Cytology (Principles and FNA Cytology)
Cytology examines individual cells and small cell clusters under the microscope. Cells are collected by aspiration, brushing, scraping or washing, or from body fluids, and smeared or concentrated on glass slides. The cytopathologist looks for the nuclear and cytoplasmic changes that separate normal, reactive, infected, pre-malignant and malignant cells.
It is used for screening (cervical cytology), for diagnosis of masses by fine needle aspiration, for examination of effusions, urine, sputum and cerebrospinal fluid, for detection of infection, and for monitoring of known disease. It is less invasive than a tissue biopsy, and a result is available in a day or two.
Cytology samples are of three main types. Exfoliative samples are cells that shed naturally (sputum, urine, effusions, cerebrospinal fluid, cervical samples). Abrasive samples are cells scraped or brushed from a surface (cervix, bronchus, oesophagus, bile duct). Aspirated samples come from needle sampling of a mass or collection.
Reports are issued in organ specific categories, from non-diagnostic and benign through atypical and suspicious to malignant. Each category is linked to a set of next steps, and the sensitivity and specificity differ between sites. Cytology is highly specific for malignancy when positive, though sensitivity is lower and depends on sampling.
Indications.
- Screening for cervical cancer and its precursors.
- Diagnosis of palpable or imaged masses by FNA.
- Pleural, pericardial and peritoneal effusions of unknown cause, and suspected malignant effusion.
- Cerebrospinal fluid for leptomeningeal malignancy and infection.
- Urine for urothelial carcinoma (surveillance and haematuria).
- Sputum, bronchial brushings and washings, and endobronchial ultrasound aspirates for lung cancer.
- Bile duct and pancreatic brushings and aspirates.
- Breast nipple discharge and cyst fluid.
- Infection: fungal elements, parasites, viral inclusions (for example, Pneumocystis in lavage, herpes in a scraping).
- Monitoring of treated disease and assessment of recurrence.
Not indicated as the only test when a tissue diagnosis is clearly needed, for example suspected lymphoma or sarcoma needing classification and grading.
Specimen requirements.
- Smears: spread thinly and either air dried at once (for Romanowsky stains) or fixed immediately in alcohol or spray (for Papanicolaou stain). A smear that dries before alcohol fixation loses nuclear detail.
- Fluids: sent fresh to the laboratory without delay, in a clean container. If delay is expected, the fluid is kept at 4°C, and not frozen. A volume of 50 to 100 mL is usually enough, and larger volumes add little. Heparin or EDTA is added to bloody samples where the laboratory advises.
- Liquid based medium: the sample or needle rinse is placed in a preservative, which gives a thin, even layer of cells and spare material for extra tests.
- Cell blocks: made from fluids and aspirates by concentrating cells into a clot or gel, and processed like tissue. They allow immunocytochemistry and molecular testing.
- Labelling: two patient identifiers on the slide (in pencil on the frosted end) and on the container, with site, type of sample and clinical details.
