PRELIM: CH6 Fixation (3)

Rapid uniform heating through thin blocks enabling faster processing

A key advantage of microwave fixation is:

10–15 mm

A limitation of microwave energy in tissue is penetration to roughly:

Specimens pre-exposed to buffered formalin, then microwaved

Microwave-assisted fixation commonly uses:

Toxic fumes when microwaving tissues in fixative

A safety consideration for microwave-assisted fixation is:

Be sliced to ~2 mm and placed in 70% ethanol

After primary microwave stabilization, tissues should:

Glyoxal (lower toxicity)

A proprietary fixative for microwave-assisted workflows may contain:

Full standardization and calibration of power, volumes, and dimensions

Which step most improves microwave fixation reproducibility?

Viable spores/pathogens may persist

A disadvantage of microwave or alcohol-only fixation is:

Phosphate-buffered 10% formalin at pH ~7.3

In the provided microwave protocol, the fixative is:

450 W, ~55°C, 1.5–4 minutes

The listed microwave exposure condition is:

Soaking blocks 1 minute in 100 mL formalin

The step immediately before microwaving blocks includes:

Black, birefringent deposits formed under acidic conditions

A characteristic of formalin-heme pigment is:

Reduce formalin pigment formation and speed fixation

Using neutral buffered formalin instead of unbuffered formalin will:

Formalin pigment formation

Phenol-formalin reduces:

Insufficient fixation time or volume

Inadequate fixation leading to “soft, feather-like” tissue is mainly due to:

Remove substances soluble in that fixative

A wrong choice of fixative can:

Inhibits enzyme and immunologic reactions

Prolonged formalin fixation typically:

Partially restore activity of some enzymes

Washing fixed tissues in running water can:

Formalin and alcohol fastest; glutaraldehyde slower; mercurials intermediate

The penetration order among common fixatives is roughly:

10–15 mm

For solid tissues like liver, a practical size limit for the longest dimension is:

≥50:1

For long-term museum specimens, recommended fixative volume is:

Shed cells and debris contaminate and deplete the fixative

Fixatives should be used only once primarily because:

Washing in water prior to processing

Zenker’s or Helly’s fixation requires:

Inflate with fixative or open and clean to remove barriers

For lungs, an approach to optimize fixation is to:

Opened and cleaned of contents to remove barriers

For GI tract specimens, fixation improves when:

Increases risk of distortion

Formalin heated to 60°C may be used for urgent biopsies but:

Section tissues thinly (2–3 mm) before extended fixation

The best overall strategy to minimize under-fixation in thick blocks is:

Prolonged or overly strong fixation; insufficient initial fixation with ethanol processing

Loss of immunohistochemical antigenicity can result from:

Post-staining Sudan Black treatment

IF (Immunofluorescence) background autofluorescence in FFPE (Formalin-fixed paraffin-embedded) sections can be reduced by:

Zenker’s secondary fixation acting as mordant for Masson’s trichrome

Which pairing of fixative and staining method is correct?

Digitonin

For cholesterol at ultrastructural level, fixation can employ:

Post-fixing with imidazole–osmium tetroxide

Improved ultrastructural lipid demonstration is achieved by:

Alcoholic formaldehyde

For human skin, compared to neutral buffered formaldehyde, better fixation may be achieved by:

Intense central eosinophilia with tissue compression

Crush artifact shows in H&E (Hematoxylin and Eosin) liver sections as:

Replace with fresh, properly prepared fixative immediately

The best tactic when a specimen arrives in dubious fixative is to: