Cytopathology

Cytopathology is a field of medicine focused on diagnosing disease by examining cells. Its roots trace back to the 19th century, with early contributions from Johannes Müller, Lionel Beale, and others, though it gained widespread recognition after George Nicolas Papanicolaou developed the Pap test in 1928. Unlike histopathology, which looks at whole tissue sections, cytopathology works with loose cells or small tissue fragments. The term "cytology," meaning the study of cells, is often used interchangeably, though less precisely.

This discipline is used to investigate conditions in many parts of the body, most commonly to detect cancer, but also to identify certain infections and inflammatory disorders. A well-known example is the Pap smear, which screens for precancerous changes in the cervix that could lead to cervical cancer. Cytopathologic tests are sometimes called smear tests because samples are often spread onto a glass slide for staining and microscopic review, though other preparation methods, like cytocentrifugation, exist. Different smear tests can also aid in cancer diagnosis, referred to as a cytologic smear.

Cells for analysis are collected in two main ways: exfoliative cytology and intervention cytology.

In exfoliative cytology, cells are gathered after being shed naturally by the body, such as cells from the pleural or peritoneal cavities found in fluid, or after being manually scraped or brushed from a surface. For instance, a Pap smear uses a spatula to scrape cells from the cervix, and bronchial brushings involve a bronchoscope to brush cells from a visible lesion in the trachea.

Intervention cytology requires the pathologist to enter the body to obtain the sample. Fine-needle aspiration (FNAC) is the primary method here, using a needle and syringe—often with suction—to collect cells from a mass or lesion. This can be done on superficial areas like the neck, thyroid, or breast by feeling the lump, or with ultrasound or CT guidance for deeper lesions. Success depends heavily on the practitioner’s skill; when a pathologist or a pathologist-cytotechnologist team performs it, diagnostic accuracy is higher because they can check the sample immediately under a microscope and repeat the procedure if needed.