The document outlines the principles and procedures for processing surgical tissue specimens, covering clinical details, fixation, dehydration, clearing, and embedding. It details the appropriate fixatives, the dehydration process using alcohol, the clearing agents used, and the embedding techniques for optimal tissue preservation. Key precautions and methodologies for tissue sectioning and embedding systems are also emphasized.

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