There are a few types of tissue specimens that may be encountered while embedding that will often be less than optimal, despite being processed in an adequate tissue processing program. These specimens include:
- Fatty tissue: It does not fix well or dehydrate easily and may be "wet" after processing. This will make a white appearance in many specimens when the block is formed due to the water present in the tissue which will not allow the paraffin to infiltrate. Unfixed or poorly dehydrated specimens will often shrink inward from the block face. This tissue may require reprocessing steps with additional fixation, dehydration, and/or wax infiltration.
- Large tissue: This includes pieces of any tissue type that has been submitted in sizes that are too large for the cassette. The tissue will often not process well, and deep grooves may be pressed into the tissue from the cassette that will have to be sectioned past to obtain a complete section.
- Specimens with inadequate decalcification: It may be possible to decalcify with decal solutions at your microtome station or use prolonged soaking to help obtain a section.
- Hair: It simply does not section well. It is best to try to remove hair if possible during gross dissection.
- Hard foreign materials such as sutures and staples: Items such as this will not section and will tear the tissue section during microtomy. It is best to remove these during gross dissection, but it may be possible to remove during embedding and placed on top of the cassette before it hardens.
- Sebaceous cyst contents: Quite often, this material does not process or section well. The material can sometimes be removed from inside the cyst and then placed on top of the block so it will not interfere with obtaining a good quality section of the cyst wall.
Many of these issues are due to poorly dissected or handled specimens that are then submitted to histology in this less than optimal condition. In other cases, the tissue type itself may present some processing challenges and it may be difficult to optimize processing programs to be optimal for the varied tissue types that most histology laboratories receive. In all instances, you will be attempting to make adjustments and corrections to the best of your abilities for these shortcomings, so that the best possible microscopic section is able to be obtained.