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 tissue is then prepared for viewing under a microscope using either chemical fixation or frozen section.
The histological slides are examined under a microscope by a pathologist, a medically qualified specialist who has completed a recognised training program This medical diagnosis is formulated as a pathology report describing the histological findings and the opinion of the pathologist. In the case of cancer, this represents the tissue diagnosis required for most treatment protocols. In the removal of cancer, the pathologist will indicate whether the surgical margin is cleared, or is involved (residual cancer is left behind). This is done using either the bread loafing or CCPDMA method of processing.
After a myocardial infarction (heart attack), no histopathology is seen for the first -30 minutes. The only possible sign the first 4 hours is waviness of fibres at border. Later, however, a coagulation necrosis initiates, with edema and hemorrhage. After 12 hours, karyopyknosis and hypereosinophilia of myocytes can be seen with contraction band necrosis in margins, as well as beginning of neutrophil infiltration. Until the end of the first week after infarction there is beginning of disintegration of dead muscle fibres, necrosis of neutrophils and beginning of macrophage removal of dead cells at border, which increases the succeeding days. After a week there is also beginning of granulation tissue formation at margins, which matures during the following month, and gets increased collagen deposition and decreased cellularity until the myocardial scarring is fully mature at approximately 2 months after infarction