The Bethesda System for Reporting Thyroid Cytopathology Explained for Practitioners: Frequently Asked Questions

Two-tier subclassification of the Bethesda category III (atypia of undetermined significance/follicular lesion of undetermined significance) in thyroid cytology

BACKGROUND

The Bethesda category III, AUS/FLUS, comprises a heterogeneous group of thyroid lesions with variable risk of malignancy (ROM). This study evaluates ROM in two subgroups of this category based on nuclear atypia and architectural atypia.

METHODS

Cases in Bethesda category III were reported based on nuclear atypia (AUS) and architectural atypia (FLUS). ROM was calculated by comparing the cytologic diagnosis to the follow-up histologic diagnosis.

RESULTS

Among the 610 Bethesda category III cases in this study, 306 (50.2%) and 304 (49.8%) cases were reported as AUS and FLUS, respectively. One hundred and eighty six of 306 AUS (60.8%) and 193 of 304 FLUS (63.5%) cases underwent surgical intervention. ROM of the cases in Bethesda category III was 12.8% if all cases were counted and 20.6% if only surgical cases were counted. When analyzing separately, ROM of AUS cases was 17.0% and 28.0% with all cases and surgical cases only, respectively. For FLUS cases, ROM was 8.6% and 13.5% with all cases and surgical cases only, respectively.

CONCLUSION

In Bethesda category III, ROM in the cases with nuclear atypia was significantly higher than the cases with architectural atypia. Sub-classifying the Bethesda Category III cases with nuclear atypia and architectural atypia, respectively may better stratify the ROM.

Comparative Cyto-Histological Genetic Profile in a Series of Differentiated Thyroid Carcinomas

INTRODUCTION

Molecular tests can contribute to improve the preoperative diagnosis of thyroid nodules. Tests available are expensive and not adapted to different populations.

AIM

This study aimed to compare the cyto-histological genetic profile and to evaluate the reliability of molecular tests using ultrasound-guided fine needle aspiration cytology (US-FNAC) in accurately diagnosing differentiated thyroid carcinomas (DTCs) and predicting biologic behavior of papillary thyroid carcinomas (PTCs).

MATERIALS AND METHODS

The series included 259 patients with paired cyto-histological samples totaling 518 samples. The genetic alterations were analyzed via PCR/Sanger sequencing. The association with clinicopathologic features was evaluated in PTCs.

RESULTS/DISCUSSION

From the 259 patients included, histologies were 50 (19.3%) benign controls and 209 (80.7%) DTC cases, from which 182 were PTCs; cytologies were 5.8% non-diagnostic, 18.2% benign, 39% indeterminate, and 37.1% malignant. In histology, indeterminate nodules (n = 101) were 22.8% benign and 77.2% malignant. Mutation frequencies in cytology and histology specimens were, respectively, TERTp: 3.7% vs. 7.9%; BRAF: 19.5% vs. 25.1%; and RAS: 11% vs. 17.5%. The overall cyto-histological agreement of the genetic mutations was 94.9%, with Cohen's k = 0.67, and in indeterminate nodules agreement was 95.7%, k = 0.64. The identified mutations exhibited a discriminative ability in diagnosing DTC with a specificity of 100% for TERTp and BRAF, and of 94% for RAS, albeit with low sensitivity. TERTp and BRAF mutations were associated with aggressive clinicopathological features and tumor progression in PTCs (p < 0.001). The obtained good cyto-histological agreement suggests that molecular analysis via US-FNAC may anticipate the genetic profile and the behavior of thyroid tumors, confirming malignancy and contributing to referring patients to surgery.

