Cytology examines individual cells; histology examines tissue architecture
Expansion
| Cytology | Histology | |
|---|---|---|
| Sample | Individual cells or clusters | Intact tissue |
| Obtained by | Fine needle aspiration, brushings, fluid, smears | Core biopsy, excision |
| Shows | Cellular detail | Architecture plus cellular detail |
| Invasion | Cannot assess | Can assess |
| Speed | Rapid, minimally invasive | Slower |
| Grading and staging | Limited | Yes |
Cytology applications: cervical screening (Papanicolaou), thyroid and breast fine needle aspiration, pleural and ascitic fluid, urine, sputum, and endoscopic brushings.
The inability to assess invasion is the fundamental limitation and explains several clinical rules: cytology cannot distinguish carcinoma in situ from invasive carcinoma, and it cannot distinguish follicular adenoma from follicular carcinoma of the thyroid, since that distinction rests entirely on capsular and vascular invasion. Both require tissue.
Liquid based cytology has replaced conventional smears in cervical screening, giving cleaner preparations, fewer inadequate samples and the ability to perform HPV testing on the same sample.
Cytology remains valuable precisely because it is quick, cheap and low risk, making it the right first test in many settings.