A biopsy sample is prepared by being embedded in paraffin wax for sectioning and microscopic examination. Here's a breakdown of the process:
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Collection: The biopsy tissue is first carefully collected from the patient.
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Fixation: The tissue is immediately placed in a fixative, usually formalin, to preserve its structure and prevent decomposition. This step is crucial for accurate diagnosis.
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Processing:
- The fixed tissue is placed in small, labeled containers called cassettes. These cassettes hold the tissue securely throughout the processing steps.
- The tissue undergoes a series of dehydration steps using increasing concentrations of alcohol to remove water.
- The alcohol is then replaced by a clearing agent, such as xylene, which is miscible with both alcohol and paraffin wax. This makes the tissue transparent.
- Finally, the clearing agent is replaced by molten paraffin wax in a process called infiltration. This step ensures the tissue is completely permeated with wax, providing support during sectioning. This processing usually occurs overnight.
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Embedding: The wax-infiltrated tissue is placed in a mold and filled with more molten paraffin wax. This is allowed to cool and solidify, forming a solid block that encases the tissue.
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Sectioning: Using a microtome, the paraffin block is trimmed and then sectioned into very thin slices (typically 3-10 micrometers thick).
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Mounting: These thin sections are carefully floated onto a warm water bath to flatten them and then mounted onto glass slides.
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Staining: The mounted sections are stained with dyes, most commonly hematoxylin and eosin (H&E), to highlight different cellular structures and make them visible under a microscope.
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Microscopic Examination: The stained slides are then examined by a pathologist, who analyzes the tissue's structure and cellular characteristics to arrive at a diagnosis.
