The Bethesda system for reporting thyroid fine needle aspirates: A cytologic study with histologic follow-up

The Bethesda system for reporting thyroid cytopathology represents a major step towards standardization, reproducibility, improved clinical significance, and greater predictive value of thyroid fine needle aspirates (FNAs).

To elucidate the utility of the Bethesda system in reporting thyroid FNAs.

We retrospectively reviewed thyroid FNAs between April 2009 and March 2012, classified them using the Bethesda system, found out the distribution of cases in each Bethesda category, and calculated the malignancy risk for each category by follow-up histopathology.

Of the 1020 FNAs, 1.2% were non-diagnostic, 87.5% were benign, 1% were atypical follicular lesion of undetermined significance (AFLUS), 4.2% were suspicious for follicular neoplasm (SFN), 1.4% were suspicious for malignancy (SM), and 4.7% malignant. Of 69 cases originally interpreted as non-diagnostic, 12 remained non-diagnostic after re-aspiration. In 323 cases, data of follow-up histopathologic examination (HPE) were available. Rates of malignancy reported on follow-up HPE were non-diagnostic 0%, benign 4.5%, AFLUS 20%, SFN 30.6%, SM 75%, and malignant 97.8%.

Reviewing the thyroid FNAs with the Bethesda system allowed a more specific cytological diagnosis. In this study, the distribution of cases in the Bethesda categories differed from some studies, with the number of benign cases being higher and the number of non-diagnostic and AFLUS cases being lower. The malignancy risk for each category correlated well with other studies. The Bethesda system thus allows standardization in reporting, improves perceptions of diagnostic terminology between cytopathologists and clinicians, and leads to more consistent management approaches.