A Trip to the Histology Laboratory

At long last, the tests for the week are over and I've found just a little down time. I can imagine that the reason there are so few blogs about pathologist's assistants is because they're all so darn busy!

Even though I intend for this blog to be mainly about pathologist's assistants, it would be unfair of me to leave out all of the behind-the-scene work that goes into diagnosing disease. When a person goes to the hospital for surgery to have something taken out of their body, there is an army of health care professionals involved in handling the tissue. Here's a very basic outline of what happens:

1) Surgeon - cuts out the tissue, then sends it to the pathology gross room.
2) Pathologist Assistant - describes the tissue and cuts it into small pieces to be placed in cassettes that are sent to the histology laboratory.
3) Histotechnologist - embeds the tissues into wax, cuts the tissue into thin strips, puts the thin slices onto microscope slides and stains the slide.
4) Pathologist - uses a microscope to look at the tissue on the slide and makes a diagnosis.

So today, I want to talk about what happens at #3, the histology laboratory! This week I had the opportunity to meet the fine people over in the histology department and they were kind enough to give me a run down of what happens after pathologist's assistants are done grossing (grossing is basically describing the appearance of a tissue in words) and submitting tissues.
 
When it comes to diagnosing a disease, a person needs to both look at the tissue macroscopically and microscopically. A pathologist's assistant is trained to describe what tissue looks like with the naked eye, but many instances of disease can only be seen microscopically. That's why it's important to have a pathologist who can look for clues in tissue too small to see by the naked eye. Well, the next question that comes is, "How do you go from looking at something so huge, like a lung or a piece of skin, to looking at it under the microscope?" That is where histotechnologists come in to save the day.

A pathologist assistant will place small pieces of cut tissue into a cassette, which look like these,

and then let the tissue sit in a bucket of formalin. The formalin hardens the tissue which will make it easier to cut into extremely thin slices.

The histolotechnologists will receive the cassettes after a day or so. The first step they do is to take out the tissue from the cassette and embed the tissue in wax. They have special metal trays which they place the tissue into and pour hot wax over it. ("hot" is an understatement! I believe all histotechs have iron fingers.)The tissue gets surrounded by the wax and becomes trapped like an ant in amber. The end result looks something like this:

Now the tissue is ready to be cut from the wax into thin strips. And when I say thin, I mean 5 microns thin. To give you some perspective, the period at the end of this sentence is about 300 microns long.


The wax block with the embedded tissue is placed into a cutting machine called a microtome. Here's what one looks like.

There is a circular "crank" on the right side of the microtome and each revolution of the crank will bring the head of the microtome down onto a razor blade. The head holds the waxed tissue and it's the black apparatus which looks like it has knobs and bars coming out of it. The razor blade is on the top of the black rectangular platform. When the had comes down onto the razor an extremely thin slice of the tissue is cut off. The cut slices are then put into a water bath. (Easier said than done!)

Next, the histotechnologist picks up the tissue from the water bath using a microscope slide. This whole process is really a fine art and takes a tremendous amount of skill to become fast. When I tried this it took me about 45 minutes to do about 15 slides whereas the histotechnologists could do 15 slides in just a couple of minutes. The slices are so thin that they'll be gone with the wind if you so much as move faster than a snail.

From here on out, the rest is automated! Of course, the pathologist can't read a slide without color, so the slides go through a staining process. This machine can handle nearly any stain that is needed.

And lastly, it's nice to put a cover slip on top so you don't damage the tissue while you're handling it.  Whoever made these machines must be feeling the anger of all the displaced laboratory assistants.

And there you have it! Off to the pathologist it goes. Bonus points to the person who can identify what tissue this is.

Many thanks to the people at histology for showing me around!