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Cytology — smears, fine-needle aspiration and reporting systems
Cytology examines individual cells, not tissue architecture: it is fast, cheap and less invasive, and excellent for detecting nuclear changes, but it cannot show invasion through a capsule or basement membrane — so its reporting systems (Bethesda, Paris) grade risk and do not always give a final diagnosis.
Why it matters in the exam
The bank asks about the difference between cytology and histology and about the categories. Exfoliative cytology collects shed cells — cervical smear, urine, sputum, pleural fluid — and fine-needle aspiration (FNA) cytology aspirates cells from a mass — thyroid, lymph node, breast, pancreas under endoscopic ultrasound. A cell block from the fluid allows immunohistochemistry, and rapid on-site evaluation (ROSE) confirms that the sample is adequate during the procedure.
In the cervical smear, the Bethesda system divides squamous cell changes — ASC-US, ASC-H, LSIL, HSIL and squamous carcinoma — and glandular cell changes (AGC). The decision on colposcopy combines the result with high-risk HPV testing. In the thyroid there are 6 categories: I nondiagnostic, II benign, III atypia of undetermined significance, IV follicular neoplasm, V suspicious for malignancy and VI malignant; in category IV cytology cannot distinguish adenoma from follicular carcinoma, because the difference is capsular or vascular invasion, and resection is needed for diagnosis.
In urine, the Paris system focuses on detecting high-grade urothelial carcinoma and is less good for low-grade tumours. In pleural fluid, reactive mesothelial cells can mimic malignancy, and immunohistochemistry on the cell block helps. An important rule: a negative cytology result with high clinical suspicion does not close the work-up, because sampling may miss the lesion.
Key points
- Exfoliative cytology and fine-needle aspiration.
- A cell block allows immunohistochemistry; ROSE confirms adequacy.
- Bethesda for the cervix, combined with HPV.
- Bethesda for the thyroid: 6 categories; IV requires resection for diagnosis.
- Paris in urine is aimed at high grade.
Summary table
| Field | Reporting system | Main categories | Limitation |
|---|---|---|---|
| Cervix | Bethesda for cervix | ASC-US, ASC-H, LSIL, HSIL, AGC | Combined with HPV |
| Thyroid | Bethesda for thyroid | 6 categories, I to VI | IV does not separate adenoma from follicular carcinoma |
| Urine | Paris | High-grade urothelial carcinoma | Weak for low grade |
| Pleural fluid | Institutional | Malignant versus reactive | Reactive mesothelial cells mimic |
| Fine-needle aspiration | By organ | Cells from a mass | No architecture or invasion |
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Sources
- The Bethesda System for Reporting Cervical Cytology, 3rd edition (2015) — Epithelial cell abnormalities
- The Bethesda System for Reporting Thyroid Cytopathology, 3rd edition (2023) — Diagnostic categories and risk of malignancy
- The Paris System for Reporting Urinary Cytology, 2nd edition (2022) — Diagnostic categories
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.