The Bethesda thyroid terminology and progress towards international agreement on thyroid FNA cytology reporting

The Impact of the 2022 WHO Classification of Thyroid Neoplasms on Everyday Practice of Cytopathology

This review outlines how the alterations in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors of the thyroid gland are likely to impact thyroid cytopathology. It is important to note that WHO subclassifies thyroid tumors into several new categories based on increased comprehension of the cell of origin, pathologic features (including cytopathology), molecular classification, and biological behavior. The 3rd edition of the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) will debut in the near future and will include changes in diagnostic category designations. The changes in the 5th edition of the WHO will in some instances subtly, and in other instances significantly, impact the cytological diagnoses. Moreover, these changes will also affect other thyroid FNA classification schemes used internationally for classifying thyroid FNA specimens.

Malignancy Rate in Thyroid Nodules with Atypia or Follicular Lesion of Undetermined Significance

Introduction  Atypia of undetermined significance (AUS) or follicular lesion of undetermined significance (FLUS) is one of the six diagnostic categories of the Bethesda System for Reporting Thyroid Cytopathology. The prevalence of malignancy among Bethesda category III cytology is variable, ranging from 5% to 37% in the literature. Objective  To determine the rate of malignancy in thyroid nodules reported as Bethesda category III. Methods  A total of 495 patients underwent surgical intervention for thyroid nodules from January 2015 to December 2017. The present study included 81 cases reported as Bethesda category III, and their medical records were reviewed. Results  Out of 495 fine-needle aspiration cytology samples, 81 (16.4%) samples were labeled as AUS/FLUS. Among these 81 patients, the mean age was 43.0 years (± 13.9), with only 11 (14%) patients older than 55 years of age. Most of our patients were female ( n  = 69; 85.2%), and the rest were male. The rate of malignancy based on the final histology was of 33.3% ( n  = 27). The majority were 17 cases (21%) of papillary carcinoma, followed by follicular carcinoma ( n  = 6) (7.4%). Conclusion  The risk of malignancy can be higher than it is commonly believed, and guidelines should be based on the data from the institutions themselves for a better assessment of the outcomes.

Preoperative detection of malignancy in fine-needle aspiration cytology (FNAC) smears with indeterminate cytology (Bethesda III, IV) by a combined molecular classifier

AIMS

Analysis of molecular markers in addition to cytological analysis of fine-needle aspiration (FNA) samples is a promising way to improve the preoperative diagnosis of thyroid nodules. Previously, we have developed an algorithm for the differential diagnosis of thyroid nodules by means of a small set of molecular markers. Here, we aimed to validate this approach using FNA cytology samples of Bethesda categories III and IV, in which preoperative detection of malignancy by cytological analysis is impossible.

METHODS

A total of 122 FNA smears from patients with indeterminate cytology (Bethesda III: 13 patients, Bethesda IV: 109 patients) were analysed by real-time PCR regarding the preselected set of molecular markers (the BRAF V600E mutation, normalised concentrations of HMGA2 mRNA, 3 microRNAs, and the mitochondrial/nuclear DNA ratio). The decision tree-based classifier was used to discriminate between benign and malignant tumours.

RESULTS

The molecular testing detected malignancy in FNA smears of indeterminate cytology with 89.2% sensitivity, 84.6% positive predictive value, 92.9% specificity and 95.2% negative predictive value; these characteristics are comparable with those of more complicated commercial tests. Residual risk of malignancy for the thyroid nodules that were shown to be benign by this molecular method did not exceed the reported risk of malignancy for Bethesda II histological diagnosis. Analytical-accuracy assessment revealed required nucleic-acid input of ≥5 ng.

CONCLUSIONS

The study shows feasibility of preoperative differential diagnosis of thyroid nodules of indeterminate cytology using a small panel of molecular markers of different types by a simple PCR-based method using stained FNA smears.

