Endocrine Abstracts

Introduction: The 2015 American Thyroid Association (ATA) guidelines on the management of thyroid nodules and cancer recommend specific size cut-offs for fine needle aspiration (FNA) cytology. We assessed the correlation between sonographic and cytological stratification as per the guidelines, with emphasis on the size cut-offs.

Methods: In a ‘real world’ prospective study, we sonographically stratified 562 thyroid nodules prior to performing ultrasound-guided FNA as cysts (1.4%), very low (3.9%), low (54.8%), intermediate (19.9%), or high (19.9%) risk. Their Bethesda cytological classification was B1, B2, B3, B4, B5 and B6 in 3.6%, 77.9%, 3.9%, 5%, 2.8% and 6.8% of nodules, respectively. Strong sonographic-cytological correlation was observed (P<0.0001); for example, B2 (benign) cytology was reported in 100% of very low, 91.2% of low, 81.3% of intermediate and 32% of high risk nodules. Excluding B1 (non-diagnostic) results and nodules without size data, the diagnostic performance of ATA-proposed cut-offs for FNA based on sonographic appearance was compared to higher cut-offs. Increasing the size-threshold for sonographically low and intermediate risk thyroid nodules would spare FNAs at the expense of missing a small proportion of B3–B6 cytological nodules and differentiated thyroid carcinomas (DTCs). The size cut-offs are compared against the cytological result of B2 (‘negative outcome’) or B3–B6 (‘positive outcome’). †Relative to number of available histopathology results. PPV, positive predictive value. NPV, negative predictive value.

Discussion: By increasing the size cut-off for low-risk nodules, the NPV value retains its excellent performance, whereas PPV remains unaffected with poor performance. By using a higher cut-off in intermediate-risk nodules, NPV and PPV performance remain unchanged. In high-risk nodules, both NPV and PPV perform poorly regardless of the size cut-off. The 20 mm and 40 mm cut-offs may have greater clinical significance in case of carcinoma, as they correspond to higher tumour grades (≥T2 and ≥T3), altering the clinical management.

Conclusion: Our results suggest that increasing the ATA size cut-off from 15 mm to 20 mm in sonographically low-risk nodules is clinically safe whilst reducing FNAs.