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Problems in Histopathological Technique
Prepared by
ROY ELLIS
IMVS Division of Pathology
The Queen Elizabeth Hospital
Woodville Road, Woodville, South Australia 5011
Email: roy.ellis@imvs.sa.gov.au
Did you know that most tissue shrinkage is not caused by fixation but by subsequent dehydration and clearing?
The mechanism of volume change of tissues during fixation is not well understood because very little work has been done on the subject. Another project for someone! But it is known that some of the intercellular substance, like collagen actually swells during fixation when water based fixatives are used.
The fixation reaction alters the protein so that tissues becomes firmer but not necessarily of a smaller volume. It is only when tissues are subjected to agents like alcohol that shrinkage begins.
It has been estimated that tissue fixed in formalin and processed through alcohols and xylene to paraffin wax loses approximately one third of its volume especially when a frozen section is compared with a paraffin embedded section of the same original piece of tissue. So it must always be borne in mind that what you see in a paraffin section is in fact an artefact and not a true representation of the live tissue.
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© Roy C. Ellis 2002