Cytomorphologic, Imaging, Molecular Findings, and Outcome in Thyroid Follicular Lesion of Undetermined Significance/Atypical Cell of Undetermined Significance (AUS/FLUS): A Mini-Review

Abstract

Objectives: Since the introduction of the entity of “Atypical cell of undetermined significance /follicular lesion of undetermined significance” (AUS/FLUS) by The Bethesda System for Reporting Thyroid Cytology (TBSRTC) in 2007, there have been many published studies about the cytomorphologic criteria, subclassification, outcome, and management of patients with the diagnosis of AUS/FLUS. There have been many studies in different aspects of this indeterminate category, i.e., cytologic and molecular findings, ultrasonographic findings, and in some instances even core-needle biopsy to address a better and safer way of the management of patients with this fine-needle aspiration cytology diagnosis. The second edition of TBSRTC and the 2015 American Thyroid Association guidelines provide an update on the follow-up and management of AUS/FLUS. A multidisciplinary team consisting of pathologists, endocrinologists, surgeons, and radiologists should be involved in the diagnosis and management of AUS/FLUS, and all of them should be aware of the heterogeneity of this lesion for the prediction of the treatment and outcome. Study Design: In this review, we consider different research platforms (2008–2017) to find the best and key reports for the above-mentioned challenging aspects of AUS/FLUS. Conclusion: AUS/FLUS is now a well-defined group of thyroid lesions, which can be most accurately diagnosed and managed with cytomorphology, molecular, and ancillary studies.

Management of Atypia of Undetermined Significant Thyroid Nodule

“…No significant difference compared to complication of FNA in terms of pain, tolerability and complications [16]. Choi et al [7] reported 65% risk of malignancy found with CNB with significantly high occurrence of PTC [7].…”

“…The Advances in Health Sciences Research, volume 46 risk of malignancy related to the nuclear atypia rather than architectural atypia. Previous study showed that the presence of 2 nuclear features will increase the risk of malignancy up to 30-33% and will reach up to 100% when 4 nuclear features appeared [6,7] The AUS category comprises a heterogeneous group of findings, and the risk of malignancy associated with the nature of the observed atypia [8]. Most guidelines have recommended close follow-up for the AUS and repeating USG-guided FNA [7].…”

The Role of Cell Blocks and Immunohistochemistry in Thyroid Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance Bethesda Category

“…The Bethesda system for reporting thyroid cytopathology (TBSRTC) is an internationally used terminology classification scheme with 6 well defined diagnostic categories, explanatory notes and management recommendations allowing comparison of results among institutions [2-5]. Atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) category is a TBSRTC-introduced heterogeneous group of cytomorphological findings of subtle atypia unable to be further classified as benign, follicular neoplasm, or suspicious for malignancy [2, 4, 6, 7].…”

Thyroid Bethesda Category AUS/FLUS in Our Microscopes: Three-Year-Experience and Cyto-Histological Correlation

“…Accordingly, the frequency of AUS/FLUS category increased from 4% in the pre-TBSRTC period to 8% in the post-TBSRTC period, even up to a 12% peak in the last analyzed year in an institutional study [12]. In the larger analyses, the AUS/FLUS diagnosis ranged from 0.8–28%, with marked interobserver and intraobserver variations based on FNA aspirator, specimen preparation, and staining method [13,14,15].…”

“…The risk of malignancy (ROM) and risk of neoplasia (RON) also differ in various studies, from 6–97% (ROM) and from 6–56% (RON), despite the aim to serve as quality control guides [14,15]. Furthermore, RON is inconsistently defined in different series [14,15,16].…”