HT Tissue Processing & Embedding 3 — Questions and Answers
Question 1: Tissue processed through a rapid microwave protocol still shows inadequate fixation in the center. What is the most likely cause?
- Microwave power too high
- Insufficient fixative volume relative to tissue size (Correct answer)
- Tissue was too cold when processing began
- Dehydration step was too short
Correct answer: Insufficient fixative volume relative to tissue size
Inadequate fixative volume prevents diffusion into the tissue core, leaving the center poorly fixed even with microwave-assisted processing.
Question 2: Which property of xylene makes it an effective clearing agent?
- High water miscibility
- Miscibility with both alcohol and molten paraffin (Correct answer)
- Low volatility at room temperature
- Ability to dissolve collagen
Correct answer: Miscibility with both alcohol and molten paraffin
Xylene is miscible with both alcohols and paraffin wax, making it an ideal transitional clearing agent between dehydration and infiltration.
Question 3: A tissue block shows a 'bubbling' artifact on cut surface after embedding. What caused this?
- Over-fixation
- Residual water carried into paraffin (Correct answer)
- Excessive paraffin temperature
- Under-decalcification
Correct answer: Residual water carried into paraffin
Residual water not removed during dehydration vaporizes in hot paraffin, creating bubbles and voids in the embedded block.
Question 4: Which tissue type requires the longest processing schedule on an automated tissue processor?
- Skin punch biopsy (3 mm)
- Liver core biopsy (1 mm)
- Lymph node (1.5 cm) (Correct answer)
- Prostate needle biopsy (1 mm)
Correct answer: Lymph node (1.5 cm)
Larger, denser tissues like a 1.5 cm lymph node require longer processing times for reagents to fully penetrate.
Question 5: What does the term 'infiltration' refer to in tissue processing?
- Entry of fixative into unfixed tissue
- Replacement of clearing agent with embedding medium (Correct answer)
- Movement of dehydrant into tissue
- Diffusion of stain into sections
Correct answer: Replacement of clearing agent with embedding medium
Infiltration refers to the replacement of the clearing agent with molten paraffin (or other embedding medium) within tissue spaces.
Question 6: Which of the following is a disadvantage of celloidin embedding compared to paraffin?
- Poor support for large tissue sections
- Cannot be used for decalcified bone
- Very slow processing time (days to weeks) (Correct answer)
- Incompatible with most staining protocols
Correct answer: Very slow processing time (days to weeks)
Celloidin (nitrocellulose) embedding requires days to weeks for processing, making it impractical for routine histology.
Question 7: When embedding a cylindrical needle core biopsy, what is the most critical orientation step?
- Placing the core flat so all of it is visible on the cut face (Correct answer)
- Orienting the core vertically in the mold
- Embedding the core at a 45-degree angle
- Cutting the core into 2 mm pieces before embedding
Correct answer: Placing the core flat so all of it is visible on the cut face
Core biopsies should be embedded flat (longitudinally) so the maximum tissue surface is exposed on the cut face for diagnosis.
HT Tissue Processing & Embedding 3
Tissue processed through a rapid microwave protocol still shows inadequate fixation in the center.
What is the most likely cause?