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Table 1 Bethesda system for cytological diagnosis of thyroid nodules [12]

From: The diagnostic value of ultrasonography in detection of different types of thyroid nodules

Category Category name Cytologic features Malignancy risk (%)
I Non-diagnostic or Unsatisfactory (ND) Insufficient cellularity, obscuring blood 5–10
II Benign Normal-appearing follicular cells arranged in sheets or macrofollicls, abundant colloid 0–3
III Atypical of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) Sparsely cellular, microfollicles, mild nuclear changes 10–30
IV Follicular lesion/suspicious for follicular lesion (FN/SFN) Hypercellular, crowding, microfollicles, scant colloid 25–40
V Suspicious for malignancy (SFM) Some features that suggest but not definitive for malignancy 50–75
VI Malignant Papillary architecture, definitive nuclear changes 97–99