Which Ultrasound Classification System is Best at Reducing Unnecessary Thyroid Nodule Biopsies?

• Laryngoscope August 2021
• Thyroid nodules:
  • Have a prevalence of 19% to 68% in the general population:
    • With only 7% to 15% harboring thyroid cancer
• Ultrasound (US):
  • Is now the primary radiologic tool for evaluating thyroid nodules:
    • With several US features being predictive of malignancy-risk and, therefore, able to guide when a fine needle aspiration (FNA) biopsy may be advisable
• Multiple medical specialty societies across the world have developed US-based risk stratification guidelines for thyroid nodules:
  • In part to curb the significant testing
  • And possible overtreatment of millions of benign thyroid nodules
• A key design feature of the guidelines:
  • Is to identify nodules with low risk of malignancy:
    • Whose cytologic assessment with FNA can be safely deferred
• Differences among the guidelines include the:
  • US lexicon
  • Risk stratification category
  • Quantitative versus qualitative grouping
  • Nodule size thresholds for FNA
• Few studies, however, have compared the different guidelines to determine, which is best at identifying high-risk nodules or thyroid cancers while minimizing the number of “unnecessary” thyroid biopsies
• These paper chose to compare studies that assessed large cohorts of thyroid nodules with known outcomes, had a blinded review of the US, and then applied various classification systems to see which performed best
• Within these investigations, “unnecessary” thyroid biopsies are defined as biopsies, which would have been indicated by the particular classification system and ultimately turned out to be benign, either by cytology or histology
• This review, we focused on the negative predictive value (NPV) of the guidelines:
  • Representing the probability that a nodule is benign
• They also looked at the rate of unnecessary FNAs and the probability that a nodule not selected for FNA was malignant:
  • The false negative rate (FNR)
• They sought to clarify, which classification performed best with respect to the NPV, unnecessary biopsy rate, and FNR
• This would indicate that the system was superior at identifying those nodules that did not require biopsy while simultaneously avoiding misclassifying malignancies as benign
• Since most guidelines have a size threshold of 1 cm for FNA, this review only applied to thyoid nodule > 1cms
• BEST PRACTICE SUMMARY:
  • Although all guidelines noted have relatively high NPV:
    • The ACR-TIRADS performed best at identifying nodules ≥1 cm:
      • That could safely avoid biopsy while demonstrating the lowest number of unnecessary FNAs
    • In addition, the ACR- TIRADS is unique among the other guidelines in that it is a point-based system rather than a pattern-based systemÑ
      • Favoring a synoptic report to make the decision easier for the individual physician
      • Therefore, universal application of this system could potentially result in less variability of the US interpretation of thyroid nodules across providers and institutions
  • The limitation of these studies due to the application of the classification systems to retrospective datasets, which can introduce the possibility of selection bias:
    • However, the blinded nature of the sonographic assessment does help to minimize this issue
  • The use of such classification schemes can help introduce evidence-based decision making in the management of thyroid nodules to reduce personal bias and potential unnecessary overtreatment
  • Certainly, other issues will always be at play, including patient preference
  • Future studies will be needed to determine consistency in performance across different interpreting physicians and validate the results in a prospective manner

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