The Bethesda System for Reporting Thyroid Cytology (TBSRTC): From look-backs to look-ahead

The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) was formalized in October 2007 by experts in thyroidology at the National Institute of Health in Bethesda, Maryland. The first edition of the TBSRTC book was published in 2010 and the second edition in 2018. The TBSRTC is widely employed in cytology practices in the United States and has also served as a model for similar tiered classification schemes for reporting thyroid cytopathology specimens. The tremendous success of TBSRTC cannot be underscored, it has provided a diagnostic framework which is well aligned with the present and the future of thyroid nodule management.

AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS, AMERICAN COLLEGE OF ENDOCRINOLOGY, AND ASSOCIAZIONE MEDICI ENDOCRINOLOGI MEDICAL GUIDELINES FOR CLINICAL PRACTICE FOR THE DIAGNOSIS AND MANAGEMENT OF THYROID NODULES--2016 UPDATE

Thyroid nodules are detected in up to 50 to 60% of healthy subjects. Most nodules do not cause clinically significant symptoms, and as a result, the main challenge in their management is to rule out malignancy, with ultrasonography (US) and fine-needle aspiration (FNA) biopsy serving as diagnostic cornerstones. The key issues discussed in these guidelines are as follows: (1) US-based categorization of the malignancy risk and indications for US-guided FNA (henceforth, FNA), (2) cytologic classification of FNA samples, (3) the roles of immunocytochemistry and molecular testing applied to thyroid FNA, (4) therapeutic options, and (5) follow-up strategy. Thyroid nodule management during pregnancy and in children are also addressed. On the basis of US features, thyroid nodules may be categorized into 3 groups: low-, intermediate-and high-malignancy risk. FNA should be considered for nodules ≤10 mm diameter only when suspicious US signs are present, while nodules ≤5 mm should be monitored rather than biopsied. A classification scheme of 5 categories (nondiagnostic, benign, indeterminate, suspicious for malignancy, or malignant) is recommended for the cytologic report. Indeterminate lesions are further subdivided into 2 subclasses to more accurately stratify the risk of malignancy. At present, no single cytochemical or genetic marker can definitely rule out malignancy in indeterminate nodules. Nevertheless, these tools should be considered together with clinical data, US signs, elastographic pattern, or results of other imaging techniques to improve the management of these lesions. Most thyroid nodules do not require any treatment, and levothyroxine (LT4) suppressive therapy is not recommended. Percutaneous ethanol injection (PEI) should be the first-line treatment option for relapsing, benign cystic lesions, while US-guided thermal ablation treatments may be considered for solid or mixed symptomatic benign thyroid nodules. Surgery remains the treatment of choice for malignant or suspicious nodules. The present document updates previous guidelines released in 2006 and 2010 by the American Association of Clinical Endocrinologists (AACE), American College of Endocrinology (ACE) and Associazione Medici Endocrinologi (AME).

Cytopathologic diagnosis of fine needle aspiration biopsies of thyroid nodules

Fine-needle aspiration (FNA) cytology is an important diagnostic tool in patients with thyroid lesions. Several systems have been proposed for the cyropathologic diagnosis of the thyroid nodules. However cases with indeterminate cytological findings still remain a matter of debate. In this review we analyze all literature regarding Thyroid Cytopathology Reporting systems trying to identify the most suitable methodology to use in clinical practice for the preoperative diagnosis of thyroid nodules. A review of the English literature was conducted, and data were analyzed and summarized and integrated from the authors’ perspective. The main purpose of thyroid FNA is to identify patients with higher risk for malignancy, and to prevent unnecessary surgeries for benign conditions. The Bethesda System for Reporting Thyroid Cytopathology is the most widely used system for the diagnosis of thyroid FNA specimens. This system also contains guidelines for the diagnosis and treatment of indeterminate or suspicious for malignancy cases. In conclusion, patients who require repeated FNAs for indeterminate diagnoses will be resolved by repeat FNA in a percentage of 72%-80%.

Utilization and impact of repeat biopsy for follicular lesion/atypia of undetermined significance

BACKGROUND

The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) created a new diagnostic category,follicular lesion/atypia of undetermined significance(FLUS/AUS). The recommended management of FLUS/AUS lesions is repeat biopsy to re-classify the lesion and guide therapy. Prior surgical studies suggest a higher than expected malignancy rate for FLUS/AUS. The present study evaluates a large institutional experience with all FLUS/AUS lesions analyzing use and impact of repeat biopsy.

