Cytopathology (from Greek κύτος, kytos, “a hollow”; πάθος, pathos, “fate, harm”; and -λογία, -logia) is a branch of pathology (founded by George Nicolas Papanicolaou in 1928) that study and diagnosis of cells under the morphological and functional profile, which evaluates, with the help of various techniques, the cellular alterations of the tissues under examination in order to identify possible morbid entities both for neoplasms and non-neoplastic diseases. The criteria of cytology are based purely on the morphological characteristics of the cells of their nuclei and cytoplasm: shapes, colors, sizes and patterns of aggregation that are evaluated and compared in order to provide the diagnosis.

There are two methods of collecting cells for cytopathologic analysis: exfoliative cytology, and intervention cytology.

Exfoliative cytology

In this method, cells are collected after they have been either spontaneously shed by the body (“spontaneous exfoliation”), or manually scraped/brushed off of a surface in the body (“mechanical exfoliation”). An example of spontaneous exfoliation is when cells of the pleural cavity or peritoneal cavity are shed into the pleural or peritoneal fluid.

Examples of exfoliative cytology that involve manual tissue brushing or scraping include:

  • Gynecological samples: Pap smear, which involves brushing off cells from cervix using a swab, is the most well-known type of exfoliative cytology.
  • Bronchial brushings: where a bronchoscope is inserted into the trachea and used to evaluate a visible lesion by brushing cells from its surface and subjecting them to cytopathologic analysis.
  • Gastrointestinal tract samples: brush off cells from the lining of gastrointestinal tract (stomach and intestines) during an endoscopy procedure for cytology testing.
  • Skin or mucus samples: scrape off cells from skin or mucous membranes, such as the inside of your nose or mouth, for cytology testing.

Examples of exfoliative cytology that involve collecting tissues or fluids that your body naturally sheds include:

  • Respiratory samples: fluids such as spit and mucus (also called phlegm or sputum) that you cough up for a respiratory cytology test.
  • Urinary samples: urine sample to use for a cytology test.
  • Discharge or secretion samples: abnormal bodily discharge, such as from eye, vagina or nipple.

After sampling, two main techniques can be used: conventional cytology and liquid-based cytology. With the latter, the sample is placed in a liquid that is then processed for further investigation.

Intervention cytology

Intervention cytology is a branch of cytology in which your healthcare provider has to “intervene” with your body to get a sample of cells to test, meaning they have to pierce your skin in some way to get a sample of cells.

The most common type of intervention cytology is fine-needle aspiration (FNA). A healthcare provider will inject a thin needle into the area that they need to sample and draw out fluid. A pathologist then examines the cells in the fluid under a microscope.

Some areas of your body that a healthcare provider may perform a fine-needle aspiration include:

  • Fluid-filled lumps (cysts) under your skin.
  • Solid lumps (nodules or masses) under your skin.
  • Your lymph nodes.
  • Your pericardial fluid, which is the fluid in the sac around your heart.
  • Your pleural fluid, which is in the space between your lung and the inside of your chest wall.
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