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Anatomical pathology is the branch of pathology that is concerned with the diagnosis of disease based on the gross and microscopic examination of cells and tissues. Contrary to popular belief, the field mostly concerns the study of tissue obtained from live patients. In fact, almost all tissues removed from a patient for any reason are examined by a pathologist. The autopsy, though, remains an important tool in gaining medical knowledge.
Role of anatomical pathology
Biopsy specimens are often taken from part of a lesion when the cause of a disease is uncertain or its extent or exact character is in doubt. Vasculitis, for instance, is usually diagnosed on biopsy. Additionally, pathologic examination of a small biopsy can help differentiate between different types of cancer and determine whether a lesion is benign or malignant. In contrast to a biopsy that merely samples a lesion, a larger specimen called a resection may come to a pathologist, typically from a surgeon attempting to eradicate a known lesion from a patient. For example, a pathologist would examine a mastectomy specimen, even if a previous nonexcisional breast biopsy had already established the diagnosis of cancer. Examination of the full mastectomy specimen would confirm the exact nature of the cancer and reveal the extent of its spread ("staging").
The procedures used in anatomical pathology include:
- Gross pathology:
- Identification of injuries, retrieval of foreign bodies and surgical material
- Examination with the naked eye - This is important especially for large tissue fragments, because diseased parts of an organ can often be visually identified.
- Histopathology and cytopathology:
- Microscopic examination of stained sections or looser collections of cells on glass slides (most commonly using haematoxylin and eosin, blue and pink stains)
- Examination with special stains for organisms, iron, calcium, elastic tissue, mucins, etc.
- Examination with immunoperoxidase and immunofluorescence stains - The pathologist can use specific antibody preparations to see the microscopic location of various substances in a specimen. This technique is especially useful in tumour pathology, in some inflammatory skin diseases, and in renal biopsies.
- Electron microscopy
- Tissue cytogenetics
- Flow immunophenotyping
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