Histopathology

SHAVING

Hi guys!
This is the last month of our internship. Wonder how you guys feel. I think time really flies. 20 weeks of attachment and 16 (or rather 17) weeks of it has already gone! :)
This month, I was assigned to.. Shaving of tissue blocks!
The pro is- this does not really require much brain cells but you will discover the trivial things that affect shaving.
The con is- it is pretty tedious having to shave 500 blocks every morning. I’m going to develop muscles soon.

Shaving
Shaving is the common term for rough cutting which is to remove the excess wax on the paraffin block to expose the tissue. This is very important for obtaining full-face sections during Microtomy. Shaving is quite similar to Microtomy just that shaving is done at 20um while Microtomy is done at 4um. After shaving, the paraffin blocks will be soaked in fabric softener for 5 min to soften the tissues while those containing bones or stones will be soaked in RDO (acid) and be the last batch of blocks to be shaved. So the blocks in RDO will be decalcified for quite some time since they will be the last to be shaved. The paraffin blocks are washed with tap water after soaking and are then cooled on the cryoplate (coldplate) before they can be sectioned.

Things to look out for:
- Warm blocks: Blocks that have yet to cool down after embedding are not ideal for shaving. They are too soft and the tissues can drop out easily due to the lack of support. Also, it is difficult to fit the block onto the block holder without ‘poking’ your finger into the warm and soft wax. This will cause a depression on the surface of the block and one may need to shave deeper to get a fully-exposed surface.

Solution: Cool the blocks in ice water (ice scraped from the inside of the fridge) for immediate shaving

- Wax on the sides of the tissue cassette: Excessive wax used during embedding will overflow and form an extra width around the cassette so the block cannot fit into the block holder.

Solution: Melt the surrounding wax on the heating block

- Tiny tissue: There are tissues the size of a ‘full-stop’ in this entry and sometimes they are not dyed (so they are white/colorless). Excessive shaving can result in block exhaustion which means the entire tissue is gone (irreversible effect). So one has to be extra careful with these blocks.

Solution: Instead of shaving at 20um, shave at 10um. And also, once the block is almost fully-exposed, stop shaving. The medical technicians sectioning can trim it at 4um.

- Thin tissue: The same as ‘tiny tissue’. If the tissue is a trucut (very small and thin), do not shave the block and just pass it to the medical technicians who will shave at 4um.

- Hard tissue: Hard tissues such as fibroids and bones can cause a loud sound during shaving. Cutting these calcified tissues will damage the blade, causing kinks which will produce score lines on the tissue sections.

Solution: Try to use one side of the blade (the more blunt side –all shaving blades are used blades from routine Microtomy) specially for hard tissue and change the blade once it is blade or with kinks. Always soak these shaved blocks in RDO for decalcification.

- Uneven surface of tissue: This can be due to a few reasons. Improper embedding of tissues (not flat on the mould), nature of tissue (eg. Bone), and improper cutting of tissue during trimming by pathologists. All these are inevitable so it is common to have blocks with uneven surface. These blocks will require deeper shaving done to expose a full surface. However, this runs the risk of exhausting one side of the tissue even before a fully-exposed surface can be obtained.

Solution: Re-block the block. However, if it is not caused by improper embedding, even after re-blocking, it will be uneven and the medical technicians would have to shave and section the block by adjusting the position of the block.

- Presence of sutures or staples: Similar to presence of bones and stones, shaving cannot be done smoothly. These sutures or staples are used in operation to hold the organ together or to be in the correct orientation. However, they are missed out during trimming and embedding because they are too small. So they are usually spotted during shaving and they can cause score lines.

Solution: One can only remove the sutures or staples immediately with pilers or forceps once they are detected.

Shaving of blocks is not that difficult but speed is quite important. Sometimes (rather most of the time), when there are more technicians sectioning, it is not easy to catch up with their speed as there is only one person shaving the blocks. It takes the cooperation of others to make work easier. Eg, when the blocks are embedded flatly, a few turns on the handle will do the job, but if it is not properly done, it will take quite a while to obtain a fully-exposed surface.

Ting Ying Chee
TG01