Effect of the Bethesda system for reporting thyroid cytopathology on thyroidectomy rates and malignancy risk in cytologically indeterminate lesions.

BACKGROUND Cytologically indeterminate thyroid nodules represent a diagnostic and therapeutic challenge. In 2007, the National Cancer Institute recommended The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) as a means of improving the accuracy of thyroid cytopathology. Our objective was to determine the effect of TBSRTC on thyroidectomy rates and malignancy risk in cytologically indeterminate lesions. METHODS We compared thyroidectomy rates and malignancy risk in patients with indeterminate thyroid cytopathology across 2 time periods, spanning January 2000 and November 2009; pre-TBSRTC (January 2000 to September 2003) and post-TBSRTC (June 2008 to November 2009). Statistical comparisons were performed using the Fisher's exact test and chi-square analysis (P = .05 significant). RESULTS We performed 938 fine-needle aspirations in the first period, 765 in the second. We identified 78 (8.3%) cytologically indeterminate lesions in the pre-TBSRTC group and 91 (11.9%) lesions in the post-TBSRTC group. We found no difference in thyroidectomy rates between the groups (37/78 [47%] pre-Bethesda versus 32/91 [35%] post-Bethesda; P = .12). However, the malignancy rate was significantly lower in the post-TBSRTC group (13/37 [35%] pre-Bethesda versus 4/32 [13%] post-Bethesda; P = .02). CONCLUSION Application of TBSRTC is associated with lower malignancy risk in indeterminate thyroid nodules, despite similar thyroidectomy rates. These findings imply that standardization of cytologic classification improves diagnostic accuracy.