Outcome of atypia of undetermined significance/follicular lesion of undetermined significance in thyroid fine‐needle aspirations: A six‐year institutional experience

Abstract

BackgroundAtypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) is one of six diagnostic categories of The Bethesda System for Reporting Thyroid Cytopathology (BSRTC). The goal of our study is to assess the outcome of cases classified as AUS/FLUS at our institution.MethodsAUS/FLUS cases were identified by computer searching of the thyroid fine‐needle aspiration (FNA) cases performed between 2010 and 2016. Outcomes were categorized as: follow‐up surgery, repeat FNA or no follow‐up available. Demographics, ultrasound findings and FNA diagnostic criteria were reviewed for AUS/FLUS cases with follow‐up surgical pathology diagnosis.ResultsOur AUS/FLUS thyroid FNA rate was 6% (117 out of 1984 FNAs). Only 15% of the AUS/FLUS cases had repeat FNA, while 41% underwent surgery. The risk of malignancy (ROM) for cases with follow‐up surgery was 17%. When considering all AUS/FLUS cases, the ROM was 7%. Statistically, benign neoplasms were more likely to be single lesions on ultrasound comparing to malignant neoplasms, and to exhibit architectural atypia as opposed to non‐neoplastic lesions on FNA. The malignancy rates among patients that directly went to surgical resection (17%) and patients having repeat FNA after the first AUS/FLUS diagnosis followed by surgery (29%) was not significantly different. However, repeat FNA was able to reclassify the majority of cases into more definitive categories.ConclusionThe outcome of the thyroid FNAs diagnosed as AUS/FLUS in our institution meets the benchmark statistics for AUS/FLUS rate and ROM. This study constitutes a valuable quality assurance measure and serves as a baseline for subsequent quality improvement.

Predictors of Malignancy in Thyroid Nodules Classified as Bethesda Category III

“…A similar finding was also described by Guleria et al(22) and Mosca et al(23). However, nuclear atypia was one of the three atypia patterns that included architectural atypia and the Hurthle cell type described by Xu et al(14). They noted that nodules with nuclear atypia had the highest malignancy rate among the three groups, although it was not statistically significant.Kaymaz et al (24) reviewed the pathologic results of 209 AUS/ FLUS nodules and found that the overall rate of malignancy was 27.8%, which decreased to 26.4% if only the nodules with nuclear atypia were assessed.…”

“…The malignancy rate in AUS/FLUS nodules varies from 17% to 83.3%, according to the current evidence ( 10 , 14 ). Although the rate in the present study was also within this range, it was surprising to note there is great variability in the incidence.…”

“…However, nuclear atypia was one of the three atypia patterns that included architectural atypia and the Hurthle cell type described by Xu et al. ( 14 ). They noted that nodules with nuclear atypia had the highest malignancy rate among the three groups, although it was not statistically significant.…”

The Role of “Critical” Ultrasound Reassessment in the Decision-Making of Bethesda III Thyroid Nodules

“…It is also suggested in this study that FLUS lesions and AUS should be assessed separately [ 43 ]. Nevertheless, the higher risk of malignancy of nodules with cellular atypia does not reach statistical significance [ 23 , 44 , 45 ].…”

“…The reasons for this variability are correlative to selection bias that make the patients recruited in the endocrinological setting very different from the surgical ones, and these differences also depend on the criterion of patient selection for cytology (clinical, ultrasound in its different aspects), but also for the subsequent surgical choice (clinical, ultrasound, criteria for distinction between AUS and FLUS, search for mutations, etc.) [ 44 , 45 , 46 ].…”