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Histopathology
continues to be a powerful, yet inexpensive part of veterinary diagnostics.
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| 1. |
Specimens
should represent typical lesions, including active margins and adjacent
(normal) tissue, rather than lesion cores or curetted debris.
Autolysis, freezing, mutilation
(forceps crushing or tearing), or removal of small samples
by electrocautery may make samples unsuitable for evaluation. |
| 2. |
Multiple specimens (from different
sites or types of lesions) should be identified
individually by size, suture tags, or separate containers. Samples
should be no thicker than 0.5 cm, to allow adequate fixation.
Brain and eyes are exceptions; they should be fixed whole. |
| 3. |
Nearly all
diagnostic histopathology can begin with tissue fixed in 10% buffered
neutral formalin.
Formula:
37-40% formaldehyde - 100 ml
distilled
water - 900 ml
sodium phosphate, monobasic - 4.0 gm
sodium phosphate, dibasic - 6.5 gm
Fixative volume
should be 10 times specimen volume. After 12 – 24 hours, specimens
can be transferred to just enough formalin to keep them moist during
shipment. There is no need to pay for transport of excess fixative.
Formalin will freeze at low temperature, damaging the tissues. Adding
1 ml of ethanol to each 9 ml of 10% formalin will prevent such freezing.
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| 4. |
Wide–mouth
plastic bottles or Whirl – Paks are preferred containers.
Do
not use baby food jars.
Narrow – mouth bottles often have to be broken or cut to release
fixed tissues.
Do not send tissues in glass containers.
Anticipate rough handling during shipment, and package accordingly.
Most bottle lids will leak; if in doubt, tape the lid, or place
the bottle and accession form in separate Whirl – Pak bags
to avoid contamination or damage. Label container(s)
adequately (owner, animal,
veterinarian, site). Interpretation of histopathologic
findings often hinges on complete clinical histories.
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| 5. |
Submit
specimens from all major organs, including brain, if in doubt about
which tissues to collect or if there are no gross lesions. |
| 6. |
Fresh
tissue, handled gently and fixed adequately in 10% buffered neutral
formalin will yield excellent results. Some pathologists, however,
have advocated using Bouin’s fixative for endometrial and endocrine
specimens. The advantages, in our opinion, of Bouin’s do not
outweigh the disadvantages of extra reagents and processing steps.
Tissues should be fixed in Bouin’s no longer than 18 hours, or
they become hard and brittle. Specimens must be washed 4 – 6
hours in several changes of alcohol to remove any picric acid
(yellow), then stored/shipped in 70% alcohol. Over
fixation with Bouin’s results in poor histologic staining. |
| 7. |
Duplicate
glass slides of specimens can be prepared for practitioner’s
use and files. The cost of these slides is listed in the fee schedule.
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