Clinical Outcome for Atypia of Undetermined Significance in Thyroid Fine-Needle Aspirations

Abstract

In the Bethesda System for reporting thyroid fine-needle aspirations (FNAs), atypia of undetermined significance (AUS) is a category with limited reported follow-up and outcome data. We report a retrospective analysis of our institution's experience during nearly 4.5 years with a tiered classification scheme conforming to the Bethesda System in which repeated FNA was recommended for most patients with an initial AUS diagnosis. Of 4,691 thyroid FNAs, 512 (10.9%) had a diagnosis of AUS. Cytologic or histologic outcome data were available for 331 cases (64.6%), of which 240 (72.5%) were benign and 91 (27.5%) were malignant. Of patients with a surgical diagnosis, there was no statistically significant difference in malignancy rate among patients who went directly to surgery after a single AUS diagnosis (37/90 [41%]), patients having 2 successive AUS FNA diagnoses (22/51 [43%]), and patients with a benign aspirate after AUS (2/7 [29%]). Although AUS confers an intermediate risk of malignancy, guidelines recommending repeated FNA for most cases should be reevaluated.

The atypia of undetermined significance/follicular lesion of undetermined significance:malignant ratio

“…5,6,8,9,[12][13][14] The data from these series are summarized in Table 1. It is interesting to note that the overall rate of AUS was 9.7% with only 2 of 8 series reporting AUS rates below the previously recommended threshold of 7%.…”

“…In fact, most initial experiences with AUS have reported AUS rates > 7%, often substantially so. 3,[6][7][8][9][10][11][12]14 Our goal in undertaking this study was to identify performance measures within TBS that would guide reasonable laboratory practice, particularly with regard to use of the AUS category. We sought to establish whether a performance measure similar to the ASCUS:SIL ratio in cervical/vaginal cytology might be identifiable within thyroid FNA, although clearly recognizing that such a parameter will have limitations much as the ASCUS:SIL ratio does.…”

“…We identified PubMed-indexed, peer-reviewed published laboratory experiences using TBS in which the categorical breakdown of all 6 reporting tiers was identified 5,6,8,9,[12][13][14] and supplemented those data with previously unpublished figures from the Massachusetts General Hospital compiled by one of the authors (W.C.F.) from 2006 to 2008 using TBS (a subset of these cases was included in a prior study 3 ).…”

“…The heterogeneity of this low-risk category inevitably means that there will be differences in its utilization with significant variability in AUS rates noted among individual practitioners as well as between laboratories. [2][3][4][5][6][7][8][9][10][11][12][13][14] Indeed, TBS only recommends a broad use range for each diagnostic category. 1 To promote uniform practice among laboratories and cytopathologists and encourage quality improvement, it is desirable to have performance measures associated with TBS, especially with regard to the AUS category.…”

“…15 The only such recommendation that accompanied TBS for thyroid cytopathology was that the AUS rate not exceed 7% 1 ; however, this proposal lacked a robust evidentiary basis and has proved to be unrealistic for many laboratories publishing their initial experiences with TBS. [2][3][4][5][6][7][8][9][10][11][12][13][14] In this study, we review the initial published experiences with AUS and TBS in conjunction with our own laboratory experiences, with the goal of identifying evidencebased performance measures that will have usefulness in measuring individual and laboratory practices. In so doing, we hope to provide a basis for quality improvement in the reporting of thyroid aspirates within TBS framework.…”