| Summary: | Histopathology (compound of three Greek words: róç histos "tissue", ráfoc pathos "disease-suffering", and -Aoyia-logia) refers to the microscopic examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, histopathology refers to the examination of a biopsy or surgical specimen by a pathologist, after the specimen has been processed and histological sections have been placed onto glass slides. In contrast, cytopathology examines free cells or tissue fragments. Histopathological examination of tissues starts with surgery, biopsy, or autopsy. The tissue is removed from the body or plant, and then placed in a fixative which stabilizes the tissues to prevent decay. The most common fixative is formalin (10% formaldehyde in water). The tissue is then prepared for viewing under a microscope using either chemical fixation or frozen section. In chemical fixation, the samples are transferred to a cassette, a container designed to allow reagents to act freely on the tissue inside. This cassette is immersed in multiple baths of progressively more concentrated ethanol, to dehydrate the tissue, followed by toluene or xylene, and finally extremely hot liquid (usually paraffin). During this 12-to-16-hour process, paraffin will replace the water in the tissue, turning soft, moist tissues into a sample miscible with paraffin, a type of wax. This process is known as tissue processing.
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