Preoperative evaluation of thyroid nodules - Diagnosis and management strategies

Thyroid cancer is the most common endocrine malignancy, with increasing incidence over the past few decades. Fine needle aspiration (FNA) biopsy is the gold standard for preoperative diagnosis of thyroid malignancies. Nevertheless, this method renders indeterminate results in up to 30% of the cases. Therefore, these patients are often referred to unnecessary surgery to establish the diagnosis. To improve the accuracy of preoperative diagnosis, several other ways, such as ultrasonography, elastography, immunohistochemical analysis, genetic testing, and core needle biopsy, have been developed and can be used either in association with or as an alternative to FNA. This review aims to evaluate all these diagnostic tools to determine the most appropriate way of managing thyroid nodules and subsequently improve the selection of cases referred to surgery.

Improve follicular thyroid carcinoma diagnosis using computer aided diagnosis system on ultrasound images

OBJECTIVE

We aim to leverage deep learning to develop a computer aided diagnosis (CAD) system toward helping radiologists in the diagnosis of follicular thyroid carcinoma (FTC) on thyroid ultrasonography.

METHODS

A dataset of 1159 images, consisting of 351 images from 138 FTC patients and 808 images from 274 benign follicular-pattern nodule patients, was divided into a balanced and unbalanced dataset, and used to train and test the CAD system based on a transfer learning of a residual network. Six radiologists participated in the experiments to verify whether and how much the proposed CAD system helps to improve their performance.

RESULTS

On the balanced dataset, the CAD system achieved 0.892 of area under the ROC (AUC). The accuracy, recall, precision, and F1-score of the CAD method were 84.66%, 84.66%, 84.77%, 84.65%, while those of the junior and senior radiologists were 56.82%, 56.82%, 56.95%, 56.62% and 64.20%, 64.20%, 64.35%, 64.11% respectively. With the help of CAD, the metrics of the junior and senior radiologists improved to 62.81%, 62.81%, 62.85%, 62.79% and 73.86%, 73.86%, 74.00%, 73.83%. The results almost repeated on the unbalanced dataset. The results show the proposed CAD approach can not only achieve better performance than radiologists, but also significantly improve the radiologists' diagnosis of FTC.

CONCLUSIONS

The performances of the CAD system indicate it is a reliable reference for preoperative diagnosis of FTC, and might assist the development of a fast, accessible screening method for FTC.

Association of Fine-Needle Aspiration of Thyroid Nodules With Final Histopathology in Diagnosing Thyroid Malignancy: A Single Institute Retrospective Study

Background Fine needle aspiration cytology (FNAC) is the gold standard for detecting thyroid nodules. It is a cost-efficient approach that affords prompt and accurate evaluation. It is crucial in deciding to treat patients with suspected malignancy of thyroid nodules that might have thyroid surgery. According to findings in cytology, patients may be observed when the cytology is benign, and surgery can be performed if the cytology is malignant, which leads to a reduction in the incidence of unneeded surgery. Aim The current study aims to assess the concordance between FNAC of thyroid nodules with final histopathology and identify the different types of detected thyroid lesions. Methodology A retrospective record-based study reviewed the medical files of all patients presenting to the Armed Forces Hospital, Southern region, with suspected thyroid nodules from April 2018 to January 2020. Data were extracted using pre-structured data extraction sheet to avoid inconsistency. Data extracted included patients' demographic data, swelling laterality, size, ultrasound, and histopathological findings.  Results The baseline characteristics of studied samples in the present study: Forty-seven samples had a mean age of 44.27 (SD=±13.5) years, and 85.1% were female gender. The study showed that 12.5% of benign samples were lymphocytic in histopathology, 25% suspicious for follicular neoplasm samples were benign multi-nodular goiter in histopathology, and all 100% of samples suspicious for malignancy were malignant in final histopathology. Conclusions The current study showed that the malignancy rate of the examined nodules was not uncommon in FNAC and histopathology. Where papillary carcinoma was the most detected malignancy, the diagnosis of malignancy using FNAC is a cost-efficient approach that affords prompt and accurate evaluation. Once diagnosed, these cases should be subjected to surgery.

