Thyroid cytopathology with an emphasis on the 'atypical cells of uncertain significance' category: a 3-year audit with cytohistologic correlation

Interobserver variability in inconclusive diagnostic categories of thyroid fine needle aspiration cytology: An urban-based tertiary hospital experience

INTRODUCTION

Thyroid nodules are typical lesions, usually non-malignant, and surgery is unnecessary in most patients. However, distinguishing between benign and malignant is challenging. Fine needle aspiration cytology (FNAC) is considered a primary diagnostic and prognostic tool with an effective cost for evaluating thyroid enlargement. Unfortunately, using FNAC to diagnose inconclusive lesions in the category III-Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance (AUS/FLUS) based on TBSRTC classification is a problematic issue. This study aimed to evaluate the interobserver variability of AUS/FLUS interpretation among pathologists.

METHODS

A retro-observational study: previous 127 AUS/FLUS cases were enrolled. Seventy-two cases met inclusion criteria and were then reclassified by different anatomical pathologists under blinded-design assignments. The concordance among pathologists and the percent alteration of the risk of malignancy (ROM) were compared to the original reports and histological diagnosis.

RESULTS

About 72 % of AUS/FLUS cases were changed after the reclassification. Approximately 46 % were changed to benign while 12.5 % were reclassified as carcinoma. Moreover, 30 % of those original AUS/FLUS were histologically diagnosed as malignant or carcinoma lesions. The concordances among consensus diagnosis and results from each pathologist are acceptable, Kappa(s) were 0.674 to 0.898 (p < 0.001) and Spearman correlations were 0.820 to 0.957 (p < 0.0001).

CONCLUSION

There are substantial interobserver differences and changes in cytological diagnosis when re-evaluation is performed by multiple pathologists using TBSRTC. A second or third opinion should be sought routinely to establish a consensus diagnosis as a supplement to the initial diagnosis of AUS/FLUS. The reclassification reduces medical expenses and the rate of unnecessary surgery, especially in patients with cytologically confirmed benign thyroid nodules. Preoperative molecular evaluation is a promising method for assisting in the diagnosis of thyroid nodules, but additional research is necessary.

Atypia of undetermined significance/follicular lesion of undetermined significance: Asian vs. non-Asian practice, and the Singapore experience

The Bethesda System for Reporting Thyroid Cytopathology has paved the way for comparisons of the practice of thyroid cytology in many different regions. However, there have been comparatively few studies documenting differences between Asian and non-Asian practice. Here, we aim to compare a few key parameters between the two regions, focusing on the indeterminate category of atypia of undetermined significance (AUS)/follicular lesion of undetermined significance (FLUS). We compared its incidence, resection rates (RRs), risk of malignancy (ROM), rate of repeat fine needle aspiration (rFNA), ROMs of cytomorphologic subcategories of nuclear atypia (AUS-N) vs. architectural atypia (AUS-A), and, finally, the incidence of papillary thyroid carcinoma (PTC) vs. follicular neoplasms (FNs) in resected AUS/FLUS cases in Asian and non-Asian regions. Where possible, these metrics were compared with the Singapore experience from a tertiary referral institution. While the incidence of AUS/FLUS was similar in both regions, we found geographical differences in the RRs and ROMs, which may reflect a higher collective threshold for surgery in Asian countries. However, both cohorts showed higher ROMs in the AUS-N subcategory as compared to the AUS-A subcategory, supporting the subclassification of the AUS/FLUS based on the presence of nuclear atypia. We also observed a higher incidence of AUS-N coupled with a higher incidence of PTC in resected AUS/FLUS nodules in Asian cohorts, while AUS-A and follicular-patterned neoplasms featured more prominently in the non-Asian cohorts. These incidences may account for the starkly different molecular approaches that we noted-in Asian (chiefly Korean and Chinese) centers, BRAF mutational analysis was favored, while gene panels and gene expression classifiers were more frequently applied in non-Asian centers (chiefly in the United States of America). Overall, the data from Singapore appears more closely aligned to non-Asian trends, despite its geographical location in Southeast Asia and its predominantly Asian population. We conclude that there is significant heterogeneity in the outcomes of the AUS/FLUS categories between and within regions, which is only partially explained by regional variations, and may also reflect different regional diagnostic and management practices. This highlights the importance of understanding the local context in the interpretation of indeterminate Bethesda categories, rather than adopting a "one-size fits all" approach.

Indeterminate thyroid nodules (TIR3A/TIR3B) according to the new Italian reporting system for thyroid cytology: A cytomorphological study

OBJECTIVE

The Italian reporting system for thyroid cytology classifies indeterminate lesions as TIR3A (low risk) or TIR3B (high risk) and is meant to provide practical guidance rather than a detailed consideration of morphological features. We aimed to assess which cytological features have the most diagnostic value and whether they are effective in classifying nodules as either TIR3A or TIR3B and in predicting histological outcomes.

METHODS

Thyroid fine-needle aspirates from 111 indeterminate nodules were reviewed blinded to clinical information, TIR3A/TIR3B classification, and histology in order to assess which cytological features (pooled into artefacts, smear background, architectural and nuclear atypia, and oncocytes) differentiate TIR3A from TIR3B, and benign from malignant histological outcomes.

RESULTS

Of the cytological features examined, those specific for TIR3B included high cellularity, nuclear atypia, oncocyte predominance and transgressing vessels. Features specific for TIR3A included artefacts, low cellularity and oncocyte sparseness. Other features, such as microfollicules/trabeculae, were non-specific. Due to the different distributions of these features, three TIR3B subgroups were identifiable: follicular lesions with oncocytic changes, pure follicular lesions, and follicular lesions with nuclear atypia, whereas no subgroups were identifiable in TIR3A. Nuclear atypia was a significant indicator of malignancy, whereas oncocyte predominance was not a reliable predictor of malignancy. High cellularity and microfollicules/trabeculae were not indicative of any histological outcome.

