Subclassification of “atypia of undetermined significance” in thyroid fine‐needle aspirates

Abstract

To identify the subtypes of atypia of undetermined significance (AUS) that confers a different magnitude for the risk of malignancy (RM), thyroid fine-needle aspiration (FNA) cases carrying a diagnosis of "atypical follicular cells" or "follicular lesion" with surgical pathology followup were included in this study. The direct smears of the aspirates were rereviewed and subclassified into four subgroups based on cytomorphology: AUS cannot exclude follicular neoplasm (AUS-FN), AUS cannot exclude Hürthle cell neoplasm (AUS-HCN), AUS cannot exclude papillary carcinoma (AUS-PTC) and AUS, not otherwise specified (AUS-NOS). Based on the followup histopathologic findings, RM not including papillary microcarcinoma (PMC), RM including PMC and the risk of neoplasm (RN) were calculated for each of the four AUS subgroups. A total of 138 AUS cases were subclassified into AUS-NOS (48), AUS-PTC (41), AUS-FN (32), and AUS-HCN (17). RM not including PMC was 32% for AUS-PTC (P < 0.001), 25% for AUS-FN, 8% for AUS-NOS, 0% for AUS-HCN, and 18% for all AUS cases. RM including PMC was 54% for AUS-PTC (P < 0.001), 34% for AUS-FN, 19% for AUS-NOS, 18% for AUS-HCN, and 33% for all AUS cases. RN was 63% for AUS-PTC (P = 0.05), 81% for AUS-FN (P < 0.01), AUS-HCN 53%, AUS-NOS 44% and 59% for all cases. In our study, subclassification enabled us to further divide AUS cases into high- and low-risk groups. The high-risk group includes AUS-PTC with a significantly higher risk of malignancy and AUS-FN with a significantly higher risks of neoplasm. AUS-HCN and AUS-NOS subgroups demonstrate a lower risk of malignancy of <10%.

An Insight into the Utility of Sub-Categorisation of Atypia of Undetermined Significance for Risk Stratification: A Retrospective Study on an Indian Cohort with Histopathological Correlation

“…Our study shows a slightly higher overall malignancy rate in smears with cytological atypia (78.3%) than in those with only architectural atypia (75.3%). This is in agreement with many previously published studies, in which the estimated risk of malignancy from smears with cytological atypia ranged from 32% [9] to 97% [7] and AUS/FLUS was shown to have a considerably higher risk of malignancy than the other sub-categories. We had only 1 case of AUS with Hürthle cells, which, on resection, was diagnosed as Hürthle cell carcinoma.…”

“…Initially, in 2007, the Bethesda guidelines stated that the rate of AUS/FLUS should be < 7% in an ideal setting [15], and that overusage of this category should be minimised as much as possible. However, various studies from tertiary care centres [6, 7, 9, 11, 12, 16] around the world have reported higher rates of AUS of up to 15.8% [17]. The latest 2017 Bethesda guidelines changed the advisable limit of AUS/FLUS to 10% [2].…”

The Bethesda System for Reporting Thyroid Cytopathology: Proposed Modifications and Updates for the Second Edition from an International Panel

“…This could be accomplished using a concise note, Common patterns that would be candidates for subclassifiers include: architectural atypia, nuclear atypia, oncocytic features, and NOS. Several studies have demonstrated that subclassification within the AUS/FLUS category can be effective to better define the ROM, and that nuclear atypia is associated with a higher ROM than other AUS/FLUS patterns [23,24,25,26,27,28]. …”

Role of Core Needle Biopsy in the Management of Atypia/Follicular Lesion of Undetermined Significance Thyroid Nodules: Comparison with Repeat Fine-Needle Aspiration in Subcategory Nodules

“…Second, RFNA may not provide a straightforward management decision for a nodule diagnosed as benign by RFNA because the false negative rate of a benign diagnosis by RFNA in nodules initially diagnosed as AUS/FLUS may be higher than that in a single benign diagnosis [7,8]. Thyroid nodules with AUS/FLUS diagnosis include various pathologies, and recent studies [4,9,10,11,12,13,14,15] demonstrate that subcategory nodules showing nuclear atypia (NA) have a higher malignancy risk than other subcategory nodules showing architectural or other atypia, which might require a different management strategy. Although several recent studies [16,17,18,19,20,21,22] have suggested the potential utility of core needle biopsy (CNB) in the management of AUS/FLUS or indeterminate nodules, the role of CNB has not been established and its utility has been little investigated for each subcategory of AUS/FLUS nodules [22].…”