The impact of concurrent Hashimoto thyroiditis on thyroid nodule cytopathology assessed by ultrasound-guided fine-needle aspiration cytology

Objective: Thyroid nodules are highly prevalent and a common clinical problem worldwide. How to identify the nature of a nodule is a major concern of clinicians. Fine needle aspiration cytology (FNAC) has an established role and is well-utilized in nodule management. However, the unsatisfactory nondiagnostic and indeterminate rates limit its usage and lead to some unnecessary surgery. Hashimoto thyroiditis (HT) is prevalently found concurrent with thyroid nodules. Whether HT can influence the accuracy of cytopathological diagnosis of nodules is still controversial. Methods: We collected medical records of 1,063 patients with thyroid nodules who had done FNAC in our hospital from 2015 to 2016. Thyroid function, anti-thyroid autoantibody levels, thyroid ultrasound records, and cytological and histopathological results of nodules were reviewed to analyze the impact of HT on FNAC outcome. Results: A total of 1,063 patients with an average age of 44 ± 13 years old were retrospectively reviewed for pathological and clinical data. Patients with different cytological diagnoses had comparable positive rates of anti-thyroid autoantibodies. One hundred patients were confirmed to have concurrent HT by histopathology after surgery. The overall nondiagnostic and indeterminate cytology rates were 11.9% and 25% respectively. No statistical difference was found either in the rate of a nondiagnostic cytology results or in the rate of indeterminate cytology results between patients with positive anti-thyroid autoantibodies and patients with negative test for anti-thyroid autoantibodies (P > 0.05). The same was true between patients with histopathologically confirmed HT and HT-negative ones (P > 0.05). Conclusions: The presence of concurrent HT, whether clinically implied with positive anti-thyroid autoantibodies or pathologically confirmed, is unlikely to predispose an FNAC diagnosis of thyroid nodules to be non-diagnostic or indeterminate.

Causes of misdiagnoses by thyroid fine-needle aspiration cytology (FNAC): our experience and a systematic review

Objective

FNA is a simple, safe, cost-effective and accurate diagnostic tool for the initial screening of patients with thyroid nodules. The aims of this study were to determine the diagnostic utility of FNAC performed in our institution, assess the cytomorphologic features that contribute to diagnostic errors and propose improvement measures.

Methods

A total of 2781 FNACs were included in the study, and 1122 cases were compared with their histological diagnoses. We retrospectively reexamined our discordant (both false-negative and false-positive) cases and performed a systematic review of previous studies on causes of misdiagnoses.

Results

When DC V and DC VI were both considered cytologic-positive, the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy were 98.3, 30.9, 94.9, 58.3 and 93.5%, respectively. If DC VI was considered cytologic-positive, the sensitivity, specificity, PPV, NPV and diagnostic accuracy of FNAC were 98.0, 84.0, 99.4, 58.3, and 97.5% respectively. The main cause of false-negative diagnoses was sampling error (13/15, 86.7%), while interpretation error led to the majority of the false-positive diagnoses (38/47, 80.9%). Overlapping cytological features in adenomatous hyperplasia, thyroiditis and cystic lesions were the major factors contributing to interpretation errors, while the size and number of nodules may have led to false-negative diagnoses because of heterogeneity and unsampled areas.

Conclusions

The sensitivity and PPV of thyroid FNAC in our institution were higher than those in the published data, while the specificity and NPV were lower. Regarding the FNA category DC V, a frozen section analysis during diagnostic lobectomy is necessary. Multiple passes should be performed in various parts of a large nodule or from different nodules to reduce the risk of false-negative findings. Cytopathologists should strengthen their criteria for the identification of adenomatous hyperplasia, thyroiditis and cystic lesions to avoid false-positive diagnoses. NIFTP has little effect on diagnostic accuracy and the distribution of diagnostic errors.

