Evolutionary analysis of indeterminate cytology and risk of malignancy in a thyroid nodule unit

The objective of this study was to analyze the evolution in the diagnosis and management of indeterminate thyroid nodules over three time periods.

In total, 3020 patients with thyroid nodules underwent cytological evaluation during three periods (2006-2008, 2012-2014, 2017-2019). Distribution of diagnostic cytologies, risk of malignancy, diagnostic performance indices of FNA, and cytologic-histologic correlation in indeterminate cytologies were analyzed.

Only 2.2% of cytology tests were insufficient for a diagnosis. 86.9% cytologies were benign, 1.7% malignant, and 11.4% indeterminate. Indeterminate cytology rates were 15.9% (2006-2008), 10.1% (2012-2014), and 10% (2017-2019). Surgery was performed in 13% of benign cytology, result-ing in malignant histology in 2.7%. All malignant and suspicious cytologies underwent surgery: malig-nancy confirmed in 98% and 77% of cases, respectively. All 'indeterminate with atypia' cytologies (2006-2008) and Bethesda IV (2012-2014; 2017-2019) un-derwent surgery, with malignancy confirmed in 19.6%, 43.8%, and 25.7%, respectively. In the 'inde-terminate without atypia' category (2006-2008) and Bethesda III (2012-2014; 2017-2019), diagnostic surgery was performed in 57.7%, 78.6%, and 59.4%, respectively, with malignancy confirmed in 3.3%, 20.5%, and 31.6%. The FNA sensitivity was 91.6% with a negative predictive value greater than 96% in all periods. The specificity exceeded 75% in the last two periods.

Bethesda system reduces indeterminate cytologies and improves the accuracy of FNA diagnosis. We reported a higher proportion of malignancy than expected in Bethesda III, underscoring the importance of having institution-specific data to guide decision-making. However, there is a need for risk stratification tools that allow for conservative management in low-risk cases.