CONCLUSIONS

The majority of the assessed features were good predictors of histological outcomes. The TIR3A category included undefined nodules due to the absence of characterising features, whereas the TIR3B category included nodules with a greater number of distinguishing features.

Determining the molecular test for indeterminate thyroid nodules best suited for our practice: A quality assurance study

INTRODUCTION

Currently, molecular studies are widely used as a guiding tool in further management of cytologically indeterminate thyroid nodules. At our institution, clinicians have recently expressed concern over receiving "less positive molecular results" upon switching from an extended 14 gene mutation panel (EGMP) to a 7 gene mutation panel (GMP). Our goal is to compare outcomes of these two tests in regards to the performance characteristics and clinical impact.

MATERIALS AND METHODS

All thyroid fine-needle aspiration (FNA) biopsy specimens sent for molecular studies from 2016 to 2017 were retrospectively studied. Cytopathology diagnosis, pertinent clinical findings, molecular results, and follow-up (F/U) surgical and cytology diagnoses were recorded.

RESULTS

Of the total 165 cases sent for molecular tests 86 (52%) were GMP and 79 (47%) EGMP. There were 21 (24%) and 40 (50%) cases with positive GMP and EGMP results, respectively. Within these positive cases (n = 61), there were a total of 33 (54%) patients who underwent surgical resection and 28 (45%) patients had no follow-up. The molecular findings and surgical pathologic diagnoses obtained are illustrated in Figures 1 through 4 for GMP and EGMP, respectively.

CONCLUSIONS

The selection of molecular testing should be directed toward optimizing patient care and facilitate clinical management. This quality assurance study helped in understanding the complexities associated with test selection best suited for our institution and in educating clinicians.

Accuracy of ultrasonography-guided fine needle aspiration cytology and significance of non-diagnostic cytology in the preoperative detection of thyroid malignancy

INTRODUCTION

Thyroid fine-needle aspiration cytology (FNAC) is an established investigation for the preoperative evaluation of thyroid nodules and is often done under ultrasonography guidance. While its accuracy has been widely reported, there is little evidence in the literature on the approach to non-diagnostic cytology results. In our study, we aimed to determine the diagnostic performance of ultrasonography-guided thyroid FNAC for the preoperative diagnosis of thyroid cancer at our institution and evaluate the significance of a non-diagnostic thyroid FNAC.

METHODS

We retrospectively reviewed the thyroid ultrasonography studies and medical records of all patients who underwent both thyroid FNAC and subsequent thyroid surgery at our institution from 2011 to 2013. FNAC results were correlated with the final histological diagnosis from surgery and the ultrasonography studies were reviewed for suspicious sonographic features.

RESULTS

FNAC predicted malignancy with sensitivity, specificity, positive predictive value, negative predictive value, false positive rate, false negative rate and total accuracy of 90.7%, 53.6%, 43.3%, 93.7%, 46.4%, 9.3% and 64.1%, respectively. We found that only one of 26 nodules with non-diagnostic FNAC results was proven malignant on a second FNAC and subsequent thyroidectomy.

CONCLUSION

The accuracy of ultrasonography-guided FNAC at our institution was comparable to that reported in the literature. There appears to be very low probability of malignancy in sonographically benign nodules with initial non-diagnostic FNAC results.

Evaluation of the Italian cytological subclassification of thyroid indeterminate nodules into TIR-3A and TIR-3B: a retrospective study of 290 cases with histological correlation from a single institution

PURPOSE

The Italian consensus to classify thyroid cytology has provided a standardized reporting scheme, including the subdivision of indeterminate for malignancy TIR-3 category into TIR-3A (low-risk) and TIR-3B (high-risk). We aimed to present our experience on this subclassification by evaluating risks of malignancy and the validity in sorting nodules with dissimilar risks. Another aim was to compare our performance against the Bethesda system.

METHODS

Fine-needle aspirates of 290 TIR-3 that underwent thyroid surgery at our hospital (2008-2013) were reviewed and divided into TIR-3A or TIR-3B, and AUS/FLUS or FN/SFN. Cytological diagnoses were then correlated to histology. Results were evaluated using univariate analysis.

RESULTS

The subclassification into TIR-3A and TIR-3B differentiated hyperplastic nodules (p = 0.000) but not adenomas (p = 0.090). Rates of malignancy were significantly different between TIR-3A (10.2%) and TIR-3B (43.8%); TIR-3B malignancies were often papillary carcinomas (83%). TIR-3A/TIR-3B accounted for high sensitivity (84.5%; CI 79.7-88.4%), accuracy (64.1%; CI 58.6-69.6%) and NPV (89.8%; CI 85.6-93.0%) as opposed to modest specificity (55.8%; CI 49.9-61.6%) and PPV (43.8%; CI 38.1-49.8%). The rate of malignancy in AUS-FLUS was higher than in TIR-3A (p = 0.007), whereas it was not different between FN/SFN and TIR-3B (p = 0.337). Sensitivity of the Bethesda system was significantly lower respect to the Italian system.

CONCLUSIONS

The study supports the Italian consensus showing a different risk of malignancy for TIR-3A as compared to TIR-3B. TIR-3A/TIR-3B subclassification is valid to sort out benign nodules (high NPV) and malignancies (high sensitivity) but not adenomas (modest specificity, low PPV). In our experience, sensitivity is the main difference between Italian and Bethesda systems.