Thyroid cytology: The reality before and after the introduction of ultrasound classification systems for thyroid nodules.

Background: Several ultrasound-based systems for classification of thyroid nodules are available. They allow for a better triage of the nodules that require cytological assessment, and lead to standardized recommendations. Our aim was to compare patients and nodules referred to fine-needle aspiration (FNA) before and after the introduction of these systems.

Methods: A retrospective study comparing two cohorts of patients referred for FNA was performed (386 patients and 463 nodules in 2015; 220 patients and 263 nodules in 2021).

Results: The sex distribution (89.1% vs 85.9% females, p=0.243), number of nodules referred to FNA per patient (median of 1), and the distribution of the Bethesda categories (p=0.082) was similar in both years. In 2021, patients were older (53.4±14.5 years vs 57.8±13.2 years, p<0.001) and nodules over one centimetre were larger (median 17.0mm vs 19.0mm, p=0.002), especially the ones categorized as Bethesda III (median size 11mm vs 23mm, p=0.043). In 2021, at least 23.1% of the nodules referred to FNA did not have any criteria, and 38.8% of the nodules were not categorized by any system.

Conclusion: This analysis draws attention to the importance of systematically applying ultrasound-based classification systems. It seems that, by not being focused mainly on size thresholds, they allow for longer surveillance periods, without aggravating the cytology results when FNA becomes indicated. Nevertheless, greater efforts are needed to ensure more standardized reports, and to increase adherence to the resulting recommendations to reduce clinical uncertainty, unnecessary FNA, and overtreatment.