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Introduction to histopathology
Introduction to histopathology

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1 Pathological processes - inflammation and infection

Histological examination of tissues can help diagnose disease, because each condition produces a characteristic set of changes in the tissue structure. There are such a wide variety of diseases that histology alone usually cannot produce a diagnosis, although in some cases the histological appearance is definitive. For example, a pathologist might see signs of a viral infection in the brain, because of tissue damage and inflammation, but would be unable to tell what virus is responsible; to identify the virus might require immunohistochemistry (IHC) for the viral protein or more likely, the diagnosis would be confirmed by the symptoms or serology. Conversely, the appearance of 'owl-eye' cells in the brain is diagnostic of a particular type of measles infection (Figure 1). Normally histopathology reports only form one part of the disease picture that the clinician is assembling.

Figure 1 Owl-eye bodies in infected neurons of a child with subacute sclerosing panencephalitis (SSPE) are characteristic of this type of viral infection, which is produced by a variant of the measles virus.

Although diseases are very diverse, the responses made by the body are more limited and fall into specific categories. For example inflammation, may be seen in response to an infection or as a result of physical damage or as part of an autoimmune disease, where the immune system attacks components of the body. The following sections outline some of the more common pathological processes and relate them to examples which can be seen in the virtual microscope.