The Bethesda System recommends limiting the percentage of cases diagnosed as indeterminate in thyroid fine-needle aspirations (TFNAs). However, studies are lacking that document how to decrease the rate of indeterminate TFNAs and its effects.
The authors modified the Bethesda criteria to reduce the rate of indeterminate TFNAs ("atypical cells of undetermined significance" and "suspicious for a follicular/Hurthle cell neoplasm") by reassigning cases that may have been categorized as indeterminate to "suspicious for papillary carcinoma" or "favor benign" for an 18-month period and correlated this with histologic follow-up.
The indeterminate rate decreased from 14.4% (Bethesda) to 8.2% (modified Bethesda; P < .001). There was no significant difference in the risk of malignancy for the 2 groups (23.6% vs 17.3%, respectively; chi-square P = .39). There were 6 false-positive diagnoses in the Bethesda group compared with none in the modified Bethesda group (P = .06). In the Bethesda group, but not in the modified Bethesda group, the indeterminate rate was correlated with the overall rate of malignant and suspicious for papillary carcinoma diagnoses.
Modifying the Bethesda criteria can decrease indeterminate TFNAs diagnoses without a significant decrease in the risk of malignancy. The modified Bethesda criteria, but not the Bethesda criteria, are independent of the malignancy rate.