Thyroid nodules 1 cm or less are related to Bethesda System nondiagnostic and suspicious for malignancy categories.

Objective: To compare the frequency of fine needle aspiration (FNA) cytological results between nodules 1 cm or less and nodules greater than 1 cm.

Methods: All FNAs performed between January 2016 and December 2019 at an institute in Brazil were analysed. For each nodule, at least two conventional slides were produced (one stained by Giemsa and the other by hematoxylin and eosin). All cases were reviewed by two cytopathologists and were reported following the Bethesda System. Clinical information (gender and age) and ultrasound data (nodule size and location) were collected. The magnitude of association was measured using the prevalence ratio (PR) with 95% confidence intervals (CIs) considering two groups of nodules: 1.0 cm or less, and greater than 1 cm.

Results: A total of 3703 nodules were analysed from 3265 patients (2906 women [88.48%], 359 men [11.51%], with a combined mean age of 52 years). Considering the prevalence ratio of Bethesda categories between these two groups of nodules, the nondiagnostic or unsatisfactory category (PR: 3.0, 95% CI: 2.2-4.2) and the suspicious for malignancy category (PR: 1.6, 95% CI: 1.1-2.4) were significantly associated with nodules measuring 1 cm or less.

Conclusion: Our results demonstrated that nodules 1 cm or less are significantly associated with the nondiagnostic and suspicious for malignancy categories of the Bethesda System when compared to nodules greater than 1 cm.