Pathology
Basic Diagnostic Cytology
Diagnostic cytology for MBBS and NEET-PG: exfoliative cytology, fine needle aspiration, Pap and Giemsa stains, criteria of malignancy and limitations, mapped to NMC codes PA8.1 to PA8.3.
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Basic Diagnostic Cytology
Diagnostic cytology for MBBS and NEET-PG: exfoliative cytology, fine needle aspiration, Pap and Giemsa stains, criteria of malignancy and limitations, mapped to NMC codes PA8.1 to PA8.3.
This chapter introduces diagnostic cytology, the examination of individual cells for the early detection of cancer and other disease. It covers exfoliative cytology and fine needle aspiration, the stains and techniques used, the criteria of malignancy, and the strengths and limitations of the method.
High-yield: Basic Diagnostic Cytology
- Cytology is the study of individual cells to detect malignancy and other disease, using exfoliated or aspirated cells rather than whole tissue.
- Exfoliative cytology examines cells shed naturally or scraped from a surface, as in the cervical Pap smear.
- Fine needle aspiration cytology (FNAC) samples cells from a mass using a thin needle and is quick, cheap and minimally invasive.
- The Papanicolaou stain is the standard stain for exfoliative cytology and gives excellent nuclear detail.
- The cervical Pap smear is the classic screening test that detects pre-invasive cervical lesions and reduced cervical cancer mortality.
- May-Grunwald-Giemsa staining is preferred for air-dried aspirates and highlights cytoplasmic and background features.
- Features suggesting malignancy include a high nucleus-to-cytoplasm ratio, nuclear pleomorphism, hyperchromasia and prominent nucleoli.
- FNAC of the thyroid, breast and lymph node is a first-line investigation for a palpable lump.
- A major limitation of cytology is that it cannot always assess tissue architecture or invasion, so histology may still be needed.
- Liquid-based cytology improves cell preservation and reduces obscuring blood and inflammation compared with conventional smears.
- The Bethesda system standardises the reporting of cervical cytology.
- Sputum, urine and effusion fluids are common specimens for exfoliative cytology.
- An adequate smear must be well spread, promptly fixed and correctly stained to allow reliable interpretation.
- Immunocytochemistry and molecular tests can be applied to cytology samples to refine the diagnosis.
Exfoliative cytology versus FNAC
- **Exfoliative:** Cells shed or scraped from a surface, such as the cervical Pap smear or sputum.
- **FNAC:** Cells aspirated from a mass with a thin needle; quick and minimally invasive.
- **Key stain:** Papanicolaou for exfoliative; May-Grunwald-Giemsa for air-dried aspirates.
- **Malignancy clues:** High nucleus-to-cytoplasm ratio, pleomorphism, hyperchromasia, prominent nucleoli.
NMC competencies in this chapter
- **PA8.1:** Diagnostic role of cytology and its application in clinical care
- **PA8.2:** Basis of exfoliative cytology, including techniques and stains
- **PA8.3:** Observe and interpret a diagnostic cytology specimen
Frequently Asked Questions
What is the difference between exfoliative cytology and FNAC?
Exfoliative cytology examines cells shed or scraped from a surface, while FNAC aspirates cells from a mass through a thin needle.
Which stain is used for the Pap smear?
The Papanicolaou stain, which gives excellent nuclear detail and is the standard for cervical and other exfoliative cytology.
What cytological features suggest cancer?
A high nucleus-to-cytoplasm ratio, nuclear pleomorphism, hyperchromasia and prominent nucleoli all point towards malignancy.
What is a limitation of cytology?
Cytology examines individual cells and cannot always assess tissue architecture or invasion, so a confirmatory biopsy for histology may still be required.
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