Embedding Summary Notes PDF

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MLSC 3230 Histotechnology 1Embedding Summary NotesObjectives: a) Describe the function of an embedding media. b) Learn the process of embedding a tissue block. c) Learn the various orientations required in embedding tissue.Once tissue specimens have been fixed, grossed, and processed, they must be e...

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MLSC 3230 Histotechnology

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Embedding Summary Notes Objectives: a) Describe the function of an embedding media. b) Learn the process of embedding a tissue block. c) Learn the various orientations required in embedding tissue.

Once tissue specimens have been fixed, grossed, and processed, they must be embedded in wax to produce a block suitable for microtomy. At the end of routine processing, tissue is left in liquid paraffin wax at approximately 58o (or 2 o above the melting point of the wax used). It is free from dehydrant and clearant and should be thoroughly infiltrated with wax. Embedding is the procedure in which tissue is carefully oriented in a mold containing hot liquid wax and then allowed to solidify into a paraffin block. The wax gives support to the tissue during microtomy. Orientation is very important to ensure proper representation of the tissue. Correct tissue orientation facilitates microscopic diagnosis. The consistency of tissue embedded in paraffin wax is approximately the same as the wax itself. Rapid solidification, using ice or special cooling plates, ensures the formation of small, even crystals within the wax. This gives the tissue improved cutting qualities for ribboning of sections in microtomy. Requirements for embedding are as follows: • a supply of clean, filtered paraffin wax held at 2-4°C above its melting point. • a cold plate to rapidly cool the wax. • a supply of molds in which to embed the tissues.

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General Embedding Procedure METHOD 1) Open the tissue cassette, check against worksheet entry to ensure the correct number of tissue pieces are present. 2) Select the mold, there should be sufficient room for the tissue with allowance for at least a 2 mm surrounding margin of wax. 3) Fill the mold with paraffin wax. 4) Using warm forceps select the tissue, taking care that it does not cool in the air; at the same time. 5) Place the tissue in the mold according to the side to be sectioned. This side should be facing down against the mold. A small amount of pressure may be used in order to have more even embedding. 6) Chill the mold on the cold plate, orienting the tissue and firming it into the wax with warmed forceps. This ensures that the correct orientation is maintained and the tissue surface to be sectioned is kept flat. 7) Insert the cassette base onto the mold.

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8) Add more paraffin into the mold to fill the cassette and mold. 9) Cool the block on the cold plate. 10) Remove the block from the mold. 11) Cross check block, label and worksheet.

ORIENTATION OF TISSUE IN THE BLOCK Correct orientation of tissue in a mold is the most important step in embedding. Incorrect placement of tissues may result in diagnostically important tissue elements being missed or damaged during microtomy. In circumstances where precise orientation is essential tissue should be marked. Usually tissues are embedded with the surface to be cut facing down in the mold. Some general considerations are as follows: • elongate tissues are placed diagonally across the block • tubular and walled specimens such as vas deferens, cysts and gastrointestinal tissues are embedded so as to provide transverse sections showing all tissue layers • tissues with an epithelial surface such as skin, are embedded to provide sections in a plane at right angles to the surface (hairy or keratinized epithelia are oriented to face the knife diagonally) • multiple tissue pieces are aligned across the long axis of the mold, and not placed at random....