Embedding and microtomy

8 DOH Abu Dhabi (HAAD) lab licensing practice questions on Embedding and microtomy, part of Histopathology and Cytology. The first 8 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 38-year-old man's vasectomy specimen contains two pieces of tubular tissue, each about 1 cm long. At grossing, the pathologist cuts a thin transverse disc from each end of each piece, places the four discs in one cassette and writes 'embed cut faces down' on the cassette request. The H&E slide shows four long strips of smooth muscle and connective tissue, with no lumen and no lining epithelium in any of them, and two deeper levels look the same. The pathologist needs complete cross sections showing the whole ring of each piece. What should be done?

   1. AMelt out the discs and re-embed them cut face down
   2. BRotate the block 90° in the clamp and recut it
   3. CRecut the same block at 2 µm instead of 4 µm
   4. DCut more deeper levels from the existing block

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   Answer: A · Melt out the discs and re-embed them cut face down

   A transverse disc has two flat cut faces that each show the whole ring of the tube, so sections cut parallel to those faces are cross sections with the lumen in the middle. Long strips of muscle with no lumen mean the discs were laid on their curved sides, so the knife is cutting along the length of the wall. The only fix is to melt the discs out of the wax and re-embed them flat, cut face down, pressed evenly to the bottom of the mold. Deeper levels stay in the same wrong plane, turning the block in the clamp changes only the direction the knife travels across the same face, and a thinner section does not change the plane at all. Orientation notes on the cassette must be read before each piece is placed in the mold.

   • B: Turning the block in the clamp changes the cutting direction, not the plane of the section.
   • C: Section thickness does not change the plane in which the tissue is cut.
   • D: Deeper levels stay in the same longitudinal plane and cannot give cross sections.

2. Question 2 · Hard

   The paraffin in use melts at 56 °C. On a flotation bath set at 55 °C, sections spread rapidly, the wax softens and the tissue pulls apart. What should be done?

   1. ACut thicker sections, about 8 µm
   2. BLower the bath to about 46 °C
   3. CAdd detergent to the bath water
   4. DRaise the bath to about 60 °C

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   Answer: B · Lower the bath to about 46 °C

   The flotation bath should be about 5 to 10 °C below the melting point of the wax, so a 56 °C wax needs roughly 46 to 51 °C. At 55 °C the wax nearly melts, the section over-expands and loosely bound tissue such as fat or lymph node separates. Too cool a bath leaves wrinkles that do not flatten out. Sections are picked up as soon as they lie flat.

   • A: Thicker sections lose detail and do not correct an overheated bath.
   • C: Detergent lowers surface tension but does not stop over-expansion.
   • D: A hotter bath would melt the wax completely and destroy the section.

3. Question 3 · Hard

   Sections of a cervix block show regular thick and thin bands running parallel to the knife edge (chatter). The tissue was over-processed and feels very hard. The blade is new and tightly clamped. What is the best next step?

   1. ACut faster with a firmer stroke
   2. BWarm the whole block to room temperature first
   3. CSoak the face in ice water, then recut
   4. DCut thicker sections at 15 µm

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   Answer: C · Soak the face in ice water, then recut

   Chatter is a vibration artifact, seen as bands of alternating thickness parallel to the knife edge. With a new, tightly clamped blade, the cause here is the hard, over-processed tissue. Soaking the exposed face in ice water, or a softening agent, for a few minutes softens the surface layers, and a slow, steady stroke then gives even sections. Only a few good sections come from each soak before it must be repeated.

   • A: A faster, harder stroke makes the vibration worse.
   • B: A warm block compresses and cuts unevenly; chilling is still needed.
   • D: Thick sections hide detail and are not acceptable for diagnosis.

4. Question 4 · Hard

   Sections alternate thick and thin, with an occasional skipped section, on every block cut on microtome 2. The same blocks cut evenly on microtome 1 with blades from the same box. The most likely cause is:

   1. AA loose block holder or blade clamp
   2. BUnder-processed, soft tissue
   3. CA nick in the microtome blade
   4. DA water bath that is too cool

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   Answer: A · A loose block holder or blade clamp

   A fault that follows the instrument rather than the block points to the microtome. A loose block holder, blade holder or clamp lets the block or blade shift with each stroke, so sections come out alternately thick and thin or are skipped. All levers are checked and tightened, and if the fault persists the feed mechanism may need service. Blocks and blades that cut well on another microtome rule out processing and blade problems.

   • B: Under-processed tissue would cut badly on both microtomes.
   • C: A nick causes a split through the section, and the blades were the same on both instruments.
   • D: Bath temperature affects flattening, not section thickness.

5. Question 5 · Medium

   Why are trimmed paraffin blocks chilled on ice or a cold plate before thin sections are cut?

   1. AIt completes fixation of the tissue
   2. BIt stops the tissue taking up water
   3. CIt helps sections flatten on the bath
   4. DIt firms wax and tissue evenly

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   Answer: D · It firms wax and tissue evenly

   Cooling hardens the paraffin and the infiltrated tissue to a similar consistency, so the blade cuts both cleanly and thin, even sections of about 3-5 µm are easier to get. A warm block gives compressed, wrinkled or uneven sections. Blocks warm quickly on the microtome, so they are re-chilled during cutting.

   • A: Fixation is finished before processing; cold does not continue it.
   • B: Chilling firms the block; water uptake is a separate effect of soaking.
   • C: Sections flatten on the warm water bath, not because the block is cold.

6. Question 6 · Medium

   When several biopsy fragments go into one block, they are pressed flat at the bottom of the mold at one level so that:

   1. ALess wax is needed per block
   2. BEach section contains every fragment
   3. CThe block cools more evenly
   4. DThe fragments cannot stick together

   Answer and explanation in LearnFree account

7. Question 7 · Easy

   How should a skin ellipse be oriented in the embedding mold?

   1. AOn edge, showing every layer
   2. BTilted at about 45 degrees
   3. CFlat, dermis facing down
   4. DFlat, epidermis facing down

   Answer and explanation in LearnFree account

8. Question 8 · Hard

   Every section from a breast block shows a split running at right angles to the knife edge. After moving to an unused part of the blade, the split still appears at the same place in the tissue. The most likely cause is:

   1. AToo small a blade clearance angle
   2. BA nick in the blade edge
   3. CA flotation bath that is too hot
   4. DCalcium or a suture in the tissue

   Answer and explanation in LearnFree account