Tissue Processing & Embedding Flashcards
What is the purpose of tissue processing?
Remove and replace water in tissue with wax, to form a solid structure to allow micro-thin sectioning.
Desribe the actual process of tissue processing
1) Formalin
2) 70% IMS
3) 90% IMS
4) 100% IMS
5) 100% IMS
6) Xylene
7) Xylene
8) Xylene
9) Wax
10) Wax
11) Wax
12) Wax
Describe the basic proess of tissue processing
1) Dehydration with alcohol.
2) Clearing with xylene.
3) Impregnation with paraffin wax.
Give some examples of alcohols that can be used in tissue processing
Isopropanol
Ethanol
Industrial methalated spirits (IMS)
What is the purpose of the clearing step with xylene in tissue processing?
Something soaked in alcohol can’t be put in molten wax as they are immiscible.
Xylene mixes with both alcohol and wax.
Tissue becomes a bit more tansclucent at this stage.
What is the purpose of impregnation with paraffin wax?
Paraffin wax gets inside tissue and makes everything rigid and preserves it for a long time.
Why is the tissue taken through a gradient of alcohols, xylenes and waxes?
Tissue is repeatedly put in IMS, xylene and wax because the solution before may have been contaminated by the solution before.
Thus to ensure all water/alcohol/xylene is removed before placing tissue into next solution, the tissue is repeatedly put through several solutions of alcohol/xylene.
(Ensure all water is removed before placing in xylene & ensuring all alcohol is removed before placing in wax & put in wax four times to remove any xylene).
Describe the different processing runs
Rapid - 3 hours
Routine overnight - 18 hours
Extended (fat) - sometimes days
Macro - 22 hours
Why does it take a macro cassette 22 hours to process?
It is four times larger than a normal cassette, thus requiring longer to process.
It is used for larger pieces of tumor that need to be kept whole in order to get information on the architecture of tissue structure.
What are the different sizes of cassettes?
Standard: 3cm by 2.5cm
Mini: 1.5cm by 1.5cm - used for smaller biopsies to ensure they don’t float out from gaps in cassette.
Macrocasette
Why is the casette used as a lid on mold?
So when wax solidifies, it sticks to cassette which has the patient number on it.
Describe the advantages of automation
Allows standardisation, preventing human errors.
Faster processing.
Doesn’t need supervision so can be left unattended and be run overnight.
Allows automated rotation of reagents.
Cheaper.
How can automation improve processing?
Use pressure, heat and agitation to improve processing.
Describe the key aspects of an embedding station
Paraffin tank - where paraffin wax is kept in a molten state.
Pre-warming chamber - where metal moulds are kept.
Metal moulds - kept really hot to ensure the molten wax doesn’t solidify when it is poured in by touching a cold metal surface.
Paraffin tray - where processed specimens are kept.
Processed specimens - come out of tissue processor (samples are inside cassettes) & kept here so they stay molten.
Cold spot - solidifies wax from bottom up to anchor specimen into position.
Molten wax dispenser - dispenses molten wax from paraffin tank.
Cooling plate - quickly solidifies wax to prevent crystals from forming.
Workspace - warm area to work on.
Describe the embedding process
1) Open cassette.
2) Select mould.
3) Fill bottom with molten wax.
4) Place tissue in mould and orientate.
5) Place on cold spot to anchor.
6) Top up with molten wax.
7) Lie on cold plate until solid.
8) Remove from mould.
