Special Veterinary Pathology

FROZEN SECTIONING

Application

• The freezing technique is employed for rapid diagnosis, localization of various chemical constituents of cells such as fat, enzyme etc. and immunohistochemistry.
• Frozen section is used in routine surgical histology where an urgent diagnosis is required, perhaps in the middle of operation e.g. whether a tumour in breast is benign or maligant, if malignant the surgeon proceeds to remove all or part of the breast.

Principle

• The tissue is rendered rigid by freezing rather than by embedding in paraffin wax or resin; the tissue water acts as the embedding medium and it is therefore capable of being cut into thin sections

Fixation

• Tissues are sectioned either fixed or unfixed depending upon the technique to be applied.
• Fixation by freezing keeps the specimen in the freezing chamber at least for 20 minutes. Materials fixed in 10% formalin can also be used for freezing. The thickness of tissue should be 2 - 4 mm for rapid and uniform freezing.

Cryostat

• Frozen sections can be produced by using a freezing microtome, a cryostat or a standard microtome modified by the addition of thermocules. The cryostat is a refrigerated cabinet in which a modified microtome is housed.
  • Tissue must be fresh and rapidly frozen
  • Block temperature must be around – 20 to –25° C

Advantages

• The tissue can be adequately frozen in a matter of few seconds to minutes
• Sections can be cut immediately
• At no stage the tissue is exposed to any organic solvents or other agents which could dissolve or destroy any lipids, enzymes or antibodies in the tissue