Cytopathology

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Cytopathology is a branch of cytology and pathology that studies and diagnoses diseases on the cellular level.^[1]

A common application of cytopathology is the Pap smear, used as a screening tool, to detect precancerous cervical lesions and prevent cervical cancer. Cytopathology is also commonly used to investigate thyroid lesions, diseases involving sterile body cavities (peritoneal, pleural, and cerebrospinal), and a wide range of other body sites. It is usually used to aid in the diagnosis of cancer, but also helps in the diagnosis of certain infectious diseases and other inflammatory conditions. Cytopathology is generally used on samples of free cells or tissue fragments, in contrast to histopathology, which studies whole tissues.

Rudolf Ludwig Karl Virchow is considered by many to be one of the fathers of cellular pathology, remembered most for his collection of lectures on the topic, published as Cellular Pathology in 1858.^[2]^[3]

Testing

Cytopathologic tests are sometimes called smear tests because the samples may be smeared across a glass microscope slide for subsequent staining and microscopic examination. However, cytology samples may be prepared in other ways, including cytocentrifugation.^[1] Different types of smear tests may also be used for cancer diagnosis. In this sense, it is termed a cytologic smear.^[4]

Collection

Two primary methods are used for collecting cells for analysis:

1. 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. This fluid can be collected via peritoneal washing for examination. Examples of mechanical exfoliation include Pap smears, where cells are scraped from the cervix with a cervical spatula, or bronchial brushings, where a bronchial brush is inserted into the trachea to collect cells from its surface and subject them to cytopathologic analysis.^[5]

2. Aspirative cytology: More specifically referred to as fine needle aspiration cytology (FNAC), the aspirative technique tends to be more invasive than exfoliative techniques. In FNAC, a hypodermic needle attached to a syringe is used to collect cells from lesions or masses in various body organs by microcoring, often with the application of negative pressure to increase yield. FNAC can be performed under palpation guidance (i.e., the clinician can feel the lesion) on a mass in superficial regions like the neck, thyroid or breast. FNAC may also be assisted by ultrasound or CAT scan for sampling of deep-seated lesions within the body that cannot be localized via palpation.^[5]

FNAC is widely used in many countries, but success rate is dependent on the skill of the practitioner. If performed by a pathologist alone, or as team with pathologist-cytotechnologist, the success rate of proper diagnosis is superior than when performed by a non-pathologist.^[6]^[5]

Preparation

Intervention cytology - in interventional cytology the pathologist intervenes into the body for sample collection. Nowadays FNAC has become synonymous to interventional cytology.

Sediment cytology – Here, the sample is collected from the fixative that was used for processing the biopsy or autopsy specimen. The fixative is mixed properly and taken into a centrifuge tube and is centrifuged. The sediment is used for smearing. These sediments are the cells that are shed by the autopsy and biopsy specimen during processing.