Histopathology
Introduction
Histopathology 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 to cytopathology, which studies cell appearance, histopathology investigates the appearance of tissues.
Principles of Histopathology
The core principle of histopathology revolves around the microscopic study of diseased tissue. It involves the application of various techniques and methodologies including staining and microscopy. The histopathological examination of tissues starts with surgery, biopsy, or autopsy. The tissue is removed and then often preserved in fixative to prevent decay.
Techniques in Histopathology
Histopathology employs various techniques, each with its own advantages and disadvantages. The most commonly used techniques include:
Fixation
Fixation is the first step in the preparation of tissue for histopathological examination. The purpose of fixation is to preserve tissue in as life-like a state as possible. Fixation helps to prevent autolysis and putrefaction.
Processing
After fixation, the tissue is processed. Tissue processing involves the removal of water and fat from the tissue and the infiltration of the tissue with paraffin wax. This is usually achieved through a series of alcohol, xylene, and paraffin wax baths.
Embedding
Once the tissue has been processed, it is then embedded into a larger block of paraffin wax. This is done to provide support to the tissue to allow for thin sectioning.
Sectioning
Sectioning is the process of cutting the tissue into extremely thin slices, usually around 5 micrometres thick. This is done using a microtome. The thin sections are then placed onto a glass slide for staining.
Staining
Staining is the process of adding colour to the tissue sections. The most commonly used stain in histopathology is haematoxylin and eosin (H&E). Haematoxylin stains cell nuclei blue, while eosin stains the cytoplasm and extracellular matrix pink.
Role in Diagnosis
Histopathology plays a crucial role in the diagnosis of various diseases. It is particularly important in the diagnosis of cancer, but is also widely used in the diagnosis of other conditions, such as inflammatory and infectious diseases. The histopathological examination allows for the identification of disease type, stage, and other characteristics that can guide treatment decisions.
Histopathology and Research
In addition to its clinical applications, histopathology is also a fundamental tool in medical and biological research. It is used in the study of the pathogenesis of diseases, in the development of new treatments, and in the understanding of basic biological processes.