HTL Tissue Processing & Fixation 2 — Questions and Answers
Question 1: During tissue processing, the graded alcohol series typically ends at which concentration before clearing?
- 70% ethanol
- 80% ethanol
- 95% ethanol
- 100% (absolute) ethanol (Correct answer)
Correct answer: 100% (absolute) ethanol
Tissue must pass through 100% (absolute) ethanol as the final dehydration step to ensure complete water removal before the clearing agent is introduced.
Question 2: What is the optimal paraffin infiltration temperature range used in automated tissue processors?
- 37–42°C
- 50–60°C (Correct answer)
- 65–75°C
- 80–90°C
Correct answer: 50–60°C
Paraffin infiltration is performed at 50–60°C, just above the melting point of standard embedding paraffin, ensuring the wax remains liquid for infiltration without damaging tissue.
Question 3: A tissue specimen shows shrinkage artifact and poor nuclear detail after processing. The most likely cause is:
- Insufficient fixation time
- Excessive dehydration time in high-concentration alcohol (Correct answer)
- Too long in the clearing agent
- Under-infiltration with paraffin
Correct answer: Excessive dehydration time in high-concentration alcohol
Prolonged exposure to high-concentration alcohol causes protein denaturation and excessive tissue shrinkage, resulting in poor morphology and nuclear detail.
Question 4: Which embedding medium is used for frozen sections when rapid diagnosis is required?
- Paraffin wax
- Epoxy resin
- Optimal cutting temperature (OCT) compound (Correct answer)
- Celloidin
Correct answer: Optimal cutting temperature (OCT) compound
OCT compound is the standard embedding medium for frozen sections because it provides support for cryostat cutting at low temperatures without requiring chemical processing.
Question 5: The fixative Bouin's solution is best suited for which type of tissue?
- Large surgical resections
- Bone marrow trephine biopsies
- Testicular and gastrointestinal biopsies (Correct answer)
- Brain tissue for neuropathology
Correct answer: Testicular and gastrointestinal biopsies
Bouin's solution (picric acid, formalin, acetic acid) is preferred for testicular and gastrointestinal biopsies because it provides excellent nuclear detail and cytoplasmic preservation.
Question 6: Tissue that has undergone autolysis prior to fixation will most likely show:
- Enhanced nuclear staining
- Ghost outlines of cells with loss of nuclear detail (Correct answer)
- Increased cytoplasmic eosinophilia only
- No histological changes
Correct answer: Ghost outlines of cells with loss of nuclear detail
Autolysis causes enzymatic self-digestion of cellular components, resulting in ghost outlines, karyolysis, and loss of nuclear and cytoplasmic detail in H&E sections.
Question 7: The term 'cold ischemia time' in tissue handling refers to:
- Time the tissue spends in fixative
- Time from tissue removal to placement in fixative (Correct answer)
- Duration of paraffin infiltration
- Time the tissue spends in the cryostat
Correct answer: Time from tissue removal to placement in fixative
Cold ischemia time is the interval between surgical removal of tissue and placement in fixative; minimizing this time reduces autolysis and preserves nucleic acids for molecular testing.
HTL Tissue Processing & Fixation 2
During tissue processing, the graded alcohol series typically ends at which concentration before clearing?