Macrofollicular Variant of Follicular Thyroid Carcinoma: A Rare Underappreciated Pitfall in the Diagnosis of Thyroid Carcinoma

Background: Follicular-patterned thyroid nodules predominantly composed of macrofollicular structures without nuclear atypia are generally regarded as benign (i.e., hyperplastic nodules or follicular adenomas). In line with this concept, fine-needle aspiration cytology (FNAC) also assigns a benign connotation to the presence of macrofollicular structures, unless thyrocytes present papillary thyroid carcinoma (PTC)-related nuclear features that raise the possibility of a macrofollicular variant of PTC. However, cases showing macrofollicular architecture, capsular invasion, and no PTC features can also be observed. Methods: We describe the clinical, cytological, histological, and molecular genetic features of four cases of encapsulated follicular neoplasms that presented histologically with a predominant (>70%) macrofollicular architecture, but which also showed clear signs of capsular invasion, and thus were classified as macrofollicular variant of follicular thyroid carcinoma (MV-FTC). Results: Cytologically, macrofollicular structures were identified in all cases, leading to a benign FNAC diagnosis in three of the four cases. Due to increasing nodule size, thyroidectomy was performed in all cases. Histology showed focal and limited capsular invasion, without vascular invasion. Next-generation sequencing (custom 394 gene panel) of each tumor compared with matched normal DNA revealed a total of 7 somatic variants, including dual (likely biallelic) mutations in the DICER1 gene in 2 patients. The clinical outcome was excellent in all cases. Conclusions: Similar to the classical minimally invasive follicular thyroid carcinoma, MV-FTC appears to behave indolently. MV-FTC has a high rate of false-negative FNAC results, but MV-FTC is very rare (<0.05% of all thyroidectomies) and apparently has an indolent behavior. Further studies comprising larger series are necessary to better clarify the biology of this diagnostically challenging rare tumor.

The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC): A report of 2,781 cases in a Chinese population

Objective

To evaluate the diagnostic utility of The Bethesda System for Reporting Thyroid Cytology (TBSRTC) at Peking University Cancer Hospital, the incidence of noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP), and the impact of reclassification on cytopathological outcomes.

Methods

We performed a retrospective study of thyroid fine-needle aspiration (FNA) cases between April 2014 and March 2019. The FNA results were classified according to TBSRTC. Post-surgery histological findings were followed up.

Results

A total of 2,781 thyroid FNAs were performed. The incidences of the 6 diagnostic categories (DCs I-VI) were 14.8%, 17.1%, 15.8%, 2.3%, 11.6% and 38.5%, respectively. A total of 1,122 patients (40.3%) had corresponding histological results. NIFTP accounted for 0.4% of papillary thyroid carcinoma (PTC) cases, and there was no significant difference in the risk of malignancy (ROM) for each TBSRTC DC between "NIFTP=carcinoma (Ca)" and "NIFTP≠Ca". When "NIFTP=Ca", the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of TBSRTC were 98.0%, 84.0%, 99.4%, 58.3%, and 97.5%, respectively. When "NIFTP≠Ca", the sensitivity, specificity, PPV, NPV and accuracy of the TBSRTC were 98.1%, 81.5%, 99.3%, 61.1%, and 97.5%, respectively.

Conclusions

TBSRTC is effective in the preoperative diagnosis of thyroid nodules in Peking University Cancer Hospital. The impact of the reclassification of NIFTP on cytopathological outcomes is limited because of its low incidence, and the revised ROMs are not suitable for Asian patients.

Impact of non-invasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) on risk of malignancy in patients undergoing lobectomy/thyroidectomy for suspected malignancy or malignant fine-needle aspiration cytology findings: a systematic review and meta-analysis

OBJECTIVE

The second version of The Bethesda System for Reporting Thyroid Cytopathology endorsed the introduction of non-invasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) as a distinct entity with low malignant potential into clinical practice. Consequently, the risk of malignancy (ROM) of cytological diagnoses has changed, but the magnitude of the change remains uncertain. The present systematic review was undertaken to obtain more robust information about the true impact of NIFTP on the ROM among patients undergoing surgery following a fine-needle aspiration cytology (FNAC) diagnosis of suspicious for malignancy (Bethesda V) or malignant (Bethesda VI). As they are managed surgically, these two diagnostic categories are the primary entities that are clinically impacted by the advent of NIFTP.

