MLT GlobeHistopathology: Microtomy & sectioning – page 2
49 Histopathology MCQs on Microtomy & sectioning with answers and explanations.
An H&E slide shows heavy staining of the glass background around the tissue. The most likely cause is:
Too much adhesive in the bath or on the slide picks up dye. Charged slides themselves do not cause background staining.
The section flotation bath is set to about:
Slightly below melting point lets sections flatten without the wax melting and components separating.
For enzyme histochemistry, which section type best preserves enzyme activity?
Heat, prolonged fixation and solvents in paraffin processing destroy most enzymes, so cryostat sections are preferred.
Paraffin sections picked up from the water bath still show folds and creases. The most likely cause is:
Flotation water just below wax melting point softens the ribbon and removes wrinkles; too cool, sections stay creased; too hot, they disintegrate.
The flotation bath for spreading paraffin sections should be set at:
Slightly below melting point softens and flattens the ribbon without melting it; hotter water breaks the section apart.
Which medium is used to support tissue for frozen sectioning?
OCT freezes into a firm, cuttable matrix within minutes; wax, celloidin and resin need lengthy processing.
Sections cut from 56 °C wax are floated on a water bath set at 70 °C. What is likely to happen?
Water above the wax melting point dissolves the support, so the section fragments; aim for 5–10 °C below melting point.
Mayer's albumin adhesive is made mainly from:
Mayer's adhesive is egg albumin with glycerol (plus a preservative such as thymol); gelatin–chrome alum and silane are other adhesives.
A bubble is trapped under a section floating on the water bath. How can it be removed?
A soft brush pushes the bubble out without tearing the tissue; heating or piercing damages the section.
Why are frozen (cryostat) sections preferred for enzyme histochemistry?
Paraffin processing uses heat, alcohol and xylene, which destroy most enzyme activity and lipids. Cryostat sections preserve them, although morphology and thinness are inferior to paraffin.
To snap-freeze a muscle biopsy with minimal ice-crystal artefact, the preferred method is immersion in:
Isopentane cooled by liquid nitrogen freezes tissue rapidly and evenly. Direct liquid nitrogen causes a vapour layer (Leidenfrost effect) that slows freezing and creates ice-crystal artefact.
Cryostat sections keep tearing and sticking. Which is the most likely cause relating to the knife?
The knife and anti-roll plate must be clean, dry and frost-free; residue and condensation make sections adhere, crease or tear. OCT use and 5 µm thickness are standard.
Fatty tissue such as breast or omentum smears when cut at −15 °C in the cryostat. What adjustment usually helps?
Fat has a lower freezing point than other tissues, so colder settings are needed for clean sections. Warmer settings make smearing worse.
Which of the following is NOT a recognized microtome knife profile?
Traditional steel knife profiles are plano-concave, biconcave, plane wedge and tool edge. A convex wedge is not a standard profile.
Which item is a knife profile rather than a hone used for sharpening?
Belgian yellow, Arkansas and carborundum are sharpening stones (hones). Plano-concave describes a microtome knife shape.
A block of uterine tissue is too hard to section cleanly. What is commonly applied to the exposed block face to soften it?
Soaking the trimmed face in water (often with ice or a softening agent) hydrates the tissue surface. Xylene would dissolve the wax and heat makes wax too soft.
Frozen sections of a muscle biopsy show numerous small holes within fibres. The most likely cause is:
Slow freezing lets ice crystals form and leaves holes. Snap freezing in isopentane cooled by liquid nitrogen prevents it.
If a flotation bath is too hot, which artifact is most likely in the floated sections?
Excessive heat overexpands sections so components pull apart. Splits come from knife nicks and holes from aggressive facing.
Randomly scattered irregular holes are seen throughout an H&E section. The most likely cause is:
Rough, thick facing tears tissue out of the block surface, leaving holes in subsequent sections. Excess adhesive causes background staining instead.
Soaking a trimmed paraffin block face in ice water before cutting is most useful for correcting:
Chatter often arises in overdried, hard tissue; brief soaking rehydrates and softens the surface. Splits reflect knife damage and need a new blade area.