METHODS

A total of 322 patients with FLUS/AUS cytology have been retrospectively identified since adoption of the BSRTC (2/2009–6/2012). Patient demographics, the results of clinical follow-up, repeat biopsy, or surgical pathology results were evaluated.

RESULTS

Among the 322 patients, 16 had concurrent cytology of higher acuity and were excluded. For the remaining 306 patients, 101 (33 %) underwent repeat biopsy, yielding 49 (48.5 %) with FLUS/AUS, 43 (42.5 %)with benign cytology, and 9 (9 %) with higher acuity cytology. Among the 205 patients without repeat biopsy,117 (57 %) chose thyroidectomy, and 88 (43 %) are being observed. Overall, 170/306 (55.6 %) patients underwent surgery to remove the index lesion, yielding a malignancy rate of 16.5 %. In contrast, the malignancy rate for the entire cohort was 28/306 (9 %).

CONCLUSIONS

Repeat biopsy was underutilized in FLUS/AUS cases. Repeat biopsy allows a significant proportion of FLUS/AUS patients without other indications for surgery to move to surveillance. In patients who have indications for thyroidectomy regardless of FLUS/AUS results,repeat biopsy does not appear necessary. Malignancy and thyroidectomy rates were similar among patients who did or did not have a repeat biopsy. Further data must be obtained to determine the long-term outcomes for surveillance of FLUS/AUS lesions in patients who do not undergo surgical removal.

The Bethesda system for reporting thyroid cytopathology: a single-center experience over 5 years

BACKGROUND

The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) was developed to refine fine-needle aspiration (FNA) cytology definitions and improve clinical management. This study evaluates the impact of the BSRTC 5 years after its adoption at a single institution.

METHODS

A total of 1,625 patients undergoing thyroidectomy in the pre-BSRTC (Group 1: July 2007-January 2009) and post-BSRTC (Group 2: February 2009-September 2013) periods were reviewed. Cytologic diagnoses in Group 1 included non-diagnostic, benign, follicular neoplasm, suspicious for malignancy and malignant. Atypia/follicular lesion of undetermined significance (AUS/FLUS) was included in Group 2. The proportions of each FNA category and malignancy rate per cytologic diagnosis were compared.

RESULTS

Fifty-four percent (187/347) of Group 1 patients had a preoperative FNA versus 61 % (777/1278) in Group 2 (p = 0.02). Group 1 FNA results included 3 % non-diagnostic, 48 % benign, 17 % follicular, 13 % suspicious for cancer, and 19 % cancer. Group 2 results included 3 % non-diagnostic, 36 % benign, 9 % follicular, 8 % suspicious for malignancy, 18 % malignant and 26 % AUS/FLUS. In Group 2, the proportions of benign, follicular and suspicious for malignancy FNAs decreased significantly (p < 0.05). In Group 2, there were more indeterminate FNA diagnoses overall (30 vs. 43 %; p < 0.001). The rate of cancer in suspicious for cancer FNA lesions increased from 44 to 65 % (p = 0.07). The AUS/FLUS malignancy rate was 15 %.

CONCLUSIONS

Since the adoption of the BSRTC at our institution, the proportion of indeterminate FNAs has increased; however, the diagnostic accuracy of the suspicious for cancer category improved. We recommend periodic review of the utilization and malignancy rates per cytologic category at each institution to help tailor clinical management.

Radiologic and clinical predictors of malignancy in the follicular lesion of undetermined significance of the thyroid

