Histopathology

Histopathology (compound of three Greek words: ἱστός histos "tissue", πάθος pathos "suffering", and -λογία -logia "study of") 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...often following expert dissection in the fresh state...placed in a fixative which stabilizes the tissues to prevent decay. The most common fixative is formalin (10% neutral buffered formaldehyde in water).

The tissue is then prepared for viewing under a microscope using either chemical fixation or frozen section.

If a large sample is provided e.g. from a surgical procedure then a pathologist looks at the tissue sample and selects the part most likely to yield a useful and accurate diagnosis - this part is removed for examination in a process commonly known as grossing or cut up. Larger samples are cut to correctly situate their anatomical structures in the cassette. This is then placed into a plastic cassette for most of the rest of the process.

In addition to formalin, other chemical fixatives have been used. But, with the advent of (IHC) staining and diagnostic molecular pathology testing on these specimen samples, formalin has become the standard chemical fixative in human diagnostic histopathology. Fixation times for very small specimens are shorter, and standards exist in human diagnostic histopathology.

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Wikipedia