HT Tissue Processing 3 — Questions and Answers
Question 1: Microwave-assisted tissue processing reduces processing time primarily by:
- Increasing reagent concentration
- Elevating tissue temperature to speed molecular diffusion (Correct answer)
- Applying centrifugal force to push reagents into tissue
- Lowering surface tension of the embedding medium
Correct answer: Elevating tissue temperature to speed molecular diffusion
Microwave energy rapidly heats tissue, which accelerates the diffusion kinetics of all processing reagents.
Question 2: When processing fatty tissue such as breast, which modification is most appropriate to prevent incomplete dehydration?
- Increasing formalin fixation time
- Adding additional alcohol dehydration steps or extending times (Correct answer)
- Using a lower paraffin infiltration temperature
- Skipping the clearing step
Correct answer: Adding additional alcohol dehydration steps or extending times
Adipose tissue resists dehydration; extended or additional alcohol steps ensure all water is removed before clearing.
Question 3: Which embedding medium is preferred when enzyme histochemistry must be performed on frozen sections?
- Paraffin wax
- Celloidin
- OCT compound (Correct answer)
- Epoxy resin
Correct answer: OCT compound
OCT (optimal cutting temperature) compound supports fresh-frozen tissue for cryostat sectioning without heat or chemical fixation that would denature enzymes.
Question 4: What is the recommended maximum tissue thickness for routine overnight paraffin processing on an automated processor?
- 1 mm
- 3–4 mm (Correct answer)
- 6–8 mm
- 10–12 mm
Correct answer: 3–4 mm
Tissues up to 3–4 mm thick allow adequate reagent penetration during standard overnight cycles; thicker pieces risk incomplete processing.
Question 5: Prolonged exposure to xylene before paraffin infiltration causes tissue to become excessively brittle primarily because:
- Xylene oxidizes proteins
- Xylene removes too much lipid and water, desiccating tissue (Correct answer)
- Xylene reduces the melting point of paraffin
- Xylene cross-links collagen fibers
Correct answer: Xylene removes too much lipid and water, desiccating tissue
Extended xylene exposure continues to extract lipids and residual water, desiccating the tissue matrix and making it fragile.
Question 6: In a rapid processing protocol, which step is most commonly shortened to save time while still maintaining acceptable tissue quality?
- Initial formalin fixation
- Dehydration in lower alcohols
- Clearing in xylene (Correct answer)
- Paraffin infiltration
Correct answer: Clearing in xylene
Modern reagents like isopropanol reduce the need for separate lower-alcohol grades, so early dehydration steps are often consolidated first, but clearing is also abbreviated in rapid schedules.
Question 7: Which characteristic of a tissue specimen most significantly affects the total processing time required?
- Color of the tissue
- Specimen thickness (Correct answer)
- Weight of the cassette
- Number of pieces per cassette
Correct answer: Specimen thickness
Reagent diffusion is governed by distance; thicker specimens require longer times for complete dehydration, clearing, and infiltration.
HT Tissue Processing 3
Microwave-assisted tissue processing reduces processing time primarily by: