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Recently, a six-tiered diagnostic risk classification system was created based on the recommendations of the National Cancer Institute (NCI) sponsored NCI Thyroid Needle Aspiration State of the Science Conference at Bethesda, MD in October 2007. The objective of the current study was to compare the frequency distribution of the various diagnostic categories to evaluate its diagnostic performance before and after implementation of The Bethesda System (TBS). A total of 5,897 thyroid Fine needle aspirations (FNAs) were reviewed; 3,207 were from 2008 after TBS implementation, and 2,690 were from 2007 immediately before TBS implementation. Follow-up consisted of reviewing corresponding histologic results. The rates of "Nondiagnostic" specimens and cases with a diagnosis of "Follicular Neoplasm" decreased from 13.1 to 11.1% and 8.6 to 5.5%, respectively, after implementation of TBS, while the rate of negative specimens increased from 68.2 to 73.8%. The other categories remained relatively stable. In addition, there also was a significant decrease in the use of noncommittal descriptive diagnoses. The diagnostic performance of thyroid FNA in identifying a neoplastic process as measured by area under the receiver operating characteristic curve increased from 0.88 to 0.89; the difference was statistically significant (P=0.03). Implementation of TBS showed a significant reduction of: nondiagnostic thyroid FNAs, of FNAs with a diagnosis of "Follicular Neoplasm," as well as cases with descriptive noncommittal diagnoses. TBS results in improved diagnostic performance and therefore more consistent and uniform reporting of thyroid FNA., (Copyright © 2013 Wiley Periodicals, Inc.)

The Bethesda 2007 Thyroid Cytology Classification defines follicular lesion of undetermined significance as a heterogeneous category of cases that are not convincingly benign nor sufficiently atypical for a diagnosis of follicular neoplasm or suspicious for malignancy. In our institution, we refer to these cases as indeterminate, and they are further sub-classified into two: (1) low cellularity with predominant microfollicular architecture and absence of colloid (IN(a)) and (2) nuclear features not characteristic of benign lesions (nuclear atypia) (IN(b)). We reviewed these indeterminate cases to document the follow-up trend using this two-tier classification. A search of the cytology records was performed for the period between January 2008 and June 2009. All thyroid fine-needle aspiration (FNA) cases were reviewed and the ones diagnosed as indeterminate were identified. Correlating follow-up FNA and/or surgical pathology reports were reviewed. The percentage of cases showing a malignancy was calculated. One hundred and seventy-one indeterminate cases were identified, representing 2.8% of the 6,205 thyroid FNA cases examined during the time under review (107 IN(a), 64 IN(b)). Records of follow-up procedures were available in 106 (61%) cases. Malignancy was identified in 27% of all indeterminate cases. This was disproportionately more in the IN(b) (56%) compared to the IN(a) (7%) cases. A diagnosis of "IN(a)" does not carry the same implication as that of "IN(b)". The IN(b) category needs a more aggressive follow-up than the IN(a) category and may justify an immediate referral for lobectomy. Despite the vague morphologic criteria for this diagnostic category, the indeterminate rate remains relatively low and falls within the NCI recommendation (<7%)., (Copyright © 2011 Wiley-Liss, Inc.)