DESIGN

Systematic review and meta-analysis.

METHODS

A comprehensive literature search of online databases was performed in November 2018. The search was conducted looking for data of histologically proven NIFTP with preoperative FNAC.

RESULTS

One-hundred fifty-seven articles were identified and nine were included in the study. Overall, there were 13,752 thyroidectomies with a cancer prevalence of 45.7%. When NIFTP was considered non-malignant, the pooled risk difference for ROM was 5.5%. Applying meta-analysis, the pooled prevalence of NIFTP among nodules with FNAC of Bethesda V or Bethesda VI was 14 and 3%, respectively.

CONCLUSION

This meta-analysis shows that the inclusion of NIFTP leads to a reduction in the ROM for the Bethesda V and Bethesda VI FNAC diagnostic categories by 14 and 3%, respectively. Clinicians should be aware of these data to avoid overtreatment.

Comparison between ultrasonographic findings and fine needle aspiration cytology in differentiating malignant and benign thyroid nodules

The purpose of research was comparing the ultrasound (US) features and fine-needle aspiration cytology (FNAC) in detecting the thyroid nodules in clinical practice. A cross-sectional analytical study retrospectively reviewed the US and FNAC findings for a total of 170 thyroid nodules. The US features that we compared included echogenicity, calcifications, shape, halo and Doppler, between 2017 and 2018. Totally, 170 nodules of thyroid were studied, which contained 72 (42.4%) benign and 98 (57.6%) malignant thyroid nodules. The sonographic features were significantly associated with malignancy such as microcalcification (97.0%), hyperechogenicity (91.5%), wider than taller shape (98.0%), absent halo (90.9%) and positive Doppler (78.0%) (P < 0.01). The altogether accuracies of calcification, echogenicity, shape, halo, and Doppler were 0.96, 0.92, 0.97,0.82 and 0.82, respectively. Our data suggest that US features could be a good sonographic criterion for recommending FNA cytology with follow‐up thyroid sonography and FNA.

Malignancy rate of atypia of undetermined significance/follicular lesion of undetermined significance in thyroid nodules undergoing FNA in a suburban endocrinology practice: A retrospective cohort analysis

BACKGROUND

The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) was created to establish a standard terminology regarding thyroid nodules that can be shared between endocrinologists, pathologists, radiologists, and surgeons. Since its inception and use in 2009, multiple large hospitals and academic institutions have performed retrospective studies to compare their classification rates, specifically those of atypia of undetermined significance (AUS) and follicular lesion of undetermined significance (FLUS), with the recommended rates created by the National Cancer Institute. The current study compared AUS/FLUS rates at a private suburban endocrine practice with those of previous publications from large institutions and the rates established by the National Cancer Institute.

METHODS

Charts from 893 patients with fine-needle aspiration (FNA) performed in 2015 were reviewed. Data specific to thyroid aspirates classified as AUS/FLUS were organized into whether patients underwent surgery, underwent subsequent repeat FNA, or required continued observation. These results then were calculated to reveal the rate of malignancy in the AUS/FLUS category with surgical pathology in the study institution.

RESULTS

A total of 893 patients underwent FNA, with 43 patients (4.82%) shown to have AUS/FLUS. A total of 21 patients proceeded to undergo thyroidectomy or lobectomy, with 7 patients (33.3%) found to have papillary or follicular thyroid carcinoma.

CONCLUSIONS

The rate of use of the AUS/FLUS category for thyroid nodules examined at the study institution was found to be within the recommended range set forth by TBSRTC. However, the malignancy rates on histopathology in the study institution were found to be higher than the new proposed malignancy rates from TBSRTC published in 2017. This finding is comparable to those of multiple other community and academic institutions performed prior to and after institution of the new guidelines.