Bethesda System for Reporting Thyroid Cytopathology

The Bethesda System for reporting thyroid cytopathology is a standardized way of reporting the results from fine needle aspiration (FNA) biopsies of the thyroid.¹
- These consensus recommendations were developed by the 2007 National Cancer Institute Thyroid Fine-Needle Aspiration State of the Science Conference to help address the significant variability in the reporting of cytological findings in thyroid FNAs.²
The Bethesda system is divided into the following diagnostic categories:
1. Nondiagnostic or unsatisfactory
2. Benign
3. Atypia of Undetermined Significance (AUS) or Follicular Lesion of Undetermined Significance (FLUS)
4. Follicular Neoplasm or suspicious for a Follicular Neoplasm
5. Suspicious for Malignancy
6. Malignant
Each of these categories was also given a predicted risk of malignancy based on literature review and expert opinion, shown below:

Bethesda Category	Estimated Risk of Malignancy (%)
Non-diagnostic or unsatisfacory	1-4
Benign	0-3
Atypia of Undetermined Significance (AUS) / Follicular Lesion of Undetermined Significance (FLUS)	5-15
Follicular Neoplasm / Suspicious for a Follicular Neoplasm	15-30
Suspicious for Malignancy	60-75
Malignant	97-99

Crippa S, Mazzucchelli L, Cibas ES, Ali SZ 2010 The Bethesda System for reporting thyroid fine-needle aspi- ration specimens. Am J Clin Pathol 134:343–344. ↩
Haugen, Bryan R., et al. “2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer: the American Thyroid Association guidelines task force on thyroid nodules and differentiated thyroid cancer.” Thyroid 26.1 (2016): 1-133. ↩

Last updated October 17, 2022