Various ultrasonographic characteristics of thyroid nodules have been associated with a higher likelihood of malignancy, and certain clinical features may also increase the likelihood of malignancy in patients. This study is designed to determine the ultrasonographic and clinical predictors of malignancy in the atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) category. A search through the cytology files at our institution was made for cases with diagnosis of AUS/FLUS. The clinical and radiologic findings were correlated with the final surgical pathology diagnosis. A total of 140 cases of AUS/FLUS with corresponding surgical intervention were identified (112 females and 28 males). There was a 79 % malignancy rate in nodules with irregular contours, compared to 51 % in nodules with regular outlines. Nodules demonstrating calcifications showed a 57 % malignancy rate, compared to 50 % in nodules without calcifications. Sixty-one percent of cases with an ultrasonographic diagnosis of indeterminate to suspicious were malignant following surgical resection. The rates of malignancy in patients with radiation exposure, symptomatic nodules, and positive family history of thyroid cancer were 22, 59, and 33 %, respectively. BRAF mutation was demonstrated in 57 % of malignant cases and in none of benign cases. No single clinical or ultrasonographic feature or combination of features is adequately sensitive or specific to identify all malignant nodules. However, a combination of solid nodules, nodules with irregular contours, symptomatic nodules, and positive BRAF mutation has high predictive value for malignancy in patients with a cytologic diagnosis of AUS/FLUS.

The bethesda system for reporting thyroid cytopathology: a five-year retrospective review of one center experience

Fine-needle aspiration (FNA) of the thyroid gland is a widely accepted and accurate method for triaging patients with thyroid nodules. Thyroid FNA suffers from a reporting confusion due to multiplicity of category terminologies. To address this, The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) was recently introduced for unifying the terminology and morphologic criteria along with the corresponding risk of malignancy.

OBJECTIVE

The aim of this study was to report the diagnostic utility of TBSRTC at our institution and report the malignancy risk for FNA of thyroid lesions among Saudi patients using this system at KAUH (King Abdulaziz University Hospital), Jeddah, Saudi Arabia.

MATERIALS AND METHODS

A retrospective study identifying 250 thyroid FNAs performed among Saudi patients between Jan 2005-Dec 2010 was undertaken. Cytology specimen data was collected through a computerized search of our cytopathology archives.

RESULTS

Among the 250 thyroid FNAs, 84 were followed by surgical resection. The overall surgical yield of malignancy was 23.8%. The malignancy rate for the 6 categories was as follows: non diagnostic: 20%, benign: 3.1%, atypia of undetermined significance: 50%, suspicious for follicular neoplasm: 20%, suspicious for malignancy: 80%, malignant: 100%.

CONCLUSION

Retrospective classification of FNAs of thyroid lesions among Saudi patients using TBSRTC at KAAUH, Jeddah, Saudi Arabia, validates the diagnostic reproducibility of this system and yields similar results for risk of malignancy as reported by others. However the associated rates found for non diagnostic (20%) raise the possibility of malignancy risk in this category and validate the past observations that sample inadequacy is a common cause of false negative thyroid FNAs.

The impact of atypia/follicular lesion of undetermined significance on the rate of malignancy in thyroid fine-needle aspiration: evaluation of the Bethesda System for Reporting Thyroid Cytopathology

BACKGROUND

The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) was developed to refine definitions and improve clinical communication and management. This study evaluates the impact of the BSRTC in a large cohort of patients undergoing thyroidectomy before and after its adoption at a single institution.

METHODS

The records from 469 patients in the pre-BSRTC (n = 187) and post-BSRTC (n = 282) periods were reviewed. Cytologic categories in group 1 included nondiagnostic, benign, follicular/Hürthle neoplasm, suspicious for malignancy, and malignant. Atypia/follicular lesion of undetermined significance (AUS/FLUS) was included in group 2. The percentage of each fine-needle aspiration (FNA) category, malignancy rate per category, and rate of AUS/FLUS utilization were calculated.

RESULTS

Group 1 FNA results included 3% (n = 6) nondiagnostic, 48% (n = 89) benign, 17% (n = 32) follicular/Hürthle, 13% (n = 25) suspicious for malignancy, and 19% (n = 35) malignant. Group 2 results included 4% (n = 11) nondiagnostic, 34% (n = 96) benign, 29% (n = 82) AUS/FLUS, 12% (n = 33) follicular/Hürthle, 10% (n = 29) suspicious for malignancy, and 11% (n = 31) malignant. The rate of cancer changed from 25% to 36% for follicular/Hürthle lesions. AUS/FLUS was utilized in 154 of 1095(14%) FNAs reviewed with a malignancy rate of 20%.

