Thyroid Nodules: Bethesda System Update Changes Clinical Practice

Roxanne Nelson, RN, BSN

January 09, 2018

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

Although much of the original TBSRTC remains the same, several "enhancements" have been introduced in the 2017 version based on new data and developments in the field.

"All of the refinements of the 2017 Bethesda System, the 2015 American Thyroid Association guidelines, and the upcoming highly anticipated American Association of Clinical Endocrinologists thyroid nodule guidelines and algorithm are attempts to reduce unnecessary thyroid surgery," says R Mack Harrell MD, president of the American College of Endocrinology, who was approached by Medscape Medical News for independent comment.  

"And when surgery is necessary, [the changes are] to make sure that the procedure performed is the most conservative one, and accomplishes the diagnostic and therapeutic goals of the intervention without rendering the patient unnecessarily thyroid hormone dependent," he added.

The 2017 revision of the Bethesda System was simultaneously published in Thyroid (2017;27:1341-1346) and the Journal of the American Society of Cytopathology (2017;6:217-222).

The End of Surgical Decision-Making Based on Viewing Slides

The original Bethesda System was widely adopted in the United States and other countries, and has also been endorsed by the American Thyroid Association.

But by 2016, it became evident that an update was needed.

At a symposium held during the 2016 International Congress of Cytology, much of the groundwork for the current revision was laid out.

Dr Harrell noted that a major "guiding principle of modern thyroid nodule management that is explicitly mentioned" in this new paper is the fact that thyroid nodule diagnosis does not exist in a cytological vacuum. 

"What we have come to realize is that thyroid cytopathology needs to be interpreted in the broader context of the clinical history, physical examination, and neck ultrasonographic findings in order to be of maximal value to the patient," he said.

"The practical upshot of this new way of thinking hinges on the understanding that cytopathologists can no longer work in a context disconnected from the patient, endocrinologist, and endocrine surgeon, and that close clinical collaboration is now essential at virtually every level," Dr Harrell added. 

"The days of surgical decision-making driven solely by a cytopathologist viewing slides in a darkened room miles away from the site of patient care are history."

Major Change Is Accommodation of NIFTP Tumors

Authored by Edmund Cibas, MD, from Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, and Syed Z Ali, MD, from Johns Hopkins Medical Institutions, Baltimore, Maryland, the 2017 update of TBSRTC includes changes to the way malignancy risks are calculated based on new data and developments.

However, the revision has left the original six diagnostic categories unchanged:

  • Nondiagnostic or unsatisfactory

  • Benign

  • Atypia of undetermined significance (AUS) or follicular lesion of undetermined significance (FLUS)

  • Follicular neoplasm or suspicious for a follicular neoplasm (FN/SFN)

  • Suspicious for malignancy

  • Malignant

Notably, the new document reinterprets the previous version in one major way, according to Dr Harrell, and that is TBSRTC's careful accommodation of the new noncancer category of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) tumors, which prior to April 2016 were categorized as thyroid cancer. 

"NIFTP tumors have nuclear changes on cytologic evaluation that are identical to other forms of thyroid cancer, but on close long-term clinical follow-up they do not appear to recur or metastasize, and therefore, they do not behave clinically like thyroid cancer," he explained. 

NIFTP tumors have atypical findings on cytological evaluation, typically fall into categories 3, 4, or 5, and can only be diagnosed as "not cancer" after a full surgical excision is performed and the entire tumor specimen is examined under a microscope.

Thus, there are several implications for practicing cytopathologists, endocrinologists, and endocrine surgeons, Dr Harrell pointed out.

The risk range of malignancy in the Bethesda 3 category now falls from 10–30% to 6–18% if NIFTP tumors are excluded. 

And as the ambient rate of thyroid cancer in all thyroid nodules is about 6–8%, "so with the advent of NIFTP, Bethesda 3's diagnostic worth has become more dubious," he explained.

Because all NIFTP tumors must be excised in order to exclude cancer, surgical decision-making has not really changed with Bethesda categories 3, 4, and 5.

However, the number of hemi-thyroidectomies offered has dramatically increased, as removal of the NIFTP tumor lobe is likely curative and thyroid tissue conservation is optimal for patients and endocrine care providers. 

Other Enhancements

There have also been a number of other enhancements with the 2017 update:

  • The option of molecular testing in the standard management of AUS/FLUS and FN/SFN has been included.

  • The definition and diagnostic criteria for FN/SFN has been modified: cases demonstrating mild nuclear changes associated with papillary thyroid carcinoma are now included.

  • The definition and diagnostic criteria for the papillary thyroid carcinoma subset of the malignant category now suggest limiting use to cases with "classical" features of papillary thyroid carcinoma.

The authors have reported no relevant financial relationships.

Thyroid. 2017;27:1341-1346. Article

J Am Soc Cytopathol. 2017;6:217-222. Article

 

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