What is the Bethesda Category of thyroid nodule biopsies?

The Bethesda System for Reporting Thyroid Cytopathology is a standardized classification system that is used to interpret and report the results of thyroid fine needle aspiration (FNA) biopsies. The system was developed to improve the accuracy and consistency of reporting and to guide the management of patients with thyroid nodules.

The Bethesda System categorizes thyroid FNA biopsy results into six diagnostic categories based on the type and degree of abnormality detected in the cells:

1. Non-Diagnostic or Unsatisfactory: The biopsy sample is inadequate for diagnosis because of a lack of cells in the biopsy. This may mean another biopsy will need to be performed.
2. Benign: The cells are normal and show no evidence of cancer or abnormal growth. This is the most common category and accounts for approximately 85% of all biopsies.
3. Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance: The cells show some abnormalities, but the significance of these changes is uncertain. Nodules in this category have a 5 – 15% risk of being cancerous.
4. Follicular Neoplasm or Suspicious for a Follicular Neoplasm: The cells suggest the possibility of a follicular neoplasm, a type of thyroid tumour that may be benign or cancerous. Surgery to remove the part of the thyroid with the nodule is usually recommended as there is a risk of cancer of up to 30% with this type of nodule. Molecular analysis of nodules in this category can be done to arrive at a more definitive diagnosis (without surgery), but is not available in Australia.
5. Suspicious for Malignancy: The cells show features suggestive of thyroid cancer, but the diagnosis cannot be confirmed definitively.
6. Malignant: The cells show clear evidence of cancer.

The Bethesda System helps to standardize the reporting of thyroid FNA biopsy results and provides guidance on the management of patients with thyroid nodules based on the diagnostic category. The system has been widely adopted and is considered an  invaluable tool in the diagnosis and management of thyroid nodules.