CONCLUSION

The new AUS/FLUS category was used more often than recommended (14%) with a higher than expected rate of malignancy (20%). Rigorous cytopathology to histopathology correlation is needed to accurately reflect the malignancy rates of the different BSRTC categories at each individual institution. Clinical management should be tailored based on such institutional findings.

Comparison of 5-tiered and 6-tiered diagnostic systems for the reporting of thyroid cytopathology: a multi-institutional study

BACKGROUND

At present, thyroid fine-needle aspiration (FNA) specimens are diagnosed using a tiered classification scheme, with the most popular of these being the 5-tiered and 6-tiered systems. In this study, the authors present their institutional experiences using these 2 different systems and evaluate their efficacy based on the surgical follow-up.

METHODS

Thyroid FNA specimens and their corresponding surgical resection specimens were collected between 2007 and 2009. The following diagnostic categories are used in both systems: unsatisfactory/nondiagnostic, benign, follicular neoplasm/suspicious for follicular neoplasm, suspicious for malignancy, and malignant. An additional category termed atypia of undetermined significance/follicular lesion of undetermined significance was used for atypical cases in the 6-tiered system. Statistical analysis was performed by comparing the different diagnostic categories.

RESULTS

The case cohort included a total of 7686 thyroid FNA specimens representing 3962 nodules and 3724 nodules, respectively, in the 5-tiered and 6-tiered systems. Negative predictive values for the benign categories (96.9% vs 97.5%; P = 1) and positive predictive values for both the follicular neoplasm categories (26.5% vs 32.1%; P = .2531) and the malignant categories (99.1% vs 99.4%; P = 1) were similar. The most significant differences between the 5-tiered and 6-tiered systems were the percentage of cases classified as benign (83.9% vs 55.4%; P < .0001) and as follicular neoplasms (4.6% vs 23.8%; P < .0001). It is interesting to note that fewer patients were referred for surgery in the 5-tiered system compared with the 6-tiered one (9.1% vs 36.5%; P < .0001).

CONCLUSIONS

Use of either the 5-tiered or 6-tiered reporting systems for thyroid FNA specimens can potentially affect the clinical management of patients with thyroid nodules.

The impact of implementation of the Bethesda System for Reporting Thyroid Cytopathology on the quality of reporting, "risk" of malignancy, surgical rate, and rate of frozen sections requested for thyroid lesions

BACKGROUND

The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) has been anticipated to improve communication between pathologists and clinicians and thereby patient outcomes. In the current study, the impact of TBSRTC on various quality and outcome measures was assessed.

METHODS

The current study included all patients who underwent fine-needle aspiration (FNA) of the thyroid between April 2006 and April 2009. Before implementation, the authors used generic diagnostic categories; after implementation, TBSRTC was used. Quality of reporting, diagnostic categories, rate of surgery, rates of frozen section, the "risk" of malignancy after a cytologic diagnosis, and errors before and after implementation of TBSRTC were compared using the chi-square and Fisher exact tests. Multilevel likelihood ratios and the receiver operating characteristic were used to compare the accuracy of FNA before and after implementation.

RESULTS

A total of 1671 FNAs (957 obtained before and 714 obtained after implementation of TBSRTC) were obtained from 1339 patients. Of these, 301 patients (191 before and 110 after implementation) underwent subsequent surgical resection. Before implementation, the reports were more ambiguous (3.7% vs 0.5%; P < .05) and implicit (5.1% vs 2.7%; P < .05) than after implementation. The overall rate of surgery decreased after implementation of TBSRTC (24.5% vs 19.6%; P < .05). The overall risk of malignancy did not appear to be affected by implementation of TBSRTC, but it decreased significantly after a benign FNA diagnosis compared with a diagnosis of an atypical lesion or follicular neoplasm. The rate of frozen section remained unchanged. The diagnostic accuracy was not found to be significantly different before compared with after implementation of TBSRTC.

CONCLUSIONS

Implementation of TBSRTC appears to improve the quality of reporting by lowering the number of ambiguous and implicit diagnoses and decreases the overall surgery rates, particularly for benign lesions, but it does not appear to have any effect on the accuracy of FNA of the thyroid, false-positive rates, or the frequency of intraoperative consultations.

