Bethesda System for Reporting Thyroid Cytopathology Updated

Roxanne Nelson, RN, BSN

August 01, 2023

The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), which attempts to standardize reporting and cytological criteria for fine-needle aspiration (FNA) of thyroid nodules and was first introduced in 2009, has been updated.

Since the publication of the first edition in 2010, TBSRTC has allowed cytopathologists to use a standardized, category-based reporting system for thyroid fine-needle aspiration. The third edition builds on the success of earlier editions, and although much remains the same, the 2023 version offers several key updates.

"This new edition has carefully reviewed the published literature over the past 5 years or so since the release of the second edition," said co-editor Paul A. VanderLaan, MD, PhD, associate professor of pathology, Harvard Medical School, Boston, Massachusetts. "In doing so, the expected risk of malignancy estimates for each diagnostic category has been updated, as well as for the first-time outlining risk of malignancy estimates for pediatric thyroid nodule FNAs as well."

A brief overview of the 2023 revision of the Bethesda System has been published online in Thyroid.

The initial 2010 Bethesda system established a simplified, six category-based reporting system for thyroid FNA, and these categories were left unchanged in the 2017 update. Both editions of TBSRTC achieved the goal of standardizing thyroid cytopathology reporting and were widely adopted in the United States and other countries. However, in the latest update, one of the most important changes cited by the authors is the assignment of a single name for each of the six diagnostic categories:

  • Nondiagnostic (Bethesda I)

  • Benign (Bethesda II)

  • Atypia of undetermined significance (Bethesda III)

  • Follicular neoplasm (Bethesda IV)

  • Suspicious for malignancy (Bethesda V)

  • Malignant (Bethesda VI)

Each one of these categories has an implied risk of malignancy, which has been updated and refined based on data reported after the second edition was released. There are defined diagnostic criteria, estimated risk of malignancy, and management recommendations for each category. The names were simplified primarily to address confusion about the diagnostic categories.

"Broadly speaking, cytology reporting systems must be succinct, unambiguous, and clinically helpful," explained VanderLaan. "With TBSRTC now well established and widely used, settling on a single name for each diagnostic category — which can be used in conjunction with the category number — should facilitate absolute clarity of communication between the cytopathologist and the clinical teams. This should avoid any confusion, especially between previously similar-sounding categories or multiple categories using the term 'suspicious'."

Additional Updates

In addition to simplifying the names of each diagnostic category, the updated version has expanded chapters on each of these six reporting categories, two new chapters, updated text, and new illustrations. It also has refined definitions, morphologic criteria, and explanatory notes.

Each reporting category has a typical management algorithm, based on recommendations by the American Thyroid Association and other professional endocrine organizations. The authors have now included an average risk of malignancy (ROM) for each category, in addition to the expected range of cancer risk. The atypia of undetermined significance (AUS) subcategorization has now been simplified into two subgroups based on the presence of nuclear atypia, which has implications for the implied ROM and molecular findings.

Other significant changes in TBSRTC 2023 include:

  • A discussion of pediatric thyroid disease has been added, and pediatric ROMs and management algorithms are discussed in the relevant sections; the ROMs have been calculated for the six reporting categories for this population and linked with the commonly practiced guidelines.

  • Nomenclature has been updated to align with the 2022 World Health Organization Classification of Thyroid Neoplasms.

  • Two new chapters have been added: one chapter addresses the significant and expanded use of molecular and ancillary testing in thyroid cytopathology, and the second summarizes clinical perspectives and imaging findings in thyroid disease.

  • Official endorsement by the European Federation of Cytology Societies, an umbrella organization of cytology professionals composed of 26 national organizations.

"Diagnostic inclusion criteria for each category remain largely unchanged in this third edition; however, subcategorization of the heterogenous Atypia of Undetermined Significance (Bethesda III) category is now recommended," said VanderLaan. "Based on numerous studies published since the initial introduction of TBSRTC, it has been shown that AUS aspirates with nuclear atypia have a higher risk of malignancy as compared to AUS aspirates with other forms of atypia, such as architectural or oncocytic change. This stratification may eventually lead to different clinical management within the AUS category."

Enhancements Help Clinical Practice

Michael Persky, MD, a surgical oncologist at NYU Langone's Perlmutter Cancer Center in New York City, noted the importance of changing these categories to a single name to help avoid confusion among treating doctors. "The majority of thyroid nodules that require surgery are treated by low-volume thyroid surgeons across this country," Persky told Medscape Medical News. "These surgeons may not have as much experience with the nuance of the older Bethesda system, affecting efficient collaboration with colleagues as well as increasing the potential for inadvertent misguided care for the patient. By making the terms succinct and unambiguous, as the authors put it, this system should enhance communication between physicians."

He pointed out that another important enhancement is a table reporting the change in the risk of malignancy for each category if the precancerous NIFTP [non-invasive follicular thyroid neoplasm with papillary-like nuclear features ] is excluded. "This is based on updated studies and should increase the accuracy of the risk stratification," he said. "Another enhancement is the subclassification of the Bethesda III category into nuclear vs non-nuclear atypia. This too will help doctors to risk stratify patients."

"However," he added, "the updated system does not appear to include any way to include molecular testing."

No funding was disclosed. The authors have made no disclosures. Persky has reported no relevant financial relationships.

Thyroid. Published Online July 8, 2023. Abstract

Roxanne Nelson is a registered nurse and an award-winning medical writer who has written for many major news outlets and is a regular contributor to Medscape.

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