PA7.1 | Diagnostic Cytology — Summary & Reflection

REFLECT

Consider a 55-year-old male smoker presenting with a 3 cm right hilar mass on chest X-ray and 8 weeks of haemoptysis.

1. List the cytological specimens you would obtain and in what sequence, giving your rationale for each.
2. If sputum cytology is reported as 'squamous cell carcinoma,' what additional information does histological biopsy provide that cytology cannot?
3. The patient's family asks: 'If the test says it's cancer, why do we need another biopsy?' How would you explain the relationship between cytology and histopathology in language they can understand?

Write your responses in your self-directed learning log before reading the summary.

KEY TAKEAWAYS

Diagnostic Cytology — Core Concepts

What cytology offers: Rapid, cheap, minimally invasive cell-level diagnosis. Lacks tissue architecture — not a substitute for histopathology in all situations.

Two broad categories:
• Exfoliative — naturally shed cells: Pap smear (cervical TZ, Bethesda system), sputum, urine, effusions (pleural/peritoneal/CSF)
• Interventional — mechanically harvested: brushings (bronchial, GI), scrapings (Tzanck, oral), FNAC (thyroid, breast, lymph node, salivary gland)

FNAC technique: 22-25G needle, Cameco pistol, fan pattern, release suction before withdrawal → air-dry smears (MGG) + wet-fix smears (Pap). ROSE reduces non-diagnostic rates.

Staining:
• Pap stain (wet-fixed) — exquisite nuclear detail, transparent cytoplasm → GYN/respiratory
• MGG/Romanowsky (air-dried) — cytoplasmic granules, mucin, matrix → FNAC
• Cell block + H&E/IHC — effusions, lymphoma subtyping

Malignancy criteria: Nuclear enlargement ↑N:C ratio, hyperchromasia, coarse/irregular chromatin, prominent nucleoli, nuclear membrane irregularity, pleomorphism, loss of cohesion

Cytology limitations: No architecture → follicular thyroid carcinoma, lymphoma subtyping, margin assessment, tumour grading all require histology

Liquid-based cytology (LBC): Thin monolayer, reduced artefact, HPV co-testing from same vial, AI-assisted screening compatible

Diagnostic role: Screening (cervical, urothelial), diagnosis (FNAC of lump), monitoring (CSF in leukaemia). Positive cytology = high specificity; negative ≠ ruled out (triple test principle).