Microscopy Solutions for Histology and Histopathology
Study the Manifestation of Disease by Microscopic Examination of Tissue Morphology
Pathology, histopathology or histology aims to study the manifestation of disease by microscopic examination of tissue morphology. In pathology, the sample to be examined under the microscope usually is the result of a surgery, biopsy or autopsy after fixation, clearing/embedding and sectioning of the tissue specimen. Alternatively, frozen section processing with a cryostat is done when rapid results are required (e.g. during surgery) or fixation would be detrimental to target structures such as lipids or certain antigens.
The tissue sections after fixation and wax embedding are typically cut into two to five micron thin slices with a microtome before staining and transfer to a glass slide for examination with a light microscope. Typical specimens in pathology are colon, kidney, pancreas, cervix, lung, breast, prostate, or connective tissue.
While various staining procedures for human/animal and plant tissues have been developed as early as the 17th century it was the German physician Rudolf Virchow who is being considered the father of modern histopathology. Virchow realized the potential of the emerging new microscope techniques of the 19th century for his groundbreaking research, published a vast amount of scientific writing and created an impressive collection of thousands of histopathological sample slides, thus building the foundation of modern histology and cancer research.
Histology slide preparation begins with fixation of the tissue specimen. This is a crucial step in tissue preparation, and its purpose is to prevent tissue autolysis and putrefaction. For best results, the biological tissue samples should be transferred into fixative immediately after collection, usually in 10% neutral buffered formalin for 24 to 48 hours. After fixation, specimens are trimmed using a scalpel to enable them to fit into an appropriately labelled tissue cassette that is stored in formalin until processing begins.
The first step of processing is dehydration, which involves immersing your specimen in increasing concentrations of alcohol to remove the water and formalin from the tissue. Clearing is the next step, in which an organic solvent such as xylene is used to remove the alcohol and allow infiltration with paraffin wax. Embedding is the final step, where specimens are infiltrated with the embedding agent – usually paraffin wax which provides a support matrix that allows for very thin sectioning. A microtome is used to slice extremely thin tissue sections off the block in the form of a ribbon, following histochemical staining (typically haematoxylin and eosin - “HE stain”) to provide contrast to tissue sections, making tissue structures better visible and easier to evaluate. In certain cases immunohistochemical stainings (IHC), such as HER2 or Ki-67, are required for further analysis.
A very good differentiation of tissue structures and clearly visible cellular details are absolute prerequisites in pathology for carcinoma and tumor cell diagnosis. Histopathologists rely on crystal-clear images of their samples with the highest color fidelity in brightfield. Other contrasting techniques include polarization, CISH, fluorescence, immunofluorescence, or FISH microscopy. While histological and immunohistochemical stains result in a good transparency of the sample and specific staining of cellular features, it is the optical quality of the microscope, the fidelity of the attached camera for digital documentation, and the ergonomic design of the instrument that can make all the difference when screening patient samples. Automated digital slide scanning systems with class-leading optics assist with high-throughput screening and archiving.