Cytopathology (Gynecologic and Non-gynecologic)
Overview
This domain tests category assignment, adequacy judgement and risk-based triage. The exam expects fluency in the Bethesda System for cervical and thyroid cytology, plus the Milan (salivary) and Paris (urinary) systems, and the practical limits of FNA.
Core rules
- Cervical Bethesda categories: NILM, ASC-US, LSIL, ASC-H, HSIL, AGC (with or without AIS), and malignancy. ASC-US is equivocal squamous atypia; ASC-H carries a much higher risk of CIN2+ and mandates colposcopy.
- Adequacy: conventional smears need roughly 8,000–12,000 well-visualized squamous cells; liquid-based preparations about 5,000. Abundant inflammation or blood can render a specimen unsatisfactory.
- Triage: ASC-US in a patient aged 25 or older goes to HPV testing or co-testing; a positive HPV result sends the patient to colposcopy. LSIL in a young patient is usually followed, since most lesions regress.
- Thyroid Bethesda: I nondiagnostic, II benign, III AUS/FLUS, IV follicular neoplasm, V suspicious for malignancy, VI malignant, each with a rising risk of malignancy and a defined management pathway.
- Ancillary stains: p16 block positivity and Ki-67 dual stain increase specificity for high-grade squamous lesions.
Worked example
A 47-year-old has a cervical sample with a few atypical squamous cells and abundant inflammation but no definite lesion. Reasoning: the atypia is equivocal, so the category is ASC-US rather than ASC-H, which requires features suggesting HSIL. Reflex HPV testing is the next step; a negative result permits return to routine screening, a positive result triggers colposcopy. Assigning ASC-H here would over-triage; assigning NILM would under-triage.
Traps
Treating ASC-US and ASC-H as interchangeable. Calling LSIL "CIN1" on a cytology report when no histology exists. Ignoring low cellularity when signing out a negative gynecologic specimen.