
Microbial invasion of subcutaneous tissue
Tracking of bacterial through subcutaneous tissues producing endo- and exotoxins causing - ischaemia, liquefactive necrosis, systemic illness
Various bacteria-associated toxins stimulate CD4 cells and macrophages to produce TNF-alpha, IL-1 and IL-6 -> SIRS -> septic shock -> MOD -> death
Final common pathway is tissue ischaemia
Key feature = thrombosis of perforating vessels to the skin due to:
- hypercoagulable state
- platelet-neutrophil plugging of vessels
- increased interstitial pressure
How are necrotising soft tissue infections classified?
- By location
- By depth
- By microbial cause
How are necrotising soft tissue infections classified by location?
Ludwig’s angina - floor of the mouth
Fournier’s gangrene - perineum
How are necrotising soft tissue infections classified by depth?
Cellulitis
Adipositis/panniculitis
Fasciitis
Myositis
How are necrotising soft tissue infections classified by micro-organism?
Type 1 - polymicrobial - most common
Type 2 - monomicrobial
Type 3 - Vibrio vulnificus
Structure of skin
Epidermis --Stratum corneum --Stratum granulosum --Stratum spinosum --Stratum basale Dermis --Papillary dermis --Reticular dermis Subcutis
What are are eccrine sweat glands (regular sweat gland)?
Skin appendage situated on skin everywhere that synthesises sweat
- predominance on palms, soles, face
- located at junction between dermis and subcutis
- SNS cholinergic supply
What are apocrine glands?
Skin appendage that is a modified sweat gland found in the axilla and groin
- secretory component in reticular dermis or subcutis
- duct carries secretion to be discharged above sebaceous duct in upper hair follicle
- no definite function in humans, scent in animals
- SNS adrenergic supply
What are sebaceous glands?
Skin appendage that secrete sebum (lipid mixture) into hair follicle o provide waterproofing
- areola, nipples, labia minora, eyelids, buccal, labial mucosal glands are independent of hair follicles and open directly onto skin or mucosa
- no motor innervation
- acted on by androgens
What is subcutaneous tissue?
Areolar tissue connecting skin to underlying bones or deep fascia by fibrous bands.
Contains fat, nerves, blood vessels and lymphatics that pass to the skin
What is deep fascia?
Membrane of fibrous tissue wrapping limbs and body wall
Varies in thickness:
- thick in limbs
- scarcely semonstartable over lower thorax and abdomen
- absent in face and ischioanal fossa
What is melanoma?
Malignant neoplasm of melanocytes which is aggressive and can spread in an unpredictable manner to involve virtually any organ
Melanocytic naevus
Any congenital or acquired neoplasm of melanocytes
- Congenital nevus
- Blue nevus
- Spindle and epithelial cell nevus (Spitz nevus)
- Halo nevus
- Dysplastic nevus
Borders of the submandibular triangle
Anterior belly digastric muscle
Posterior belly digastric muscle
Inferior border of mandible
Fight bite microbiology
Typical polymicrobial oral flora:
- Eikenella corrodens (GNB) 30%
- Staphylococcus aureus 30%
- Streptococcus
- Corynebacterium species
- Bacteriodes (anerobe)
- Peptostreptococcus (anaerobe)
Dog bite microbiology
Cat bites similar
Polymicrobial with animal oral flora, recipient skin flora and environmental organisms:
- Pasteurella species
- Staphylococcus
- Streptococcus
- Capnocytophaga canimorsus (GNB)
Define keratocanthoma
Cutaneous tumour most commonly presenting as a dome-shaped nodule with a central keratin-filled crater
What is Hutchinson sign?
Extension of pigment to the proximal or lateral nail fold or free edge of nail plate in nail melanoma
What is Mohs micrographic surgery?
Specialised surgical procedure combining staged resection with comprehensive surgical margin examination resulting in high cure rates for even high-risk lesions together with maximal preservation of normal tissues
What is a rodent ulcer?
A centrally ulcerated nodular BCC
Types of BCC
Nodular - 60% Superficial - 30% Morphoeic - 5% Pigmented Basosquamous
because (BCC) No Sex Makes People Bad
BCC excision margin
5mm ideally
10mm for morphoeic/sclerosing and recurrence
often satisfied with 2mm on the face
0.5mm microscopically acceptable
Macroscopic features of BCC
Translucent elevated nodules Pearly rolled edges Telegectasia \+/- ulceration \+/- pigmentation
High risk factors for BCC
- Large size
- Situated central face - eyes, nose, lips, ears
- Poorly defined lesions
- Certain types - morphoeic, micro-nodular, basosquamous
- Perineural and/or perivascular invasion
- Recurrence
- Immunosuppression
What is a Marjolin ulcer?
SCC occurring in a burn scar -> aggressive with poor prognosis
Follow-up points about BCC
45% will develop another BCC within 3 years so require education and regular skin checks.
Only 40% of those incompletely excised will recur within 5 years
What is SCC?
Carcinoma arising from keratinocytes
Carcinoma of the epidermal cells forming the superficial keratinous squamous layer
What is BCC?
Carcinoma arising from the basal layer of the epidermis
How is a lymphoscintogram performed
Hours prior to surgery, a sulphur colloid tagged with Tc-99m is injected peritumourally and scintigraphic imaging is performed at 10 and 60 minutes.
A gamma probe and blue dye is used intra-operatively to identify the mapped sentinel node(s).
What is Breslow thickness?
Depth measured in mm from the granular layer of the epidermis to the point of deepest invasion in malignant melanoma.
The main indicator for prognosis.
How is melanoma staged?
AJCC TNM system
Tis = in situ (within epidermis)
T1 4.0 mm
a) absence or b) presence of ulceration
N1 = 1 L
N2 = 2-3 or in-transit mets with no LN mets
N3 = 4+
a) micro b) micro
M1a = skin, subcutis, distant LN, normal LDH M1b = lung, normal LDH M1c = visceral mets or any mets with abnormal LDH
Stage I = T1, T2a - 85-100% 5YS
Stage II = T2b-T4 - 40-85%
Stage III = nodal disease - 25-60%
Stage IV = metastatic disease - 15%
What are the most important prognostic indicators for melanoma?
Breslow thickness
Presence of ulceration
Mitotic rate
NODAL DISEASE
WLE margins for melanoma
Tis - 5mm
T1 - 1cm
T2 - 1-2cm
T3+ - 2cm
Risk of lymph node metastasis based on Bresow thickness
<0.75mm - rare
0.75-1.0mm - 5%
1-4mm - up to 30%
4mm - 40%+
Clark’s levels
Outdated except when tumours < 1mm where they still retain their prognostic significance
I - confined to epidermis / melanoma in situ / above BM II - Invasion into papillary dermis III - Filling papillary dermis IV - Invasion into reticular dermis V - Invasion into subcutaneous fat
MSLT1
n=1661, tumours 1+mm or Clark IV or V - 2cm margins
SLNBx +/- CLND vs Observation + CLND if clinical disease
No melanoma-specific survival benefit
DF10YS benefit for SLNB for tumours 1.2mm+
SLNB gives prognostic info to patient
In tumours 1.2-3.5mm and node positive, there was MS10YS benefit as well as DF10YS benefit
Xeroderma pigmentosum
Autosomal recessive Deficient repair of DNA damage due to UV radiation. NER genes mutated 1000x BCC/SCC/MM <40% live beyond 20 years Most die from metastatic SCC/melanoma
Immunohistochemistry for melanoma
S100
HMB-45
Melan-A
Ki-67
