Definition it is a branch of pathology which deals with the study of disease in a tissue section. The tissue undergoes a series of steps before it reaches the examiners desk to be thoroughly examined microscopically to arrive at a particular diagnosis. To achieve this it is important that the tissue must be prepared in such a manner that it is sufficiently thick or thin to be examined microscopically and all the structures in a tissue may be differentiated.
2. Gross cutting (Observation. To handle common surgical pathology specimens including importance of slicing large specimens. Salient features to be described as per recommended guidelines.)
3. Tissue processing
4. Special precaution for tissue to be sent for (electron microscopy, special biopsies, immuno-fluorescence etc)
5. Decalcification
6. Basic Molecular Biology Techniques & FISH testing for Her-2-neu/solid tumors
Fixation of tissues can be achieved by chemical or physical means.
Physical methods include heating, micro-waving and cryo-preservation (freeze drying).
Chemical fixation is usually achieved by immersing the specimen in the fixative (immersion fixation) or, in the case of small animals or some whole organs such as a lung, by perfusing the vascular system with fixative (perfusion fixation). For some specialised histochemical procedures fixatives have occasionally been applied in the vapour form. For example paraformaldehyde and osmium tetroxide can be used to vapour-fix freeze-dried tissues.
Tissues removed from the body for diagnosis arrive in the Pathology Department and are examined by a pathologist, pathology assistant, or pathology resident. Gross examination consists of describing the specimen and placing all or parts of it into a small plastic cassette which holds the tissue while it is being processed to a paraffin block. Initially, the cassettes are placed into a fixative.
When a malignancy is suspected, then the specimen is often covered with ink in order to mark the margins of the specimen. Different colored inks can be used to identify different areas if needed. When sections are made and processed, the ink will mark the actual margin on the slide.
Fixation is the foundation step behind the study of pathology and essentially exists to prevent the autolysis and degradation of the tissue and tissue components such that they can be observed both anatomically and microscopically following sectioning. A number of fixatives exist, either having being in use for decades, or in the case of formaldehyde over a century, whilst others have only been created in the last 10 years. To attempt to classify this chaos, fixatives can be place
Tissues from the body taken for diagnosis of disease processes must be processed in the histology laboratory to produce microscopic slides that are viewed under the microscope by pathologists. The techniques for processing the tissues, whether biopsies, larger specimens removed at surgery, or tissues from autopsy, are described below. The persons who do the tissue processing and make the glass microscopic slides are histotechnologists.
Tissue specimens received in the surgical pathology laboratory have a request form that lists the patient information and history along with a description of the site of origin. The specimens are accessioned by giving them a number that will identify each specimen for each patient.