The interobserver reproducibility of thyroid fine-needle aspiration using the UK Royal College of Pathologists' classification system

The overall interobserver reproducibility of thyroid fine-needle aspiration (FNA) has not been comprehensively assessed. A blinded 6-rater interobserver reproducibility study was conducted of 200 thyroid FNA cases using the UK System, which is similar to The Bethesda System for Reporting Thyroid Cytology: Thy1, nondiagnostic; Thy2, nonneoplastic; Thy3a, atypia, probably benign; Thy3f, follicular lesion; Thy4, suspicious of malignancy; and Thy5, malignant. There was good interobserver agreement for the Thy1 (κ = 0.69) and Thy5 (κ = 0.61), moderate agreement for Thy2 (κ = 0.55) and Thy3f (κ = 0.51), and poor agreement for Thy3a (κ = 0.11) and Thy4 (κ = 0.17) categories. Combining categories implying surgical management (Thy3f, Thy4, and Thy5) achieved good agreement (κ = 0.72), as did combining categories implying medical management (Thy1, Thy2, and Thy3a; κ = 0.72). The UK thyroid FNA terminology is a reproducible and clinically relevant system for thyroid FNA reporting. This study demonstrates that international efforts to harmonize and refine thyroid cytology classification systems can improve consistency in the clinical management of thyroid nodules.

Fine-Needle Aspiration and Intraoperative Consultation in Thyroid Pathology: When and How?

Fine-needle aspiration (FNA) and frozen section evaluation are traditional components of the management of thyroid lesions. Their role and usefulness are dictated by some basic facts about thyroid pathology: ( a) nodules are very common; ( b ) they are benign in the majority of cases; and ( c) the diagnosis of malignancy is primarily based on cytologic features in the case of papillary carcinoma, and on the presence of invasion of the tumor capsule or of blood vessels in the case of follicular carcinoma. The common occurrence of benign thyroid nodules mandates a cost-effective effective method for preoperative screening. Since, as already stated, the diagnosis of papillary thyroid carcinoma (by far the most common thyroid malignancy) is based on the identification of characteristic cytologic features, FNA has easily emerged in the past 30 years as the most accurate and cost-effective tool—indeed a true cornerstone—for the preoperative management of thyroid nodules. Standardized terminology to report cytologic diagnoses is highly recommended and is being implemented worldwide. Conversely, the importance of intraoperative frozen section diagnosis has been constantly decreasing over the past years, as a direct consequence of the widespread application of FNA. It may, however, be very useful in cases that are suspicious for papillary carcinoma on FNA and in selected cases with an indeterminate cytologic diagnosis.

Diagnostic terminology for reporting thyroid fine needle aspiration cytology: European Federation of Cytology Societies thyroid working party symposium, Lisbon 2009

A European Federation of Cytology Societies (EFCS) working party of 28 members from 14 European countries met at the European Congress of Cytology in Lisbon in September 2009, with two observers from the USA, to discuss the need for standardising thyroid FNA nomenclature in the light of the National Institute of Cancer (NCI) recommendations resulting from the State of the Science conference in Bethesda in 2007. The data were obtained through two questionnaires sent by email and a transcript of the live discussion at the congress, which is presented in full. The surveys and discussion showed that there were currently no national terminologies for reporting thyroid FNA in the different European countries except in Italy and the UK. Personal, 'local', surgical pathology and descriptive terminologies were in use. All but one of the working party members agreed that thyroid FNA reporting should be standardised. Whilst almost a third would adopt the NCI Bethesda terminology, which offers the advantages of a 'risk of cancer' correlation and is linked to clinical recommendations, more than half favoured a translation of local terminology as the first step towards a unified nomenclature, as has been done recently in the UK. There was some disagreement about the use of: a) the six-tiered as opposed to four or five-tiered systems, b) the use of an indeterminate category and c) the 'follicular neoplasm' category, which was felt by some participants not to be different from the 'suspicious of malignancy' category. The conclusions will be passed to the different national societies of cytology for discussion, who will be asked to map their local terminologies to the Bethesda classification, observe its acceptance by clinicians and audit its correlation with outcome.