Anatomical pathology is vital in those parts of medicine where a specimen of tissue or a sample of tissue cells is taken from the patient and sent to the laboratory. In these situations anatomical pathology is the specialty that gives the definitive diagnosis and allows clinicians to give the most appropriate advice and treatment to their patients. Although one of the frequent uses of anatomic pathology is to help identify and manage various types of tumors or cancers, it is also valuable in evaluating other conditions, including kidney and liver diseases, autoimmune disorders, and infections, for example.
There are two main subdivisions within anatomical pathology. The first is histopathology, which involves the examination of sampled whole tissues under the microscope. This is often aided by the use of special staining techniques and other associated tests.
Special staining Pathologists use different special stains in addition to the routine hematoxylin and eosin (H&E) stain. These may highlight fat, different tissue fibers, mucus, microbes such as bacteria or fungi, proteins, or other biochemical substances that might be useful in identifying key elements that are characteristic of certain diseases.
Immunohistochemistry This technique takes advantage of the unique properties of antibodies that have been developed to recognize specific components on or within cells.
Electron microscopy The electron microscope uses high voltage to create a wide beam of electrons that are directed at a specially stained sample.
These molecular techniques are used to identify mutations that help to guide therapy of malignant tumors, such as:
- HER2—breast cancer
- EGFR—adenocarcinoma of the lung
- KRAS—colon cancer
- BRCA 1 & 2—breast cancer and ovarian cancer
- BRAF—melanomas
- JAK2—myeloproliferative neoplasms
The second subdivision is cytopathology (cytology), which is the examination of single cells.
Exfoliative cytology This is the analysis of cells that are shed from body surfaces. The cervical (Pap) smear is the most common example, but samples from the urinary bladder, abdominal cavity, chest cavity, cerebrospinal fluid, and washings from the lung are also frequently examined.
Fine needle aspiration This is performed using a thinner needle than that used in a core biopsy but with a similar technique. The FNA is particularly useful in evaluating the presence of normal or abnormal cell types.
Flow cytometry This technique is commonly employed in the diagnosis of cancers of the blood cells (leukemias and lymphomas).