IMVS Division of Pathology
The Queen Elizabeth Hospital
Woodville Road, Woodville, South Australia 5011
Cutting thick and thin sections
This of course can happen to alternate section or it can happen within the same section.
This is a section of
uterus stained Haematoxylin and Eosin and showing thick and thin
areas. The thick area, of course, stains more darkly than the thin
One reason for this is a loose knife or loose block. So always ensure that the knife is held firmly in place and also the block and remember a loose knife can destroy a block.
The block might be too large for the microtome in use. If there is very little clearance between the bottom of the block and the top of the knife it can be difficult to cut through tissue with a smooth action. This often results in thick and thin areas in the resultant section. The solution is to use a different microtome with a greater clearance or if you haven't got another microtome, to persuade your pathologist to cut smaller pieces of tissue for processing.
If the knife clearance angle is too fine this produces an effect at the knife edge similar to a blunt knife. The block face is much too close to the bevel so that as the knife cuts, there is a small expansion of the block face caused by the friction between the two surfaces forcing the block face up against the bevel making it very difficult to cut in a smooth action and usually producing thick and thin areas in the section.
Excessively hard tissue or wax can also be a problem especially when trying to cut hard tissues with disposable blades because these blades are much thinner than conventional knives and so tend to vibrate more. So it is more important to ensure that disposable blades are held firmly in place or you will find that even cutting soft tissues can produce this type of artefact.
Areas of calcification present in tissue can cause the knife to jump and vibrate and so can produce thick and thin areas in the section as well as damaging your knife edge. If minute areas of calcification are present surface decal for 15 to 30 minutes should remove the offending particles.
Bad technique is another factor to consider. New staff members when learning to cut often produce thick and thin sections because they find it difficult to produce the steady, smooth rhythm required in the cutting action to produce a good section. So if everything else seems to be in order, look at technique.
Or maybe its the Microtome which needs a service. Parts do wear and usually the first sign that a microtome needs a bit of care and attention is when it starts to cut thick and thin. This is usually related to the microtome feed mechanism. The feed mechanism on the old Jung microtomes was badly designed and was notorious for feed mechanism problems usually in the form of thick and thin sections.
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© Roy C. Ellis 2002