Paraffin embedding is the most commonly used and basic method for preparing tissue specimens. If not performed properly, it is also the step most likely to destroy tissue sections. Pathology technicians must be familiar with the elements of each embedded tissue specimen, carefully analyze their structure, and carefully Determine their position in the embedding mold; communicate more with the sample collection personnel to understand the nature of the tissue, and mark the tissue that needs to be marked with ink so that the embedding operation can be carried out correctly. We summarize the precautions for paraffin embedding as follows for your reference:

Figure 1. A method to process cells grown in Matrigel for paraffin embedding. (Pinto MP, et al.; 2011)

Correct Placement

The specimen must be placed in the correct direction, such as the largest cut surface facing downwards; the lumen, cyst wall, skin and other layers must be clearly visible and buried vertically, so that the tissue structures at all levels can be seen under the microscope after the cut surface is stained (for example, the skin must have epidermis and The dermis or subcutaneous tissue, the intestinal wall and gastric wall must have mucosa, submucosa, muscularis and serosal layers, and the kidney must have cortex and medulla, etc.).

Suitable Mold

Choose a mold of the appropriate size for each specimen. If the mold is too small, the sample will hit the edge of the mold and the slicing process will be difficult. When embedding, a 1mm gap should be maintained around the tissue block and the bottom edge of the embedding box. For small pieces of tissue, use a small embedding box.

Wax Injection Cost

Fill it once without overflowing. Note that the liquid level should not be higher than the upper edge of the embedding box. When covering the embedding box, be sure to keep it parallel to the bottom plane of the model. After the surroundings solidify, add wax twice. It should be noted that the second waxing cannot be too full.

Tweezers to Avoid Overheating

Before picking up the tissue, the forceps are heated to a temperature where the wax just melts. Overheating will cause deformation of the contact area of the forceps, causing local damage and making it impossible to diagnose.

Paraffin Temperature

The paraffin should not be heated too high. If it is too high, it will easily burn the tissue and make the finer punctured tissue hard, brittle, and curled.

Prevent Tissue Contamination

The work surface should be cleaned at all times during embedding, and the next one should be removed after embedding; heat the tweezers and wipe them with paper to prevent contamination, and pay attention to whether there is any tissue left on the embedding cover.

Wax Block Quality Control

Establish quality control of embedding, record the total number of embedding wax blocks every day, and check the number of tissue blocks in each embedding box. The total number of wax blocks and sections should be checked after staining. At the same time, the slices should also be compared with the wax blocks with corresponding numbers to check whether they are consistent, whether there are any errors, whether the section is complete, whether there are any omissions, whether the pathological number of the slices is wrong, etc. This is the most important step and is indispensable in your work.

Embedding quality requirements of different organizations:

The transverse section of the tubular structure tissue is downward, and the transverse section of the cyst wall-like tissue is embedded in the vertical direction;

Puncture the specimen, flatten each strip, and arrange them neatly with gaps;

Multiple pieces of small tissue, arranged together with gaps, and wrapped together;

For adipose tissue, use filter paper to absorb the oil and then embed it;

When the tissue has a multi-layer structure, the epithelial structure should be on top so that the slices can show the tissue structure of each layer;

Pay attention to foreign objects such as lint knives, iron nails, pieces of paper, etc., and remove them promptly;

The embedding horizontal plane has the same height and the same arrangement direction;

When the same tissue is embedded in a wax block, it is arranged closely together in a straight line or square shape.

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1. Pinto MP, et al.; An immunohistochemical method to study breast cancer cell subpopulations and their growth regulation by hormones in three-dimensional cultures. Front Endocrinol (Lausanne). 2011, 2:15.

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