The diagnosis of certain illnesses frequently requires special (microscopic) examination of samples of the organ or tissue involved. These examinations are carried out in the laboratory by a pathologist, who has specialized in the study of disease processes. Two sub-specialists within pathology are involved: the cytologist , who concentrates on small numbers of individual cells obtained from the external or internal surfaces of the body; and the histopathologist , who examines whole organs or parts of them by looking at their cells in their natural arrangement within the tissue or organ. Both use a light-microscope, together with a number of special stains and dyes that highlight important features of the structures being examined.
Several techniques exist for obtaining specimens of cells and pieces of tissue. In cytology, cells are gathered by physical means, and are specially prepared and stained for microscopic examination. They may be rubbed, scraped, brushed or washed from the (inner) surface of the body. A well-known example is the cervical smear test, in which cells are scraped from the cervix (neck of the womb) with a spatula. Abnormal cells are seen in cases of pre-cancer or early cancer, and may thus be detected when otherwise unsuspected. Such early diagnosis may allow the condition to be cured by a relatively small operation on the tip of the cervix.
Some lumps beneath the skin may be examined by fine-needle aspiration, in which a thin hypodermic needle, like those used to draw blood, is inserted into the lump without an anaesthetic. Strong suction with a syringe draws specimen cells up the needle. The technique may be used in examining breast lumps and in diagnosing some swellings of the neck. Pieces of tissue removed for histological examination are termed biopsies. Tissue may be extracted using a very stout needle, which removes a core of tissue, but more usually, cut out under local or general anaesthetic, depending on the area being investigated. Skin lumps that appear suspicious may be removed completely, under local or general anaesthetic. This removal of an entire diseased lump is termed ‘excision biopsy’ (or ‘lumpectomy’). It may be all that is needed to cure some skin cancers. Breast lumps, lymph nodes (’glands’) and other tissue masses may be similarly removed. An additional advantage of removing the whole suspected lump is that if it is malignant, there is less chance of spreading cancer cells in the operated area by cutting through it.
In some cases, the piece of tissue removed may be examined immediately by the technique of frozen section, in which the specimen is frozen and cut into thin sections for microscopic scrutiny. This is very quickly done, in a matter of minutes, in contrast to the usual method of embedding the tissue in a waxy substance before slicing, which may span two or three days. Although the frozen section technique is not quite so accurate it may give the doctors information about the diagnosis while the patient is still anaesthetized, and any necessary further surgery may then be performed at once. This option is previously discussed with the patient to obtain his or her consent.