Numerous variables impact the outcome of tissue processing and each variable must be considered when deciding on an optimal processing protocol.
- Tissue size (biopsy versus resection)
- Tissue thickness
- Tissue density
- Lipid content in tissue
Factors such as specimen size and thickness are determined during the collection and tissue preparation or grossing phase, which the laboratory typically has very little influence over. In order for processing reagents to penetrate tissue quickly and effectively, the tissue must be less than 4 mm thick and tissue pieces must not be crowded in the processing cassettes. Tissue size and tissue type will determine how quickly the reagents penetrate the sample. Biopsies, such as liver and prostate cores or colon biopsies, typically require less time for fixation and processing since they are 1-3 mm in size. Surgical tissue that is cut very thick, such as a liver resection, will require more time for reagent penetration. This is also true for tissue cassettes that are overly crowded with tissue pieces. Tissue that is dense, such as uterus and bone, will require more time for reagent penetration as well as tissue that is very fatty, such as breast tissue and brain sections.