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1. PRINCIPLE OF TISSUE
PROCESSING

2. Surgical Specimen
 Clinical Details
 Adequate specimen
 Proper Fixative

3. Gross Examination
Description:
 Specimen weight &
measurement
(approx)
 Consistency
 Cut section

4. Taking Samples:
Edge of lesions.
 Wall of cysts.
 Whole specimen if
small.
 Direction, mark

5. Inking the Margins
 To mark surgical
margin.
 Spread of lesion
 Malignancy
 Adequacy of
removal
 Different colors to
identify margins

6. Fixation:
 Specimen bits are
placed in porous
cassettes
 Not more than 5mm
thick
 In 10% formalin
 1mm/hour fixation
 ~ 6 hour

7. Types of fixative:
 Acetic acid
 Formaldehyde
 Ethanol
 Glutaraldehyde
 Methanol and Picric acid.

8. Dehydration
A. Definition: removal of water
B. Rationale: for paraffin embedding/sectioning
C. Steps
1. wash out fixative
2. graded series of alcohol
 70%, 95%, 100%, 100%
3. replace water by diffusion
4. not too long, not too short

9. Dehydration
Procedure;
 1. automatic tissue
processor
 a. overnight
 2. Baths: water,
70,95,100,100 %
alcohol
 3. Clearing agent: 2
baths of xylene

10. Clearing:
• replacing the dehydrating fluid with a fluid that is totally
miscible with both the dehydrating fluid and the embedding
medium.
Choice of a clearing agent depends upon the
following
- Intended processing conditions such as temperature,
vacuum and pressure.
- Safety factors.
- Cost and convenience.
- Speedy removal of dehydrating agent .
- Ease of removal by molten paraffin wax .
- Minimal tissue damage .

11. is the process by which tissues are
surrounded by a medium such as agar,
gelatin, or wax which when solidified will
provide sufficient external support during
sectioning.
Embedding

12. Embedding
• Procedure;
• 1. Place tissue cassette
in melted paraffin
• 2. Fill mold with
paraffin
• 3. Place tissue in
mold
• 4. Allow to cool

13. Embedding
A. Orient tissue
1. cross section
2. longitudinal section
B. Dissection orientation
C. Avoid bubbles

14. Precaution while embedding in wax
 The wax is clear of clearing agent.
 No dust particles must be present.
 Immediately after tissue embedding, the wax must be rapidly
cooled to reduce the wax crystal size.

15. There are four main mould systems and associated
embedding protocols presently in use :
• 1- traditional methods using paper boats
• 2- Leuckart or Dimmock embedding irons or metal containers
• 3- the Peel-a-way system using disposable plastic moulds and
• 4- systems using embedding rings or cassette-bases

16. Embedding:
 Paraffin block with
embedded tissue
 consistency to cut
 Paraffin blocks taken
for sectioning