For this blog, I will be describing my exciting first week in the Histology lab! For those of you who are not familiar with this department of the lab, it is where tissues are sent in order to identify diseases. The pathologist is responsible for reading tissue slides microscopically to diagnose disease. These slides are made by technologists, and there are several steps involved in the production of the final slide.

First, when tissue is received in the lab, it is accessioned and given a specimen number. It is then sent to be ‘grossed’, which means it is given a macroscopic description. Next, it is cut into small pieces that are put into cassettes. These cassettes contain either a single piece or several pieces of tissue that will be made into a slide. The cassettes are then processed in machines that make them easier to cut while maintaining the microscopic characteristics of tissues. Once they are processed, tissues are then embedded into paraffin blocks, cut into thin slices using a microtome, stained and sent to the pathologist to read.

During my first week in Histology, I was observing the accessioning process, as well as the gross examination of tissues. At the accessioning station of the laboratory, tissues from the operating room were received in containers with formalin. Formalin is a popular fixative used in Histology that preserves the structure of cells and stabilizes proteins present in the tissue. The process of fixation also prevents tissue autolysis and bacterial putrefaction. In order for complete fixation to occur, the fixative must take up 15 to 20 times the amount of space in relation to the tissue.  In some cases, tissues can be sent to the lab without formalin, however these tissues have to be kept moist with a wet gauze, and kept in the refrigerator until fixation occurs. Once tissues are received in the lab, they are then given accession numbers and cassettes are printed.

Example of incorrect tissue to fixative ratio. In this container, the fatty breast present is much too large for the container and tissue will not be properly fixed.

Once tissues are accessioned, they are sent to the grossing room where they are grossed by pathologist assistants (PAs). Tissues are given a gross description of color, dimensions, weight, as well as any other distinguishing characteristics. These characteristics are dictated by the PAs, and computer software translates their dictation into typed words. After tissues are described, they are cut into smaller pieces that can be put into cassettes. Not all of the tissue is cut into smaller pieces, and for some tissues, only the margins and some representative sections are needed. When cutting small pieces of tissues for cassettes, it is important to have the orientation of the tissue clear for future embedding and cutting. Orientation of the tissue is assisted with the use of India ink, which marks the margins of tissues. Additionally, if large tissues (such as bowels) are sent to the grossing room, they must first be cut open and left in formalin overnight so that fixation can occur throughout the entire tissue. Between the gross examinations of each specimen, it is very important for the PAs to clean their workstations in order to prevent carryover of tissues.

Subcutaneous tissue with India Ink (black) marking the margins.

Throughout the week I saw many interesting specimens coming into the grossing room. Among these specimens were an infectious uterus, several double mastectomies, and excess fat from a lipectomy. I also had the chance to see a dermoid cyst! Dermoid cysts are cysts that contain follicles, sweat glands, hair, teeth and/or nerves. These types of cysts are created during fetal development whenever skin and other structures become trapped. They can be found on the face or the spinal cord, but most commonly occur in the ovaries, which is where the one I saw originated from. Another interesting specimen that I came across was a uterus with its ovaries. While first observing the tissue, I noticed that it looked fairly healthy, which is uncommon to come across in the grossing room. It was from a patient with gender dysphoria. The patient was most likely going through gender reassignment surgery in order to be more in line with their gender identity. It was even possible to tell that the patient was on hormone therapy, as the Fallopian tubes were shrunken, most likely due to the testosterone they were taking.

Another interesting procedure that I performed this week was the decalcification of bones, using a chemical decalcifier named RDO. In order for bone specimens to be properly sectioned with a microtome, their calcium salts must be removed. If they are not removed, they will damage the microtome blade and create ragged sections. By using the commercial acid solution of RDO Rapid Decalcifier, calcium salts are dissolved into their ions, leaving the bone, and entering the solution instead. The decalcification of bones using RDO typically takes four hours to perform. After this time, a manual check of tissue hardness is performed by pushing on the tissue to see if it is softer. After tissues have been decalcified, they must be rinsed with water for 15 minutes before having any contact with formalin. If RDO and formalin come in contact together, they will produce a toxic gas.

RDO Decalcifier

Finally, throughout my first week in Histology, I had completed several assignments and tests in order to keep me updated on my knowledge. One thing that I was tested on was the gross identification of ten unknown tissues. While getting some practice recognizing known tissues, I observed, made note and felt for any distinguishing characteristics. Once I was comfortable with identifying those tissues, I then performed the test within 30 minutes. I am happy to say that I was able to identify all of the tissues correctly!